Michael v State of New South Wales

Supreme Court of NSW|2011-02-09|Before: Fullerton J, Harrison J

Judgment 1HER HONOUR : The plaintiff brings proceedings in negligence seeking damages for injuries he claims to have suffered whilst a prisoner at the Metropolitan Special Program Centre at Long Bay Correctional Complex in 2001. The proceedings were filed in the District Court in 2004 and were transferred to this Court by consent in 2009. 2On 30 November 2010 Harrison J made orders pursuant to Pt 28 Div 2 r 28.2 of the Uniform Civil Procedure Rules, that five questions be determined as separate issues before the hearing: (a)What is the ambit of the conclusionary effect of the Appeal Panel Medical Assessment Certificate issued pursuant to s 328(5) of the Workplace Injury Management and Workers Compensation Act 1998? (b)Is the Appeal Panel Medical Assessment Certificate issued pursuant to s 328(5) of the Workplace Injury Management and Workers Compensation Act 1998 conclusive beyond the threshold requirement for economic and non-economic loss pursuant to section 26C of the Civil Liability Act 2002? (c)Does the Appeal Panel Medical Assessment Certificate issued pursuant to s 328(5) of the Workplace Injury Management and Workers Compensation Act 1998 extend to the causation of the relevant impairment in a medical sense? (d)Do the Appeal Panel findings give rise to an estoppel in respect of the issues they were required to determine including causation? (e)Does any estoppel issue arise from the conduct of the Plaintiff in respect of the Appeal Panel's decision?

Background 3On 6 April 2000 the plaintiff was sentenced to 12 months periodic detention for stealing a mobile phone. He was at the time aged 23. 4On 1 November 2000 the periodic detention order was revoked for non-compliance and he was sentenced to a fixed term of 10 months imprisonment commencing on 30 November 2000. Thereafter he was held variously at Parramatta, Silverwater and Windsor Correctional Centres before being transferred to the Metropolitan Special Program Centre at Long Bay Correctional Complex in August 2001 awaiting transfer to Junee Correctional Centre where, at his own request, he was to serve the balance of his sentence in protective custody. 5On 16 August 2001 he was assaulted in the shower facilities at the Long Bay Correctional Complex as a result of which he suffered facial fractures and bruising to his ribs, back and spleen. He served the balance of his sentence at the Metropolitan Medical Transient Centre within Long Bay Correctional Centre. 6Following his release from custody on 29 September 2001 he experienced headaches, memory loss and episodic loss of consciousness. 7On 11 March 2002 he suffered what was diagnosed as a grand mal epileptic seizure which caused him to fall to the ground and strike his head. He was hospitalised. A CT scan revealed a bi-frontal extradural haematoma. Two craniotomies were performed. He was discharged on 25 March 2002. He has continued to suffer epileptic seizures since that time.

The pleadings 8The plaintiff contends that the injuries for which the defendant is liable in damages include facial fractures, bruising and brain damage (with associated behavioural disorders), and that his disabilities include the epilepsy with which he was diagnosed six months after his release from custody. 9On 7 July 2006 the defendant filed a defence in which it admitted it had a duty to take reasonable care for the safety of prisoners in the correctional system but denied that the plaintiff suffered the assault in breach of that duty. The extent of the plaintiff's injuries and disabilities claimed to be causally related to the assault was also put in issue. 10By an amended defence filed on 6 October 2009 the defendant admitted breach of its duty of care. It also admitted that the plaintiff suffered facial fractures and bruising as a result of the breach, but denied liability for the balance of the plaintiff's injuries and disabilities. The defendant contends that the plaintiff's history of poly-substance drug abuse and past head injuries are the proximate causes of his neurological and psychiatric condition. 11The defendant also raises the application of Pt 2A of the Civil Liability Act 2002 in answer to the whole of the plaintiff's claim.

Part 2A of the Civil Liability Act 12It is not controversial that the plaintiff falls within the class of persons defined in Pt 2A of the Civil Liability Act as "an offender in custody" and that the defendant is "a protected defendant", also as defined in Pt 2A of the Act. Part 2A was incorporated into the Civil Liability Act by the Civil Liability Amendment (Offender Damages) Act 2004 ("the amending Act"). 13The parties did not take me to the Second Reading Speeches whether to put into context the operation of Pt 2A relative to the general provisions in Pt 1A of the Act, or to put into context the way in which relevant provisions of the Workplace Injury Management and Workers Compensation Act 1998 ("the 1998 WC Act") operate when proceedings in negligence against the Crown are brought by an offender injured in custody. For reasons which I will expand upon later in this judgment I have found the Second Reading Speeches instructive in elaborating upon the object to which the amending Act was directed and the legislative purpose of Pt 2A within the structure of the Civil Liability Act as a whole. I have, however, utilised these materials conscious of the need to have regard to the words ultimately used by the Parliament to effect its legislative purpose consistent with the approach in Harrison v Melhem [2008] NSWCA 67; 72 NSWLR 380, an approach that was endorsed and expanded upon by Allsop P in Wilson v State Rail Authority of New South Wales [2010] NSWCA 198 at [12]-[14]. 14In addition to imposing a statutory threshold on the recovery of damages by offenders who bring proceedings against the Crown for injuries sustained in custody (or performing community service orders), s 26BB (also within Pt 2A of the Civil Liability Act ) operates to impose obligations on a claimant to give notice of a claim within six months of the relevant date of claim and to furnish specified information and produce specified documents or records in order to enable the Crown to vouchsafe the validity of a claim for damages and to enable an early assessment of liability to be made. Section 26BD affords the Crown a right to apply to have the proceedings dismissed if the claimant fails to comply with these statutory obligations. The Court is obliged to dismiss the proceedings unless satisfied that there has been compliance or the claimant provides a "full and satisfactory explanation" for non-compliance and that notice of the claim was given within a reasonable time. 15Since it is the plaintiff's case that he was injured whilst he was an offender in custody and that his injury was caused by the defendant's negligence, (the precise language in s 26B which attracts the application of Pt 2A), he has no entitlement to damages unless his injury results in a degree of permanent impairment assessed as at least 15% of whole person impairment as provided for in s 26C. Section 26D provides that the degree of permanent impairment is to be assessed in accordance with the procedure in Div 2 of Pt 2A of the Act and Pt 7 of Ch 7 of the 1998 WC Act . Section 26D(2) provides that Pt 7 of Ch 7 applies as if an assessment under Pt 2A were an assessment under and for the purposes of Pt 7 of Ch 7, and as if a reference to a worker were a reference to an offender and the Crown were the worker's employer. 16Sections 26D(3) and (4) of the Civil Liability Act provide: (3) If there is a dispute about the degree of permanent impairment of an injured offender, a court may not award damages unless the degree of permanent impairment has been assessed by an approved medical specialist in accordance with the 1998 WC Act. (3A) A dispute about the degree of permanent impairment of an injured offender cannot be referred for assessment unless the offender has provided the protected defendant with a medical report by a medical practitioner that assesses that the degree of permanent impairment of the injured offender is at least 15% and sets out the medical practitioner's reasons for that assessment. (4) A court may, at any stage in proceedings on a claim for damages, refer the matter for assessment of the degree of permanent impairment by an approved medical specialist in accordance with the 1998 WC Act. 17Section 26D(2)(f) provides that the provisions apply with "such other modifications as may be prescribed by the regulations". Modifications are defined to include "addition, omission or substitution". There have been no regulations enacted since the passage of the amending Act.

Assessment process under the 1998 WC Act 18In October and November 2007 the dispute between the parties concerning the extent of the plaintiff's injuries attributable to the assault crystallised into a medical dispute as defined in s 319 of the 1998 WC Act. 19Section 319 defines "a medical dispute" to mean: A dispute between a claimant and the person on whom a claim is made about any of the following matters or a question about any of the following matters in connection with a claim: (a) the worker's condition (including the worker's prognosis, the aetiology of the condition, and the treatment proposed or provided), (b) the worker's fitness for employment, (c) the degree of permanent impairment of the worker as a result of an injury, (d) whether any proportion of permanent impairment is due to any previous injury or pre-existing condition or abnormality, and the extent of that proportion, (e) the nature and extent of loss of hearing suffered by a worker, (f) whether impairment is permanent, whether the degree of permanent impairment of the injured worker is fully ascertainable. 20Under the 1998 WC Act an approved medical specialist is authorised to determine the matters referred for assessment and to issue a Medical Assessment Certificate (MAC). 21Section 325 provides that the MAC is to: (a) set out details of the matters referred for assessment, (b) certify as to the approved medical specialist's assessment with respect to those matters, (c) set out the approved medical specialist's reasons for that assessment, and (d) set out the facts on which that assessment is based. 22The following matters are presumed by s 326 to be conclusively correct in any proceedings before a court or the Commission with which the MAC is concerned: (1) ... (a) the degree of permanent impairment of the worker as a result of an injury, (b) whether any proportion of permanent impairment is due to any previous injury or pre-existing condition or abnormality, (c) the nature and extent of loss of hearing suffered by a worker, whether impairment is permanent, whether the degree of permanent impairment is fully ascertainable. (2) As to any other matter, the assessment certified is evidence (but not conclusive evidence) in any such proceedings." 23Section 323 provides that: (1) In assessing the degree of permanent impairment resulting from an injury, there is to be a deduction for any proportion of the impairment that is due to any previous injury (whether or not it is an injury for which compensation has been paid or is payable under Division 4 of Part 3 of the 1987 Act) or that is due to any pre-existing condition or abnormality. (2) If the extent of a deduction under this section (or a part of it) will be difficult or costly to determine (because, for example, of the absence of medical evidence), it is to be assumed (for the purpose of avoiding disputation) that the deduction (or the relevant part of it) is 10% of the impairment, unless this assumption is at odds with the available evidence. (3) The reference in subsection (2) to medical evidence is a reference to medical evidence accepted or preferred by the approved medical specialist in connection with the medical assessment of the matter. 24The medical dispute between the parties was referred to Dr Teoh, a specialist in psychiatry, and Dr Mellick, a specialist neurologist. They were each provided with medical reports obtained from a range of medical experts retained by the plaintiff and the defendant together with psychological assessments and clinical records which they took into account for the purposes of assessing the plaintiff's permanent impairment. Both doctors interviewed the plaintiff. 25On 29 November 2007 both doctors issued MACs. Although the form of the certificates complied with the requirements of s 325, the defendant took issue with the findings of both doctors concerning the degree of permanent impairment certified to be as a result of the injury the plaintiff suffered in custody (s 326(a)) and the proportion of his permanent impairment that was due to a previous injury or pre-existing condition or abnormality (s 326(b)). 26Dr Teoh assessed the plaintiff's whole person impairment at 13% and issued a MAC in those terms. In making this assessment he took into account the psychological injury suffered by the plaintiff which predated the assault in prison and which presented following his release from custody after the immediate impact of the physical injuries suffered in the assault had resolved. Dr Teoh made no deduction for the plaintiff's psychological injuries that predated the assault whether related to the plaintiff's past drug use or otherwise. 27Dr Mellick assessed the impairment to the plaintiff's central and peripheral nervous system (taking into account his epilepsy and emotional and behavioural disorders) at a combined value of 45%. He reduced the degree of impairment by 10% by reason of the plaintiffs admitted chronic drug use and the trauma he had suffered both to his head and face in circumstances unrelated to the head injury he suffered in prison. 28In the result, Dr Mellick's assessment of the plaintiff's whole person impairment exceeded the statutory threshold of 15% thereby entitling the plaintiff to pursue his claim for damages against the Crown, while Dr Teoh's assessment did not. 29One of the issues comprehended by the questions referred for separate determination is the extent to which the question of causation in the substantive proceedings is to be resolved in accordance with Pt 1A of the Civil Liability Act where there has been an assessment of the degree of the plaintiff's impairment as a result of the assault in prison under Pt 7 of the 1998 WC Act for the purposes of compliance with Pt 2A of the Civil Liability Act . 30Section 5A of the Civil Liability Act provides that Pt 1A applies to any claim for damages for harm resulting in negligence save for civil liability (and awards of damages in those proceedings specifically excluded from the operation of Pt 1A by s 3B. 31Section 5D(1) provides that a determination that negligence caused particular harm comprises the following elements: (a) that the negligence was a necessary condition of the occurrence of the harm ( factual causation ), and (b) that it is appropriate for the scope of the negligent person's liability to extend to the harm so caused ( scope of liability ). 32In the substantive proceedings, the defendant denies that its negligence was a necessary condition of the occurrence of the extent of harm for which the plaintiff seeks compensation thereby putting "factual causation" in issue. 33Section 5E provides that in determining liability for negligence the plaintiff always bears the onus of proving any fact relevant to the issue of causation on the balance of probabilities (see Adeels Palace Pty Ltd v Moubarak; Adeels Palace Pty Ltd v Bou Najem [2009] HCA 48; 239 CLR 420) . 34In the proceedings before me the defendant submitted that the combined effect of these provisions reflects a clear and unambiguous intention on the part of the legislature that the operation of Pt 2A of the Civil Liability Act is to be read subject to Pt 1A such that once a claimant's entitlement to maintain an action against a protected defendant is supported by an assessment of permanent impairment exceeding the 15% statutory threshold (as is the case here), the action falls to be determined strictly in accordance with the general provisions in Pt 1A. 35In December 2007 the defendant appealed against the assessments of both Dr Mellick and Dr Teoh to a Medical Appeals Panel ("the Appeal Panel") invoking the procedure in s 327 of the 1998 WC Act. The grounds cited and upon which the Registrar determined the matter to be appropriate for referral under s 327(3)(d) was that both certificates contained demonstrable errors. 36The Appeal Panel accepted the defendant's submission that Dr Teoh was in error in his approach to the medical assessment of the plaintiff's psychological impairment. It held: The AMS examined the Applicant on 6 November 2007. The AMS was requested to assess the whole person impairment due to psychological/psychiatric injury as a result of injury occurring on 1 July 2001. The Panel notes that the reference to 1 July 2001 is probably an error and should be reference to the 16 August 2001. The referral was for the purposes of assessing whole person impairment pursuant to section 26D of the Civil Liability Act 2002. Section 26D(5) provides that section 151H of the 1987 Act applies for the purposes of assessment of whether the degree of permanent impairment resulting from an injury is at least 15 percent. Section 151H(2) provides that impairment resulting from physical injury is to be assessed separately from impairment resulting in psychological injury and in assessing impairment resulting from psychological injury, no regard is to be had to impairment that results from a secondary psychological injury. 37The Appeal Panel revoked the certificate issued by Dr Teoh and issued a fresh certificate in which the plaintiff's impairment was assessed at 0%. There is no challenge to the correctness of the Appeal Panel's assessment. 38Although the defendant did not challenge Dr Mellick's assessment of the plaintiff's permanent impairment due to episodic loss of consciousness and his emotional and behavioural disorders at 29% respectively, it submitted that Dr Mellick was in error in reducing the plaintiff's degree of impairment by the statutory ratio of 10% (as provided for in s 323(2) of the 1998 WC Act) when the medical evidence was eloquent of him having suffered previous head injuries and long term drug use which justified a significantly greater reduction. 39The Appeal Panel conducted a preliminary review of the medical assessment undertaken by Dr Mellick in the absence of the parties after which it determined that it was not necessary for the plaintiff to undergo a further medical examination. (I note that the defendant did not urge the Panel to re examine the plaintiff.) It also had before it the very considerable documentation that was available to Dr Mellick and expressly took that material into account when making its determination. 40After considering the plaintiff's lengthy history of drug use, including the intravenous administration of recreational drugs, his history of head injuries and, from a medical perspective, the relationship of withdrawal from benzodiazepines to the onset of epileptic seizures, on 31 March 2008 the Appeal Panel issued a fresh MAC pursuant to s 328(5) of the 1998 WC Act in which the plaintiff's whole person impairment was reassessed at 28%. Section 328(5) of the 1998 WC Act provides that s 326 applies to the new certificate. It is in this way that the ambit of the conclusionary effect of a MAC arises in this case, and why the first and second questions referred for determination are expressed to be referable to s 328(5) of the 1998 WC Act. 41While Dr Mellick accepted that the paroxysmal and the emotional and behavioural disorders were partly due to the plaintiff's exposure to illicit drugs, such that he allowed a reduction of only 10% in whole person impairment, the Appeal Panel was of the view that he did not adequately explain his reasoning in coming to that view. The Panel noted as follows: [25] The evidence discloses that whilst there was a deterioration in the memory disorder and the personality change since the assault the condition, nonetheless, was present prior to that date. The Panel is of the view that the previous head injuries would also have contributed to the development of the current impairment. In particular the Panel notes that in 1994 a CT scan disclosed a large CSF collection in the left frontal pole with displacement of the frontal pole that was possibly due to old trauma rather than a recent collection. The existence of the large collection at that time is consistent with the earlier injuries having commenced the process which ultimately lead to the seizures. In the circumstances the Panel is satisfied that the prior head injuries and the history of drug use both make a significant contribution to the current impairment. The Panel is satisfied that there is sufficient evidence to make an assessment of the section 323 deduction. The Panel is of the view that 50 per cent of both the episodic loss of consciousness or awareness and the emotional and behavioural disorders is due to pre-existing injury, condition or abnormality. [26] For these reasons, the Panel has therefore determined that the Medical Assessment Certificate dated 29 November 2007 given in this matter should be revoked, and a new Medical Assessment Certificate should be issued... 42The Appeal Panel also invited the parties to file written submissions directed to the issue of the binding effect of the MAC issued by Dr Mellick in the context of what the parties considered to be the issues in dispute in the substantive litigation. 43In its written submissions the defendant contended that Dr Mellick's approach to assessment was in error since it proceeded on the basis that the assault in prison (and the injuries sustained at that time) caused the plaintiff's epilepsy when that was a matter in dispute between the parties to be resolved in accordance with Pt 1A of the Civil Liability Act . The defendant submitted that in making a finding of medical causation as a factual finding Dr Mellick exceeded the ambit of the medical dispute that was referred to him for assessment. 44In written submissions the plaintiff accepted that causation is a matter to be determined by the Court and that a certificate issued under s 326 is only conclusive as to whether the plaintiff has a greater than 15% whole person impairment. This is contrary to the plaintiff's position in the substantive proceedings (and in the proceedings before me) giving rise to what the defendant submits is an estoppel either by conduct or by convention. Whether the position advanced by the plaintiff in submissions filed with the Appeal Panel is binding on him in this way is one of the specific questions referred by Harrison J for separate determination. 45In dealing with the defendant's submission concerning what was claimed to be Dr Mellick's erroneous approach to the issue of causation (a position that the defendant submitted at the hearing before me was clarified by the Appeal Panel so as to accord with the approach it now contends to be correct), the Panel reasoned as follows: [20] The defendant submits that the Approved Medical Specialist was in error by assessing the Whole Person Impairment solely on the basis that the alleged assault of 16 August 2001 caused the seizure on 11 March 2002. This is a matter that is in dispute between the parties. The defendant submits that the Approved Medical Specialist has made a determination of causation which is not permitted by section 319(c). That section defines a "medical dispute" to mean, amongst other things, a dispute about the degree of permanent impairment of the worker as result of an injury. The defendant points out that an AMS is limited to determining any matters falling within a "medical dispute". The defendant's submission in this respect is unclear. The Act clearly empowers an AMS to determine the degree of permanent impairment as result of an injury. To that extent the Approved Medical Specialist is entitled to make a determination of causation. This was fully explained by Deputy President Roche in Conner v Trustees of the Roman Catholic Church for the Archdioceses of Sydney [2006] NSWWCCPD 124 and in Spicer Axle Australia Pty Ltd v Merza [2007] NSWWCCPD 148. What the Approved Medical Specialist is not entitled to do is to make a determination of what constitutes the injury. [21] In this case the Approved Medical Specialist was required to carry out an assessment on the basis that there is a causal connection between the assault and the seizures subsequently suffered. This approach is consistent with what was said by the Supreme Court in Wikaira v Registrar of the Workers Compensation Commission of NSW and Anor [2005] NSWSC 954 and Merza v Registrar of the Workers Compensation Commission and Anor [2006] NSWSC 939. It is a matter for a court to ultimately determine what the injury was that was suffered by the Respondent worker. The Medical Assessment Certificate does not determine that issue. [22] The Respondent referred the panel to the decision of the Court of Appeal in Pham v Shui [2006] NSWCA 373. In that case the Court of Appeal held that a medical assessment certificate issued for the purposes of the Motor Accidents Compensation Act 1999 was only conclusive in determining whether the claimant had a greater than 10 per cent WPI. It did not determine questions of injury. If the court determines that the seizure was caused by the assault on 16 August 2001 the certificate will operate as conclusive evidence of the whole person impairment resulting from that injury. If the court determines that the injury is not as assumed by the Approved Medical Specialist then the court can refer the matter for assessment in accordance with its findings pursuant to section 26D(4) of the Civil Liability Act 2002. 46The plaintiff also raises issue estoppel which he contends prevents the defendant from arguing in the substantive proceedings that he did not suffer a 28% whole person impairment as a result of the assault, since the Appeal Panel had jurisdiction, which derived from statute, to determine the issue of medical causation, and that it determined that question in a manner that is now binding on the parties. This is the third question referred for separate determination. 47On 5 November 2010 the plaintiff filed a reply to the defendant's amended defence filed on 6 November 2009. On 24 November 2010 the defendant filed a rejoinder. On these pleadings, the plaintiff's revised position is that he seeks to proceed to the hearing on the basis that the MAC issued by the Appeal Panel is conclusive as to medical causation of the injuries identified in the MAC issued by them, while the defendant seeks to proceed on the basis that the MAC is conclusive only as to the degree of the plaintiff's whole person impairment and that factual and medical causation remain a matter in issue to be determined by the Court in accordance with Pt 1A of the Civil Liability Act .

The defendant's submissions as to the conclusionary effect of a MAC (Separate questions a, b and c) 48Mr Weinstein submitted that s 326 of the 1998 WC Act neither supports the conclusion that a MAC is conclusive for all purposes relating to issues of causation, nor that it is the role of a medical assessor (or the Appeal Panel under s 328(5)) to determine questions of causation. He submitted that while an enquiry into the aetiology of the plaintiff's condition was a matter with which the Appeal Panel was concerned (it being one of a number of matters included within the definition of a medical dispute in s 319(a) of the 1998 WC Act and referred for assessment under Pt 2A of the Civil Liability Act ), the certificate issued by them was not conclusive of the medical aetiology of the plaintiff's condition as a matter of legal or factual causation but only for the purposes of determining whether the statutory threshold was exceeded under Pt 2A. He submitted that causation must be decided in accordance with ss 5D and 5E within Pt 1A of the Civil Liability Act . 49Mr Weinstein submitted that by amending the Civil Liability Act so as to provide for a regime for regulating actions for damages brought by offenders in custody the Legislature should not be should not be taken to have intended that Pt 1A was to have no continuing application where the civil liability of the State was at issue in the absence of express words that the amendments were intended to have that effect. 50As I have already noted, the Legislature made express provision in s 3B of the Act that Pt 1A was to have no application to, or in respect of, civil liability (and awards of damages) in whole or in part in specified proceedings. That section was not amended at the time of the passage of the amending Act to include actions brought by offenders in custody under Pt 2A. In addition, s 3B(3) provides that the regulations may exclude a specific class or classes of civil liability (and awards of damages in those proceedings) from the operation of all or any part of the Civil Liability Act . There have been no regulations enacted to include actions brought by offenders in custody. In the Second Reading Speech when the Civil Liability Amendment (Offender Damages) Bill was before the Parliament the Honourable John Hatzistergos, then Minister for Justice, said: ... The scheme introduced by the bill is fault-based. Liability in negligence must be established under the Civil Liability Act 2002 . No damages can be awarded unless the injury results in the death of the offender or a degree of permanent impairment of at least 15 per cent, with the degree of impairment being assessed in the same way that it is under the Workplace Injury Management and Workers Compensation Act 1998. Damages for economic loss for past and future loss of earnings will be limited in the same way that those damages are limited under the Workers Compensation Act 1987 for damages for workplace injury. (emphasis added) 51Mr Weinstein submitted that in Berowra Holdings Pty Ltd v Gordon [2006] HCA 32; 225 CLR 364 at [23] Gleeson CJ, Gummow, Hayne, Heydon and Crennan JJ observed that the approach of the courts has consistently been to require very clear legislative intent before treating a statutory provision as taking away the common law rights of a plaintiff where an alternate construction is available, and that the same analysis should obtain where the common law rights of the State as defendant are liable to be diminished (see also the views of Allsop P in Wilson v State Rail Authority of New South Wales [2010] NSWCA 198 at [172], albeit in the context of a derogation of the common law rights of an injured worker). 52Mr Weinstein submitted that s 326 is in clear terms and that the conclusive effect of a MAC issued under that section is limited to certifying the degree of permanent impairment of a worker "as a result of an injury", which in this case translates as the degree of permanent impairment of the plaintiff "as a result of an injury" he suffered whilst in custody. He submitted that just as a MAC is not conclusive as to whether a worker's injury is compensable under the Workers Compensation Scheme, neither is it conclusive in this case of the question whether the extent of the plaintiff's injuries and disabilities were caused by any breach of duty on the part of the defendant such as to entitle him to an award of common law damages under the Civil Liability Act . 53Mr Weinstein also directed argument to the operation of Pt 7 in the context of the 1998 WC Act generally in order to make good his ultimate submission that the questions of causation that arise in this case are reserved for determination by the Court. 54He submitted that the consistent references to "an injury" in Pt 7 of the 1998 WC Act - in particular the phrase "as a result of an injury" in ss 319(c) and 326(1)(a) - must be taken to mean " a personal injury arising out of or in the course of employment" given that injury is defined in s 4 of the Act in those terms. This is said to be in contrast to "work injury" in other parts of the Act where that phrase is defined in s 4 to mean "an injury in respect of which compensation is payable". Mr Weinstein submitted that this supports the conclusion that the Legislature did not intend that all references to injuries under Pt 7 of the 1998 WC Act would be compensable injuries. He submitted that analysed in this way the operative provisions in Pt 7 which refer to the degree of impairment arising as a result of an injury (as in s 319(c) or s 326 (1)(a)) or resulting from an injury (as in ss 322(2) and 323) are a reference to an injury that the worker asserts arose out of or in the course of employment, or that the worker asserts is a compensable injury. He submitted that whether an injury is a compensable injury is a legal question to be resolved by the Workers Compensation Commission ("the Commission") preliminary to the recovery of damages and not a question that is referred to a medical assessor for assessment under the Act. 55This analysis is said to be borne out by the approach in Issott v North Sydney Leagues Club Ltd t/as Seagulls Club [2005] NSWWCCPD 38 where, notwithstanding a certified finding by a medical assessor that a worker had suffered permanent impairment as a result of injury, an award was made in favour of the employer. At paragraphs 54 to 56 Acting Deputy President Moore said as follows: [54] The Appellant Worker submits that in certifying as to the degree of permanent impairment, the AMS certifies the degree of impairment is as a result of injury, and that accordingly, if there were no injury, there would be no impairment. [55] However, the 'injury' can only ever be that which is asserted by the parties. For example, a worker might state 'I fell off the truck and injured my knee'. The employer might say 'his mates told us he injured his knee playing football on the weekend'. There may be no dispute that the worker has an injured knee - one injury is compensable, the other is not. [56] The task of the AMS is medical, and is to resolve a medical dispute between the parties. Unless specifically requested, it is not the role of the AMS to determine whether injury occurred, or occurred in the course of employment or any other of the multiplicity of questions that can arise in determining 'injury' within the meaning of the 1987 Act. 56In Connor v Trustees of the Roman Catholic Church for the Archdiocese of Sydney [2006] NSWWCCPD 124 at [48] , the Commission observed that: ... the determination of the issue of 'injury' requires not only an assessment of whether the 'injurious event' occurred in compensable circumstances but also whether the pathology found to exist (if any) has been caused by the work event. These are both threshold liability issues to be decided by the Commission not by an AMS or an Appeal Panel. Employment must be a substantial contributing factor to the work event and to the pathology found before liability arises under the legislation. The determination of these issues requires a consideration of all of the factual and legal issues in the case. It is not simply a medical question. 57The extent to which a MAC issued under Pt 7 is binding on the parties was also considered by the Commission in Jopa Pty Ltd t/as Tricia's Clip-n-Snip v Edenden [2004] NSWWCCPD 50 where Deputy President Fleming said at [27]: However the issue of a MAC does not equate to a determination of the dispute by the Commission. There are obvious reasons why the legislature would have intended that the ultimate determination of the matter rests with an Arbitrator. There may be a number of issues in dispute between the parties which, while not medical issues, must be agreed, or determined by an Arbitrator, in order to finally resolve the matter. These may include issues of liability and associated claims for compensation by way of weekly benefits and medical expenses. Procedural fairness, the filing of evidence and compliance with the procedural requirements of the Workers Compensation Acts ('the 1987 Act and the 1998 Act') may also need to be considered. 58These decisions have been consistently cited with approval in the Commission (see for example Davies v Bisaxa Pty Ltd t/as Sir Joseph Banks Nursing Home [2006] NSWWCCPD 103 and New South Wales Fire Brigades v Turton [2008] NSWWCCPD 66). 59Mr Weinstein submitted that there is further support within the 1998 WC Act for the medical assessor's role (or the role of the Appeal Panel in this case) not extending to determining issues of causation (irrespective of whether they are characterised as legal, factual or medical) in two provisions that either expressly or impliedly require a person or entity other than the medical assessor (or Appeal Panel) to assess liability issues. 60Section 321(1) provides that a medical dispute may be referred for assessment under Pt 7 of the 1998 WC Act by a court, the Commission or the Registrar, either of their own motion or at the request of a party to the dispute. However, s 321(4) provides that the Registrar may not refer a medical dispute concerning permanent impairment of an injured worker where liability is in issue and where it has not been determined by the Commission under Pt 7. Mr Weinstein submitted that were the role of the medical assessor to determine liability (including causation), and the MAC was conclusive as to that issue, then there would be no work for s 321(4) to do. He emphasised that it is not open to me to regard any of the operative provisions within Pt 7 (or any part of those provisions) as superfluous or insignificant as all words of an enactment must be given some meaning and effect consistent with the principles of statutory construction (see Project Blue Sky Inc v Australian Broadcasting Authority [1998] HCA 28; 194 CLR 355). 61While there is some force in that submission, for reasons that the parties could not explain, the Registrar was persuaded to refer the medical dispute between the parties in this case for assessment under s 321 prior to any determination as to liability by the Court or any admission as to liability by the defendant. (I note that there is express power in s 26D(4) of the Civil Liability Act for the Court to have referred the plaintiff's degree of permanent impairment for assessment but again, for reasons neither apparent nor explained, this was not done.) The fact that the matter was referred for assessment by the Registrar is an example of one of the procedural anomalies that have resulted from the wholesale importation of a regime specific to the assessment of workplace injuries under the Workers Compensation legislation into the Civil Liability Act which, aside from Pt 2A, is an Act of general application. That there is this anomaly (perhaps amongst others) underpins the reason for the referral of the questions for separate determination and their complexity.

The plaintiff's submissions as to the conclusionary effect of a MAC (Questions a, b and c) 62Mr Cranitch QC submitted that by importing Pt 7 of the 1998 WC Act into the Civil Liability Act the Legislature has incorporated a streamlined and efficient process for the resolution of issues of medical causation by specialist assessors where the proceedings relate to injuries sustained by offenders in custody caused by the Crown's negligence. 63He submitted that the very dispute the Appeal Panel was required to determine concerned causation since it involved a review of Dr Mellick's assessment of the degree of permanent impairment the plaintiff had suffered as a result of being injured in prison and the extent to which the impairment was attributable to cause s other than the assault. Despite the Appeal Panel's restrictive approach to the issue of causation (which Mr Cranitch submitted revealed both internal inconsistencies and a misunderstanding of application of the decisions of this Court cited by the Appeal Panel) in coming to the concluded view that there should be a reduction of 50% due to the plaintiff's drug use and previous head injuries, he submitted the Appeal Panel necessarily decided the question of medical causation in the plaintiff's favour when finding that the balance of his impairment was attributable to the prison assault. 64Mr Cranitch also submitted that the findings of the Appeal Panel fix the plaintiff's percentile disability for which the defendant is responsible through its admitted negligence conclusively at 28%, and since that assessment exceeds the statutory threshold under s 26C of the Civil Liability Act , the only question that remains in dispute between the parties is the assessment of damages. He stressed that the fact that the plaintiff has exceeded the statutory threshold does not dictate or even influence the calculation of damages. It simply gives him an entitlement to pursue a claim in damages which, subject to ss 26E-26I under Pt 2A the Civil Liability Act , will be assessed by the Court in the ordinary way. He also argued that since the plaintiff could not avoid going into evidence at the damages hearing, it is open to the defendant to challenge the evidence relating to his drug use both before and after the onset of his epileptic seizures, and any other issues which the defendant claims it has been deprived of the opportunity to test in the non-adversarial medical assessment process under Pt 7 of the 1998 WC Act. He freely conceded that were the Court not persuaded of the truth or reliability of the account the plaintiff gave to Dr Mellick, and to the other doctors whose reports were considered by Dr Mellick and the Appeal Panel, then his damages will be diminished accordingly. 65Mr Cranitch went further and submitted that if in the damages hearing the Court were to come to the view that the integrity of the medical assessment of permanent disability was undermined by the plaintiff's unreliability as a historian (or even vitiated entirely by reason of dishonesty), and the question arose as to whether his impairment in fact exceeds the statutory threshold, then there is express power in s 329 for the matter to be referred for further assessment. Section 329 provides that: (1) A matter referred for assessment under this Part may be referred again on one or more further occasions for assessment in accordance with this Part, but only by: (a) the Registrar as an alternative to an appeal against the assessment as provided by section 327, or (b) a court or the Commission. (1A) ... (2) A certificate as to a matter referred again for further assessment or reconsideration prevails over any previous certificate as to the matter to the extent of any inconsistency. 66Clearly enough "the matter" being referred under s 329(1) is a medical dispute (as defined) since that is the only matter into which a medical assessor may enquire. 67While the Court has power to refer a medical dispute of its own motion, Mr Cranitch accepted that it could not direct a medical assessor to arrive at an assessment on the basis of any view it might hold concerning the plaintiff's veracity or reliability, any more than the assessor has any statutory power to make conclusive findings as to a claimant's credit, although it can require a claimant to submit to examination for the purposes of a medical dispute and it is required to provide reasons for its findings which might involve or include a non-binding view touching on issues of credit. 68Mr Cranitch acknowledged that in dealing with the defendant's submission that Dr Mellick exceeded his statutory authority by determining what the defendant described as factual causation, the Appeal Panel regarded itself as bound by decisions of the Commission. He did not submit that these cases were decided in error. Rather, he identified a circularity in the Appeal Panel's reasoning in reliance upon them for the purposes of this case if they intended to hold that the MAC operates as conclusive evidence of the plaintiff's whole person impairment as a result of the injury he suffered in prison only if the Court is ultimately satisfied that the seizures are causally related to the assault, when a determination of that question as a medical question is inherent in their finding that 50% of his impairment was due to causes other than the prison assault. 69Mr Cranitch relied upon Merza v Registrar of the Workers Compensation Commission & Anor [2006] NSWSC 939 and the distinction Hoeben J drew between medical causation and legal causation. In Merza his Honour had occasion to consider whether error had been established where a medical assessor certified that a worker had suffered no permanent impairment in circumstances where the referral of the medical dispute by the arbitrator was expressed in terms of the plaintiff suffering sexual dysfunction as a result of an injury to his lower back sustained in the course of employment. The plaintiff relied upon Wikaira v Registrar of the Workers Compensation Commission of NSW & Anor [2005] NSWSC 954 as authority for the proposition that where an arbitrator had made an express finding of relevant injury it was not open to the assessor to find no relevant injury because there was no evidence of injury. In Wikaira Malpass AJ was satisfied that where this was the assessor's certified position the MAC contained a "demonstrable error" warranting the matter being referred for further assessment. Hoeben J was not persuaded that the plaintiff had made out error of that kind. His Honour was satisfied that there was a clear issue raised in the referral by the arbitrator as to the nature and extent of the work injury suffered by the plaintiff which required the expertise of the medical assessor to resolve and that a general statement as to the nature of the injury in the referral was necessary in order for the assessor to determine "the precise pathological process of the injury" as a medical question. In resolving to the view that there was in fact no causal connection between the back injury and resultant dysfunction and the work injury, his Honour was of the view that the assessor was determining a medical issue not a legal one. He regarded that finding as well supported by the materials available to the assessor which was reflected in a well reasoned and comprehensive statement of reasons that formed part of the MAC under challenge. 70Mr Cranitch submitted that although the assessment regime in Pt 7 of the 1998 WC Act has been imported without qualification into Pt 2A of the Civil Liability Act , it does not follow that the same limitation on the conclusivity of a certificate issued under s 326 should apply in the context of a common law action in negligence. He emphasised that Pt 2A is concerned with injuries sustained by an offender in custody, being injuries that are caused by the negligence of a protected defendant, a proposition that s 26B puts beyond doubt. That s ection provides: (1) This Part applies to and in respect of an award of personal injury damages against a protected defendant in respect of: (a) an injury to a person received while the person was an offender in custody, or (b) the death of a person resulting from or caused by an injury to the person received while the person was an offender in custody, being an injury caused by the negligence (that is, the failure to exercise reasonable care and skill) of the protected defendant or caused by the tort (whether or not negligence) of another person for whose tort the protected defendant is vicariously liable. (emphasis added) 71He submitted that for this reason the decisions of the Commission that concern the conclusivity of a MAC for a work related injury should not dictate the approach to a certificate in proceedings brought under Pt 2A of the Civil Liability Act . He emphasised that the Commission is not concerned with injuries caused by negligence where damages are assessed at common law (subject to the operation of Pt 2 and Div 3 and 4 of Pt 2A of the Civil Liability Act ), but with injuries arising out of or in the course of employment where the payment of compensation is comprehensively regulated by a statutory scheme which has significantly modified a worker's common law rights to damages (as to which see the enactment history of the Workers Compensation Acts comprehensively reviewed by Allsop P in Wilson ). 72Mr Cranitch supplemented his written submissions orally by arguing that it is not to the point that the Legislature may not have intended that in cases where the statutory threshold is exceeded, s 326 of the 1998 WC Act would operate to resolve, conclusively, the extent of an injured offender's disability caused by a protected defendant's negligence, when the fact and extent of a worker's disability suffered as a result of a workplace injury certified under the same section does not have that effect. He submitted that the general words of causation in s 26B of the Civil Liability Act are critical. 73That submission, however, fails to recognise that Ch 7 of the 1998 WC Act, concerned with what are described as "New Claims Procedures" which were introduced by the Workers Compensation Legislation Amendment Act 2001 and the Workers Compensation Legislation Further Amendment Act 2001, distinguishes between "work injury damages" and "compensation" in a way that parallels s 26B of the Civil Liability Act . 74Work injury damages are defined in s 250(1) in Pt 1 of Ch 7 as: damages recoverable from a worker's employer in respect of: (a) an injury to the worker caused by the negligence or other tort of the employer, or (b) the death of the worker resulting from or caused by an injury caused by the negligence or other tort of the employer, whether the damages are recoverable in an action for tort or breach of contract or in any other action, but does not include motor accident damages. (emphasis added) 75Compensation is defined in s 4 of the 1998 WC Act as a monetary benefit (and other benefits). I note that Pts 6 and 7 of Ch 7 are concerned only with court proceedings for work injury damages. Part 6 is procedural, specifying a number of requirements a claimant must satisfy before commencing proceedings. Importantly, for current purposes, s 313 (within Pt 6) requires that the personal injury suffered by a worker sufficient to attract an award of work injury damages (that is, an injury caused by the negligence or other tort of the employer) must be assessed as at least 15% under Pt 7 before court proceedings are commenced. In this way the statutory threshold in s 313 brings actions by offenders for damages for injuries sustained in custody into alignment with actions by injured workers for "work injury damages". This was one of the stated objectives and the mischief to which the amendments to the Civil Liability Act were directed as reflected in the Second Reading Speech of the amending Bill by the Honourable John Hatzistergos, then Minister for Justice: Under the amendments proposed by this bill, liability will be assessed uniformly, injuries will be assessed uniformly, catastrophic injuries will result in compensation to no greater extent than catastrophic injuries suffered by injured workers in civilian employment, minor injuries will not be eligible for compensation, and other injuries will be eligible for limited compensation. If an offender suffers a genuine serious injury due to the negligence of a government agency or a management company exercising an official function with respect to offenders in custody, he or she will receive fair compensation. This bill will remove some of the more fanciful claims from offenders that the community are entitled to regard as spurious by setting thresholds on injuries and limits on damages payable to offenders. ... I will move now to the detail of the Bill. The Civil Liability amendment (Offender Damages) Bill will establish one faultbased negligence scheme for inmates, periodic detainees, home detainees and offenders performing work under a community service order-that is, one scheme combining liability, assessment of injury and payment of damages. The object of the bill is to amend the Civil Liability Act 2002 to impose special restrictions on the damages that can be recovered by a person for injury resulting from the negligence of a protected defendant suffered while the person was an offender in custody... 76Mr Cranitch's reliance on s 26B as the critical point of distinction between proceedings brought under Pt 2A of the Civil Liability Act and those under the 1998 WC Act also fails to grapple with the fact that although s 26B is a substantive provision (unlike s 250 which, as Allsop P noted in Wilson , is a definition section and therefore an aid to the construction of the statute) the very clear legislative intent revealed in the Second Reading Speech in the extract set out in [75] above is that the Crown's liability must be established under the Civil Liability Act . Furthermore, the Civil Liability Act must be construed as a whole in the way identified in Project Blue Sky . In Wilson Allsop P regarded what was said by McHugh, Gummow, Kirby and Hayne JJ in Project Blue Sky of particular relevance in resolving the questions of statutory construction that presented in that case. Their Honours' observations are also apposite in the context of the issues raised by the questions referred for separate determination in this case. Their Honours said: [69] The primary object of statutory construction is to construe the relevant provision so that it is consistent with the language and purpose of all the provisions of the statute. The meaning of the provision must be determined "by reference to the language of the instrument viewed as a whole". In Commissioner for Railways (NSW) v Agalianos , Dixon CJ pointed out that "the context, the general purpose and policy of a provision and its consistency and fairness are surer guides to its meaning than the logic with which it is constructed". Thus, the process of construction must always begin by examining the context of the provision that is being construed. [70] A legislative instrument must be construed on the prima facie basis that its provisions are intended to give effect to harmonious goals. Where conflict appears to arise from the language of particular provisions, the conflict must be alleviated, so far as possible, by adjusting the meaning of the competing provisions to achieve that result which will best give effect to the purpose and language of those provisions while maintaining the unity of all the statutory provisions. Reconciling conflicting provisions will often require the court "to determine which is the leading provision and which the subordinate provision, and which must give way to the other". Only by determining the hierarchy of the provisions will it be possible in many cases to give each provision the meaning which best gives effect to its purpose and language while maintaining the unity of the statutory scheme. [71] Furthermore, a court construing a statutory provision must strive to give meaning to every word of the provision. In The Commonwealth v Baume Griffith CJ cited R v Berchet to support the proposition that it was "a known rule in the interpretation of Statutes that such a sense is to be made upon the whole as that no clause, sentence, or word shall prove superfluous, void, or insignificant, if by any other construction they may all be made useful and pertinent". 77In the result, I am persuaded to the view that Pt 2A of the Civil Liability Act must be read subject to Pt 1A and that an injury caused by the negligence of the protected defendant in s 26B must be construed as "allegedly caused" and that the issue of factual causation in s 5D of the Civil Liability Act is reserved for determination by the Court. This construction is consistent with the approach taken by the Appeal Panel and the decisions of the Commission to which I have referred. I am however persuaded that there is also force in Hoeben J's approach in Merza and, as my answer to question (c) makes plain, the question of medical causation can be distinguished.

The significance of cases in this Court to which the parties have referred bearing upon the questions posed for separate determination 78For completeness I shall refer briefly to some recent authorities which were cited in argument although, in the result, they simply confirm the view I have reached in answering the questions posed for separate determination. 79Mr Cranitch referred to Motor Accidents Authority of New South Wales v Mills [2010] NSWCA 82 in support of his contention that the MAC issued by the Appeal Panel is conclusive on the issue of medical causation. This case and Pham v Shui [2006] NSWCA 373 concern the Motor Accidents Compensation Act 1999 ("the MACA") a legislative scheme that also requires medical assessments to be conducted by authorised assessors in order to determine the degree of impairment for persons injured in motor vehicle accidents as with the 1998 WC Act. 80Mr Weinstein submitted there are significant differences in the language used in relevant provisions of the MACA as compared to the 1998 WC Act which distinguish both decisions for present purposes. Under s 58 of the MACA it is the degree of permanent impairment as a result of injury caused by a motor accident that must be assessed at greater than 10% before damages for economic loss can be awarded, whereas under the 1998 WC Act the enquiry is into whether the degree of permanent impairment of the worker as a result of the injury exceeds 15% such as to entitle the worker to institute proceedings for the recovery of work injury damages. The difference in the language constituting "a medical assessment matter" in s 58(1) of the MACA and a "medical dispute" in s 319 of the 1998 WC Act (with a causative link in the language used in the MACA) is the salient point of distinction between the two statutory schemes. It is submitted that this also serves to differentiate the ambit of conclusivity in the certificates issued by authorised assessors under the respective statutory schemes. 81Mr Cranitch submitted that the differences in language between the two pieces of legislation is not decisive. He submitted that the careful consideration given to the question of the extent to which a certificate issued under the MACA was conclusive on the issue of causation in Mills was instructive, in particular the clear exposition of the position by Handley AJA which he submitted supported the construction of the conclusive effect of a certificate issued under Pt 7 of the 1998 WC Act for which he contended. 82The issue in Mills concerned the correctness of orders made by a District Court Judge in the course of a damages hearing pursuant to which only the degree of permanent impairment suffered by the plaintiff was referred for further assessment under s 62(1) of the MACA, thereby excluding any fresh consideration as to whether the injury was caused by a motor vehicle accident. The application to refer the plaintiff for reassessment was made in circumstances where the MAC certified that there was no permanent impairment in the plaintiff's lumbar spine related to the motor vehicle accident but where his Honour was satisfied that the assessment by the medical assessor was based upon a number of false assumptions compounded by plaintiff, in his Honour's view, being a poor historian. His Honour was satisfied on the evidence led in the damages hearing that the plaintiff's back injury was in fact causally related to the motor vehicle accident. 83The Motor Accidents Authority considered it was not able to direct the assessor to whom the matter was referred to disregard the question of causation because the relevant guidelines required an assessor to consider that question (as to which see the extract of the guidelines set out in full at [86] in Ackling v QBE Insurance (Australia) Ltd and Anor [2009] NSWSC 881; 75 NSWLR 482 ). His Honour was invited to reconsider the terms of the order referring the matter for further assessment and to broaden it to include the issue of causation. He declined on the basis that he had decided the question of causation. 84Giles JA (with whom Tobias JA and Hanley AJA agreed) held that whilst his Honour had power in the damages hearing to consider the degree of permanent impairment (including whether it was caused by the motor accident) and to refer the degree of permanent impairment the plaintiff for further assessment, he did not have the power to bind the medical assessor on the issue of causation as both causation and the degree of permanent impairment comprise "the matter" referred under s 62(1) and were for the medical assessor to determine. This was in accordance with Ackling which their Honours held was correctly decided . 85In reasoning to that conclusion both Giles JA and Handley AJA gave consideration to the status of a certificate issued under s 62(1) and the extent to which it is of conclusive on the question of causation although, as Giles JA noted at [57], consideration of the question was not essential to the disposition of the matter the subject of the appeal. That said, both Giles JA and Handley AJA concluded that in the scheme for medical assessments under Pt 3.4 of the MACA the legislature had made plain its intention that a certificate issued by a medical assessor was conclusive on the issue of causation (or "medical causation of the relevant injury" being the way the issue of causation is understood in the context of the operation of the MACA, as to which see Santow JA in Pham v Shui at [96] discussed by Giles JA at [65]-[69]). 86Handley AJA reasoned that s 61(2)(a) did not, in its terms, make a certificate conclusive evidence of the causation of the degree of impairment. However, since the words of the section provide that the certificate is conclusive evidence as to the matter certified where the certificate dealt with causation an element of ambiguity was introduced. His Honour then said: [96] The section must be read with the other provisions dealing with matters referred for assessment, and the effect of certificates of the degree of permanent impairment. Section 58 defines the matters to be referred for assessment. It relevantly provided: '(1) This Part [ie Pt 3.4] applies to a disagreement between a claimant and an insurer about any of the following matters: ... (d) The degree of permanent impairment of the injured person as a result of the injury caused by the motor accident, ... (2) This part also applies to any issue arising about such a matter in proceedings before a court ...' [97] The disagreement referred to is not about the degree of the injured person's impairment generally, but about the degree of that impairment "caused by the motor accident". Section 57 defines "a medical dispute" as one "to which this Part [ie Pt 3.4] applies". A dispute as to the degree of the permanent impairment caused by the motor accident is a medical dispute so defined. Section 60(1) provides that a medical dispute may be referred for assessment under this Part. Where that dispute relates to the degree of permanent impairment it necessarily involves the question of causation. [98] Thus when s 62(1) provides that the medical assessor "is ... to give a certificate as to the matters referred for assessment under this Part" (ie Pt 3.4), that certificate must deal with the degree of permanent impairment caused by the motor accident. The degree of any other permanent impairment is not a matter referred for assessment, although it may have to be identified in order to be excluded from the assessment. [99] Thus, when understood in its immediate context, that part of s 61(2) which made "such [a] certificate" conclusive evidence as to the degree of permanent impairment made such a certificate conclusive on causation. 87Giles JA was also of the view that there was what he described as strong emphasis in the Act and in the scheme's legislative history on leaving for assessment under Pt 3.4 whether there was the degree of permanent impairment necessary for an award of damages for non-economic loss (being permanent impairment as a result of the injury caused by the motor accident) and, save for where the certificate was vitiated by procedural unfairness, the medical assessor's certificate was conclusive. His Honour considered the power in s 61(2) to refer again for assessment was "a safety valve" enabling the Court to involve itself in the question for the purposes of assessment of damages but not in such a way as to bind the assessor. In considering the submissions advanced by the plaintiff seeking to limit the conclusivity of the certificate his Honour said: [78] Mr Mills further submitted to the effect that the Act should be construed on the basis that it was inappropriate for a medical assessor to make findings on questions of causation, which could well involve non-medical issues including the credit of the injured person. He submitted to the effect that the medical assessor did not have meaningful investigative powers and the parties could not use compulsive curial procedures to put materials before the assessor, and that that was reason for the court's ability to determine a question of causation upon which the assessor then assessed a degree of permanent impairment. Acknowledging that the court could refer again no matter what conclusiveness was given to a certificate, Mr Mills raised the spectre of a stalemate between court and medical assessor, the court taking one view of causation and the assessor another. He referred also to the possible anomaly of a conclusive assessment of less than 10 per cent permanent impairment because of no causation, excluding an award of damages for non-economic loss, but a court finding causation and awarding damages for economic loss. [79] The submissions face the difficulty that the degree of permanent impairment as a result of the injury caused by the motor accident (s 58(1)(d); s 131) was unequivocally for the medical assessor, including the element of causation. That was accepted in Pham v Shui at [96], and it was correctly so held in Ackling v QBE Insurance (Australia) Ltd at [77]-[79]. The legislature accepted such constraints as there may have been on investigation or being provided with materials, and dealt with that amongst other possible deficiencies in a medical assessment by what I have called the safety valve of a court's power to refer again. The legislature having chosen to provide the threshold in s 131 of the Act and brought it within the scheme for medical assessment under Pt 3.4, the possibility of anomoly was met by the safety valve. [80] A stalemate was unlikely; a court would take note of the medical assessor's reasons, and in inquiring into any issue "in such manner as they think fit" (MAA Medical Guidelines, issued under s 44(1)(d) of the Act, para 11.1) a medical assessor could and would take note of the court's reasons. It is not to be assumed that the power to refer again under s 62(1) would be exercised unnecessarily. [81] These submissions were essentially directed to how the Act should have operated, and were intended to support the primary submission as to disagreement. I do not think they can be accommodated within the terms of the Act. 88Although the scheme in Pt 7 of the 1998 WC Act for the resolution of medical disputes between employer and worker has some features in common with the scheme under the MACA there are obvious and distinct differences. Of itself that may not have been productive of different outcomes concerning the question of conclusivity of medical certificates issued under both Acts. In my view, what is determinative is the very different statutory language used in defining the matters referred for assessment. As both Giles JA and Handley AJA observed in Mills , the referral of a medical dispute under the MACA, and the effect of the issue of a certificate directed to resolving it, necessarily involves the question of causation. The same cannot be said with anything like the same degree of certainty of the related provisions under Pt 7 of the 1998 WC Act where the conventional language of causation is not used. Section 326 provides that it is the certified degree of permanent impairment of the worker as a result of an injury , and (where relevant) whether any proportion of permanent impairment is due to any previous injury or pre-existing condition or abnormality that is conclusive and not whether that injury is caused by the employer's (or in this case the Crown's) negligence despite the fact that, as s 26B of the Civil Liability Act makes clear, it is only in those circumstances that Pt 7 of the 1998 WC Act has any application.

The principle of estoppel 89The parties did not address lengthy written submissions or oral argument as to how the principle of estoppel might apply to the controversy to which questions (a), (b) or (c) have given rise (beyond identifying what was said to be the circumstances in which the principle might be invoked as I have noted in paragraphs [43] and [45] above). I am not critical of that approach. The construction of the relevant statutes was doubtless seen by both counsel to warrant their primary focus. 90Questions (d) and (e) require me to determine whether estoppel arises. The answer to question (d) makes plain my reasons for answering that question in the negative. In so far as question (e) is concerned, my reasons for also answering that question in the negative are as follows. 91Mr Weinstein referred me to the published views of Brereton J in a speech to the Australian Law Journal Conference ( Equitable Estoppel in Australia: The Court of Conscience in the Antipodes , 16 March 2007) where his Honour identified the matters upon which the common law doctrine of estoppel by convention depends which, so far as they apply to this case, are: ...(1) that [the defendant] has adopted an assumption as to the terms of its legal relationship with the [plaintiff]; (2) that the [plaintiff] has adopted the same assumption; (3) that both parties have conducted their relationship on the basis of that mutual assumption; (4) that each party knew or intended that the other act on that basis; and (5) (arguably) that departure from the assumption will occasion detriment to the plaintiff. 92As his Honour pointed out, equitable promissory estoppel is distinguished from conventional estoppel because the latter operates where both parties have adopted the same assumption as the basis of their relationship, often without appreciating that any departure from the strict legal position is involved, so as to hold both parties to their common understanding, without any requirement that one party has induced the other or acquiesced in the other party adopting that position. His Honour went on to observe that in promissory estoppel it is the defendant's knowledge of the potential of the plaintiff to incur detriment if it remains silent that may attract equitable relief whereas, in conventional estoppel, all that it required is the mutual adoption of the relevant assumption which both parties are then estopped from denying. Although the issue may not be entirely free of doubt, detriment remains an element of conventional estoppel where the assumption as to the terms of the legal relationship between the parties is shown to be erroneous (see MK & JA Roche Pty Ltd v Metro Edgley Pty Ltd [2005] NSWCA 39). In this case, and to the extent that the Crown is obliged to establish that it will suffer detriment or disadvantage if the plaintiff is permitted to depart from the position it adopted before the Appeal Panel in 2008, Mr Weinstein submitted (albeit somewhat faintly) that the detriment was in terms of costs. On the assumption that the other matters upon which estoppel by convention depends are established, I am not persuaded that cost considerations place the Crown in a position of sufficient disadvantage as a litigant to bind the plaintiff to a position he had assumed to be correct but has since abandoned.

Question (a) 93The conclusionary effect of the MAC issued by the Appeal Panel pursuant to s 328(5) of the 1998 WC Act is limited to the specific matters set out at s 326(1). Because causation is in dispute in the proceedings, the MAC is not conclusive as to whether the harm allegedly suffered by the plaintiff as an offender in custody was caused by the tortious conduct of the Crown as the protected defendant. The defendant's liability in negligence must be established in accordance with Pt 1A the Civil Liability Act . 94An assessment of permanent impairment in excess of 15% certified under s 326 of the 1998 WC Act is only conclusive upon a finding of liability by a court, or as agreed between the parties. In this case, and notwithstanding the defendant's admitted breach of duty, whether the assault on 16 August 2001 caused the extent of harm claimed by the plaintiff remains in issue and is to be determined by the Court.

Question (b) 95No. If an offender in custody is assessed under a MAC as having at least 15% permanent impairment, a court may award damages in proceedings. If a MAC assesses an offender as having less than 15% permanent impairment, a court may not award damages: s 26C of the Civil Liability Act . 96If there is a dispute about the degree of permanent impairment of an injured offender, a court may not award damages unless the degree of permanent impairment has been assessed by an approved medical specialist in accordance with the 1998 WC Act: s 26D(3) of the Civil Liability Act . This is consistent with the operation of s 26C as a threshold provision.

Question (c) 97A MAC issued by an Appeal Panel pursuant to s 328(5) of the 1998 WC Act will extend to the causation of the relevant impairment in a medical sense but only if a court is satisfied that the injuries the subject of assessment in the MAC were caused by the breach of duty. If a court does not find the necessary causation, or finds that the facts presumed by the assessor are inconsistent with the court's factual findings, then the conclusiveness of the MAC will not extend to the causation of the relevant impairment in a medical sense.

Question (d) 98No. If a court finds a set of circumstances different from those upon which the Appeal Panel relied in preparing the MAC the court is not bound by the MAC. Section 26D(4) of the Civil Liability Act expressly provides that the court may at any stage in proceedings refer the matter for assessment of the degree of permanent impairment in accordance with the 1998 WC Act. Section 26D(4) of the Civil Liability Act operates in like fashion to s 321(1) of the 1998 WC Act which permits a court (as well as other prescribed bodies) to refer a medical dispute for assessment (see for example Wikaira v Registrar of the Workers Compensation Commission of NSW & Anor [2005] NSWSC 954 ). In addition, s 329 provides that a matter referred for assessment may be referred again by a court (or the Commission) on one, or more than one occasion, and that a MAC issued in those circumstances prevails over any previous certificate.

Question (e) 99No. Although the plaintiff adopted a position on the issue of conclusionary effect of a MAC in submissions before the Appeal Panel which was later abandoned, and although he has taken no steps to challenge the decision, the plaintiff is not estopped from taking a different position in the substantive proceedings.

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