Secondly, his Honour held that it was "clearly" open to him, on the medical evidence, to find that "the degenerative process, and the pain and restriction in the knee, could have been aggravated by the fall and that that aggravation could have continued for some time": see [49] of the reasons.
68 Based on these findings his Honour accepted (at [84]) that:
"[84] … [T]here was a significant increase in pain and restriction of movement which progressively became worse following the fall and that this extra pain and limitation continued, as far as the left knee is concerned, for some years and probably up to the arthroscopy in 2007."
69 The primary judge further found that the condition of Mr Paterson's knee was such that the degeneration would ultimately have brought about a need for treatment, and perhaps an arthroscopy, but these consequences would have occurred later than when they in fact occurred.
70 The primary judge took the injuries to the right knee into account as a factor in the assessment of general damages "on the basis that it may, to some degree, have been caused by the left knee problems or at least its condition accelerated by the favouring of the left leg" see [84] of the reasons.
71 On the basis of these findings, his Honour assessed general damages at $50,000.
72 In challenging the primary judge's assessment of this head of damages, Air Link relied on three grounds of appeal, namely:
(a) His Honour failed to deal with the evidence relating to the cause of the "knee disability".
(b) His Honour erred in determining Mr Paterson's injuries by reference to his evidence as to the effect on him of the injuries that he suffered.
(c) His Honour erred in failing to determine the nature and extent of Mr Paterson's injuries by reference to the expert evidence.
73 Mr R Williams QC, who together with Mr Stanton appeared for Air Link, submitted that Mr Paterson never fully recovered (as he admitted) from the condition that had been detected in March 1997. He repeated that, at that time, Mr Paterson was almost 49 years old and, although his ideal weight for height was 85 kg, between early 1997 and July 1998 he was at least 40 kg above that weight. In November 1998, Mr Paterson advised his doctor that he was improving and did not seek any further treatment until 2007. Mr Williams submitted that the primary judge should have found that the fall caused a temporary exacerbation of the pre-existing injury for a few months, but thereafter what occurred was inevitable because of that pre-existing injury.
74 Mr Williams drew attention to the fact that orthopaedic surgeons on each side offered their views as to whether the meniscus had been torn by the fall and as to whether the symptoms the respondent experienced over the relevant period were caused significantly by the fall or would have been experienced in any event because of Mr Paterson's pre-existing condition. Mr Williams submitted: "The judge elected not to determine the issue by reference to the medical evidence but to what [Mr Paterson] said about it". He argued that his Honour was not entitled to resolve the issue "of what impact the fall had on [Mr Paterson's knee]" by simply basing his finding on Mr Paterson's evidence (which, according to Mr Williams is what his Honour did).
75 In Zurich Australian Insurance Ltd v Raman; Gyimah v Mackay [2009] NSWCA 221, the reliability of lay witnesses in large measure depended upon how differences between experts were resolved. These differences were capable of being resolved rationally by examination and analysis and the trial judge made no demeanour findings in regard to the experts. The judge, nevertheless, decided the matter on the basis of demeanour, not of the experts themselves, but of the lay witnesses. His Honour resolved the difference between the experts, without any rational analysis of their opinions, but by preferring the opinion that was consistent with his credibility findings concerning the disputed evidence of lay witnesses. His approach was held to be erroneous.
76 The circumstances of this case, however, are entirely different. Firstly, the credibility of Mr Paterson's testimony was not dependent on which expert opinion was to be preferred. It was common ground that he had a pre-existing condition. Secondly, his Honour did subject the use of the expert witnesses to rational analysis and also took into account their demeanour, as he was entitled to do (Wiki v Atlantis Relocations (NSW) Pty Ltd [2004] NSWCA 174; 60 NSWLR 127). His Honour referred to and examined hospital notes, a note by Dr Yelland, (Mr Paterson's general practitioner), the notes of Dr Ohmsen, an MRI report, extracts of the evidence of Drs Wallace and Pentis (orthopaedic specialists called by Mr Paterson), the report of Dr Millons (a specialist whose report was commissioned by Air Link but tendered by Mr Paterson) and the evidence of Dr Coolican (an orthopaedic specialist called by Air Link).
77 Having conducted what amounted to an appropriate review of the testimony, the primary judge concluded that Mr Paterson had not proved that the fall caused the tear in the meniscus. As regards the degree and duration of the exacerbation that had occurred, his Honour was unable to decide which of the views of the experts was to be preferred. It was implicit, however, in his Honour's reasons that he accepted that, on the evidence, there was a reasonable possibility that the "degenerative process, and the pain and restriction in the knee, could have been aggravated by the fall and that that aggravation could have continued for some time": see [49] of the reasons. This inference is to be drawn from his Honour's observation (also at [49]) that it was "clearly open" to him to make such a finding.
78 In Sydney South West Area Health Service v Stamoulis [2009] NSWCA 153, Ipp JA (with the agreement of Beazley and Giles JJA) after referring to Seltsam Pty Ltd v McGuiness [2000] NSWCA 29; 49 NSWLR 262 (at 276 [89], 278 [98] and 287 [153]), EMI Australia Ltd v BES [1970] 2 NSWR 238 (at 242) and Fernandez v Tubemakers of Australia Ltd [1975] 2 NSWLR 190 (at 239, 240), said at [138]:
"The fact that experts do not infer causation on a balance of probabilities does not mean that a court may not: Seltsam v McGuiness at [143]-[144]. A finding of causal connection may be made even when the expert evidence does not rise above the possible; the question is always whether the evidence as a whole establishes causation on a balance of probabilities: Seltsam v McGuiness at [89], [94]-[96], [98]-[100], [102], [143], [144] and [155]."
79 His Honour's findings as to the degree and the length of the period of exacerbation were made on entirely orthodox principles. Ordinarily, it is necessary for a trial judge to attempt to resolve differences between expert witnesses, particularly when that can be done by rational analysis. In this case, the primary judge explained, carefully, why he was unable to do so. That finding was open. We would not accept Air Link's criticism of the way in which his Honour dealt with the expert testimony.
80 Another way to approach the issue of the expert testimony is to analyse the situation by reference to the rule in Watts v Rake [1960] HCA 58; 108 CLR 158 as explained in Purkess v Crittenden [1965] HCA 34; 114 CLR 164. That rule (as expressed in Purkess v Crittenden (at 168) per Barwick CJ, Kitto and Taylor JJ) is as follows:
"[W]here a plaintiff has, by direct or circumstantial evidence, made out a prima facie case that incapacity has resulted from the defendant's negligence, the onus of adducing evidence that his incapacity is wholly or partly the result of some pre-existing condition or that incapacity, either total or partial, would, in any event, have resulted from a pre-existing condition, rests upon the defendant."
81 The rule in Watts v Rake only operates to place an evidential onus on a defendant when the plaintiff establishes that the defendant's negligence has, in fact, caused a change in the plaintiff's condition. This is what his Honour found in Mr Paterson's case (and it was not in contest). The evidential burden then shifted to Air Link to adduce evidence that Mr Paterson's incapacity was the result of his pre-existing condition or that that incapacity, either total or partial, would, in any event have resulted from the pre-existing condition. Air Link adduced evidence to this effect, but the primary judge found that, upon the whole of the evidence, Mr Paterson had satisfied him of the extent of the injuries caused by the fall.
82 Again, in our view, on this basis the reasoning of the primary judge was unexceptionable. Accordingly, we would dismiss the appeal against the assessment of general damages.