Statement of Principles concerning pilonidal sinus (Reasonable Hypothesis) (No. 27 of 2019)

The central concept is “pilonidal sinus”, defined in subsection 7(2) as an inflammatory tissue reaction of the skin to an embedded hair, manifested by a sinus or fistula. It includes pilonidal cyst and pilonidal fistula but expressly excludes ingrown hair. This definition is narrower than common clinical usage in some contexts; the exclusion of ingrown hair is significant because ingrown hairs are a separate condition that may have different causative factors. The instrument notes that pilonidal sinus principally occurs in the sacrococcygeal region (the cleft at the top of the buttocks) but can also occur in interdigital webs of the hands and other regions. The ICD-10-AM code L05 is assigned, but the instrument’s own definition governs.

The SoP distinguishes anatomical sites because the factors differ. For pilonidal sinus of the hand or foot only, the factors relate to hairdressing/barber work or cutaneous exposure to animal hair (milking, shearing, grooming, clipping, or slaughtering). For the sacrococcygeal region only, the factors are driving or being a seated passenger in a motorised vehicle, sitting on a hard or vibrating surface, or being overweight or obese. For the sacrococcygeal and umbilical regions only (but not hand or foot), there is a factor about inability to shower or bathe more than two times per week for at least four weeks. The umbilical region is grouped with sacrococcygeal, which suggests the RMA considers that hygiene limitations are plausibly causal for these sites but not for hand/foot.

“Being overweight or obese” is defined in the Dictionary as a Body Mass Index (BMI) of 25 or greater. BMI is calculated as weight in kilograms divided by height in metres squared. This is a low threshold: a BMI of 25 is the start of the “overweight” category, meaning many people will meet it. The instrument does not require morbid obesity; a modest elevation suffices.

“Cutaneous exposure to animal hair” is narrowly defined as milking, shearing, grooming, clipping, or slaughtering animals. This excludes casual contact such as handling a pet or wearing wool clothing. It is an occupationally oriented factor.

“Relevant service” is defined in the Dictionary to include operational, peacekeeping, hazardous, and British nuclear test defence service under the VEA, and warlike and non-warlike service under the MRCA. This is the service that must be causally linked to the factor under section 10. The instrument does not apply to peacetime service under the VEA that is not designated as operational, peacekeeping, hazardous, or British nuclear test defence service; claims for such service would be determined under a different standard and may not be covered by this SoP.

“Terminal event” is defined as the proximate or ultimate cause of death, including pneumonia, respiratory failure, cardiac arrest, circulatory failure, or cessation of brain function. This extends the SoP to death cases where pilonidal sinus contributed to one of these events.

The “relationship to service” requirement in section 10 is crucial: the existence of a factor must be related to the relevant service rendered. For worsening (aggravation) factors in subsections 9(4) to 9(7), the person’s pilonidal sinus must have been suffered or contracted before or during service but did not arise out of service. This prevents double counting: the pre-existing condition is considered not service-caused, but its worsening can be service-related.

The primary persons affected are veterans, members of Peacekeeping Forces, and members of the Forces under the VEA who have rendered relevant service, as well as members under the MRCA who have rendered warlike or non-warlike service. Specifically, any person who makes a claim for compensation for pilonidal sinus under the VEA or MRCA and whose claim is subject to the reasonable hypothesis standard will be assessed against this SoP. Death claims from pilonidal sinus are also covered.

The instrument also affects decision-makers: the Repatriation Commission, the Military Rehabilitation and Compensation Commission, the Veterans’ Review Board, the Administrative Appeals Tribunal, and the Federal Court. They must apply the factors as set out in section 9 and cannot accept a reasonable hypothesis that does not conform to them, unless the SoP is successfully challenged.

Medical assessors, including specialist surgeons and occupational physicians, are indirectly affected because they must provide opinions consistent with the SoP’s definitions and factors. For example, a doctor’s opinion that pilonidal sinus was caused by prolonged sitting will be weighed against the specific thresholds of 20 hours per week for three months. The instrument constrains medical evidence by providing a bright-line rule.

The instrument affects the Repatriation Medical Authority itself, which is responsible for maintaining and amending SoPs based on sound medical-scientific evidence. The inclusion of the “sitting on a hard or vibrating surface” factor in 2021 shows that the RMA responds to new evidence or advocacy. The RMA also has a duty to ensure the SoP remains current.

Practitioners - lawyers and claims advocates - must understand the SoP to advise clients on prospects and evidence-gathering. The SoP creates a checklist: is the pilonidal sinus in the hand/foot, sacrococcygeal, or umbilical region? Does the claimant have a BMI of 25 or more? Did they drive or sit for 20+ hours/week in service? Were they a hairdresser or exposed to animal hair? Could they not shower regularly? Each factor must be matched to service circumstances.

Employers and the Department of Veterans’ Affairs (DVA) are affected indirectly through compensation costs. If the SoP makes it easier to establish a connection to service, it may increase the number of successful claims, which affects the Compensation Budget. Conversely, the SoP may restrict claims that would otherwise succeed under a broader medical theory, saving costs. The instrument is a tool of fiscal control by standardising causation.

Finally, the instrument affects future claimants because the factor list is exhaustive. A person who develops pilonidal sinus from a non-listed cause - such as repeated trauma not involving sitting or vehicle exposure, or genetic predisposition - cannot rely on this SoP. They would need to argue that the SoP does not apply (e.g., because the condition does not meet the definition) or that the SoP is invalid.

For claimants, the key duty is to establish that at least one factor in section 9 existed and that the factor was related to their relevant service as required by section 10(1). This is an evidentiary burden. The right that flows from meeting that burden is that a “reasonable hypothesis” is raised, and the decision-maker must then consider the claim under the applicable standard of proof (section 120(1) of the VEA for operational service). If the claim is for clinical worsening of pilonidal sinus that was pre-existing, the factors in subsections 9(4) to 9(7) apply, and section 10(2) requires that the condition was suffered or contracted before or during service but did not arise out of service.

The Repatriation Medical Authority has a duty under section 196B(2) of the VEA to determine statements of principles when it is of the view that sound medical-scientific evidence indicates a connection between a disease and service. The Authority must base its factors on that evidence (section 8). It also has the power to amend SoPs, as occurred with Amendment No. 115 of 2021.

The Repatriation Commission and the Military Rehabilitation and Compensation Commission have a duty to apply the SoP in assessing claims. They cannot ignore a factor that is satisfied. Conversely, if no factor is satisfied, they must reject the claim unless the claimant can show the SoP is invalid or inapplicable.

Claimants have a right to have their claim determined in accordance with the SoP. They also have a right to seek review of a decision that incorrectly applies the SoP, whether by the Veterans’ Review Board or the Administrative Appeals Tribunal, and ultimately judicial review.

For decision-makers, the SoP provides a structured assessment that reduces discretion. It also imposes a duty to interpret the factors correctly. For example, “driving or being a seated passenger in a motorised vehicle for an average of at least 20 hours per week for a period of at least three months” requires careful calculation of average hours over a qualifying period. The factor does not require continuous three-month service; it can be any three-month window within the six months before clinical onset. Similarly, “being overweight or obese” is defined by BMI, which is objective but requires evidence of weight and height at the relevant time.

The instrument also creates a duty for claimants to provide evidence that the factor existed and related to service. If the claimant cannot produce records of driving hours or BMI, they may rely on sworn statements, but the decision-maker will assess credibility.

Section 11 introduces a cross-referencing duty: if a factor refers to an injury or disease covered by another SoP, the factors in that other SoP apply. For example, if a factor required the presence of another condition (none appear in this SoP), the practitioner would need to check that condition’s SoP. Currently, none of the factors explicitly reference another injury or disease, but the provision is a safety net.

This SoP does not impose penalties in the traditional sense. It is not a criminal or regulatory instrument that fines or prosecutes. Instead, its enforcement mechanism is administrative: if a claimant fails to meet the factors, the claim for compensation for pilonidal sinus will be refused. The refusal may be appealed.

The absence of a factor does not automatically mean the condition is not service-related; it means the reasonable hypothesis standard cannot be met under the SoP. For claims where the standard is balance of probabilities (e.g., for non-operational service under the VEA or under MRCA in some circumstances), the SoP may still be relevant because it represents the RMA’s view of sound medical-scientific evidence, but it is not binding for such claims - only for claims under sections 120A and 338. That said, in practice the SoPs are often applied beyond their strict legislative reach.

There is a risk that a false or exaggerated claim may lead to a criminal penalty under other provisions of the VEA (e.g., making a false statement). However, this SoP does not itself create an offence. Enforcement is indirect: the cost of failure is a denial of benefits.

For decision-makers who misapply the SoP - for example, by ignoring a factor that is satisfied - the remedy is review, not penalty. The Administrative Appeals Tribunal can set aside a decision and remake it. The Federal Court can grant judicial review for jurisdictional error.

The instrument also has a self-enforcing quality: because it is a legislative instrument registered on the Federal Register of Legislation, it is binding on the Commonwealth and decision-makers. Failure to apply it correctly may expose the decision to being set aside, but no personal penalty attaches to the decision-maker.

The “penalty” for the Repatriation Medical Authority if the SoP is based on inadequate evidence is not specified; the SoP could be challenged in judicial review proceedings on the ground that the required view (sound medical-scientific evidence) was not reasonably open. This is a high bar.

In summary, the SoP is an evidence-shaping device, not a punitive one. Its enforcement lies in the claim outcome. Practitioners should treat the factors as a checklist: if a claimant cannot satisfy any factor, the claim will likely fail unless a challenge to the SoP itself succeeds.

The SoP is made under subsection 196B(2) of the VEA, which is part of a scheme that also includes section 120 (standard of proof) and section 120A (statements of principles). Section 120A provides that for claims to which it applies, the question of whether a reasonable hypothesis is raised must be assessed in accordance with the relevant SoP. Thus, the SoP is not a free-standing code; it is integrated into the VEA’s claims process.

The instrument also applies to claims under section 338 of the MRCA, which mirrors the VEA provision for members covered by that Act. The MRCA has its own standard of proof provisions, but the SoP applies to the reasonable hypothesis standard for warlike and non-warlike service.

The SoP interacts with other statements of principles via section 11: if a factor refers to an injury or disease covered by another SoP, the factors in that other SoP apply. This prevents fragmentation and ensures consistency. For example, if a service-related back condition led to prolonged sitting, the back condition might have its own SoP; but here, the factor is the sitting itself, not the back condition.

The definition of “pilonidal sinus” uses ICD-10-AM code L05, but subsection 7(3) explicitly says the meaning of pilonidal sinus is that given in subsection (2), not the ICD code. This prevents confusion if the ICD coding changes. The ICD reference is merely to assist classification for data purposes.

The SoP interacts with the general law of causation in compensation. Under the VEA, the “reasonable hypothesis” standard is lower than the civil standard: it requires only that the hypothesis be reasonable, not proven on the balance of probabilities. The SoP essentially sets the minimum elements for a hypothesis to be considered reasonable. If the factors are met, the decision-maker cannot dismiss the hypothesis as unreasonable solely on medical opinion.

The SoP does not override privacy or evidence laws. Claimants must provide evidence such as medical records, service records, and personal statements. The DVA’s ability to request information is governed by other provisions.

Interaction with state workers’ compensation or motor vehicle accident compensation is indirect. The SoP is specific to military service. A person could potentially claim for pilonidal sinus under a state scheme if the cause is non-service related, and the state scheme would not apply this SoP. But if the person also makes a DVA claim, the SoP governs the DVA claim.

The Amendment Statement of Principles No. 115 of 2021 added subsections 9(2)(aa) and 9(5)(aa) - sitting on a hard or vibrating surface. This change interacted with pre-existing law by expanding the factors. Claimants whose disease onset or worsening occurred before the amendment date (20 December 2021) would be assessed under the original SoP unless the amendment has retrospective effect? The instrument likely applies from its commencement date. The compilation notes that the amendment commenced on 20 December 2021. Claims made before that date but determined after may depend on transitional provisions; none are indicated. Practitioners should check the precise application provision in the amending instrument.

The original SoP, Statement of Principles concerning pilonidal sinus (Reasonable Hypothesis) (No. 27 of 2019), was registered on the Federal Register of Legislation on 5 March 2019 and commenced on 25 March 2019. This original version included the factors for hand/foot (hairdressing/barber, animal hair exposure), sacrococcygeal (driving/seated passenger, being overweight or obese), and sacrococcygeal/umbilical (inability to shower/bathe). The original instrument also had sections 2 and 4, which were later repealed by operation of the Legislation Act 2003 (sections 48D and 48C respectively, which automatically repeal certain provisions). The compilation shows that sections 2 and 4 are marked “rep LA s 48D” and “rep LA s 48C” - these are standard provisions relating to commencement and definition of terms that were repealed because they were spent or covered elsewhere.

The key amendment occurred via Amendment Statement of Principles concerning pilonidal sinus (Reasonable Hypothesis) (No. 115 of 2021), registered on 29 November 2021 and commencing on 20 December 2021. This amendment added two new subparagraphs: subsection 9(2)(aa) (for clinical onset in the sacrococcygeal region) and subsection 9(5)(aa) (for clinical worsening in the sacrococcygeal region). Both new factors read: “sitting on a hard or vibrating surface for an average of at least 20 hours per week for a period of at least three months, within the six months before the clinical onset [or worsening] of pilonidal sinus.” These additions sit alongside the existing factor (2)(a) and (5)(a) for driving or being a seated passenger in a motorised vehicle.

The amendment history in Endnote 4 shows that only these two provisions were added; no other changes were made. The instrument therefore now has a more comprehensive coverage of seated activities. The original factor (a) focused on motorised vehicles, which would include cars, trucks, tanks, and other military vehicles. The new factor (aa) covers sitting on any hard or vibrating surface, such as a hard chair, bench, or vibrating machinery seat, regardless of whether it is in a vehicle. This broadens the reach, especially for service personnel who sit on hard surfaces in offices, workshops, or field conditions. The amendment reflects evolving understanding that prolonged sitting on hard surfaces can compress the sacrococcygeal area and contribute to hair penetration.

The compilation date is 20 December 2021, and no further amendments are noted in the compilation. The instrument is still in force. The endnotes indicate that uncommenced amendments are not shown, meaning no future amendments were in the pipeline at the time of compilation.

Practitioners should note that the amendment history is relevant for claims where the onset or worsening occurred before 20 December 2021; the factor of sitting on a hard/vibrating surface would not have been available under the original SoP. Claimants who rely solely on that factor must ensure that the relevant time period (the six months before clinical onset or worsening) falls after the commencement date, or that the claim was determined after the amendment and the decision-maker applies the current SoP. The VEA generally applies the law in force at the time of decision unless transitional provisions specify otherwise.

The provided text does not contain any references to specific litigation. The instrument itself is a legislative instrument, and its validity could be challenged in the Federal Court or the High Court on grounds such as that the Repatriation Medical Authority did not have a reasonable basis for its view that sound medical-scientific evidence supported the factors, or that the instrument is ultra vires the VEA. Such challenges are rare but have occurred for other SoPs.

Given the instrument’s specific and technical nature, litigation is more likely to occur at the merits review stage (Veterans’ Review Board or Administrative Appeals Tribunal) rather than a direct challenge to the SoP. In those tribunals, the interpretation of the factors is frequently tested. For example, what constitutes “driving or being a seated passenger in a motorised vehicle” may be disputed: does a motorbike qualify as a motorised vehicle? Is a person “seated” if they are standing in a vehicle? The definition of “motorised vehicle” is not given in the SoP, so ordinary meaning applies. That could lead to argument.

Similarly, “sitting on a hard or vibrating surface” - what is “hard”? A padded seat may still be hard depending on the material. “Vibrating” is not defined; does a tool operator sitting on a vibrating seat count? The three-month average of 20 hours per week calculation may be contested, particularly if service records are incomplete.

The factor “inability to shower or bathe more than two times per week for a period of at least four weeks” - what constitutes inability? Is it a medical restriction, or a lack of facilities during operational service? The phrase “inability” suggests the person could not shower, not that they chose not to.

The “being overweight or obese” factor - BMI of 25 or greater - is objective, but the relevant time is within six months before clinical onset. Claimants may have lost weight between that time and the claim assessment. Evidence of weight at the relevant time may be difficult to obtain, leading to reliance on recollections or service medical records.

No notable judicial decisions are publicly recorded in the source. However, the broader SoP scheme has been litigated in cases such as Repatriation Commission v Bey (1997) and Ward (various), establishing that SoPs are binding and that the reasonable hypothesis standard requires the hypothesis to be consistent with the SoP. Those cases are not specific to this SoP but provide the interpretive framework.

Practitioners should monitor the AAT’s decisions on pilonidal sinus SoP to see how factors are applied. Because the SoP is relatively niche, litigation volume is likely low.

The most significant gotcha is the exclusion of ingrown hair from the definition of pilonidal sinus (subsection 7(2)(c)). A common misdiagnosis is that a hair follicle infection or ingrown hair is called a pilonidal sinus. If a claimant’s condition is classified as ingrown hair in medical records, the SoP will not apply, and the claim may fail despite similar symptoms. The claimant would need to establish that the condition meets the SoP definition: an inflammatory tissue reaction to an embedded hair with a sinus or fistula.

A second gotcha is that the factors are strictly tied to anatomical site. For pilonidal sinus in the sacrococcygeal region, only the sacrococcygeal factors apply. For hand/foot, only the hand/foot factors apply. The inability to shower factor applies only to sacrococcygeal and umbilical regions - but note that umbilical region is not sacrococcygeal; it is grouped separately. If the claimant has pilonidal sinus in the axilla or perineum, none of the factors may apply, and the claim could fail even if there is a plausible service connection. The SoP does not list factors for other regions.

A third gotcha is the time window: most factors require the factor to exist within the six months before the clinical onset or clinical worsening. This means a claimant who drove extensively 10 years before onset cannot rely on that factor. The three-month duration requirement for driving/sitting adds another layer: the activity must be sustained, not occasional. A person who drove 20 hours per week in one week but not in others will need to show an average over three continuous months.

The definition of “being overweight or obese” as BMI of 25 or greater is a low bar. Many people, especially older veterans, may meet it. However, the BMI must be calculated from weight and height at the relevant time (within six months before onset). If the claimant was not overweight then but became overweight later, the factor is not satisfied. Conversely, if they were overweight at the time, the factor is satisfied regardless of current weight.

The “cutaneous exposure to animal hair” definition is narrow: it includes only milking, shearing, grooming, clipping, or slaughtering animals. A shepherd who does not clip or slaughter but handles wool constantly may not qualify. The factor requires active manipulation, not passive contact.

The “inability to shower or bathe more than two times per week for a period of at least four weeks” - what does “inability” mean? If the claimant was denied access to shower facilities due to operational conditions (e.g., deployed in field), that likely qualifies. But if they simply chose not to shower due to laziness, that may not meet the definition of “inability.” The word suggests a constraint beyond personal preference.

Section 10(2) is a trap for worsening claims: it requires that the pilonidal sinus was suffered or contracted before or during service but did not arise out of service. If the condition arose out of service (i.e., was already service-related), then worsening is not the relevant path; the original condition should be claimed. The claimant must prove that the original condition was not service-caused, which may be difficult if it occurred during service.

Section 11 cross-referencing is a potential hidden hurdle: if a factor refers to another injury or disease covered by another SoP, those factors apply. In this SoP, none of the factors explicitly reference another injury, but if future amendments add such a reference, practitioners must check multiple SoPs.

Finally, the instrument does not provide for a factor of “genetic predisposition” or “family history,” which are sometimes cited in medical literature. The RMA has apparently determined that sound medical-scientific evidence does not support a link via heredity alone. Claimants cannot rely on such theories under this SoP.

For a practitioner advising a veteran or member with pilonidal sinus, compliance with this SoP means systematically gathering evidence to satisfy one or more factors in section 9. The first step is to determine the anatomical site of the pilonidal sinus from medical records. If the site is not specified, the practitioner should obtain a specialist opinion to confirm whether it is sacrococcygeal, hand/foot, or umbilical. The SoP does not cover other sites, so if the site is elsewhere, the claim may need a different strategy.

Next, identify the relevant time: the date of clinical onset (first diagnosis or manifestation) and the date of clinical worsening if the condition was pre-existing. Then identify service periods that fall within the six months before those dates. The factor must have existed during that window.

For sacrococcygeal pilonidal sinus, the strongest factors are likely being overweight or obese (BMI >=25) or prolonged sitting. To comply, the practitioner should obtain:

• Service medical records showing weight and height. If not available, sworn statements or physical training records may suffice.
• A log of driving hours or sitting hours during service. This could be from unit diaries, vehicle logs, or personal testimony. The average must be at least 20 hours per week over three continuous months. For example, a truck driver or tank crew member likely meets this. A desk-bound officer may also meet the sitting factor if they sat in a hard office chair. For the sitting factor added in 2021, the same thresholds apply.
• If relying on the inability to shower factor: service records showing hygiene facilities, operational postings, or medical restrictions. Statements from fellow service members can help.

For hand or foot pilonidal sinus: obtain evidence of work as a hairdresser or barber (pay records, job descriptions) or evidence of cutaneous exposure to animal hair (milking, shearing, etc.) within the six months before onset. This will be relevant for service personnel who worked in animal handling roles (e.g., Army veterinary corps, farm duties). Civilian employment before service does not count unless it was during service (e.g., reservists with civilian jobs). The factor must be related to relevant service under section 10.

For all claims, the practitioner must also show that the factor is related to service. For example, driving a military vehicle as part of duties, or being stationed in a location where showering was limited due to operational conditions. The factor must arise out of the person’s service, not merely coincidental.

For worsening claims: the claimant must also establish that the pilonidal sinus was present before or during service but did not arise out of service. This could be shown by pre-enlistment medical records. The worsening factors mirror the onset factors.

Document everything in a structured submission to the Repatriation Commission. The claim should include a covering letter referencing the specific factor(s) and how they are satisfied, with supporting evidence. The decision-maker will then apply the SoP. If the factors are met, the reasonable hypothesis is raised, and the claim should succeed for operational service claims (if no contrary evidence disproves the hypothesis beyond reasonable doubt). For non-operational service, a different standard applies, but the SoP still guides.

Finally, keep abreast of amendments. The 2021 amendment added the seated surface factor; future amendments could add or remove factors. Practitioners should check the Federal Register for the latest version. Failure to use the current SoP could lead to an erroneous outcome.