Neville v Accident Compensation Corporation

IN THE DISTRICT COURT AT WELLINGTON [2012] NZACC 196 UNDER The Accident Compensation Act 2001 IN THE MATTER OF an appeal pursuant to section 149 of the Act (Appeal No. AI 514/09) BETWEEN GARRY WAYNE NEVILLE Appellant AND ACCIDENT COMPENSATION CORPORATION Respondent Hearing: 8 February 2011 Appearances: Mr D Heperi advocate for appellant Mr A D Barnett for respondent Judgment: 15 June 2012 RESERVED JUDGMENT OF JUDGE D A ONGLEY [1] The question in this appeal is whether the Corporation was correct to decline funding for surgery for postero-lateral lumbar fusion with instrumentation. T ground for refusing funding was that the need for surgery was caused by a gradual process condition rendered symptomatic by an accident. [2] This judgment was delayed to enable the appellant to provide more medical information. Some months ago the parties advised that no further time was required. Unfortunately that advice was not conveyed to me and delivery of the judgment has been unduly delayed. [3] Mr Neville was injured on 17 August 2007 when he was working in an engineering firm while shifting a very heavy trolley laden with metal. At a review hearing he desribed the trolley gaining momentum and as it travelled away from him he heaved on it twice to avoid it hitting a pillar. The second time he pulled, he heard and felt a "loud bang" in his back and he collapsed to the ground. The accident happened on a Friday and his back got worse over the weekend. On Monday 20 August he attended his GP, Dr Keung, who lodged an ACC claim for cover. The Corporation accepted cover for a lumbar spine injury and sciatica. Summary of investigations [4] On 12 September 2007, Mr Neville was assessed by Dr Milne, sports physician, who diagnosed a back strain and left sciatica secondary to S1 nerve root impingement, with background grade 1 spondylothesis. At that stage, x-rays showed no fracture, bony injury or malalignment. The disc spaces also appeared well preserved. During the following 18 months Mr Neville attended his GP and physiotherapist. [5] The symptoms continued and in February 2009 Mr Somerville, orthopaedic surgeon, arranged an MRI scan and then examined Mr Neville and reported in March 2009. The scan showed lytic spondylolisthesis at L5/S1 and a foraminal disc extrusion on the left impinging on the L5 nerve root. It also showed a left paracentral protrusion at L4/5. Mr Somerville considered that the symptoms were caused by a disc protrusion caused by the accident. He lodged an Assessment Report and Treatment Plan (ARTP) for funding for surgery. [6] The Corporation referred the ARTP and medical records to its Clinical Advisory Panel (CAP). On behalf of the CAP Mr Ray Fong, orthopaedic specialist, advised that the appellant was suffering from L5/S1 lytic spondylolisthesis, which he described as a developmental and gradual process condition rendered symptomatic following the accident. [7] ACC then declined the surgery request in a decision issued on 12 May 2009. Mr Somerville wrote to the Corporation requesting that ACC reconsider its decision on grounds that the MRI showed significant disc injury coinciding with onset of persistent symptoms. Mr Fong confirmed his advice to the Corporation and recommended that the Corporation obtain an opinion from Mr Brian Otto, orthopaedic surgeon. [8] Mr Neville was then examined by Mr Peter Robertson, orthopaedic surgeon who reported on 4 June 2009 and on 2 December 2009. [9] Mr Otto examined the medical record and provided an opinion to the Corporation on 30 July 2009 in which he said that the appellant's spondylolisthesis resulted in an unshielded disc susceptible to degenerative changes. He considered that there was likely to have been degenerative change unmasked by an accident event, but the symptoms reflected a pre-existing change. [10] Mr Heperi, as advocate for Mr Neville, referred the appellant to Dr Chris Milne, sports medicine specialist. Dr Milne considered that the appellant's sharp radicular pain was caused by disc lesion and nerve root compression, and was not caused by his spondylolisthesis. He considered that it was not a gradual process condition but was caused by trauma. [1 1] Mr Fong then advised the Corporation that he agreed with Mr Otto's opinion. Mr Robertson was again consulted and wrote a fairly long opinion supporting the case for personal injury by accident. The Corporation referred Mr Robertson's opinion to Mr Otto, who also wrote a long opinion describing the gradual degenerative process, in cases generally, consequent on spondylolisthesis in the lumbar spine and again advising that the dominant cause was disc degeneration in an unshielded disc. [12] In a review hearing the appellant was unsuccessful. The Reviewer traversed the medical opinions and correctly applied the law. She reached the conclusion that Mr Otto's opinion should be preferred. The decision is a difficult one. After careful consideration I have reached a different conclusion. Medical reports and opinions [13] I will deal with the medical opinions under headings relating to the practitioners rather than in strict chronological order. Mr Richard Somerville, orthopaedic surgeon [14] When Mr Neville's symptoms did not resolve, he was referred to Mr Somerville who obtained an MRI scan and examined him in March 2009. The MRI showed "Lytic spondylolisthesis L5. Broad based bulge at L4/5 is static. Focal foraminal disc protrusion on the left has less mass effect although nerve compression remains evident". Mr Somerville reported: "With regard to pre-existing conditions, he does have an L4/5 spondylolisthesis which, as I have stated in my letter of 4 March, almost certainly predates his injury. However, he was asymptomatic prior to injuring his back at work and my hypothesis is that he now has a disc protrusion in addition to a spondylolisthesis which is causing his current symptoms." [15] On 18 March 2009 Mr Somerville completed an Assessment Report and Treatment Plan (ARTP) requesting funding for a posterior lateral lumbar fusion of the lumbar spine and spinal stenosis decompression at two or more levels. In the ARTP, Mr Somerville indicated that the surgery was required as a result of personal injury by accident, however, he also stated "it is almost certain that Gary had an L4/5 spondylolisthesis that predated his injury. However it was silent and until the time of the accident he had been asymptomatic, doing a very heavy job in a very heavy industry, with a minimum of previous pain". [16] Mr Barnett submitted that Mr Somerville provided very little basis to his reasoning in terms of causation, but that he clearly accepted the presence and potential impact of the appellant's pre-existing spondylolisthesis. Therefore, it was submitted, his opinion is not inconsistent with that of Mr Otto and the Panel. Mr Somerville relied on the fact that the appellant was asymptomatic prior to injury to indicate that the injury was at least, in part, causative of current symptoms, but that opinion does not distinguish between injury and aggravation. Mr Ray Fong, orthopaedic surgeon [17] On 11 May 2009, Mr Ray Fong, orthopaedic surgeon advising the Corporation on behalf of the CAP, stated "opinion Garry is suffering from his L5/S1 lytic spondylolisthesis - a developmental/gradual process condition rendered symptomatic following an accident". That was an abbreviated opinion without extended reasons, based on the view that Mr Neville was suffering from a gradual process condition. Mr Fong recommended obtaining an opinion from Mr Brian Otto. After Mr Otto's first opinion on 30 July 2009, Mr Fong advised the Corporation that he agreed that "the condition now needing surgery is largely and substantially that of lytic spondylolisthesis - a very longstanding developmental condition - that at best can develop symptoms following an accident" [18] Those views are strongly based on a medical understanding that lytic spondylolisthesis is a gradual process condition, in other words that it proceeds naturally through stages resulting in lumbar disc protrusion and foraminal nerve root compression. That point is in dispute in the medical opinions provided in this appeal. It is not a medical question that the Court can resolve other than in the narrow context of the present appeal and in reliance on the opinions that have been provided. Mr Somerville [19] After the Corporation declined funding for surgery, Mr Somerville wrote on 25 May 2009 questioning the decision and reiterating that in his view the appellant's condition was related "certainly in terms of time" to his accident. He wrote: "At no point has anyone denied the fact that the spondylolisthesis was a pre- existing factor. However, Gary was asymptomatic and has been working in a very physical job all his adult life without any problems relating to his back. His MRI does show a disc protrusion in the midline at L4/5 and a foraminal disc protrusion, left and right, at L5/S1, which fits now his claudicant leg pain. As such I think his present symptoms of discomfort in his leg directly relates, certainly in terms of time, to his accident, and that treatment directed to this is indicated as a consequence of personal injury." [20] Mr Barnett submitted that Mr Somerville placed much weight on the temporality between injury and the onset of symptoms, without an adequate basis for his conclusion that the personal injury was the cause of the ongoing symptoms requiring surgery. He submitted that Mr Somerville did not attempt to differentiate between the pre-existing condition, and the presence of disc protrusions at L4/5 and L5/S1 in order to relate the disc protrusions to the September 2007 injury, as opposed to being part and parcel of the pre-existing spondylolisthesis. Mr Peter Robertson, orthopaedic surgeon [21] Mr Robertson saw the appellant and reported to Dr Keung on 4 June 2009. He stated: "Plain x-rays demonstrate a grade 1 isthmic lumbosacral spondylolisthesis. MR scans performed on two occasions confirm this with pars defects seen. There is desiccation of the L5/S1 disc and clear cut compression of the exiting L5 root on the left side. There is also desiccation of the L4/5 disc on MR scan with a small central bulge. The proximal levels appear normal. Assessment Dr Keung, I think that Gary has significant mechanical pain coming from the spondylolisthesis, and his left leg pain is coming from compression of the exiting L5 root in the foramen. He has been considerably distressed and disabled by this. The imaging is relatively clear cut. He has a very good history of personal injury by accident." [22] Dr Robertson described the condition as isthmic spondylolisthesis, whereas the description applied by the other practitioners was lytic spondylolisthesis. There is no medical comment suggesting that the difference is significant in the context of this appeal. [23] In a further letter on 2 December 2009, Mr Robertson responded to some points made by Mr Otto. First he submitted that spondylolisthesis was neither an ageing process nor a disease. He then wrote: "The next point of concern relates to whether or not Mr Neville was suffering from a gradual process. I note that in Mr Fong's correspondence, Mr Otto's correspondence and the subsequent review, that spondylolisthesis is often referred to as a developmental condition and a gradual process condition. This is not correct. The literature tells us that spondylolysis is an acquired condition normally occurring in childhood or adolescence when a failure of the pars interarticularis of the vertebra occurs under load, akin to a stress fracture. Once it has occurred, it tends not to heal and the condition is stable. It is not a progressive condition. For these reasons, it is my opinion that Mr Neville's ongoing disability is not excluded for cover given the terminology used in the Act." [24] A crucial point of difference underlying the opinions of Mr Robertson and Mr Otto is whether spondylolisthesis is a gradual process condition. Having made the point that, in his view, spondylolisthesis is not a disease and is not a progressive condition, Mr Robertson went on to consider whether the disc condition might have been a consequence of spondylolisthesis, rendered symptomatic by the accident. He wrote: "Much focus has occurred as to whether or not this pre-existing condition was rendered symptomatic by the accident. In the review document, previous case law decisions are quoted, indicating that ACC are not liable to continue cover if a pre-existing condition has merely been brought to light by an accident. To investigate this further it is appropriate to look to the medical literature to ascertain the likelihood of a previously asymptomatic spondylolysis, or isthmic spondylolisthesis with a minor degree of slip, becoming symptomatic through life. There is now high quality observational literature available, suggesting that the patients with spondylolysis and isthmic spondylolisthesis, are at no greater risk for back pain problems through life than the normal person (Kalichman et al, Spine 34(2009) 199-205: Beutler et al, Spine 28(2003) 1027-1035; Osterman et al, Clinical Orthopaedics 297 (1993) 65-70). This means that had Mr Neville not sustained a clearly defined personal injury by accident it is highly likely that he would not have had significant problems with his back in any way different from a normal member of the population. He did not have a condition that was about to spontaneously become painful or disabling, according to the literature. He did not have a condition that would have become symptomatic regardless. He had a subsequent personal injury that is wholly or substantially due to the accident that occurred. I realise this opinion is at variance from the opinion given by Mr Otto, particularly in his discussion of symptoms that might arise from a spondylolisthesis in paragraph 4 of his letter dated 30.7.09. Whilst this description is superficially attractive and plausible, I am unable to find literature to support this. I emphasise that the high quality observational studies, in peer reviewed journals, of spondylolisthesis, as quoted above, do not support Mr Otto's opinion." The reference to para 4 was to Mr Otto's view that spondylolisthesis renders unshielded disc more susceptible to injury than a normal disc, and with consequent degenerative changes. [25] Mr Robertson then set out his reasoning in applying the legal test to the medical findings in this case. He did so in some detail and with a reasonably accurate summation of the legal principles. In answer to specific questions, Mr Robertson : a) In Mr Neville's case, is it medically possible to distinguish the results of any pre-existing gradual process, disease or infection from any further damage to his spine that may have been sustained through the events at his work on 17.8.07? We medically distinguish between his pre-injury status where a spondylolisthesis existed but was asymptomatic and his post injury, status by the history of injury and the findings on MR scan x-rays and investigation with discography, allowing us to proceed to surgical planning where indicated. The situation is symptomatic as a consequence of the accident. It is difficult to be specific, but it is likely that symptoms arise from the disc at L5/S1, where a herniation was noted, and the nerve root which is compressed at this level. Discography has demonstrated a positive pain response at L4/5 and conventional wisdom suggests that this should be incorporated in the fusion. b) On the balance of probabilities, is the compression of the exiting L5 root in the foramen caused wholly or substantially by a gradual process, disease or infection; or the result of personal injury sustained by Mr Neville on 17.8.07? Answer: On the balance of probabilities, the symptoms from the compressed exiting L5 nerve root are wholly or substantially caused by the personal injury. The literature notes that patients with a pre-existing spondylolisthesis and isthmic spondylolisthesis with minor degrees of slippage have no greater risk of back or back related problems than the general population. c) What is the appropriate treatment to relieve the symptoms of the compression of the exiting LS root in the foramen? Answer: The nerve root needs decompression at the site of the foramen. A decompression alone would destabilise the spine and therefore fusion is necessary. Where there is a retrolisthesis and spondylotic change at the disc above, this is often incorporated in the fusion, hence the need for a decompression and fusion. [26] The appellant claims that the probable compression of the LS nerve root was caused by the accident and brings about the need for surgery. The surgery would also address a resulting destabilisation and a fusion procedure is also necessary. [27] The respondent submits that Mr Robertson, in his first report, did not relate the appellant's ongoing symptoms to any specific personal injury, rather he that the appellant is suffering from significant mechanical pain coming from his spondylothesis and nerve root compression. In his second report Mr Robertson indicated that the pre-existing and previously asymptomatic condition of spondylolisthesis was rendered symptomatic through injury, but it is submitted that the occurrence of symptoms does not make the injury the cause of the symptomatic condition. It was submitted that Mr Robertson was unable to identify any injury related pathology, but thought that on the balance of probabilities, the symptoms from the compressed exiting L5 nerve root were wholly or substantially caused by the personal injury. Mr Barnett submitted that Mr Robertson equated this temporality with causation and was only saying that an injury had rendered a previously asymptomatic condition symptomatic. The condition that is requiring surgery has not been caused by injury, and no specific injury related condition is identified. Dr Chris Milne, sports medicine specialist [28] The appellant obtained a further opinion from Dr Chris Milne, sports medicine specialist. Dr Milne had seen the appellant in September 2007 before the MRI scans had been taken. Mr Heperi produced Dr Milne's qualifications including his experience as an ACC contracted independence allowance assessor and medical case reviewer. Incidentally, Dr Milne noted that Mr Robertson is a fulltime spinal surgeon and would be regarded as one of New Zealand's foremost experts in the field. [29] On 7 August 2009 Dr Milne reported: "a. In Mr Neville's case, I believe it is medically possible to distinguish the results of pre-existing gradual process disease or infection from further damage that has been sustained through the events at his work on 17-08-07. I say this because symptoms related to the pre-existing spondylolisthesis would be primarily extension-related pain and would not be expected to cause much in the way of referred pain to either leg. In particular, they would not cause the sharp radicular pain that is characteristic of a disc lesion and nerve root compression. He very clearly has this phenomenon and it has been documented by all the clinicians who have seen him b. On the balance of probabilities, the compression of the exiting L5 nerve root in the foramen is overwhelmingly likely to have been caused by the personal injury sustained by Mr Neville on 17-08-07. It is not the picture of a gradual process disease or infection. In other words, personal injury by accident would be regarded by most authorities as being the reason why he has his left sided radiculopathy. c. The appropriate treatment to relieve the symptoms of the compression of the exiting L5 nerve root is as advised in Mr Robertson's letter. In other words, he proposes careful investigation via discogram to exclude an associated symptomatic disc at a second level. If the discograph shows only a positive result at L4/5 level then a single leg fusion would be considered. Double fusion is rather more involved and has a less favourable long term prognosis. The treatment would be as outlined in Mr Robertson's letter with decompression and fusion." [30] Concerning the natural history of spondylolisthesis, Dr Milne wrote: "The natural history has been studied in several large groups and the risk of progressive spondylolisthesis is regarded as low. There is very little data on disc degeneration developing in association with spondylolisthesis, see page 283 of the reproduced material . The authors conclude that the studies MacAuley, Domhnall and Thomas M Best. Evidence-based Sports Medicine. Second Ed. Blackwell Pub., 2007 p 283 reported on this particular area, have been small and it is not clear if there are differences between those patients with unilateral or bilateral lesions or those with or without associated spondylolisthesis. In other words, the linkage between spondylolisthesis and the development of secondary disc changes is regarded as a weak association at best." Mr Brian Otto, orthopaedic surgeon [31] After Mr Fong's initial opinion, the Corporation requested advice from Mr Brian Otto, orthopaedic surgeon. Mr Otto reported on 30 July 2009. He stated that: 'From a clinical standpoint the primary pathology that is being dealt with are the consequences of the spondylolisthesis, a pre existing change that leads to an unshielded disc at the L5-S1 level with a high potential to degenerative change, and that degenerative change can be unmasked by an injury event. That is to say that the changes are not wholly or substantially due to personal injury by accident, but are more accurately reflecting a pre existing susceptible change in the lumbosacral junction of the spine, where a long standing developmental defect exists. [32] A difficulty with Mr Otto's opinion is that he appeared to apply a wrong test, that is to say whether the condition was wholly or substantially due to personal injury by accident. That is not the legislative test for cover. The first question is whether there is a causal nexus between the accident and the injury for surgery. That has been observed in numerous cases: see ACC v Mitchell [1992] 2 NZLR 436; ACC v Ambros [2007] NZCA 204. That association does not require the injury to be wholly or substantially due to personal injury by accident. The causal nexus is however broken if ongoing incapacity is wholly or substantially due to a gradual process including ageing or disease. [33] After Mr Robertson's second opinion was received by the Corporation, Mr Otto was asked to comment further. He wrote a comprehensive letter on 13 January 2011. Explaining the cumulative effects of degeneration, he stated: "The weight of evidence and the clinical histories of individuals with spondylolisthesis, are towards repetitive episodes of back pain often with increasingly shortened intervals between such episodes, and greater difficulty with time with settling those episodes, because of the accumulated effect of wear and degeneration within the unshielded disc. . ... It might be said that the final giving way of the degenerative annular margin of the disc from a stated injury event, is the final straw that causes the endpoint compression that is so difficult to settle with conservative means and often tips the scales towards surgical intervention." [34] I have omitted two intervening paragraphs describing the pathology frequently seen at surgery. The point of Mr Otto's advice was that a spondylolisthesis with repeated (minor) trauma is likely to finally give way. He continued: "The question then arises whether the presence of a spondylolisthesis and an unshielded disc with loading has a propensity to accelerated degenerative change and ultimately symptom production, and whether the changes in that situation with added components of compression likely to be present from the mid zone stenosis and fibrous tissues in the olisthetic area, and the alignment change with the over hanging margin of the bony structures in the root canal, are major contributors to the canal stenosis, and weight the incidence of root compression towards even minor trauma, tipping the scales in such cases. That is to say that the pre existing changes are of significance to the point where even a small increase in the amount of bulging of the disc that may have followed the accumulative degenerative change at that level, pre exist and pre dispose the individual to the clinical situation that has occurred with Mr Neville." [35] Mr Otto then made two comments which cause considerable difficulty in applying his opinion in the context of other evidence. He said: "To then state that the clinical situation of back pain and unresolved leg pain is wholly and substantially due to personal injury by accident, is to ignore the effects of that pre existing pathology, its potential to jeopardise the exiting nerve root canal capacity, and ultimately lead to the need for surgical management. It is on that basis that the statement is made that the clinical situation is not wholly or substantially due to personal injury by accident." [36] When applying the wrong test, it is not at all clear whether Mr Otto drew any distinction between cases in which the pre-existing pathology may be stable but susceptible to trauma, compared with progressive deterioration which is exacerbated by an accident. There is of course a great deal of difficulty in analysing the pathology in terms of the legal distinction between an injury because of predisposition and an event that is part of a process (rendering an existing condition symptomatic). Ultimately the question is whether the resulting pathology is wholly or substantially caused by the underlying degenerative process. [37] Concerning Dr Milne's opinion of an accident cause of compression of the L5 nerve root, Mr Otto said that: "In the presence of two levels of disc pathology the surgeon cannot be certain that an injury event has selected the change at one level compared with the other, and confidently choose one level to be an injury related component as compared with the other level that is reflecting a central annular bulge in the degenerative process within the disc. In the presence of two levels of disc degeneration, the separation of injury as compared with the degenerative process, is not a confidently separated ability for any clinician. The comments by Dr Milne don't take into account the contribution to the narrowing of the root canal that is made by the olisthetic process, and the further insult to the canal capacity that occurs as the degenerative disc bulges further and completes the compression of the nerve in its root canal." [38] Mr Barnett for the respondent submitted that that the Panel, along with Mr Otto, have provided the most cogent and thorough reasoning to support the opinion that the surgery is not required for an injury related condition. He submitted that, while Mr Robertson and Dr Milne have examined the appellant, this does not provide them with any greater advantage in relation to a consideration of the medical issues in this appeal. Mr Otto and the Panel do not dispute their clinical findings, indeed they rely upon them. Where the practitioners diverge is in relation to their interpretation of the clinical and radiological findings. Discussion [39] The first question is whether some injury was caused by the accident. Mr Barnett submitted that Mr Somerville based his opinion on the onset of symptoms, which could be consistent with either traumatic injury or aggravation of the existing condition. It is possible that the associated disc protrusion occurred independently, either before or after the accident on 17 August 2007. As usual, there is no before and after imaging that would prove the point. Mr Otto did not address that question directly because he did not regard the accident as a whole or substantial cause (his description). His opinion centered on the natural progression of spondylolisthesis and associated causes of foraminal narrowing including degenerative discs. His opinion did not start with the appellant's history as did the opinions of Mr Robertson and Dr Milne (also Mr Somerville), who regarded the patient history and clinical examination as sufficient evidence that the disc protrusion was caused by the accident. The question is primarily within the scope of the medical evidence and I accept the opinions of those doctors who attributed the cause to the accident on 17 August 2007 [40] Mr Otto's mis-statement of the test for cover undermines the value of his opinion. He proceeded from a description of the natural process of lytic spondylolisthesis and viewed the clinical history of the appellant's case as fitting within that process. Thus it was logical to conclude that the condition requiring surgery was not wholly or substantially caused by the accident. But Dr Otto did not answer the two required questions, first whether there was a causal nexus between the accident and the L5 nerve compression, and secondly whether the ongoing incapacity was wholly or substantially due to a gradual process including ageing or disease. Mr Otto arrived at an answer that may well be correct, but he did not appear to consider the main point of the appellant's claim, namely, that while the appellant's spondylolisthesis caused a predisposition to compression of the L5 nerve, the accident may nevertheless have been a significant cause none the less. [41] A significant point on which the opinions diverge is the question of stability of lytic spondylolisthesis in general. The Corporation's view is that it is a gradual process condition. Mr Otto described a degenerative process, resulting naturally in compression of the L/5 nerve. His opinion implies that all resulting nerve root compressions will be aggravations or exacerbations of the pre-injury condition. He does not appear to admit of another possibility in this particular case. The opinions of Mr Robertson and Dr Milne consider the accident related possibility and reach fairly firm opinions of a traumatic cause of nerve root compression by a disc protrusion. [42] Dr Milne referred to literature indicating that the risk of progressive spondylolisthesis is low. Mr Otto acknowledged that clinical experience is statistically biased by the fact that only symptomatic cases are referred to orthopaedic surgeons. Structured studies are thus likely to be more informative concerning the overall incidence of progressive degeneration. Then there is the separate question of increased risk of disc degeneration. Mr Otto considered that the risk caused by an unshielded disc is high. Dr Milne referred to the MacAuley text as concluding that "the linkage between spondylolisthesis and the development of secondary disc changes is regarded as a weak association at best". [43] I have considered Mr Otto's description of the composite causes of nerve root compression, including fibrous tissue and the bony overhanging margin. In view of Mr Robertson's clinical experience, it can be assumed that he has also taken those factors into account. Mr Robertson's rejoiner was that "Whilst this description is superficially attractive and plausible, I am unable to find literature to support this. I emphasise that the high quality observational studies, in peer reviewed journals, of spondylolisthesis, as quoted above, do not support Mr Otto's opinion" [44] The appeal is not without difficulty. Opposing medical opinions are difficult to evaluate, and more so when the legal test for personal injury by accident does not fit neatly with medical conclusions. I bear in mind that Mr Somerville and Mr Robertson referred to the onset of symptoms as an indication of injury, but it is clear from Mr Robertson's opinion that he did not overlook the point that an accident causing symptoms from a pre-existing injury is not a basis for injury cover. [45] On balance, I consider that Mr Robertson's opinion should be preferred, primarily for these reasons: (a) He focused on the appellant's case rather than on a general proposition that a degenerative condition tends to exclude a probability of personal injury by accident. (b) He is supported by Dr Milne in opposing the view that spondylolisthesis is a gradual process condition leading to disc protrusion and nerve compression. (c) He gave careful consideration to the legal test for personal injury by accident and the s 26 exclusions, and gave reasons for the manner in which he applied the test. [46] For those reasons, I find that it is more probable than not that the appellant suffered a disc protrusion caused by an accident on 17 August 2007, and that the surgery for which funding was sought was required to address the consequences of that injury. While the surgery may also have addressed an underlying spondylolisthesis, the surgery was required because of the appellant's personal injury by accident. [47] The appeal is allowed. The review decision is quashed and the Corporation's is directed to fund the appellant's surgery as required by the legislation. The appellant will have costs of $2,500 and reasonable disbursements. Judge D A Ongley District Court Judge