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23/02/2026
This claim failed following a preliminary issue trial on causation. The decision reminds us of the dangers of conflating correlation and causation. Even in a ‘material contribution’ case, the fact that two conditions were suffered coincidentally is not sufficient.
It also highlights the need for reliable evidence of cause and effect. Unconfirmed anecdotal reports of “one or two cases” are unlikely to be sufficient.
Finally, it underscores the importance of testing expert evidence on causation. Where a clinical finding potentially undermines an expert’s theory as to causation, it is important to explore this in advance of trial.
Summary
The Claimant had a history of chronic back pain. She underwent elective spinal surgery in July 2015. The Defendant admitted it had negligently failed to prescribe the appropriate anticoagulant following surgery. She suffered a deep vein thrombosis (“DVT”) and post-thrombotic syndrome (“PTS”) in her left leg as a result.
The Claimant went on to develop severe pain, ulceration and a fixed deformity of her left leg. The cause of the pain was not clear. Some treating doctors diagnosed her with complex regional pain syndrome (“CRPS”). She underwent venous stenting to improve blood flow. This had a positive effect, but only temporarily.
The Claimant subsequently underwent an above-knee amputation in 2018.
The Issues
The Claimant argued that the amputation was caused by the Defendant’s negligence. She argued that the symptoms leading to her decision to amputate – allodynia, ulceration and the fixed deformity – were caused by the DVT.
The Defendant argued that these symptoms were caused by the Claimant developing CRPS, and not by the DVT. It argued there was no basis for finding that CRPS was caused by the DVT.
The Claimant’s alternative case was that, if she did develop CRPS, it was caused by the DVT. Her fallback position was that the DVT made at least a material contribution to the need for an amputation.
On causation, HHJ Dight cited the well-known case of Bailey v Ministry of Defence [2008] EWCA Civ 883:
“…If the evidence demonstrates that ‘but for’ the contribution of the tortious cause the injury would probably not have occurred, the claimant will (obviously) have discharged the burden. In a case where medical science cannot establish the probability that ‘but for’ an act of negligence the injury would not have happened but can establish that the contribution of the negligent cause was more than negligible, the ‘but for’ test is modified, and the claimant will succeed.”
The Experts
Vascular
The Claimant relied upon evidence from Mr Jenkins. The Defendant relied upon Professor Stansby. Mr Jenkins opined that the DVT was the ‘trigger’ for a series of clinical complaints leading to the amputation. Professor Stansby took the view that CRPS, rather than the DVT/ PTS, was the cause of the amputation; as such, the amputation would have occurred in any event.
Mr Jenkins made significant concessions in cross[1]examination. He accepted that the allodynia and the ulceration were not consistent with DVT/ PTS. The failure of stenting to relieve pain also suggested that this was not related to venous insufficiency. These concessions undermined his thesis based upon the DVT being the ‘trigger’.
Professor Stansby had never seen or heard of a case where CRPS was caused by a DVT in the leg. There was only one case reported in the literature, and that did not involve a leg. On the other hand, a history of back problems and spinal surgery were both well described causes of CRPS.
Pain
The Claimant relied upon Dr Towlerton. The Defendant relied upon Dr Simpson. If CRPS had developed, then the experts differed as its cause. Dr Towlerton did not accept that the surgery itself (rather than the negligence) had caused the CRPS. However, he reluctantly accepted in cross-examination that there were no reports of DVT or PTS causing CRPS. He ultimately accepted that he could not say the DVT was a causative factor in the development of CRPS.
Dr Simpson explained she had seen hundreds of CRPS cases, but she had never seen one caused by vascular surgery. There were 3 potential causes of CRPS in this case: spontaneous (an unlikely coincidence); spinal surgery (rare but reported); or a vascular cause. A vascular cause for CRPS was “just something we do not see”.
The Court’s Analysis
The causes of amputation were allodynia, ulceration and the fixed position of the leg. As to each:
a) The vascular experts ultimately agreed that severe allodynia was not consistent with DVT or PTS.
b) They agreed the ulceration seem was not consistent with DVT or PTS.
c) The preponderance of the expert opinion was that the fixed position of the leg was not consistent with DVT or PTS but was consistent with CRPS.
The Judge therefore found that the Claimant was suffering from CRPS, and that CRPS caused the amputation. The Claimant could not prove that CRPS was caused by the DVT. There was nothing to support anything more than “an anecdotal connection” between the two:
a) Neither the medical literature nor the experience of the experts supported this.
b) Whilst one treating doctor’s note referred to having “seen a couple of cases where this appears to have occurred”, this was not accepted. The doctor was not called by either party. No details were given of these cases. This doctor’s anecdotal experience conflicted with the experience of the experts.
c) HHJ Dight warned himself against the temptation of deciding the case based upon coincidence between the DVT and the development of CRPS.
Material Contribution
In order to establish liability, the Claimant would have to show that the DVT had added to the decision to amputate. Ultimately, the Judge could not conclude that the DVT made more than a negligible contribution (if any) to the allodynia. In those circumstances, it did not materially contribute to the decision.
Practice Points
1) Scrutinise anecdotal reports with care. Is there any support in the literature for a proposed causation mechanism? If not, does it fit with the clinical experience of the expert(s)? In Tuffin, the treating clinician who gave the anecdotal evidence was not called at trial. There was nothing to confirm the ultimate diagnosis in those cases where the outcome “appear[ed] to have occurred”. Ultimately, this was an anecdotal, non-specific comment which could not be properly evaluated. Moreover, it conflicted with the experience of the experts.
2) Are there results or findings that are potentially inconsistent with a proposed causation mechanism? It is important to explore with experts how such findings might impact upon their opinion. In this case, for instance, the Claimant’s expert ultimately accepted that the failure of stenting to relieve the pain suggested that venous insufficiency (and thus the DVT/ PTS) was not the cause of allodynia.
3) Experts can assist the court by providing coherent critiques of alternative mechanisms. Dr Simpson’s exploration of the 3 potential causes of CRPS, and her ability to rule out two of these, was persuasive.
4) Beware the appeal of coincidence. The fact that B follows A does not mean that A caused B.
