Quantifying Material Contribution in General Surgery Breach of Duty Claims

The Legal Framework of Causation in Surgical Claims

In general surgery clinical negligence claims, the assessment of causation is frequently the most complex element of the litigation. While the ‘but-for’ test remains the primary point of enquiry—requiring the claimant to demonstrate that, on the balance of probabilities, the injury would not have occurred but for the defendant’s breach—surgical cases often involve multifactorial clinical pathways. Where a defendant’s breach combines with other non-negligent factors to produce an indivisible injury, the courts may consider the principle of material contribution, as discussed in Bailey v Ministry of Defence [2008] and Williams v Bermuda Hospitals Board [2016].

In practice, a surgeon may be asked to evaluate how distinct elements of a clinical pathway contributed to the final outcome. This is particularly relevant in cases involving delayed recognition of complications, such as anastomotic leaks or bowel perforations, where the initial surgery may have been performed to a reasonable standard, but the subsequent postoperative management is alleged to constitute a breach. The expert surgeon’s role is to delineate the degree to which the delay contributed to the final morbidity, as opposed to the progression of the underlying condition itself.

The Expert’s Role in Distinguishing Causation

Under CPR Part 35, the expert witness has an overriding duty to the court to provide independent, objective evidence. When instructed to address causation, the surgeon’s task is to provide a granular analysis of the clinical timeline, beginning with the index event—such as a laparoscopic procedure—and evaluating the subsequent clinical milestones. An adverse surgical outcome alone does not provide evidence of a breach of duty; the expert must first address whether the care provided fell below a reasonable standard under the Bolam/Bolitho framework.

Only after establishing a breach should the expert move to causation. In complex scenarios, it may be necessary to instruct experts across multiple disciplines; for instance, a general surgeon might work alongside an intensivist if the alleged negligence involves a failure to escalate care. Many practitioners find it helpful to articulate the nuances of material contribution to ensure that multidisciplinary evidence remains coherent and technically aligned. If the court directs that evidence be given by a single joint expert, that expert is instructed in accordance with CPR 35.8, rather than the court’s power to direct under CPR 35.7.

Challenges in Evidential Disputes

Disputes in surgical causation often arise when the harm is considered ‘indivisible’. If a delay in diagnosis occurs, the claimant’s condition may have deteriorated due to a combination of their underlying health status and the failure to act. If the evidence cannot establish that the breach was the ‘but-for’ cause, but it is clear that the breach contributed more than a negligible amount to the injury, the material contribution argument may be invoked. This requires the expert to move beyond binary ‘yes/no’ causation and provide an opinion on the relative weight of the breach compared to other clinical factors.

Experts must also remain mindful of Gregg v Scott [2005], which effectively excludes claims based solely on a lost opportunity for a better outcome in the clinical negligence context unless the injury itself was caused by the breach. The expert report should focus on the injury sustained and the causal link, rather than hypothetical outcomes that might have occurred had the care been different.

Practical Guidance for Instructing Solicitors

• Comprehensive Clinical Documentation: Ensure the expert has access to the full surgical record, including operative notes, imaging results, and WHO surgical safety checklist documentation.
• Precise Causation Questions: Draft instructions that ask the expert to distinguish between the natural outcome of the underlying disease process and the specific morbidity alleged to have been caused by the breach.
• Collaborative Expert Discussions: Where the court directs or experts agree that a discussion is necessary, CPR 35.12 facilitates the production of a joint statement, which can clarify whether a difference of opinion is clinical or stems from a misunderstanding of the factual matrix.
• Expert Independence: Maintain the integrity of the process by ensuring instructions focus on the expert’s independent clinical assessment rather than defending a party’s position.