Distinguishing material contribution from but-for causation in gastrointestinal surgery expert evidence

The scope of the but-for test in surgical claims

In clinical negligence litigation involving gastrointestinal surgery, the identification of the correct causation test is central to the resolution of a claim. The primary question for an expert witness is whether the claimant’s injury would have occurred ‘but for’ the alleged breach of duty. This standard analysis requires the expert to reconstruct the clinical timeline, assessing the patient’s condition immediately before the surgery, the operative findings, and the post-operative monitoring. If the claimant would have suffered the same injury even with competent care, the claim in negligence generally fails because the breach did not cause the damage.

The evidential base for this analysis rests on the complete medical records, including pre-operative imaging and pathology reports. Where records are incomplete, the expert should state the limitations this places on their opinion. The report must identify which clinical findings support the conclusion that the injury resulted from a specific act or omission, rather than a known risk or inherent patient factor that would have manifested regardless of the quality of the procedure.

The application of material contribution

The material contribution analysis in England and Wales arises in specific circumstances where it is not possible to demonstrate that the breach was the sole cause of the harm, but the breach contributed in a ‘more than de minimis’ way to that injury. Experts must avoid conflating this with the but-for test. The case of Bailey v Ministry of Defence [2008] established that where the evidence shows a cumulative effect of multiple causes, the claimant does not need to show that the negligence was the primary cause, provided it contributed to the outcome in a material way.

In gastrointestinal surgery, this may involve cases where a delay in diagnosis occurs alongside a pre-existing condition, and the interplay between the two makes it difficult to isolate the injury to the delay alone. When professionals articulate material contribution in complex litigation, the expert must maintain a rigorous focus on the causal link between the breach and the specific injury sustained. This analysis requires a nuanced understanding of the physiological progression of disease, particularly when distinguishing between a state of injury that was inevitable and one that was worsened by the clinical error.

Establishing breach under the Bolam and Bolitho standards

An expert opinion on breach must be calibrated against the standard of a responsible body of surgical opinion at the time of the procedure, rather than with the benefit of hindsight. Under the principles set out in Bolam v Friern Hospital Management Committee [1957] and Bolitho v City and Hackney Health Authority [1998], the court determines whether the surgery was carried out in accordance with a responsible body of professional opinion. Even if a particular technique has a high failure rate, it may not be negligent if it represents a recognised approach.

The report must clarify whether the alleged breach relates to the surgical technique, the decision to operate, or the failure to obtain informed consent. Regarding the latter, the Montgomery v Lanarkshire Health Board [2015] framework mandates that a patient must be informed of any material risks involved in the surgery. The expert’s role is to define what risks ought to have been discussed, and whether a reasonable person in the claimant’s position would have attached significance to those risks.

Expert duties and procedural requirements

Gastrointestinal surgery claims frequently require expertise from multiple disciplines. When instructions involve multiple experts, the procedural requirements of CPR Part 35 in England and Wales ensure that evidence remains focused on the issues. Where the court directs or experts consider it appropriate, a joint statement process under CPR 35.12 serves to clarify areas of agreement and isolate specific medical facts that remain in dispute. Notably, a single joint expert appointed under CPR 35.7 does not engage in a joint statement with a second expert, as they represent the sole source of expert evidence on that issue.

• CPR 35.3 mandates that the expert’s primary duty is to the court, overriding any obligation to the instructing party.
• CPR 35.8 governs the formal instructions provided to a single joint expert.
• CPR 35.10 outlines the required content of an expert report, including the expression of professional opinion and the disclosure of information relied upon.
• Evidence that appears to advocate for a party’s case rather than assisting the court is rarely helpful and risks being disregarded.