Why it's essential to understand causation in medico-legal reporting


To succeed in a claim for damages for personal injury, and this is equally applicable to clinical negligence claims, it is necessary for the legal expert to prove (on the balance of probabilities):

(i) that the defendant is in breach of a duty owed to the claimant;

(ii) that injury, loss or damage has been caused to the claimant (sufficient to form the basis of a claim in law) as a result of the breach of duty; and

(iii) the nature and extent of the injury, loss or damage sustained. 

Under (ii) it is necessary to prove that some (more than minimal) damage has been suffered in order to have a cause of action (a black eye or painful neck or back will be enough). This is referred to as ‘legal causation’. Without some (more than minimal) damage there is no claim.

Once it is proved that there has been some damage, it is for the claimant to prove the extent of the damage caused by, or arising from, the breach of duty. This is referred to as ‘factual causation’.

In order to establish that there is some damage and its extent, it is necessary to address what the position would have been ‘but for’ the breach of duty, and to compare this with the position that has occurred and will occur in the future. Damages will be awarded for this difference – the damage caused by or arising from the breach of duty.

This can frequently be the main battleground between the parties to litigation. The question therefore is, even if there was a breach of duty – for example negligence - did it make any difference (legal causation), and if so, what difference (factual causation).

There are several ways of expressing the test. Lawyers often refer to causation as the ‘but for’ test:

”but for”, or “in the absence of”, or “without the act or omission, what was the claimant’s situation likely to have been in any event?”

Then it is necessary to go on to see if the situation as it is now, is different, and if so, in what way.

Medical reports need to clarify what the result of the said accident is

Judges and lawyers alike want to know what injuries, if any, the claimant has actually suffered as a result of the accident. Usually, there is little difficulty in identifying the injury (or injuries) with which the claimant has presented. However, one of the most important purposes of a medico-legal report is to distinguish between those injuries, symptoms, effects and consequences that have been caused by the accident from those that have not. In all injury claims, expert medical evidence is crucial in addressing causation. It may be necessary for a number of expert witnesses within different disciplines to address different aspects of the alleged injury.

The crucial point to remember is that a claimant can only recover damages for the consequences arising from the accident and not for anything that would probably have occurred or been suffered in any event. The medical evidence must establish clearly which of the claimant’s complaints and concerns since the accident and which of the concerns in relation to the claimant’s medical health for the future are a consequence of the accident and would not have arisen in the absence of the accident.

A very real difficulty for the medical expert is that in clinical practice the issues of causation and of consequential loss are not generally part of a medical practitioner’s assessment of a patient and are not written about in medical reports to colleagues or in learned articles. For the most part, causation is irrelevant to medical practice. What the patient’s situation would have been if the circumstances were to have been different is of no, or very little, significance.

Having a clear understanding of causation is one of the fundamental components of the medico-legal mind. So, also, is expressing the opinion on causation in an accurate and precise language which the lawyer will immediately understand.
To be clear, the difficulty in forming opinions on causation is that a claimant may have had some symptoms prior to the accident, on to which the symptoms resulting from the injury have been superimposed. The claimant may have had a pre-existing condition which was likely to have an impact on the quality of life in due course in any event. There may be pre-existing degenerative changes, asymptomatic prior to the accident but contributing to the situation since the accident or which might do so in the future. There may also be some other unrelated disease or condition that will affect the future. All of these issues can make causation a challenging principle to apply.

A further difficulty is that when addressing causation, the medical mind is far more comfortable with giving opinions on the situation as it is now than on giving opinions on what the situation would have been in the absence of (i.e. but for) the accident. The medico-legal mind understands that without the second half of the opinion dealing with the ‘but for’ position, the opinion is incomplete and the claim cannot be valued – the medico-legal report is therefore useless!

Issues of causation need to be considered carefully

Every medical expert addressing quantum, and therefore the value of a claim, must have the issues of causation in mind, whether dealing with what may appear to be a simple road traffic claim or complicated clinical negligence. Simply taking at face value that the condition of the claimant now is the result of the accident or adverse event concerned is potentially negligent.

Every such medical report must clearly set out the situation as it now is, and will be into the future, and also the situation as it would have been but for the accident or adverse event, and must explain and describe the difference between the two situations.

Giles Eyre is a retired barrister and an Associate Member of Chambers at 9 Gough Square, London, having practised for many years in the field of injury claims and at the interface of law and medicine. He continues to provide training and workshops for experts on providing effective expert reports and evidence, and on medico-legal issues. He is co-author of Writing Medico-Legal Reports in Civil Claims – an essential guide, and author of Clinical Practice and the Law – a legal primer, both published and sold by Professional Solutions Publishing. Giles blogs on issues relevant to court experts in civil claims at Medico-legal Minder.