The terms ‘acceleration’ and ‘exacerbation’ are not medical or legal terms of art. They have no defined meaning, and indeed I have seen them used to mean different things. They exist as a shorthand medico-legal description and should describe the difference between (1) the situation since an accident and (2) the likely progression of a pre-existing condition in the absence of the accident. This is part of the crucial evidence on causation of damage in personal injury cases.

Experts and lawyers alike talk about ‘a three-year acceleration case’ as one where the level of symptoms the claimant is now suffering has been brought forward in time by three years. Similarly, experts and lawyers will discuss an increase in symptoms following an injury as ‘an exacerbation of a pre-existing condition’.

The medical basis for opinions formed on the underlying principles these terms signify is challenged by some medical experts and for some experts and lawyers, these terms are seen simply as a fiction to attempt to provide a fair award of damages to be calculated. Others regard them as the best approach available for predicting what would have happened to the claimant in the absence of the accident and so represent the only sensible way of calculating an award of damages for the effects of the accident. A few regard the terms as simply a way to humour lawyers and their obsession with quantification.

What is meant by ‘acceleration’

The accurate use of the term would suggest that the injuries, symptoms and effects that the claimant suffered as a result of the accident are exactly the same as those that the claimant would have suffered in the absence of the accident, but are experienced earlier as a result of said accident. Where, for example, a disc prolapse is said to have occurred earlier because of an accident than it would have done naturally – in that case, the symptoms, consequences, treatments and so on are likely to be the same as they would have been in the absence of the accident, but can be said ‘merely’ to have occurred at an earlier date.

However, where the claimant suffered from, say, a degenerative spinal condition, but as a result of an accident suffers spinal symptoms earlier than expected, the onset of symptoms, their consequences and treatment are likely to be different. Where a relatively swift onset of symptoms has resulted from an accident compared with a slow onset in the absence of the accident, this point of difference might well have a significant impact on the damages recovered. 

The slow onset might have enabled the claimant to remain in employment, adapting duties for example, and receiving some therapy to assist. A swift onset might result in a sudden cessation of employment. In that case, the loss of employment has not been ‘accelerated’ by the same period as the onset of the symptoms has been ‘accelerated’.

The tenuous nature of the ‘acceleration method’

The law recognises the somewhat tenuous nature of the ‘acceleration method’ for assessing future loss but sees it as, in appropriate cases, a convenient and fair approach. In the case of Smithurst v Sealant Construction Services Ltd the claimant suffered a disc prolapse after handling heavy weights at work. Medical evidence indicated that he was more at risk of such a prolapse than the majority of the population. The court had to consider the correct way to assess damages allowing for that risk and therefore the chance that the consequences of the disc prolapse would have been experienced by the claimant at some uncertain date in any event.

On the basis of strict legal principle, if there was, in the absence of the accident, a 25% risk of prolapse in five years, a 50% risk in 10 years and say a 75% risk in 15 years, then the losses now suffered as the result of the prolapse would be discounted by a proportion of the loss for each of those periods to reflect that risk. (This would result, in crude terms, in an award of 75% of losses for the first five years, 50% for the second 5 years and 25% for the third lot of five years.)

However, recognising that the assessment of damages is to some extent inevitably imprecise despite the strict legal principle, the court accepted the practicality in many cases of using the acceleration method, which, although less refined, ‘will be fair to the claimant if it properly reflects the medical evidence’. It is worth stating also though that it involves ‘an element of swings and roundabouts’. In that particular case, the court approved using the acceleration method, which would result in recovering damages calculated at the full rate over two years but nothing thereafter, as opposed to carrying out a detailed calculation based on valuation of chance under which damages would be calculated at a progressively diminishing rate over a longer period.

It is important to note that this case addressed the situation where an identical event (in this case a disc prolapse) occurred as the result of an accident in different circumstances at an earlier time than would otherwise probably have occurred. This was not the more common situation following an accident of the comparison of the consequences of an acute onset with the slow natural development of a degenerative condition. That situation would be likely to result in an even more difficult task if the risks involved in the equivalent development of the condition or of symptoms were to be accurately assessed and timed.

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.

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