Acceleration from an orthopaedic perspective: the medico-legal interface

The problem to be addressed

This is the difficulty in describing the medical position the claimant would be in ‘but for the accident’. The reason this is difficult for clinicians is due to the problem in identifying the ‘normal’ ageing trajectory and, therefore, the signs and symptoms the claimant is likely to be displaying at various stages of life. Ageing is an individual experience and dependent upon many factors, including and most importantly genetics. Other factors from a musculoskeletal perspective would include the previous loading history, previous significant trauma, metabolic illness, such as diabetes and rheumatoid arthritis etc, smoking and BMI. The ageing process alone can produce symptoms in the spine and joints without significant trauma and is the reason for the vast majority of outpatient consultations leading to joint replacements or spinal interventions. Dr Mark Burgin stated in Law Brief in 2022 that case law suggests that courts see the terms exacerbation and acceleration as meaning a serious deterioration of the underlying condition, which is not how they are used in a report.

Clinical practice

In clinical practice, there is little attention paid to a previous history of trauma as the attitude is ‘we are where we are now’ and treatment decisions are based upon the current diagnosis and the level of symptoms experienced by the patient. Ultimately, it is the patient that is treated, not the scan. This is relevant as it can be said that by the age of 50, 80% of the population will have radiological signs of disc degeneration and, by the age of 30, MRI scans will show degenerative changes in 70%. In fact, degenerative changes appear to commence in the spine in the mid-20s. There is, however, a poor correlation between the appearance of degenerative changes and the level of symptoms experienced. There is also a range of tolerance to symptoms with psychological factors being of importance due to the complex interaction between psychology and musculoskeletal symptoms. Invariably those patients that say they have a high pain threshold, do not.

The concept of acceleration

This is the term used in the legal arena to explain where the claimant would be, in terms of symptoms, treatment, effect on activities of daily living, social life and employment if the index accident had not occurred. It is a foreign concept to clinicians as it purports to explain the speed of the ageing process, which is a unique biological experience. It is not likely that the biological clock, which is ticking for all of us, has been suddenly accelerated or speeded up, as a result of a musculoligamentous injury. In fact, it is not whole-body acceleration, but an increase in ageing in the affected part. True cases of biological acceleration can occur in fractures into joints where the smooth surface is disrupted or in spinal fractures where an interruption to the nutrient supply to the discs can occur. The majority of ‘acceleration’ cases are not true acceleration, but the concept is used to explain the position claimants find themselves in after an accident. This, therefore, is more of an attempt to describe whether symptoms they are likely to have experienced as part of their individual ageing process have been advanced. This is then described in terms of years, which can be translated into monetary value for a claim. The term advancement would sit more easily with clinicians trying to explain to the court where the claimant would have been ‘but for the accident’ as this does not rely on a permanent acceleration of the ageing process.

The science

The article by Professor Adams in Bone and Joint published in April 2014 deals with mechanical influences in disc degeneration and prolapse. He states that mechanical loading of a disc cannot entirely be blamed for diverting a disc onto a degeneration pathway as it depends upon the state of the disc when so subjected. He notes that even trivial loading can disrupt a very weak disc and that tissue weakening depends on genetic inheritance and ageing. In the absence of significant force, the symptoms would be blamed on ageing and genetics. Whereas substantial force implicates the injury or work practice. In practice, this may come down to a percentage as genetics and ageing are both continuous variables. A disc is therefore not either ‘normal or diseased’. A previous history of relevant symptoms would be important in determining ‘vulnerability’.

The predictors

To predict ‘when but for the accident’ a claimant would have developed symptoms is an important consideration. The life time prevalence of back pain is stated to be around 80% and the most accurate predictor of future back pain is regarded as being a positive previous history. In a personal injury claim, a number of other factors are relevant. Elena Sirbu, in Archives of Medical Science 2023, noted that the reaction to low back symptoms was influenced by factors such as socio-demographics, including age, sex, work status and BMI. Pain characteristics are also important, including localisation, causes and regularity. Psychological factors including yellow flags of fear inhibition, catastrophising behaviour and hypervigilant behaviour are relevant. It is also argued that if the claimant had no relevant previous symptoms or obvious risk factors, then they were at no more risk than the general population for developing similar symptoms. They, therefore, would not be cases of true acceleration.

Timeframe calculations

To calculate where the claimant would have been if the index accident had not occurred is very difficult for clinicians as there is little or no science and, therefore, relies upon experience and opinion. Despite there being a number of individual factors which can aid this calculation, factors arguing for a longer time frame estimation would be a negative previous history, significant trauma or loading, immediate symptoms, emergency medical management, significant radiological findings and structural injury. The previous history of similar symptoms is important. It is often said that the most accurate measure of future back pain is a previous history. That is certainly true with mechanical back pain as it is usually repetitive. A previous history of trauma to the same area and a previous history of surgery or significant therapy to the same area would be important. Factors arguing for a shorter timeframe would be a positive previous history of similar problems, low force trauma, the lack of a requirement for medical attention at the scene or transfer to a medical facility, delayed onset of symptoms, radiological investigations ruling out structural injury and confirming significant degenerative change which was previously symptomatic. Michael Foy in Bone and Joint April 2016 points out that corroborative evidence of the symptoms following an accident is important.

The timeframes discussed are difficult to arrive at objectively in view of the lack of science. Estimations are therefore made taking into account the discussion above. A short time period would probably be regarded as up to 2 to 3 years, a moderate period 3 to 6 years and a long timeframe 6 to 10 years. Beyond that the accident-related symptoms are likely to be permanent and it would be expected that the claimant had suffered a significant and structural injury having never had such symptoms in the past. The development of contributing non-orthopaedic conditions would have to be considered, requiring opinions from the relevant expert or experts.

In relation to repetitive work practices, opinions vary. It has been stated by Professor Michael Adams that mechanical loading, above the level that an intervertebral disc can accept, can divert a disc from its normal ageing pathway to a separate degenerative pathway. It is not known, however, what the fate of that disc would have been absent the abnormal loading. It would, therefore, be important to determine the relative importance of predisposing and precipitating factors as described above.

The place of exacerbation is different and describes a temporary increase in symptoms already experienced before returning to the pre-accident baseline level. The symptoms exacerbated are likely to be over a short timeframe.

The legal position

According to Andrew Benzeval, in Expert Witness Magazine published in April 2019, the court will, in assessing damages, attempt to put the claimant back in the position they would have been, but for the injury suffered. The concept of acceleration relates to damages being applicable during the acceleration period. The role of the expert is considered to be to determine on balance the ‘but for’ position considering the following:

1. the condition may have been present before the accident but asymptomatic and would have remained so;
2. the condition may have been present but would have become symptomatic being relieved by prompt and appropriate treatment;
3. the condition may have been present but would have become symptomatic, but in a different way and with different consequences;
4. the condition may have been present but would have become symptomatic in the same manner and therefore an acceleration occurred.

Where are we now

All these factors leave us in the realm of ‘opinion’, which is based upon a combination of factors. The expert would need to have a background of treating patients in the area in which an opinion is being provided. It is only through regularly seeing and treating patients that an understanding of underlying disease processes is obtained. There is a difference in medical practice between what is seen in the medico-legal environment and what is seen clinically. For example, whiplash-associated disorder is very rarely seen in clinics. Patients do, though, often link their current problems to some incident years before their presentation as many are ‘conditioned’ to believe their symptoms are a result of trauma rather that the ageing process or another unrelated disease. The history detailed in medico-legal reports is by its very nature more comprehensive than in a clinical setting. This needs to concentrate on the previous history, force applied, immediate symptoms and potentially genetics, to arrive at an opinion on acceleration.

Acceleration and exacerbation roundtable

I will be participating in the Acceleration and Exacerbation Expert Witness Roundtable hosted by the Expert Witness Institute on 17 October 2024 to explore these issues further. You can find more details here.

Andrew Quaile FRCS is a Consultant Orthopaedic and Spinal Surgeon, Deputy Editor of International Orthopaedics and a Member of the Expert Witness Institute.