The phrase “inevitable condition” can make the answer sound simpler than it is. It may suggest that the accident is medically irrelevant because the underlying disease already existed. That does not follow. An accident may fail to cause the disease itself while still bringing forward symptoms or accelerating the need for treatment.
The expert’s task is to separate what was already present from what the accident changed.
“Inevitable” requires caution.
Very few medical outcomes are inevitable in the strict sense. Degenerative change does not produce the same symptoms in every person or follow a fixed timetable. NICE states that osteoarthritis does not inevitably worsen; symptoms may fluctuate and periods of increased symptoms can settle. It also recommends that management should be guided by symptoms and physical function rather than imaging alone.
An expert should therefore be cautious about saying that a claimant would certainly have developed the same disability. The evidence may support a probability that symptoms would have emerged, but the timing, severity and functional effect may remain uncertain.
A person may have significant degeneration for years without seeking treatment or reducing work. The condition may make later symptoms more likely, but it does not establish that they would have begun on a particular date.
Pre-existing vulnerability is not pre-existing disability.
Medical records and imaging may show that a claimant was vulnerable before the accident. That vulnerability may consist of osteoarthritis, spinal degeneration, a partially torn tendon, osteoporosis or another progressive condition.
The expert should ask whether the condition was symptomatic before the incident. If so, what symptoms were present and what effect did they have on activity? A claimant who occasionally used pain relief but remained fully active is in a different position from someone already awaiting surgery or regularly absent from work.
The report should describe the claimant’s actual baseline. Previous consultations, medication, investigations, treatment, employment records and reported activities may all assist. An accident does not become the sole cause of every later problem because the claimant was previously functioning well. Equally, the discovery of degeneration does not justify treating the post-accident presentation as inevitable.
Acceleration, aggravation and triggering.
A temporary aggravation occurs where an accident worsens an existing condition for a limited period, after which the claimant returns to the course they would have followed without it. Acceleration means that the accident brings forward a stage that would have occurred later. Symptoms, treatment, incapacity or surgery may arise earlier than expected. The condition may eventually reach the same position, but it reaches it sooner.
An accident may also trigger symptoms from a previously silent condition. Whether that represents temporary aggravation or lasting acceleration depends on the subsequent course and the available evidence, and the expert should state which mechanism is being proposed. A conclusion that the accident “made things worse” leaves unanswered whether the effect lasted weeks, years or indefinitely.
Constructing the alternative history.
The central question is what would probably have happened without the accident. This is hypothetical, but it should not be speculative.
The expert should consider the natural history of the condition, the claimant’s age, previous symptoms, rate of progression, occupational demands and treatment history. Evidence that surgery had already been recommended may support a short acceleration period. An incidental imaging finding in a claimant with no previous symptoms may justify a more guarded opinion.
The actual post-accident course must then be compared with that alternative. Did symptoms begin immediately? Was there a clear increase in treatment? Did function decline consistently with the injury? Were there later incidents or unrelated changes that could better explain the deterioration? Where the evidence is weak, a range may be more honest than a single date.
Imaging cannot determine the answer alone.
Imaging can identify degeneration, disease or structural vulnerability. It rarely establishes when symptoms would have started.
NICE advises that osteoarthritis is usually diagnosed clinically and that imaging should not routinely guide non-surgical management. This reflects the importance of symptoms and function rather than an assumption that the image dictates the person’s experience.
Severe changes may support the view that the claimant was closer to becoming symptomatic, but they do not prove that substantial disability was imminent. The records before and after the accident often provide more useful evidence about timing.
Estimating the acceleration period.
A useful opinion should attempt to address duration. Saying that the accident accelerated the condition without estimating its effect gives little assistance.
The expert may conclude that symptoms were brought forward by several months, that surgery occurred earlier than it otherwise would have done, or that the accident caused a temporary increase before the natural course resumed. The conclusion should identify what was accelerated: symptoms, restriction, treatment or another medical event.
False precision should be avoided. The evidence may justify a range rather than an exact period. The report should explain the factors supporting the estimate and those limiting confidence. Different consequences may also require separate opinions. Pain might have been accelerated for one period while the need for surgery was unaffected.
What the report should make clear.
Practice Direction 35 requires expert evidence to be independent, objective and based on all material facts, including those that may detract from the opinion. It also requires the expert to explain where a definite opinion cannot be reached and to summarise any reasonable range of opinion.
The report should identify the pre-accident condition, the claimant’s baseline, the effect of the accident, the likely course without it and the period for which the accident altered that course. It should distinguish between causing the disease and accelerating its consequences.
The presence of a probable future condition does not make an accident irrelevant. Nor does the timing of symptoms prove that the accident caused the whole subsequent history. An accident may act upon a vulnerable person, bringing forward symptoms or treatment that would have arisen later. The expert’s responsibility is to explain how much earlier, on what evidence and with what degree of certainty.
“Inevitable” should never be used as a shortcut. The real question is whether the accident changed when the condition emerged, how severely it presented or how soon it affected the claimant’s life.
