Regardless of the injury sustained, the frailty and fragility of a claimant is no defence in a tort claim. The thin skull rule, also known as the “egg- shell rule”, is a well-established principle in both English tort and criminal law. InOwens v Liverpool Corp  1KB 394, it was held that “it is no answer to a claim for a fractured skull that the owner had an unusually fragile one”.
The case of Reaney v University Hospital of North Staffordshire NHS Trust  EWHC 3016 has put this rule to the test and has raised a number of questions about causation and the quantification of damages in cases where a claimant has a pre-existing injury.
Mrs Reaney was a 61 year old woman who experienced sudden back pain and weakness in her legs. On admission to A&E, she was diagnosed with transverse myelitis, a rare inflammatory condition, which caused irreversible damage to her spinal cord. This condition left her paralysed as a T7 paraplegic.
It is accepted that this condition was non-negligently caused. However, during her hospitalisation, Mrs Reaney developed grade four pressure sores. The severity and deepness of these sores were such that she subsequently developed infection of her bone marrow, shortening of the muscle tissue in her legs and a hip dislocation. When sitting, Mrs Reaney slumped to the left thereby leaving her in a “windswept” position. Her condition was such that she was predominantly bed ridden.
The Judge had to consider the extent to which the negligently caused pressure sores had made Mrs Reaney’s condition worse than it would have been but for their development. When ruling on causation, the Judge found that the Defendants’ negligence had made Mrs Reaney’s position materially and significantly worse than it would have been but for that negligence and that she would not have required the significant care package that she then required but for the negligence.
The Judge accepted Mrs Reaney’s argument that had she not suffered these pressure sores she would have had a much better quality of life, been able to use a wheelchair from which she would have been able to self- transfer to some extent. Although the Judge recognised that Mrs Reaney would have required some care as a paraplegic, it was estimated that this would equate to seven hours of professional care weekly until attaining the age of 70. Subsequent to the Defendants’ negligence, Mrs Reaney would require continuous care from two carers until the end of her life and would need to move into a bigger property to accommodate the carers.
The Judge took a practical approach and justified his decision by relying on the thin skull rule. He reiterated that a tortfeasor must take his victim as found and would have to make full compensation for the worsened condition. He considered what Mrs Reaney was receiving by way of care prior to the negligence and found that as a consequence of negligence, she needed significantly more care and support. The defendants would be liable for this because causation had been established. It reflects the principle that injuring someone who is already injured is much more serious. This was illustrated in the case of Paris v Stepney Borough Council  AC 367 where the court held that the loss of sight in one eye is significantly worse for a one-eyed man than for a man with full eyesight.
Other jurisdictions have taken different approaches when quantifying damages in cases involving non-negligently caused pre-existing injuries and have drawn a distinction between thin skulls and crumbling skulls. This distinction is best described by the Canadian Supreme Court in Athley v Leonati  3 S.C.R 458. When discussing the concept of crumbing skulls, the Court held:
“The defendant need not put the plaintiff in a position better than his or her original position. The defendant is liable for the injuries caused, even if they are extreme, but need not compensate the plaintiff for any debilitating effect of the pre-existing condition which the plaintiff would have experienced anyway. The defendant is liable for the additional damage but not the pre-existing damage.”
Interestingly, although the Canadian Supreme Court discussed thin and crumbling skulls at length, Mr Athley was deemed to be neither. Mr Athley suffered damage to his back and neck. Soon after the accidents, he experienced a disc herniation during a stretching exercise (which incidentally had been recommended by his doctor). He was hospitalised and unable to resume work. During the first instance trial, the Judge found that the defendants had pre-existing back problems and was involved in two successive car accidents during which he in the two vehicle accidents should only pay 25% of his damages because of his pre-existing weakness in his back. On appeal, the Supreme Court found that the accidents materially contributed to the disc herniation and that the defendants were liable for full compensation because causation had been established.
Thin vs crumbling skulls
In Shaw v Clark 11 BCLR (2d) 46, the Canadian courts continued to differentiate between thin and crumbling skulls by looking at the stability or instability of a claimant’s condition. A thin skull “although thinner than the average skull, is in a stable condition before the accident, and, but for the accident, would have remained so”. In contrast, the crumbling skull “is where the skull, whether thick or thin, is not in a stable condition before the accident but in the state of continuing deterioration which the accident has merely accelerated”. A crumbling skull is one which is already crumbling regardless of the accident.
The implication of this distinction is that a defendant is fully liable for the claimant’s injury even if they are unexpectedly severe due to a pre-existing (yet stable) condition. However, according to the crumbling skull doctrine, the defendant is liable for the injuries caused even if extreme, but need not compensate the claimant for debilitating effects of the pre-existing condition which the plaintiff would have experienced anyway.
In Mrs Reaney’s case, it appears that she would remain in a stable condition until the age of 70 at which time her care needs would increase. It is likely that if this case was heard in Canada, the Claimant would argue that she is has a thin skull and entitled to full compensation whereas the Defendant would endeavour to limit their liability by using the crumbling skull arguments.
In practice, the distinction between crumbling and thin skulls is fraught with difficulties. As demonstrated in Mr Athley’s case, some claimants will fit neither category. Mrs Reaney’s case was heard in the Court of Appeal on 21 October and judgement is awaited. It is hoped that it will bring clarification on the approach to adopt in cases involving pre-existing injuries.