AVASCULAR NECROSIS

As a complication of excessive corticosteroid therapy, AVN (= aseptic necrosis, osteonecrosis) has a good track record for successful medical malpractice litigation.

Collapse of critical areas of certain bones appears to arise from widespread blockage of small arteries by fat embolism^[21]. The commonest anatomical location is the head of the femur (thigh-bone at the hip-joint). Less commonly affected are knees and shoulders.

The Canadian Medical Protective Association acknowledges that prescribing doses^[22] and or durations^[23] too large for the acuity of the illness may be indefensible, even though Causation remains controversial.

The central Causation problem is that the dose-effect relationship is weak. Although AVN has been described after low dose oral^[24] or even local skin therapy^{[25], [26]}, there are instances where the complication has arisen in the course of the disease in question without the use of corticosteroid therapy. Similarly, there are many instances in which much larger and more prolonged courses have been administered without AVN supervening.

Nevertheless, meta-analysis^[27] has shown a strong relationship between daily total dose and the rate of AVN, even though case-control studies suggest a wide range of individual susceptibility.

Part of the reason for the unpredictable occurrence of AVN may be the multifactorial^[28] Causation of the disease. In particular, heavy alcohol intake alone^{[29], [30]} may cause AVN, and probably through the same pathological mechanism. Thus, corticosteroids and alcohol may have an additive or multiplicative Causal relationship. This relationship is not sufficiently widely recognised to require that physicians advise against alcohol during corticosteroid therapy.

In some diseases, notably Crohn's Disease, acuity of disease can be judged more objectively by clinical^[31] and laboratory^[32] measurement. Where such evidence is available, there may be a more scientific basis for medicolegal judgment of the appropriateness of the dosages and duration of corticosteroid treatment.

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