August 2000 Bulletin

Causation is more than patient’s word

By John C. Lyons, MD, FACS, MSME

Increasingly in our society orthopaedists are being called upon to provide expert opinions regarding injury causation. Whether in the context of Workers’ Compensation claims, civil suits or other settings, physicians are asked to correlate a diagnosis with an event, "with a reasonable degree of medical certainty."

Commonly, this opinion is offered based upon the patient’s relayed history, but without sound scientific scrutiny. To endorse the patient’s lay opinion on causation may be a common practice, as medical focus is principally directed toward diagnosis and care issues, but it is not necessarily a sound approach. For instance, when confronted with a symptomatic herniated disk with radiculopathy, how and why a disk may have herniated is often subordinate to the surgeon’s concern for optimal medical care.

Certainly, mechanism of injury is of some clinical concern to clinicians. If a carpal tunnel is suspected from repetitive activity, efforts are often directed toward a conservative approach such as activity avoidance, splinting, use of nonsteroidals, etc. The efforts may well be effective, reflecting the influence of environmental and mechanical factors in the disease process. But mechanical treatment measures are not always effective. These failures highlight the often multifactorial and sometimes non-mechanical nature of disease.

Considering for a moment carpal tunnel syndrome, in the scheme of musculoskeletal disorders it is not an uncommon, but certainly not a universal, syndrome. Numerous studies have reported various associations and dissociations. It is relatively uncommon in children for instance. It may occur with Colles fractures, but even with higher-grade fracture patterns, the syndrome is not common. The association with repetitive stress occupations is increasingly discussed, but what about the secretaries, pianists, carpenters and others that labor for years but are unaffected? It may be easy to ascribe carpal tunnel to repetitive activities, since there are increasing reports of such association, but reasonable scientific certainty of causation demands further scrutiny. Patient history may provide insight into causation, but it is infrequently the last word on the matter.

Causation analysis has many facets. A patient may claim the onset of back pain from lifting a box. Investigation may reveal ruptured herniated disk. A clinician may associate the herniation with the lifting event and may even do so "with a reasonable degree of medical certainty," but is this really so? Could it be that the patient had a strain event superimposed on a preexisting underlying asymptomatic disk herniation? We know that asymptomatic disk herniations exist in the general population. We also know that people strain their backs and have no disk herniations. Scientific causation analysis requires more than reliance on patient history.

Many physicians may be disinclined toward causation analysis. After all, biomechanics is a subspecialty unto itself, and rather dry in nature to many orthopaedists. It requires time and effort to identify and eliminate various potential causal etiologies, and the effort may not alter the treatment plan. There may be a social bearing to causation analysis, in terms of insurance, liability issues, etc., but often not so to treatment alternatives, so why expend the effort? Unfortunately the choice is not always ours.

As orthopaedists are increasingly confronted with demands for opinion on causation, as these opinions may have significant social implications, and as many of these opinions are coming under more critical scientific scrutiny by peer reviewers, perhaps more attention needs to be focused upon the analysis than traditionally offered. If not, perhaps clinicians are best advised to respond to causation inquiry proportionately to their level of skill and study. There exists an increasing body of interdisciplinary data that assists in formation of a sound scientific judgment on causation. There is also an increasing body of junk science of which one must be cognizant.

Practice demands include causation analysis, particularly with regard to mechanisms of mechanical injury. A study of the environmental event and application of biomechanical principles is critical to a sound judgement. If a physician concludes a causal association, based upon a plausible patient history, but where the environmental details are not scrutinized and contributing factors such as underlying conditions are not examined for contribution, then perhaps a response to inquiry is best phrased as: "with a reasonable degree of medical certainty, based on the patient’s relayed history, there appears to be a relationship between the patient’s injury and [the identified event(s)]." Otherwise an opinion given "with a reasonable degree of medical certainty," but without detailed knowledge of the actual event or prior patient history, may expose a physician to criticism from a scientific biomechanical perspective.

For more information, contact the Committee on Biomedical Engineering in the Research section of the Academy home page at

John C. Lyons, MD, FACS, MSME is in private practice adult reconstruction and clinical biomechanics.

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