Although the pathophysiologic concept of compartment syndrome as progressive myoneural ischemia caused by elevated intracompartment pressure is well accepted, it is not an entity that is easily diagnosed. The difficulty in diagnosing compartment syndrome is problematic because the consequences of missed compartment syndrome can be profound (rhabdomyolysis, muscle fibrosis and contracture, and permanent neurologic deficit), and the only effective prophylactic or therapeutic option of surgical fasciotomy has its own morbidity, expense, and potential complications. Thus, “getting it right” is both extremely important and extremely difficult.
Currently, clinical examination findings and use of intracompartmental pressure monitoring are both most useful in telling us who does not need fasciotomy rather than who does. We can be confident that most patients without concerning physical findings and all patients who have a perfusion pressure (diastolic blood pressure minus intracompartmental pressure) of >30 mm Hg can be safely observed. What we do not know is what we should do with patients who have positive clinical findings or perfusion pressure of <30 mm Hg. Such patients often undergo fasciotomy, but once fasciotomy is done, it is unknown whether compartment syndrome was really present (unless there was necrotic muscle), and therefore whether the fasciotomy was prophylactic, therapeutic, or completely unneeded. This inability to distinguish among traumatized limbs with true ischemic compartment syndrome in its early stages before tissue necrosis has occurred, those with impending compartment syndrome, and those with no compartment syndrome is responsible for our lack of consensus on how to manage at-risk patients.
The senior authors of this article, Dr. McQueen and Dr. Court-Brown, have long been advocates of continuous compartment pressure monitoring, which has been the standard of care at their institution for nearly twenty years. In their two classic articles published in 1996, they showed that a perfusion pressure of >30 mm Hg was safe, that use of this pressure as a threshold for fasciotomy dramatically reduced the rate of unnecessary fasciotomy while not leading to missed compartment syndrome1, and that continuous pressure monitoring led to earlier diagnosis of compartment syndrome with improved outcomes compared with clinical monitoring alone2.
Despite these seemingly clear findings, continuous pressure monitoring continues to be controversial and infrequently used in North America. Other investigators have felt that routine use of continuous pressure monitoring leads to overtreatment with fasciotomy3. Some comparative clinical trials have concluded that there is no benefit to continuous pressure monitoring compared with very strict clinical monitoring alone4.
In this article, McQueen et al. report the sensitivity and specificity of continuous pressure monitoring, using a perfusion pressure of <30 mm Hg for two hours as being diagnostic of acute compartment syndrome. Calculating these parameters requires knowledge of the number of true and false positive and negative diagnoses. This is no small task, as these calculations require that one distinguish patients who had fasciotomy but did not need it (the false positives) from those who really did (the true positives), as well as those who did not have a fasciotomy but had a missed compartment syndrome (the false negatives). The authors made these assessments retrospectively, using criteria that make sense, but of course are somewhat subjective and unvalidated. In particular, I wonder whether the proportion of fasciotomy wounds that could be closed in forty-eight hours is an accurate indicator of the rate of unnecessary fasciotomy. It seems plausible that some patients who actually did not have ischemic compartment syndrome could still have had enough swelling that closure was not attempted, and they would have been incorrectly classified as a true positive rather than a false positive. Thus, the false positive rate in this study must be considered to be underestimated. Similarly, patients who did not undergo fasciotomy but did have sensory and/or motor deficits or muscle contracture at the time of follow-up were assumed to have had a missed compartment syndrome. However, some of these cases might have had direct myoneural damage from the trauma rather than injury from missed compartment syndrome, so the number of false negatives is likely overestimated. Carrying this logic through, the actual sensitivity of continuous pressure monitoring using the threshold for fasciotomy described in this article may be >94%.
The article by McQueen et al. provides very important information for clinicians managing patients at risk for acute compartment syndrome. The reported sensitivity of 94% establishes continuous pressure monitoring using the authors’ suggested threshold of <30 mm Hg for two hours as a useful screening test that is more accurate than clinical findings alone. However, McQueen et al. report a fasciotomy rate in their 850 monitored patients of 17.9%, which is higher than expected. Because McQueen et al. also report that the fasciotomy rate in their entire cohort, which included 205 non-monitored patients, was 14.1%, it is clear that even at the authors’ own institution, the use of continuous compartment pressure monitoring increases the rate of fasciotomy compared with clinical monitoring alone. The reasons for this difference are either that continuous pressure monitoring leads to overtreatment (as suggested by others), or that clinical diagnosis results in some cases of missed compartment syndrome. Unfortunately, we still do not know which one is the correct answer, and surgeons must balance for themselves this possible risk of overtreatment against the very real clinical and medicolegal consequences of missed compartment syndrome.