The Use of Quantitative Abductor Pollicis Brevis Strength Testing in Patients with Carpal Tunnel Syndrome

Sir: I enjoyed the well-documented and detailed article by Liu et al. entitled “The Use of Quantitative Abductor Pollicis Brevis Strength Testing in Patients with Carpal Tunnel Syndrome.”1 There is a particular difficulty in obtaining long-term follow-up of study patients, and the efforts to document a group of them and report their results 7 years later are commendable. Having performed abductor pollicis brevis strength assessments in some 4000 carpal tunnel patients over the past 14 years, I am confident of its validity and consistency in objectively evaluating carpal tunnel syndrome.2 There is a remarkable correlation between strength and clinical progress in both surgical and nonsurgical patients. The more symptomatic hand is invariably weaker on abductor pollicis brevis testing. Objective assessments of abductor pollicis brevis strength changes in patients with improvement or deterioration of symptoms is invaluable, whether they have undergone surgical or conservative treatment. I also believe that correlation of electromyographic testing combined with abductor pollicis brevis strength testing is worthwhile. My colleagues and I have just completed a 50-patient study which we intend to publish shortly. We hope it will help establish recognition of the merits of abductor pollicis brevis strength testing as a simple, reliable, inexpensive, and objective examination. The accuracy of the measuring devices for clinical use can be much less exacting than that of the laboratory-quality instruments often used in muscle measurement studies. There is such a profound loss in abductor pollicis brevis strength in the typical carpal tunnel patient (1 kg or so) that a 50-g accuracy is well within acceptable tolerances.3 The other anecdotal comment I should make is that patients with abductor pollicis brevis strength of less than 1 kg on presentation often do much less well in terms of symptom resolution. They almost invariably are relieved of their pain, but they may still be symptomatic in terms of numbness with repetitive activities or when sleeping or driving. Warning them ahead of time about this possibility avoids many prolonged discussions postoperatively. Even when patients still have subjective symptoms, almost all will demonstrate some increase in abductor pollicis brevis strength. This may require several months to achieve. There is a documented, objective preoperative and postoperative strength measurement. This is especially helpful in the unhappy patient with compensation and insurance claims, who complains postoperatively that he or she is really not better. The patient often implies some fault on the surgeon’s part. This measurement, which a patient cannot fool, has saved many prolonged discussions and avoided what could potentially have become a somewhat confrontational situation. In summary, I strongly support Liu et al.’s suggestion that this test offers a valid and objective measurement of the status of a patient’s carpal tunnel syndrome. It correlates well with other clinical findings. Their article also outlines the steps we must all take to objectively determine the true role of the abductor pollicis brevis strength measurement in becoming a useful standard examination for evaluating carpal tunnel syndrome. Michael S. G. Bell, M.D. The Ottawa Hospital Civic Campus 1053 Carling Avenue Ottawa, Ontario K1Y 4E9, Canada [email protected]

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