The dominant limb is the limb preferred for performing an activity that requires one hand or for performing the more demanding part of an activity that requires both hands. For example, most playing card dealers use their dominant limb to distribute cards (the more demanding part of the activity) and their nondominant limb to hold the rest of the pack (the less demanding activity). Although a relationship between nocturnal hand paresthesias and daily hand activities has been known for more than a century, it was not until more recently that it was recognized that unilateral carpal tunnel syndrome (CTS) more commonly involves the dominant limb.1,2
Among people with CTS, the dominant limb tends to be affected earlier and, in the setting of bilateral involvement, more severely.3,4 This relationship, however, is not absolute. In 1983, Falck and Aarnio reported that CTS could be more pronounced on the nondominant side whenever upper extremity usage requirements, especially occupational requirements, stressed that limb to a greater extent than they stressed the dominant limb.5
Regarding occupation, particular CTS risk factors and associations have been reported. One study found that the most common work-related risk factor was repetitive bending and twisting of the hands and wrists.6 In another study, the incidence of CTS was almost 10-fold higher among workers performing high force, high repetition jobs than among those performing low force, low repetition jobs.7-10 A meta-analysis identified a strong causal relationship between forceful, repetitive work and development of CTS.11 A more recent and controversial study found no association between heavy use of computers and CTS.12 In 1911, Hart reported an association between repetitive gripping and thenar atrophy.13 Although he misattributed the association to trauma of the recurrent thenar motor branch, 2 of the 3 described patients reported a period of episodic hand paresthesias preceding the development of thenar eminence atrophy and thus more likely had typical CTS.
The present study was prompted by the clinical and electrodiagnostic (EDX) features of a 27-year-old right-hand–dominant man who presented to the EDX laboratory for assessment of bilateral hand paresthesias. The patient reported episodic bilateral hand tingling that was much more pronounced on the left (nondominant) side. Consistent with his report, EDX assessment revealed bilateral CTS that involved the nondominant limb to a much greater extent than that of the dominant limb. As a blackjack dealer, the patient was using his nondominant hand to “tightly grip 2 decks of cards” and the dominant hand to distribute those cards.
Similar history and EDX patterns (bilateral CTS more pronounced on nondominant side) were subsequently noted in 2 other patients, both of whom were using their nondominant limb to perform an activity that required sustained gripping. One of these patients was a minnow counter. He was using his nondominant hand to firmly grip the top of a bucket and the dominant hand to “deal” the fish into separate tanks. The other patient was a mason. He was using his nondominant hand to firmly hold a brick or stone in place and the dominant hand to apply cement. The clinical and EDX features of these 3 patients suggested that sustained gripping might be a significant risk factor for development of CTS. That all 3 of these patients were using their dominant hand for a repetitive activity (dealing) further suggested that, compared with repetitive activity, sustained gripping was more significant as a risk factor for development of CTS.
As unilateral CTS typically occurs on the dominant side, and bilateral CTS typically is more pronounced on the dominant side, the term backward CTS is applied to cases in which unilateral CTS occurs on the nondominant side or bilateral CTS involves the nondominant side to a greater extent than the dominant side.
Although many investigators have purported an association between CTS and a particular upper extremity activity, their conclusions are limited by use of poorly validated symptom surveys, use of faulty epidemiologic methods, selection of a specific basis for clinical diagnosis (eg, isolated hand pain), or lack of EDX confirmation. Associations between a particular activity and development of CTS are best addressed by studies that include both clinical and EDX assessments and that fully characterize the individual hand usage patterns.
This study identified the upper extremity usage patterns associated with development of CTS among patients found in the EDX laboratory to have backward CTS (unilateral CTS in nondominant limb or bilateral CTS involving nondominant limb more than dominant limb). Thus, whenever patients who were referred to the EDX laboratory for upper extremity studies were noted to have backward CTS, an extensive upper extremity usage assessment was immediately performed. Both the EDX studies and the upper extremity usage assessments were performed by the author during the same encounter.