Linburg–Comstock anomaly of the flexor tendons of hand

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The Linburg–Comstock anomaly, due to a tendinous connection between the flexor pollicis longus (FPL) and the flexor digitorum profundus (FDP) of the index finger, was described in 1979.1 It might be asymptomatic in majority of patients but can occasionally cause pain and simultaneous flexion of the thumb and the index fingers, with significant disability. We report a similar condition in one of our patients and review the relevant literature.
A 35‐year‐old lady presented with complaints of pain in the right hand and difficulty to write for a longer duration because of the reduction of her grip on the pen. After writing a few lines, her index finger would lose contact with the pen, and she would grip the pen only between her thumb and her middle finger. These complaints were aggravated about 3 months earlier.
On physical examination, there were signs of early triggering of right index and middle fingers, but more significantly there was simultaneous flexion of the interphalangeal joints of the index and the middle fingers of the right hand on flexion of the interphalangeal joint of the right thumb (Fig. 1). It was noticed that the metacarpophalangeal joint of the right index finger would get extended involuntarily that would result in the index finger losing contact with the pen. There were no neurological deficits, and her nerve conduction study was normal for the ulnar and median nerves. A diagnosis of Linburg–Comstock anomaly was made and considering the extent of the functional limitation, surgical exploration was considered.
The lower part of the forearm was explored through an incision of about 3 inches just medial to the palmaris longus tendon, the FPL tendon was identified and mobilization of the FPL caused simultaneous flexion of the thumb, the index and the middle fingers. Exploration was continued distally to the carpal tunnel, where an abnormal tendinous connection of about 3 cm and a width of 3 mm was identified (Fig. 2). The tendinous connection extended from the FPL proximally to the index FDP distally and on mobilizing it, there was flexion of the index and the middle fingers. The connection was excised following which, independent movements of the thumb and the index and middle fingers could be demonstrated. Through a transverse incision in the palm, A1 pulleys of the index and the middle fingers were also released. Early mobilization of the fingers was started in the immediate post‐operative period.
Two months after the surgery, the patient was able to independently move the thumb and index fingers (Fig. 3) and was able to write with near‐normal grip.
Normally, there is an independent flexion of the thumb and other fingers. Because of a common phylogenic derivation from the pronatoflexor group of Humphrey, there have been reports of tendinous connections between the FDP of the index and the FPL.2 Based on their dissection of 43 cadavers, Linburg and Comstock in 1979 demonstrated anomalous tendinous slips on one side in 25% and on both the sides in 6% of specimens.1 They clinically demonstrated this anomalous movement in 89 of 194 asymptomatic patients, of which 28 were bilateral. Similarly, Hamitouche et al.3 demonstrated this anomalous movement in 98 of 264 (37%) asymptomatic patients, women being more commonly affected than men. Based on cadaveric dissections, they described three types of anomalous connections: the most frequent one being a tendinous connection between the FPL and the FDP of the index finger, similar to the one described in this report. In two clinical cases, there was a separate muscle with a bifid tendon for the thumb and index.
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