Abstract
Abductor pollicis longus (APL) muscle is known to exhibit different variations with respect to its attachments. Various studies have reported the splitting of the APL muscle. Comparative anatomical findings of split insertion of APL is commonly found in chimpanzees, gorillas and gibbons. In the present study, we describe an anomalous APL muscle, which originated from the posterior surface of the shaft of the radius and ulna and traversed a course deep to the extensor retinaculum. Interestingly, immediately after emerging form the deeper aspect of extensor retinaculum, the thin tendon of the APL muscle continued again as a muscular belly in relation to the dorsolateral part of the 1st metacarpal bone, to end as a tendon with its attachment to the base of the proximal phalanx. Such an unusual variation of APL with its attachment into proximal phalanx is a rare finding and may be of importance in altering the mechanics of the thumb during abduction. The clinical significance of such an anatomical variation of APL may be important during reconstructive surgeries involving thumb and also of academic interest.
Highlights
Several research studies have highlighted the anomalies involving the Abductor pollicis longus (APL) muscle
The APL muscle after originating from the posterior surface of the radius and the ulna, continued as a tendon under the extensor retinaculum, thereafter became a muscle belly in relation to dorsolateral aspect of Ist metacarpal bone and descended distally as a tendon to insert into the base of proximal phalanx
There are various reports on the variations in the number of slips of the APL tendon, to the best of our knowledge, there are hardly any studies which report the tendon of APL becoming a muscle belly and again a tendon to be inserted to the proximal phalanx instead of its normal attachment to the metacarpal
Summary
Immediately after emerging form the deeper aspect of extensor retinaculum, the thin tendon of the APL muscle continued again as a muscular belly in relation to the dorsolateral part of the 1st metacarpal bone, to end as a tendon with its attachment to the base of the proximal phalanx. Such an unusual variation of APL with its attachment into proximal phalanx is a rare finding and may be of importance in altering the mechanics of the thumb during abduction.
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