Subcutaneous Transposition of the Flexor Pollicis Longus: Does It Provide Increased Length for Tendon Repair? A Cadaveric Study.

Abstract

Background: Flexor pollicis longus (FPL) tendon lacerations typically occur via sharp mechanisms such as knife injury. When the injury is chronic, it may be difficult to perform a tension free repair, and tendon lengthening may be required. This article proposes a technique that transposes the proximal tendon stump over the thenar eminence subcutaneously, out of the carpal tunnel, in an attempt to gain additional tendon length by eliminating the sharp turn the FPL takes. Methods: A total of 17 cadaveric hands were used. The FPL tendon was identified and affixed to soft tissue in the distal forearm as well as at the thumb metacarpophalangeal (MP) joint with hypodermic needles. The tendon was then transected at the level of the MP joint of the thumb, removed from the carpal tunnel, and transposed on top of the thenar eminence to reach where it had been transected. The length gained by transposing the tendon was recorded by measuring the overlap of the tendon ends at the MP joint. Results: The mean amount lengthened was 7.6 mm with a standard deviation of 2.4 mm, ranging from as little as 5 mm to as high as 13 mm. Conclusions: To our knowledge, transposition of FPL tendon is a novel technique that has not been reported. Based on our cadaveric study, it can be used to bridge gaps between approximately 5 mm and 10 mm. Clinically, this amount of gap could potentially be more easily managed by simply making the repair tighter than usual as opposed to transposing the tendon.