Tendon with Z Lengthening (TWZL) Technique: Anatomic Considerations
Megan S Crosmer, MD; Paul Nielson, MD; Jeffrey A. Greenberg, MD, MS; Indiana Hand to Shoulder Center, Indianapolis, IN
Introduction: Autologous tendon grafts are used for tendon repairs and transfers. Harvesting grafts can result in donor site deficiencies, and, occasionally, autograft is not easily available. The TWZL technique was developed to obtain more tendon length without the need for harvesting tendon autograft. Our study aimed to determine the length obtainable as well as the most distal structures that can be reached using the TWZL technique.
Methods: In 15 cadaveric upper extremity specimens, the flexor digitorum superficialis to the long finger(FDS-L) and the flexor pollicis longus (FPL) tendons were cut at the volar wrist crease to simulate a volar wrist laceration, the extensor pollicis longus (EPL) was cut at Lister's tubercle to simulate EPL rupture, and the extensor carpi radialis brevis (ECRB) was released from its insertion on the third metacarpal and passed between the second and third metacarpals to simulate transfer to the adductor pollicis (AP). For each tendon, an L-shaped incision was made proximally at the level of the musculotendinous junction to the center of the tendon, and then extended distally to 1 cm proximal to the cut tendon edge. The tendon flap was then reflected 180 degrees. The most distal anatomic point to which the reflected tendon edge reached as well as the length of the flap from the distal edge of the reflected tendon edge to the musculotendinous junction cut was recorded.
Results: On average, the FDS-L total tendon length from the musculotendinous junction to the transposed tendon end was 21.2 cm and extended 0.1 cm distal to the metacarpophalangeal crease of the long finger. The FPL measured 23 cm in length and extended 2.8 cm proximal to the thumb tip. The EPL measured 14.1 cm in length and extended 3 cm distal to the first carpometacarpal joint. The ECRB measured 31 cm in length and extended 0.5 cm distal to the thumb tip. All ECRB flaps reached the AP.
Discussion: This study serves as a framework to help determine the tendon length that can be achieved using the TWZL technique without harvesting autograft. The measurements can serve as a guide to determine if the TWZL technique will provide enough length for repair after tendon laceration or rupture of the FDS-L, FPL, and EPL, if the most proximal extent of the distal tendon stump is known. This study also demonstrates that using the TWZL technique for ECRB to AP transfer precludes the need for tendon autograft.
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