Comparison of Z-Lengthening to Fractional Lengthening of Forearm Flexor Tendons: A Biomechanical Cadaveric Analysis

Contractures of the extrinsic forearm flexor units can be surgically treated with various procedures that lengthen the musculotendinous unit. Z-lengthening performed at the tendon level and fractional lengthening (FL) performed at the musculotendinous junction are two common interventions to address contractures. The purpose of this study was to compare the biomechanical properties of flexor tendons undergoing Z-lengthening versus FL.

Seventy-two flexor tendons were harvested from 12 paired upper extremities, including flexor carpi radialis, flexor carpi ulnaris, flexor pollicis longus, and flexor digitorum superficialis tendons. Tendons for each set of paired upper-extremities were subjected to either FL or Z-lengthening, so that each type of tendon in an upper extremity pair received a different lengthening procedure. Z-lengthened tendons were lengthened 20 mm and repaired with a pair of 2-0 horizontal mattress sutures. For fractionally lengthened tendons, a transverse tenotomy was made at the musculotendinous junction at the level corresponding to 75% of its maximal width, followed by a second tenotomy 1 cm distal to the first. The maximum load at failure and excursion at failure for each tendon type were measured and compared with the contralateral side.

Z-lengthened tendons demonstrated a significantly greater load to failure compared with the fractionally lengthened tendons (24.1 N vs 17.3 N). Maximum tendon excursion at failure was also significantly greater for Z-lengthening compared with FL. Among Z-lengthened tendons, 91% (32/35) failed because of suture pullout.

Z-lengthened forearm flexor tendons had greater overall tensile strength and excursion at failure compared with fractionally lengthened tendons.

Surgeons should consider performing Z-lengthening as an alternative method for tendons that are susceptible to failure with FL.