Turnover Tendon Lengthening Does Not Alter Biomechanical Strength of Pronator Teres–to–Extensor Carpi Radialis Brevis Tendon Transfer

Abstract

Background: The pronator teres (PT) to extensor carpi radialis brevis (ECRB) tendon transfer reestablishes wrist extension. Occasionally, the PT periosteal extension is of suboptimal quality to support a strong transfer. In these instances, turnover lengthening techniques can increase usable tendon length. This study characterized the optimal length of tendon turnover and the effect of lengthening on transfer strength. Methods: Twenty-seven cadaveric extensor tendons were lengthened using the turnover lengthening technique with 1 to 3 cm of tendon overlap. PT-to-ECRB tendon transfers were performed with native or lengthened ECRB tendons. Tensile testing was used to evaluate stress relaxation and load to failure. Results: The median maximum load to failure increased with increasing overlap length, measuring 35.6 N (quartile 1, 30.2 N; quartile 3, 38.6 N) for 1 cm, 66.0 N (quartile 1, 59.1 N; quartile 3, 74.7 N) for 2 cm, and 96.6 N (quartile 1, 85.9; quartile 3, 114.9 N) for 3 cm of overlap (P < 0.05). Failure occurred most frequently at the junction of the central overlap and native tendon. Tendons lengthened with 2 and 3 cm of overlap displayed greater stiffness than those with 1 cm (P < 0.05). Lengthening the ECRB tendon with 2 or 3 cm of overlap did not disrupt the strength or stiffness of subsequent PT-to-ECRB tendon transfers. Conclusions: Turnover tendon lengthening does not detrimentally affect PT-to-ECRB tendon transfer. Greater overlap lengthening distance confers greater stiffness and resistance to rupture. When the periosteal extension of the PT tendon avulses or is of poor quality, the ECRB tendon can be lengthened using the turnover tendon lengthening technique to facilitate a robust transfer.