Pronator teres is an appropriate donor muscle for restoration of wrist and thumb extension

Objective: To compare the detailed architectural properties of the pronator teres (PT), extensor carpi radialis brevis (ECRB), and extensor pollicis longus (EPL) muscles to evaluate the suitability of PT-to-ECRB and PT-to-EPL surgical procedures. Methods: Muscle physiologic cross-sectional areas and region-specific muscle fiber lengths were measured in cadaveric PT, ECRB, and EPL muscles (n = 10 muscles of each type). One-way repeated-analyses of variance measures and post hoc t tests with Bonferroni corrections were used for statistical comparisons. Results: The ulnar head of the PT was present in 8 of 10 specimens. The average PT fiber length was similar to that of the ECRB (7.02 ± 0.49 cm vs 6.17 ± 0.27 cm) but was significantly longer than that of the EPL (5.44 ± 0.25 mm). Fiber length in the humeral head of the PT was longer compared with the ulnar head (7.19 ± 0.52 cm vs 4.14 ± 0.25 cm). The average physiologic cross-sectional area of the PT was similar to that of the ECRB (3.5 ± 0.4 cm² vs 3.3 ± 0.3 cm²) but was significantly larger than that of the EPL (3.5 ± 0.4 cm² vs 1.1 ± 0.1 cm²). Conclusions: From an architectural point of view the PT is an excellent donor choice for transfer to the ECRB for restoration of wrist extension or to the EPL for restoration of thumb extension. Because there is fiber length heterogeneity within the PT, however, when the ulnar head is present it may limit the total excursion of the donor muscle. These data suggest that releasing the ulnar head of the PT before transfer may result in larger excursions of this important motor in tendon transfer surgery.