Forearm Extensor Tendon Fractional Lengthening: An Anatomic Feasibility Study.

Purpose: Fractional tendon lengthening (FL) of the forearm flexors involves multiple tenotomies at the musculotendinous junction. However, the feasibility of this technique with respect to forearm extensor muscles has not been well-studied. This study sought to evaluate the anatomy of forearm extensors, analyze the extent of muscle-tendon overlap, and identify the safest area to perform FL.

Methods: Nine soft-embalmed adult cadaver forearms from the midhumerus to the wrist were dissected through a dorsal longitudinal incision. For each muscle, we defined and measured the total overlapping zone with each tendon and the corrected overlapping zone. The useful zone (UZ) was recognized as the corrected overlapping zone, excluding the distal 2-6 cm, where there is minimal muscle-tendon overlap.

Results: Great variability in the average UZ among extensors was noted. For wrist extensors, the UZ for extensor carpi radialis brevis and extensor carpi radialis longus were considerably shorter (0.6 and 0.1 cm, respectively) than that of extensor carpi ulnaris (5.1 cm), which still had great variability in its UZs between specimens. Finger extensors had similar UZ values. The longest UZ was for extensor pollicis longus (5 cm), followed by extensor digitorum communis (3.6 cm) and extensor digiti minimi (3.1 cm). The UZ for extensor indicis proprius was consistently short (1.7 cm).

Conclusions: The area available for FL depends on the musculotendinous junction anatomy of each muscle and varies among the forearm extensors.

Clinical relevance: Surgeons should consider alternative lengthening methods for extensor tendon reconstruction, as most extensor compartment muscles have limited musculotendinous junctions suitable for free lengthening.