Intracompartmental Versus Extracompartmental Transposition of the Extensor Pollicis Longus for Treating Thumb-in-Palm Deformity: A Biomechanical Comparison.

PURPOSE: Transecting the extensor pollicis longus (EPL) tendon and rerouting it through the first extensor compartment is an established technique for treating thumb-in-palm deformity (TIPD). An alternative technique that approximates the trajectory of the first extensor compartment without violating the compartment or transecting the EPL tendon can be accomplished by creating an artificial sheath from the extensor retinaculum to radialize the tendon glide path. This study compares this extracompartmental (EC) EPL transposition to the established, intracompartmental (IC) transposition by evaluating, in a cadaver model, the extent of thumb extension in both techniques.

METHODS: Eighteen fresh-frozen cadaveric hands were each tested under 3 different conditions: EPL in situ (baseline); EPL rerouted above the first extensor compartment (EC); and EPL rerouted through the first extensor compartment (IC). A controlled traction of 10 N was applied to the EPL under each condition. The range of thumb extension with respect to the fixed index finger was recorded utilizing infrared reflective markers and digital video capture.

RESULTS: The mean extension of the thumb with the EPL tendon in situ was 16.7°. The mean extension of the thumb was 22.0° with the EC transposition versus 25.0° with the IC technique. The measured thumb extension in both the EC and the IC techniques were found to be similar because both EPL transpositions yielded a significant difference in thumb extension when compared with baseline.

CONCLUSIONS: This biomechanical model demonstrates that radial transposition of the EPL tendon enhances extension of the thumb regardless of whether the tendon is routed through, or superficial to, the first extensor compartment.

CLINICAL RELEVANCE: A novel technique, the EC EPL transposition, offers a similar enhancement in measured thumb extension as the already-described IC EPL transposition.