Measurement of Gliding Resistance of the Extensor Pollicis Longus and Extensior Digitorum Communis II Tendons within the Extensor Retinaculum

Purpose: The etiology of spontaneous extensor pollicis longus (EPL) tendon rupture is still largely unknown. It is possible that friction within the sheath may play a role. The purposes of this study were to compare gliding resistance of the EPL tendon with that of the extensor digitorum communis tendon of the index finger (EDC II) and to find the wrist position that gives the EPL tendon the lowest gliding resistance. Methods: Fifteen fresh-frozen cadavers were used. Gliding resistance was measured directly in 7 different wrist positions. Results: The mean gliding resistance of the EPL tendon was 0. 16 ± 0.08 N and that of the EDC II tendon was 0.11 ± 0.06 N. This difference was significant. There was also a significant effect on gliding resistance due to wrist position. For the EPL tendon, the gliding resistance was significantly greater in 60° wrist flexion compared with all other wrist positions tested. Additionally the gliding resistance of the EPL in 30° flexion, 60° extension, and 15° radial deviation was significantly higher than wrist positions of 30° extension, neutral, and 30° ulnar deviation. Conclusions: Positioning the wrist close to neutral flexion/extension and in some ulnar deviation minimizes the friction within the EPL sheath. Such positions may be advantageous for splinting patients at risk for EPL rupture.