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 of the index finger (EDC II) tendon and to find the wrist position that gives the EPL tendon the least gliding resistance.

Methods: Fifteen fresh frozen cadavers were used. Mean gliding resistances were measured directly in seven wrist positions: 60 degrees extension, 30 degrees extension, 0 degrees, 30 degrees flexion, 60 degrees flexion in neutral deviation and 30 degrees ulnar deviation, 15 degrees radial deviation in neutral extension/flexion.

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 (p<0.001). There was also a significant effect due to wrist position (p<0.001) and a significant interaction between wrist position and the tendons (p<0.009). For the EPL tendon, the gliding resistance was significantly greater in 60 degrees wrist flexion compared to all other wrist positions tested (p<0.001). Additionally, the gliding resistance of the EPL in 30 degrees flexion, 60 degrees extension, and 15 degrees radial deviation was significantly higher than that in the other positions (p<0.001).

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.

Figure Mean values ± SD of the gliding resistance of the EPL and EDC II tendons. D had significant difference with X and ● (p<0.001). X had significant difference with ● (p<0.001).