Optimum tensioning position for extensor indicis to extensor pollicis longus transfer.

ABSTRACT

This study evaluates various wrist and thumb positions for tensioning the extensor indicis proprius when transferred to the extensor pollicis longus tendon to determine which positions provide optimum passive range of flexion and extension of the thumb. In five adult cadaver upper limbs, transfer of the extensor indicis proprius to the extensor pollicis longus was simulated. The limbs were fixed with the elbow in 90 degrees flexion and the forearm and wrist in neutral. Surface bone markers were digitized to determine the thumb and wrist positions in three-dimensional space and their intersegmental joint angles. Twelve combinations of thumb (the interphalangeal and metacarpophalangeal joints) and wrist positions for tensioning were tested. A fixed tension of 80 N was applied to the tendon ends for each of the tensioning positions and during the transfer to ensure that the tendon remained taut. A wrist tenodesis effect was used subsequently to assess the passive range of thumb motion as an indicator of the outcome of the transfer. The results showed that the better tensioning position was with the thumb fully extended and the wrist in neutral. In six patients in whom an extensor indicis proprius to extensor pollicis longus transfer was done, the tendons were tensioned with the thumb in full extension and the wrist in neutral. A prospective review and functional assessment at an average of 18.6 months' followup was done. No significant differences between the surgically treated and normal thumbs were seen for the Jebsen Taylor, 9-peg, and grip and pinch strength tests. The study suggests that in an extensor indicis proprius to extensor pollicis longus transfer, tensioning of the tendons with the thumb in full extension and the wrist in neutral gives good thumb flexion and extension range.