Split flexor pollicus longus tendon transfer for stabilization of the thumb interphalangeal joint: a cadaveric and clinical study.

The split flexor pollicus longus (FPL) tendon transfer is a surgical technique using the radial half of the FPL tendon rerouted dorsally and inserted into the extensor pollicis longus tendon for correction of Froment's sign. A cadaveric model was designed to investigate the effects of the split FPL tendon transfer on pinch strength. Pinch strength was compared for extrinsic thumb flexion (1) without the split FPL and (2) with the split FPL, tensioned at 3 different positions (0 degrees flexion, 30 degrees flexion, and 60 degrees flexion). We report the clinical results of key pinch strength using split FPL tendon transfer as part of thumb reconstruction for 12 thumbs in 10 patients at an average follow-up time of 2 years. The cadaveric study showed no significant difference in pinch force between specimens with or without split FPL transfer or when comparing tensioning at 0 degrees versus 30 degrees versus 60 degrees. Froment's sign wa s reproduced in all cadavers with pinch activation without split FPL transfer and was eliminated in all specimens after the split FPL transfer. In the clinical portion of this study 12 transfers in 10 patients had an average follow-up pinch strength of 33.7 N (range, 18-80 N) and no evidence of Froment's sign. We conclude that the split FPL tendon transfer is an effective method for correction of Froment's sign due to intrinsic paralysis of the thumb.