Prevention of extensor lag after indicis proprius tendon transfer.

An experiment on fresh cadaver hands showed that a longitudinal incision of the hood did not affect index extension when traction was made on the common extensor tendon, but that excision of a portion of the hood containing the indicis proprius caused an extensor lag. The lag was eliminated by repair of the hood, providing that the closure was not too tight to prevent normal excursion of the hood. These findings were correlated with findings in patients who had undergone indicis proprius tendon transfer. Extensor lag after indicis proprius transfer is not caused by removal of the force of the tendon per se, but by factors which cause either disruption of normal hood function or tethering of its normal excursion.