Gliding characteristics of human tendons.
Friction between sheath and tendon following tendon repair or grafting may be an important determinant of ultimate tendon excursion. We developed a system that measures the gliding resistance between a tendon and its pulley. Fresh human cadaveric flexor digitorum profundus, extensor indicis proprius, and palmaris longus tendons were studied within the finger flexor tendon sheath. Resistance to gliding was least with the flexor digitorum profundus and greatest with the palmaris longus. Resistance to gliding with the extensor indicis proprius was dependent on the orientation of the tendon. When the portion of the tendon which normally moved under the extensor retinaculum was placed within the flexor sheath, resistance was significantly less than that observed when the extrasynovial portion of the extensor indicis tendon was placed within the tendon sheath. Subsequent studies showed that the surface of intrasynovial tendon is coated with an alcian blue positive substance, which is not present in extrasynovial tendons. When the alcian blue-positive substance is removed by enzymatic digestion with hyaluronidase, gliding resistance of intrasynovial tendons increases to the level noted with extrasynovial tendons. Scanning electron microscopy showed no change in surface collagen architecture after enzymatic treatment, suggesting that the change in gliding resistance was due to the loss of hyaluronic acid bound to the surface of intrasynovial tendons. As a result of this study, it would appear that intrasynovial tendons would make much better tendon grafts than would extrasynovial tendons.