The application of force to the healing tendon

Abstract

This paper redefines the term "active motion" in postoperative tendon management programs as "minimal active muscle-tendon tension" (MAMTT), and reports a study of internal forces applied to a repaired tendon with MAMTT, with specific guidelines for joint angle and external load application, that allows a repeatable and reliable technique for the application of active stress to a healing tendon repaired with some currently available popular suture techniques. A comparative analysis of the reported tensile strengths of 28 different repair techniques comparing methods of study with conversion of newtons to grams provides the therapist easy access to a workable equation for force application being less than the tensile strength of any specific repair. The "active" hold position or MAMTT for the digital flexor system is calculated mathematically, with drag eliminated, and joint angle position of 45 degrees wrist extension, metacarpophalangeal joint flexion of 83 degrees, proximal interphalangeal joint flexion of 75 degrees, and distal interphalangeal joint flexion of 40 degrees, and an external load applied at the fingertip of 50 grams. In this position, the internal force on the flexor digitorum profundus is 41 grams, and that on the flexor digitorum superficialis is 605 grams. These forces dramatically increase as joint angles become greater, creating forces that exceed the tensile strengths of most repairs. Internal forces along the extensor system are calculated mathematically at approximately 300 grams when the wrist is positioned at 20 degrees of flexion, and the digital joints at a position of 0 degrees of extension in an active hold position. Postoperative management of the repaired flexor or extensor tendon with immediate active motion described as MAMTT is supported by a clinical review of 165 tendons treated with this technique.