Investigation of Resistance of Digital Subcutaneous Edema to Gliding of the Flexor Tendon: An In Vitro Study

Abstract

Although edema generally is considered to contribute to resistance to tendon mobilization and is a cause of tendon overload during postoperative motion exercise, it is unclear exactly how edema of the peritendinous tissues affects tendon mobilization. We assessed the effects of simulated subcutaneous edema on the gliding resistance of the flexor tendon in an in vitro model using chicken toes. Thirty long toes of white Leghorn chickens were used. Twenty-two toes were divided into 2 groups and another 8 toes were used to determine the preconditions needed. In group 1 we produced 3 levels of edema severity in the subcutaneous tissue over a 1-cm segment by means of saline injection. In group 2 we created moderate tissue edema over 1-cm, 2-cm, or 3-cm segments of the toes. The work required to move the flexor digitorum profundus tendon over a fixed excursion and ultimate force were recorded with a testing machine after each run of flexion. Work and ultimate force increased significantly in the toes with simulated tissue edema in proportion to the severity and area of the edema. Even the least severe edema increased the work and force; a further increase to moderate edema tripled the energy needed to flex the toes. Increases in edema from 1-cm to a 2-cm and then to a 3-cm toe segment increased the work and force for each increment of extension. Simulated edema significantly increases energy and force required to move the tendons. The increase in resistance was proportionate to the severity and area of the edema. These results suggest that postoperative edema may increase significantly the resistance to tendon motion and that limiting both the severity and size of edema likely will reduce the resistance.