Anterior tibial translation during a maximum quadriceps contraction: Is it clinically significant?

Abstract

Quadriceps exercises are used sparingly in the early rehabilitation of ACL reconstructions because of con cern about prematurely stretching the ACL graft. The aim of this study was to determine if a maximum isometric quadriceps contraction significantly translates the tibia anteriorly at 15°, 30°, 45°, 60°, and 75° of flexion. Secondly, the role of the ACL in knee stability was analyzed by comparing the amount of tibial trans lation in normal, ACL deficient, and reconstructed knees. Thirdly, the location in the motion arc where a quadriceps contraction produces anterior tibial transla tion was determined. Anterior tibial translation was measured using an arthrometer (KT-1000) during an 89 N and manual maximum translation applied to the knee at rest. The manual maximum translation test determines the mag nitude of anterior tibial translation produced by a high anterior force applied directly to the proximal calf. These translations were compared to the tibial translation intrinsically induced by a quadriceps contraction. Test ing was performed in normal ( N = 22), ACL deficient ( N=10), and reconstructed (N = 10) knees. Anterior tibial translation produced by a maximum quadriceps contraction was measured at 15°, 30°, 45°, 60°, and 75° of flexion. The extension exercise resulted in less anterior tibial displacement than an 89 N drawer and half the translation produced by a manual maximum translation (P < 0.001). Instrumented laxity testing pro duced greater anterior translation of the tibia than a maximum isometric quadriceps contraction. Anterior tibial translation was the same during maximum iso metric knee extension in all tested knees. Anterior translation in the isometrically loaded knee occurred during the terminal 60° of knee extension, and was controlled by the compression forces driving the con gruent articular surfaces together, and not the ACL. Instrumented laxity testing is an accepted technique that has been safely used to serially measure knee stability after an ACL reconstruction. Early postopera tive knee extension exercises can be expected to in duce less strain in the ACL than instrumented laxity testing. These data raise the question of whether the anterior tibial displacement produced by a maximum quadriceps contraction is detrimental to a recently re constructed ACL.