Anterior tibial translation during progressive loading of the ACL-deficient knee during weight-bearing and nonweight-bearing isometric exercise

Many protocols for rehabilitating the knee following anterior cruciate ligament (ACL) injury or repair call for the use of both weight-bearing and nonweight-bearing exercises. However, not much is known about the strain these exercises place on the passive restraining mechanisms. The purpose of this study was to examine the effect of progressive loading of the knee extensors on anterior tibial translation during weight-bearing and nonweight-bearing isometric exercise. Fourteen subjects diagnosed as ACL-deficient via arthroscopic surgery participated in the study. An arthrometer was used to measure anterior tibial translation during weight-bearing and nonweight-bearing exercises with the knee in 20 degrees of flexion and with a quadriceps load equivalent to 25, 50, 75, and 100% of body weight. Hamstring muscle activations during all testing were monitored to eliminate the possibility of substantial cocontractions. During the weight-bearing exercise, anterior tibial translation was found to be significantly less than that measured during the Lachman's evaluation and the 50, 75, and 100% nonweight-bearing exercises. For the nonweight-bearing exercises, anterior tibial translation was either equivalent to or greater than the Lachman's evaluation. During the weight-bearing exercises, anterior tibial translation was not different under the different loading conditions. During the nonweight-bearing exercises, anterior tibial translation progressively increased with increased loading. The results from this study imply that weight-bearing exercises minimize strain to the passive restraining structures whereas nonweight-bearing exercises will strain these structures, and the magnitude of this strain appears to be proportional to the knee extensor moment.