The Effects of Compressive Load and Knee Joint Torque on Peak Anterior Cruciate Ligament Strains

BACKGROUND: High graft strains incurred during rehabilitation after anterior cruciate ligament reconstruction may be minimized if an external compressive load is simultaneously applied to the joint during closed kinetic chain exercises. HYPOTHESES: Peak anterior cruciate ligament strains will 1). increase with an increase in resistance torque during an exercise that involves concentric contraction of the extensor mechanism, 2). decrease with an increase in resistance torque during an exercise that involves concentric contraction of the flexors, and 3). decrease when an external compressive load is applied to the knee during both exercises relative to the no external compressive load condition. STUDY DESIGN: Controlled laboratory study. METHODS: Strains in the anteromedial bundle were measured in 10 subjects with normal ligaments. Flexor and extensor exercises were performed against controlled resistance torques with and without a compressive load applied to the foot. RESULTS: An increase in resistance produced an increase in peak anterior cruciate ligament strain for the extensor exercise with no compressive load applied. During the flexor exercise without a compressive load, an increase in resistance produced a decrease in peak strains. During the extensor exercise, the peak anterior cruciate ligament strain was not reduced with the application of the external compressive force. CONCLUSIONS: Extensor and flexor exercises that incorporate an external compressive load do not shield the anterior cruciate ligament from strain. However, no additional increase in strain occurs with an increase in resistance when the external compressive load is applied. Thus, it may be possible to increase the activity of the quadriceps muscles without increasing the strain by applying a compressive load (as with closed kinetic chain exercises).