Human hip and knee torque accommodations to anterior cruciate ligament dysfunction

It has been postulated that the adaptations of lower extremity function exh ibited by anterior cruciate ligament (ACL) deficient and post-ACL surgical patients represent early accommodations to the loss of ACL function after i njury so that excessive anterior displacement of the tibia is prevented. Pr ior studies have suggested that compensation patterns in ACL deficient and post-ACL surgical subjects may affect joint moments of the knee as well as the hip. However, the variance in knee and hip forces between ACL deficient , post-surgical ACL and uninjured groups has not been clearly elucidated. T he purpose of this study was to as sess hip:knee extensor torque ratios rel ative to anterior tibia shear in pre-surgical-ACL deficient, post-surgical and uninjured subjects. Measurements of hip and knee joint moments and ante rior tibia shear were recorded from 45 injured and uninjured subjects (21 m en, 24 women) during lower extremity, variable resistance exercise. Anterio r tibia shear was computed by decomposing joint moments and reaction forces according to a model derived from cadaver knee dissections and radiography , in combination, to estimate the tibio-femoral compressive and shear force s generated by the patellar tendon at various angles throughout the knee jo int range. Three groups of subjects were studied: recently injured ACL defi cient pre-surgical subjects who were scheduled for immediate surgery (PRE; n = 15); postsurgical subjects who had undergone ACL reconstructive surgery at least 1 year prior to testing (POST; n = 15); and uninjured controls (C ON; n = 15). All PRE and POST subjects had a normal contralateral limb. Tes ts were conducted under six conditions: 1 and 1.5 Hz cadence and maximal sp eed at 33% and 50% one repetition maximum resistance. The results revealed that the hip:knee ratios were significantly greater for the post-ACL surgic al group than the PRE and CON groups (P < 0.01 P < 0.03). There were signif icant negative correlations between the hip extensor:knee extensor torque r atios and maximal anterior tibia shear. across all groups. The hip:knee ext ensor torque ratio increased with decreased anterior tibia shear in all gro ups with significant correlations ranging from -0.55 to -0.88 (P < 0.01) fo r the injured limbs of PRE and POST groups, and -0.64 to -0.78; (P < 0.01) for the CON group. The highest overall correlations were found for the post -surgical subjects. The results revealed that anterior tibia shear declined significantly with speed (P < 0.01) in all groups. However, the converse w as true for the hip:knee extensor torque ratio across speeds. The ratio inc reased significantly with speed(P < 0.001) for all groups at the 33% and 50 % resistances. The results suggest (1) that post-ACL surgical subjects appe ar to accommodate to ACL substitution by using hip extensors to a significa ntly greater extent than the uninjured controls in closed-chain lower extre mity exercise; (2) that the hip:knee extensor torque ratio is significantly related to the magnitude of anterior tibia shear; and (3) that the anterio r tibia shear is significantly reduced as speed increases in closed-chain l ower extremity exercise.