Dynamic control and conventional strength ratios of the quadriceps and hamstrings in subjects with anterior cruciate ligament deficiency

The hamstrings:quadriceps muscle strength ratio has been used as an indicat or of normal balance between the knee flexors and extensors. A more functio nal approach to this strength ratio would be to compare opposite muscle act ions of antagonistic muscle groups. The dynamic strength control ratio (DSC R) should give a more appropriate measure relating to knee function. There is a lack of normative data relating to DSCR for anterior cruciate ligament (ACL) deficient subjects. Effects of ACL deficiency on isokinetic peak tor que for eccentric and concentric muscle actions of the quadriceps and hamst rings, in conjunction with isometric peak torque, were examined in 10 patie nts awaiting reconstructive surgery (male= 8, female= 2; age= 32.8+/-8.3 ye ars; height= 1.77+/-0.08 m; mass= 72.1+/-12.5 kg). These variables were ass essed using an isokinetic dynamometer. The results were considered in terms of the conventional ratio and DSCR. Anterior tibial drawer was measured us ing a knee ligament arthrometer to confirm clinical diagnosis of ACL ruptur e. The isokinetic peak torque data analysed were for angular velocities of 1.05 rad s(-1) (60 degrees s(-1)). Significant strength deficits were appar ent between normal and injured sides for: concentric isokinetic quadriceps action (p <0.05); isometric quadriceps action at 70<degrees> of knee flexio n (p <0.05); isometric quadriceps action at 40<degrees> of knee flexion (p <0.01); eccentric isokinetic hamstrings action (p <0.05). With bilateral co mparison, the conventional strength ratios showed no significant difference , as did the DSCR. The bilateral comparison of isometric strength ratios re vealed significant losses in quadriceps strength for the injured side (p <0 .05) but no significant losses in hamstring strength (p >0.05). Thus, diffe rences can be seen in conventional ratios and DSCR for ACL-deficient subjec ts. This is an area of clinical interest with the increasing frequency of A CL reconstruction using hamstrings tendons.