No abstract

Since the proximal tendon of the gastrocnemius muscle wraps around the posterior aspect of the tibia, its contraction could potentially strain the anterior cruciate ligament (ACL) by pushing the tibia anteriorly. However, the relationship between contraction of the gastrocnemius muscle and ACL strain has not been studied in vivo. The objectives of this study were to evaluate the ACL strain response due to isolated contractions of the gastrocnemius muscle and to determine how these strains are affected by cocontraction with the hamstrings and quadriceps muscles. Six subjects with normal ACLs participated in the study; they underwent spinal anesthesia to ensure that their leg musculature was relaxed. Transcutaneous electrical muscle stimulation (TEMS) was used to induce contractions of the gastrocnemius, quadriceps and hamstrings muscles while the strains in the anteromedidl bundle of the ACL were measured using a differential variable reluctance transducer. The ACL strain values produced by contraction of the gastrocnemius muscle were dependent on the magnitude of the ankle torque and knee flexion angle. Strains of 2.8'!% and 3.5% were produced at 5" and 15" of knee flexion, respectively. The ACL was not strained at 30" and 45". Changes in ankle angle did not significantly affect these strain values. Co-contraction of the gastrocnemius and quadriceps muscles produced ACL strain values that were greater than those produced by isolated activation of either muscle group when the knee was at 15" and 30". Co-contraction of the gastrocnemius and hamstrings muscles produced strains that were higher than those produced by the isolated contraction of the hamstrings muscles. At 15" and 30" of knee flexion, the co-contraction strain values were less than those produced by stimulation of the gastrocnemius muscle alone. This study verified that the gastrocnemius muscle is an antagonist of the ACL. Since the gastrocnemius is a flexor of the knee, this finding may have important clinical ramifications in ACL rehabilitation since flexor torques are generally thought to be protective of a healing ACL graft.

The ACL strain responses produced during these CKC exercises were equal and similar to those produced during other rehabilitation exercises (i.e., squatting, active extension of the knee) previously tested.

We investigated the effect of functional bracing on anterior cruciate ligament strain in humans by arthroscopic implantation of a differential variable reluctance transducer on the ligament and measurement of its strain behavior. Strains were measured while "injury mechanism" loads were applied to the weightbearing and nonweightbearing knees for both braced and unbraced conditions. For the unbraced knee, there was a significant increase in ligament strain values when subjects went from a seated position (minimal shear and compressive loads across the knee) to a standing posture (substantial shear and compressive loads across the knee). Similar strain values were found between these same seated and standing postures when a 140-N anterior-directed load was applied to the tibia. This indicates that the ligament is strained during weightbearing and demonstrates that the compressive load across the knee produced during weightbearing does not significantly reduce ligament strain values in comparison with the unweighted joint with relaxed muscles for the 140-N load limit of our anterior shear test. Bracing produced a protective effect on the ligament by significantly reducing the strain values for anterior-directed loading of the tibia up to 140 N with the knee in both weightbearing and nonweightbearing conditions. Likewise, bracing produced a protective effect on the ligament by significantly reducing strain values in response to internal-external torque of the tibia up to 6 N-m with the knee nonweightbearing. The brace strap that contacts the tibia just distal to the insertion of the patellar tendon was instrumented with a load sensor, allowing us to measure the posterior-directed loads applied by the brace to the tibia. Adjustment of strap tension between low and high settings did not modulate the protective effect of the brace on the ligament.

In this investigation we evaluated the effect of ACL reconstruction and functional knee bracing on knee proprioception. Twenty subjects who experienced acute ACL disruption and underwent reconstruction with a bone-patellar tendon-bone graft participated in a controlled rehabilitation program and were studied at a mean follow-up of 2 years. A control group of ten subjects were also studied. In both groups proprioception was evaluated by measuring the threshold to detection of passive motion (TDPM) with the knee at 15 degrees of flexion with and without a functional knee brace applied. The Knee Osteoarthritis Outcome Score, Cincinnati knee score, and two functional knee tests were also used as outcome measurements. Anterior-posterior displacement of the tibia relative to the femur was evaluated with the KT-1000 arthrometer. There were no significant differences in TDPM between the ACL-reconstructed and contralateral knees, or between the ACL reconstructed group and the healthy control group. Bracing did not produce a significant change in the TDPM for the ACL-reconstructed group or for the control group. There were low to moderate correlations between TDPM and the other outcome measurements. This study indicates that there is no significant differences in proprioception between the ACL-reconstructed knee and the contralateral uninvolved knee 1 year or more after surgery. Functional knee bracing does not seem to improve proprioception in patients who have undergone ACL reconstruction and been followed up on average 2 years after surgery.