Changes in Neuromuscular Coordination with Jump Training After ACL Reconstruction

Of the nearly 200,000 young athletes who undergo anterior cruciate ligament (ACL) reconstructive surgery every year in the United States, approximately half will be diagnosed with early-onset osteoarthritis within 10-15 years. Chronic impairments in mechanics and neuromuscular coordination are thought to decrease the ability of the knee to attenuate forces and accept weight during high-demand activities such as landing from a jump or hop. Specifically, decreased knee bending and a concomitant increase in co-contraction of the anterior and posterior thigh musculature are thought to increase compressive forces during landing. While brief instruction has been found to elicit a transient improvement in mechanical and neuromuscular behaviors in landing, there has been limited research into the effect of extended jump training in this population. No research has been done into the extent to which co-contraction can be modified with training, thereby ameliorating the risk of early-onset osteoarthritis. PURPOSE: To determine the effects of a best-practice jump training program on mechanical and neuromuscular behaviors in people with impaired weight acceptance following ACL reconstruction. METHODS: Twenty-five subjects completed a biomechanical screening evaluation (Wk0) of a single leg land from a 20 cm platform utilizing an 8-camera motion capture system with dual force plates. Peak vertical ground reaction force (VGRF) and peak internal extension moment during landing were both normalized to body weight (BW). They and peak knee bending in degrees served as a measure of performance. Quadriceps and hamstring recruitment were analyzed using surface electromyography (sEMG) and normalized to maximum voluntary isometric contraction. Instantaneous hamstring/quadriceps co-contraction was defined as the ratio of the two muscles multiplied by the sum of their activations with a minimum of 0 and maximum of 1. The instantaneous co-contraction was integrated over the weight acceptance phase of landing to generate a co-contraction index (CoI) with a minimum of 0 and maximum of 100. Fifteen subjects were found to have deficits in mechanical function and were enrolled in an 8-week training program. These subjects underwent twice-weekly jump training sessions, with re-testing utilizing the same protocols at mid-training (Wk4), immediately post-training (Wk8), and two months after training (Wk16). The change in kinematic and kinetic variables as well as CoI were analyzed with paired t-tests with a priori significance set to p=0.05. RESULTS: As of this writing, 14 subjects had completed Wk4 and Wk8 testing. One subject left the study after Wk4. Six had completed Wk16 testing. CoI decreased significantly with training (mean±SD; Wk0: 38.3±16.1; Wk4: 24.4±14.9 (p=0.003); Wk8: 21.3±11.3 (Wk0-Wk8 p=0.0003)). Peak knee flexion increased significantly with training as well (Wk0: 58.0°±10.9°; Wk4: 68.0°±10.1° (p=0.0004); Wk8: 73.3°±7.9° (Wk4-Wk8: p=0.037; Wk0-Wk8: p DISCUSSION: All mechanical and neuromuscular variables responded to training as expected. While jump training following ACL reconstruction has been recommended, only one other study has demonstrated its effectiveness in ameliorating mechanical risk factors for re-injury and osteoarthritis in this population. We are unaware of another study demonstrating effectiveness in changing neuromuscular behaviors that can increase compressive loads and thereby increase the risk of osteoarthritis. At this time, extensive jump training following ACL reconstruction is uncommon, with most athletes released to practice based on time from surgery or strength symmetry. These results underscore the need for more extensive rehabilitation to improve long-term outcomes for these young athletes

Early Quadriceps Strength Loss After Total Knee Arthroplasty : The Contributions of Muscle Atrophy and Failure of Voluntary Muscle Activation

While total knee arthroplasty reduces pain and provides a functional range of motion of the knee, quadriceps weakness and reduced functional capacity typically are still present one year after surgery. The purpose of the present investigation was to determine the role of failure of voluntary muscle activation and muscle atrophy in theearly loss of quadriceps strength after surgery

Early quadriceps strength loss after total knee arthroplasty

Background: While total knee arthroplasty reduces pain and provides a functional range of motion of the knee, quadriceps weakness and reduced functional capacity typically are still present one year after surgery. The purpose of the present investigation was to determine the role of failure of voluntary muscle activation and muscle atrophy in the early loss of quadriceps strength after surgery. Methods: Twenty patients with unilateral knee osteoarthritis were tested an average of ten days before and twentyseven days after primary total knee arthroplasty. Quadriceps strength and voluntary muscle activation were measured with use of a burst-superimposition technique in which a supramaximal burst of electrical stimulation is superimposed on a maximum voluntary isometric contraction. Maximal quadriceps cross-sectional area was assessed with use of magnetic resonance imaging. Results: Postoperatively, quadriceps strength was decreased by 62%, voluntary activation was decreased by 17%, and maximal cross-sectional area was decreased by 10% in comparison with the preoperative values; these differences were significant (p < 0.01). Collectively, failure of voluntary muscle activation and atrophy explained 85% of the loss of quadriceps strength (p < 0.001). Multiple linear regression analysis revealed that failure of voluntary activation contributed nearly twice as much as atrophy did to the loss of quadriceps strength. The severity of knee pain with muscle contraction did not change significantly compared with the preoperative level (p = 0.31). Changes in knee pain during strength-testing did not account for a significant amount of the change in voluntary activation (p = 0.14). Conclusions: Patients who are managed with total knee arthroplasty have profound impairment of quadriceps strength one month after surgery. This impairment is predominantly due to failure of voluntary muscle activation, and it is also influenced, to a lesser degree, by muscle atrophy. Knee pain with muscle contraction played a surprisingly small role in the reduction of muscle activation

Adaptation of Quadriceps and Hamstring Activation Patterns Following Landing Instruction in Patients with ACL Reconstruction

With more than 200,000 people undergoing anterior cruciate ligament (ACL) reconstruction (ACLR) of the knee each year, optimal preventive and post-operative rehabilitation strategies are critical not just to individuals working to improve their physical health, but as a public health measure. A growing body of evidence suggests knees which have undergone ACLR exhibit compromised ability to accept weight and attenuate force during high demand activities. This predisposition contributes to relatively poor long-term outcomes for ACLR, including a high risk of re-injury, low rates of return to prior level of function, and significantly increased risk of early onset osteoarthritis (OA). Fortunately, the movement patterns involved in this tendency can be mitigated with instruction and training. Two dominant schools of thought propose divergent training paradigms, however, hampering rehabilitative and preventive effort. One advocates stiffening the joint to protect ligamentous structures by increasing the ratio of hamstring (the muscle that bends the knee) to quadriceps (straightens the knee) activity. The hamstring is thought to protect the ACL; therefore, avoiding a “quadriceps-dominant” movement strategy may decrease injury risk. The other advocates for responsiveness during high-level landing, necessitating a level of compliance in the knee joint and decreased hamstrings to quadriceps activity ratio. Given that most instructional protocols use similar cues to achieve a visually appropriate landing technique, we ask what actually happens during training? Purpose: To explore changes in muscular activity surrounding the knee during instruction for improved knee performance in landing. Methods: Thirty physically active subjects with unilateral ACLR and good clinical results participated in a one-time session analyzing single leg landing of the involved limb off a 20 cm platform using 3-D motion analysis system with force plates. Vertical ground reaction force (VGRF) and peak knee bending served as measures of performance. Vastus lateralis (quadriceps) and biceps femoris (hamstrings) activity were analyzed using surface electromyography (sEMG) and normalized to maximal voluntary isometric contraction (MVIC). Testing was repeated after 5 minutes of instruction in desired landing patterns. Hamstring/quadriceps activity ratios were calculated over the weight acceptance phase of landing, and results were analyzed with paired t-tests. Results: Landing performance improved with training, with increased peak knee bending (mean±SD; pre: 55±11°; post: 78±11°;