We quantified the lower extremity dynamics developed during the volleyball spike and block jumps to find out if predictive relations exist between jump dynamics and patellar tendinitis. Lower extremity movement biomechanics were analyzed for 10 members of the 1994 Canadian Men's National Volleyball Team (all right-handed hitters). Based on physical examination, 3 of the 10 players had patellar tendon pain associated with patellar tendinitis at the time of testing. In masked biomechanical and logistic regression analyses, we discovered that the vertical ground-reaction force during the take-off phase of both spike and block jumps was a significant predictor of patellar tendinitis-correctly predicting the presence or absence of patellar tendinitis in 8 of 10 players. Deepest knee flexion angle (during landing from the spike jump) predicted 10 of 10 cases correctly for the left knee. The external tibial torsional moment (during the takeoff for the right knee with the spike jump and for the left knee with the block jump) was also a significant predictor of tendinitis. In these players, the likelihood of patellar tendon pain was significantly related to high forces and rates of loading in the knee extensor mechanism, combined with large external tibial torsional moments and deep knee flexion angles.

Coupling the results of the current analysis of ankle joint complex dynamics with previously reported results of knee joint dynamics related to patellar tendinopathy suggests that a cluster of variables linked to patellar tendinopathy includes: high ankle inversion-eversion moments, high external tibial rotation and plantarflexion moments, large vertical ground reaction forces, and high rate of knee extensor moment development.

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Background and Purpose. The purpose of this case report is to describe the evaluation, treatment, and short-term outcome for an individual with chronic, progressively worsening instability of the knee during gait associated with anterior cruciate ligament (ACL) insufficiency. Case Description. The patient was a 34-year-old man who sustained bilateral ACL injuries. Subsequently, an autograft reconstruction of the left knee ACL was performed. Eight months post-reconstruction, the left knee was unstable despite bracing. Gait analysis and tests to determine the presence of muscle inhibition were performed prior to and after 12 weeks of training. Isometric torque of the knee extensors and flexors was measured with the knee in 90 degrees of flexion. A training program primarily consisted of electromyographic biofeedback during thigh muscle exercises, balance exercises, and gait. Outcomes. Muscle inhibition decreased and maximal isometric knee flexion and extension torques increased during the 12-week training period. Gait analysis demonstrated a 50% decrease in the maximum knee extensor moment and an increase in walking speed. Discussion. Selected gait variables, torque production, and muscle inhibition may change in a person with an unstable knee. The measurement of variables that have previously been documented as mechanisms of knee instability during walking allows for the selection of a specific treatment approach. ͓Maitland ME, Ajemian SV, Suter E. Quadriceps femoris and hamstring muscle function in a person with an unstable knee. Phys Ther. 1999;79:66 -75 1 Because the ACL is the primary connective tissue constraint to anterior translation of the tibia on the femur, increased tibiofemoral joint laxity was found with passive displacement tests 2 and isolated quadriceps femoris muscle contraction. 3 During gait, a person with an ACL-deficient knee may also respond to external forces by using muscles for stability.There is evidence that muscular control of knee joint stability is impaired following an ACL injury. 4 -6 Hamstring muscle contractions in response to postural perturbations, for example, were found to be slower, 4 postural sway during one-leg standing was found to be greater, 5 and the threshold to detect passive motion of the knee joint was found to be decreased 6 in subjects with ACL deficiencies compared with uninjured subjects. Disability in people following an ACL injury may be caused by changes in muscular control. 7 Persistent muscle weakness has been attributed to patients' inability to voluntarily activate the muscles. 8 Researchers have described associations between the inability to control the activity of the quadriceps femoris muscles and pain, 8 joint effusion, 9 immobilization, 10 and altered joint receptor function. 7 We are not aware of any studies in which the influence of other potential sources of muscle inhibition, such as psychological and emotional aspects, are documented.The evaluation of knee dysfunction in people with possible problems in motor control presents a c...