A biomechanical analysis of anterior cruciate ligament reconstruction with the patellar tendon

Abstract

Eleven patients, 2 years after ACL reconstruction with a patellar tendon graft, returned for follow-up testing consisting of: 1) subjective assessment and functional analysis, 2) objective examination for residual ligamen tous instability, 3) isokinetic quadriceps and hamstrings strength assessment, 4) radiographic assessment, 5) instrumented measurement of anterior shear displace ment via a knee arthrometer, and 6) force plate and film analysis while performing cutting maneuvers in a laboratory setting. All 11 patients had been tested preoperatively through all steps except the fifth. The group subjectively rated the postoperative knee as 83% of the preinjury status, an increase from a 53% mean prior to reconstruction. Six of 11 patients were able to return to their full preinjury level of competition, with or without a brace. Four patients had positive drawer tests, five had positive Lachman examinations, and all subjects had negative pivot shifts. Significant quadri ceps torque deficits remained ( P < 0.0005), with the postoperative knee extensors approximately 85% of the contralateral limb. The involved limb hamstrings were equal in strength to the nonoperated limb. Radio graphic evaluation revealed four, five, and four patients with positive findings of the patellofemoral joint, medial joint space, and lateral joint space, respectively. Only one patient had normal radiographs. Instrumented knee laxity testing revealed the operated knee to be signifi cantly looser only during maximum passive displace ment (7.2 mm versus 5.3 mm, P < 0.01) and not during the other measurements. Biomechanical analysis of the straight cut maneuver revealed no significant differ ences between the nonoperated and operated limbs at the 2 year postoperative mark. Values for the cross cut were now similar between limbs, abolishing the deficit that had existed preoperatively. This study confirms, in a laboratory setting, that a patellar tendon reconstruction of the ACL can improve the functional status of the knee and enhance athletic performance.