The effect of insufficient quadriceps strength on gait after anterior cruciate ligament reconstruction

Abstract

Objective. To determine the effect of quadriceps strength and joint stability on gait patterns after anterior cruciate ligament injury and reconstruction.

Design. Cross-sectional comparative study in which four groups underwent motion analysis with surface electromyography.

Background. Individuals following anterior cruciate ligament rupture often demonstrate reduced knee angles and moments during the early stance phase of gait. Alterations in gait can neither be ascribed to instability nor to quadriceps weakness alone when both are present.

Methods. Twenty-eight individuals with complete anterior cruciate ligament rupture (10 patients with acute rupture, 8 patients following reconstruction with quadriceps strength >90% of the uninvolved side [strong-anterior cruciate ligament reconstructed group], and 10 patients after reconstruction with quadriceps strength <80% of the uninvolved side [weak-anterior cruciate ligament reconstructed group]), and 10 uninjured subjects underwent an examination of their lower extremity to collect kinematics, kinetics, and electromyography during walking and jogging. Anterior cruciate ligament reconstruction was arthroscopically assisted and a double loop semitendinosis-gracilis autograft or allograft was used as a graft source. All reconstructed subjects had stable knees, full range of motion, and no effusion or pain at the time of testing (more than three months after surgery).

Results. Knee angles and moments of the strong group were indistinguishable from the uninjured group during early stance of both walking and jogging. The weak subjects had reduced knee angles and moments during walking, and jogged similarly to the deficient subjects. Regression analysis revealed a significant effect between early stance phase knee angles and moments and quadriceps strength during both walking and jogging.

Conclusion. Inadequate quadriceps strength contributes to altered gait patterns following anterior cruciate ligament reconstruction.
Relevance

Rapid strengthening following anterior cruciate ligament injury or reconstruction may contribute to a safe return to high-level activities.

Introduction

Injury to the anterior cruciate ligament (ACL) is common amongst both regular participants in sports and other active individuals, and precipitates excessive anterior tibio-femoral laxity [1]. An inability to control this laxity results in joint instability and is usually manifested as an episode of giving way, a common complaint among individuals who are ACL deficient [2], [3], [4]. Research has shown that the amount of joint laxity is not associated with a patient's instability following an ACL rupture, so the terms laxity and instability are not synonymous [5], [6]. Many patients require reconstruction of the ACL to reduce the symptoms of instability and allow a return to high levels of activity [1].

Individuals who experience instability with ACL rupture do so when the injured limb accepts the weight of the body in early stance. During weight acceptance, the limb accepts full support of the body and attenuates shock through knee flexion that is controlled by an eccentric contraction of the quadriceps. When people experience knee instability, they alter their movement patterns at this point in the gait cycle through reduced knee flexion and reduced internal knee extensor moments [7], [8]. These gait alterations may result from the unwillingness to fully activate the quadriceps muscles at a range close to full knee extension. Berchuck and Andriacchi [7] termed the reduced knee extensor moment “quadriceps avoidance” because near full extension, a quadriceps contraction may lead to anterior tibial translation [9], [10] that could initiate an episode of giving way. The reduced knee moment, however, could represent either a reduction in quadriceps activation, or an increase in flexor activity provided by the hamstrings [2], or the gastrocnemius [11] and EMG data must be used to fully understand the implications of a reduced knee extensor moment. Altered movement patterns persist following anterior cruciate ligament reconstruction [12], [13] despite surgical restoration of knee stability. This suggests that instability is not the sole cause of the gait adaptations.

While the literature provides some evidence that altered joint angles and moments are compensations for knee instability, it is conceivable that they are also the result of quadriceps femoris strength deficits. Quadriceps strength deficits are ubiquitous following both ACL rupture [14], [15], [16], and ACL reconstruction [17], [18], [19], and have been correlated with movement characteristics during both walking [11], [20] and jogging [11], [21]. This indicates that both instability and quadriceps strength deficits could be contributing to the gait deviations seen in these patient populations.

ACL rupture has been associated with early degenerative changes to the articular cartilage of the knee [1], [22]. The instability that often accompanies an ACL rupture may contribute to the development of articular cartilage defects [23]. Degenerative changes also occur after reconstructive surgery, despite the elimination of the patient's instability [1], [22], [23], which suggests that instability is not the sole cause of the degenerative changes. Quadriceps muscle weakness, which is prevalent in both ACL deficient and reconstructed patients, has recently been suggested to contribute to knee osteoarthritis [24]. If quadriceps femoris weakness contributes to altered movements and muscular adaptations, then reduced quadriceps strength might also contribute to the increased risk of arthritic changes in patient populations following ACL rupture or reconstruction. In addition, many of the gait deviations occur during weight acceptance, when an eccentric quadriceps contraction is necessary to control knee flexion and provide shock absorption. So insufficient quadriceps strength could reduce the ability of the knee to attenuate shock, which could lead to degenerative changes.

The purpose of this study was to investigate the effect of quadriceps femoris strength and instability on gait in persons with anterior cruciate ligament rupture who undergo operative stabilization. Those who have quadriceps weakness following surgery were expected to exhibit diminished knee angles and reduced internal knee extensor moments during weight acceptance, similar to the adaptation that ACL deficient subjects exhibit following injury [8]. Subjects with nearly normal quadriceps strength following reconstruction were expected to resume movement characteristics that are similar to uninjured subjects.