Dynamic stability after ACL injury: who can hop?

Abstract

Single-leg hops are used clinically to assess knee function in patients following anterior cruciate ligament (ACL) rupture and reconstruction. Researchers study ACL-deficient individuals in order to identify movement strategies in the absence of a major knee stabilizer, thereby providing information to clinicians regarding treatment options. Single-leg hops represent an activity which places higher demands on the knee than walking or jogging. Hops are thought by some to represent demands that are more comparable to those found during high level sports. Therefore hopping might provide more information about knee stability during dynamic activities than less strenuous activities. This paper reflects one component of a larger study involving comparisons of joint motions and muscle activity patterns in uninjured individuals (n=10) and two groups of athletes who had complete ACL ruptures; one group had substantial knee instability (noncopers, n=10), and the other had no signs of knee instability (copers, n=11). In this paper we report the findings from the single-leg hop activity. The results indicate that coper subjects move in a manner nearly identical to uninjured persons. Kinetic data suggest that copers stabilize their knees with greater contributions from the ankle extensor muscles. Muscle activity data demonstrate that there is no reduction in quadriceps femoris activity in the coper subjects. In the group of ten subjects with knee instability (noncopers) who participated in the overall study involving walking, jogging, hopping, and a step activity only four were willing to hop. Work in our laboratory has established that when high level athletes rupture their ACL, the majority of them cannot return to high level sports. The small number of noncopers in this study who were willing to hop supports our previous findings. Those noncopers who did hop displayed reduced knee range of motion and external knee flexion moments, a movement strategy remarkably similar to that found during other activities. Neither the copers nor the noncopers showed evidence that quadriceps activation was diminished.

Return to Sport after Anterior Cruciate Ligament Reconstruction: A Literature Review

“…It is well supported in the literature that quadriceps strength is highly correlated with good outcome post ACL reconstruction [63][64][65][66] and deficits in quadriceps strength are associated with low self-reported function and performance measures [67]. Deficits on quadriceps strength have been shown to predict performance based functions better than other factors, like graft type, knee pain or asymptomatic knee [67].…”

“…The most commonly used tests known for their reliability are the 4 available hop tests (single hop, triple hop, crossover hop and timed hop test) [9,[93][94][95][96]. All these tests can assess the functional performance and the neuromuscular control of an individual by imitating the high demands of the knee during high level activities [65,94,97,98]. Taking the results of these 4 hop tests Limb Symmetry Index (LSI) is calculated for each test separately.…”

“…Each study sets different criteria before allowing an athlete to return back to sports activities. For some studies the amount of time from ACL reconstruction is the only criterion, for some others the time together with subjective criteria are important and very few authors set objective criteria, such as muscle strength, hop tests, clinical assessment tests and related questionnaires [65]. There is no one or two tests that have to be performed.…”

Rehabilitation of a Knee Injury: Tensions Between Standard Exercises and Lived Experiences

“…Research using biomechanical measurements of the hip, ankle, and knee joint, and electromyographical measurements of the musculature in the lower extremities shows that, biomechanically speaking, all people move differently. Research results show no constant or reliable difference in movement strategies between patients who sustain an ACL injury and persons not injured (Rudolph, Axe, & Snyder-Mackler, 2000). However, some research has shown differences in movement patterns and muscular activity in the legs during walking, running, and jumping following ACL injury (Rudolph et al, 2000).…”

“…Research results show no constant or reliable difference in movement strategies between patients who sustain an ACL injury and persons not injured (Rudolph, Axe, & Snyder-Mackler, 2000). However, some research has shown differences in movement patterns and muscular activity in the legs during walking, running, and jumping following ACL injury (Rudolph et al, 2000). Fitzgerald and Kelley (2000) claim that there is a limited understanding of the role of neuromuscular control mechanisms play in maintaining knee stability.…”