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Dynamic stability after ACL injury: who can hop?
K S Rudolph1, M J Axe, L Snyder-Mackler
1Department of Physical Therapy, University of Delaware, Newark 19716, USA.
Summary
Patients with anterior cruciate ligament (ACL) rupture who can stabilize their knee (copers) exhibit near-normal single-leg hop function. Noncopers show altered knee motion and reduced knee flexion moments during hops, indicating compensatory strategies.
Area of Science:
- Orthopedics
- Sports Medicine
- Biomechanics
Background:
- Single-leg hops are a clinical tool to assess knee function after anterior cruciate ligament (ACL) injury.
- Understanding movement strategies in ACL-deficient individuals informs treatment and rehabilitation.
- Hopping activities place higher demands on the knee, potentially mimicking athletic movements.
Purpose of the Study:
- To compare single-leg hop performance in uninjured individuals, ACL-ruptured patients with knee instability (noncopers), and ACL-ruptured patients without knee instability (copers).
- To analyze joint motion and muscle activity during single-leg hops to understand knee stabilization strategies.
Main Methods:
- Comparison of joint kinematics and kinetics during single-leg hops.
- Electromyography to assess muscle activity patterns.
- Inclusion of uninjured controls, copers (n=11), and noncopers (n=10) with ACL ruptures.
Main Results:
- Coper subjects demonstrated movement patterns nearly identical to uninjured individuals.
- Copers utilized greater ankle extensor muscle contributions for knee stabilization.
- Noncopers who hopped showed reduced knee range of motion and external knee flexion moments.
- Quadriceps femoris activation was not diminished in either coper or noncoper groups during hopping.
Conclusions:
- Individuals who can maintain knee stability after ACL rupture (copers) exhibit functional hop performance similar to uninjured individuals.
- Noncopers employ compensatory movement strategies, including altered knee motion and reliance on ankle muscles.
- Hopping ability and performance can be indicative of knee function and stability post-ACL injury.