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Effect of knee joint laxity on long-loop postural reflexes: evidence for a human capsular-hamstring reflex
R P Di Fabio1, B Graf, M B Badke
1Department of Otolaryngology, University of Minnesota, Minneapolis 55455.
Experimental Brain Research
|January 1, 1992
Summary
Anterior cruciate ligament (ACL) insufficiency alters postural responses by incorporating hamstring muscle activation to compensate for knee joint laxity. This suggests a capsular-hamstring reflex modulates central programming for improved joint stability.
Area of Science:
- Biomechanics
- Neuroscience
- Orthopedics
Background:
- Ligamentous laxity, particularly from anterior cruciate ligament (ACL) insufficiency, can compromise knee joint stability.
- Preprogrammed postural responses are crucial for maintaining balance during external perturbations.
- The role of specific muscle synergies in compensating for joint laxity requires further investigation.
Purpose of the Study:
- To investigate if ligamentous laxity at the knee joint alters the structure of synergistic activation in postural responses.
- To determine the impact of anterior cruciate ligament (ACL) insufficiency on the onset latency and discharge amplitude of postural muscle activation.
- To explore the potential modulation of central programming by joint afference in response to localized joint hypermobility.
Main Methods:
- Electromyography (EMG) was used to record automatic postural responses from tibialis anterior (T), quadriceps (Q), and medial hamstrings (H) muscles bilaterally.
- Twelve subjects with unilateral and one with bilateral ACL insufficiency stood on a moveable platform subjected to external balance perturbations.
- Experimental conditions included unilateral/bilateral stance, knee flexion/extension, and restricted/free ankle motion to alter knee joint stress.
Main Results:
- ACL-deficient limbs exhibited restructured postural responses, including earlier and less variable hamstring (H) activation (100 ms latency).
- A dominance of hamstring activity (H/Q ratio) was observed in the ACL-deficient limb during both unilateral and bilateral stances.
- Greater normalized EMG amplitudes for T, H, and Q were found during unilateral stance on the lax limb, indicating increased response gain.
Conclusions:
- A capsular-hamstring reflex is integrated into postural synergies to compensate for ligamentous laxity in ACL-deficient knees.
- Joint afference can modulate central programming to control localized joint hypermobility, as evidenced by increased response gain.
- These findings contribute to understanding postural control mechanisms in the context of joint instability and reflex modulation.