Knee Flexion Contracture Alters Neural Control of Ankle Muscles Beyond Mechanical Constraints
A bioRxiv preprint study found that individuals with chronic knee flexion contracture (KFC) due to haemophilic arthropathy show altered neural control of ankle plantar flexors during walking that cannot be explained solely by restricted knee range of motion. Researchers compared EMG activity and intermuscular coherence between chronic KFC patients, healthy controls, and healthy individuals fitted with an artificial knee constraint mimicking the same degree of flexion. The findings suggest the nervous system undergoes lasting adaptations in response to chronic KFC, with implications for rehabilitation strategies targeting neuromuscular function.
Researchers recorded surface electromyography (EMG) from ankle plantar flexors in three groups — eight individuals with haemophilia and chronic KFC, fifteen healthy controls, and fifteen healthy individuals wearing an artificial knee constraint — during 30-metre overground walking at 1 m/s. The chronic KFC group exhibited greater knee flexion angles (24–29 degrees) compared to controls (2–20 degrees), higher EMG amplitude at foot contact, and elevated intermuscular coherence in the alpha (8–12 Hz) and beta (12–30 Hz) frequency bands during mid-stance. Crucially, despite the artificially constrained group achieving comparable sagittal knee kinematics (20–32 degrees), their early-stance EMG amplitude and mid-stance beta-band coherence remained lower than those of the chronic group. This divergence indicates that mechanical restriction of knee range of motion alone is insufficient to account for the neural changes observed in chronic KFC patients. The authors interpret the heightened intermuscular coherence as evidence of increased common neural input to the plantar flexors, reflecting genuine neuromotor adaptation rather than a purely biomechanical compensation. These results suggest that chronic KFC, even in the absence of primary neurological disease, drives central or peripheral neural reorganisation. The study was posted as a preprint on bioRxiv and has not yet undergone peer review.
What's missing
The study's own limitations include a small chronic KFC sample (n = 8), which reduces statistical power and generalisability. The cross-sectional design prevents causal inference about whether neural adaptations preceded or followed the contracture. The artificial constraint model cannot replicate pain, altered proprioception, or soft-tissue changes present in chronic haemophilic arthropathy, which may themselves contribute to the observed neural differences. Long-term follow-up data and imaging of neural structures are absent, leaving the anatomical substrate of the coherence changes uncharacterised. As a preprint, the findings have not yet been peer-reviewed.
What different sources said
- bioRxivCenter
The Limited Range of Motion of the Knee Does Not Fully Explain the Altered Neural Control of Plantar Flexors During Gait in Non-Neurological Knee Flexion Contracture
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