Can Altering Hip Joint Fluid Volume and Intra-Capsular Pressure Influence Muscle Activation Patterns? Neuromuscular Implications on Clinical Practice
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Although the integrated relationship that exists between the lumbar spine and hip joints is frequently acknowledged in scientific journals and by medical professionals, specific functional and injury relationships, are speculative and have not been substantiated. Lumbar spine and hip dysfunctions are suspected to be associated with inhibition of the surrounding extensor musculature, particularly the gluteal muscles, and facilitation of the flexor musculature. This phenomenon has been observed in other joints following effusion and is often termed ‘arthrogenic inhibition’. Its apparent occurrence about the hip has never been validated. The primary objective of this thesis was to investigate whether arthrogenic inhibition occurred about the hip. If inhibition was found to exist, its relationship with volume vs pressure was investigated to determine if either of these factors were a more appropriate predictor of inhibition. Finally, compensatory motor patterns in response to apparent inhibition were of interest. Participants were allocated to the following groups: 1) Control 2) Intervention I (magnetic resonance arthrogram) or 3) Intervention II (therapeutic arthrogram). Electromyography was collected on the rectus abdominis, erector spinae, gluteus maximus and semimenbranosis bilaterally during hip rehabilitation exercises prior to and following the intervention. Intra-capsular pressure was measured during the intervention. The findings provided support for the presence of extensor-inhibition in the hip following infusion of intra-articular fluid with intra-capsular pressure being the most appropriate predictor of the magnitude of inhibition. Hip extensor inhibition appeared to be compensated for by lumbar spine extensors during the selected tasks. Arthrogenic inhibition should be considered in the clinical evaluation and management of patients with hip joint effusions and/or elevated intra-capsular pressure.