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P&F Grant Awards

Year 10

Grant # 20

Muscle Performance after Periacetabular Osteotomy for Hip Dysplasia

PI: Michael Harris, PhD


Specific Aims

Our long-term goal is to identify structural and functional deficiencies at the hip, which contribute to mechanical and metabolic pathways of osteoarthritis (OA) development. The current project introduces an innovative approach to understanding the pathogenesis of OA in cases of developmental dysplasia of the hip (DDH). The specific aims of the project will elucidate abnormalities in muscle performance and hip biomechanics in patients with DDH who have undergone hip preservation surgery, but remain at elevated risk for early OA.

DDH is a major etiological factor in OA development and increases an individual’s likelihood of OA by 4.3 fold. DDH is characterized by abnormal acetabular and femoral geometry, which cause altered intra-articular loading that can damage the articular cartilage and acetabular labrum. Without correction, soft-tissue damage progresses to OA and may require total joint arthroplasty.

Periacetabular osteotomy (PAO) is a common surgical technique designed to preserve the articular cartilage of the hip by reorienting acetabular coverage of the femoral head. Short-term results from PAO show improved femoral coverage and return to full activity at 4-9 months. However, 30 years after PAO, 71% of hips have progressed to advanced OA or arthroplasty.  Furthermore, 20% of patients treated with PAO for unilateral symptoms of DDH, develop symptoms on the contralateral hip within 18 months.10 Thus, current PAO treatment cannot guarantee elimination of symptoms, long-term restoration of activity, or delay OA.

Beyond the bony structure treated with PAO, factors such as muscle function, strongly contribute to the mechanical environment at the hip and are likely factors in the development of contralateral symptoms and altered joint loading that lead to OA. Joint mechanics after PAO are severely understudied, and the limited results have been inconclusive. Instead, most post-PAO investigations focus on patient reported outcomes (e.g. quality of life, pain) or joint survivorship. No study has considered post-PAO joint mechanics (motion and loading) during activities that are common to young adults returning to activity after PAO. Furthermore, despite six major muscles of the hip being directly affected by PAO surgery, no study has investigated muscle morphology (e.g. atrophy), neuromuscular coordination, and muscle strength at the time of return to full activity after PAO, when patients are expected to perform similar to healthy individuals.
We hypothesize that muscles, as the primary movers and stabilizers of the hip: (Hyp1) have inferior strength and volume, (Hyp2) manifest abnormal neuromuscular coordination, and (Hyp3) contribute to abnormal joint mechanics at the time of return to full activity after PAO. These abnormalities are suspected to cause asymmetries in hip loading and lead to contralateral symptom development and long-term progression to OA.

Quantifying the role of muscle in the setting of DDH is innovative, highly translational, and can provide invaluable insight into the mechanical environment of the dysplastic hip and the pathogenesis of OA. An immediate impact of our results will be to identify areas for improved post-PAO rehabilitation strategies. Knowing motion and loading of both the surgical and nonsurgical limbs, during dynamic activities can provide valuable, macroscale knowledge about potential mechanisms of future damage. As such, results from this project may also inform microscale and animal studies targeting mechanical and metabolic changes to the musculature in response to an array of bone and articular cartilage surgeries.

Aim 1: Asymmetries in muscle morphology and strength between surgical and nonsurgical limbs in patients after PAO compared to normal limb-to-limb asymmetries in healthy controls. Hyp1 will be tested using bilateral 3D reconstructions of hip musculature to measure muscle volume and isometric strength measures of muscle torque in hip muscles affected by PAO.
Aim 2: Asymmetries in neuromuscular coordination between surgical and nonsurgical limbs in patients after PAO compared to healthy controls during static and dynamic activities. Hyp2 will be tested using electromyography (EMG) to quantify muscle activity patterns in major hip muscles during static isometric muscle strength tests and biomechanically challenging activities (e.g. gait, running, squatting).
Aim 3: Differences in hip joint mechanics (motion, loading) between patients after PAO and controls during dynamic activities of increasing biomechanical demand. Hyp3 will be tested using 3D motion capture and inverse dynamics modeling to quantify hip mechanics (motion, loading) during dynamic tasks that are expected of patients who have returned to full activity.