P&F Grant Awards

Year 11

Grant # 23

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 that contribute to the pathophysiology of osteoarthritis (OA) in developmental dysplasia of the hip (DDH) and related diseases. Our ongoing work focuses on in-vivo movement patterns and muscle performance in patients with DDH before and after corrective surgery. In this renewal, we propose coupling in-vivo analyses with musculoskeletal and probabilistic modeling to quantify the effect of surgical correction on joint-level loading in the hip.
DDH is a major etiological factor in early hip OA. DDH is characterized by abnormal acetabular and femoral geometry, which cause insufficient coverage of the femoral head, and result in altered joint loading that can damage the articular cartilage and acetabular labrum.  Without correction, tissue damage progresses to OA.
Periacetabular osteotomy (PAO) is a common corrective surgery for DDH that involves reorienting the acetabulum, and optionally reorienting the proximal femur. 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.
A barrier to improving long-term joint survival in DDH cases is the lack of information about how PAO reorientation alters joint loading. While PAO addresses bony structure, muscle function and movement patterns strongly contribute to loading at the hip and are likely factors in the development of articular tissue damage and contralateral symptoms. Specifically, hip joint reaction forces (JRFs) represent the cumulative load that muscle and ground reaction forces place on the hip during dynamic motion, and influence how stresses on the cartilage and labrum will be distributed.9 Joint reorientation during PAO likely alters JRFs, but such alterations have not been quantified, and the sensitivity of JRFs to variability in surgical reorientation is unknown.
In the current proposal, we will use musculoskeletal modeling and probability analysis to quantify JRFs and muscle forces. Musculoskeletal models are useful for estimating variables, such as JRFs, that cannot be measured directly. Our models will be the most specific for DDH to-date by including subject-specific bone and muscle geometry, and will be validated with experimental data from our ongoing studies. We will also apply probabilistic analysis to determine the sensitivity of JRFs to post-PAO acetabular and femoral orientation. Probability analyses quantify the effects of input variability (e.g. PAO reorientation in a given direction) upon outputs (e.g. JRFs) and will provide important information for optimizing PAO planning.

Aim 1: Develop pre- and post-PAO musculoskeletal models that incorporate subject-specific bone geometry, muscle lines of action, and muscle strength to estimate joint level loading (muscle forces and JRFs). Utilizing in-vivo data collected in our ongoing project (motion data, electromyography, magnetic resonance imaging, muscle strength), we will develop musculoskeletal models at a level of subject-specificity not previously achieved for the DDH population. We will validate model outputs using industry-standard methods including comparison to in-vivo muscle activation patterns and net joint load estimates.
Aim 2: Compare hip JRF changes after PAO during level walking, inclined/declined walking, and squatting. Pre- and post-PAO motion data from our ongoing work will be applied to the subject-specific musculoskeletal models to quantify how PAO changes hip loads in patients who are returning to high levels of activity. We hypothesize that post-PAO, hip JRFs will be lower than pre-PAO values for each activity, and will be redirected more toward joint compression (i.e. away from the acetabular rim).
Aim 3: Characterize the sensitivity of JRFs to acetabular and femoral reorientation. Using probabilistic analyses, we will identify the sensitivity of hip JRFs to individual degrees of PAO reorientation (acetabular extension, acetabular adduction, medial translation, and femoral rotation). We hypothesize that hip JRFs will be most sensitive to surgical corrections that affect the lateral coverage of the femoral head.

The proposed project is a natural and important extension of our in-vivo measurements of hip mechanics. By applying our in-vivo results to detailed musculoskeletal models of DDH, we will elucidate important changes in joint loading that occur because of PAO. We will also develop a tool to inform surgeons about the sensitivity of joint loads to specific PAO reorientation parameters. Understanding how PAO changes hip mechanics will provide valuable insights into short term post-surgical outcomes. The proposed and ongoing projects will also lay the groundwork for larger studies to significantly advance our understanding of how contemporary interventions change the mechanical environment of dysplastic hips and how these changes may then alter the potential for OA development.