Poster 208: Predicting Patient-Specific Hip Motion During Functional Activities After Periacetabular Osteotomy

Abstract

Objectives: Developmental dysplasia of the hip (DDH) is a condition in which the hypoplastic acetabulum provides inadequate coverage of the femoral head. This abnormal coverage, while pathological, may be advantageous in some sporting and recreational activities needing significant hip range of motion (ROM), including dance, ballet, and performing arts. Although DDH allows patients to perform activities requiring supraphysiologic hip motion, subluxation of the hip joint generates excessive articular stresses, leading ultimately to pain, osteoarthritis (OA), and total joint arthroplasty. In some DDH patients, this degenerative pathway can be interrupted by performing a periacetabular osteotomy (PAO) to reorient the acetabular fragment, which increases femoral head coverage and reduces intra-articular stresses. This improved coverage is believed to come at the sacrifice of range of motion, particularly noticed while performing high-demand activities requiring supraphysiologic end-range motion. This study addresses the questions: 1. Does a PAO reduce the range of motion of the hip enough to reduce a patient’s ability to perform daily living, recreational and sporting activities? 2. If so, what activities are most impacted by these changes? Methods: We created an inventory of daily living, recreational and sporting activities commonly performed by patients with hip dysplasia. A systematic review of the literature provided the maximum hip range of motion required (required ROM) to perform eight activities of daily living (ADL) and thirteen sporting movements. The concurrent peak value for each anatomic component of hip motion, (i.e flexion/extension; adduction/abduction; internal/external rotation) was classified for every activity in terms of physiologic demand relative to the average ROM of the adult hip. Based on these values, we created a 7-level ordinal scale according to the peak kinematic demand required to perform each activity (Table 1), ranging from low to extreme difficulty. To examine the impact of a PAO on the limits of hip motion, we selected, with IRB approval, a cohort of 24 dysplastic hips (12 left and 12 right). Patient-specific 3D models of each pelvis and hip joint were created from preoperative CT scans, and each activity in our hip inventory was simulated using a custom Matlab hip simulation routine. For each activity, the ROM of the hip was recorded as the point at which either bony impingement was detected, or the specified movement was successfully completed. The percentage of the required motion successfully completed (percent function) was then calculated (100*measured ROM/required ROM) for each movement. This procedure was repeated on the same hips after completion of a computer-simulated PAO according to the technique described by Ganz and colleagues in which the LCEA was increased to 35° and reoriented anteriorly to appropriately restore head coverage. Wilcoxon Signed Rank tests were performed to compare preoperative and postoperative percent function for each movement. Results: When all activities were combined, there was no significant difference (p > 0.05) between preoperative function (99.2 ± 0.6%) and postoperative function (98.0 ± 1.1%). The flexion portions of the right and left grand écart latéral, commonly used ballet movements, were the only activities where percent function was significantly decreased after PAO. Before surgery, the left hips performed 96.8 ± 1.8% of the motion required for the left grand écart latéral whereas after surgery hip function decreased to 82.5 ± 7.6% (p < 0.05). Preoperatively, the right hips performed the right grand écart latéral at 96.7 ± 3.3% compared to 77.4 ± 8.3% postoperatively (p < 0.05). There were no significant differences between preoperative and postoperative function for any other activities within the hip inventory. Conclusions: After testing a broad range of movements found in both daily life and sporting and recreational activities, just two of the twenty-one activities were significantly impaired after a computer-simulated PAO. A lack of significant change in percent function for most movements between preoperative and postoperative hips indicates that even high performing patients who undergo a PAO can expect little to no change in their ability to perform many of the activities they enjoyed before surgery. A significant change, however, was seen in the ballet positions right and left grand écart latéral and patients requiring performance of these activities after PAO should be counseled preoperatively regarding the demands of their sporting and recreational activities and their postoperative expectations. [Figure: see text]