Paper #48 - ISHA Annual Scientific Meeting 2016

Which Morphologic Factors Predict the Range-of-Motion of the Human Hip?

Hani Mayassi, BS, Biddeford, ME UNITED STATES
Charles M Lawrie, MD, Miami, FL UNITED STATES
Andrew J Murphy, MD, Houston, TX UNITED STATES
Sabir K. Ismaily, PhD, Houston, TX UNITED STATES
Rikin Patel, MS, Houston, TX UNITED STATES
Joshua David Harris, MD, Houston, TX UNITED STATES
Melvyn Harrington, MD, Houston, TX UNITED STATES
Philip C. Noble, PhD, Houston, TX UNITED STATES

The Institute of Orthopedic Research and Education, Houston, TX, UNITED STATES

FDA Status Not Applicable

Summary: We have identified key morphologic determinants that can serve as a preoperative assessment in an effort to restore normal ROM in patients with FAI; therefore, by using standard imaging modalities, physicians can retrieve vital femoroacetabular morphologic data to use as a diagnostic tool in conjunction with patient symptoms and clinical examinations.

Abstract:
Introduction: Range-of-motion (ROM) is dependent upon joint position and osseous morphology. While it is well appreciated that morphologic abnormalities limit hip motion in patients with abnormal head coverage, slipped capital epiphysis and cam- and pincer-type femoro-acetabular impingement (FAI), the fundamental relationship between each component of hip morphology and range of motion of the joint has not been elucidated. In this study, we have developed predictive relationships to describe the morphology of the femur and acetabulum and the resulting range of motion of the joint.

Methods: 3D computer models of 36 hips were prepared from CT scan data. Twenty-one morphologic parameters—14 femoral and 7 acetabular—were measured from each model using CAD software. The ROM of each hip model was measured using customized computer routines in which iteratively repositioned the femoral head to minimize local interference with the acetabulum until translations converged to 0.02mm. Two maneuvers were simulated: (i) Anterior impingement during internal rotation at 90° flexion and 15° adduction (Anterior ROM), and (ii) Posterior impingement during external rotation in 20° of extension (Anterior ROM).Stepwise linear regression was performed to examine the association between each measure of hip ROM and the parameters describing the morphology of the femur and acetabulum.

Results: Overall, 58% of the variation of Anterior ROM (average: 13.8±10.0°) was explained by 5 of the morphologic parameters (p=0.0001): (i) the anterior width of the femoral neck (ANW, 15.4±1.7 mm), (ii) acetabular depth (AD, 19.7±2.7 mm), (iii) femoral anteversion (FV, 8.8±8.1°), (iv) the alpha angle (4OC, 53.3±13.8°), and the head extrusion index (EI, 0.117±0.08) The relative contribution of these parameters to Anterior ROM was neck width: 22%, acet depth:12%, anteversion: 6%, alpha angle:13%, and extrusion index: 5%. Posterior ROM (average external rotation: 38.3±14.1°) was most affected by femoral version (FV, 8.8°±8.1°) and posterior head-neck offset (PO, 10.4±3.1 mm; p=0.0001), with contributions of 28% and 12%, respectively.

Discussion: Historically, the alpha angle has been popularized as the primary morphologic indicator of cam-type FAI, and the lateral center edge angle a similar indicator of pincer-type FAI. However, in the case of the hip, it is well recognized that multiple morphologic parameters can act synergistically to compensate for the effect of dysmorphic components individual parameters. In addition, previous studies have shown that there is little relationship between joint motion and single parameters, including the alpha angle, hence the number of individuals in population–based studies who are found to have large alpha angles in combination with an asymptomatic joint. This study identifies the key determinants—ANW, AD, FV, 4OC, and EI for anterior ROM and FV and PO for posterior ROM—for further correlative studies identifying the intricate mechanism of premature femoroacetabular impingement and ROM capabilities.

Significance: We have identified key morphologic determinants that can serve as a preoperative assessment in an effort to restore normal ROM in patients with FAI. By using standard imaging modalities, physicians can retrieve vital femoroacetabular morphologic data to use as a diagnostic tool in conjunction with patient symptoms and clinical examinations.