ePoster #306 - ISHA Annual Scientific Meeting 2016

Computed Tomography (CT) Analysis Of Femoral Head Translation: A Cadaveric Investigation

Benjamin Kuhns, MD, Chicago, IL UNITED STATES
Alexander Weber, MD, Chicago, IL UNITED STATES
Gregory Cvetanovich
Alejandro Espinoza-Orias, MD, PhD, Chicago, IL UNITED STATES
Nozomu Inoue, MD, PhD, Chicago, IL UNITED STATES
Richard C. Mather, MD, MBA, Durham, NC UNITED STATES
Shane J. Nho, MD, MS, Chicago, IL UNITED STATES
Gift C. Ukwuani, MD, Chicago, IL UNITED STATES

Rush University Medical Center, Chicago, Illinois, UNITED STATES

FDA Status Not Applicable

Summary: We present data evaluating the three-dimensional (3D) translation of the hip joint at different hip positions.

Introduction: The kinematics of the hip joint is poorly understoon, but previous studies have demonstrated that hips may show a combination of rotation and translation depending on the three dimensional morphology. The motion path of the femoral head is difficult to study in a dynamic model due to the insensitivities of digital motion analysis sensors. The purpose of this study was to determine the three-dimensional (3D) translation of the hip joint at different hip positions in a cadaveric model and determine if there are differences bases on 3D morphology. Methods: Four fresh-frozen cadaveric bilateral hips with no prior hip or acetabular surgery were selected for this study. Each hip was individually mounted onto a custom-made computed tomography (CT) compatible positioner. The hip was then fixed in a series of positions to simulate physiologic hip motions. These positions included; 1) neutral resting position, 2) 45 degrees of flexion (Flex45), 3) 90 degrees of flexion (Flex90), 4) flexion adduction internal rotation (FADIR), and 5) flexion abduction external rotation (FABER). A 3-D CT was conducted in each position. Following the initial CT, the hip was dissected down to the capsuloligamentous structures and each hip was rescanned in each of the 5 positions. Translation was measured in the mediolateral, craniocaudal, and anteroposterior directions compared to a reference neutral position and analyzed using a validated, high precision 3D-3D registration technique. Alpha angle, lateral center edge angle (LCEA), and Tonnis angle were measured to correlate translation to commonly employed radiologic variables. Results: All specimens were male and without prior hip or pelvic surgery. The mean alpha angle, LCEA, and Tonnis angles were 48.8±11.1°, 30.7±5.1°, and 9.4±3.9° respectively. Factoring in all planes of motion, the average translation in the Flex45 position was 1.0±0.21mm. The average translation in the Flex90 position was 1.33±0.32. The average translation in the FADIR and FABER positions was 1.32±0.21 and 1.45±0.15, respectively. The average total translation did not change significantly with the soft tissues removed to the level of the hip capsule except for the FADIR position, which demonstrated a significant increase in total translation (1.49±0.56; p=0.05). Hips with larger alpha angles were associated with increased total translation in Flex45 position (r=0.8; p=0.03) and the FADIR position (r=0.79; p=0.02). Increasing alpha angle was also associated with increased anterior translation of the femoral head in the FADIR position (r=0.85; p=0.008). Increased LCEA was associated with decreased total translation in the Flex45 position (r=0.9; p=0.006) and the FADIR position (r=0.75; p=0.03). Changes in Tonnis angle were not associated with changes in total femoral head translation. Conclusion: This study demonstrates that in intact hip specimens, femoral head translation occurs as the hip moves through a physiologic range of motion as well as during impingement positions. Preliminary results suggest that cam-type impingement (hip with increased alpha angles) may increase femoral head translation, whereas overcoverage (hips with increased LCEA) may decrease femoral head translation.