ePoster #812 - ISHA Annual Scientific Meeting 2016

Differences In Acetabular Rim Thickness Between The Symptomatic And Asymptomatic Hip In Patients With Unilateral Femoroacetabular Impingement

Alexander Weber, MD, Chicago, IL UNITED STATES
Benjamin Kuhns, MD, Chicago, IL UNITED STATES
Gregory Cvetanovich
Nozomu Inoue, MD, PhD, Chicago, IL UNITED STATES
Richard C. Mather, MD, MBA, Durham, NC UNITED STATES
Asheesh Bedi, MD, Ann Arbor, MI 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 computed tomographic data describing the location and magnitude of difference in acetabular rim morphology between the symptomatic and asymptomatic acetabula in a cohort of patients with symptomatic unilateral pincer-type or mixed FAI.

Abstract:
Introduction: Appropriate level of acetabular rim resection in femoroacetabular impingement (FAI) is crucial to avoid the complications of under- or over-resection, which can include painful residual deformity or iatrogenic hip instability, respectively. The purpose of this study was to identify the location and magnitude of difference in acetabular rim morphology between the symptomatic and asymptomatic acetabula in a cohort of patients with symptomatic unilateral pincer-type or mixed FAI. Methods: After IRB approval, computed tomography (CT) scans of the bilateral hips in 33 patients (17 males, 16 females) diagnosed with unilateral pincer-type or mixed FAI were obtained. CT images of both hips were imported in DICOM format and segmented into 3-dimensional (3D) hemi-pelvises using 3D reconstruction software (Mimics, Materialise, Leuven, Belgium). The point-cloud data of the asymptomatic hemi-pelvis was mirrored onto the symptomatic side. Protrusion of the symptomatic side was recorded as a positive value. Data were collected in 3-degree intervals around the acetabular rim. Additionally, the rim morphology was broken into quadrants using the clock face method in order to analyze the location of greatest magnitude of difference between affected and unaffected acetabula. Statistical difference was set a p < 0.05 for all testing. Results: Of the 33 hips included, 14 were isolated pincer-type FAI and 19 were mixed FAI. The average preoperative symptomatic side lateral center edge angle (LCEA) was 37.5 ± 7.2 degrees compared to 29 ± 5.1 degrees on the asymptomatic side (p<0.001). The average preoperative alpha angle on the symptomatic side was 61.1 ± 12.7 degrees. The symptomatic acetabular rim was on average 0.43 ± 0.18 mm thicker than the corresponding location on the asymptomatic rim. When the acetabular clock face was broken up into quadrants, reflecting the 12-3, 3-6, 6-9, and 9-12 o’clock positions, the 12-3 o’clock position demonstrated the greatest difference between symptomatic and asymptomatic sides. The 12-3 o’clock quadrant demonstrated significantly greater difference between symptomatic and asymptomatic sides (0.55 ± 0.18 mm) as compared to the 3-6 o’clock position (0.4 ± 0.28 mm; p=0.006), the 6-9 o’clock position (0.34 ± 0.07 mm; p<0.001), and the 9-12 o’clock position (0.38 ± 0.03; p<0.001). In the 12-3 o’clock position, the magnitude of rim thickness difference between the symptomatic and asymptomatic sides positively correlated with increasing age (p=0.04); however, this correlation was not present in the 3-6, 6-9, or 9-12 o’clock positions. There was no correlation between gender, body mass index (BMI), or symptom duration and magnitude of rim thickness difference at any clock face location. Conclusions: Patients with unilateral, symptomatic pincer-type or mixed FAI demonstrate significant differences in rim thickness between the affected and unaffected acetabula. The most significant rim thickness differences are present in the 12-3 o’clock position consistent with the area of known FAI mechanical loading. Small changes in acetabular rim morphology, on the order of 0.5 mm or less can be the difference between symptomatic FAI and the healthy, asymptomatic state.