1051 - Is Plain Anterior-Posterior Pelvis Radiograph Adequate for Assessment of Radiographic Implant Migration Evaluation in Total Hip Arthroplasty?

INTRODUCTION: Cam-type femoroacetabular impingement (FAI) is implicated as a mechanism in the premature development of osteoarthritis (OA) of thehip joint [1]. The aspherical femoral head leads to the eventual development of OA through cartilage damage, especially in the anterolateral region of theweight bearing surface [2]. Recent research on cam-type FAI using proteoglycan (PG) sensitive imaging techniques (such as T1u03c1 mapping [3]) revealed thatan early degenerative change is present in the cartilage tissue of symptomatic as well as asymptomatic subjects with cam-FAI [4]. While symptomatic cam-FAI patients undergo physiotherapy or surgery, longitudinal measurements are necessary to research the asymptomatic cam-FAI in order to develop andmonitor treatment strategies. The purpose of this study was to measure the cartilage T1u03c1 relaxation time in patients with bilateral (symptomatic andasymptomatic) cam-type FAI on the asymptomatic side after the symptomatic cam-FAI was surgically corrected. The subjects were re-imaged longitudinallyto determine if any changes occur in the cartilage matrix.METHODS: The research ethics board at our institution approved this study and all participants provided informed consent prior to enrollment. 9 patients (8male, 1 female, mean age: 38.8 years, age range: 27.8 u2013 48.4 years at day of surgery) undergoing surgical osteochondroplasty for symptomatic cam-type FAIwere recruited and enrolled prospectively. Patients were included if they had unilateral painful hip with radiographic evidence of a cam deformity at thefemoral head-neck junction in both hips. As part of a larger study protocol, patients underwent computer tomography of both hips and the alpha angle wasmeasured at the anterior (3:00) and anterosuperior (1:30) positions. Subjects underwent T1u03c1 MRI of the contralateral, asymptomatic hip at an average of 124days (range: 64 u2013 285 days) after surgery. A consecutive T1u03c1 follow-up scan was performed using the same protocol after a mean of 4.8 years (range: 3.2 u20136.0 years). T1u03c1 mapping was performed on a 1.5T MRI scanner (Siemens) using a spin-lock preparation module combined with a turbo spin echo acquisitionscheme in a sagittal oblique orientation. Further parameters: FOV = 180x180mm2, slices = 22, slice thickness = 3mm, matrix = 384x384, resolution =0.47x0.47mm2, TR = 274ms, TE = 13ms. Five different spin-lock times (TSL) of 12/18/25/35/45ms and a spin-lock field of B1 = 400Hz were used. Thetotal scan time for T1u03c1 mapping was 21 minutes. The cartilage was segmented as a bilayer in seven to eight slices, starting from the lateral sourcil marginand extending medially. The joint was subdivided into anterior and posterior regions and the slices were divided into lateral, intermediate or medial zones,resulting in six region of interest (ROI) for analysis: Antero-Lateral (AL), Antero-Intermediate (AI), Antero-Medial (AM), Postero-Lateral (PL), Postero-Intermediate (PI) and Postero-Medial (PM) (Figure 1). Statistical analysis (paired t-test) was performed using the statistical toolbox in Matlab, withstatistical significance set at p<0.05.RESULTS: The mean alpha angles were 50u00b0 (range: 42 u2013 64u00b0) at 3:00 and 63u00b0 (range: 56 u2013 70u00b0) at 1:30 position for the surgical side and 54u00b0 (range: 50 u201360u00b0) at 3:00 and 63u00b0 (range: 51 u2013 70u00b0) at 1:30 position for the contra-lateral side. Figure 2 summarizes the results of the hip cartilage T1u03c1 relaxation timesfrom the six different regions for the initial and the follow-up scan (shown as mean T1u03c1 values with the standard deviation as error bars). There was nosignificant difference in T1u03c1 between two the two scans, except in the anterior-medial (AM) region of the hip. The T1u03c1 relaxation time decreased there from31.9 u00b1 3.7 ms to 28.3 u00b1 4.2 ms significantly (p< 0.05).DISCUSSION: The findings of this study show that in five of the six analyzed cartilage regions no significant changes in PG content occur within anaverage of 4.8 years in asymptomatic hips with a cam deformity in subjects who underwent surgical osteochondroplasty on the contra-lateral side before. Inthe anterior medial (AM) a small, but significant decrease in T1u03c1 was detected which implies an increased PG content. The decreased T1u03c1 relaxation time ispossible illustrating a repair/regeneration mechanism within the cartilage in this region. None of the regions showed a significant increase in the T1u03c1 valueimplicating that no PG depletion occurred and OA did not proceed in the cartilage tissue. A limitation of the study is the small sample size of only 9 subjects.SIGNIFICANCE/CLINICAL RELEVANCE: The cartilage of the contralateral hip in patients with unilateral cam-type FAI did not show PG depletion andtherefore no further degeneration between the initial and the follow up scan based on T1u03c1 mapping. The changes were not clinically significant; the contralateralhips remained stable.REFERENCES: [1] Ganz R, et al. Clin Orthop Relat Res. 2003;(417):112-20. [2] Beaulu00e9 PE, et al. J Orthop Res. 2005;23:1286-92. [3] Wheaton AJ, et al.Magn Reson Med. 2005;54:1087-93. [4] Anwander H, et al. J Orthop Res. 2016;34:1004-9.ACKNOWLEDGEMENTS: Canadian Institutes of Health Research (CIHR) (Funding number: MOP 97778) for funding of the study.

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