HOW DOES THE DGEMRIC INDEX CHANGE AFTER SURGICAL TREATMENT FOR FAI? PRELIMINARY DATA OF A PROSPECTIVE COMPARATIVE LONGITUDINAL SINGLE-CENTRE STUDY

Objectives Delayed gadolinium enhanced MRI of cartilage (dGEMRIC) is a novel MRI-based technique with intravenous contrast agent that allows an objective quantification of biochemical cartilage properties. It enables a ‘monitoring' of the loss of cartilage glycosaminoglycan content which ultimately leads to osteoarthritis. Data regarding the longitudinal change of cartilage property after joint preserving hip surgery is sparse. We asked (1) if and how the dGEMRIC-index changes in patients undergoing open/arthroscopic treatment of femoroacetabular impingement (FAI) one year postoperatively compared to a control group of patients with non-operative treatment; (2) and if a change correlates with the clinical short term outcome. Methods IRB-approved prospective comparative longitudinal study of two groups involving a total of 61 hips in 55 symptomatic patients with FAI. The ‘operative' group consisted of patients that underwent open/arthroscopic treatment of their pathomorphology. The ‘non-operative' group consisted of conservatively treated patients. Groups were comparable for preoperative radiographic arthritis (Tonnis score), preoperative HOOS- and WOMAC-scores and baseline dGEMRIC indices. All patients eligible for evaluation had preoperative radiographs and dGEMRIC scans at baseline and repeated dGEMRIC scans using the same scanner and protocol. (1) dGEMRIC indices of femoral and acetabular cartilage were assessed separately on the initial and follow-up dGEMRIC scans. Radial images were reformatted from a 3D T1 map for measurements. Regions of interest were placed manually peripherally and centrally within the cartilage based on anatomical landmarks at the 12 ‘hour' position of the clcok-face with the help of radial high-resolution PD-weighted MR images. (2) Patient-reported outcome was evaluated at baseline and at 1 year follow-up: Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Hip disability and Osteoarthritis Outcome Score (HOOS). Statistical analysis included Student's t-Tests, Mann-Whitney U-tests and Wilcoxon signed-rank tests (p<0.05). 1. On the acetabular side, the dGEMRIC index decreased significantly (p<0.05) in 17/20 (85%) zones respectively in 21/24 (88%) of femoral zones in the operated group [Fig. 1]. In the non-operative group, no acetabular zone and 2/24 (8%) femoral zones presented with a significant drop [Fig. 2]. 2. After one year the WOMAC and the HOOS scores significantly improved (58±42 to 33±42; p= 0.007 respectively 63±16 to 74±18; p= 0.028) for the operative group, while there was no change (55±45 to 48±50; p= 0.825 respectively 63±14 to 66±19; p= 0.816) for the non-operative group. Discussion Interestingly joint-preserving surgery for FAI led to a decline in biochemical cartilage properties on MRI at a one year follow-up despite the significant improvement of patient outcome. This short-term phenomenon was described after periacetabular osteotomy for correction of hip dysplasia in literature with a normalization of the dGEMRIC values at 2 years.

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