MARS MRI for the Diagnosis of Aseptic Stem Loosening in Cementless Total Hip Arthroplasty

BACKGROUND: Despite the increasing use of MARS (metal artifact reduction sequence) MRI to investigate painful total hip arthroplasties (THA), no validated criteria exist for diagnosing femoral stem loosening. PURPOSE: To evaluate MARS MRI for the diagnosis of aseptic stem loosening and determine its diagnostic accuracy. MATERIALS AND METHODS: One hundred fourteen consecutive cases with THA revision surgery and MARS MRI of the hip were retrospectively included. Two blinded musculoskeletal radiologists independently assessed periprosthetic bone resorption (PPBR), bone marrow edema (BME), periosteal reaction (PR), and periprosthetic osteolysis (PO) in 14 Gruen zones (GZ). Intraoperative findings at revision surgery served as the ground truth. A predictive model was created using binomial logistic regression models to predict the probability of a loose stem with maximizing positive predictive value (PPV) and accuracy. Interobserver reliability was assessed with absolute agreement, Cohen κ and Gwet AC1. RESULTS: During surgery, 66 stems were fixed and 48 loose. PPBR occurred significantly more frequently in loose stems across all GZs except GZ11. Proximal PPBR was also observed in fixed stems (up to 23%), whereas middle and distal PPBR were rare (≤3%). BME was most prevalent proximally in all stems (fixed/loose: 39%/60%) with significant differences medially and distally. PR was significantly more frequent in loose stems in the middle and distal GZs. PO were rare, most occurred in GZ7. The predictive model considering proximal PPBR, mid-distal PPBR, mid-distal PR, and distal BME performed with a sensitivity of 0.708, specificity of 0.970, PPV 0.944, negative predictive value 0.821. Interobserver agreement (Gwet AC1) in the considered zones was for PPBR between 0.80 and 0.98, BME 0.91 to 0.99, PR 0.87 to 0.97. CONCLUSIONS: MARS MRI is reproducible and accurate for assessing stem loosening. PPBR, BME, and PR can also be found in fixed THA in the proximal region, whereas they indicate loosening in the middle and distal stem region.