The Clinical Value of New-Generation Low-Field MR Imaging in Patients with Hip Pain Following Total Hip Arthroplasty

Objectives To evaluate the clinical value of low-field MRI compared to routine radiography in patients with painful total hip arthroplasty and to clarify its diagnostic advantages. Methods Forty-eight patients (68 ± 14 years, 25 female) with total hip arthroplasty and equivocal hip pain who underwent both low-field MRI and standard radiographs were retrospectively included. MRIs were acquired on a 0.55 T system between 05/2021-04/2022. Two fellowship-trained musculoskeletal radiologists reviewed radiographs and MR images. MRI findings not apparent on radiographs were graded on a five-point patient management relevance scale (0 = none, 1 = unlikely, 2 = unclear, 3 = probably, and 4 = definitely). Results Twenty-nine (60%) patients demonstrated additional relevant pathologies on low-field MRI. Fourteen findings were rated as “probably” and fifteen as “definitely” relevant for further patient management. Definitely relevant findings identified only on MRI were periprosthetic lysis (n = 6), occult periprosthetic (n = 3) and pelvic ring fractures (n = 2), suspected periprosthetic joint infection due to periprosthetic fluid collections (n = 2), and tendon/muscle ruptures with secondary hematoma (n = 2). Lower-grade findings included iliopsoas tendon lesions (splitting, low-grade partial tearing, and bursitis) in 13 patients, and extensive fatty muscle atrophy of the gluteal muscles (Goutallier 3 or 4) in 26 patients. Conclusion More than half of patients with equivocal hip pain following arthroplasty would have benefited from complementary low-field MRI at their initial presentation. Advances in knowledge Half the patients with an explanatory radiograph presented new, treatment-relevant MRI findings. Low-field MRI may be a reasonable addition to existing diagnostic algorithms.