Abstract
Background
Ultrasound and MRI are recommended tools in evaluating postoperative pain in metal-on-metal hip (MoM) arthroplasty.
Aim
To retrospectively compare MRI and ultrasound results of the hip with histopathology results in failed (MoM) hip arthroplasty.
Methods
25 hips (16 patients) who underwent revision hip surgery for painful (MoM) hip replacement/resurfacing were included in this study (March 2011 to May 2012). Average age 50.4 yrs (37–69y). Blood test for cobalt and chromium levels, ultrasound and MRI were done prior to revision surgery. 23 hips had ultrasound scan. 21 of these hips also had MRI scan prior to surgery. Scans were done at an average of 50 months from primary metal-on-metal surgery. All the ultrasound & MRI were done and reported by a single musculo-skeletal radiologist. During surgery multiple tissue samples were taken from acetabulum, capsule as well as tissue surrounding the femoral neck and sent for histopathology. 21 hip histopathology results were positive for metalosis. 2 hip histopathology results were negative for metalosis. Metalosis as defined by our histopathologist as that which is showing the presence of sheets of macrophages with dark brown pigmentation in their cytoplasm under polarized light.
Results
Ultrasound examination was positive for fluid collection in 18 (78.2%)
MRI was positive in 16 (76.1%). 4 patients (19%) had negative ultrasound and MRI results but were revised due to pain and were found to have histopathology positive metalosis. One patient had ultrasound positive for fluid collection with negative MRI. One patient was MRI positive for fluid but normal ultrasound findings.
Conclusion
Although ultrasound and MRI are useful in screening of MoM patients still there are a significant percentage of hips, which failed with negative radiology findings.
