British researchers recommend that both imaging results and patient symptoms be reviewed when considering revision surgery to remove faulty metal-on-metal hip arthroplasty systems.
While surgeons can use MRI and ultrasound equipment to detect metallosis in potential revision patients, the researchers recommend that patient symptoms must be taken into consideration, as well, said Healio/Orthopedics Today.
“Although ultrasound and MRI are useful in the treating of metal-on-metal patients, there is a significant percentage of hips that have pain with negative radiology findings,” Naveed Ahmed, MBBS, MSc, of Prince Charles Hospital in Merthyr Tydfil, United Kingdom, stated in his presentation at the British Orthopaedic Association Congress, wrote Healio/Orthopedics Today.
Ahmed and colleagues retrospectively reviewed the imaging results from 25 hips (16 patients) between March 2011 and May 2012. Of those, said Healio/Orthopedics Today, 23 hips underwent ultrasound scans; 21 of these also underwent MRI scans following surgery. The average patient age range was 37-69 years of age and untrasound was conducted on an average of 50 months after primary total hip replacement. MRI and ultrasounds were reported by musculoskeletal radiologists and all patients underwent blood tests for cobalt and chromium levels, Ahmed told Healio/Orthopedics Today. “During surgery, multiple samples were taken from the acetabulum, capsule, as well as tissue lining the femoral neck and sent for histopathology,” Ahmed noted.
The researchers reviewed fluid collected from patients during revision surgery for metallosis. MRIs were positive for fluid collection in 16 of the patients reviewed and ultrasound was positive in 18. Four patients tested with both a negative MRI and ultrasound results; they underwent revision over pain and were found to have “histopathology positive metallosis,” said Ahmed. The histopathologist involved in the study defined metallosis as the “presence of sheets of macrophages with dark brown pigmentation in the cytoplasm under polarized light,” Ahmed told Healio/Orthopedics Today. One patient tested with a positive ultrasound and a negative MRI result; another patient tested with a positive MRI and a normal ultrasound, he added.
“MRI and ultrasound are useful in screening of hips with metal-on-metal arthroplasty,” Ahmed told Orthopaedics Today Europe. “Still there are a significant percentage of hips which have failed with negative radiology findings,” Ahmed explained to Healio/Orthopedics Today.
Metal-on-metal hip implants have been linked to high rates of implant failure and early revision. In March, The Lancet published a study showing that all-metal hip implants fail at a rate of six percent in five years, compared to the two percent seen in plastic or ceramic devices. These findings prompted the authors to call for an end to their use.
The FDA also addressed risks associated with metal-on-metal hip implants and asked 21 manufacturers to conduct post-market safety studies on the devices to assess whether they release dangerous amounts of metal ions into the body. This summer, an FDA advisory panel met to discuss the pros and cons of the devices. At the conclusion of the three-day meeting, the experts advised that metal hip patients undergo yearly physicals, imaging scans, and possible blood screening for metal ions in order to detect complications. Some panelists questioned whether or not metal-on-metal hip replacements should be used at all in the future.