The study, published yesterday in Clinical Orthopaedics and Related Research, is the first to evaluate the presence and risk of local tissue complications after hip replacements made of different materials in patients, including those who are asymptomatic. Previous studies have been limited to metal-on-metal implants.

Hip replacement parts are made of plastic, ceramic, metal or a combination of these materials. The components move against each other and wear down slowly through regular use. Small wear particles can break free from the hip replacement material over time and damage local joint tissues. MRI is a non-invasive imaging technique that uses a large magnet and radiofrequency energy to produce digital images without the use of ionizing radiation. MRI is often used in orthopedics to visualize the soft tissues around total hip replacements that are affected by the small wear particles.

“We found that patients can be completely asymptomatic and have high-functioning hip scores while harboring reactions that could start to destroy the soft tissues around the hip,” said Hollis G. Potter, MD, chairman of the Department of Radiology and Imaging and the Coleman Chair in MRI Research at HSS and the study’s senior author. “This finding is important because tissue reactions typically worsen over time. Delayed detection results in unnecessary pain, longer and more complicated revision operations and more challenging recoveries.”

Matthew F. Koff PhD, the lead study author said, “The study also indicates that MRI is clinically useful for patients who receive a ceramic-on-polyethylene or metal-on-polyethylene implant, in addition to patients who received a hip resurfacing arthroplasty.”

Drs. Potter and Koff and HSS colleagues prospectively evaluated 206 patients (243 hip replacements) at least one year after having hip resurfacing arthroplasty or total hip replacement. The researchers examined the volume of joint tissue reaction using MRI images, levels of metal particles in the blood and patients' responses on a survey called the Hip Disability and Osteoarthritis Outcome Score annually over the course of 3 years. The researchers compared results for patients who received hip resurfacing arthroplasty (HRA) with patients who received ceramic-on-polyethylene and metal-on-polyethylene total hip replacements.

During the study, MRI identified adverse local tissue reactions in 25 percent of patients who had hip resurfacing arthroplasty. This finding was surprising, since these patients reported symptoms similar to or less severe than patients with ceramic-on-polyethylene and metal-on-polyethylene total hip replacements implants. Patients who received hip resurfacing arthroplasty had a significantly larger volume of joint tissue reaction on MRI, a nearly five-times-higher risk of having tissue complications than patients who had a ceramic-on-polyethylene total hip replacement. Metal ion levels were inconsistently elevated in the patients with these reactions.

“By sharing our findings, we hope physicians will start incorporating MRIs into patient assessments, leading to earlier detection of issues and better outcomes for patients,” Dr. Potter said. “Widespread use of MRI to assess soft tissue damage may also help identify patterns that could ultimately improve implant design in the future.”