MRI Can Spot Hip Resurfacing Inflammation

Hip resurfacing inflammation may be detected early with MRI

/ Author:  / Reviewed by: Chris Galloway, M.D.

(RxWiki News) Many surgeons today choose hip resurfacing over total hip replacement since it offers several advantages including higher patient satisfaction and better cost-effectiveness.

In some cases, however, complications and inflammatory reactions may occur without obvious symptoms. 

A recent study highlighted the importance of detecting problems early to avoid complex revision surgery. 

Results from that study showed that magnetic resonance imaging (MRI) may be a useful tool in spotting such problems.

"Ask your orthopedic surgeon about signs of hip resurfacing inflammation."

This study was conducted by Danyal H. Nawabi, MD, FRCS (Orth) and colleagues at the Hospital for Special Surgery, New York along with collaborators from Applied Science Laboratory at General Electric Healthcare. The objective of this study was to investigate the role of MRI in early detection of joint inflammation after hip resurfacing surgery.

Hip resurfacing, an alternative to total joint replacement, is a preferred option for younger and active patients. During the procedure, a metal cap is placed over the head of the femur along with a matching metal cup in the hip socket. This helps preserve more of a patient’s thigh bone than conventional total joint replacement.

But the metal-on-metal implants may be associated with failures due to inflammatory responses in the joint and the surrounding membrane, a condition called synovitis. 

The inflammation, known as a “pseudotumor,” does not give rise to symptoms early on. To make things worse, it is not detectable on routine X-rays or computed tomography (CT) scans. Usually, in such cases, by the time the patient is diagnosed, the dead tissue surrounding the knee joint makes revision surgery harder and leads to poor outcomes. No studies examining the extent of this inflammation were previously available.

In this study, the researchers included 69 subjects (total 74 hip procedures) who had a metal-on-metal hip resurfacing surgery.

Patients were classified into three categories: patients who had no symptoms (22 patients), those who had unexplained pain (20 patients) and patients who had symptoms with a mechanical cause such as loose implants, fractures around the implant area or faulty positioning (32 patients).

The three groups were similar with respect to age, body mass index and time elapsed since resurfacing surgery. But the proportion of female subjects was higher in the unexplained-pain group.

All the study participants underwent an MRI and the scans were examined by two musculoskeletal radiologists for synovitis and other signs of inflammation. The study was blind, which means that the radiologists did not know which group any particular MRI scan belonged to. Synovitis was defined as solid-appearing material around the hip capsule area.

In cases of implant surface wear, debris is released in the joint and blood vessels in the form of tiny metal particles. The researchers recorded serum cobalt and chromium ion levels when available to check whether the level of metals could be used for early detection of implant failure. Most patients also underwent X-rays of the hip joint.

The results showed that 68 percent of the patients without symptoms, 75 percent of the symptomatic patients and 78 percent of the patients with unexplained pain had hip joint synovitis. Thus, the researchers did not find a significant difference between these groups. 

The difference in the average volume of synovitis – 5.0 cm3 in the asymptomatic group, 10.2 cm3 in the mechanical causes group and 31.0 cm3 in the unexplained pain group – also was not significant.

The difference between the symptomatic group and other groups reached significance only when the symptomatic group showed adverse local tissue reaction as determined on microscopic examination of joint tissue. 

There were also no significant differences in X-rays or serum ion levels, indicating that these tests cannot be used as valid monitoring tests for synovitis.

The researchers did note that the small number of patients in the study and abnormal inflammatory responses in some patients, especially females, might have influenced study results.

The authors also stated that they were not aware of any data directly connecting synovitis in asymptomatic patients with implant failure.

Further studies with MRIs of subjects without symptoms are required since it is unclear at what point asymptomatic patients should be subjected to further tests.

Though the study did not establish synovitis and inflammation as clear indicators of implant failure, it does demonstrate that patients with no symptoms may be just as likely to develop tissue inflammation as those with pain following hip resurfacing. Waiting for symptoms to develop might lead to complications, making revision surgery a challenge.

The study was published in the May issue of The Journal of Bone and Joint Surgery. GE Healthcare provided funding for the study.

Reviewed by: 
Review Date: 
May 16, 2013
Last Updated:
September 17, 2013