Failure rates ‘unacceptably’ high with large-bearing hybrid metal-on-metal hip

Bolland BJRF. J Bone Joint Surg (Br). 2011;93-B:608-615. doi:10.1302/0301-620X.93B5.26309.

United Kingdom researchers found high failure rates with a large diameter hybrid metal-on-metal total hip replacement.

B.J.R.F. Bolland, MBBS, MD, FRCS, of Southampton University, and colleagues studied the mid-term results of a large-bearing hybrid metal-on-metal total hip replacement (THR) in 199 hips in 185 patients. Mean follow-up was 62 months with a range of 32 months to 83 months.

Thirteen patients were lost to follow-up, and two patients died of unrelated causes. Seventeen hips have been revised; 14 more are awaiting surgery. All revisions were symptomatic. Fourteen revision cases showed signs of adverse reactions to metal debris, the authors wrote. The revised patients or those awaiting revision had significantly higher whole blood cobalt ion levels. There was no significant difference in acetabular component size or position compared with the unrevised patients.

There was increased wear at the trunnion-head interface, normal wear levels at the articulating surfaces and corrosion the stem surface, according to a wear analysis.

The 5-year cumulative survival rate, with revision for any reason, was 92.4%. When the researchers included the patients who are awaiting surgery, they found that the revision rate would be 15.1% with a cumulative survival at 5 years of 89.6%.

“This hybrid metal-on-metal total hip replacement series has shown an unacceptably high rate of failure, with evidence of high wear at the trunnion-head interface and passive corrosion of the stem surface,” the authors wrote. “This raises concerns about the use of large heads on conventional 12/14 tapers.”

The authors report the mid-term results of a large-bearing metal-on-metal total hip replacement in 199 hips (185 patients) with a mean follow-up of 62 months (32 to 83). There was an unacceptably high rate of failure, with evidence of high wear at the trunnion-head interface and passive corrosion of the stem surface.

Large-bearing metal-on-metal hip arthroplasty was originally used more than 50 years ago, and the modern generation of such devices arose initially as an apparently attractive option for revision of failed hip resurfacing. The concept then rapidly expanded, and a large number of total hip arthroplasties with large metal bearings were implanted worldwide. It has become clear that problems with this kind of implant were not anticipated by simulator studies, with considerable wear occurring at the trunnion using existing 12/14 taper technology. This was combined with fretting and crevice corrosion. Many of these effects resulted from component distortion and torque.

Metal-on-metal hip replacement has a higher early revision risk (according to the Australian National Joint Registry) for all head sizes over 36 mm. Some designs have had a disastrous track record in recent times and have been withdrawn.

The series by Bolland et al introduces a further variable: Use of components from different manufacturers. Radial clearance (and the tolerances imparted) are specific to each design. Moreover, the design of the 12/14 taper varies from one manufacturer to another. Therefore, large bearing metal-on-metal hip replacement is receiving increasing scrutiny and criticism, and (if considered appropriate for a particular patient) should incorporate components from the same manufacturer. However, the emerging advice appears to favor selection of alternative large-bearing options, and surgeons should exercise considerable caution in relation to large bearing metal-on-metal total hip replacement. While metal-on-metal hip resurfacing may achieve a niche among active young and middle-aged men, the use of the same bearing technology in total hip replacement carries considerable risk.

Robert F. Spencer, MD
Consultant Orthopaedic Surgeon
Weston General Hospital and the Avon Orthopaedic Centre
UK, Editor-in-Chief
Hip International