Abstract
Introduction:
Uncemented acetabular component fixation has been considered the most reliable fixation method in contemporary metal-on-metal hip resurfacing arthroplasty (HRA). During prospective long-term follow-up of a HRA device, we have encountered a surprisingly high incidence of this complication and wish to alert surgeons and manufacturers of this problem.
Methods:
The study group was comprised of all 373 HRAs performed by a single surgeon using this hybrid hip resurfacing implant from May 2001 to March 2005. The acetabular component features a dual-coated bone ingrowth surface of plasma-sprayed titanium plus hydroxylappatite. There were a total of 34 revisions identified at the time of this study.
Results:
There were 5 other cases (1.3%) of late acetabular loosening all occurring greater than 8 years postoperatively at an average of 9 ± 1 years after the primary surgery. All of theses patients were functioning well with radiographically stable implants for at least 8 years. Intraoperative findings included debonding of large portions of the porous coating which remained adhered to the underlying bone. We concluded that these cases represented primary mechanical implant failures. There was a moderate amount of wear debris, presumably from the backside. There was no bone loss evident. There were no soft tissue masses. There were also 2 cases of adverse wear failure with pain and soft tissue masses diagnosed preoperatively with well-fixed implants. One of these patients also suffered component debonding prior to revision. Two (2/5; 40%) cases had an acetabular inclination angle ≥50°. Implant Debonding accounted for 5/8 (63%) of all acetabular failures and 14.7% (5/34) of all failures, while failure of ingrowth caused only 1/34 (3%) and adverse wear failures accounted for only 6% (2/34) of all failures.
Conclusion:
We recommend that manufacturers re-evaluate the fixation strength of their own particular methods of bonding titanium plasma spray to a cobalt-chrome substrate, particularly in regards to fatigue failure and that they make improvements to ensure a longer duration of bone-implant fixation.
