Cleveland Center for Joint Reconstruction, Inc., Cleveland,
Ohio USA

Introduction: The suitability of third generation metal-on-metal
hip resurfacing for patients with a primary diagnosis of osteonecrosis
(ON) has been debated. The preservation of femoral head bone
stock for femoral prosthetic support is essential for long term
stability of the implant. We hypothesized that the Kaplan-Meier
survival estimates for resurfacing patients with a primary diagnosis
of ON would be significantly lower than the survival estimates for
resurfacing patients with a primary diagnosis of osteoarthritis (OA).

Methods: One thousand one hundred and forty-eight patients were
implanted with a modern hip resurfacing system as part of a
United States multi-center investigational device exemption (IDE)
study. Of these, 116 subjects had a preoperative diagnosis of ON. A
multivariate analysis of variance was performed to identify risk
factors for component revision for any reason.

Results: A diagnosis other than OA was found to be one significant
risk factor for revision. However, the survival estimates were
not significantly different (95.9% and 95.8% at 24 months for OA and
ON, respectively, p=0.46) when comparing the OA group to the ON
group. Comparing only the Ficat stage III and IV to the OA population
also did not show a significant difference in implant survival (95.9%
OA and 96.1% ON III/IV at 24 months,p=0.57).

Discussion: Resurfacing arthroplasty for patients with ON appears
to be a reasonable alternative using judgments of implant size,
patient gender, and size of proximal femoral deficiency. Further
characterization will be needed to identify those specific patients
with ON for whom resurfacing arthroplasty is not appropriate. For
most patients, however, it appears to be a safe and reasonable
option.

The abstracts were prepared by Lynne C. Jones, PhD.
and Michael A. Mont, MD. Correspondence should be addressed to Lynne
C. Jones, PhD., at Suite 201 Good Samaritan Hospital POB, Loch
Raven Blvd., Baltimore, MD 21239 USA.