DOS BULLETIN - Dansk Ortopædisk Selskab

2010-378_DOS nr. 3 2010 29/09/10 10:08 Side 122
Increased wear of polyethylene coupled with yttriastabilized
zirconia femoral heads.
A 10 year follow-up and clinical assessment
Maiken Stilling, Kjeld Anton Nielsen, Kristian Larsen, Kjeld Søballe:,
Ole Rahbek
Aarhus University Hospital; Randers Regional Hospital;
Holstebro Regional Hospital
Background: Experimental studies predicted zirconia femoral heads to reduce the wear
of conventional ultra high molecular weight polyethylene (UMHWPE) in total hip
arthroplasty (THA). Later on, it was discovered that frictional heating and mechanical
stresses on THA bearings surfaces during clinical use resulted in phase transformation
of yttria-stabilized zirconia (YSZ) and initiated surface roughening of the femoral head.
Purpose: We hypothesized increased PE wear- rate and poorer clinical outcome at 10
years for PE coupled with YSZ femoral heads in comparison with PE coupled with
Cobalt-Chrome (CoCr) femoral heads.
Methods: 71 patients (76 hips) at a mean age of 52 years (range, 24 – 64) were treated
by one surgeon for hip arthritis by primary THA during 1996-1999. 61 patients (66 hips)
participated in a 10 year follow-up (nonparticipants: 7 dead, 2 early revisions, and 1 with
poor health). There were 32 hips with CoCr and 34 hips with YSZ femoral heads. Components
were cementless HA coated MH-Solid Finned Ringloc Shells (Biomet), Arcom
PE liners (Biomet), cemented Exeter stems (Stryker), and 28 mm CoCr and YSZ femoral
heads (Stryker). The two cohorts were compared at 10 years for two- dimensional (2D)
linear PE wear, osteolysis, clinically by three questionnaires (Self-report Harris Hip
Score (HHS), SF-36, and EQ-5D) and demographic data.
Findings: Demographic data was comparable. At 10 years, the 2D linear PE wear-rate
with YSZ femoral heads (n = 34) of 0.16 mm/year, SD 0.05 (range, 0.06 – 0.30) was 25%
higher (P < 0.01) than with CoCr femoral heads (n = 32) of 0.12 mm/year, SD 0.06
(range, 0.03 – 0.30). Variance was similar (P = 0.31). Maximum 2D linear wear was 2.8
mm in both cohorts. There were 2 revisions in the YSZ group within the observation period
(P = 0.26). There were no evident cup migration and osteolysis was minimal. In the
group with YTZ femoral heads (n = 33) HHS was 90 and EQ-5D was 0.88 (P > 0.25). In
the group with CoCr femoral heads (n = 27) HHS was 87 and EQ-5D was 0.87 (P >
0.25). For SF-36 the two physical dimensions were poorer for the two cohorts compared
with the Danish background population aged 45 – 54 years) (P < 0.01). In general 93%
of the patients (n = 60) were satisfied with the THA.
Conclusion: YSZ femoral heads resulted in a 25% higher PE wear-rate compared with
CoCr femoral heads, but it did not influence the THA revision rate, the health-related
life-quality, and disease- specific measures at 10 years of follow- up. Clinical long-term
follow-up of YSZ femoral heads do not reflect the positive wear-profile, which experimental
studies predicted. YSZ femoral heads have now all but completely disappeared
from the market, however, thousands of patients are still implanted with YSZ femoral
heads and clinicians should pay attention to wear-related problems of in these patients.
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