This review compared survival rates and annual polyethylene wear between zirconia and non-zirconia polyethylene heads in total hip arthroplasty. The authors concluded that high-quality zirconia heads appeared to be similarly effective to traditional materials, although differences may arise according to head quality. Lack of clarity regarding study selection and quality made the reliability of this conclusion unclear.

To compare survival rates and annual polyethylene wear between zirconia-polyethylene and non-zirconia-polyethylene heads in total hip arthroplasty.

PubMed, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) were searched. Search dates were from 1966 to 2007. Search terms were reported. Japanese articles were sought from Japana Centra Revuo Medicina (1983 to 2007).

Studies with at least five years follow-up of patients who had received total hip arthroplasty (cemented or cementless) and that compared zirconia-polyethylene with non-zirconia-polyethylene femoral heads, were eligible for inclusion in the review. Case series designs were excluded, as were studies that included only enhanced UHMWPE (Hylamer), those that focused only on ceramic materials and studies that did not report the number of revised cases. Included were randomised controlled trials (RCTs) and non-RCTs (which included cohort and historical cohort studies) conducted in Europe and Asia. Mean age of participants was 56.8 years and 57% were women. Just over half of patients had osteoarthritis. Four manufacturers of zirconia heads were identified: Ceraver (France); Nippon Tokushu Tougyou (Japan); JMM (Japan); and DePuy (United Kingdom). Traditional polyethylene (UHMWPE) was used in all studies. Head diameter ranged from 22mm to 32mm. The included control materials of femoral heads were stainless steel, Co-Cr and alumina ceramics. Cement fixation was used in most studies. Annual linear polyethylene wear was measured by films, computer-aided and digital radiographs.

The authors did not state how many reviewers selected studies for the review.

An 11-item checklist was used to assess the quality of included studies (criteria not reported). Two reviewers independently performed quality assessment. Disagreements were resolved by discussion.

Numbers of revised and unrevised cases were extracted in order to calculate the risk difference and 95% confidence intervals (CI) of revision surgery across comparison groups. Cases of revision due to infection or fracture were removed from the analysis. Means, standard deviations and 95% CIs were collected to determine annual polyethylene wear.

Data were extracted by one reviewer and checked by a second reviewer. Disagreements were resolved by discussion.

Risk differences and 95% CIs were pooled in a meta-analysis. Where statistical heterogeneity was considered substantial (I²>50%) a random-effects model (DerSimonian and Laird) was used. A fixed-effect model (Mantel-Haenszel) was used where I² was less than 50%. L'Abbé plots were also used to explore heterogeneity. Means, standard deviations and 95% CIs of polyethylene wear were combined in a random-effects meta-analysis. Subgroup analysis was performed according to manufacturer and the implant fixation method. The impact of heterogeneity was explored in a sensitivity analysis. Publication bias was examined in a funnel plot (not presented) and by Begg's and Egger's tests.

Seven studies were included in the review (586 patients, 769 hips). There were three RCTS and four non-RCTs. Mean quality score for RCTs was 6.3 (range 6 to 7) and for non-RCTs was 4.5 (range 4 to 5). Mean follow up was 89.2 months (range 60 to 155 months). Publication bias was reported in the clinical results for zirconia-polyethylene total hip arthroplasty.

The pooled risk difference of revision surgery was 0.05 (95% CI 0.02 to 0.08; seven studies), which indicated that zirconia-polyethylene total hip arthroplasties resulted in a statistically significant higher rate of revision surgery. There was some heterogeneity (I²=34.9%). When the source of heterogeneity was removed in sensitivity analysis, results still favoured the control intervention (risk difference 0.03; 95% CI 0.00 to 0.06; six studies), as did the analysis of three RCTs alone (although this was not statistically significant). Zirconia heads manufactured by Ceraver resulted in a higher rate of revision surgery (risk difference 0.08; 95% CI 0.03 to 0.14; I²=0%), but those manufactured by DePuy did not show any significant difference (three RCTs). Higher rates of revision were also noted in cemented total hip arthroplasties with zirconia heads (risk difference 0.06; 95% CI 0.02 to 0.10, I²=2.8%).

There was no statistically significant difference in mean annual polyethylene wear between zirconia head and control groups (five studies). Ceraver manufactured zirconia heads were not included in this analysis.

Total hip arthroplasty with high-quality zirconia heads appeared to have prosthesis survival rates and polyethylene wear that was equivalent to total hip arthroplasties that used traditional materials. Differing quality among zirconia heads could lead to poor survivorship of prostheses.

The review question was clear and detailed inclusion criteria were provided for interventions and outcomes. Relevant data sources were searched for studies in various languages. It appeared that no unpublished studies were sought. Publication bias was noted in the analysis. The processes of validity assessment and data extraction were carried out with sufficient attempts to minimise error and bias, but it was unclear how studies were selected for the review. Neither the specific criteria for quality assessment nor any interpretation of the scoring system was provided. This made the reliability of included studies difficult to determine. The chosen methods of synthesis appeared appropriate. Heterogeneity was explored in sensitivity analysis. The authors' conclusion reflected the evidence presented. The lack of clarity about study selection and the inability to interpret study quality made the reliability of this conclusion unclear.

Practice: The authors stated that urgent cessation of zirconia-polyethylene was not justified.

Research: The authors stated that further research was needed to determine outcomes of total hip arthroplasty with zirconia ceramics using cross linked UHMWPE.

Health and Labour Sciences Research Grants.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.