To examine the hypothesis that the clinical performance of the cementless, threaded acetabular cup is equivalent to that of the cemented and porous-ingrowth acetabular cups.

MEDLINE was searched from January 1985 to December 1992 using the followiing keywords: 'total hip', 'hip prosthesis', 'hip joint', 'acetabular cup', 'acetabulum', 'bone-cement', 'cementless', 'uncemented', 'noncemented', 'porous' and 'implant'. Manuscripts from clinical investigators, bibliographies of the retrieved articles, and the Summary of Safety and Effectiveness reports for FDA (Food and Drug Administration)-approved total hip prostheses were also reviewed. The search was limited to English language literature.

Study designs of evaluations included in the review

Articles of any study design, which contained sufficient demographic, methodologic and outcome data on a minimum of four cases, were included.

Specific interventions included in the review

Threaded acetabular cup prostheses (Mecring, T-TAP, S-ROM, Accu-Path, Link V), porous-ingrowth acetabular cup prostheses (PCA, AML, Whitesides, APR, BIAS total hip systems) and cemented total hip prostheses (Charnley, Aufranc-Turner, Muller or Dual-Lock, Harris or HD-s, STH-2, Trapezoidal-28, Stanmore or PCA, AlloPro, and CAD implants).

Participants included in the review

No disease or participant inclusion criteria are stated. The age of the patients ranged from 12 to 99 years, and the age, follow-up and gender details for each of the groups were reported.

Outcomes assessed in the review

Aseptic loosening of the acetabular components, measured primarily by the revision rates following the index total hip arthroplasty procedure. Other measures were clinical rating scores, pain scores, frequency of radiolucencies according to location and size, progressive radiolucencies and component migration. Outcome measures were defined as success or failure by grouping together score ratings where necessary.

How were decisions on the relevance of primary studies made?

Each article was reviewed independently by two investigators.

Articles were not rated for the quality of the study design, implementation or analysis, since none of the studies were prospective or randomised, none contained a blinded assessment of the radiographs and none had independent clinical evaluations.

Each article was reviewed for the following data: number of individual cases (or hips) implanted with the device, age range of participants, mean age of participants, sex distribution of study populations, indications for index total hip arthroplasty procedures, length of follow-up period, identity of the implants, and method of acetabular cup fixation. Participants with bilateral total hip arthroplasties were regarded as two separate cases.

How were the studies combined?

The studies were combined using a fixed-effect meta-analysis, weighting the individual study results by their standard error.

How were differences between studies investigated?

The studies were classified into two subgroups, those with revision cases only, and those with a combination of primary and revision cases. No other prognostically-distinct subgroup could be isolated.

There were 95 studies (87 published articles, 4 detailed abstracts, 2 FDA reports, 1 submitted manuscript, 1 book chapter): 17 for the threaded cup group (1,148 cases), 22 for the porous control group (1,979 cases) and 56 for the cemented control group (10,230 cases).

The threaded cup group had a significantly higher rate of revision than the cemented and porous control groups (3.58 compared with 1.61 and 1.44%, respectively, p<0.05). The same was true for pain score (15.10 compared with 4.53 and 3.01%, respectively, p<0.05), and migrations (8.85 compared with 1.48 and 0.64%, respectively, p<0.05). For clinical score, the threaded cup group had a significantly higher rate than the cemented control group (9.22 compared with 3.38%, p<0.05), but the rate was not significantly higher than the porous control group (6.01%).

The threaded cup group had a significantly higher rate of progressive radiolucencies than the cemented and porous control groups (7.64 compared with 6.08 and 1.97% respectively, p<0.05). The threaded cup group, compared with the cemented control group, also had a significantly lower rate of Zone 1 radiolucencies (7.01 and 18.1%, respectively, p<0.05), and a significantly higher rate of radiolucencies >1mm in size (55.15 and 19.07%, p<0.05) and incomplete radiolucencies (52.45 and 27.83%, p<0.05). All other differences were non significant.

No significant differences were found between groups in terms of location of radiolucencies.

Restricting attention to cases which were revisions only, the threaded cup group still had a significantly higher rate of revision than the cemented and porous control groups (14.59, 3.35 and 3.68% respectively, p<0.05).

Despite the limitations of meta-analyses and the poor state of the orthopaedic literature database, this study has demonstrated a significantly greater rate of failure for the threaded acetabular cup design. With the lack of clinical information in support of threaded acetabular cups and the high incidence of their early failure, we conclude that the generalised use of threaded acetabular cups in total hip arthroplasty should be abandoned and be limited to carefully controlled clinical investigations.

No details of the primary studies included in the meta-analysis are given, so the sample size and characteristics of the individual studies are not available. There is no way to assess the impact of confounding factors, e.g.comorbid conditions and lifestyle, which might influence clinical performance. Homogeneity was not tested nor was the quality of the included studies assessed, and from the descriptive data there are differences in sex, age and follow-up between the groups. Some of the results reported in the text do not match those presented in tables. The definition of revision cases used by the authors, which excludes certain reoperations, is unclear. The lack of reliable data limits the interpretation of results, and the strength of the authors' conclusions do not follow from the quality of the available data and the results presented.

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.