The review concluded that there was insufficient evidence of improved range of motion or functional performance after high-flexion knee arthroplasty compared with total knee arthroplasty. The limited review methodology used means the reliability of the authors' conclusions is uncertain.

To determine whether there is a significant increase in knee range of motion or function in patients who receive a high-flexion total knee arthroplasty compared with those who receive a standard total knee arthroplasty.

MEDLINE, EMBASE, CINAHL, and the Cochrane Library were searched for studies in English, without date restrictions; search terms were reported.

Studies that compared patients who received a high-flexion total knee arthroplasty with those who received a standard total knee arthroplasty were eligible for inclusion. High flexion total knee arthroplasty was defined as involving a prosthesis specifically designed to achieve knee flexion greater than 120°.

Patients in included studies had a mean age of 67 years; 84% were women. The main reason for total knee arthroplasty was osteoarthritis. Over half of the studies were in Asian populations. Most studies used a legacy posterior stabilised prosthesis. The primary outcomes were range of motion and knee flexion.

Two authors selected studies for inclusion.

The authors did not appear to formally assess study quality, although use of assessor blinding and a sample size calculation were reported.

The authors did not state how many reviewers extracted data.

A narrative synthesis was presented, grouped by outcome, and differences between studies were discussed.

Nine studies were included in the review (three randomised controlled trials and six case-control studies; 399 knee joint implants in 370 patients), with sample sizes ranging from 25 to 72 patients. Follow-up periods ranged from one to 2.9 years (mean 17.6 months). Three trials reported use of a sample size calculation and two used some form of assessor blinding.

Four of the seven studies that reported flexion, and two of the four studies that reported range of motion, reported significant improvements with high-flexion arthroplasty when compared with standard knee arthroplasty. No studies reported significant differences in functional outcome measures.

There was insufficient evidence of improved range of motion or functional performance after high-flexion knee arthroplasty.

The review addressed a clear question using appropriate inclusion criteria. Attempts to identify relevant studies were undertaken by searching electronic databases, but it appeared that no search was made for unpublished studies, and the restriction to searching for studies in English meant that some relevant studies may have been missed. It was not clear that suitable methods (e.g. independent, duplicate assessments) were employed to reduce the risks of reviewer error and bias for the processes of study selection and data extraction.

Although it was unclear whether or not a formal assessment of study quality was made, the authors did discuss key quality issues and reported that quality was generally low. A narrative synthesis appeared appropriate considering the evident clinical or methodological heterogeneity.

The authors' conclusions reflected the evidence presented, but the basic search for studies, coupled with the use of limited review processes (or limited reporting of the processes), means their reliability is uncertain.

Practice: The authors did not state any implications for practice.

Research: The authors stated that well-designed, longer-term randomised controlled studies with accurate, blinded, range of motion measurement are required to investigate the proposed benefits of implants; these should involve validated functional tests which assess higher levels of functional knee flexion, such as stair climbing or rising from sitting. They added that any future research using satisfaction scores should separate domains such as pain and function.

Not stated.

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.