The review concluded there was little difference in clinical or radiological outcomes of minimally invasive surgery for total hip arthroplasty compared to conventional surgery, although minimally invasive surgery posed a significantly increased risk of transient lateral femoral cutaneous nerve injury. The limited quality of the included studies and unknown variation across studies for many outcomes make the reliability of the authors' conclusions questionable.

To compare minimally invasive surgery with conventional surgery for total hip arthroplasty on short- and long-term outcomes.

AMED, British Nursing Index, CINAHL, EMBASE and MEDLINE were searched to April 2010. Scopus, BioMed Central, Zetoc and The Cochrane Library were searched; the broad search terms used were reported. There were no language or publication restrictions.

Unpublished studies were sought by searching the Open SIGLE electronic databases, trial registries and several conference proceedings (to April 2010). References lists of included studies were searched. Investigators were contacted in order to identify any further studies.

Randomised controlled trials (RCTs) and non-RCTs that compared conventional surgery with minimally invasive surgery for total hip arthroplasty were eligible for inclusion. Clinical and/or radiological outcomes had to be reported. The primary outcome was the Harris hip score. Studies that used multiple incisions for minimally invasive surgery were excluded.

The mean age of participants was around 62 years and (where stated) about half were male. Minimally invasive surgery approaches included mini-posterior, mini-anterolateral, mini-posterolateral and mini-lateral. Conventional approaches included posterior, anterolateral, posterolateral, posterior, standard lateral, direct lateral and translateral.

Two reviewers independently selected studies for inclusion.

Study quality was assessed using the 11-item PEDro tool.

The authors did not state how many reviewers evaluated study quality.

Data were extracted to enable calculation of mean differences (MD), standardised mean differences (SMD) or odds ratios (OR), with 95% confidence intervals (CI). The authors stated that risk ratios were to be calculated but it appeared that odds ratios were used for binary outcomes. Authors were contacted for missing data when necessary.

Data were extracted by one reviewer and checked by a second reviewer.

Meta-analyses were performed to calculate pooled odds ratios, mean differences or standardised mean differences using a fixed-effect model or a random effects model where the Ι² value for heterogeneity was greater than 20%. The Χ² test was also used to assess heterogeneity. Publication bias was assessed using a funnel plot. A subgroup analysis was planned to look at the effect of computer navigation assistance but was not conducted as only one study used this method (for a small number of patients).

Twenty-eight studies (2,825 patients) were included: 12 RCTs and 16 non-RCTs. Four studies reported adequate methods for allocation concealment. Six studies used a power calculation. Eighteen studies achieved baseline comparability. Eleven studies blinded outcome assessors and three studies blinded patients. Ten studies reported results for a minimum of 85% of the recruited patients. Where reported, follow-up ranged from five days to five years.

There was no statistically significant difference between groups for Harris hip score (MD 1.49, 95% CI -0.08 to 3.06; 17 studies) or for surgical duration (MD -4.65, 95% CI -9.45 to 0.15; 14 studies). There was a statistically significant difference in incision length (MD -7.56, 95% CI -8.17 to -6.95; 17 studies, units not reported) and less perioperative blood loss (MD -42.4, 95% CI -60.1 to -24.7; 12 studies, units not reported) in favour of minimally invasive surgery when compared to conventional surgery.

There were no significant differences for surgical duration (MD -4.65 minutes, 95% CI -9.45 to 0.15; Ι²=91%; 14 studies), drained postoperative blood loss (six studies), total blood loss (15 studies), requirement for blood transfusion (seven studies) and all six radiological outcomes analysed.

Minimally invasive surgery was associated with greater incidence of iatrogenic nerve palsy (OR 5.3, 95% CI 2.6 to 10.9; 13 studies). The result remained significant for transient lateral femoral cutaneous nerve injury (three studies) but not for sciatic nerve palsy (three studies). There were no significant differences for any of the other complication outcomes.

The authors reported that there was limited evidence for publication bias (the funnel plot was slightly asymmetrical).

The forest plot for the primary outcome (Harris Hip score) appeared to present results for a different outcome (surgical duration).

The review indicated that there was little difference in clinical or radiological outcomes of minimally invasive surgery compared to conventional surgery for total hip arthroplasty, although minimally invasive surgery posed a significantly increased risk of transient lateral femoral cutaneous nerve injury.

The review addressed a clear question using reproducible eligibility criteria. Efforts were made to identify all eligible studies regardless of language and publication status; there was little evidence for publication bias. Independent duplicate processes were used during study selection and data extraction to reduce risks of reviewer error and bias affecting the review results (although no process details were presented for the quality assessment). Study quality was assessed and this highlighted limitations in the primary studies; both randomised and non-randomised studies were sought.

Suitable methods were used to pool data and assess heterogeneity, although randomised and non-randomised studies were pooled together without also using a sensitivity analysis to explore any possible difference in effect between study designs. Estimates of heterogeneity were presented for only three outcomes and the possible source of the heterogeneity was not explored. Meta-analysis results for iatrogenic nerve palsy and transient lateral femoral cutaneous nerve injury were based on low event rates in most studies and most of these events came from two non-randomised studies. The authors noted methodological deficiencies in many of the primary studies.

The limited quality of the included studies and unknown variation across studies for many outcomes make the reliability of the authors' conclusions questionable.

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

Research: The authors stated a need for future studies to have longer follow-up periods, and to compare different types of minimally invasive procedures.

None.