Patient-specific instrumentation for unicompartmental knee replacement: better function?

Polish version: Endoproteza jednoprzedziałowa kolana — czy indywidualne prowadnice poprawiają wynik?

Patient-specific guides are intended to help reproduce planned component positioning in unicompartmental knee replacement, but a meta-analysis found no corresponding advantage in patient-reported function. Greater technical sophistication does not automatically mean better clinical outcomes.

Why this study matters

Accurate component placement matters in unicompartmental arthroplasty. Patient-specific instrumentation (PSI), produced from preoperative imaging, aims to improve reproducibility. The review compared PSI with conventional instrumentation to assess pain, function and outcomes important to patients rather than assuming that technical accuracy guarantees benefit.

Review methods

The PRISMA-based review searched MEDLINE, Embase and the Cochrane Library. Fourteen studies included 1,680 knees in 1,670 patients: five RCTs and nine retrospective comparative studies. All RCTs had low overall risk of bias, while some observational studies were weaker.

Main outcomes were Oxford Knee Score (OKS) at 1 year and change from baseline. Knee Society Score, KOOS, WOMAC and revision data were also assessed.

Main results

OKS at 12 months did not differ significantly: mean difference 0.90 points (95% CI −2.65 to 4.45; I² = 0%). Knee Society Score and KOOS showed no significant PSI advantage at 3 months or assessments at least 1 year after surgery. WOMAC data were insufficient for reliable pooling.

Revision data were too heterogeneous for a meaningful combined analysis. The effect on later reoperation or implant survival therefore remains uncertain.

Clinical interpretation for an orthopaedic surgeon

Current evidence does not confirm better functional outcomes with PSI than with conventional instrumentation. PSI may assist planning or technical steps, but should not be presented as a guarantee of less pain, better function or greater satisfaction. New technology warrants assessment through patient-reported outcomes, safety, durability and total pathway costs alongside technical and radiographic measures.

Limitations

• Only five of the 14 studies were randomized; most evidence was retrospective.
• Some observational studies had moderate or high risk of bias.
• PSI systems, techniques and patient populations varied.
• The strongest functional evidence concerns approximately 1 year, not long-term durability.
• Revision evidence could not be pooled reliably.

Implications for practice

Where PSI is used, the rationale should rest on specific technical or organisational benefits rather than a promised improvement in patient-reported function. The review does not exclude usefulness in particular anatomical situations, establish equivalence between every PSI system or show that component accuracy is unaffected. It answers the narrower question that available evidence shows no functional advantage over well-performed surgery with standard instruments.

References

Ruhle V, Rudran B, Leung B, Merle C, Murray D, Price A, Alvand A. Functional outcomes of patient-specific instrumentation versus conventional instrumentation for unicompartmental knee replacement: A systematic review and meta-analysis. The Knee. Published online 25 August 2026;63:104608. DOI: 10.1016/j.knee.2026.104608. PMID 42641204.

The numerical findings above are limited to information publicly available in the abstract and publication metadata. In the conflict-of-interest declaration, one author reported an institutional grant, consulting payments and royalties from Zimmer Biomet.

Related resources

For Doctors and Physiotherapists · Research Updates, Literature and Evidence-Based Medicine

Content prepared by: Tomasz Poboży - orthopaedic surgeon.