Three dimensional printing in unicompartmental knee arthroplasty: current evidence and future directions

Additive manufacturing (3D printing) is increasingly used in unicompartmental knee arthroplasty (UKA), including patient-specific instrumentation (PSI)/cutting guides, additively manufactured cementless implants, and fully patient-specific implant workflows. However, these applications differ substantially in purpose, evidence level, cost structure, and implementation burden; therefore, their clinical value should not be inferred from technical feasibility alone.

This narrative review was updated through December 2025 and was informed by a structured search of PubMed/MEDLINE, Embase, and the Cochrane Library, supplemented by reference screening. Search concepts combined UKA with 3D printing, additive manufacturing, PSI, patient-specific implants, custom implants, porous cementless fixation, osseointegration, navigation/robotics comparators, cost, and implementation. Study selection, eligibility criteria, evidence domains, outcomes, and anticipated sources of bias were predefined to improve reproducibility.

Randomized trials and meta-analyses show that PSI in UKA does not consistently reduce alignment outliers or improve patient-reported outcome measures (PROMs), with recurrent technical vulnerability at tibial registration, slope, and rotation. Cadaveric studies support feasibility but mainly report surrogate technical endpoints. For additively manufactured cementless UKA implants, implant-specific long-term cohort data suggest acceptable survivorship and clinically meaningful PROM improvement, but evidence remains implant-specific. Patient-specific implants may improve anatomic fit in selected morphologies, yet comparative studies have not demonstrated consistent short-term clinical or gait advantages over well-executed standard UKA.

Current evidence supports selective, indication-driven adoption rather than routine use of 3D-enabled UKA technologies. PSI is best viewed as an execution aid for specific workflows or training contexts, porous cementless 3D-printed implants require implant-specific survivorship surveillance, and patient-specific implants should be reserved for carefully justified morphology-driven indications. Future research should prioritize standardized reporting, surgeon-volume stratification, long-term failure mechanisms, registry linkage, and cost-effectiveness across the complete care pathway.