Improved positioning of the tibial component in unicompartmental knee arthroplasty with patient-specific cutting blocks.

PURPOSE: Unicompartmental knee arthroplasty (UKA) has recently regained popularity for the treatment of osteoarthritis of the knee. Numerous authors have cited alignment as an important prognostic factor in the survival of UKA. Limb alignment affects not only the longevity of UKA by influencing wear of polyethylene, but also affects the unreplaced contralateral compartment. Malpositioning of the components may result in unequal wear patterns, thus further leading to early failure and additionally influencing clinical outcome as well. However, there is a lack of techniques to assure a high accuracy of the implant positioning.

METHODS: In this study, we investigated tibia component alignment of 28 medial UKAs implanted with patient-specific cutting blocks. Three patients were excluded due to bad imaging. Measurements of tibial component alignment from postoperatively computed tomography (CT) scans were compared to respective CT-based preoperative plannings to assess the accuracy of implant positioning.

RESULTS: Our results show excellent high accuracy of tibial implant position in tibial varus/valgus (Δ 0.3° ± 1.7°), posterior slope (Δ 1.1° ± 2.6°) and external rotation (Δ 1.5° ± 3.3°).

CONCLUSION: We conclude that patient-specific cutting blocks improve the accuracy of tibia component positioning in unicompartmental knee arthroplasty.

LEVEL OF EVIDENCE: Case series with no comparison group, Level IV.