Comparison of tibial implant positioning between symmetrical and anatomical design implants in unicompartmental knee arthroplasty for Japanese patients

Purpose: In unicompartmental knee arthroplasty (UKA) procedures, maximizing the bone coverage of the tibial implant and eliminating the medial and posterior overhang would be optimal. We commonly used Physica ZUK (R) (ZUK), which is a symmetrical design. Alternatively, since Persona Partial Knee (R) (PPK) was developed in 2017 with an anatomical design to improve bone coverage, we started PPK. We hypothesized that the PPK facilitated better bone coverage than the ZUK without obvious overhangs. This study evaluated the bone coverage and the medial and posterior overhang of these differently designed tibial implants. Methods: Seventy-nine knees from 68 patients who underwent UKA were evaluated. Cases were categorized into the ZUK (41 knees) and PPK (38 knees) groups. CT images were acquired before surgery and 1 week after surgery. We measured the tibial bone coverage, and the medial and posterior overhang by 3D software. Results: The bone coverages were 103.8 +/- 4.8% and 102.0 +/- 3.0%, the medial overhangs were 2.2 +/- 1.2 mm and 1.4 +/- 1.1 mm, and the posterior overhangs were 0.6 +/- 1.3 mm and 0.4 +/- 1.2 mm for the ZUK and PPK groups, respectively. The bone coverage and medial overhang were significantly different between the groups, with ZUK being larger. Conclusion: Patients who received PPK had significantly smaller medial overhangs and better bone coverage. PPK is more likely to give better results than ZUK.