The spacer block technique is widely used in medial fixed-bearing unicompartmental knee arthroplasty (UKA) for osteoarthritis (OA) and osteonecrosis (ON), while it is still unclear if there is any difference in the extension gap between UKAs for the two conditions. To clarify the question, the data from 87 consecutive patients (OA: 57 patients and ON: 30 patients) who underwent medial fixed-bearing UKA with the spacer block technique were retrospectively collected and analyzed. The component gap between the medial tibial osteotomy surface and the femoral trial prosthesis in extension was measured using a UKA tensor, and the preosteotomy gap was calculated in each condition. Also, pre- and postoperative coronal hip–knee–ankle (HKA) angles, the thickness of the insert, and the amount of distal femoral and proximal tibial osteotomy were measured and compared between the two groups. As a result, the mean preosteotomy gap in Group OA and Group ON was 5.4 and 3.7 mm, respectively (p < 0.001). The amount of change in HKA angle following UKA in Group OA and Group ON was 4.4and 3.8 degrees, respectively (p = 0.044), while no significant difference was found regarding pre- and postoperative HKA angle between them. Also, thinner inserts tended to be used in Group ON than in Group OA, while no significant difference in the amount of osteotomies was found between them. Since knees with OA and ON showed different biomechanical conditions at medial fixed-bearing UKA probably for the difference in the amount of remaining cartilage, the surgical technique should be carefully considered for each condition.

All procedures were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Written informed consent was obtained from all patients.

Written informed consent was obtained from all patients.

The authors declare that they have no competing interests.

The authors can confirm that all relevant data are included in the article.

Received: 16 March 2023

Accepted: 01 March 2024

Article published online:
29 March 2024

© 2024. Thieme. All rights reserved.

Thieme Medical Publishers, Inc.
333 Seventh Avenue, 18th Floor, New York, NY 10001, USA