• Arch Orthop Trauma Surg · Jan 2023

    Approximately 41% of knees have a looser gap in full extension than in 20° flexion after Oxford unicompartmental arthroplasty.

    • Shotaro Araki, Takafumi Hiranaka, Kenjiro Okimura, Takaaki Fujishiro, and Koji Okamoto.
    • Department of Orthopaedic Surgery and Joint Surgery Centre, Takatsuki General Hospital, 1-3-13, Kosobe-cho, Takatsuki, Osaka, 569-1192, Japan.
    • Arch Orthop Trauma Surg. 2023 Jan 1; 143 (1): 495500495-500.

    IntroductionIn Oxford unicompartmental knee arthroplasty (OUKA), the flexion and extension gaps should be adjusted to prevent mobile-bearing dislocation. The extension gap is recommended to be evaluated in the 20° flexion position to avoid underestimation due to tension of the posterior capsule. However, we have become aware of a looser gap in full extension than in 20° flexion in some instances.Materials And MethodsWe retrospectively investigated 83 knees in 60 patients who underwent OUKA between January and June 2020. During surgery, the extension gaps were measured in both full extension and 20° flexion. The knees were classified into two groups: the gap was looser in full extension (0° group), and the gap was equal or looser in 20° flexion than in full extension (20° group). The hip-knee-ankle angle (HKAA), the lateral distal femoral angle (LDFA), the medial proximal tibia angle (MPTA), the posterior tibial slope angle (PTSA), and the last spigot size were also measured and compared between the groups.ResultsThere was looseness in approximately 41% of knees (34 out of 83 knees) in full extension. In the knees in the 0° group, the last spigot size was significantly smaller (median 1 and 2, P < 0.01). However, there were no significant differences in the HKAA, MPTA, LDFA or PTSA between the groups.ConclusionsApproximately 41% of knees have a looser gap in full extension than in 20° flexion after OUKA. Further investigation is needed to better understand which extension gap should be used in such cases, and to find the contributing factors in loose full extension gap other than the size of the last spigot.© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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