Small change in the arithmetic hip-knee-ankle angle during unicompartmental knee arthroplasty improves early postoperative functional outcomes

• Published in: Archives of orthopaedic and trauma surgery 2024-05, Vol.144 (5), p.2297-2304
• Main Authors: Kokubu, Yasuhiko, Kawahara, Shinya, Hamai, Satoshi, Akasaki, Yukio, Sato, Taishi, Nakashima, Yasuharu
• Format: Article
• Language: English
• Subjects: Joint replacement surgery; Knee; Knee Arthroplasty; Medicine; Medicine & Public Health; Orthopedics
• ISSN: 1434-3916; 0936-8051; 1434-3916
• DOI: 10.1007/s00402-024-05309-2

Introduction The optimal lower-limb alignment after unicompartmental knee arthroplasty (UKA) remains controversial. This study aimed to investigate the optimal lower-limb alignment for functional improvement in the early post-UKA period. We hypothesized that a small change (Δ) in the arithmetic hip-knee-ankle (aHKA) angle during surgery would result in better postoperative knee function. Materials and methods This single-centered, retrospective study analyzed 91 patients (91 knees) who underwent UKA from April 2021 and December 2022. Preoperative and postoperative standing whole-leg radiographs were used to evaluate the mechanical HKA angle and aHKA angle. The aHKA angle was calculated from the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA). We defined restored aHKA angle as a postoperative aHKA angle within ± 3° of the preoperative aHKA angle. Functional improvement was evaluated using the preoperative and one-year postoperative Knee Society Scoring 2011 (KSS 2011). A multivariate regression analysis was performed to investigate the optimal lower-limb alignment for functional improvement. Result Postoperative restored aHKA angle ( p  = 0.020) was the only significant factor for improved KSS 2011 scores. Postoperative restored aHKA angle was obtained in 64 patients (70%). ΔMPTA ( p