The Alterations of the Ankle Joint Following Supramalleolar Osteotomy in Primary Ankle Varus Osteoarthritis
Authors: Ahn Jiyong , Peiffer Matthias , Karaismailoglu Bedri , Ashkani-Esfahani Soheil , Lee Woo-Chun 
Published: December 2024

Category: Ankle; Ankle Arthritis Introduction/Purpose: Supramalleolar osteotomy (SMO) is a surgical procedure commonly used for load shifting in ankle arthritis, particularly in cases of early varus ankle arthritis. Correction of the tibial plafond into valgus alignment has been proposed to address varus ankle arthritis, with the belief that a larger medial distal tibial angle (MDTA) aids in load shifting. However, evidence supporting the amount of the correction as superior for joint preservation is lacking. We hypothesized that the load distribution of the ankle joint was unevenly changed following the supramalleolar osteotomy (SMO) in primary ankle osteoarthritis. The aim of the study is to investigate the specific load distribution change of the ankle joint and three-dimensional radiographic changes after the SMO in primary ankle osteoarthritis. Methods: A single-center retrospective study conducted in Seoul, Korea, analyzed 36 cases of SMO performed from 2018 to 2022 for primary varus ankle osteoarthritis at Takakura stage 3a. The study included 17 female and 19 male patients with an average follow-up of 54 months. Preoperative and final follow-up assessments involved clinical evaluations using visual analog scale (VAS) for pain and foot function index (FFI), along with radiological assessments using weight-bearing plain radiograph and CT measurements such as medial distal tibial angle (MDTA), anterior distal tibial angle (ADTA), talar tilt, medial clear space (MCS), and talus center migration (TCM) were taken preoperatively and at the last follow-up. Hindfoot alignment parameters were also measured and compared. The contact stress changes between the distal tibia and talar dome were evaluated preoperatively. At the last follow-up, the contact stress changes were assessed according to four sections of the talus. Results: The study demonstrated significant improvements in various parameters following SMO. Preoperatively, the mean medial distal tibial angle (MDTA) was 87.75±3.57, significantly improving to 93.54±2.97 postoperatively (p=0.001). Talar tilt decreased from 3.19±2.86 to 2.24±2.40 (p=0.002), and talar center of migration (TCM) shifted laterally (p=0.001). Hindfoot alignment angle (HAA) and hindfoot alignment ratio (HAR) significantly improved (p=0.001). Visual analog scale (VAS) and foot function index (FFI) scores decreased significantly (p=0.001). The size of the medial open wedge correlated positively with changes in MDTA and negatively with changes in HAR and hindfoot moment arm (HMA). Median medial clear space (MCS) increased postoperatively (p=0.001), correlating moderately with the change in open wedge size (p=0.03). Contact stress on the talus decreased significantly, particularly in the anteromedial aspect (p=0.001). Conclusion: Supramalleolar osteotomy in primary varus ankle osteoarthritis demonstrates clinical and radiological improvement. However, the degree of medial open wedge in SMO affects variables such as MDTA, TCM, HAR, and HMA, while it does not influence talar tilt or HAA. Additionally, a negative correlation exists between the degree of medial open wedge and FFI, indicating that increased wedge size correlates with decreased FFI. SMO in primary ankle osteoarthritis may lead to anteromedial load changes as a result of open wedge osteotomy of the tibia; it may not influence talus rotation.