Extensor hallucis longus tendon is a new distal landmark for coronal tibial component alignment in total knee arthroplasty: A study of magnetic resonance imaging

Purpose: In total knee arthroplasty (TKA), various landmarks are generally used to ensure correct osteotomy. In this study, we examined whether the tibialis anterior tendon (TAT) or the extensor hallucis longus tendon (EHLT) could be used as a landmark of the center of the ankle joint in patients with knee osteoarthrosis (OA), using magnetic resonance imaging (MRI). Methods: The subjects were 61 patients with OA in 79 knees (males: 8 with 9 knees and females: 53 with 70 knees). With the ankle joint secured in the intermediate position, MRI from the knee joint to the ankle joint was performed in the same foot position. We prepared individual lines connecting the center of the ankle joint with the TAT or EHLT to measure the angle difference (Delta A) from Akagi's line in the knee joint. We analyzed whether the Delta A might be affected by deformity of the knee joint or foot region, and tibial torsion. Results: At the ankle joint level, the Delta A of EHLT was the smallest, with an average of 1.6 +/- 3.4 degrees. The Delta A for the femorotibial angle, hallux valgus angle, and varus-valgus angle showed no correlations with deformity of the knee joint and foot region, or tibial torsion. Conclusions: MRI findings showed that EHLT would be useful as a landmark of the ankle joint center in extramedullary tibial osteotomy in TKA for medial knee OA. It was also clarified that the landmark would not be affected by severe deformity of the knee joint, deformity of the foot region, or external torsion of the tibia.