Accuracy of Ratio for Centre of the Ankle Method as a Landmark for Proximal Tibial Cutting in Computer Assisted Total Knee Arthroplasty Compared with Extramedullary Method

Proximal tibial resection is an important surgical step in total knee arthroplasty (TKA). Normally, an anterior surface of tibia used as anatomical landmark (extramedullary method), this method based on visual judgment. (D.C. Marchant, 2005) calculated ratio for center of the ankle, ratio of lateral distance to total inter-malleolar distance was observed at 0.57 in normal ankle sample. However, there is no study documenting about accuracy of ratio for center of the ankle as a landmark for proximal tibial resection in computer assisted TKA (CAS TKA). This was prospective study on 65 patients with osteoarthritis knees scheduled to receive CAS TKA from January to December 2018. Proximal tibial resection was simulated by extramedullary method and ratio for center of the ankle respectively. Tibial resection alignment were recorded by CAS. Tibial resection alignment within 3 degrees was 84.6 and 92.3% for extramedullary method and ratio for center of the ankle method. The average total tibial resection alignment was 0.84 and 0.66 degrees of valgus (p = 0.497), the average tibial resection alignment within 3 degrees from mechanical axis was 0.33 and 0.55 degrees of valgus (p = 0.513) and the average tibial resection alignment more than 3 degrees from mechanical axis was 3.60 and 1.5 degrees of valgus (p = 0.049) for extramedullary method and ratio for center of the ankle method respectively. Ratio for center of the ankle demonstrated result in numeric value and anatomical landmark of lateral and medial malleoli was simple to identified. Our results shown the tibial resection alignment with ratio for center of the ankle method had higher accuracy and lower average degrees of outlier than extramedullary method.