Palpable ankle landmarks provide reliable measures for tibial component coronal alignment in total knee arthroplasty

Controversy exists regarding the optimal tibial coronal alignment in total knee arthroplasty. Many believe navigation or robotics are required to set kinematic alignments or 'safe' limits as extremes may risk tibial component loosening. Most navigation or robotic systems require the surgeon to identify the ankle malleoli intra-operatively. This study radiographically assessed the relationship between these bony landmarks and the tibial mechanical axis to determine if they could be used to achieve, or set safe boundaries for, personalised alignment strategies.

Long-leg weight-bearing alignment radiographs were analysed independently by two orthopaedic surgeons at two time points, eight weeks apart. Angles were measured between the long axis of the tibia (TIB) and: 1. lateral border of lateral malleolus (TIB-LM), 2. lateral border of the talus (TIB-LT) and 3. medial border of the medial malleolus (TIB-MM). Intra- and inter-rater reliabilities were assessed.

167 radiographs in 119 patients were analysed. Mean angles (95% CI) were: TIB-LM 4.8° (4.7-4.8°), TIB-LT 2.6° (2.5-2.6°) and TIB-MM 4.2° (4.1-4.2°). Inter-rater reliability was ICC = 0.84 for TIB-LM, ICC = 0.80 for TIB-MM, and ICC = 0.67 for TIB-LT. Intra-rater reliability was ICC ≥0.80 for all measures.

There are consistent radiological angles for tibial component alignment to palpable ankle landmarks. Using the medial and lateral malleolar landmarks, with standard instrumentation and alignment checks would allow surgeons to define safe limits of 4.8° tibial varus or 4.2° tibial valgus without the need for added technology. Additionally, an alignment check to the lateral border of the talus equates to a 2.6° varus cut.