Distal tibial osteophytes are more accurate than medial malleolar anatomy when using patient specific instrumentation in total ankle replacement.

Total ankle replacement (TAR) is a treatment for end stage ankle arthritis. Patient specific instrumentation (PSI) has been used and shown to allow for accurate placement and alignment in TAR in the coronal and sagittal plane. PSI systems are available and use different anatomic landmarks for the cutting guides. This is a retrospective matched case control study comparing accuracy in alignment using 2 different PSI systems. The case series uses a medial malleolar landmark (MM Group), and each case patient was matched based on preoperative coronal plane alignment with 2 ankles in the control series using the distal tibial osteophytes as landmarks (DT Group), as this system has been in use and studied more. A total of 48 ankles were studied, 16 in the MM Group and 32 in the DT Group matched by coronal plane alignment. There was a difference in accuracy of postoperative coronal plane alignment, with the MM Group deviated from expected by 1.6° ± 1.3° compared to the DT Group at 1.1° ± 0.6°, p = 0.04. This corresponded to 68.8 % of MM Group ankles being within 2° of expected compared to 93.4 % of DT Group ankles. There was no statistically significant difference in sagittal plane alignment between the groups, p = 0.57. Procedure time was the only other statistically significant difference with the MM Group taking longer than the DT Group, 97.4 min and 80.6 min, respectively, p = 0.04. While both groups show good accuracy, alignment based on the distal tibial osteophytes is more accurate than using the medial malleolus.