Intraoperative Assessment of the Axial Rotational Positioning of a Modern Ankle Arthroplasty Tibial Component Using Preoperative Patient-Specific Instrumentation Guidance.

Abstract

The use of patient-specific instrumentation (PSI) in modern total ankle replacement (TAR) has augmented positioning of the tibial component, eliminating the need for complex jigs. Coronal and sagittal alignment are intuitive with this design and have been studied, but axial rotation has not. The purpose of this study was to assess the relationship between the planned preoperative axial rotation as set by the PSI guide and the rotation determined intraoperatively with non-PSI instrumentation. This was a prospective cohort study of 22 consecutive cases. The axial rotation angle between the medial gutter and the tibial implant position on the preoperative CT-scan based plan was extracted. At the time of surgery, the medial gutter alignment instrument from the non-PSI instrumentation was inserted and an intraoperative axial photograph obtained to record the angle between the medial gutter and the axial rotation guide pins set by the PSI instrumentation. The 2 measurements were compared and further statistical analysis included Pearson correlation and paired Student t test. The average axial rotation angle between the medial gutter and the implant on the PSI preoperative plan was 5.4 ± 2.9 degrees, whereas the intraoperative photograph from the medial gutter alignment instrument to the pin was 5.9 ±3.8 degrees. This demonstrated a Pearson correlation of R = 0.54 and a P value of .53. The average difference between the two was -0.46 (95% CI: -2.04, 1.10), meaning that components were either slightly externally rotated or that the fork was aimed internally. Based on this group, 50% (11/22) were within 2 degrees of the target and 77% (17/22) were within 4 degrees of the target. Patient-specific guides allowed for reproducible rotational tibial component implantation in modern TAR. Further work is needed to better understand the biomechanical effects of the rotational profile and consequences on survivorship. Level IV, case series.