Abstract
Introduction
Post-operative clinical outcomes of TKA are dependent on a multitude of surgical and patient-specific factors. Malrotation of the femoral and/or tibial component is associated with pain, accelerated wear of the tibial insert, joint instability, and unfavorable patellar tracking and dislocation. Using the transepicondylar axis to guide implantation of the femoral component is considered to be an accurate anatomical reference and is widely used. However, no gold standard currently exists with respect to ensuring optimal rotation of the tibial tray. Literature has suggested that implantation methods, which reference the tibial tubercle, reduce positioning outliers with more consistency than other anatomical landmarks. Therefore, the purpose of this evaluation is to use data collected from intraoperative sensors to assess the true rotational accuracy of using the mid-medial third of the tibial tubercle in 98 TKAs.
Methods
The data for this evaluation was retrieved from 98 consecutive patients who underwent primary TKA from the same highly experienced surgeon. Femoral component rotation was verified in every case via the use of the Whiteside line, referencing the transepicondylar axis, and confirming appropriate patellar tracking. Tibial tray rotation was initially established by location of the mid-medial third of the tibial tubercle. Rotational adjustments of the tibial tray were evaluated in real-time, as the surgeon corrected any tibiofemoral incongruency and tray malpositioning. The initial and final angles of tibial tray rotation were captured with intraoperative video feed, and recorded. A z-test of differences between pre- and post-rotational correction was performed to assess the statistical significance of malrotation present in this cohort.
Results
All patients in this study received a primary TKA, using the mid-medial third of the tibial tubercle to dictate tibial tray rotation. After the sensor-equipped tibial insert was implanted, it was shown that 63.1% of patients exhibited unfavorable rotation. Of those patients, 70% were shown to have internal rotation; 30% were shown to have external rotation. The average malrotation of the tibial tray deviated from a neutral position by 6.3° ± 4.3°, ranging from 0.5° to 19.2°. The z-test of differences yielded a p-value <0.0001, indicating that the proportion of malrotation was statistically significant. The 95% confidence interval of this cohort was calculated to be between 44.8% and 71.8% of malrotation.
Discussion
Malrotation in TKA isassociated with poor clinical outcomes. While no gold standard anatomic landmark currently exists for positioning the tibial tray, the mid-medial third of the tibial tubercle is widely used as a reference. However, the data from this evaluation demonstrates that, not only is this landmark insufficient for establishing optimal rotation (p < 0.0001), but that it had guided the surgeon to an average of 6.3° outside of the optimized implant congruency zone. The large confidence interval indicates that the rotational alignment of the tibial tray—based on the location of the mid-medial third of the tibial tubercle—is not only inaccurate, but also highly variable. Based on this intraoperative sensor data, we suggest that care should be taken when utilizing the tibial tubercle as the sole rotational landmark for the tibial tray.
