Comparison of planned and achieved implant position in total knee arthroplasty with patient-specific positioning guides

Background and purpose — Intraoperatively, patient-specific positioning guides (PSPGs) represent the preoperatively planned alignment. We investigated the degree of correlation between preoperative planning and the alignment achieved postoperatively with the PSPG technique.

Patients and methods — TKAs performed with the PSPG technique between 2009 and 2011 were included. 39 patients (42 TKAs) volunteered for a postoperative CT scan. 2 independent observers performed the postoperative CT measurements. Preoperative component angles (target angles) in the coronal and axial planes were defined as 0 degrees, and in the sagittal plane on average 2.8 degrees for the femoral component and 3 degrees for the tibial component. A postoperative full-length standing anteroposterior radiograph was carried out in 41 TKAs.

Results — The femoral component was on average 1.2 (SD 1.5) degrees in varus, 4.4 (SD 4.0) degrees in flexion, and 0.5 (SD 1.4) degrees in external rotation. The tibial component was on average 0.4 (SD 2.5) degrees in varus and 3.7 (SD 2.3) degrees in flexion. A statistically significant difference between the target (preoperative software plan) and postoperative CT measurement was found for the femoral component angle in the frontal plane (p < 0.001; CI: 0.8–1.7), the sagittal plane (p = 0.01; CI –5.6 to –3.1), and the axial plane (p = 0.03; CI: 0.04–0.88). HKA angles were greater than 3 degrees from the neutral axis in 10 of the 41 cases.

Interpretation — We found our postoperative component alignment angles to be close to the software plan, especially for the tibial component. However, we found outliers in all planes and we cannot therefore conclude that the PSPG technique is a method that reproduces preoperatively planned alignment in a consistent manner.