Reliability of Imageless Computer-Assisted Navigation for Femoral Rotational Alignment in Total Knee Arthroplasty

@#Introduction: The aim of this study was to evaluate the reliability of the femoral component rotation on intraoperative data recorded in a computer-assisted navigation system (CAN-FRA) compared with the post-operative femoral component rotation observed on computed tomography (CT-FRA). Material and method: Computer-assisted total knee arthroplasty (TKA) or primary osteoarthritis of the knee was performed in 51 knees in 36 patients with a mean age of 69.51 years. All procedures were performed by a single surgeon using the same implant design. The intraclass correlation coefficient (ICC) was used to compare the intraoperative CAN-FRA with the post-operative CT-FRA. The angle between the anatomical epicondylar axis and the posterior condylar axis of the implant (CT-FRA) was measured at two separate timepoints by three observers who were blinded to the intra-operative CAN-FRA. Internal rotation was defined as rotation in the negative direction, while external rotation was defined as positive. Results: The mean intra-operative CAN-FRA was 0.1° ± 2.8° (range -5.0° to 5.5°). The mean post-operative CT-FRA was -1.3° ± 2.1° (range -4.6° to 4.4°). The mean difference between the CAN-FRA and the CT-FRA was -1.3° ± 2.2° (range -7.9° to 2.4°). The respective ICC values for the three observers were 0.92, 0.94, and 0.93, while the respective intra-observer coefficients were 0.91, 0.85, and 0.90. The ICC for the intra-operative CAN-FRA versus the postoperative CT-FRA was 0.71. Conclusion: This study shows that using a computerassisted navigation system in TKA achieves reliable results and helps to achieve optimal positioning of the femoral component and rotation alignment correction.

The Correlation of Postoperative Femoral Component Rotation Angle and Patella Tilt Angle with Clinical Results in Total Knee Arthroplasty

PURPOSE: The aim of this study was to analyze the correlation of postoperative femoral component rotation angle and patella tilt angle with clinical results for total knee arthroplasty. MATERIALS AND METHODS: Ninety-six cases in 48 patients who underwent total knee arthroplasty between March 2002 and February 2010 were enrolled. Femoral component rotation angle (FRA) and patella tilt angle (PTA) were measured with postoperative computed tomography. Clinical results were evaluated using American Knee Society knee score & function score and Feller's patella score. We analyzed the correlation of FRA and PTA with clinical outcomes. We also compared clinical results between the PFC(R) Sigma group and the Scorpio NRG(R) group, and the patello-femoral symptom group and a symptom-free group. RESULTS: The mean FRA was 1.40degrees of internal rotation. The patellar tilt angle was 3.79degrees of lateral tilt. The mean knee score was 90.5, the function score was 77.4, and the patella score was 23.9. There was a significant difference between FRA and knee scores (p=0.031, r=-0.284). There were no significant differences between FRA and function score or patella score. The correlation of PTA and clinical results was not significant. The mean FRA was 2.00degrees of internal rotation in the PFC(R) Sigma group, and it was significantly different than for the Scorpio NRG(R) group which had 0.81degrees of internal rotation; but there were no significant differences between the two groups in clinical results. The patello-femoral symptom group deviated more from the mean FRA than did the symptom-free group. CONCLUSION: Internal rotation of the femoral component is correlated with poor clinical results after total knee arthroplasty. The correlation of patella tilt angle and clinical results was not significant.

Anatomical Assessment of the Distal Femur and Tibia for Optimal Femoral Rotational Alignment in Total Knee Arthroplasty

PURPOSE: This study aimed 1) to identify the rotational axis of the femur that provides a balanced 90degrees flexion space in TKA, 2) to assess the changes in the flexion space in deep flexion, and 3) to assess the changes in rotational alignment, with using the posterior condylar axis (PCA) as a guide, and as the changes are related to asymmetric cartilage erosion of the posterior condyle. MATERIALS AND METHODS: The axial MR images of the distal femur in knee extension and the coronal images of the distal femur and the entire tibia at 90 and 130degrees were examined in 40 healthy adults. RESULTS: The clinical transepicondylar axis (TEA) provides a balanced 90degrees flexion space on average. The balanced flexion space in 90degrees became an asymmetrical space with relative narrowing of the medial side in 130degrees. Every 1 mm of asymmetrical cartilage erosion between the posterior condyles changed the femoral rotation by approximately 1degrees when using the PCA as a guide. CONCLUSION: This study suggests that the clinical TEA is the rotational reference that provides a balanced flexion space. When using the PCA as a rotational reference, a surgeon should consider the potential change in the rotational angle that is caused by asymmetrical cartilage erosion.