2015 ISAKOS Biennial Congress ePoster #1113

Three Dimensional Analyses in Varus and Valgus Osteoarthritis of the Knee

Masashi Tamaki, MD, PhD, Suita, Osaka JAPAN
Tetsuya Tomita, MD, PhD, Suita, Osaka JAPAN
Takashi Miyamoto, MD, Osaka JAPAN
Keiji Iwamoto, MD, PhD, Osaka, Osaka JAPAN
Takafumi Ueda, MD, PhD, Osaka JAPAN
Kazuomi Sugamoto, MD, PhD, Suita, Osaka JAPAN
Dept. of Orthopaedics, Osaka National Hospital, Osaka, JAPAN

FDA Status Not Applicable

Summary: We evaluated the 3D deformities using bone models. The flexion and external rotation were larger in knees with increased varus. The femoral neck anteversion in the valgus was larger than varus.

Abstract:

Introduction

The deformity in osteoarthritis(OA)of the knee has been evaluated mainly in the frontal plane two dimensional X-ray using femorotibial angle. Although the presence of underlying rotational deformity in the varus knee and coexisting hip abnormality in the valgus knee have been suggested, three dimensional (3D) deformities in the varus and valgus knee were still unknown. We evaluated the 3D deformities of the varus and valgus knee using 3D bone models.

Methods

Preoperative computed tomography (CT) scans of twenty seven OA knees (fifteen varus and twelve valgus knees) undergoing total knee arthroplasty were assessed in this study. An Institutional Review Board approved this research and all patients signed informed consent for the procedure. CT scans of each patient’s femur and tibia, with a 2 mm interval, obtained before surgery. We created the 3D digital model of the femur and tibia using visualization and modeling software developed in our institution. The femoral coordinate system was calculated by the 3D mechanical axis and clinical transepicondylar axis, and the tibial coordinate system was calculated by the 3D mechanical axis and Akagi’s line. The 3D deformities of the knee were determined by the relative position of the femorotibial coordinate system, and described by the tibial position relative to the femur. The anteversion of the femoral neck were calculated to evaluate the relationship between the valgus knee and hip region. Two independent observers repeated all measurements. The mean value of the two observers` measurements for each knees was used for analysis. Pearson correlation test was used to analyze the correlation each deformities.

Results

The 3D deformities of the varus knee were 12.1±5.5°varus (5.4 to 22.6°) , 6.8±6.3°flexion (1.7 to 21.7°) and 6.5±6.1 °external rotation (-1.2 to 23.2°). The flexion and external rotational deformities were larger in knees with increased varus deformities. (the correlation between flexion and varus deformities was r = 0.51; P<0.001, and the correlation between external rotation and varus deformities was r = 0.42; P<0.001. ) The 3D deformities of the valgus knee were 10.2±4.2°valgus (0.6 to 15.0°) , 9.5±8.8°flexion (-5.2 to 23.7°) and 2.3±7.3°external rotation (-9.4 to 16.1°). Although there was no tendency about the 3D deformities in the valgus knee, the anteversion of the femoral neck in the valgus knees was 31.9°compared with 10.8°in the varus knees.

Discussion

Results of current study indicate that the varus knee is associated with flexion and external rotational deformity. The tibia tended locates in flexion and external rotated position in the knees with severe varus deformity. It helps elucidate the pathogenesis of the varus OA of the knee. It has been hypothesized that cartilage degeneration starts anteromedially and progress posteromedially. The tendency for the varus knee to flex and rotate externally has substantiated hypothesis. In contrast, there was no tendency about the 3D deformities in the valgus knee. It has been reported that the valgus knee was associated with a wider pelvis, shorter femoral neck and head-shaft distance. In addtion to that, the current study revealed that the valgus knee is associated with a large anteversion of the femoral neck. The valgus knee has a biomechanical background originating from hip anatomy.

Conclusion

The varus deformity in OA of the knee is associated with significant flexion and external rotational deformity. In contrast, the valgus deformity has a biomechanical background originating from the anteversion of the femoral neck.