Preoperative planning of constitutional varus alignment in patients with varus knees and coronal femoral lateral bowing

Abstract

Objective: To investigate the preoperative constitutional varus alignment (CA) inpatients withvarus osteoarthritic knees and coronal femoral lateral bowing (FLB) by comparing the femoral axis of the patients and volunteers' with straight femoral shaft (SFS) and healthy knees, which would be used to guide the selection of valgus correction angle(VCA) of distal femur in total knee anthroplasty (TKA). Methods: From January 2018 to December 2018, 45 nonconsecutive patients (90 knees) with varus osteoarthritic knees and obvious FLB (>5°) received primary TKA,and 50 limbs with healthy knees and SFS in 25 volunteers were studied at Xinqiao Hospital.The medial proximal femoral angle (MPFA) and anatomic lateral distal femoral angle (a-LDFA) were measured and compared between the two groups.The VCA formed by distal femoral mechanical axis (DMA) and distal femoral anatomic axis (DAA) in patients and the VCA based on neutral mechanical axis (NMA) in volunteers were also compared. The Pearson's correlation analysis was performed between the angle of bowing (α) and the VCA based on NMA in patients. The measurement data was compared with t test between the two groups. Results: The results showed that the MPFA and the a-LDFA were not significantly different between the volunteers with SFS and patients with FLB (MPFA:84.9°±3.7° vs 85.6°±1.8° and a-LDFA:81.7°±1.7° vs 81.2°±1.6°, t=1.26, 1.70, both P>0.05). The VCA based on NMA in volunteers with SFS was 5.5°±0.6°(4.5°-7.4°), the preoperative DAA-DMA angle was 5.3°±0.7°(4.3°-7.8°) in patients with FLB, there was no significant difference between the two groups (t=1.70, P=0.09). The angle of bowing (α) was 7.9°±2.9° (6°-16°), the VCA based on NMA was 8.4°±1.5°(5°-10°), there was a significantly positive correlation between VCA and α (R=0.607, P<0.01). Conclusion: There is no significantly proximal or distal femoral deformity in patients with varus osteoarthritic knee and FLB (>5°), the degree of the DMA-DAAangle based on the DMA doesn't change with the increasing angular deformity of the bowing, then the bowing would be reserved if the distal femur is cut based on DMA in TKA and the preoperative CA should be restored successfully.