Is the femoral component flexion affected by the sagittal femoral shaft bowing in conventional intramedullary guided TKA?

Background The aim of the present study was to investigate the influence of sagittal femoral bowing on sagittal femoral component alignment, and whether there was correlation between sagittal femoral component alignment and coronal femoral component alignment. Methods We retrospectively reviewed 77 knees in 71 patients who had undergone primary TKA for advanced osteoarthritis. All surgeries were performed by using a standard medial parapatellar approach. The osteotomy was performed with a conventional technique using an intramedullary rod for the femur and a mechanical extramedullary guiding system for the tibia. All patients enrolled in the study were evaluated with full-length lower extremity load-bearing standing scanograms, and the patients had preoperative and postoperative radiographs of the knees. Coronal femoral bowing angle (cFBA), sagittal femoral bowing angle (sFBA), and postoperatively, mechanical tibiofemoral angle of the knee (mTFA), beta angle (femoral component flexion angle) were measured. The radiographic results of both groups were compared using Student's t test. A two-sided Pearson correlation coefficient was obtained to identify the correlations between FBA in the coronal and sagittal planes, as well as FBA and age or BMI, sFBA and beta angle, cFBA and mTFA. Comparison of FSB incidence between different genders was made using Chi-square test. The p value < 0.05 indicates a statistically significant difference. Results The mean sFBA, cFBA, beta angle, mTFA were 9.34 degrees +/- 3.56 degrees(range 1 degrees-16 degrees), 3.25 degrees +/- 3.79 degrees(range - 7 degrees to -17 degrees), 3.91 degrees +/- 3.15 degrees(range - 1 degrees to -13 degrees), 0.60 degrees +/- 1.95 degrees(range - 3 degrees to -6 degrees), respectively. There was no correlation between age and sFBA (CC = 0.192, p = 0.194) or cFBA (CC = 0.192, p = 0.194); similarly, there was no correlation between age and sFBA (CC = 0.067, p = 0.565) or cFBA (CC = 0.069, p = 0.549). The sFBA was correlated with cFBA and beta angle (CC = 0.540, p < 0.01; CC = 0.543, p < 0.01, respectively), and the cFBA was correlated with mTFA (CC = 0.430, p < 0.01). There was no significant difference (p = 0.247) of cFBA between the patients with sFSB and the patients without sFSB. Conclusions The current study showed that the sFBA was correlated with cFBA in the patients undergoing TKA and the patients with sFSB usually presented non-cFSB. We also found that sFSB could affect the femoral component alignment in the sagittal plane and cFSB could affect the femoral component alignment in the coronal plane. The sFBA or cFBA was not correlated with age, BMI, or gender.

Automated summary

The current study demonstrated a correlation between sagittal femoral bowing angle and coronal femoral bowing angle in patients undergoing total knee arthroplasty (TKA), with patients with sagittal femoral bowing usually not presenting coronal femoral bowing. Sagittal femoral bowing angle could affect femoral component alignment in the sagittal plane, while coronal femoral bowing angle could affect femoral component alignment in the coronal plane. Age, BMI, and gender were not correlated with sagittal femoral or coronal femoral bowing angles.