Is the Femoral Component Flexion Affected by the Sagittal Femoral Shaft Bowing in Conventional Intramedually Guided TKA?

Abstract 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 intramedullar rod for the femur and a mechanical extramedullar 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. cFBA(coronal femoral bowing angle), sFBA(sagittal femoral bowing angle),and postoperatively, mTFA(mechanical tibiofemoral angle of the knee), β 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 β angle, cFBA and mTFA. Comparison of FSB incidence between different genders was using chi-square test. The p value <0.05 indicates a statistically significant difference.Results: The mean sFBA, cFBA, β angle, mTFA were 9.34°±3.56°(range 1°-16°), 3.25°±3.79°(range -7°-17°), 3.91°±3.15°(range -1°-13°), 0.60°±1.95°(range -3°-6°), 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 β 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.