Morphology of the black Kenyan adult distal femur based on normalized ratios - A cadaveric study

Abstract

Background: The morphology of the adult distal femur has been described in geometrical shapes using normalized ratios. The normalized ratios are derived from linear measurements and include the mediolateral/anteroposterior (ML/AP) ratio, the anteromedial/ posteromedial (AML/PML) ratio, and the medial anteroposterior/lateral anteroposterior (MAP/LAP) ratio. These ratios define the distal femur as either a square or a rectangle in the ML/AP ratio, triangular or rectangular in the AML/PML ratio, or being parallel in the anterior and posterior condylar axes or not according to the MAP/LAP ratio. These ratios vary among ethnic groups as well as between the male and female gender. The distal femoral components of the total knee arthroplasty (TKA) available globally are based on the morphology of the distal femur of the Caucasian population. These implants have been found to have shortcomings in non- Caucasian populations due to the differences in the morphologies. Currently no data exists on the morphology of the distal femur of the black Kenyan adult population hence no comparison can be made to the commercially available implants of the distal femur in our locality. Objective: To describe the morphology of the black Kenyan adult distal femur. Methods: An anatomical cross-sectional descriptive study of the adult distal femora of prosected cadavers at the human anatomy laboratories of Moi University and University of Nairobi was carried out during the month of October 2015. A sample size of 90 femora was required for the study. Using a pair of digital sliding callipers, the ML width, AML length, PML length, MAP height, and LAP height were measured. The AP height was taken as MAP or LAP depending on which dimension was greater. The ML/AP, AML/PML, and MAP/LAP ratios were then calculated and tabulated. Statistical analysis was computed using the student’s t-test and two sample Wilcoxon rank-sum test for parametric and non-parametric data respectively. Two-sample t test was used to compare normalized ratios from this study to those of other races as from literature. Results: A total of 87 femora were studied: 77 were from male cadavers and 10 were from female cadavers. The mean values of the linear measurements were: ML 75.519mm (SD: 5.928mm), AP 69.305mm (SD: 4.686mm), AML 37.815mm (SD: 3.721mm), PML 51.934mm (SD: 5.006mm), MAP 66.301mm (SD: 4.786mm), and LAP 69.146mm (SD: 4.673mm). The mean ML/AP ratio was 1.091 (SD: 0.074), AML/PML ratio 0.733 (SD: 0.089), and MAP/LAP ratio 0.959 (SD: 0.038). The ML/AP ratio of male cadaveric distal femur was significantly greater than that of female cadavers (p<0.001). The male and female black Kenyan distal femora were smaller than the Caucasian distal femora in all the ratios (p<0.05). Conclusions: The black Kenyan adult distal femur is more of a square in the ML/AP ratio; and more triangular than rectangular in AML/PML ratio. The condylar axes are not parallel in the MAP/LAP ratio, and the female distal femur is comparatively narrower than that of males. The black Kenyan distal femur is narrower and shorter than the distal femur of the Caucasian population. Recommendation(s): A study to be done to compare the distal femoral measurements and ratios from this study with the commercially available distal femoral components of TKA. A wide based study to be done to encompass the distal femoral measurements of various communities within Kenya.