Yifei Dai, PhD
Weimin Yue, PhD
Laurent Angibaud, Dipl. Ing.
Morphological fit of the femoral component is important for the success of total knee arthroplasty (TKA)1. As mismatched femoral component size may affect proper flexion-extension gap balancing, patellofemoral kinematics, and tension in soft tissue. Furthermore, it has been shown that excessive femoral overhang (more than 3mm) may be related to postoperative knee pain2, and this phenomenon is believed to be more prevalent in Asian knees compared to Caucasian knees. To avoid the negative impact from excessive overhang, it is important to understand ethnic differences in the distal femoral morphology, and its correlation with contemporary TKA designs. The purpose of this study was to evaluate distal femoral morphology in Asian and Caucasian knees and compare to two new TKA designs, Depuy Synthes Attune® and Exactech Truliant®.
MATERIALS AND METHODS
Digital femoral surface models of 50 Chinese (25M/25F) and 50 Caucasian (25M/25F) bones were used in this study. The anteroposterior (AP) dimension of the femur was measured from the anterior cortex to the tangent plane of both posterior condyles. A distal TKA resection was then performed virtually on each femur (3-matic Research, Materialise NV, Leuven, Belgium). The mediolateral dimension (ML) of the bones was measured at the anteroposterior mid-point of the distal resection. AP and ML dimensions, as well as the aspect ratio (ML/AP), were compared for the two ethnicities. The bone data was compared to two contemporary femoral implant designs with different sizing philosophies. Attune has multiple ML size offerings in the mid-size range. Truliant has a single ML offering across each AP size. Statistical significance was defined as p<0.05.
Significant differences found between ethnicities and genders are presented in Table 1. The majority of the differences were between male and female, but with less difference seen for ethnicity. Both the two contemporary designs assessed had component aspect ratios following the lower bound of the bone data across the sizes, therefore minimizing overhang (Figure 1). Truliant was shown to have aspect ratios slightly lower than Attune in small sizes, between the two sizing offerings of Attune in median sizes, and matching Attune in large sizes.
The study compared femoral morphology between the Chinese knees and Caucasian knees, and demonstrated the majority of the differences exist between genders for these two ethnicities. The two newly released contemporary designs both have aspect ratios at the lower bound of the bone data, which may be translated to minimized component overhang in the dataset. Compared to Attune, Truliant varies the aspect ratio across the bone size range to match the morphology of the distal femoral resection.
Virtual analysis of 100 femora demonstrated gender and ethnic differences in distal resection morphology between Caucasian and Chinese. Two newly released contemporary femoral component designs with different sizing philosophies (single and multiple ML offerings) both demonstrate minimization of component overhang.
1. Bonnin MP, Schmidt A, Basiglini L, et al. Mediolateral oversizing influences pain, function, and flexion after TKA. Knee Surg Sports Traumatol Arthrosc. 2013;21:2314–24.
2. Mahoney OM, Kinsey T. Overhang of the femoral component in total knee arthroplasty: risk factors and clinical consequences. J Bone Joint Surg [Am]. 2010;92-A:1115–21.