Unique morphology of intraoperative measurement of distal femur in northern Malaysian females and its correlation with total knee arthroplasty implant sizing

Abstract

Accurate implant sizing is one of the major determinants in defining the success of total knee arthroplasty (TKA). Current TKA implants are based on Caucasian knee morphometry which is well documented to be larger than Asian knees. Even more, with regards to sizing, implant mismatch tends to be more evident in the female population. This study was designed to evaluate the distal femur dimensions of Malaysian female patients who underwent TKA in our institution and to compare them with the current prosthetic system in use. A total of 199 female patients (207 knees) who underwent TKA were enrolled in this study. Intraoperatively, the AP dimensions (medial and lateral condyles) and mediolateral (ML) width were measured. Known dimension of the femoral component of the prosthetic knee system currently in use were compared with the morphological data. The average femoral component overhang was 2.11 mm (SD 3.94 mm). There was significant difference between the mean ML width of the resected femur and the femoral component (p<0.01). Analysis also revealed a significant positive and weak relationship between both, AP (medial and lateral) and ML dimension. The aspect ratio (ML/AP) of the native femur was generally smaller than the implant aspect ratio which is likely to cause overhang in our population. In general, this study shows that the knees of our female sub-population are even narrower than the other Asian female knees from previous studies. Implants should be designed based on the morphological data of the local population. Implant manufactures should tailor them to accommodate a smaller change in ML width for an increment in the AP length and provide several ML widths for one AP length to obtain a better fitting prosthesis hence curbing the problem of ML overhang.