Morphometric Analysis of the Knee: A Comprehensive Evaluation of Knee Morphology in Designing Arthroplasties of Knee

The primary objective of knee arthroplasty is to alleviate chronic pain and reinstate functionality of the impaired knee. The leading etiologies for TKA failures have been identified as microbial infections, instability, malfunctioning of the prosthetic, aseptic loosening, implant fracture, gangrene in the patella, and improper axial positioning. Excessive implant overhang over the bony resection boundary, especially in the mediolateral direction, has been shown to associate with soft tissue impingement and inflammation and cause significantly worse knee outcomes and pain. Intraoperatively, a surgeon can avoid excessive overhang by reducing the size of the implant. The resolution to the struggle between minimizing implant overhang, improving implant bony coverage, and maintaining proper rotation is the anatomically appropriateness in the implant design. Generally, a set of metrics are used to measure the dimensions of the articulating area in the bone. The mediolateral (ML) width of the proximal tibia, distal femur, and patellar, and the anterolateral (AP) length of the proximal tibia and distal femur, and the proximal distal (PD) length of the patella are taken into consideration while designing a knee implant. Furthermore, the ratio between medial and lateral sides of the bone in these dimensional measurements (aspect ratio) is commonly used to depict the asymmetry between the two compartments, which is a representation of the shape of the bone. These measurements and ratios vary with gender and ethnicity, and hence, they need to be devised as per the target population. It is also emphasized through multiple studies that anatomical designs exhibited improved lateroposterior (LP) coverage than the symmetrical standard designs in the ML and MP dimensions. These results may help surgeons and manufacturers to better understand their patient population and improve the fit of the designed implants.