Femoral Component and Patella

Abstract

The first resurfacing component for the distal femur developed in the 1950s, the Massachusetts General Hospital femoral condyles, was a close replica of the anatomic geometry. In contrast, the first two cemented metal femoral components of an artificial knee, invented in the late 1960s and early 1970s, were far from anatomic. The first was Gunston’s hemi-disc which fitted into a slot cut into each femoral condyle. The second was Freeman and Swanson’s hemi-roller which fitted over the flat resected surface of the distal femur. This idea of using straight bone cuts for fitting the femoral component was a simple but a major step forward. After 1970, many different femoral component designs emerged, with and without a patella flange, some geometrically simplified. The Ewald and Seedhom knees, being shells of the exact anatomic surfaces, were not easy to fit surgically, while manufacture was difficult and expensive. Other designs were of a simplified shape, with straight facets for bone fitting and with geometrically defined surfaces. These designs included the Townley, and the Total Condylar designed by Walker, Insall, and Ranawat. By then it was realized that an integral patella flange was required on the femoral component. This led to the invention of a resurfacing component for the patella itself. It was found that a dome-shaped patella “button” was the most practical shape which allowed for tilting and motions in multiple directions without edge loading.