Custom constrained condylar total knees using CAD-CAM

There are a number of pathological conditions involving abnormal geometry, including extremely small sizes, where standard off-the-shelf total knees do not suffice. Usually, these conditions require total joints which provide varus–valgus stability. This report concentrates on condylar knees with intercondylar stability, namely the constrained condylar type. The design and manufacture of these custom implants can be time-consuming and expensive. In this study, a constrained condylar was designed with special attention to laxity, stability and strength. The design was parameterised such that for a custom case, only the A–P and M–L dimensions of the knee were required. Special software was then written and interfaced with CNC machines, such that the custom knees could be designed and manufactured simply, efficiently, and at low cost. Five case examples are reported, where constrained condylar knees were specially designed and manufactured to suit patient requirements. Follow-up examinations showed good geometrical fit and satisfactory function.