The standard prosthesis for most arthritic conditions is a tricompartmental type. Patellar resurfacing should be done in most cases. The question of cruciate preservation or substitution is unresolved, and both types give equivalent clinical results. No advantage has been shown for left or right components. Correction of deformity occurs by soft-tissue release and ligament balancing, rather than by bone resection. Most primary replacements can be performed in this manner, but alignment is critical to the function and survival of a functioning arthroplasty. Most failures can be attributed to incorrect ligament balance or incorrect alignment. Cement fixation of the components has proved effective, and there is no immediate need for alternative methods such as bone ingrowth; new methods will have to prove themselves against the standard already established for cemented prostheses. Patellar complications such as fatigue fracture of the patellar bone now constitute the majority of problems following total knee arthroplasty.