A total of 344 patients underwent bilateral total knee replacement (TKR) using a different prosthesis on each side. Four knee prostheses were used: anterior and posterior cruciate-retaining (ACL-PCL), posterior cruciate-retaining (PCL), medial or lateral pivot (MLP), and posterior cruciate-substituting (PS).

All patients had good or excellent results. The range of movement, relief from pain, alignment, and stability did not vary among any of the prostheses.

Forty-one of 46 patients (89%) preferred the ACL-PCL to the PS knee and 27 of 35 patients (77%) the MLP knee to the PS knee. Of the patients with an ACL-PCL knee on one side and a MLP on the other, an equal number preferred each type. The MLP knee was preferred to the PCL by 34 (79%) patients. PS and PCL knees were preferred equally. Patients with bilateral TKRs preferred retention of both their cruciate ligaments or substitution with a medial or lateral pivot prosthesis.

Substance P is readily detected in the synovial fluid of the knee in which it acts as a powerful inflammatory agent in response to injury and disease. It may be an objective predictor of pain after knee replacement surgery.

The level of substance P was measured in the synovial fluid in both knees of 114 patients having unilateral and in 86 patients having bilateral total knee replacement for osteoarthritis. All had severe pain in the knee to be replaced and joint destruction. Substance P was elevated in 73% of replaced knees but not in normal or asymptomatic knees. Good or excellent pain relief was achieved in 97% of patients with an elevated preoperative level of substance P and in 61% of those with a normal preoperative level (p < 0.05 compared with preoperative values).