A prospective clinical and radionuclide study was done to ascertain the effect of a lateral release on patella vascularity in total knee arthroplasty. Although the basic surgical procedure was the same in all 36 knees, postoperative technetium bone scans revealed a higher incidence (9 of 16, 56.4%) of vascular compromise in knees with a lateral release than in those without a lateral release (3 of 20, 15%). Although only one clinical complication (fractured patella not requiring secondary surgery) occurred, the lateral release itself appears to have a causal relationship with patella viability. It does not seem to be the sole determinant, however, because the development of a "cold" patella in three knees that did not have a lateral release implicates other factors, such as thermal necrosis and anatomic variation of the blood supply.