Long-term outcomes of contralateral knees after unilateral total knee arthroplasty for osteoarthritis.

One hundred fifty-six patients who underwent unilateral total knee arthroplasty (TKA) between 1970 and 1985 were evaluated for the development, progression, and eventual TKA in the contralateral knee. At the time of TKA, 113 patients were diagnosed with osteoarthritis in the opposite knee, while in the remaining patients, the opposite knee was normal. The probability of the normal knee developing osteoarthritis and requiring a TKA at 7 years is 21 and 5%, respectively. The chance of a knee diagnosed as osteoarthritic at the time of surgery needing a TKA at 10 years is 37%.