Why Do Knee Implants Fail? (Biloine Young @ OTW)
How often do total knee arthroplasties fail? And why do they? Richard D. Scott, M.D., of the Harvard Medical School, Boston, tells his patients that their implants are “not like a battery. You are going to have a definite reoperation rate that starts at year one, and goes [up] at about 0.5% per year for the first 25 years.”
As reported on the Ortho SuperSite, Scott has undertaken a 27-year study of 4,222 consecutive primary posterior cruciate-retaining total knee arthroplasty (TKA) cases consisting of 3,432 fixed bearing and 790 mobile-bearing prostheses. He found that polyethylene wear was the most common reason for reoperation, occurring in 119 cases.
Among the fixed-bearing TKAs Scott studied, 222 knees needed revising (5.6%) at an average follow-up of 13 years. By comparison, there were 11 reoperations among the mobile bearing TKAs.
Discussing implant survivorship, Scott said, “There is a 95% chance you will get 10 years [and] a 90% chance you will get 20 years” of use per implant. Today’s revision rates are as low as 1%, he reported in his paper presented at the Current Concepts in Joint Replacement winter meeting in Orlando, Florida.
In his paper, titled “Why knees fail in 2011: Patient, Surgeon, or Device?” Scott noted that there is a 20 times higher incidence of reoperation with un-resurfaced patellae than there is in resurfaced ones. “[Pain] doesn’t occur in the first decade. [Implants] start to hurt 15, 18, 20 years down the line,” he said.
Although cemented tibial implants, all-polyethylene patellar implants, and both cemented and cementless femoral components have proved to be lasting, Scott believes that long-term tibial implant survivorship requires further study. He speculates that better polyethylene, better locking mechanisms and the polished chromium cobalt trays currently being developed will further reduce the revision rate.