The most common complications following total knee arthroplasty (TKA) include aseptic loosening, infection, instability, and periprosthetic fracture. The most common cause of early TKA failure (within 2 years) is infection, while the most common cause of late failure is aseptic loosening. Approximately 40% of TKA failures overall result from aseptic loosening, and 27% are due to septic failure. Aseptic prosthetic loosening can be caused by a variety of factors, including implant malalignment, malpositioning, instability, and poor bone quality. This patient has a long, uncemented revision metal stem, and the implant is press fit into the tibial canal. The press fit metal component has no bony ingrowth potential at the implant-bone interface, so any excess motion of the stem can cause the surrounding bone to fatigue. Pain made worse with weight bearing is a sign that the metal implant is starting to cause fatigue, or a stress reaction, at the tibial diaphysis. This is confirmed on the patient’s bone scan.

In the work-up of aseptic loosening, X-rays are often negative early in the presentation. With normal X-rays, a bone scan is the next best study of choice. A bone scan can be positive up to 2 years after TKA, so results should be correlated with the clinical scenario. This patient has a positive bone scan 5 years from revision TKA, so the changes in the tibial stem can be ruled pathological. The patient’s bone scan shows increased uptake at the implant-bone interface of the tibial stem, suggesting aseptic loosening. Unfortunately, when stress reactions occur, as did in this patient, conservative treatment with a period of non-weight bearing is often unsuccessful, and a revision surgery is generally required.1,2

Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).

References

  1. Sharkey PF, Lichstein PM, Shen C, Tokarski AT, Parvizi J. Why are total knee arthroplasties failing today—has anything changed after 10 years? J Arthroplasty. 2014;29:1774-1778.
  2. Lonner JH, Lotke PA. Aseptic complications after total knee arthroplasty. J Am Acad Orthop Surg. 1999;7:311-324.
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