Unusual Patellar Problems after Total Knee Replacement Surgery

A 76-year old woman in England isn't getting the most out of her total knee joint replacements. She had both knees replaced six years ago. Her left kneecap (patella) was getting way off track, but not quite dislocating. This is called subluxation. In fact, both her patellae have this problem. The left subluxes most often, but the right actually dislocates.

She's had several falls right onto her knees. Both knees hurt, and she's having trouble getting up and down stairs. Her doctors found the case interesting enough to write it up as a case report. There are no other reports like this in the medical journals. After a thorough exam and X-rays, here's what the doctors found.

When the new joints were put in, the upper half of the implant probably wasn't rotated quite enough. This set the woman's patellae slightly off track. She had an operation to cut a band of fibrous tissue along the outside (lateral side) of her knees. This procedure, called lateral release, often helps even out the pull on the patella and helps them track more in the middle.

The lateral releases didn't help. The patella subluxation got worse. The doctors used an arthroscope to look inside her knee joints. They found the patellae had come apart. When the knee replacement is done, sometimes a plastic insert is attached to the back of the patella. The insert had separated from the patellae. This is called patellar dissociation.

The doctor removed the insert but left the patellae in place. The undersides of the patellar bones were covered with fibrous tissue and cartilage. This is a normal finding, so nothing more was done to them. The patient had a rapid recovery from the operation. She was much better after rehab was done to strengthen the muscles and improve patellar tracking.

The doctors who wrote this case report say this case really shows the benefits of arthroscopic surgery. Using this tool to look inside the knee joint helped them find and fix the problem.


Ilias Bisbinas, MSc, FRCS, FEBOT, et al. Case Report: Bilateral Patellar Component Dissociation in a Patient with Total Knee Arthroplasties. In Arthroscopy. October 2003. Vol. 19. No. 8. Pp. 21-24.


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