Locking mechanism failure between tibial baseplate and polyethylene insert in cruciate retaining total knee arthroplasty.

We describe a case of total knee arthroplasty performed with one type of cruciate retaining knee prosthesis (Vanguard CR, Zimmer Biomet), wherein failure of locking mechanism occurred between the tibial baseplate and the polyethylene insert 10 months after initial surgery. While there are very few case reports in literature describing such locking mechanism failure, all of these have been in constrained and posterior stabilized knees. This case, to the best of our knowledge is the first such case seen with a cruciate retaining knee design. A 73-year old lady, having undergone left total knee arthroplasty with the above-mentioned prosthesis, presented 10 months after the index surgery with a 3-week history of worsening knee pain and medially protruding hardware. She mentioned an episode of minor twisting of her knee after which she developed pain and swelling over the medial aspect, and was found to have the locking bar backed out on X-rays. She underwent revision surgery, wherein the locking bar was found to have buttonholed through the medial capsule. She underwent polyethylene liner exchange, with a new locking bar. There was no evidence of infection. Her symptoms fully settled following revision surgery.