"The Disappearing Patella": an unusual sequel following total knee replacement

Patello femoral complications have been described following total knee replacement (TKR) surgery. Majority of the reports are on the position and the biomechanics across the patello femoral joint. An unusual finding which shows the patella to be gradually disappearing following a TKR has not been reported. We report this finding in a 74-year-old lady who underwent a right total knee replacement (TKR) 5 years ago. Check radio graphs taken at 2 years showed osteolysis and on follow up at 5 years the right patella has become very thin and appears to be disappearing. The right patella measured 17 mm (anterior posterior thickness) at time of surgery and now measures 4 mm. There is osteolysis adjacent to the tibial and femoral components. However, there are no features of infection and there is no history of trauma. The patient continues to be asymptomatic and mobilises with a normal pain free gait. This interesting and unusual sequel is being reported for its rarity. A similar finding following a TKR has not been cited in literature.