Patellar instability following total knee replacement -- the dangers of constant design evolution.

Patellar instability following total knee replacement although infrequent can cause disabling symptoms. We report a case of symptomatic patellar instability caused by insertion of left femoral component into a right knee. We highlight that all members of the surgical and theatre team need to be familiar both with the implant equipment and of any recent design modifications, particularly if they have been used to using one system for a long time, in order to prevent surgical errors. In addition this possibility should be born in mind by surgeons looking for causes of post-operative patellar instability.