Abstract
The purpose of this study was to evaluate the reasons for patellar instability in modular rotating hinge TKR, with regards to design of the prosthesis offering unlimited rotation, component positioning and the role of compromised soft tissues.
We reviewed six patients with rotating hinge TKR operated over the past 3½ years for either ligamentous instability, bone loss or both. The problem of patellar instability was identified in all patients. Five patients had realignment of extensor mechanism for patellar maltracking, while the remaining one patient with patellar instability was asymptomatic.
Post-realignment the HSS scores revealed good results in 3 knees, fair in 2 and poor in 1 patient. All patients had a well aligned knee with satisfactory component positioning.
The unlimited rotation offered by the modular rotating hinge TKR because of the absence of a rotational stop causes excessive demands on the soft tissue and is a reason for patellar instability in patients with compromised medial soft tissue integrity.
The high incidence of patellar instability compromises the results of TKR and is a cause of concern and this implant should be reserved for patients with severe ligamentous instability and bone loss not amenable to ligament balancing.
The abstracts were prepared by Mr Roger Smith. Correspondence should be addressed to him c/o British Orthopaedic Association, Royal College of Surgeons, 35-42 Lindoln’s Inn Fields, London WC2A 3PN.
