Abstract
Large articulations are increasingly being used to reduce dislocation, the most common early complication following THR. However, potential benefits of large articulations in reducing dislocation have not been proven in a well-controlled clinical trial.
The aim of our randomised controlled trial was to compare the one-year incidence of dislocation between 36 and 28 mm metal on highly cross-linked polyethylene articulations.
Patients were excluded if they had a high risk of dislocation due to, for example, abnormal anatomy, neuromuscular disease, previous infection or dislocation. Eligible patients were stratified according to a number of other factors which may influence dislocation risk, including primary or revision THR and, if primary THR, by surgeon, age, diagnosis, sex and Charnley grade. Patients were randomised intra- operatively to either a 28 or 36 mm articulation. Dislocation incidence was determined using a hip instability questionnaire and a hospital visit questionnaire. A dislocation was diagnosed if there was radiological evidence and reduction by a doctor was required. Six-hundred-and-forty-four patients undergoing primary or revision THR were entered into the study.
Overall, the incidence of dislocation at one year following THR was 5.4% with a 28 mm articulation and 1.3% with a 36 mm articulation (p=.004). Incidence in primary THR patients was 4.4% with a 28 mm articulation, compared to 0.8% with a 36 mm articulation (p=.007). Incidence in revision THR patients was 12.2% and 4.9% with 28 and 36 mm articulations, respectively. For both primary and revision THR patients, sex distribution, age and BMI of patients who dislocated were similar to those of the total samples of primary or revision patients.
This large randomised study unequivocally shows for the first time that, compared to a 28 mm articulation, a 36 mm articulation in THR is efficacious in reducing the incidence of dislocation in the first year following THR.
