One of the most common early complications after hemiarthroplasty is dislocation, with an incidence of 2 to 4%. After dislocation the mortality and morbidity are significantly increased to in excess of 50%.

It has been claimed that a bipolar hemiarthroplasty has a lower risk of dislocation than a unipolar implant. In addition it has been suggested that patients with either Parkinson’s disease or a previous stroke are at increased risk of dislocation. We investigated these claims by performing a comprehensive literature search of articles published in the last 40 years and data obtained from our own hip fracture database.

From the literature review, 133 reports involving 21,872 patients were retrieved. A further 1235 hip fractures treated by hemiarthroplasty were recorded from our database. 791 (3.4%) dislocations were recorded. Dislocation rate for unipolar prosthesis was higher than bipolar prosthesis (3.9% versus 2.5%). Dislocation rate for posterior surgical approach was higher than for anterior approach (5.1% versus 2.4%). Dislocation rate for cemented prosthesis was 3.6% versus 2.3% in un-cemented prosthesis. However, the effect of the type of implant becomes non-significant on adjusting for the use of cement and surgical approach. The incidence of open reduction after dislocation was increased with bipolar implants. Patients with Parkinson’s disease showed a highly statistically significant increase in dislocation rate (8.7% to 3.4%). The dislocation rate with respect to ipsilateral hemiplegia was 1.6%.

This study indicates there is no difference in the dislocation rate between a unipolar and bipolar prosthesis but if a bipolar prosthesis dislocates, there is an increased risk of failure to reduce the prosthesis by closed means. Patients with Parkinson’s disease are at an increased risk of dislocation but this is not the case for those with a hemiplegia. To minimise the risk of dislocation of a hemiarthroplasty, particularly in those patients with Parkinson’s disease, a unipolar hemiarthroplasty inserted via an antero-lateral approach is recommended.