RESUMO
BACKGROUND: Dislocation of primary THA (total hip arthroplasty) is one of the most undesirable complications with an incidence ranging from 2% to 5%. Several risk factors are described, related to the patient, surgery, or prosthetic design. The aim of the study was to assess risk factors and their potential influence on dislocation. MATERIALS AND METHODS: 387 primary THA were performed between September 2005 to December 2008 at our institute (Varese, Italy) through a modified posterior-lateral approach. Clinical evaluation was based on range of motion (ROM) and Harris Hip Score; femoral offset, acetabular inclination, and anteversion were measured on plain radiograms. Data were analyzed by SPSS software (SPSS, Inc., Chicago, Illinois). RESULTS: Excellent ROM and Harris Hip Scores were achieved in more than 95% of patients (p<0.05). The offset was restored in all patients. Most of the cases had their cup positioned in the "safe zone" (both inclination and anteversion). Six dislocations (1.87%) occurred: significant correlation was found between dislocation and preoperative diagnosis of femoral neck fracture. CONCLUSIONS: THA dislocation rate appears not to be related to patient biometric parameters and prosthesis design. Femoral neck fracture is reported as the major risk factor for this complication, probably caused by higher preoperative activity and lesser compliance of the patient.