Introduction:

In Uruguay, all replacements have been registered by law since 1980. Instability is the second cause of revision in hip replacements.

Objective:

To know the incidence of instability, and its relationship with the surgical approach.

Material and methods:

Observational and analytical study of a historical cohort of 1,738 hip replacements conducted in 2014. Random sample stratified according to the surgical approach: posterior (AP) and anterolateral (AAL). All patients who had suffered any dislocation were identified, their incidence was estimated and bivariate and multivariate tests were performed, to identify factors related, associated with the patient, to the surgeon (surgical approach and experience), to the environment, and to the implant.

Results:

633 patients, minimum follow-up of three years and 16 patients with dislocation, with an incidence of 1.95% (95% CI: 1.14-3.31) in general, 1.4% (95% CI: 0.64-3.03) in AAL and 4.9% (95% CI: 2.67-8.83) in AP (p = 0.009, RR = 3.35). Factors associated with dislocation were: a) AP with an OR of 6.18 (CI 95%: 1.99-19.26); b) patient from the private health subsector with an OR of 13.74 (95% CI: 1.87-101.15); c) antecedent of hypothyroidism with an OR of 3.51 (IC 95%: 1.09-11.29); d) osteoarthritis secondary to inflammatory arthritis and dysplasia with an OR of 5.24 (CI 95%: 1.16-23.66); e) surgical center number three with an OR of 8.80 (CI 95%: 1.50-51.51).

Conclusions:

The incidence of early dislocation was within the usual ranges. Posterior surgical approach with increased risk of instability from preoperative risk factors.