Abstract
Introduction: Instability of THR is a problem both for the patient and the surgeon. Its frequency varies from 3 to 20% in multioperated patients. When the cause is known treatment usually gives good results and one way of preventing dislocation is to increase the size of the prosthetic head. The cause for instability is multifactorial and sometimes the patients have predisposing factors: muscular weakness or neurological alterations that determine the need for constrained and bipolar cups.
Materials and methods: Constrained cups capture the prosthetic head preventing dislocation and studies have been published with widely differing results. The bipolar cup introduced by Busquet is based on a metal cup coated with hydroxyapatite that is fixated by means of 2 plots to the ischium and the pubis. The polyethylene insert captures a head of 22.2 or 28 mm. Dislocation, when it takes place, is between the metal cup and the insert, and a force much greater than that needed to dislocate a head of 22.2 or 28 mm in diameter is needed.
Results: In a multi-center study carried out on 238 bipolar cups, Leclerc reports a 3.3 % failure rate. Philippot using 106 bipolar cups, reports no dislocation and a survival of 94.6% at 10 years. Our personal series comprised 75 cases, (54 primary and 21 revisions) with only one episode of dislocation due to significant trauma.
Conclusions: The bipolar cup can be used in primary and revision surgery and is effective in decreasing dislocations in high-risk patients and is our option of choice in patients with neuromuscular alterations or multiple surgeries.
The abstracts were prepared by E. Carlos Rodríguez-Merchán, Editor-in-Chief of the Spanish Journal of Orthopaedic Surgery and Traumatology (Revista de Ortopedia y Traumatología). Correspondence should be addressed to him at: Sociedad Española de Cirugía Ortopédica y Traumatología, calle Fernández de los Ríos 108, 28015-Madrid, Spain
