Abstract
Introduction
The dual mobility cup was introduced in the 1970s to allow extensive range of motion associated with great stability thanks to double articulation; the first between the head and polyethylene, the second between the polyethylene and the cup.
The original plan was to install a stainless-steel uncemented cup coated with a thin layer of alumina and a metal head of 22,2 mm with a polyethylene liner of first generation.
Long term follow-up case studies are cited in the literature showing excellent results in reducing dislocations; however wearing and aseptic loosening are noted.
The new dual-mobility cups, with reticular polyethylene and titanium and hydroxyapatite coating are proving as reliable as the older ones in terms of stability whilst they appear to be more durable.
Furthermore, cemented dual-mobility cups are available, these are the topic of this study. One of the most frequent complications in the major revisions of hip replacement is dislocation. This study summarises our experience gathered in the use of dual-mobility cups during revisions of complex cases (GIR III-IV femoral or acetabular).
Materials and Methods
Between July 2014 to March 2015, we have implanted 13 cemented cups with dual-mobility (Avantage® Biomet) each in different patients, who have undergone revision with severe ostheolysis (GIR III-IV femoral or acetabular). The mean age of patients was 71.5 years old (46 to 89).
Indications for revisions were: aseptic loosening in 7 patients (two at third surgery), recurrent dislocation in 3 patients, 1 septic loosening, 1 revision after spacer removal e 1 post-traumatic.
We used dual-mobility cup in revision surgery when implant stability could have been compromised due to difficult positioning of acetabular component in cases of walls defects or muscolar laxity. The patients have been evaluated clinically and radiographically.
Results
In most difficult cases with a severe lack of acetabular walls (9 patients), and thus difficulties in correct cup positioning, we have choosen to implant a cemented cup inside a Burch-schneider® (Zimmer) ring; in those cases where acetabular morphology was still sufficient, a dual-mobility cup was directly cemented to the bone.
No dislocations occured during the folllow-up, neither infections, neurological events or DVT.
Discussion
Dual mobility cups are often used both as primary implant or as a revision cup. Dislocation rate in primary total hip replacement is comparable to other kind of cup normally used, while in revision cases, the incidence of dislocation decrease from a range of 5–30% to 1,1–5,5%.
Our results are not yet comparable to those in literature due to short follow-up, but first impressions are comforting thanks to the lack of dislocation even in really severe cases.
Conclusions
The dual-mobility cup in acetabular revisions, is one of the possible choice to keep in mind in more complex cases, where obtaining stability is difficult or impossible using other revision implants.
In the literature, the available follow up are not yet long enough to be sure of implant longevity and so it's important to pay attention to use this cup in those patients with long life expectancy.
