الفهرس 
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Abstract
Intertrochanteric fractures occur in the transitional bone between the femoral neck and the femoral shaft. These fractures may involve both the greater and the lesser trochanters. Transitional bone is composed of cortical and trabecular bone. These bone types form the calcar femorale posteromedially, which provides the strength to distribute the stresses of weight bearing. Consequently, the stability of intertrochanteric fractures depends on the preservation of the posteromedial cortical buttress. (1)
With the increase of the average life expectancy, fractures of the proximal part of femur have been marked as one of the biggest problems of the contemporary civilization. The patients with this type of fracture occupy at least 30% of beds in the orthopaedic institutions, intertro-chanteric fractures are around four times more frequent than the fracture of the proximal part of the femur, and they are a usual occurrence in older patients, above 65 years of age, when there is far greater loss of the skeletal mass (osteoporosis). (2,3)
The goal of treatment remains the return of patient to his or her preoperative status in earliest possible time with low morbidity and mortality and with the least cost and to ensure motion in the appropriate time.(4)
Management of intertrochantric fracture can be conservative (as traction) or surgical. Operative management of intertrochanteric fractures consists of many methods either by open reduction and internal fixation with nails or plates, or by external fixator or by arthroplasty.(5)
Arthroplasty has been used for unstable intertrochanteric fractures since 1971 and then there are several studies indicating the effectiveness of arthroplasty as the primary treatment for unstable osteoporotic intertrochanteric fractures and in failed internal fixation in elderly patients.(6)
Instability is an extremely significant cause of morbidity following Total Hip Replacement (THR). The incidence of instability after primary and revision replacement has been reported to be as high as 7% and 25%, respectively(6). The cumulative risk of first time dislocation is 2% at one year and 7% after 25 years of primary hip replacement. (7)
The concept of dual mobility articulation was developed in 1970 by Bousquet to increase the range of motion and to decrease dislocation risk.
In order to increase the stability while avoiding the excessive stress on the cup/bone interface that invariably occurs in fully constrained systems, Bousquet in France designed the “double mobility cup” in 1976.
This system consists of a combination of two apparent joints, one large unconstrained joint between the metal cup and the liner, and a smaller constrained joint between the liner and a standard metallic head that is attached to the femoral component. As such, the large diameter of the unconstrained joint (i.e. effective head size) theoretically reduces the risk of dislocation. Nevertheless, many surgeons have been hesitant to use tripolar cups due to fears of excessive polyethylene wear. In vitro studies have shown that large metal-polyethylene friction surfaces are associated with increased polyethylene wear rates. However, these studies are based on experimental models using standard THA with various head sizes.(8)
The dual-mobility cup is a tripolar cup with a fixed porous-coated or cemented metal cup, which articulates with a large mobile polyethylene liner .Into the latter, a standard head (usually 22 or 28 mm) is inserted. (Fig. 1).