The aim of this paper is to present a new solution in treating osteoarthritis after congenital dysplasia. In the First Orthopaedic Clinic in Prague, we have obtained, by using oval-shaped cups, excellent results in the treatment of acetabular deficiency occurring in THA loosening. These positive results have also encouraged us to use the implants in THA for secondary coxarthrosis.

In severe acetabular defects, an endoprothesis is very difficult to implant. A whole range of methods has been described for fixing the acetabular component. We prefer not to use cemented implants with middle-aged patients. Methods using bulk bone grafts are being scaled down. Cup implantation to the neoacetabulum is disadvantageous because forces inherent to the hip joint are considerably higher in the superior lateral position. Cotyloplasty and controlled fracture impair the medial wall with the enhanced risk of implant protrusion to the pelvis. The implementation of an oval cup eliminates the above-mentioned disadvantages.

During the period of 1994 to 1998, we applied the LOR cup in treating secondary coxarthrosis eight times in six women (mean age: 54 years). 83% had already been operated for congenital hip dislocation. The stage of the dysplasia was classified as Crowe II in two hip joints, Crowe III in four, and Crowe IV in two. An average of four screws were used for a 52x64 cup. Mean follow-up was 4.8 years.

The mean Harris hip score at follow-up was 92 points. There were no infections, luxations, implant migrations, or screw failures. The radiograph evaluations revealed just one case of a translucent line 1 mm wide in the b,c zone. Osteointegration was perfect with the other implants.

Using the oval-shaped cup does not usually require implementation of bulk bone grafts. Implant shape and the option of implementing an eccentric inlay enables preservation of the rotational centre, which is advantageous in terms of biomechanics. Implantation of the cup is easy and fast. Because of the good results, we suggest introducing the oval-shaped cup as a standard method of THA primo-implantation with patients who have acetabular dysplasia. The LOR cup was designed as a revision implant, but a disadvantage is the insufficient size scale and the 32 insert. For widespread application, it is therefore necessary to design a smaller size 28 inlay cup. We are currently developing our own acetabular component with a more suitable size scale and a plasma-sprayed hydroxyapatite ceramic coating.