There are some special features involving replacement surgery of totally dislocated or severely dysplastic hips (Eftekhar Stage C and D). To achieve abduction strength strong enough to balance the pelvis and reliable fixation of the acetabular component, the cup must be seated near the anatomic level or even lower. Therefore, the femoral component in most cases is to be mounted below the intertrochanteric level in order to get the prosthesis reduced and the greater trochanter with intact attachment of the gluteus medius muscle distally advanced. At these levels the femoral diaphysis is straight and requires a straight stem. We started these techniques over 15 years ago with Lord’s madreporic prosthesis, but the stem – especially the calcar part – was too curved. A totally straight cementless, collared stem was designed with Biomet Inc. and has been used since 1988.

For this stem the femur was prepared with broaches, but it was far too easy to get a proximal split when rasping the cortical bone or inserting the stem. For this reason a new stem with a tapered, oval proximal part was designed in 1993. The femur is prepared with reamers and no broaches are needed. Because the stem is collarless, vertical/rotational stability is achieved by the oval wedge shape of the proximal stem, and not by the collar. Therefore, rotational instability and loosening of the stem are avoided.

We present the operative methods. The collarless stem has been used since 1993 in 58 hips of 43 patients. Mean age of the patients was 54 years (range: 21 to 71). Only six of the patients were men. The most common cause of hip deformity was DDH (47 hips). Five hips had congenital coxa vara, two cases had tuberculosis of the hip, and two patients had diastrophic dysplasia. There was one arthrogryphosis multiplex patient and one congenital proximal femoral deficiency. Schanz osteotomy had been performed in 11 of the DDH cases. Forty-four of the 47 DDH hips were high dislocations (Eftekhar C or D).

Complications: There were three dislocations, three late fractures of the greater trochanter fixed with a hookplate, two splits of the proximal diaphysis fixed with a cable, and one late fracture dislocation revised with a collared stem. Deep infection occurred in one case and removal of the prosthesis was necessary. In two cases the stem migrated 3 to 7 mm but stabilised spontaneously with osteointegration. In one case the stem migrated 15 mm. Fibrous union remained, but it is painless.

The final outcome was good in all other cases, but the patient with deep infection is waiting for a rearthroplasty, and the case with fibrous union is likely to be revised when it becomes symptomatic. Pain relief and the functional results including improvement of gait and abduction strength were generally good. Most of the patients were highly satisfied.