[Total hip arthroplasty with shortening subtrochanteric osteotomy and custom-made prosthesis in Crowe type IV developmental dysplasia]

AIM

Total hip arthroplasty in patients with a Crowe type IV developmental dysplasia is a technically demanding procedure with a higher complication rate compared to a standard total hip replacement. Specific anatomic features and the necessity of a femoral shortening osteotomy are the reasons for more complications. In this retrospective study we intended to find out whether the use of a custom-made stem based on a CT scan will lead to a better outcome including a lower complication rate. MATERIAL UND METHOD: From 2003 to 2010 we implanted a cementless CTX® individual stem in combination with a subtrochanteric Z-shaped shortening osteotomy in 25 patients with a high hip dislocation, four of them were men (one bilateral) and 16 women (four bilateral). Mean age of the patients was 44.6 years. In all cases the cup was implanted at the level of the anatomic hip centre. Patients were followed with a clinical and radiographic assessment. The morphology of the femur was analysed by CT scans.

RESULTS

The average amount of femoral shortening was 3.4 cm (max. 4.2/min. 2.6 cm). Lengthening of the leg was achieved with an average of 3.8 cm (max. 4.4/min. 3.2 cm). The remaining leg length discrepancy was 0.8 cm (max. 1.2/min. 0.4 cm). In none of the cases did an intraoperative fracture of the femur occur, either in the proximal or in the distal part of the femur. Enlargement of the intramedullary canal was not necessary in any case. The planned depth of the prosthesis could be achieved in all patients. We did not observe any problems with wound healing in our patients. The average Harris hip score was 90 (83 up to 100). Additional cerclage wires are not necessary with this technique when the osteotomy is well adapted. After complete healing the osteotomy can just be noticed by a certain hypertrophy of the cortical bone. In our cases we had a complication rate of 16 %, significantly lower in comparison to literature values.

CONCLUSIONS

Total hip arthroplasty in type IV developmental dysplasia with a custom-made stem based on a CT scan is a procedure that respects the special anatomic features preoperatively und is able to correct the deformity with the individually manufactured prosthesis. High femoral anteversion is corrected at the level of the neck of the stem. There is no necessity for a derotation at the level of the osteotomy. The osteotomy is stabilised by the Z-shape and through a perfect intramedullary fit of the stem. The anatomic shape of the subtrochanteric region is perfectly suitable to perform a femoral shortening.

[In-vivo wear of the slide combinations ceramics-polyethylene as opposed to metal-polyethylene]

The present study deals with long-term dimensional changes in cemented Müller-type total hip endoprostheses. Creep and wear contribute to different extents to the dimensional changes in polyethylene. The total amount of polyethylene wear is represented by the displacement of the femoral head into the socket. Within the first postoperative years, the head shifts up to a relatively high rate of about 0.5 mm per year. This rate diminishes after 5 years to an average of about 0.1 mm (ceramics) and 0.2 mm (metal) per year. Values exceeding 0.2 mm per year for the shift of the femoral head are considered to be unfavourable with regard to a probable loosening of the prosthesis. In this study we determined the orientation of the centre of the prosthetic head in relation to the wire marker of the polyethylene cup, comprising in all 369 total hip prostheses. After an average of 77 months, 96% of the prostheses with ceramic heads (n = 109) had a wear rate of less than 0.2 mm per year. Using metal heads (Protasul-2 and Protasul-10) this rate could only be measured in 71% (n = 109) of the prostheses (61.5 months). The combination ceramics-polyethylene produces half of the total amount of wear produced by metal-polyethylene. Younger patients should preferably be treated with a ceramic ballhead.