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[Is there a need of an additional extramedullary fixation in transverse subtrochanteric shortening in primary total hip arthroplasty for patients with severe hip dysplasia? Short-term experience in seven patients with congenital dislocation].

AIM
Total hip arthroplasty for high developmental hip dislocations should restore the anatomic hip centre by implanting the acetabular cup in the true acetabulum. The normalisation of the position of the hip may require femoral shortening to avoid the risk of neurological traction injury. In this study group a subtrochanteric transverse shortening with a cement-free stem (Alloclassic-SL) with a rectangular square diameter was used to secure rotation stability.


METHOD
With this technique seven primary hip arthroplasties were performed in Crowe grade types III and IV. The age at time of operation averaged 41.7 years (range: 29 to 64 years). Average follow-up was 18 months. An average subtrochanteric resection of 4.2 cm (range: 3 to 5 cm) by a transverse subtrochanteric osteotomy without external fixation was performed.


RESULT
There was one symptomatic stem loosening 15 months postoperatively. The average Harris hip score preoperatively of 43 points (range: 29 to 61 points) improved to a mean of 77 points (range: 66 to 90 points) at the time of follow-up. The hemispherical cups were implanted in all cases at the place of the original acetabular site. Meanwhile, there was no loosening on the acetabular side. All transverse osteotomies healed with evidence of union at the osteotomy site. At the last follow-up six of the seven Alloclassic-SL stems presented a secondary osseointegration.


CONCLUSION
The subtrochanteric transverse shortening osteotomy in total hip arthroplasty is a safe and predictable method for restoring the anatomic centre in high development hip dislocation. The intramedullary stability will be secured by the distal rotation stability of the inherent cross-sectional geometry of this stem design without external stabilisation. A Z-shaped osteotomy of the subtrochanteric shortening or additional augmentation with allograft struts and cables is not necessary.