LOCKED STEMS FOR REVISION TOTAL HIP ARTHROPLASTY: RESULTS BY TYPE OF FIXATION

Abstract

Purpose: A consecutive series of 32 metaphyseal locked hydroxyapatite coated stems were reviewed at a maximum 5 years to analyse the effect of the type of distal (diaphyseal) and proximal (metaphyseal) fixation on clinical and radiological outcome (distal shaft fixation: tight or moderate; hydroxyapatite coating: complete or limited to metaphysic; approach: window or endofemoral).

Material and methods: Stems were used to treat femoral osteolysis (35% SOFCOT stage III and IV femoral loosening) with significant acetabular osteolysis (59% segmentary osteolysis and 47% revisions with structural allografts). Nineteen stems were implanted with a femoral window and 13 via endofemoral access. Twenty-six were screw locked. To study the effect of the type of fixation on clinical and radiographic outcome, we studied metaphyseal “regeneration”, and intraoperative diaphyseal anchorage. Anchorage was considered tight when the endosteum and the stem were in contact over at least 40 mm, and the difference in diameter between the stem and the endosteum was 1 mm or less. Anchorage was considered moderate when the height of contact was less than 40 mm and the endosteumstem difference in diameter was greater than 2 mm.

Results: The results were encouraging, with a clinical score (PMA) of 15/18, and stable diaphyseal fixation of the prosthesis in 31 hips (one migration of about 1 cm with secondary blockage in one non-locked stem). There were few complications: no infections, one isolated dislocation, one screw fracture, but three replacements of overly long stems, one trochanteric non-union which was not reoperated. In 22 hips with more than one year follow-up, shaft fixation of the stem was complete (no osteolytic lucent line), and a line of bone densification (particularly in hips with less solid anchorage) was seen in ten hips. There appeared to be bone regeneration around the hydroxy-apatite metaphysis in 50% of the cases. There were no cases of secondary osteolysis. This “regeneration” did not appear to be different after window or endofemoral replacement. It was the same with tight (63% of hips) or moderate anchorage. There was no stress shielding even when the distal stem was coated with hydroxyapatite.

Conclusion: It appears that good results can be obtained at mid-term with this type of prosthesis using a short distal (60 mm) fixation, limiting the diaphyseal escalation and requirement for femoral window.