XXXX of cementless femoral stems at the mid-stem junction in modular revision hip arthroplasty systems.

@entity1 @entity13843 @entity1295 @entity174
BACKGROUND: Mechanical failure of femoral stems at the modular junction of revision hip arthroplasty systems has been reported only infrequently. In the current study, the cause of six stem @entity174 , which occurred in vivo, was analyzed with use of clinical data and failure analysis. METHODS: Six @entity1 with a @entity174 at the mid-stem junction of a modular revision hip implant were identified in our database of @entity1 who had undergone revision arthroplasty. The characteristics of the @entity1 with a fractured stem were compared with those of 165 @entity1 from the same prospective database who had a modular stem implanted, had at least two years of follow-up, and had not had a @entity174 of the stem. Failure analysis of three implants (six @entity174 surfaces) was carried out, with use of microscopic, chemical, and microhardness characterization techniques. RESULTS: @entity1 with a fractured stem had significantly higher body mass indices than @entity1 without a stem @entity174 . Radiographs demonstrated that these femoral implants lacked adequate osseous support of the junction area of the stem. All stems failed approximately 1 to 2 mm proximal to the body-stem junction, thus indicating the presence of a bending moment. The chemical composition and microhardness matched those of @entity13843 . Evidence of wear and @entity1295 were found on the @entity174 surface. A wear strip was also observed along the circumference of the stem near the junction. CONCLUSIONS: We concluded that the stem failure was initiated by a fretting @entity1295 mechanism and was propagated by a pure bending @entity1295 mechanism. Risk factors for @entity174 of the modular junction include excessive body weight and inadequate proximal osseous support because of trochanteric osteotomy, reduced preoperative bone stock, osteolysis, loosening, and/or implant undersizing. Surgeons should consider the use of implants with strengthened junctions when using modular stems in such @entity1 .
