REDUCED FRACTURES AND STEM SUBSIDENCE AT SIX MONTHS WITH COLLARED STEMS IN DIRECT ANTERIOR CEMENTLESS TOTAL HIP ARTHROPLASTY

Many femur fractures in total hip arthroplasty (THA) occur during advancement of the final stem, especially during a direct anterior approach (DAA). Calcar collars are a re-emerging trend among cementless stem designs which may reduce fracture risk by both preventing subsidence and acting as an intraoperative cue for sufficient stem advancement. We hypothesize that collared femoral stems have lower risk of intraoperative and post-op periprosthetic fracture and stem subsidence compared to collarless designs in DAA THA at 6 months. A retrospective review of 348 DAA THAs on a Hana table performed from 2017–2020 by a single surgeon, fellowship trained in arthroplasty, was done. Three cementless stems with similar broach systems were studied: Zimmer ML Taper, Avenir & the Avenir-Complete with a collar. Only patients with Dorr A or B femurs received cementless THA. Incidence of intraoperative fractures and post-operative Vancouver AL/B fractures within 6 months were recorded. Radiographic stem subsidence was measured and compared at 6-months by the attending surgeon and 2 independent observers. Routine 3-dimensional post-operative imaging to quantify subsidence was not feasible at our institution. Fisher-Exact test was used to compare outcomes between the collared vs non-collared designs with p 3mm was deemed clinically significant based on prior studies for similar broached stems. Both groups were comparable in sex, smoking history, diabetes, Dorr type and BMI. Patients with the collared stem had significantly fewer femur fractures compared to collarless stem designs (0/99 vs. 11/249) (p=0.043). 3 patients had intra-operative calcar cracks requiring cerclage and 8 required revision post-op. Radiographic subsidence >3 mm was also significantly lower in the collared stem group (p < 0.001) at 6 months. No statistically significant differences were observed in infection (p=0.55), hematoma formation (p=0.10), or wound complications (p=0.47). The use of collared cementless femoral stems in DAA THA resulted in significant reduction in periprosthetic femur fractures and subsidence compared to collarless stems. This was likely due to the collar acting as an intraoperative and post-operative calcar stop against over-advancement in the canal. There were no cases of early loosening with any of the stems. A prospective multi-surgeon study comparing collared and collarless versions of the Avenir-complete stem would yield stronger data. Subsidence would be more reliably measured with 3D imaging and radiostereometry. Implementing collared femoral stem designs may lead to further cost-savings and lower fracture rate in patients undergoing DAA THA.