Girdlestone resection arthroplasty for femoral neck fractures has poorer outcomes than hemiarthroplasty in frail patients with increased risk for arthroplasty-related complications : a retrospective case study of 21 patients / Petri Bellova, Marcus Linne, Anna Elisabeth Postler, Klaus-Peter Günther, Maik Stiehler, Jens Goronzy