The impact of proximal femoral morphology on failure strength with a mid-head resection short-stem hip arthroplasty

Abstract

Mid-head resection short-stem hip arthroplasty is a conservative alternative to conventional total hip replacement and addresses proximal fixation challenges in patients not suitable for hip resurfacing. It is unclear whether proximal femoral morphology impacts the ultimate failure load of mid-head resection implanted femurs, thus the aim of this study was to investigate the effect of native neck-shaft angle (NSA) and coronal implant alignment on proximal femoral strength. In total, 36 synthetic femurs with two different proximal femoral morphologies were utilized in this study. Of them, 18 femurs with a varus NSA of 120° and 18 femurs with a valgus NSA of 135° were each implanted with a mid-head resection prosthesis. Femurs within the two different femoral morphology groups were divided into three equal coronal implant alignment groups: 10° valgus, 10° varus or neutral alignment. Prepared femurs were tested for stiffness and to failure in axial compression. There was no significant difference in stiffness nor failure load between femurs implanted with valgus-, varus- or neutrally aligned implants in femurs with a NSA of 120° (p = 0.396, p = 0.111, respectively). Femurs implanted in valgus orientation were significantly stiffer and failed at significantly higher loads than those implanted in varus alignment in femurs with a NSA of 135° (p = 0.001, p = 0.007, respectively). A mid-head resection short-stem hip arthroplasty seems less sensitive to clinically relevant variations of coronal implant alignment and may be more forgiving upon implantation in some femoral morphologies, however, a relative valgus component alignment is recommended.

Femoral neck prostheses: A systematic analysis of the literature

“…were able to show, that implanting a femoral neck prosthesis in valgus angle acts protective against the occurrence of periprosthetic fractures. 15 The biomechanical advantage of a valgus angle (a minimum of 10° of relative valgus) is on the one hand the increase of compressive forces of the proximal femur and on the other hand simultaneously reducing sheer forces acting upon the femoral neck. 15,43…”

“…Furthermore, Olsen et al could show that there is high correlation between bone mineral density (BMD) of the femoral neck and resulting fracture loads. 15 BMD was thus considered as a prognostic factor regarding patient’s preselection. 15 In addition, implant size correlated negatively with fracture load.…”

“…15 BMD was thus considered as a prognostic factor regarding patient’s preselection. 15 In addition, implant size correlated negatively with fracture load. 15,43 Whereas, Aghayan et al .…”

“…15 In addition, implant size correlated negatively with fracture load. 15,43 Whereas, Aghayan et al . found a positive correlation between implant size and fracture load.…”

“…Valgus angle (a minimum of 10° of relative valgus) and good BMD were considered to be crucial for primary stability. 15,43 Bone mineral density of the proximal femur seems to be less affected when using femoral neck prostheses compared to conventional implants. 19…”