title: The role of inter-prosthetic distance, cortical thickness and bone mineral density in the development of inter-prosthetic fractures of the femur: a biomechanical cadaver study.
abstract: It is becoming increasingly common for a patient to have ipsilateral hip and knee replacements. The inter-prosthetic (IP) distance, the distance between the tips of hip and knee prostheses, has been thought to be associated with an increased risk of IP fracture. Small gap distances are generally assumed to act as stress risers, although there is no real biomechanical evidence to support this. The purpose of this study was to evaluate the influence of IP distance, cortical thickness and bone mineral density on the likelihood of an IP femoral fracture. A total of 18 human femur specimens were randomised into three groups by bone density and cortical thickness. For each group, a defined IP distance of 35 mm, 80 mm or 160 mm was created by choosing the appropriate lengths of component. The maximum fracture strength was determined using a four-point bending test. The fracture force of all three groups was similar (p = 0.498). There was a highly significant correlation between the cortical area and the fracture strength (r = 0.804, p < 0.001), whereas bone density showed no influence. This study suggests that the IP distance has little influence on fracture strength in IP femoral fractures: the thickness of the cortex seems to be the decisive factor.
authors.affiliation: University Medical Center Hamburg-Eppendorf, Department of Trauma-, Hand- and Reconstructive Surgery, Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Weiser
authors.affiliation: University Medical Center Hamburg-Eppendorf, Department of Trauma-, Hand- and Reconstructive Surgery, Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: M A
authors.initials: MA
authors.lastname: Korecki
authors.affiliation: TUHH Hamburg University of Technology, Institute of Biomechanics, Hamburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Sellenschloh
authors.affiliation: University Medical Center Hamburg-Eppendorf, Department of Trauma-, Hand- and Reconstructive Surgery, Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Fensky
authors.affiliation: University Medical Center Hamburg-Eppendorf, Department of Trauma-, Hand- and Reconstructive Surgery, Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Püschel
authors.affiliation: TUHH Hamburg University of Technology, Institute of Biomechanics, Hamburg, Germany.
authors.forename: M M
authors.initials: MM
authors.lastname: Morlock
authors.affiliation: University Medical Center Hamburg-Eppendorf, Department of Trauma-, Hand- and Reconstructive Surgery, Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: J M
authors.initials: JM
authors.lastname: Rueger
authors.affiliation: University Medical Center Hamburg-Eppendorf, Department of Trauma-, Hand- and Reconstructive Surgery, Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Lehmann
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D015519:Bone Density; D002102:Cadaver; D005260:Female; D005264:Femoral Fractures / Q000175:diagnosis* / Q000503:physiopathology; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D058866:Osteoporotic Fractures / Q000175:diagnosis* / Q000503:physiopathology; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed
keywords: Femur; Inter-prosthetic Fracture; Inter-prosthetic distance; Peri-prosthetic Fracture