title: Biomechanical measurements of cortical screw purchase in five types of human and artificial humeri.
abstract: Humerus shaft fracture fixation is largely dependent on cortical screw purchase in host bone. Only 2 prior studies assessed cortical screw purchase in human humeral shafts, but were of very limited scope and did not fully assess humerus material properties. Also, no studies evaluated the human dried or artificial humeri both commercially available from Sawbones. Vashon, WA, USA. Therefore, present authors measured cortical screw purchase in human fresh-frozen (FF) (n=19), human embalmed (EM) (n=18), human dried (DR) (n=14), artificial "normal" (AN) (n=13), and artificial "osteoporotic" (AO) (n=13) humeri. Each humerus had 2 bicortical screws of 3.5-mm diameter inserted 20mm apart through the shaft's anterior and posterior cortices. Absolute force, displacement, and energy for screw-bone interface failure were measured by screw pullout tests, afterwhich data were normalized by total surface area engaged at the screw-bone interface. For absolute force, AN humeri reached a higher load than EM (p=0.001) and AO (p<0.001) humeri, whilst AN humeri achieved lower normalized force than DR humeri (p=0.018). For absolute displacement, AO humeri achieved a lower level than FF humeri (p=0.013), whilst for normalized displacement AN humeri had lower levels than all other groups (p≤0.005) and AO humeri had lower values than EM humeri (p=0.029). For absolute and normalized energy, there were no statistical differences (p≥0.066). Human bone mineral density (BMD) ranged from 0.7 to 1.8g/cm(2) and was linearly correlated to screw pullout parameters in 14 of 18 cases (R=0.61 to 0.96), whilst humerus age was not. Consequently, it is recommended that human fresh-frozen, human embalmed, and human dried humeri can be used interchangeably for cortical screw purchase, since they were statistically equivalent for all comparisons. However, artificial humeri were involved in all statistical differences observed and, thus, may not replicate cortical screw purchase in human humeri. To date, this is the most comprehensive study on cortical screw purchase in human and artificial humeral shafts.
authors.affiliation: Martin Orthopaedic Biomechanics Lab, St. Michael's Hospital, Toronto, Canada M5B 1W8; Institute of Medical Science, University of Toronto, Toronto, Canada M5S 1A8.
authors.forename: Mina S R
authors.initials: MS
authors.lastname: Aziz
authors.affiliation: Martin Orthopaedic Biomechanics Lab, St. Michael's Hospital, Toronto, Canada M5B 1W8.
authors.forename: Bruce
authors.initials: B
authors.lastname: Nicayenzi
authors.affiliation: Martin Orthopaedic Biomechanics Lab, St. Michael's Hospital, Toronto, Canada M5B 1W8.
authors.forename: Meghan C
authors.initials: MC
authors.lastname: Crookshank
authors.affiliation: Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada M5B 2K3.
authors.forename: Habiba
authors.initials: H
authors.lastname: Bougherara
authors.affiliation: Martin Orthopaedic Biomechanics Lab, St. Michael's Hospital, Toronto, Canada M5B 1W8; Department of Surgery, Faculty of Medicine, University of Toronto, Toronto, Canada M5S 1A8.
authors.forename: Emil H
authors.initials: EH
authors.lastname: Schemitsch
authors.affiliation: Martin Orthopaedic Biomechanics Lab, St. Michael's Hospital, Toronto, Canada M5B 1W8; Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada M5B 2K3. Electronic address: zderor@smh.ca.
authors.forename: Radovan
authors.initials: R
authors.lastname: Zdero
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal; D006801:Humans; D006810:Humeral Fractures / Q000503:physiopathology / Q000601:surgery; D006811:Humerus / Q000293:injuries / Q000503:physiopathology; D008297:Male; D008422:Materials Testing; D055595:Mechanical Phenomena; D008875:Middle Aged
keywords: Artificial; Biomechanics; Cortical screw; Human; Humerus; Pullout; Purchase