title: Anatomical and biomechanical evaluation of an intramedullary nail for fractures of proximal humerus fractures based on tuberosity fixation.
abstract: BACKGROUND
  For unstable proximal humerus fractures, both plates and nails may be recommended. We introduce an anterograde nail designed for the treatment of 3- and 4-parts proximal humerus fractures. The aim of this study is to compare the biomechanics of this nail versus a plate and then to analyze the relationships of the screws with the axillary nerve. Our working hypotheses are as follows: (1) this nail is biomechanically equal or better to the reference plate and (2) it does not endanger the axillary nerve.
  
  
  METHODS
  Biomechanical study: using 40 sawbones, a reproducible 4-part fracture was created and fixed first with an angle-stable plate for proximal humeral fracture, then fixed with the nail using 2 posterior screws. All specimens were mounted in a custom testing apparatus. Two trails were performed needing each time 5 "normal" and 5 "osteoporotic" bones.
  On 20 unpaired shoulders, a nail was inserted with all screws through a superior approach (deltoid split approach). Dissection of all shoulders was done to identify the axillary nerve. The distance between each screw and the axillary nerve or its branches was measured.
  
  
  RESULTS
  The proximal humerus nail demonstrated higher values than locking plate for both stiffness and load to failure. The failure mode differs in function of the type of osteosynthesis. The lowest distance between a screw and the axillary nerve was 20.13 mm.
  
  
  CONCLUSIONS
  We introduce a biomechanically efficient nail without increased neurological risks to improve the pullout strength of the screws to provide more secure fixation of proximal humeral fractures.
  
  
  METHODS
  Basic Science Study, Anatomic Cadaver Study.
authors.affiliation: Biomechanical Laboratory of the GEBOAS, Faculty of Medicine, Institute of Normal Anatomy, Fédération de Médecine Translationnelle, FMTS, 4 rue Kirschleger, Strasbourg Cedex 67085, France; Laboratoire d'Ingénierie des Surfaces de Strasbourg Groupe LISS du LGECO, EA3938, INSA Strasbourg, 24 boulevard de la victoire, Strasbourg Cedex 67084, France. Electronic address: philippe.clavert@chru-strasbourg.fr.
authors.forename: Ph
authors.initials: P
authors.lastname: Clavert
authors.affiliation: Department of Orthopedics, Western Orthopaedics, 1830 Francklin St., Denver, CO 80218 USA. Electronic address: armandhatzi@yahoo.com.
authors.forename: A
authors.initials: A
authors.lastname: Hatzidakis
authors.affiliation: Department of Orthopaedic Surgery and Sports Traumatology, Hôpital de L'Archet, University of Nice-Sophia-Antipolis, 151, Route de St Antoine de Ginestière, Nice 06202, France. Electronic address: Boileau.P@chu-nice.fr.
authors.forename: P
authors.initials: P
authors.lastname: Boileau
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001365:Axilla / Q000294:innervation; D001696:Biomechanical Phenomena; D001858:Bone Nails; D001860:Bone Plates; D002102:Cadaver; D005121:Extremities; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D006811:Humerus / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D009336:Necrosis; D012782:Shoulder / Q000294:innervation / Q000601:surgery; D012784:Shoulder Fractures / Q000601:surgery*
keywords: Biomechanics; Neurovascular injury; Proximal humerus fracture; Screw fixation; Shoulder