title: Biomechanical comparison of pull-out force of unicortical versus bicortical screws in proximal phalanges of the hand: a human cadaveric study.
abstract: BACKGROUND
  Bicortical fixation of proximal phalangeal fractures may damage underlying flexor tendons secondary to drilling and screw protrusion in the dorsal-ventral direction. The aim of this study was to measure and compare the pull-out force of unicortical screws compared to bicortical screws in human cadaveric proximal phalanges to identify optimal configuration for internal fixation.
  
  
  METHODS
  Forty proximal phalanges were harvested. Bicortical and unicortical self tapping 1.7mm screws were inserted into paired phalanges at the distal and proximal metaphysis and at the mid-diaphysis placed in the dorso-ventral direction. Pull-out force of unicortical and bicortical screws were measured and compared.
  
  
  RESULTS
  Bicortical screw pull-out force is significantly higher than that of unicortical screws in the dorsal-ventral direction. Pull-out strength of unicortical screws at the mid-diaphysis was significantly higher than the pull-out strength of bicortical screws at the proximal metaphysis (181.8N versus 31.5N, P<0.0001).
  
  
  CONCLUSIONS
  Diaphyseal fixation is stronger than metaphyseal for both unicortical and bicortical configurations. Unicortical mid-diaphyseal is stronger than bicortical proximal metaphyseal screw pull-out strength. This study provides biomechanical data that may be helpful for individualizing fracture fixation techniques at the proximal phalanx.
authors.affiliation: Birmingham Hand Centre, University Hospital Birmingham, Selly Oak Hospital, Birmingham, UK.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Khalid
authors.forename: Kanthan
authors.initials: K
authors.lastname: Theivendran
authors.forename: Mubashir
authors.initials: M
authors.lastname: Cheema
authors.forename: Vaikunthan
authors.initials: V
authors.lastname: Rajaratnam
authors.forename: Subodh C
authors.initials: SC
authors.lastname: Deshmukh
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D003198:Computer Simulation; D019544:Equipment Failure Analysis; D005260:Female; D050278:Finger Phalanges / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013718:Tensile Strength