title: Effect of hoop stress fracture on micromotion of textured ingrowth stems for radial head replacement.
abstract: BACKGROUND
  Successful bone ingrowth around cementless implants requires adequate initial stability. Hoop stress fractures during stem insertion can potentially hinder prosthesis stability.
  
  
  OBJECTIVE
  We hypothesized that an oversized radial head prosthetic stem (1 mm "too large" and causing a hoop stress fracture during insertion) would result in an unacceptable amount of micromotion.
  
  
  METHODS
  Grit-blasted radial head prosthetic stems were implanted into cadaveric radii. Rasp and stem insertion energies were measured, along with micromotion at the stem tip. The sizes were increased until a fracture developed in the radial neck.
  
  
  RESULTS
  Prosthetic radial head stems that were oversized by 1 mm caused small cracks in the radial neck. Micromotion of oversized stems (42 ± 7 μm) was within the threshold conducive for bone ingrowth (<100 μm) and not significantly different from that for the maximum sized stems (50 ± 12 μm) (P ≥ .4).
  
  
  CONCLUSIONS
  Contrary to our hypothesis, hoop stress fractures caused by implantation of a stem oversized by 1 mm did not result in loss of stability. Stem micromotion remained within the range for bone ingrowth and was not significantly diminished after the fracture. This suggests that if a crack occurs during the final stages of stem insertion, it may be acceptable to leave the stem in place without adding a cerclage wire.
  
  
  CONCLUSIONS
  A small radial neck fracture occurring during insertion of a radial head prosthetic stem oversized by 1 mm does not necessarily compromise initial stability.
authors.affiliation: Biomechanics Laboratory, Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Cholawish
authors.initials: C
authors.lastname: Chanlalit
authors.forename: Dave R
authors.initials: DR
authors.lastname: Shukla
authors.forename: James S
authors.initials: JS
authors.lastname: Fitzsimmons
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
authors.forename: Shawn W
authors.initials: SW
authors.lastname: O'Driscoll
mesh_terms: D000369:Aged, 80 and over; D000704:Analysis of Variance; D057929:Arthroplasty, Replacement, Elbow / Q000009:adverse effects* / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D020099:Coated Materials, Biocompatible; D004551:Elbow Joint / Q000601:surgery*; D058569:Elbow Prosthesis; D005260:Female; D015775:Fractures, Stress / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control*; D006801:Humans; D008297:Male; D009038:Motion; D016348:Osseointegration / Q000502:physiology; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011884:Radius / Q000601:surgery*; D011897:Random Allocation; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D020099:Coated Materials, Biocompatible