title: Stability of acute dorsal fracture dislocations of the proximal interphalangeal joint: a biomechanical study.
abstract: OBJECTIVE
  We performed a cadaveric biomechanical study to characterize proximal interphalangeal joint stability after an injury to different amounts of the volar articular base of the middle phalanx (intact, 20%, 40%, 60%, and 80% volar defects).
  
  
  METHODS
  Eighteen digits on 6 hands were tested through full proximal interphalangeal joint range of motion using computer-controlled flexion and extension via the digital tendons. We collected proximal interphalangeal joint kinematic cine data in a true lateral projection with mini-fluoroscopy. We measured the amount of dorsal middle phalanx translation in full proximal interphalangeal joint extension. As we cycled the joint from full flexion into extension, we recorded the angle at which subluxation occurred.
  
  
  RESULTS
  No specimens with 20% volar bony defect subluxated. All specimens in the 60% and 80% groups subluxated at an average flexion angle of 67° (range, 10° to 90°) in the 60% group and at all degrees of flexion in the 80% group. In the 40% group, 28% of specimens demonstrated subluxation at an average flexion angle of 14° (range, 4° to 40°). Mean dorsal translation of the middle phalanx in relation to the proximal phalanx at full digital extension was 0.2 mm in the 20% group, 0.8 mm in the 40% group, 3.2 mm in the 60% group, and 3.1 mm in the 80% group.
  
  
  CONCLUSIONS
  Simulated volar articular bony defects of 20% were stable, whereas those with 60% and 80% defects were unstable during digital motion. Stability in the 40% group was variable and appeared to be the threshold for stability.
  
  
  CONCLUSIONS
  Knowledge of the typical amount of middle phalanx defect and degree of proximal interphalangeal joint extension that can lead to joint instability may improve management of mechanically important proximal interphalangeal joint fracture dislocations.
authors.affiliation: Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Tyser
authors.affiliation: Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Tsai
authors.affiliation: Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD.
authors.forename: Brent G
authors.initials: BG
authors.lastname: Parks
authors.affiliation: Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD. Electronic address: anne.mattson@medstar.net.
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Means
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology; D005383:Finger Injuries / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D005384:Finger Joint / Q000503:physiopathology* / Q000601:surgery*; D005471:Fluoroscopy; D006801:Humans; D057072:Intra-Articular Fractures / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D004204:Joint Dislocations / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D008953:Models, Anatomic; D016059:Range of Motion, Articular
keywords: Proximal interphalangeal joint; dislocation; fracture; instability