title: Impact of Joint Position and Joint Morphology on Assessment of Thumb Metacarpophalangeal Joint Radial Collateral Ligament Integrity.
abstract: OBJECTIVE
  A 2-part biomechanical study was constructed to test the hypothesis that coronal morphology of the thumb metacarpophalangeal joint impacts the assessment of instability in the context of radial collateral ligament (RCL) injury.
  
  
  METHODS
  Fourteen cadaveric thumbs were disarticulated at the carpometacarpal joint. Four observers measured the radius of curvature of the metacarpal (MC) heads. In a custom jig, a micrometer was used to measure the RCL length as each thumb was put through a flexion and/or extension arc under a 200 g ulnar deviation load. Strain was calculated at maximal hyperextension, 0°, 15°, 30°, 45°, and maximal flexion. Radial instability was measured with a goniometer under 45 N stress. The RCL was then divided and measurements were repeated. Analysis of variance and Pearson correlation metrics were used.
  
  
  RESULTS
  The RCL strain notably increased from 0° to 30° and 45° of flexion. With an intact RCL, the radial deviation was 15° at 0° of flexion, 18° at 15°, 17° at 30°, 16° at 45°, and 14° at maximal flexion. With a divided RCL, instability was greatest at 30° of flexion with 31° of deviation. The mean radius of curvature of the MC head was 19 ± 4 mm. Radial instability was inversely correlated with the radius of curvature to a considerable degree only in divided RCL specimens, and only at 0° and 15° of flexion.
  
  
  CONCLUSIONS
  The RCL contributes most to the radial stability of the joint at flexion positions greater than 30°. The results suggest that flatter MC heads contribute to stability when the RCL is ruptured and the joint is tested at 0° to 15° of metacarpophalangeal flexion.
  
  
  CONCLUSIONS
  The thumb MC joint should be examined for RCL instability in at least 30° of flexion.
authors.affiliation: Division of Hand Surgery, New York University Hospital for Joint Diseases, New York, NY.
authors.forename: Noah D
authors.initials: ND
authors.lastname: Shaftel
authors.affiliation: Division of Hand Surgery, New York University Hospital for Joint Diseases, New York, NY. Electronic address: omri.ayalon@nyumc.org.
authors.forename: Omri
authors.initials: O
authors.lastname: Ayalon
authors.affiliation: Division of Hand Surgery, New York University Hospital for Joint Diseases, New York, NY.
authors.forename: Shian
authors.initials: S
authors.lastname: Liu
authors.affiliation: Division of Hand Surgery, New York University Hospital for Joint Diseases, New York, NY.
authors.forename: Anthony
authors.initials: A
authors.lastname: Sapienza
authors.affiliation: Division of Hand Surgery, New York University Hospital for Joint Diseases, New York, NY.
authors.forename: Steven
authors.initials: S
authors.lastname: Green
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D017885:Collateral Ligaments / Q000033:anatomy & histology* / Q000502:physiology*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology; D008297:Male; D008662:Metacarpophalangeal Joint / Q000033:anatomy & histology* / Q000502:physiology*; D011884:Radius / Q000033:anatomy & histology* / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013314:Stress, Mechanical
keywords: Cadaveric study; metacarpophalangeal joint; radial collateral ligament; radial instability; radius of curvature