title: Influence of the pronator quadratus and supinator muscle load on DRUJ stability.
abstract: OBJECTIVE
  To determine the effects of altering the load contributions of the pronator quadratus and supinator muscles on in vitro distal radioulnar joint (DRUJ) stability during pronation and supination and before and after ulnar head excision.
  
  
  METHODS
  Multiple pronation trials were conducted with incremental loading of the pronator quadratus relative to the pronator teres muscle; supination trials were similarly conducted with incremental loading of the supinator relative to the biceps muscle. All trials were conducted using an upper-limb apparatus capable of simulating muscle/tendon loading and displacement. Stability measurements included dorsal-volar translations of the radius relative to the ulna and DRUJ diastasis and convergence.
  
  
  RESULTS
  Increased pronator quadratus loading did not affect intact DRUJ stability but effects were noted after ulnar head excision when the forearm was positioned between neutral and full pronation. Incremental loading of the supinator muscle did not modify DRUJ stability in the intact or ulnar head excised state.
  
  
  CONCLUSIONS
  Pronator quadratus muscle activity aggravates forearm instability after ulnar head excision. Immobilization of the forearm in mid- to full supination should minimize pronator quadratus activity and optimize soft-tissue healing. This information may be useful to develop in vitro muscle-loading scenarios and analytical forearm models.
authors.affiliation: Bioengineering Research Laboratory, Hand and Upper Limb Centre, St Joseph's Health Care London, London, Ontario, Canada.
authors.forename: Karen D
authors.initials: KD
authors.lastname: Gordon
authors.forename: Cynthia E
authors.initials: CE
authors.lastname: Dunning
authors.forename: James A
authors.initials: JA
authors.lastname: Johnson
authors.forename: Graham J W
authors.initials: GJ
authors.lastname: King
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D006801:Humans; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D011403:Pronation / Q000502:physiology*; D013484:Supination / Q000502:physiology*; D014955:Wrist Joint / Q000502:physiology*