title: Biomechanical contributions of posterior deltoid and teres minor in the context of axillary nerve injury: a computational study.
abstract: OBJECTIVE
  To determine whether transfer to only the anterior branch of the axillary nerve will restore useful function after axillary nerve injury with persistent posterior deltoid and teres minor paralysis.
  
  
  METHODS
  We used a computational musculoskeletal model of the upper limb to determine the relative contributions of posterior deltoid and teres minor to maximum joint moment generated during a simulated static strength assessment and to joint moments during 3 submaximal shoulder movements. Movement simulations were performed with and without simulated posterior deltoid and teres minor paralysis to identify muscles that may compensate for their paralysis.
  
  
  RESULTS
  In the unimpaired limb model, teres minor and posterior deltoid accounted for 16% and 14% of the total isometric shoulder extension and external rotation joint moments, respectively. During the 3 movement simulations, posterior deltoid produced as much as 20% of the mean shoulder extension moment, whereas teres minor accounted for less than 5% of the mean joint moment in all directions of movement. When we paralyzed posterior deltoid and teres minor, the mean extension moments generated by the supraspinatus, long head of triceps, latissimus dorsi, and middle deltoid increased to compensate. Compensatory muscles were not fully activated during movement simulations when posterior deltoid and teres minor were paralyzed.
  
  
  CONCLUSIONS
  Reconstruction of the anterior branch of the axillary nerve only is an appropriate technique for restoring shoulder abduction strength after isolated axillary nerve injury. When shoulder extension strength is compromised by extensive neuromuscular shoulder injury, reconstruction of both the anterior and posterior branches of the axillary nerve should be considered.
  
  
  CONCLUSIONS
  By quantifying the biomechanical role of muscles during submaximal movement, in addition to quantifying muscle contributions to maximal shoulder strength, we can inform preoperative planning and permit more accurate predictions of functional outcomes.
authors.affiliation: Virginia Tech-Wake Forest University School of Biomedical Engineering and Sciences, Winston-Salem, NC 27157, USA. dcrouch@wfubmc.edu
authors.forename: Dustin L
authors.initials: DL
authors.lastname: Crouch
authors.forename: Johannes F
authors.initials: JF
authors.lastname: Plate
authors.forename: Zhongyu
authors.initials: Z
authors.lastname: Li
authors.forename: Katherine R
authors.initials: KR
authors.lastname: Saul
mesh_terms: D001365:Axilla / Q000294:innervation; D001696:Biomechanical Phenomena; D057645:Deltoid Muscle / Q000294:innervation*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation*; D016067:Nerve Transfer / Q000379:methods*; D016571:Neural Networks, Computer; D059348:Peripheral Nerve Injuries / Q000503:physiopathology* / Q000601:surgery*; D010525:Peripheral Nerves / Q000637:transplantation; D016059:Range of Motion, Articular / Q000502:physiology; D012782:Shoulder / Q000294:innervation*; D000070599:Shoulder Injuries