title: Effects of posterior capsule tightness on subacromial contact behavior during shoulder motions.
abstract: BACKGROUND
  Although posterior capsule tightness is believed to cause abnormal contact in the subacromial space, it is not clear whether this tightness changes the contact between the acromion and humeral head.
  
  
  METHODS
  Nine fresh, frozen cadaveric shoulders were used to measure contact pressure on the coracoacromial arch during passive flexion, abduction, and internal and external rotation at 90° of elevation in the scapular plane, as well as horizontal adduction and abduction. The site where the peak contact pressure occurred was also observed. The posterior capsule in the region from 8 to 10 o'clock in the right shoulder was plicated to simulate posterior capsule tightness.
  
  
  RESULTS
  Peak contact pressure significantly increased with the tightened posterior capsule during flexion. Although peak contact pressure on the coracoacromial ligament during internal rotation significantly increased after capsule tightening, there was no significant increase in pressure when considering the entire coracoacromial arch. The angle where the peak contact pressure occurred during flexion was not significantly far from the end range. The site of the peak contact pressure in 7 of 9 shoulders was on the lesser tuberosity during flexion, regardless of the posterior capsule tightness.
  
  
  CONCLUSIONS
  Posterior capsule tightness increased contact pressure mainly on the lesser tuberosity during flexion. The peak contact pressure occurred close to the end range of flexion, mainly on the lesser tuberosity. These findings are useful to understand the contribution of posterior capsule tightness to subacromial contact.
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Muraki
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Yamamoto
authors.forename: Kristin D
authors.initials: KD
authors.lastname: Zhao
authors.forename: John W
authors.initials: JW
authors.lastname: Sperling
authors.forename: Scott P
authors.initials: SP
authors.lastname: Steinmann
authors.forename: Robert H
authors.initials: RH
authors.lastname: Cofield
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
mesh_terms: D000174:Acromion; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D058430:Humeral Head; D008297:Male; D008875:Middle Aged; D011312:Pressure; D016059:Range of Motion, Articular; D012785:Shoulder Joint / Q000502:physiology*