title: Anatomic study and electromyographic analysis of the teres minor muscle.
abstract: BACKGROUND
  The teres minor muscle is a focused topic on the treatment of massive rotator cuff tears and reverse total shoulder arthroplasty. Its precise anatomy and function have not been completely investigated. The purposes of this study were to anatomically investigate the muscle and analyze electromyographic (EMG) activities during shoulder motion.
  
  
  METHODS
  This anatomic study used 20 shoulders from deceased donors (mean age, 75.0 years). EMG data were recorded from 10 healthy volunteers (mean age, 21.7 years) during flexion, abduction, and external rotations at 0° of abduction, at 90° of abduction, and at 90° of flexion in their dominant arms synchronized with a computerized 3-dimensional motion analysis system.
  
  
  RESULTS
  The muscle in all specimens consisted of 2 distinct muscular bundles: the upper and lower portions. The upper portion attached to the round area of the greater tuberosity, and the lower portion inserted into the linear shaped area. Both portions were independent in their origins, insertions, and innervation. The muscle engaged force during each shoulder motion. EMG activities of abduction and the 3 forms of external rotation were similar. Maximal voluntary contraction in the 3 forms of external rotation was 32% in maximum external rotation in the neutral position, 25% in flexion, and 40% in abduction.
  
  
  CONCLUSIONS
  The teres minor consists of independent upper and lower portions. The muscle engages force in all ranges of 5 shoulder motions, and maximum external rotation in abduction is a reliable method to evaluate potential activity of the muscle.
authors.affiliation: Department of Orthopaedic Surgery, Kuwano Kyoritsu Hospital, Fukushima, Japan. Electronic address: i-hamada@koriyama-h-coop.or.jp.
authors.forename: Junichiro
authors.initials: J
authors.lastname: Hamada
authors.affiliation: Unit of Clinical Anatomy, Graduate School of Medicine and Dental Science, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Akimoto
authors.initials: A
authors.lastname: Nimura
authors.affiliation: School of Physical Therapy, Koriyama Institute of Health Sciences, Fukushima, Japan.
authors.forename: Kunio
authors.initials: K
authors.lastname: Yoshizaki
authors.affiliation: Unit of Clinical Anatomy, Graduate School of Medicine and Dental Science, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Akita
mesh_terms: D000368:Aged; D002102:Cadaver; D004576:Electromyography; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D012399:Rotation; D017006:Rotator Cuff / Q000033:anatomy & histology* / Q000502:physiology*; D055815:Young Adult
keywords: Teres minor muscle; abduction; anatomy; electromyography; external rotation; flexion; lower portion; superior portion