title: Subacromial morphometric assessment of the clavicle hook plate.
abstract: BACKGROUND
  Clavicle hook plates are an effective plate fixation alternative for distal clavicle fractures and severe acromioclavicular joint dislocations. However, post-operative complications associated with the subacromial portion of the hook include acromial osteolysis and subacromial impingement. We examine and quantify the three-dimensional position of the subacromial portion of the hook plate relative to surrounding acromial and subacromial structures in a series of cadaveric shoulders to determine if hook positioning predisposes the shoulder to these noted post-operative complications.
  
  
  METHODS
  Fifteen cadaveric shoulders (seven males, eight females) were implanted with 15- or 18-mm hook plates. Dimensions of the acromion and hook plate were digitised and reconstructed into a three-dimensional model to measure acromion dimensions and distances of the subacromial hook relative to surrounding acromial and subacromial structures.
  
  
  RESULTS
  Inter-specimen dimensions of the acromion were highly variable. Mean acromion width and thickness were greater in males than in females (p=0.01). The posterior orientation of the subacromial hook varied widely (mean posterior implantation angle=32.5+/-20 degrees, range 0-67 degrees). The hook pierced the subacromial bursa in 13/15 specimens, made contact with the belly of the supraspinatus muscle in 9/15 specimens, and had focal contact at the hook tip with the undersurface of the acromion in 9/15 specimens.
  
  
  CONCLUSIONS
  The wide range of acromial dimensions leads to a high degree of variability in the positioning of the subacromial hook. The observed frequency of hook contact with surrounding subacromial structures in a static shoulder confirms that the position of the hook portion of the implant can predispose anatomic structures to the post-operative complications of subacromial impingement and bony erosion.
authors.affiliation: St. Joseph's Health Centre, Department of Orthopaedic Surgery, Toronto, Ontario, Canada.
authors.forename: Amr W
authors.initials: AW
authors.lastname: ElMaraghy
authors.forename: Moira W
authors.initials: MW
authors.lastname: Devereaux
authors.forename: Kajeandra
authors.initials: K
authors.lastname: Ravichandiran
authors.forename: Anne M
authors.initials: AM
authors.lastname: Agur
mesh_terms: D000173:Acromioclavicular Joint / Q000033:anatomy & histology / Q000293:injuries* / Q000601:surgery; D000174:Acromion / Q000033:anatomy & histology*; D000368:Aged; D000369:Aged, 80 and over; D001860:Bone Plates / Q000009:adverse effects; D002061:Bursa, Synovial; D002102:Cadaver; D002968:Clavicle / Q000293:injuries*; D004210:Dissection; D005260:Female; D005593:Fracture Fixation, Internal / Q000009:adverse effects / Q000379:methods*; D050723:Fractures, Bone / Q000601:surgery*; D006801:Humans; D021621:Imaging, Three-Dimensional; D004204:Joint Dislocations / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010014:Osteolysis / Q000209:etiology; D019919:Prosthesis Implantation / Q000009:adverse effects / Q000379:methods; D019534:Shoulder Impingement Syndrome / Q000209:etiology