title: The anterior borders of the clavicle and the acromion are not always aligned in the intact acromioclavicular joint: a cadaveric study.
abstract: BACKGROUND
  The aim of this study was to find reliable anatomic landmarks of the normal acromioclavicular joint (ACJ) that could enable the precise evaluation of the horizontal displacement of the clavicle after dislocation. The hypothesis was that the anterior borders of the acromion and the clavicle are always aligned in intact ACJs.
  
  
  METHODS
  In 30 cadaveric specimens, the anterior and posterior borders of the ACJ's articular facets and the most prominent anterior and posterior bony landmarks of the acromion and the clavicle were identified. The anterior and posterior overhang of the acromion and the clavicle was measured in relation to the borders of the articular facets. Therefore, the possible anterior and posterior alignment of the ACJ was evaluated.
  
  
  RESULTS
  Anteriorly, only 18 ACJs (60%) were aligned whereas 7 (24%) had major overhang of the acromion and 3 (10%) had major overhang of the clavicle. Similarly, 18 cases (60%) were posteriorly aligned, whereas 6 (20%) had major clavicular overhang and 4 (14%) had major overhang of the acromion. In 78% of these cases, the ACJ was aligned as well anteriorly as posteriorly (P < .001). Finally, the larger the width of the acromion (P = .032) or the clavicle (P = .049), the better the posterior joint alignment.
  
  
  CONCLUSIONS
  Our hypothesis was not verified. The acromion and clavicle are not perfectly aligned in a significant number of specimens with intact ACJs (40% of cases). The most reliable landmarks remain their articular facets.
authors.affiliation: Department of Orthopaedic Surgery, Centre Osteoarticulaire des Cèdres, Grenoble, France. Electronic address: jrhbarth@yahoo.fr.
authors.forename: Johannes
authors.initials: J
authors.lastname: Barth
authors.affiliation: Department of Orthopaedic Surgery, Centre Osteoarticulaire des Cèdres, Grenoble, France.
authors.forename: Achilleas
authors.initials: A
authors.lastname: Boutsiadis
authors.affiliation: Department of Shoulder Surgery, Sanatorio Allende, Córdoba, Argentina.
authors.forename: Pablo
authors.initials: P
authors.lastname: Narbona
authors.affiliation: Division of Orthopaedics and Trauma Surgery, La Tour Hospital, Meyrin, Switzerland; Faculty of Medicine, University of Geneva, Geneva, Switzerland; Division of Orthopaedics and Trauma Surgery, Department of Surgery, Geneva University Hospitals, Geneva, Switzerland.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Lädermann
authors.affiliation: Università degli studi di Milano-Policlinico San Donato, Milano, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Arrigoni
authors.affiliation: Department of Orthopaedics, NCH Hospital, Naples, FL, USA.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Adams
authors.affiliation: San Antonio Orthopaedic Group, San Antonio, TX, USA.
authors.forename: Stephen S
authors.initials: SS
authors.lastname: Burkhart
authors.affiliation: Southern Oregon Orthopedics, Medford, OR, USA.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Denard
mesh_terms: D000173:Acromioclavicular Joint / Q000473:pathology* / Q000503:physiopathology; D000174:Acromion / Q000473:pathology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D002968:Clavicle / Q000473:pathology*; D005260:Female; D006801:Humans; D004204:Joint Dislocations / Q000209:etiology / Q000473:pathology*; D008023:Ligaments, Articular / Q000473:pathology; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular
keywords: AC joint reconstruction; Acromioclavicular joint alignment; Rockwood classification; acromioclavicular joint dislocation; shoulder anatomy; stabilization