title: Morphological analysis of acromion and hook plate for the fixation of acromioclavicular joint dislocation.
abstract: OBJECTIVE
  Acromioclavicular (AC) joint dislocation is a common sports injury. Hook plate fixation is currently widely used to treat this injury, as it can promote the natural healing of the ligament with good clinical outcomes. However, subacromial erosion and impingement are frequently observed post-operatively. It was hypothesized that the morphology and the contact characteristics between the hook portion and the acromion are the main causes of complications after hook plate fixation with the currently available commercial designs.
  
  
  METHODS
  Three-dimensional reconstructed models of the AC joint obtained from the computed tomographic scans of 23 male and 23 female patients (mean age, 61.1 ± 6.3 years) were evaluated, and multiple anatomical parameters were measured. For the subacromial positioning of the hook plate, an actual hook plate (Synthes Inc., West Chester, PA, USA) was scanned, and the contact between the hook plate and the acromion was estimated.
  
  
  RESULTS
  The thicknesses of the acromion and distal clavicle were 9.7 ± 1.5 mm (10.7 mm in men; 8.6 mm in women) and 11.3 ± 1.6 mm (11.6 mm in men; 10.0 mm in women), respectively. The width of the acromion was 28.5 ± 3.6 mm. The mean inclination angle between the hook plate and the acromion was 29.3° ± 9.7° (27.9° in men; 30.6° in women). The hook plate made a point contact with the acromion at 9.2 ± 3.3 mm (31.5 %) from the lateral end of the acromion.
  
  
  CONCLUSIONS
  The results revealed that the hook made a pinpoint contact with the undersurface of the acromion, and this might explain why complications commonly occur after hook plate fixation. The force concentration phenomenon associated with the hook plate of existing designs results from cases of morphological mismatch, such as excessive inclination and improper occupation of the subacromial space.
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Kyung Pook National University, Daegu, South Korea.
authors.forename: Jong Pil
authors.initials: JP
authors.lastname: Yoon
authors.affiliation: Department of Biomedical Engineering, College of Medical Science, Catholic University of Daegu, 5 Geumrak St, Hayang-EUP, Daegu, Gyeongsan-Si, Gyeongbuk, 712-702, South Korea. biomechanics.yslee@gmail.com.
authors.forename: Yeon Soo
authors.initials: YS
authors.lastname: Lee
authors.affiliation: Department of Biomedical Engineering, College of Medical Science, Catholic University of Daegu, 5 Geumrak St, Hayang-EUP, Daegu, Gyeongsan-Si, Gyeongbuk, 712-702, South Korea.
authors.forename: Geun Soo
authors.initials: GS
authors.lastname: Song
authors.affiliation: Department of Orthopaedic Surgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seoul, South Korea.
authors.forename: Joo Han
authors.initials: JH
authors.lastname: Oh
mesh_terms: D000173:Acromioclavicular Joint / Q000000981:diagnostic imaging / Q000293:injuries / Q000473:pathology* / Q000601:surgery*; D000174:Acromion / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D001860:Bone Plates; D002968:Clavicle / Q000000981:diagnostic imaging / Q000473:pathology; D004867:Equipment Design; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D004204:Joint Dislocations / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D014057:Tomography, X-Ray Computed
keywords: Acromioclavicular joint; Acromion; Hook plate; Morphology