title: In vivo 3D kinematics of normal forearms: analysis of dynamic forearm rotation.
abstract: BACKGROUND
  Forearm rotation is an indispensable activity of daily living and comprises complex motions with rotational and translational components. It is thought that changes in these motions with injury or disease may affect diagnostic indices. Several studies have assessed in vivo forearm kinematics with static conditions, but dynamic forearm kinematics have not yet been reported. The purpose of this study was to analyze forearm kinematics during dynamic rotation using radiographic 3D-2D registration methods.
  
  
  METHODS
  Ten forearms of five healthy males with the mean age of 37 years old were enrolled. Lateral fluoroscopic images were taken during forearm rotation from maximum supination to maximum pronation with their elbows flexed to approximately 45°. Geometric bone models were created from CT scans of the humerus, the radius and the ulna. Three-dimensional kinematics were determined using 3D-2D model registration techniques with the images and models, and the arc of axial rotation of the radius, volar/dorsal translation of the ulna at the distal radioulnar joint and rotation axis of forearm were computed.
  
  
  RESULTS
  The radial rotation arc was 157°. The ulna translated 3.9 mm (SD 1.5mm) dorsally during activity. The rotation axis of the forearm passed through the center of the radial head and the ulnar head at the 1.9 mm (SD 0.7 mm) posterior from its geometric centroid.
  
  
  CONCLUSIONS
  The posteriorly deviated rotation axis at the ulnar head may result in the ulnar head translating dorsally during pronation. These data provide a basis for objective assessment of pathological forearm function.
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of Florida, 330 MAE-A PO Box 116250, Gainesville, FL 32611-6250, USA. k-oz@kg7.so-net.ne.jp
authors.forename: Kei O
authors.initials: KO
authors.lastname: Matsuki
authors.forename: Keisuke
authors.initials: K
authors.lastname: Matsuki
authors.forename: Shang
authors.initials: S
authors.lastname: Mu
authors.forename: Takahisa
authors.initials: T
authors.lastname: Sasho
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakagawa
authors.forename: Nobuyasu
authors.initials: N
authors.lastname: Ochiai
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Scott A
authors.initials: SA
authors.lastname: Banks
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D015992:Body Mass Index; D005471:Fluoroscopy / Q000379:methods; D005542:Forearm / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008297:Male; D011403:Pronation; D011884:Radius / Q000473:pathology; D012399:Rotation; D013484:Supination; D014457:Ulna / Q000473:pathology