title: An intra-bone axial load transducer: development and validation in an in-vitro radius model.
abstract: BACKGROUND
  Accurate measurement of forces through the proximal radius can assess the effects of some surgical procedures on radioulnar load sharing, but is difficult to achieve given the redundant loading nature of the musculoskeletal system. Previously reported devices have relied on indirect measurements that may alter articular joint location and function. An axial load transducer interposed in the diaphysis of the radius may accurately quantify unknown axial loads of the proximal radius, and maintain articular location.
  
  
  METHODS
  An in-vitro radius model was developed by interposing an axial load transducer in the diaphysis of the proximal radius. Static loads of 20, 40, 60, 80, and 100 N were applied with a servo-hydraulic actuator to the native radial head at angles of 10°, 20°, 30°, and 40° in the anterior, posterior, medial and lateral directions.
  
  
  RESULTS
  Linear regression of five repeatability trials showed excellent agreement between the transducer and applied loads (R (2) = 1 for all trials). For off-axis net joint loads, the majority of measured loading errors were within the inter-quartile range for mean loads up to 80 N. Loads below 80 N and outside the inter-quartile range had errors of less than 1 N.
  
  
  CONCLUSIONS
  The repeatability and off-axis net joint load results of this study validate the effectiveness of the interposed axial load transducer to accurately quantify proximal radius loads. The surgical technique preserves the native articular location and soft-tissue constructs, like the annular ligament. The modular design allows for testing the effects of length-changing osteotomies in subsequent biomechanical studies.
authors.affiliation: Roth|Mcfarlane Hand and Upper Limb Centre, Surgical Mechatronics Laboratory, St. Josephs Health Care, 268 Grosvenor St., London, N6A 4V2, ON, Canada. nknowle@uwo.ca.|Department of Biomedical Engineering, The University of Western Ontario, 1151 Richmond St., N6A3K7, London, ON, Canada. nknowle@uwo.ca.
authors.forename: Nikolas K
authors.initials: NK
authors.lastname: Knowles
authors.affiliation: Roth|Mcfarlane Hand and Upper Limb Centre, Surgical Mechatronics Laboratory, St. Josephs Health Care, 268 Grosvenor St., London, N6A 4V2, ON, Canada. mgladwell2009@emailforlife.fmd.uwo.ca.|Schulich School of Medicine and Dentistry, The University of Western University, 1151 Richmond St., N6A3K7, London, ON, Canada. mgladwell2009@emailforlife.fmd.uwo.ca.
authors.forename: Michael
authors.initials: M
authors.lastname: Gladwell
authors.affiliation: Roth|Mcfarlane Hand and Upper Limb Centre, Surgical Mechatronics Laboratory, St. Josephs Health Care, 268 Grosvenor St., London, N6A 4V2, ON, Canada. louis.ferreira@sjhc.london.on.ca.|Schulich School of Medicine and Dentistry, The University of Western University, 1151 Richmond St., N6A3K7, London, ON, Canada. louis.ferreira@sjhc.london.on.ca.
authors.forename: Louis M
authors.initials: LM
authors.lastname: Ferreira
keywords: Axial load transducer; Bone-bridge; Forearm loading; Joint loading; Radial head; Radiocapitellar joint; Radioulnar load sharing