Accuracy of digital radiography: regional scaling factors for trauma.

BACKGROUND: Surgical planning in trauma is essential for optimal patient care and best patient outcomes. Digital radiography has improved the availability, convenience and access to radiographs worldwide as used in every trauma centre in Australia. One shortcoming, however, is the variability in magnification error associated with different anatomic regions. Accurate assessment of radiographs is paramount to proper surgical planning.

METHODS: A retrospective review of 513 post-operative trauma radiographs of implants at a single centre, collected from January 2015 to August 2016, was measured by the four individual investigators. A comparison of the digital calliper reading with the known implant size, taken from operation reports and company implant data, was conducted. Magnification scales were created for different anatomic regions: femur, tibia, humerus, elbow, wrist and hand, foot and ankle.

RESULTS: Precise regional scaling factors increase accuracy of digital radiography. Average magnification for hand, wrist, ankle and forearm is 5% (1-16%). Average magnification for foot, knee, tibia and elbow is 8% (3-11%). Humerus magnification is 10.3% (3-17%) and shoulder and femur approximately 15% (12-18%). Inter-rater Pearson's R reliability testing is 0.985-0.995 and intra-observer reliability is 0.998.

DISCUSSION: Applying regional scaling factors improves accuracy of digital imaging, therefore improving clinical decision-making regarding fractures, distance from bony landmarks, component sizing and reduction assessment. Femoral and tibial fracture measurements with appropriate scaling factors allow the accurate estimation of nail diameter required for fixation and screw diameter for fragment fixation.