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Background
Static radiographic imaging is an integral part of the work up for musculoskeletal (MSK) conditions. With the advent of dynamic digital radiography (DDR), x-ray obtained during motion is now available at the clinical point of care. Only a single study has been published evaluating the utility of DDR in the shoulder. In this exhibit we present DDR techniques, utilization for other MSK conditions, and provide case examples where DDR provided added clinical benefit.

Educational Goals / Teaching Points
To describe the principles and techniques for DDR image acquisition, review patient positioning in MSK imaging, and demonstrate potential utilizations with MSK case.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The basic principles and image acquisition technique for DDR are reviewed, including positioning, motion instructions, and relative added dose compared to radiographic and CT. In MSK imaging, DDR enables visualization of contiguous joint motion to identify findings not apparent on static imaging like instability, altered rhythm or decreased range of motion (ROM). In our practice, DDR imaging is added to static imaging for specific clinical presentations provided by the patient or outlined on the requisition such as trauma, instability or decreased range of motion (ROM). In the shoulder, transaxillary (TA) DDR allows contiguous visualization of humeral translation on the glenoid during abduction and external rotation (ABER), and flexion to extension. Anteroposterior (AP) DDR demonstrates the degree of glenohumeral (GH) internal and external rotation. Case examples include normal GH motion on DDR, and GH instability on DDR, not seen on static imaging, after a subluxation event which initiated further specialist referral. For the wrist, a single dynamic AP DDR is obtained moving the wrist in radial and ulnar deviation with clenched fist. In the thumb, passive DDR performed with stabilized carpometacarpal joint, and with patient-applied radial pressure at the metacarpophalangeal (MCP) joint with gentle radial deviation of the tuft. A case demonstrating subtle widening of the ulnar MCP joint on DDR suggests a low grade ulnocarpal ligament (UCL) sprain not apparent on stressed static imaging. UCL sprain was confirmed on ultrasound and the patient was referred to sports medicine. In the lower extremity, DDR is performed weight-bearing (WB). In the knee, WB AP and skyline DDR during extension through flexion is obtained. An example of more advanced joint space narrowing across the medial knee on DDR compared to static X-rays resulted in a sooner referral for arthroplasty. For the ankle, AP and oblique AP during WB inversion and eversion performed to visualize the mortise and syndesmosis alignment. A case shows marked widening of the lateral ankle in dynamic inversion, not seen on static imaging, initiated urgent orthopedic referral.

Conclusion
DDR has the potential to demonstrate additional findings during active joint motion compared to static images alone. For patients with MSK concerns, DDR may improve x-ray diagnostic ability and enable triaging of further imaging, specialist referral or other treatments for improved patient outcomes.