Background
Radial head subluxation (nursemaid’s elbow) is a common musculoskeletal disorder in young children, often occurring in the setting of sudden axial traction applied to a pronated and extended forearm. Though radial head subluxation can often be diagnosed clinically, radiographs are commonly used in cases of an unclear mechanism of injury or following unsuccessful attempted reduction. Few studies have investigated the role of ultrasonography in diagnosis of radial head subluxation. Most authors have described the displacement of the annular ligament into the radiocapitellar joint, and some have recently suggested displacement of posterior synovial fringe between the annular ligament and radial head. Others propose that some unsuccessful reductions are due to rupture of the annular ligament. The mechanisms of these findings as well as their clinical significance have not been well defined. Sonographic techniques have been described in varying detail, which not only raises concerns about reproducibility in research but also limits the establishment of a standard sonographic protocol for nursemaid’s elbow.
Educational Goals / Teaching Points
This exhibit will review the sonographic musculoskeletal anatomy of the young pediatric elbow. The clinical presentation and common demographics will be described. Sonographic findings as well as normal variations will be reviewed. Treatment options will be discussed with an emphasis on the role of imaging. This exhibit is intended to benefit radiology trainees, practicing radiologists, and referring providers.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The predisposing and affected pediatric elbow anatomy will be reviewed in detail (e.g., ossification center variability, osteochondral morphology of the radial head, posterior synovial fringe, etc.). Some proposed pathophysiology, such as interposition of the annular ligament, has been demonstrated to be pathologic in cadaveric models, and others such as interposition of synovial fringe have not been as well described. The technique of closed reduction will be discussed in support of understanding proposed mechanisms of injury. The various sonographic findings reported in the literature will be summarized. Similar findings with different descriptions will be clarified (e.g., J-sign vs. the hook sign). The possibility of different tissues having similar appearances will be addressed. Reported findings of questionable significance will be critically reviewed. Ultrasound techniques including probe selection, image optimization, probe placement, and patient positioning will be described. The potential role of dynamic maneuvers will be considered.
Conclusion
Ultrasound may play an important role in the evaluation of nursemaid elbow in select situations. Understanding the sonographic anatomy of the young pediatric elbow is essential for accurate diagnosis and treatment recommendations. A comprehensive literature review may help clarify the literature, improve clinical care, and guide further research.
