Musculoskeletal Imaging

Pseudarthrosis

a pathologic condition occurring after fracture nonunion and characterized by presence of a synovium-lined cavity resulting from persistent motion at the site of nonunion (Fig.1). Pseudarthroses may be congenital or acquired.

In congenital (present at birth) or infantile pseudarthrosis the tibia is the most common site of involvement, although pseudarthroses may also be seen in the fibula, femur, clavicle, humerus, ulna, radius, rib and other bones. In some cases the stigmata of neurofibromatosis or fibrous dysplasia may be seen. In the infantile variety, radiographic features include anterior bowing of the lower half of the tibia, which may or may not be associated with abnormality of the adjacent fibula. Sclerosis, narrowing of the medullary canal and cystic abnormality may indicate impending fracture of the tibia and pseudarthrosis. In congenital pseudarthrosis of the clavicle, the right side is almost always affected because of the presence of the subclavian artery and cervical ribs. A painless swelling typically occurs over the middle third of the clavicle. The absence of pain and visible callus usually allows this type to be differentiated from a posttraumatic pseudarthrosis.

Pseudarthroses of spinal grafts may occur after spinal fusion and may be evaluated by numerous imaging methods. Conventional radiography and tomography, CT and MR imaging are useful for evaluating structural integrity. Functional integrity is assessed using stress views (typically lateral flexion and extension views), dynamic fluoroscopy, stereophotogrammetric analysis, scintigraphy and MR imaging. Frequently the standard diagnostic criterion for pseudarthrosis is segmental motion on flexion and extension views; however, five criteria are needed to diagnose pseudarthrosis with confidence:

  • lack of trabecular continuity;

  • collapse of graft height with a gap between the vertebral endplate and graft material;

  • shift in graft position after healing is expected to have occurred;

  • dislodgment or fracture of internal hardware after healing is expected to have occurred; and

  • unexplained pain in the area of the fusion.

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    Fig.1

    a. AP radiograph of the elbow demonstrates nonunion of a proximal ulnar fracture. b. CT scan in the coronal plane demonstates gas within the fracture.
    Pseudarthrosis, Fig.1 (a)
    Pseudarthrosis, Fig.1 (b)