Normal Skeletal Maturation and Imaging Pitfalls in the Pediatric Shoulder.

A growing number of magnetic resonance (MR) imaging studies of the shoulder are being performed as a result of greater and earlier participation of children and adolescents in competitive sports such as softball and baseball. However, scant information is available regarding the MR imaging features of the normal sequential development of the shoulder. The authors discuss the radiographic and MR imaging appearances of the normal musculoskeletal maturation patterns of the shoulder, with emphasis on (a) development of secondary ossification centers of the glenoid (including the subcoracoid and peripheral glenoid ossification centers); (b) development of preossification and secondary ossification centers of the humeral head and the variable appearance and number of the secondary ossification centers of the distal acromion, with emphasis on the formation of the os acromiale; (c) development of the growth plates, glenoid bone plates, glenoid bare area, and proximal humeral metaphyseal stripe; and (d) marrow signal alterations in the distal humerus, acromion, and clavicle. In addition, the authors discuss various imaging interpretation pitfalls inherent to the normal skeletal maturation of the shoulder, examining clues that may help distinguish normal development from true disease (eg, osteochondral lesions, labral tears, abscesses, fractures, infection, tendon disease, acromioclavicular widening, and os acromiale). Familiarity with the timing, location, and appearance of maturation patterns in the pediatric shoulder is crucial for correct image interpretation.

MR imaging of entrapment neuropathies of the lower extremity. Part 1. The pelvis and hip.

Entrapment neuropathies can manifest with confusing clinical features and therefore are often underrecognized and underdiagnosed at clinical examination. Historically, electrophysiologic evaluation has been considered the mainstay of diagnosis. Today, cross-sectional imaging, particularly magnetic resonance (MR) imaging and specifically MR neurography, plays an increasingly important role in the work-up of entrapment neuropathies. MR imaging is a noninvasive operator-independent technique that allows identification of the underlying cause of injury, differentiation between surgically treatable and untreatable causes, and guidance of selective diagnostic anesthetic nerve blocks. Pathologic conditions affecting the lumbosacral plexus and major motor and mixed nerves of the pelvis and hip include neuropathies of the lumbosacral plexus, femoral nerve, lateral femoral cutaneous nerve, obturator nerve, and sciatic nerve; piriformis muscle syndrome; and injury of the gluteal nerves. Diagnosis of entrapment neuropathies of the pelvis and hip with MR imaging requires familiarity with the normal MR imaging anatomy and awareness of the anatomic and pathologic factors that put peripheral nerves at risk for injury.

MRI features of posterior capitellar impaction injuries.

OBJECTIVE: Posterior capitellar injury is a scantly recognized entity in the literature. Furthermore, irregularity of the posterior capitellum, termed the "pseudodefect" of the capitellum, has been touted as a normal MRI finding, not to be misinterpreted for impaction injury. Our objectives, based on 11 MRI studies, were to report the MRI features of a true posterior capitellar impaction injury and to document associated clinical, osseous, and soft-tissue abnormalities that may shed light on the cause of this injury. CONCLUSION: Traumatic posterior impaction injuries can occur in the capitellum, albeit infrequently. These lesions often present clinically with elbow instability, have a high incidence of lateral ulnar collateral and radial collateral ligament injuries, and show osseous abnormalities typical of elbow dislocation. Thus, MRI evidence of posterior capitellar impaction injuries, to be distinguished from the pseudodefect of the capitellum, should raise the possibility of previous elbow dislocation or posterolateral rotatory instability.