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.
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