This is Barry Bellosis, one of the musculoskeletal radiology fellows at Stanford University. 11-year-old male planted on his right leg during soccer game and felt sudden pop in his right hip, concern for hip dislocation. The patient in this case presented with this hip radiograph demonstrating superior lateral dislocation of the right femoral head, likely secondary to posterior hip dislocation, which is the most common type of dislocation. Although it is challenging to definitively tell the exact type of dislocation, the superior and lateral dislocation of the right femoral head suggests that it is a posterior hip dislocation. Additionally, the non-visualization of the laceratrocantor suggests that this is a posterior hip dislocation because the hip is internally rotated. This is in comparison to an anterior hip dislocation where we see the femoral head anterior and inferior medially displaced, so it would have been in this location. The patient in this case underwent MRI follow-up at some point, approximately four weeks, which demonstrates some labral tearing. Also we can see that the ligamentum teres has thickened, likely related to prior injury. Here we can see some associated muscle edema and fluid outside the hip joint capsule, consistent with history of hip dislocation. Ligamentum teres or the foveolar artery is a small-caliber artery arising from the obturator artery that perfuses the perifovial region and only is typically vestigial with an insignificant contribution. Its contribution to stability remains controversial. The main blood supply to the weight-bearing femoral head is actually supplied by the medial femoral circumflex artery, which arises from the profunda femoris artery. Non-concentric reduction would demonstrate asymmetric joint space throughout the hip joint compared to the contralateral side, whereas a non-concentric reduction will demonstrate asymmetric joint space within the same hip. Determining the reduction positioning is important as non-concentric reduction could be detrimental and it could be caused by underlying osseous body or displaced labrum. This isn't the same patient, just demonstrating edema again surrounding the right hip joint and some tearing of the superior labrum and also affected ligamentum teres. The CT coronal reformat of the same patient demonstrates symmetric hip joint space after reduction consistent with concentric reduction. The positioning after reduction is important and in some cases CT may be necessary to exclude any occult acetabular wall fracture or any joint bodies or displaced labrum within the joint space. Additionally, if there is concern for femoral neck fracture, reduction should not be pursued and additional imaging should be performed to exclude femoral neck as that could be contraindicated for closed reduction.

2nd Edition, CASE 23

2nd Edition

Hip

posterior hip dislocation

labral tearing

femoral head

concentric reduction

femoral neck fracture