Femoral stress fracture imaging

Stress fracture images.

History: A 15-year-old male presented with a 1-month history of pain in the distal left femur. Prior to the onset of pain, he had recently returned to high school football after a 1-year hiatus due to an L5 pars fracture (acute spondylolysis). Radiographs of the left knee were normal. MRI of the left knee to evaluate for internal derangement (not shown) demonstrated edema in the distal left femur leading to the immediate performance of an MRI of the left thigh.

(A, B) Coronal (A) and sagittal (B) STIR images of the distal left femur demonstrate high STIR signal in the bone marrow (asterisks in A and B) and the periosteum (dashed arrows in A) consistent with bone marrow edema and periosteal reaction. There is a dark, oblique line in the medial aspect of the distal femoral diaphysis (arrows in A and B) consistent with a stress fracture. This corresponds to a Grade IV tibial stress fracture in the Fredericson classification. However, this study was initially interpreted as concerning for tumor or osteomyelitis, prompting referral for further evaluation.

(C) Radiographs of the left femur were repeated and demonstrated subtle sclerosis and periosteal reaction corresponding to the focal uptake on bone scan. The constellation of findings was consistent with a stress fracture.

(D-F) Two-phase whole-body Tc-99m MDP bone scan was performed. Anterior spot blood pool images (D) and anterior (E) and posterior (F) whole-body images demonstrate focal, linear, increased radiopharmaceutical accumulation (arrow in D-F) corresponding to the oblique fracture line seen on MRI. There is mild increased radiopharmaceutical accumulation in the distal left femoral diaphysis and metaphysis secondary to hyperemia corresponding to the bone marrow edema seen on MRI (asterisks in D-F). The asymmetry of the ischiopubic synchondrosis (arrowheads in E and F) is a benign developmental variant that should not be mistaken for pathology.