Diagnosis

Bilateral shin splints with two possible early focal stress fractures of the right tibia.

Findings

#1 - Tc99m MDP Radionuclide angiogram of the lower legs demonstrates no definite areas of hyperemia. #2 - Blood pool phase of the bone scan of the lower legs demonstrates no definite abnormal areas of radiotracer localization #3 & #4 Delayed images demonstrate linear uptake along the posteromedial mid-to-distal tibias, right more extensive than left. At the most cephalad and caudal aspects of the abnormality in the right tibia there are more fusiform areas of increased tracer uptake involving cortex.

Discussion

The term shin splints describes a combination of clinical and scintigraphic findings. Patients complain of exercise-induced pain along the medial or posteromedial aspect of the tibia. Frequently these symptoms are bilateral and can be asymmetric. Shin splints are believed to result from focal periostitis, microperiosteal tears at points of periosteal stress, at the insertion of the soleus muscle and its fascia. This fascia envelopes the soleus muscle and extends along the posterior medial border of the tibia. Scintigraphically this appears as mild to moderate radiotracer uptake, often of varying intensities, along the posteromedial aspect of the middle to distal tibia, involving at least one third of the bone. A more focal component to the uptake can predict further injury if the causative stress persists. Stress fractures in this region occur predominantly at the middle third-lower third junction of the tibia in the posteromedial cortex. Focal, fusiform increased radiotracer localization on delayed images is the classic finding. Intense hyperemia on the radionuclide angiogram and blood pool phase can help distinguish stress fractures from shin splints, which typically have normal radionuclide angiogram and blood pool uptake. Stress fractures occur when resorption of bone outpaces replacement during remodeling secondary to the increased activity. It is a continuum of injury spanning an early remodeling reaction to an overt fracture. A four-grade scintigraphic classification can be applied. Grade I lesions show an ill-defined cortical increase in uptake. Grade II lesions are larger, more well-defined, and demonstrate moderate increased activity. Grade III lesions have a wide fusiform corticomedullary region of activity, and Grade IV lesions demonstrate an extensive transmedullary region of increased uptake. In this case, the more focal areas of tracer uptake in the right tibia were concerning for an early stress fracture, low grade, in this athlete. Demonstration of hyperemia on the angiographic and blood pool phases would have made the diagnosis of concurrent stress fractures definitive.

Skeletal Nuclear Medicine, Collier Jr., Fogelman, Rosenthall. Essentials of Nuclear Medicine Imaging, 4th edition, Mettler and Guiberteau.