What is the diagnosis?

Proximal tibial stress fracture

• Pearl: Stress fractures in runners are most common in the tibia [1].

• Pearl: It is common to not visualize a fracture line in stress injuries as they occur on a spectrum. If you do see a definitive line (the dreaded black line), this is indicative of a significant stress injury. 

What are risk factors for injury?

Risk factors for tibial stress fractures generally fall into three categories. They can be activity-related, such as a sudden increase in activity or changes in terrain or biomechanical, such as calf muscle weakness and leg-length discrepancy. Metabolic factors including bone demineralization and nutritional deficiencies can lead to stress fractures as well.

What physical exam and history findings are expected?

Unless the stress fracture is a direct result of trauma, pain is usually insidious in onset and increases with activity. Occasionally, pain may be more moderate or chronic in the setting of bone stress that finally fractures, causing sudden increase in pain. Pain should localize to a discrete area along the bone, and local swelling may be present. This helps differentiate from medial tibial stress syndrome, where tenderness along the shin is more diffuse.

• Pearl: Inability to hop on the symptomatic leg for ten consecutive hops without inducing pain is the most sensitive physical exam finding, though it should be interpreted in clinical context [2].

Which imaging modalities can be used?

Initial imaging assessment for suspicion of stress fracture is with a plain radiograph, which is a specific, but insensitive test. Symptoms may precede appearance on radiographs. If clinical suspicion is high, you may proceed with an MRI, which can detect early edematous signs of stress fractures and more subtle periosteal changes, making it a significantly more sensitive test [3]. 

• Pearl: There are several systems used to grade MRI bone stress injuries. These systems delineate severity by assessing for periosteal edema, bone marrow edema, and cortical fracture lines. While there are several different grading systems, differentiating between a low-grade and high-grade stress fracture offers prognostic value for time to return to sports [4].