Presentation
Patient reports 3 months of ongoing sharp right hip and knee pain after military basic training and daily stair use. The pain is worsened with walking and stair ascension.
Patient Data
Normal pelvis, right hip, and right knee radiographs, without evidence of injury or abnormality.
- Intense, focal, ovoid radiotracer uptake in the right, distal, medial, femoral diaphyseal cortex
- Mild, focal, ovoid radiotracer uptake in the left greater than right, posterior, medial, middle tibial diaphyseal cortex
- SPECT/CT of the right femur localizes the intense focal right, distal, medial, femoral diaphyseal cortex uptake to an area of focal smooth periosteal reaction
Lateral and frontal images of the distal femur demonstrate smooth cortical thickening in the distal medial femoral diaphysis.
Axial and coronal T1 and STIR images demonstrate edema in the distal, medial femoral diaphysis periosteum, cortex, and bone marrow. Smooth bony callus overlies the area of edema. No definite fracture line is seen.
Case Discussion
Stress injuries are a common entity in health bone with abnormal stress or unhealthy bone with normal stress. As such, stress injuries are commonly found in athletes, military members (particularly trainees), elderly patients and patients with malignant or pathologic bone disease. Stress fractures often result from repeated trauma to the bone that results in cortical microfractures. If rest is not instituted, stress fractures can result in completed fractures.
The appropriate first study for any suspicion of stress injury is X-ray. If the X-ray is negative, ACR recommends follow-up evaluation with MRI. Nuclear Medicine bone scan and CT are considered as "May be appropriate" in the most recent ACR Appropriateness Criteria.
For MRI, the commonly used grading system is based on the Fredericson system for tibial stress injuries, which are commonly applied to other osseous structures. The system involves T1- and T2-weighted sequences and assesses for periosteal, bone marrow, and cortical edema, as well as fracture lines.
The classically used grading system for grading stress injuries in Nuclear Medicine is the Zwas system, which incorporates subjective intensity and shape. At our institution, we grade stress fractures based on the intensity relative to the ASIS and distribution across the lateral width of the shaft.
In this case, the following are present:
- Grade 4a (Fredericson system) healing stress fracture of the right distal, medial femoral diaphysis
- Stress injuries of the left greater than right mid tibial diaphyses, without stress fracture