Stress Fracture of the Hip/Pelvis
In a young patient with acute groin and hip pain after squatting 175 lb with negative plain radiographs, the most likely diagnosis is a stress fracture, and you should proceed directly to MRI without IV contrast as the next imaging study 1.
Why MRI is the Next Step
When radiographs are negative or indeterminate but clinical suspicion for fracture remains high (as in your case with acute traumatic mechanism), cross-sectional imaging is essential to detect radiographically occult fractures 1. MRI without IV contrast is the preferred next imaging study because:
- It can detect stress fractures within hours of injury by showing bone marrow edema patterns 2
- It provides superior soft tissue detail to identify associated muscle/tendon injuries
- It avoids radiation exposure in a young patient
- It has supplanted bone scintigraphy as the imaging of choice when radiographs are negative 2
Why Not Other Imaging?
Bone scintigraphy is no longer recommended as the next step because:
- It lacks specificity (arthritis, synovitis, and tumors appear similar) 2
- It's time-consuming and frequently requires supplemental MRI anyway 2
- There is consensus in the literature that cross-sectional imaging should supersede bone scintigraphy 2
CT is less ideal because while it can show periosteal reaction or sclerosis if the patient has been symptomatic for several weeks, it may miss acute stress fractures and provides inferior soft tissue evaluation 2.
Critical Imaging Protocol Details
When ordering the MRI, ensure the protocol includes:
- Coverage of both the hip AND sacrum - sacral stress fractures can radiate pain to the hip/groin region 2
- Large field-of-view fluid-sensitive sequences to exclude conditions that can mimic or coexist with stress fractures 3
- No IV contrast is needed for stress fracture detection 1
Common Pitfalls to Avoid
- Don't assume normal radiographs exclude fracture - radiographs have low sensitivity for stress fractures, particularly in the pelvis and sacrum where overlying soft tissue obscures visualization 2
- Don't wait for symptoms to worsen - early MRI detection allows for appropriate activity modification and reduces risk of progression to complete fracture
- Don't order bone scan - this is outdated practice that delays definitive diagnosis 2, 1
Alternative Diagnoses to Consider
While stress fracture is most likely given the acute traumatic mechanism (squatting heavy weight), the MRI will also evaluate for:
- Adductor muscle strain/tendinopathy (most common cause of athletic groin pain) 4
- Hip labral tears (though typically more insidious onset) 5
- Muscle/tendon injuries including obturator internus pathology 6
The acute traumatic mechanism with significant load (175 lb squat) strongly favors stress fracture over these alternatives, making MRI the definitive next step to guide management.