Differentiating Stress Fracture from Muscle Pain in the Lower Left Side

Clinical Assessment

The American College of Radiology recommends starting with plain radiographs of the affected area, and if negative but clinical suspicion remains high, proceeding directly to MRI without contrast, which can definitively distinguish between stress fracture and muscle injury 1, 2
Muscle pain typically has a more acute onset related to a specific event or overexertion, with pain that may be present at rest and during stretching, as noted by the American College of Radiology 3

The American College of Radiology suggests that plain radiographs should always be obtained first in at least two planes, despite low sensitivity of 15-35% 4, 1, 5
If radiographs are negative, MRI without contrast is the preferred second-line modality and procedure of choice for early diagnosis, with sensitivity and specificity superior to bone scintigraphy, as recommended by the American College of Radiology 1, 2, 5
MRI demonstrates stress abnormalities as early as bone scintigraphy with superior specificity, and fluid-sensitive sequences (STIR or T2-weighted) are the favored initial sequences, according to the American College of Radiology 8, 9, 3
The American College of Radiology notes that MRI findings that differentiate stress fracture from muscle/tendon injury include fracture line surrounded by bone marrow edema on fluid-sensitive sequences, and linear hypointensity on T1-weighted images for stress fracture, and soft tissue edema without osseous involvement for muscle/tendon injury 4, 9, 2

The American College of Radiology advises against relying solely on negative initial radiographs when clinical suspicion is high, as they miss 65-85% of early stress fractures 4, 5
The American College of Radiology recommends not attributing symptoms to recent injury without further investigation, as history of injury does not exclude stress fracture 6
The American College of Radiology suggests avoiding waiting 2-3 weeks for repeat radiographs if urgent diagnosis is needed; instead, proceed directly to MRI 7
The American College of Radiology notes that IV contrast provides no additional diagnostic information for stress injuries and should not be used for either MRI or CT 1, 2, 5

The American College of Radiology recommends obtaining immediate MRI if the lower left side pain involves high-risk locations such as the femoral neck, anterior tibial diaphysis, medial malleolus, navicular or talus, or fifth metatarsal base, due to risk of displacement, nonunion, or avascular necrosis 5

The American College of Radiology notes that radiographs may remain negative for 2-3 weeks after symptom onset, but follow-up films increase sensitivity to 30-70% 7, 4
The American College of Radiology recommends MRI as it detects abnormalities within days of symptom onset, equivalent to bone scintigraphy timing 8, 3
The American College of Radiology suggests that bone scan shows stress fractures days to weeks earlier than radiographs 8, 2