Stress fracture is a fracture type developing from repetitive mechanical loading on normal bone — caused by cumulative microtrauma exceeding bone remodeling capacity. Two subtypes: fatigue fracture (excessive loading on normal bone — runners, military) and insufficiency fracture (normal loading on weakened bone — osteoporosis, radiotherapy). MRI is the gold standard for early diagnosis: periosteal and bone marrow edema indicate stress reaction (Fredericson Grade 1-3), while linear low signal fracture line on T1 indicates true stress fracture (Grade 4). Metatarsals, tibia, and femoral neck are the most common locations.
Age Range
15-45
Peak Age
25
Gender
Equal
Prevalence
Common
Normal bone undergoes continuous remodeling: osteoblasts produce new bone, osteoclasts resorb old bone. Repetitive loading disrupts this balance: microdamage accumulation > repair capacity → progressive structural weakness. Four stages: (1) Periosteal stress reaction — periosteal inflammation and edema → periosteal edema on MRI (Fredericson 1). (2) Bone marrow edema — intramedullary stress response → STIR marrow edema (Fredericson 2-3). (3) Fracture line formation — trabecular microfractures coalesce into macroscopic fracture line → T1 linear low signal (Fredericson 4). (4) Complete fracture — complete cortical fracture (rare if rested). Femoral neck stress fractures may require urgent surgery — 'tension side' (superior) fractures risk displacement.
MRI combination of periosteal and marrow edema on STIR/T2 (stress reaction) + linear low signal fracture line on T1 within the edema area is the diagnostic finding combination for stress fracture (Fredericson Grade 4).
On STIR/T2 fat-sat, periosteal edema (hyperintense band on bone surface) and intramedullary bone marrow edema (diffuse hyperintense signal) are seen. Periosteal edema is the earliest MRI finding corresponding to Fredericson Grade 1. Addition of marrow edema indicates Grade 2-3. Edema is usually focal and localized to the activity-related region.
Report Sentence
Periosteal edema and bone marrow edema are noted on STIR, consistent with stress reaction (Fredericson Grade [X]).
On T1-weighted images, a linear low signal line is seen in cortical or trabecular bone within the marrow edema area — this is the fracture line defining Fredericson Grade 4. Grade 4a: partial fracture; Grade 4b: complete fracture line. Fracture line is more conspicuous on T1 than surrounding edema because T1 contrast well demonstrates bone anatomy. Fracture line typically runs perpendicular to the loading axis.
Report Sentence
A linear low signal fracture line is seen within the marrow edema area on T1, consistent with stress fracture (Fredericson Grade 4).
CT may show cortical fracture line (thin low-attenuation line) or periosteal new bone formation (thickened cortical margin). CT is more specific than MRI for fracture line detection but does not show early stress reaction (edema). Thin-section CT (<1mm) with multiplanar reformat is most sensitive for detecting subtle fracture lines.
Report Sentence
Cortical fracture line and/or periosteal reaction are noted on CT, consistent with stress fracture.
On Tc-99m MDP bone scintigraphy, focal increased uptake is seen at the stress fracture site. Bone scan has high sensitivity (95%+) but low specificity — infection, tumor, and degenerative changes also show uptake. With MRI widespread availability, scintigraphy use has decreased but remains useful for multi-site screening.
Report Sentence
Focal increased uptake is noted at the stress fracture location on bone scintigraphy, consistent with bone stress response.
In chronic stress response, low signal thickening at the endosteal (inner) surface of cortical bone may be seen on T1 — reflecting reactive sclerosis/new bone formation. This finding is more prominent in subacute/chronic stress fracture and indicates the healing process.
Report Sentence
Endosteal thickening is noted at the cortical bone on T1, consistent with chronic stress response.
Criteria
Grade 1: periosteal edema only. Grade 2: marrow edema (STIR), T1 normal.
Distinct Features
No fracture line. Recovery in 4-6 weeks with rest. Good prognosis.
Criteria
Marrow edema on both T1 and STIR. No fracture line yet but high risk.
Distinct Features
T1 marrow signal drop (fat loss). Longer rest period (6-12 weeks). Careful monitoring especially for femoral neck.
Criteria
Linear fracture line on T1. Grade 4a: intracortex fracture; Grade 4b: full cortical fracture.
Distinct Features
Non-weight-bearing, 8-16 weeks recovery. Femoral neck tension side and navicular stress fractures are 'high-risk' — may need surgical fixation.
Distinguishing Feature
AVN shows double-line sign and geographic necrotic zone in subchondral region, while stress fracture shows cortical/trabecular T1 linear fracture line with surrounding edema
Distinguishing Feature
Transient osteoporosis shows diffuse homogeneous marrow edema without fracture line, while stress fracture has focal edema and T1 linear fracture line
Distinguishing Feature
Bone metastasis shows multifocal involvement, irregular margins, soft tissue mass, and diffusion restriction, while stress fracture shows focal linear fracture line with reactive surrounding edema
Urgency
urgentManagement
conservativeBiopsy
Not NeededFollow-up
6-monthStress fracture treatment is planned by Fredericson grade and anatomic location — location-based risk stratification is critical. Low-risk locations (posteromedial tibia, metatarsal shafts, fibula, pelvis): Grade 1-3: rest, cross-training (swimming, cycling — non-weight-bearing), activity modification, gradual loading program — 4-12 weeks, excellent prognosis. Grade 4: non-weight-bearing (crutches, orthopedic boot), 8-16 weeks, orthopedic follow-up, control MRI to verify healing. High-risk locations — these carry risk of complete displaced fracture and some require surgical fixation: (1) femoral neck tension side (superior cortex) — most dangerous stress fracture, high displacement risk, early surgical fixation (cannulated screws) recommended; compression side (inferior) lower risk, may be conservative, (2) tarsal navicular — avascular central 1/3 has poor healing potential, 6-8 weeks cast + non-weight-bearing, surgery if not healing, (3) anterior tibia ('dreaded black line') — chronic anterior cortex stress fracture, difficult healing, may need intramedullary nailing, (4) fifth metatarsal proximal diaphysis (Jones fracture) — vascular watershed at metaphysis-diaphysis junction, high nonunion risk. In insufficiency fractures, treating underlying osteoporosis is critical — DEXA scan, calcium + vitamin D, bisphosphonate or denosumab. In female athletes, 'female athlete triad' (energy deficit, amenorrhea, osteoporosis) should be investigated. Return to activity must be gradual and pain-free — premature return increases recurrence risk.
Stress reactions (Grade 1-3) heal with conservative treatment in 4-8 weeks (activity modification, weight bearing reduction). Grade 4 fracture treatment depends on location: femoral neck medial side conservative, superior side (tension side) requires surgical intervention. Anterior tibial cortex fractures heal slowly ('dreaded black line'). Follow-up MRI shows edema resolution.