Signal Abnormality Along Plantar Surface of 2nd Metatarsal Head on MRI
A signal abnormality along the plantar surface of the second metatarsal head most commonly indicates either a subchondral stress fracture/bone marrow edema, plantar plate pathology, or adventitious bursitis, and requires clinical correlation to determine which is causing symptoms.
Primary Differential Diagnoses
The location you describe—plantar surface of the 2nd metatarsal head—is a high-stress area prone to several specific pathologies:
1. Subchondral Stress Fracture/Bone Marrow Edema
- Most common in women with forefoot pain 1
- The dorsal third of the metatarsal articular surface is involved in 79% of cases, but plantar involvement occurs 1
- MRI typically shows:
- Subchondral fracture line with severe marrow edema (71% of cases) = early stage
- Metatarsal head collapse with subchondral sclerosis and mild/absent edema (29%) = late stage 1
- The second metatarsal head is affected in 71% of subchondral fractures 1
2. Plantar Plate Tear or Degeneration
- Signal abnormality may represent adjacent soft tissue pathology affecting the plantar plate attachment
- MRI is the most sensitive imaging modality for plantar plate tears (93% sensitivity) 2
- Risk factors include:
- Look for associated findings: plantar plate thickening, discontinuity, or fluid signal 2
3. Adventitious Bursitis
- Develops from friction and high pressure at metatarsal head prominences 5
- Can present as a heterogeneous mass with solid component
- Shows intermediate to high T2 signal with thick nodular enhancement 5
- May mimic neoplasm but regresses with pressure offloading 5
Clinical Correlation Algorithm
Step 1: Assess the MRI signal characteristics
- T1 hypointense + T2 hyperintense = bone marrow edema pattern (stress injury)
- Subchondral linear T1/T2 hypointensity = fracture line 6
- Soft tissue signal abnormality plantar to bone = plantar plate or bursa
Step 2: Evaluate for associated findings
- Metatarsal head flattening or collapse = late-stage subchondral fracture 1
- Plantar plate discontinuity = tear
- Fluid collection with solid component = bursitis 5
Step 3: Correlate with clinical presentation
- Point tenderness directly over metatarsal head = likely osseous pathology
- Pain with toe dorsiflexion or "drawer sign" = plantar plate tear
- Palpable plantar mass = consider bursitis 5
Step 4: Check radiographs
- Measure second metatarsal protrusion (Coughlin method)
- Look for subtle sclerosis or flattening
- Radiographs have only 12-56% sensitivity for stress fractures 2
Management Implications
For subchondral stress fracture:
- Second metatarsal head fractures are low-risk and can be treated non-operatively 6
- Offloading with appropriate footwear or orthoses
- Follow-up imaging if symptoms persist
For plantar plate pathology:
- Consider surgical intervention if conservative treatment fails
- May require metatarsal shortening osteotomy (Weil) if significant protrusion present 4
For adventitious bursitis:
- Trial of offloading and pressure reduction
- Biopsy only if mass doesn't regress or if solid enhancing component raises neoplastic concern 5
Critical Pitfall to Avoid
Do not overcall plantar fasciitis or assume all plantar signal abnormality is inflammatory. MRI findings must correlate with clinical symptoms, as bone marrow edema and other findings can be seen in asymptomatic individuals, particularly athletes 2, 7. In one study, 82% of asymptomatic professional ballet dancers had bone marrow edema on MRI, with the talus and first metatarsal most common 7.
The second metatarsal head location specifically suggests mechanical overload pathology rather than systemic inflammatory disease, especially in the absence of polyarticular involvement.