Bilateral Navicular Bone Swelling: Other Causes
Beyond infection and trauma, bilateral navicular bone swelling most commonly results from Charcot neuroarthropathy (especially in diabetics), chronic non-bacterial osteitis (CNO), spontaneous osteonecrosis (Müller-Weiss disease), inflammatory arthropathies (psoriatic arthritis, axial spondyloarthritis), and symptomatic accessory navicular bones.
Primary Differential Diagnoses to Consider
Charcot Neuroarthropathy
The navicular and naviculo-cuneiform joints represent the most common anatomic site for Charcot arthropathy (type I arthropathy) 1. This condition presents with:
- Diffuse bone marrow edema on MRI involving navicular, cuneiforms, cuboid, and metatarsal bases 2
- Bilateral flat feet with hindfoot valgus deformity
- Progressive fragmentation and joint destruction
- Critical pitfall: MRI bone marrow edema in acute/subacute Charcot mimics osteomyelitis on T2/STIR sequences 1
Distinguishing features: Look for absence of ulceration, cellulitis, or sinus tracts. Distribution pattern favors midfoot (Lisfranc/Chopart joints) rather than toes/metatarsal heads where osteomyelitis predominates 1.
Spontaneous Osteonecrosis (Müller-Weiss Disease)
This represents idiopathic avascular necrosis of the navicular in adults, distinct from pediatric Köhler disease 3, 4:
- Bilateral in 80% of cases, predominantly affects women
- Characteristic radiographic findings: comma-shaped navicular, decreased size, increased radiodensity, fragmentation, medial/dorsal osseous protrusion 4
- Associated with pes planus and hindfoot valgus deformity
- MRI confirms marrow alterations consistent with osteonecrosis 4
Pathogenesis: Chronic stress from physiologic pressure on medial longitudinal arch in hindfoot valgus plus tension forces from plantar aponeurosis during weight-bearing 4.
Chronic Non-Bacterial Osteitis (CNO)
An autoinflammatory bone disorder that can affect the midfoot 5:
- Bone marrow edema on MRI (though lacks specificity)
- Elevated CRP/ESR
- Key distinguishing features: Absence of fever, bacteremia, or presumable infection port of entry
- May involve multiple skeletal sites (consider whole-body imaging)
Diagnostic approach: MRI preferred for detecting bone marrow and soft tissue edema; exclude infectious osteomyelitis through clinical context and negative cultures 5.
Inflammatory Arthropathies
Psoriatic Arthritis: Consider when bilateral navicular involvement occurs with 5:
- Psoriasis (current, history, or first-degree family history)
- Enthesitis, dactylitis
- Juxta-articular new bone formation on foot radiography
- Nail dystrophy
Axial Spondyloarthritis: Evaluate for 5:
- Inflammatory back pain, sacroiliitis
- HLA-B27 positivity
- Asymmetrical inflammatory arthritis
- Elevated CRP, response to NSAIDs
Symptomatic Accessory Navicular Bone
Type II accessory navicular is the most commonly symptomatic variant 6:
- Bilateral in 50-90% of cases
- Higher incidence in women
- Localized chronic or acute-on-chronic medial foot pain
- Inflammation of overlying soft tissues
- Diagnostic approach: Plain radiographs insufficient; ultrasound allows comparison with asymptomatic side and pain localization; MRI demonstrates bone marrow and soft tissue edema 6
Diagnostic Algorithm
Step 1: Initial Imaging
Radiography bilateral feet (three views: dorsoplantar, lateral, medial oblique) 2, 7:
- Assess for comma-shaped navicular, fragmentation, increased density (osteonecrosis)
- Identify accessory ossicles
- Evaluate for joint space narrowing, erosions, osteophytes
- Document foot alignment (pes planus, hindfoot valgus)
Step 2: Clinical Context Assessment
Determine presence of:
- Diabetes: Strongly suggests Charcot (especially with flat foot deformity)
- Ulceration/skin breakdown: Favors osteomyelitis over Charcot 1
- Systemic inflammatory symptoms: Consider CNO or inflammatory arthropathy
- Trauma history: May indicate stress fractures or post-traumatic changes
- Steroid use, lupus, alcohol: Secondary osteonecrosis risk factors 3
Step 3: Advanced Imaging Based on Clinical Suspicion
MRI without contrast is the next appropriate study for most scenarios 8, 9:
- High sensitivity/specificity for osteonecrosis, bone marrow edema patterns
- Differentiates Charcot from osteomyelitis (look for ulceration, sinus tracts, soft tissue abscesses as "secondary signs" of infection) 1
- Evaluates soft tissue involvement, tendon pathology
- Limitation: Cannot reliably distinguish Charcot bone marrow edema from osteomyelitis edema in acute/subacute phases 1
When Charcot with superimposed osteomyelitis suspected: WBC imaging or [18F]FDG PET/CT more effective than MRI for differentiation 1.
Step 4: Laboratory Evaluation
- Elevated CRP/ESR: Supports infection or inflammatory arthropathy (but also seen in CNO)
- HLA-B27, RF, anti-CCP: When inflammatory arthropathy suspected 5
- Blood cultures: If systemic infection concern
- Bone/wound cultures: When osteomyelitis cannot be excluded clinically
Critical Pitfalls to Avoid
Do not assume bilateral = non-infectious: While bilateral involvement favors spontaneous osteonecrosis or systemic conditions, bilateral osteomyelitis can occur in diabetics with bilateral ulcers 2.
Do not rely solely on MRI bone marrow edema: This finding occurs in osteomyelitis, Charcot, CNO, osteonecrosis, stress fractures, and even healthy individuals 5, 1. Pattern recognition and clinical correlation are essential.
Do not miss secondary causes of osteonecrosis: Always inquire about steroid use, lupus, renal failure, trauma, and alcohol consumption 3, 4.
Do not overlook accessory navicular: Bilateral medial foot pain with normal-appearing navicular on cursory review may represent symptomatic type II accessory navicular requiring ultrasound or MRI for diagnosis 6.
Do not forget vascular assessment in diabetics: Ischemia (WIfI classification) significantly impacts treatment decisions and prognosis 2.