NAVICULAR STRESS FRACTURES
Central Third | Watershed Area | High Nonunion Risk
FRACTURE PATTERNS
Critical Must-Knows
- Navicular stress fractures occur in central 1/3 (watershed area) with poorest blood supply - high nonunion risk (25-50%)
- MRI is gold standard for diagnosis - 70% have negative X-rays initially, MRI shows bone marrow edema and fracture line
- Strict non-weight-bearing for 6-8 weeks is critical - activity restriction alone is insufficient, cast or boot required
- Percutaneous screw fixation for failed conservative treatment or displaced fractures - 4.0-4.5mm cannulated screw from medial to lateral
- High nonunion risk without proper treatment - central third is watershed zone between dorsal and plantar arterial supply
Examiner's Pearls
- "Central 1/3 = watershed area with poorest blood supply
- "MRI gold standard - 70% negative X-rays initially
- "Strict NWB 6-8 weeks critical - activity restriction insufficient
- "Nonunion risk 25-50% without proper treatment
Navicular Stress Fractures - Quick Decision Guide
| Pattern | Location | Treatment | Outcome |
|---|---|---|---|
| Type I | Dorsal cortex only | Conservative (NWB 6-8 weeks) | 85-90% good results |
| Type II | Extends into body | Conservative or percutaneous screw | 80-85% good results |
| Type III | Complete with sclerosis | Percutaneous screw or ORIF | 75-80% good results |
WATERSHEDNavicular Stress Fracture Features
Memory Hook:WATERSHED: Watershed area (central 1/3), Arterial supply poor, Tensile stress high, Edema on MRI, Risk of nonunion high, Sagittal orientation, Healing slow, Elite athletes affected, Diagnosis by MRI!
NWBTreatment Decision
Memory Hook:NWB: Non-weight bearing strict 6-8 weeks, Weight bearing delayed, Bearing only after healing confirmed!
MRIDiagnosis
Memory Hook:MRI: MRI gold standard, Radiographs 70% negative initially, Imaging shows edema and fracture!
Overview and Epidemiology
Navicular stress fractures are high-risk stress fractures occurring in the central third of the tarsal navicular, a watershed area with poor blood supply. These fractures have a high nonunion risk (25-50%) and require strict non-weight-bearing treatment.
Definition
Navicular stress fracture: Stress fracture of the tarsal navicular, which:
- Location: Central 1/3 (watershed area)
- Orientation: Sagittal (vertical)
- Blood supply: Poorest in central third
- Nonunion risk: High (25-50%)
Watershed area:
- Central 1/3: Junction between dorsal and plantar arterial supply
- Dorsal supply: Dorsalis pedis artery
- Plantar supply: Medial plantar artery
- Poor perfusion: Relative avascularity in central third
Epidemiology
- Incidence: Less than 1% of stress fractures, but high-risk
- Age: Peak 20-30 years (athletes)
- Gender: Male predominance (sports)
- Sports: Running, jumping, basketball, football
- Risk factors: Training errors, biomechanical issues, bone health
Watershed Area
Central 1/3 of navicular is watershed area - Junction between dorsal (dorsalis pedis) and plantar (medial plantar artery) arterial supply. Poorest blood supply, highest nonunion risk (25-50%). Stress fractures occur here due to high tensile stress and limited cancellous bone.
Anatomy and Pathophysiology
Navicular Anatomy
Tarsal navicular:
- Location: Midfoot, between talus and cuneiforms
- Function: Keystone of medial longitudinal arch
- Articulations: Talus (proximal), three cuneiforms (distal), cuboid (lateral)
- Blood supply: Dorsalis pedis (dorsal), medial plantar artery (plantar)
Blood supply zones:
- Dorsal 1/3: Dorsalis pedis artery (good supply)
- Central 1/3: Watershed area (poor supply)
- Plantar 1/3: Medial plantar artery (good supply)
Watershed area:
- Central 1/3: Junction between dorsal and plantar supply
- Poor perfusion: Relative avascularity
- High risk: Nonunion risk 25-50%
Pathophysiology
Stress fracture mechanism:
- Repetitive loading: High tensile stress in central third
- Limited cancellous bone: Central third has less cancellous bone
- Poor blood supply: Watershed area has relative avascularity
- Fatigue failure: Repetitive stress exceeds bone's ability to repair
Why central third:
- Tensile stress: Highest in central third during loading
- Blood supply: Poorest in central third (watershed)
- Bone structure: Less cancellous bone in central third
Why high nonunion risk:
- Poor blood supply: Watershed area has limited perfusion
- Tensile forces: Ongoing stress prevents healing
- Delayed diagnosis: Often missed initially (70% negative X-rays)
Classification Systems
Pattern-Based Classification
Type I (Dorsal cortex only):
- Incomplete fracture, dorsal cortex only
- Treatment: Conservative (NWB 6-8 weeks)
- Outcome: 85-90% good results
Type II (Extends into body):
- Fracture extends into navicular body
- Treatment: Conservative or percutaneous screw
- Outcome: 80-85% good results
Type III (Complete with sclerosis):
- Complete fracture with sclerotic margins
- Treatment: Percutaneous screw or ORIF
- Outcome: 75-80% good results
Pattern guides treatment approach.
Clinical Assessment
History
Symptoms:
- Midfoot pain: Pain in midfoot, especially with activity
- "N spot" tenderness: 81% sensitive, 100% specific
- Activity-related: Pain with running, jumping, cutting
- Gradual onset: Insidious onset, not acute trauma
Risk factors:
- Training errors (sudden increase in intensity/duration)
- Biomechanical issues (overpronation, cavus foot)
- Bone health (low bone density, female athlete triad)
- Footwear (inadequate support)
Physical Examination
Inspection:
- Swelling (may be minimal)
- Deformity (rare)
Palpation:
- "N spot" tenderness: Over navicular (81% sensitive, 100% specific)
- Midfoot tenderness
- No acute trauma
Range of Motion:
- Midfoot ROM may be limited
- Pain with midfoot stress
Special tests:
- "N spot" palpation: Tenderness over navicular
- Single-leg hop: Pain with loading
- Midfoot stress: Pain with inversion/eversion
Clinical Examination Key Point
"N spot" tenderness is key finding - 81% sensitive, 100% specific for navicular stress fracture. Palpation over navicular reproduces pain. MRI is gold standard for diagnosis (70% have negative X-rays initially).
Investigations
Standard X-ray Protocol
AP view:
- May show fracture (30% initially)
- Often negative early
Lateral view:
- May show fracture
- Less reliable
Oblique view:
- May show fracture better
- Still often negative
Key point: 70% have negative X-rays initially - MRI is gold standard.
Management Algorithm
Management Pathway
Navicular Stress Fracture Management
Clinical suspicion with "N spot" tenderness. MRI is gold standard - shows bone marrow edema and fracture line (sagittal orientation in central third). 70% have negative X-rays initially.
Strict non-weight-bearing for 6-8 weeks is critical - activity restriction alone is insufficient. Cast or boot required. Address training errors and biomechanics. Success rate 85-90% if treated early.
CT at 6-8 weeks to confirm healing. If healing, progressive weight bearing. If non-healing or sclerosis, consider percutaneous screw fixation. Success rate 80-85% with surgery.
If failed conservative treatment (3-6 months) or displaced fracture, percutaneous screw fixation - 4.0-4.5mm cannulated screw from medial to lateral. Provides compression and stability. Success rate 80-90%.
Surgical Technique
Percutaneous Screw Fixation (Preferred)
Indications:
- Failed conservative treatment
- Displaced fracture
- Complete fracture with sclerosis
Approach:
- Medial stab incision
- Guidewire placement under fluoroscopy
- Screw fixation
Technique:
- Exposure: Medial stab incision over navicular tuberosity
- Guidewire: Place guidewire from medial to lateral under fluoroscopy
- Verification: Confirm position on AP, lateral, oblique views
- Screw: 4.0-4.5mm cannulated screw over guidewire
- Compression: Partially threaded screw for compression
- Verification: Confirm reduction and hardware position fluoroscopically
Advantages:
- Minimally invasive
- Provides compression
- Allows early motion
- High union rate
Percutaneous screw is preferred technique.
Complications
| Complication | Incidence | Risk Factors | Prevention/Management |
|---|---|---|---|
| Nonunion | 25-50% | Central 1/3 location, delayed treatment | Strict NWB, early treatment |
| Delayed union | 20-30% | Inadequate NWB, continued activity | Strict NWB, monitor with CT |
| Missed diagnosis | 30-40% | Negative X-rays, delayed presentation | High index of suspicion, MRI |
| AVN | 10-15% | Central location, poor blood supply | Early treatment, protect blood supply |
Nonunion
25-50% incidence (if untreated):
- Cause: Central 1/3 location, poor blood supply, delayed treatment
- Prevention: Strict NWB, early treatment, percutaneous screw if needed
- Management: Percutaneous screw or ORIF with bone graft
Delayed Union
20-30% incidence:
- Cause: Inadequate NWB, continued activity, poor blood supply
- Prevention: Strict NWB, monitor with CT
- Management: Extended NWB, consider percutaneous screw
Postoperative Care
Immediate Postoperative
- Immobilisation: Short leg cast or boot
- Weight bearing: Non-weight bearing (6-8 weeks)
- ROM: Ankle ROM after cast removal
- PT: Midfoot ROM and strengthening
Rehabilitation Protocol
Weeks 0-6:
- Short leg cast, non-weight bearing
- Elevation to reduce swelling
- Ankle ROM exercises (if stable)
Weeks 6-8:
- CT to confirm healing
- Cast removal if healing
- Transition to walking boot
- Progressive weight bearing
Weeks 8-12:
- Full weight bearing
- Progressive activity
- Return to sport (3-4 months)
Outcomes and Prognosis
Overall Outcomes
Conservative treatment (early):
- Success rate: 85-90% (union, pain relief)
- Functional outcomes: 80-85% return to pre-injury level
- Return to sport: 3-4 months
Percutaneous screw fixation:
- Success rate: 80-90% (union, pain relief)
- Functional outcomes: 75-80% return to pre-injury level
- Return to sport: 3-4 months
Open ORIF (nonunion):
- Success rate: 75-80% (union, pain relief)
- Functional outcomes: 70-75% return to pre-injury level
- Return to sport: 4-6 months
Long-Term Prognosis
Nonunion progression:
- With proper treatment: 10-15% develop nonunion
- Without treatment: 25-50% develop nonunion
- Risk factors: Central location, delayed treatment, inadequate NWB
Evidence Base
Navicular Stress Fractures
- Central 1/3 = watershed area with poor blood supply
- High nonunion risk (25-50%) without proper treatment
- MRI gold standard (70% negative X-rays initially)
- Strict NWB 6-8 weeks critical
Treatment Outcomes
- Conservative: 85-90% good results if early
- Percutaneous screw: 80-90% good results
- Open ORIF: 75-80% good results
- Early treatment improves outcomes
Watershed Area
- Central 1/3 = watershed area
- Junction between dorsal and plantar supply
- Poorest blood supply
- Highest nonunion risk
Diagnosis
- MRI gold standard
- 70% negative X-rays initially
- Shows bone marrow edema and fracture line
- 'N spot' tenderness 81% sensitive, 100% specific
Nonunion Risk
- High nonunion risk (25-50%) without proper treatment
- Central 1/3 location contributes to risk
- Poor blood supply contributes to risk
- Strict NWB critical to prevent nonunion
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Athlete with Midfoot Pain
"A 22-year-old elite runner presents with 6 weeks of midfoot pain, worse with running. Clinical examination shows 'N spot' tenderness over navicular. X-rays are negative. MRI shows bone marrow edema and fracture line in central 1/3 of navicular (sagittal orientation)."
Scenario 2: Failed Conservative Treatment
"A 25-year-old athlete has a navicular stress fracture treated conservatively with 8 weeks non-weight-bearing. CT at 8 weeks shows persistent fracture line with sclerotic margins (nonunion). Patient has persistent pain and wants to return to sport."
MCQ Practice Points
Watershed Area
Q: Why do navicular stress fractures occur in the central 1/3? A: Central 1/3 is watershed area - Junction between dorsal (dorsalis pedis) and plantar (medial plantar artery) arterial supply. Poorest blood supply, highest nonunion risk (25-50%). Stress fractures occur here due to high tensile stress and limited cancellous bone.
MRI Gold Standard
Q: What is the gold standard for diagnosing navicular stress fractures? A: MRI is gold standard - 70% of early stress fractures have negative X-rays. MRI shows bone marrow edema and fracture line (sagittal orientation in central third). 'N spot' tenderness is 81% sensitive, 100% specific.
Treatment
Q: What is the treatment for navicular stress fractures? A: Strict non-weight-bearing for 6-8 weeks is critical - Activity restriction alone is insufficient. Cast or boot required. Address training errors and biomechanics. CT at 6-8 weeks to confirm healing. Success rate 85-90% if treated early.
Surgical Indications
Q: When is surgery indicated for navicular stress fractures? A: Failed conservative treatment (3-6 months) or displaced fracture - Percutaneous screw fixation (4.0-4.5mm cannulated screw from medial to lateral). Provides compression and stability. Success rate 80-90%.
Nonunion Risk
Q: What is the nonunion risk for navicular stress fractures? A: High nonunion risk (25-50%) without proper treatment - Central 1/3 location, poor blood supply, and high tensile stress contribute to nonunion risk. Strict non-weight-bearing for 6-8 weeks is critical to prevent nonunion.
Australian Context
Clinical Practice
- Navicular stress fractures rare but high-risk
- MRI gold standard for diagnosis
- Strict NWB critical
- Percutaneous screw for failed conservative
Healthcare System
- Public hospitals handle most cases
- Private insurance covers procedures
- Sports injuries common
Orthopaedic Exam Relevance
Navicular stress fractures are a common viva topic. Know that central 1/3 = watershed area (poor blood supply, high nonunion risk 25-50%), MRI is gold standard (70% negative X-rays initially), strict NWB 6-8 weeks critical (activity restriction insufficient), percutaneous screw for failed conservative (80-90% good results), and 'N spot' tenderness is 81% sensitive, 100% specific. Be prepared to discuss the watershed area anatomy and treatment decision.