High Yield Overview
Trapezoid Fractures
Rare Carpal Fracture | Second Metacarpal Articulation
less than 1%of Carpal Fractures
RareIncidence
AxialMechanism
ConservativeMost Treatment
Trapezoid Fracture Types
Non-Displaced
PatternFracture without significant displacement.
TreatmentCast/Splint
Displaced
PatternSignificant displacement or comminution.
TreatmentORIF / K-wires
With Dislocation
PatternCMC or intercarpal dislocation component.
TreatmentORIF
Critical Must-Knows
- Rarest Carpal Fracture: Less than 1% of all carpal fractures.
- Location: Distal carpal row. Articulates with Trapezium, Capitate, Scaphoid, and 2nd MC.
- Protection: The trapezoid is well-protected (recessed in the distal row, keystone of 2nd CMC).
- Mechanism: Axial load through 2nd metacarpal (punch, fall on flexed wrist).
- Treatment: Non-displaced = Cast. Displaced/Dislocated = ORIF.
Examiner's Pearls
- "Trapezoid is the RAREST carpal bone to fracture.
- "Look for associated injuries (2nd CMC dislocation, scaphoid fracture).
- "CT is essential for diagnosis and surgical planning.
- "Most non-displaced fractures can be managed with immobilization.
Trapezoid Fracture Pitfalls
Missed on X-ray
CT is Key. Trapezoid fractures are easily missed on X-ray due to overlapping carpal bones. Get CT if suspicious.
Associated Injuries
2nd CMC Dislocation. Often associated with 2nd CMC fracture-dislocation. Assess entire carpus.
Rare = Forgotten
Keep in Differential. Because it's rare, it may be overlooked. Maintain high suspicion with dorsal wrist pain after axial load.
Arthrosis
Post-Traumatic OA. Important for wrist biomechanics. Articular fractures may lead to 2nd CMC arthrosis.
At a Glance: Carpal Fracture Frequency
| Bone | Frequency | Key Associated Injury |
|---|---|---|
| Scaphoid | ~70% | Distal Radius, Perilunate |
| Triquetrum | ~15% | Perilunate, Lunate |
| Lunate | ~3% | Kienböck's (if AVN) |
| Trapezium | ~3% | Thumb CMC, Bennett's |
| Capitate | ~2% | Scaphocapitate Syndrome |
| Hamate | ~2% | Hook fracture, Boxer's |
| Trapezoid | less than 1% | 2nd CMC Dislocation |
| Pisiform | ~1% | FCU tendon injury |
Mnemonic
She Looks Too Pretty; Try To Catch HerCarpal Bones
S
Scaphoid
Proximal row, radial
L
Lunate
Proximal row, central
T
Triquetrum
Proximal row, ulnar
P
Pisiform
Sesamoid (on triquetrum)
T
Trapezium
Distal row, radial (thumb)
T
Trapezoid
Distal row, central-radial
C
Capitate
Distal row, central (largest)
H
Hamate
Distal row, ulnar (hook)
Memory Hook:Carpal bone order: Proximal then Distal.
Mnemonic
TRAP-2Trapezoid Articulations
T
Trapezium
Radial (thumb side)
R
Radius
Indirectly via Scaphoid
A
Articulates
With scaphoid proximally
P
Points
Capitate ulnarly
2
2nd Metacarpal
Key articulation - CMC joint
Memory Hook:Trapezoid is the keystone of 2nd CMC.
Mnemonic
PUNCHMechanism
P
Punch
Direct force through 2nd MC
U
Upward
Axial load transmission
N
Narrowest
Trapezoid is narrow distally
C
Compression
Compressed against scaphoid
H
Hyperflexion
Wrist in flexed position
Memory Hook:Punch injury mechanism.
Overview and Epidemiology
Definition: Trapezoid fractures are fractures of the trapezoid bone, the second bone of the distal carpal row. It is the rarest carpal bone to fracture, accounting for less than 1% of all carpal fractures.
Epidemiology:
- Incidence: Extremely rare.
- Mechanism: Axial load through 2nd metacarpal (punch, fall on flexed wrist).
- Associated Injuries: 2nd CMC dislocation, Perilunate injury, Scaphoid fracture.
Why Rare:
- Trapezoid is recessed within the distal carpal row.
- Protected by surrounding bones.
- Strong ligamentous attachments.
- Keystone of the rigid 2nd CMC joint.
Anatomy and Pathophysiology
Anatomy:
- Location: Distal carpal row. Between trapezium (radial) and capitate (ulnar).
- Shape: Wedge-shaped. Narrow dorsally, wider volarly.
- Articulations:
- Proximal: Scaphoid.
- Distal: 2nd Metacarpal base (key articulation).
- Radial: Trapezium.
- Ulnar: Capitate.
Biomechanics:
- 2nd CMC Joint: Most stable CMC joint (index finger ray). Keystone is the trapezoid.
- Force Transmission: Axial load through 2nd MC can fracture trapezoid.
Blood Supply:
- Enters from dorsal and palmar surfaces.
- AVN is rare.
Classification
Simple Classification
- Non-Displaced: Fracture without significant articular step-off.
- Displaced: Significant displacement or articular incongruity.
- With Dislocation: Associated 2nd CMC or intercarpal dislocation.
- Comminuted: Multiple fragments (often with high-energy).
CT is necessary to classify accurately.
Clinical Assessment
History:
- Mechanism: Punch? Fall on flexed wrist? Axial load?
- Pain Location: Dorsal wrist, over 2nd MC base.
Physical Examination:
- Tenderness: Over trapezoid (dorsal, between 1st and 2nd MC bases).
- Swelling: Dorsal wrist.
- Pain: With axial loading of 2nd metacarpal.
- ROM: Painful wrist flexion/extension.
- Neurovascular: Usually intact.
Investigations
Imaging:
- X-ray (PA, Lateral, Oblique): May show fracture, but often missed due to overlap.
- CT Scan: Essential for diagnosis. Defines fracture pattern, displacement.
- MRI: Rarely needed. For occult fractures or soft tissue assessment.
Key Findings:
- X-ray: Subtle cortical irregularity. Overlap with scaphoid/capitate.
- CT: Clearly delineates fracture. Assess articular involvement.
Management Algorithm
📊 Management Algorithm
Click to expand
Non-Displaced Fractures
Conservative Management.
- Immobilization: Short arm cast or thumb spica for 4-6 weeks.
- Follow-up: Repeat X-ray/CT at 4-6 weeks for healing.
- Rehabilitation: ROM exercises after cast removal.
Most non-displaced fractures heal well.
Surgical Technique
Dorsal Approach
Incision: Dorsal longitudinal incision centered over 2nd MC base
Structures at Risk:
- Radial artery (anatomical snuffbox)
- Extensor tendons (EPL, ECRL, ECRB)
- Superficial branch radial nerve
Exposure: Capsulotomy between 2nd and 3rd extensor compartments
Complications
Complications
| Complication | Risk Factor | Management |
|---|---|---|
| Post-Traumatic Arthrosis | Articular fracture | Fusion (CMC) / Excision |
| Malunion | Inadequate reduction | Osteotomy / Accept |
| Stiffness | Prolonged immobilization | Physiotherapy |
| Non-union | Rare (good blood supply) | Bone graft / Fixation |
Postoperative Care
After Cast/Conservative:
- ROM exercises at 4-6 weeks.
- Strengthen at 6-8 weeks.
After ORIF:
- Splint 2 weeks, then cast/removable splint.
- ROM at 4-6 weeks.
- K-wire removal at 6-8 weeks if used.
Outcomes
- Non-Displaced: Good prognosis with immobilization.
- Displaced/Dislocated: Risk of 2nd CMC arthrosis if not anatomically reduced.
Evidence Base
Trapezoid Fractures
Key Findings:
- Reviewed rare trapezoid fractures.
- Often associated with 2nd CMC injury.
- CT is essential for diagnosis.
Clinical Implication: CT for all suspected carpal fractures with normal X-ray.
Limitation: Case series
Carpal Fracture Frequency
Key Findings:
- Scaphoid is most common (70%).
- Trapezoid is least common (less than 1%).
Clinical Implication: Know the relative frequencies.
Limitation: Epidemiological
2nd CMC Dislocations
Key Findings:
- Described 2nd CMC fracture-dislocations.
- Often associated with trapezoid injury.
- ORIF recommended for displaced injuries.
Clinical Implication: Assess CMC joint with trapezoid fractures.
Limitation: Case series
CT for Carpal Fractures
Key Findings:
- CT superior to X-ray for carpal fracture detection.
- Essential for surgical planning.
Clinical Implication: Get CT if X-ray is negative but clinical suspicion is high.
Limitation: Diagnostic
Surgical Outcomes
Key Findings:
- Anatomic reduction improves outcomes.
- Non-anatomic reduction leads to arthrosis.
Clinical Implication: Aim for anatomic reduction in displaced fractures.
Limitation: Expert opinion
Viva Scenarios
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
The Rare Fracture
EXAMINER
"What is your next step?"
EXCEPTIONAL ANSWER
**High Suspicion for Occult Carpal Fracture. CT is Needed.**
1. **History**: Axial load through 2nd MC (punch). Classic for trapezoid or 2nd CMC injury.
2. **Examination**: Tenderness over trapezoid (dorsal, 2nd MC base). Pain with axial load.
3. **X-ray 'Normal'**: Not reassuring. Trapezoid fractures easily missed due to overlap.
4. **Next Step**: CT Wrist.
5. **CT Findings**: May show trapezoid fracture, 2nd CMC dislocation.
6. **Management**:
- *If Non-Displaced*: Cast 4-6 weeks.
- *If Displaced/Dislocated*: ORIF.
KEY POINTS TO SCORE
CT for 'normal' X-ray with clinical suspicion
Trapezoid = Rarest carpal fracture
Punch mechanism
2nd CMC injury often associated
COMMON TRAPS
✗Trusting the X-ray
✗Missing the injury
LIKELY FOLLOW-UPS
"Where exactly is the trapezoid?"
"What articulates with the trapezoid?"
VIVA SCENARIOStandard
The Rarest Question
EXAMINER
"Answer the question."
EXCEPTIONAL ANSWER
**The Trapezoid.**
1. **Frequency**: Less than 1% of all carpal fractures.
2. **Why Rare**:
- Recessed in distal row (protected by surrounding bones).
- Strong ligamentous attachments.
- Keystone of the rigid 2nd CMC joint.
3. **Mechanism**: Axial load through 2nd metacarpal (punch, fall).
4. **Associated Injury**: 2nd CMC fracture-dislocation.
5. **Diagnosis**: CT (X-ray often misses).
KEY POINTS TO SCORE
Trapezoid = Rarest
Less than 1% of carpal fractures
Protected position
CT for diagnosis
COMMON TRAPS
✗Saying pisiform (also rare but more common)
✗Not knowing why it's rare
LIKELY FOLLOW-UPS
"What is the most common carpal fracture?"
"What is the 2nd CMC joint?"
VIVA SCENARIOStandard
The Carpal Frequency
EXAMINER
"Provide the ranking."
EXCEPTIONAL ANSWER
**Carpal Fracture Frequency (Most to Least Common):**
1. **Scaphoid**: ~70% (Most common).
2. **Triquetrum**: ~15%.
3. **Lunate**: ~3% (Kienböck's if AVN).
4. **Trapezium**: ~3% (Thumb CMC).
5. **Capitate**: ~2%.
6. **Hamate**: ~2% (Hook fracture).
7. **Pisiform**: ~1%.
8. **Trapezoid**: less than 1% (Rarest).
**Mnemonic**: Think of the 'vulnerable' bones - Scaphoid (snuffbox), Hamate hook (grip), Triquetrum (dorsal impaction).
KEY POINTS TO SCORE
Scaphoid = Most common (70%)
Trapezoid = Rarest (less than 1%)
Triquetrum = 2nd most common
COMMON TRAPS
✗Getting the order wrong
✗Not knowing trapezoid is rarest
LIKELY FOLLOW-UPS
"What is the mechanism for scaphoid fracture?"
"What is the hook of hamate fracture mechanism?"
MCQ Practice Points
Frequency
Q: What is the rarest carpal bone to fracture? A: Trapezoid (less than 1% of carpal fractures).
Location
Q: Where is the trapezoid located? A: Distal carpal row. Between the trapezium (radial) and capitate (ulnar). Articulates with the 2nd metacarpal distally.
Mechanism
Q: What is the typical mechanism for trapezoid fracture? A: Axial load through the 2nd metacarpal (e.g., punch injury, fall on flexed wrist).
Associated Injury
Q: What is the most common associated injury with trapezoid fractures? A: 2nd CMC (carpometacarpal) fracture-dislocation.
Imaging
Q: What imaging is best for trapezoid fractures? A: CT scan. X-rays often miss trapezoid fractures due to overlapping bones.
Australian Context
- Hand Surgery Referral: Displaced trapezoid fractures should be referred to hand surgery.
- CT Access: Readily available in Australia for carpal injury workup.
High-Yield Exam Summary
Key Facts
- •Rarest carpal fracture
- •less than 1% of carpal fractures
- •Distal row (2nd CMC)
- •Punch mechanism
Diagnosis
- •X-ray often negative (overlap)
- •CT is essential for diagnosis
- •Tenderness at 2nd MC base
- •Pain with axial load of index finger
Treatment
- •Non-displaced: Short arm cast 4-6 weeks
- •Displaced: ORIF via dorsal approach
- •Fixation: Headless screws or K-wires
- •Post-op: Cast 4-6 weeks, ROM after healing
Associated
- •2nd CMC dislocation (most common)
- •Perilunate injuries (greater arc)
- •Scaphoid fractures (high-energy)
- •Multiple carpal fractures (assess entire carpus)