High-yield overview
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.
Clinical 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.
| 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)
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
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
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
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
| 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
Evidence
Relative Incidence of Carpal Fractures
Key Findings:
- Prospective audit of 1,000 consecutive hand fractures in Bergen, Norway over ~10 months.
- Carpal bones accounted for 18% of all hand fractures; the scaphoid alone made up 10.6% of the total series.
- Trapezoid fractures were essentially absent from this unselected series, confirming their status as the rarest carpal fracture.
Clinical implication: Population data establish the scaphoid as dominant and the trapezoid as exceptionally rare — keep trapezoid injury low in the differential but never absent after axial 2nd-ray load.
Limitation: Single-centre Scandinavian cohort; no DOI indexed.
Evidence
Occult Undisplaced Trapezoid Fracture
Key Findings:
- Two cases of isolated, undisplaced trapezoid fracture diagnosed with CT/MRI after negative or equivocal radiographs.
- Authors argue the lesion has historically been under-diagnosed and that modern cross-sectional imaging makes detection more frequent.
- Both undisplaced fractures healed with immobilisation alone.
Clinical implication: A negative radiograph does not exclude a trapezoid fracture; advanced imaging both detects occult injury and supports non-operative management when undisplaced.
Limitation: Case report (n=2); no DOI indexed.
Evidence
First True Isolated Trapezoid Fracture
Key Findings:
- First reported isolated trapezoid fracture with NO accompanying dislocation or associated metacarpal, carpal or distal radius injury.
- Managed non-operatively with a favourable clinical outcome.
- Reviews presentation, diagnostic workup and treatment of trapezoid fractures generally.
Clinical implication: A genuinely isolated, undisplaced trapezoid fracture can be treated successfully with immobilisation — surgery is reserved for displacement or associated dislocation.
Limitation: Single case report; no DOI indexed.
Evidence
Trapezoid Dislocation — Missed on Plain Films
Key Findings:
- Isolated trapezoid dislocation following high-speed motor-vehicle trauma.
- Highlights that these injuries are commonly missed on standard radiographs.
- Management invariably required open reduction and internal fixation.
Clinical implication: High-energy trapezoid displacement/dislocation is easily missed on radiographs and typically mandates ORIF — maintain suspicion and obtain CT.
Limitation: Single case report.
Evidence
Palmar Trapezoid Dislocation in Polytrauma
Key Findings:
- Rare palmar trapezoid dislocation with associated distal radius fracture in a major-trauma patient.
- Distracting injuries risk misdiagnosis or delayed diagnosis of the carpal component.
- ORIF performed after stabilisation of major injuries yielded satisfactory hand and wrist function.
Clinical implication: In polytrauma, deliberately scrutinise the carpus — distracting injuries cause delayed diagnosis of trapezoid displacement; ORIF restores function.
Limitation: Single case report.
Evidence
2nd CMC Fracture-Dislocation with Trapezoid Fracture
Key Findings:
- Dorsal 2nd CMC dislocation with trapezoid fracture plus a Rolando fracture after a road-traffic crash.
- Treated by closed reduction with percutaneous K-wires then CT-guided open trapezoid reduction and K-wire fixation.
- Literature review of 71 cases of injuries involving 2nd CMC dislocation; good pain-free outcome at 1 year.
Clinical implication: The trapezoid is the keystone of the 2nd CMC joint — a trapezoid fracture should prompt assessment for an associated 2nd CMC fracture-dislocation, which is itself an ORIF indication.
Limitation: Case report with literature review; French language.
Viva Scenarios
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
Viva scenarioStandard
The Rare Fracture
Clinical prompt
“What is your next step?”
Practical approach
**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 clinical points
CT for 'normal' X-ray with clinical suspicion
Trapezoid = Rarest carpal fracture
Punch mechanism
2nd CMC injury often associated
Common pitfalls
Trusting the X-ray
Missing the injury
Further questions
“Where exactly is the trapezoid?”
“What articulates with the trapezoid?”
Viva scenarioStandard
The Rarest Question
Clinical prompt
“Answer the question.”
Practical approach
**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 clinical points
Trapezoid = Rarest
Less than 1% of carpal fractures
Protected position
CT for diagnosis
Common pitfalls
Saying pisiform (also rare but more common)
Not knowing why it's rare
Further questions
“What is the most common carpal fracture?”
“What is the 2nd CMC joint?”
Viva scenarioStandard
The Carpal Frequency
Clinical prompt
“Provide the ranking.”
Practical approach
**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 clinical points
Scaphoid = Most common (70%)
Trapezoid = Rarest (less than 1%)
Triquetrum = 2nd most common
Common pitfalls
Getting the order wrong
Not knowing trapezoid is rarest
Further questions
“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.
Differential Diagnosis
The trapezoid fracture presents as dorsal wrist pain at the index-ray base after axial load — overlapping with several commoner injuries. CT is the discriminator.
| Diagnosis | Distinguishing Feature | Best Test |
|---|---|---|
| Trapezoid fracture/dislocation | Tenderness at 2nd MC base; pain on axial load of index ray; often missed on plain film | CT |
| 2nd CMC fracture-dislocation | Dorsal prominence of index MC base; cascade-line disruption; commonly coexists | Lateral/oblique radiograph + CT |
| Scaphoid fracture | Anatomical snuffbox and scaphoid tubercle tenderness; radial-sided | Scaphoid views; CT/MRI if occult |
| Trapezium fracture | Thumb-base tenderness; pain on thumb axial load (Bennett-type force) | CT; carpal tunnel/Bett view |
| Wrist sprain (no fracture) | Diffuse tenderness, no bony point tenderness; normal CT | Clinical + negative CT |
Controversies & Areas of Uncertainty
The literature on trapezoid fractures is limited to case reports and small series, so several questions remain unresolved:
- Imaging threshold: There is no consensus on which patients with a "normal" radiograph warrant CT. Most authorities favour a low threshold for cross-sectional imaging given how often the injury is missed, but the cost-effectiveness of routine CT after axial index-ray trauma is undefined.
- Screw vs K-wire fixation: No comparative data exist for displaced fragments. Headless compression screws are preferred for fragments large enough to accept them; K-wires are used for comminuted or small fragments. Choice remains surgeon preference.
- Management of the associated 2nd CMC instability: Whether transarticular K-wiring alone, ligament repair, or temporary CMC fixation gives the best long-term result is unknown — the rarity of the injury precludes trials.
- True incidence: Historical "less than 1%" figures predate routine CT. The real incidence of occult, undisplaced trapezoid fractures is probably higher than classically reported, as several authors have argued.
- Late presentation: Optimal treatment of a missed/chronic trapezoid fracture or dislocation (delayed ORIF vs excision vs limited fusion) is not established.
Guidelines, Registries & Global Practice
There are no condition-specific society guidelines or arthroplasty-registry data for trapezoid fractures given their rarity; practice is governed by general carpal-injury and hand-trauma principles.
Global epidemiology
- Carpal bones contribute roughly 18% of hand fractures, of which the scaphoid dominates (~60% of carpal fractures); the trapezoid is consistently the least frequently fractured carpal bone (classically under 1%).
- Reported cases cluster in young men after high-energy axial mechanisms (punch injury, falls on the flexed wrist, motor-vehicle trauma).
Side-by-side guideline principles
| Body | Relevant Principle |
|---|---|
| BOA / BOAST (UK) | Clinically suspected carpal injury with normal radiographs should be immobilised and re-imaged or progressed to advanced imaging rather than discharged. |
| AAOS / ASSH (US) | Cross-sectional imaging (CT) for occult or complex carpal fractures and pre-operative planning; anatomic reduction of displaced intra-articular carpal fractures. |
| AO Foundation | Articular congruity and stable fixation of displaced carpal fractures; transarticular K-wires for associated CMC instability. |
| EFORT / European consensus | Low threshold for CT in high-energy wrist trauma and polytrauma to avoid missed carpal injuries among distracting fractures. |
High- vs limited-resource practice variation
- Well-resourced settings: Ready CT access enables early detection and ORIF of displaced fractures and associated 2nd CMC dislocations; this is the main reason reported incidence is rising.
- Limited-resource settings: Reliance on plain radiographs means occult and undisplaced trapezoid fractures are frequently missed; immobilisation of the clinically suspicious wrist with delayed re-imaging is a reasonable strategy where CT is unavailable.
- Referral: Displaced fractures and fracture-dislocations warrant referral to a hand/upper-limb surgeon wherever the resource pathway allows.
Exam day cheat sheet
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)