PISIFORM FRACTURES
Rare Sesamoid Carpal Bone | FCU Insertion | Ulnar Nerve at Risk
FRACTURE PATTERNS
Critical Must-Knows
- Only sesamoid bone in the carpus - embedded in FCU tendon
- Direct blow mechanism - fall onto hypothenar eminence with wrist extended
- Guyon canal runs adjacent - ulnar nerve and artery at risk
- Pisotriquetral joint forms articulation with triquetrum
- Excision is effective treatment for symptomatic fractures
Examiner's Pearls
- "Pisiform is the most ulnar and volar of the proximal carpal row
- "Only carpal bone with a single articular surface (pisotriquetral)
- "FCU inserts onto pisiform - force transmitted to hook of hamate via pisohamate ligament
- "Carpal tunnel view best visualizes the pisiform
Critical Pisiform Fracture Exam Points
Anatomy
Sesamoid bone within FCU tendon. Forms pisotriquetral joint (only articulation). Guyon canal immediately radial - ulnar nerve/artery at risk. Force transmitted via pisohamate ligament.
Mechanism
Direct blow to hypothenar eminence with wrist extended is most common. Less commonly: avulsion by FCU contraction, or repetitive stress in cyclists/racquet sports.
Imaging
Standard PA view often misses pisiform due to overlap. Carpal tunnel view and lateral view best visualize. CT confirms fracture pattern and displacement. MRI for occult fractures.
Treatment
Acute non-displaced: Short arm cast 4-6 weeks. Displaced/comminuted: Excision often preferred. FCU function preserved after excision via distal tendon continuity.
At a Glance - Quick Decision Guide
| Pattern | Key Features | Treatment |
|---|---|---|
| Non-displaced chip/avulsion | Small fragment, minimal symptoms | Splint 3-4 weeks, symptomatic treatment |
| Non-displaced body fracture | Intact articular surface | Short arm cast 4-6 weeks |
| Displaced fracture (over 2mm) | Articular incongruity | Consider excision vs ORIF |
| Comminuted/crush fracture | Multiple fragments, articular damage | Pisiform excision |
| Chronic nonunion/malunion | Persistent pain, pisotriquetral OA | Pisiform excision |
PISOPISO - Pisiform Key Features
Memory Hook:PISO reminds you of this unique bone's key anatomical features for the exam
ULNARULNAR - Complications to Consider
Memory Hook:ULNAR complications are the main concern due to Guyon canal proximity
EXCISEEXCISE - Indications for Pisiform Excision
Memory Hook:When in doubt, EXCISE - pisiform excision has excellent outcomes
Overview and Epidemiology
Pisiform fractures represent a rare but clinically significant injury pattern, accounting for only 1-2% of all carpal fractures. The pisiform is unique among carpal bones as it is the only sesamoid bone in the carpus, lying entirely within the tendon of flexor carpi ulnaris (FCU). This distinctive anatomy has important implications for injury mechanisms, clinical presentation, and treatment options.
Key Exam Concept
The pisiform has a single articular surface (pisotriquetral joint), making it unique among carpal bones. It serves as a fulcrum to increase the mechanical advantage of FCU, contributing approximately 20% to wrist flexion power. The proximity to Guyon's canal means ulnar nerve and artery injuries must always be assessed.
Epidemiology
- 1-2% of carpal fractures
- More common in males
- Peak incidence: 20-40 years
- Often associated with other wrist injuries
- Frequently missed on initial imaging
Mechanism
- Direct blow to hypothenar eminence (most common)
- Fall onto outstretched hand with wrist extended
- Avulsion by FCU contraction (rare)
- Repetitive stress in cyclists, racquet sports
- Tool use with vibration exposure
Key Clinical Points
- Point tenderness at hypothenar base
- Pain with resisted wrist flexion
- Assess ulnar nerve function always
- Often requires specialized views
- Excision is effective definitive treatment
Commonly Missed Diagnosis
Pisiform fractures are frequently missed on initial presentation due to:
- Overlap with triquetrum on standard PA views
- Patient may attribute symptoms to "wrist sprain"
- May present with delayed presentation weeks after injury
- Associated injuries may distract from pisiform assessment
Always obtain dedicated carpal tunnel views if pisiform injury is suspected clinically.
Anatomy and Biomechanics
Unique Anatomical Features
The pisiform is the only sesamoid bone in the carpus. Unlike other carpal bones with multiple articulations, the pisiform has a single articular surface (pisotriquetral joint). It lies entirely within the FCU tendon and acts as a fulcrum to increase FCU mechanical advantage.
Pisiform Anatomical Relationships
| Structure | Relationship | Clinical Significance |
|---|---|---|
| FCU tendon | Pisiform embedded within tendon | Sesamoid function, force transmission |
| Triquetrum | Pisotriquetral joint (only articulation) | Site of OA, grind test location |
| Hook of hamate | Connected by pisohamate ligament | Force transmission to distal row |
| 5th metacarpal base | Connected by pisometacarpal ligament | Forms hypothenar eminence base |
| Guyon canal | Pisiform forms ulnar border | Ulnar nerve/artery at risk |
| Ulnar nerve | Passes immediately radial | Compression can cause neuropathy |
Blood Supply
- Blood supply from ulnar artery branches
- Nonunion is uncommon due to good vascularity
- Unlike scaphoid, AVN is rare
- Sesamoid status provides tendon-derived nutrition
Biomechanical Function
- Increases FCU moment arm by 20%
- Acts as fulcrum for wrist flexion
- Transmits force to hook of hamate
- Excision reduces grip strength by 10-20%
Guyon Canal
Guyon canal is a fibro-osseous tunnel on the ulnar side of the wrist. The pisiform forms its ulnar border and floor. The hook of hamate forms the radial border. Contains ulnar nerve and artery. Pisiform fractures can cause compression neuropathy within this canal.
Classification Systems
Pisiform Fracture Classification
| Type | Description | Treatment |
|---|---|---|
| Type I - Comminuted | Multiple fragments, crush injury | Excision recommended |
| Type II - Transverse | Body fracture through middle | Cast or excision based on displacement |
| Type III - Chip/Avulsion | Small fragment at FCU insertion | Conservative usually successful |
| Stress fracture | Repetitive microtrauma | Activity modification, may need excision |
Clinical Presentation and Assessment
Ulnar Nerve Assessment
Always assess ulnar nerve function in pisiform fractures. The ulnar nerve passes through Guyon canal immediately radial to the pisiform. Test hypothenar sensation, finger abduction (interossei), and thumb adduction (adductor pollicis). Document findings.
History
- Direct blow to hypothenar eminence (fall, sports)
- Repetitive stress in cyclists (handlebar pressure)
- Pain localized to ulnar palm/wrist
- Aggravated by gripping and wrist flexion
Examination
- Point tenderness over pisiform (palpate at hypothenar base)
- Pain with resisted FCU contraction (wrist flexion + ulnar deviation)
- Pisiform grind test - compress pisiform against triquetrum
- Ulnar nerve motor and sensory assessment
Pisiform Palpation
The pisiform is easily palpated at the base of the hypothenar eminence, at the proximal wrist crease on the ulnar side. Have the patient flex the wrist against resistance to tense the FCU - the pisiform becomes prominent. Direct pressure reproduces pain in fractures.
Pisiform Fracture vs Pisotriquetral Arthritis
| Feature | Acute Fracture | Pisotriquetral OA |
|---|---|---|
| Onset | Sudden (trauma) | Gradual/chronic |
| Swelling | Present acutely | Minimal |
| Grind test | May be positive | Typically positive |
| X-ray | Fracture line visible | Joint space narrowing, osteophytes |
| History | Clear trauma | Repetitive use, prior injury |
Investigations
Standard X-rays
- PA view: Pisiform overlaps triquetrum - often missed
- Lateral view: Pisiform visible as separate structure anteriorly
- Carpal tunnel view: Best visualization of pisiform
- 30-degree supinated oblique: Alternative view
Advanced Imaging
- CT scan: Confirms fracture pattern, displacement, comminution
- MRI: Occult fractures, bone marrow edema, ligament injuries
- Ultrasound: Dynamic assessment of FCU, soft tissue
Carpal Tunnel View
The carpal tunnel view (axial view) is obtained with wrist in maximum extension and X-ray beam angled 25-30 degrees to the palm. This view provides the best visualization of the pisiform, hook of hamate, and carpal tunnel. Essential for suspected pisiform pathology.
Imaging Findings
| Finding | Significance | Management Implication |
|---|---|---|
| Non-displaced fracture line | Stable fracture | Conservative treatment likely |
| Displacement over 2mm | Articular incongruity | Consider surgical intervention |
| Comminution | Unreconstructable | Excision usually indicated |
| Pisotriquetral joint narrowing | Established OA | Excision for persistent symptoms |
| Associated hook of hamate fracture | Combined injury pattern | Address both injuries |
Management Algorithm
Treatment Algorithm
Confirm diagnosis with appropriate imaging (carpal tunnel view, lateral). Assess ulnar nerve function. Splint in neutral wrist position. Ice and elevation for swelling.
Review imaging for fracture pattern. Non-displaced: proceed with casting. Displaced or comminuted: discuss excision. Ulnar nerve symptoms: urgent decompression.
Conservative: Short arm cast or splint for 4-6 weeks. Surgical: Pisiform excision for comminuted/displaced fractures. Repeat X-rays at 2-3 weeks to confirm position.
Wrist ROM exercises after cast removal. Grip strengthening when comfortable. Return to sport/work based on strength recovery and symptoms.
Surgical Technique
Setup and Approach
- Position: Supine, arm on hand table
- Anesthesia: Regional or general
- Tourniquet: Upper arm
- Approach: Volar longitudinal along FCU tendon
Key Steps
- Identify and protect ulnar nerve in Guyon canal
- Incise FCU tendon sheath longitudinally
- Shell out pisiform from within tendon
- Preserve distal FCU continuity to 5th metacarpal
Critical Surgical Point
FCU function is preserved after pisiform excision because the tendon continues distally to insert on the hook of hamate (via pisohamate ligament) and the base of the 5th metacarpal (via pisometacarpal ligament). This is why excision is safe and effective.
Danger Structures
The ulnar nerve and artery run immediately radial to the pisiform in Guyon canal. Meticulous dissection and identification of these structures is essential before any bone work. Consider using loupe magnification.
Complications
Critical Neurovascular Assessment
All pisiform fractures require careful assessment of the ulnar nerve and artery due to their proximity in Guyon's canal. Delayed recognition of ulnar nerve compression can lead to permanent intrinsic muscle weakness and sensory deficits.
Complications and Management
| Complication | Risk Factors | Treatment |
|---|---|---|
| Ulnar nerve palsy | Displaced fracture, hematoma, late OA | Decompression, Guyon canal release |
| Pisotriquetral OA | Malunion, articular damage | Conservative initially, excision if refractory |
| Nonunion | Inadequate immobilization, displacement | Pisiform excision (definitive) |
| Chronic pain | Undiagnosed fracture, OA | Injection trial, then excision |
| FCU weakness | Post-excision (mild) | Rehabilitation, usually not limiting |
| Ulnar artery injury | Direct trauma, iatrogenic | Vascular repair if symptomatic |
Ulnar Nerve Zones in Guyon Canal
- Zone 1: Motor and sensory (proximal to bifurcation)
- Zone 2: Motor only (deep branch) - intrinsic weakness, NO sensory loss
- Zone 3: Sensory only (superficial branch) - numbness, NO weakness
- Pisiform fractures typically affect Zone 1 or 2
Differentiating Ulnar Neuropathies
- Guyon canal (pisiform): NO dorsal hand sensory loss
- Cubital tunnel (elbow): HAS dorsal hand sensory loss
- Both: Weakness of interossei, lumbricals 3-4
- Key: dorsal ulnar cutaneous branch
Guyon Canal Compression
Guyon canal syndrome from pisiform fractures presents with weakness of the intrinsic muscles (interossei, lumbricals 3-4, hypothenar muscles) and sensory loss over the hypothenar eminence and ulnar 1.5 digits. Unlike cubital tunnel syndrome, there is no dorsal hand sensory loss (dorsal ulnar cutaneous branch exits proximal to Guyon canal).
Postoperative Care and Rehabilitation
Post-Excision Rehabilitation Protocol
Soft bulky dressing with wrist splint. Finger ROM exercises encouraged. Elevation to reduce swelling. Wound check at 10-14 days for suture removal.
Transition to removable wrist splint. Begin active wrist ROM exercises. Continue finger exercises. Scar massage when wound healed.
Wean from splint during day. Light grip strengthening exercises. Progress ROM to full. Avoid heavy lifting.
Full activity as tolerated. Progressive grip and wrist strengthening. Sport-specific rehabilitation. Most return to full activity by 8-12 weeks.
Rehabilitation Goals
- Full wrist ROM by 6-8 weeks
- Functional grip strength by 8-12 weeks
- Pain-free activity by 12 weeks
- Return to sport by 3-4 months
Red Flags
- Increasing pain after initial improvement
- Numbness/tingling in ulnar distribution
- Weakness of intrinsic muscles
- Infection signs: redness, swelling, discharge
Outcomes and Prognosis
Conservative Treatment
- 90% union rate for non-displaced
- Full recovery in most cases
- 4-6 weeks immobilization
- Low complication rate
Pisiform Excision
- 90%+ pain relief reported
- 10-20% grip strength reduction
- Minimal functional deficit
- High patient satisfaction
Return to Activity
- 3-4 months for most patients
- Sport-specific rehab guides return
- Occupational demands influence
- Full recovery expected
Prognostic Factors
| Factor | Favorable | Unfavorable |
|---|---|---|
| Fracture pattern | Non-displaced, simple | Comminuted, displaced |
| Time to diagnosis | Acute presentation | Delayed diagnosis |
| Treatment compliance | Adherent to protocol | Poor compliance |
| Associated injuries | Isolated fracture | Multiple carpal injuries |
| Nerve involvement | No ulnar symptoms | Guyon canal compression |
Long-term Outcomes
Pisiform fractures generally have favorable long-term outcomes. Non-displaced fractures heal reliably with conservative treatment. Even when excision is required, functional outcomes are excellent with minimal grip strength loss. The key to good outcomes is early diagnosis, appropriate treatment selection, and attention to ulnar nerve status.
Evidence Base
Pisiform Excision Outcomes
- Pisiform excision provides excellent pain relief with minimal grip strength reduction (10-15%). FCU function preserved through distal tendon continuity.
Pisiform Fracture Patterns
- Classification of pisiform fractures into comminuted (Type I), transverse (Type II), and chip/avulsion (Type III) patterns. Direct blow mechanism most common.
Pisotriquetral Joint Biomechanics
- Pisiform increases FCU moment arm by approximately 20%. Excision reduces grip strength but preserves functional wrist flexion.
Imaging of Pisiform Pathology
- CT and MRI superior to plain radiographs for pisiform fracture detection. Carpal tunnel view improves plain film sensitivity.
Conservative vs Surgical Treatment
- Non-displaced fractures heal reliably with 4-6 weeks immobilization. Displaced or comminuted fractures have high nonunion rate with conservative treatment.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Pisiform Fracture Assessment in Cyclist
"A 35-year-old cyclist presents with ulnar-sided wrist pain after falling off their bike onto an outstretched hand. X-rays are reported as normal. How would you proceed?"
Pisiform Nonunion with Arthritis
"A 45-year-old presents with chronic ulnar-sided wrist pain after a fall 6 months ago. CT shows a pisiform nonunion with early pisotriquetral arthritis. What are your treatment options?"
Pisiform Anatomy and Clinical Significance
"What is unique about the pisiform bone's anatomy, and how does this influence injury patterns and treatment decisions?"
MCQ Practice Points
Anatomy Questions
- Pisiform is the only sesamoid in the carpus
- Single articulation with triquetrum only
- Forms ulnar border of Guyon canal
- Embedded within FCU tendon
- Increases FCU moment arm by 20%
Clinical Questions
- Best view: Carpal tunnel view
- PA view misses due to overlap with triquetrum
- Test: Pisiform grind test
- Must assess: Ulnar nerve function
- Mechanism: Direct blow to hypothenar
Treatment Questions
- Non-displaced: Cast 4-6 weeks
- Comminuted: Excision
- Nonunion: Excision (definitive)
- Post-excision grip loss: 10-20%
- FCU preserved via: Pisohamate/pisometacarpal ligaments
Complications Questions
- Guyon canal compression: NO dorsal sensory loss
- Cubital tunnel (contrast): HAS dorsal sensory loss
- Zone 2 lesion: Motor only (intrinsic weakness)
- Zone 3 lesion: Sensory only (numbness)
- Late complication: Pisotriquetral OA
Anatomy Question
Q: Which carpal bone is the only sesamoid bone and has only a single articulation?
A: Pisiform. It is the only sesamoid bone in the carpus (embedded within the FCU tendon) and articulates only with the triquetrum at the pisotriquetral joint.
Imaging Question
Q: A patient has hypothenar pain after a direct blow but PA wrist X-rays are normal. What additional view should be ordered?
A: Carpal tunnel view (axial view). This view profiles the pisiform and prevents overlap with the triquetrum seen on PA views. Alternatively, a true lateral view can also visualize the pisiform.
Clinical Differentiation
Q: How do you clinically differentiate Guyon canal syndrome from cubital tunnel syndrome?
A: Dorsal hand sensation. In Guyon canal compression, there is NO dorsal sensory loss (dorsal cutaneous branch comes off proximal to Guyon canal). Cubital tunnel syndrome affects the dorsal cutaneous branch, causing numbness over the dorsal ulnar hand.
Treatment Question
Q: What is the definitive treatment for pisiform nonunion?
A: Pisiform excision. This is the treatment of choice for nonunion, comminuted fractures, and symptomatic pisotriquetral arthritis. FCU function is preserved through intact pisohamate and pisometacarpal ligaments with only 10-20% grip strength reduction.
Biomechanics Question
Q: What happens to FCU function after pisiform excision?
A: FCU function is preserved with minimal grip strength loss (10-20%). The pisiform increases FCU moment arm by approximately 20%, but excision does not disrupt the FCU tendon itself - it passes over where the pisiform was. Pisohamate and pisometacarpal ligaments maintain distal FCU attachment.
Mechanism Question
Q: What is the most common mechanism of pisiform fracture?
A: Direct blow to the hypothenar eminence. The pisiform is subcutaneous and vulnerable to direct trauma. Common scenarios include falls onto outstretched hands (landing on hypothenar), cycling handlebar injuries, and racquet sport impacts.
Australian Context
Epidemiology:
- Sports injuries common: cycling, golf, racquet sports
- Occupational injuries from falls and manual handling
- More common in active males aged 20-40 years
- Frequently missed diagnosis on initial presentation
Management considerations:
- Sports medicine physicians may manage acute non-displaced fractures
- Subspecialty hand surgery referral for persistent symptoms or surgical candidates
- WorkCover considerations for occupational injuries
- Generally good prognosis with appropriate treatment
Implant availability:
- Mini-fragment screws available if ORIF considered (rare)
- No implants needed for excision (most common surgery)
- Excision can be performed at any hand surgery center
Exam Context
Be prepared to describe the unique anatomy of the pisiform (sesamoid, single articulation) and its relationship to Guyon canal. Know the imaging strategy (carpal tunnel view) and indications for excision vs conservative treatment. Understand why excision is safe (FCU continuity preserved) and effective (excellent outcomes).
Pisiform Fractures - Exam Summary
High-Yield Exam Summary
Key Anatomy
- •Only sesamoid bone in carpus - embedded in FCU tendon
- •Single articulation - pisotriquetral joint only
- •Guyon canal - pisiform forms ulnar border (ulnar nerve at risk)
- •Increases FCU moment arm by 20%
Clinical Features
- •Direct blow to hypothenar eminence - most common mechanism
- •Point tenderness at base of hypothenar eminence
- •Pain with resisted FCU contraction
- •Always assess ulnar nerve function
Imaging
- •Carpal tunnel view - best visualization
- •PA view misses pisiform (overlaps triquetrum)
- •CT for fracture characterization
- •MRI for occult fractures
Treatment Principles
- •Non-displaced: Short arm cast 4-6 weeks
- •Comminuted/displaced: Pisiform excision
- •Nonunion or OA: Excision is definitive
- •Excision preserves FCU function - minimal strength loss
Exam Pearls
- •Only carpal bone with single articulation
- •Excision outcomes excellent - pain relief with 10-20% grip strength reduction
- •Guyon canal syndrome - weakness of intrinsics, NO dorsal hand sensory loss
- •FCU continuity maintained after excision via pisohamate/pisometacarpal ligaments