8 carpal bones: Scaphoid, Lunate, Triquetrum, Pisiform (proximal row – noted as crease on volar as of wrist), Trapizeum (umm..beside the thUMb), Trapezoid, Capitate, Hamate (Distal row – very stable) (Mneumonic: Some Lovers Try Positions They Can’t Handle – Scrubs Video).
No direct tendons on carpal bones.Two arches of ligaments basically centered around the lunate. Space between them is Space of Poirier which is a weakness point (dislocations).
Anatomic Snuffbox: scaphoid location. Triangle of bony radial styloid proximally, extensor pollicis brevis tendon radially, and extensor pollis longus (big tendon connected to thumb when you abduct) ulnarally.
PA view: No radius/ulnar overlap, 3rd metacarpal should be parallel with radius. Gilula arcs (3 arcs): proximal and distal lines of proximal row, proximal line of capitate/hamate. All should be 1-2mm separation between each other. Scaphoid should be elongated. Distal radius should articulate with 1/2 the lunate. Best view for looking for: scapholunate dissociation,
Lateral view: Three Cs: radius, lunate, and capitate. Look at angles of axis of scaphoid and lunate (should be between 30-60 degrees). Radius volar tilt should be less than 10-15 degrees. Best view for looking for: perilunate/lunate dislocation, distal radius fractures, capitate fracture.
Scaphoid view: cone-down PA view of scaphoid in ulnar deviation. Best view for looking for: scaphoid fractures.
Oblique view: Best view for looking for: trapezium fracture.
Carpal tunnel view: view thru carpal tunnel. Best view for looking for: pisiform and hook of hamate fractures.
3 Dislocations of worsening severity in carpal instability: scapholunate dissociation, perilunate dislocation, and lunate dislocation. All outstretched hand, forceful dorsiflexion.
Scapholunate dissociation: MCC injuried wrist ligament. Look for >3mm (usually 5mm) of widening between scaphoid and lunate on PA view. Terry Thomas sign. Scaphoid tilts shortening it on PA view and appears as signet ring. Can get clenched fist view to furthur separate space. Treatment: radial gutter splint or short arm volar posterior mold. Usually require pinning or ORIF.
Perilunate dislocation: continued tear around volar ligament. Usually associated carpal bone fractures. Swelling/pain, usually no gross deformity. Lateral view: capitate displaced dorsally from the lunate. Lunate keeps contact with radius. PA view: capitolunate space is missing, bones overlapping. Add trans + carpal bones to beginning of nomenclature is associated fracture. Treatment: emergent reduction, ortho consult. If able to reduce, long arm splint. Usually will have failed reduction and need OR.
Lunate dislocation: Most severe of the 3. PA view: lunate appears triangle shape (‘piece of the pie’). Lateral view: lunate has dislocated off radius (spilled teacup). Treatment: same as perilunate: emergent reduction, ortho consult. Likely reduction unsuccessful and needs OR. Complications: median nerve compression.
Scaphoid fracture: MCC carpal bone fractured. Axial load to thumb. Anatomic snuffbox tenderness. Look at soft tissue fat pad adjacent to radial aspect. Has distal radial blood supply leading to avascular necrosis if not properly treated. 10-20% missed on xrays. If clinical suspicion, treat. Splint in dorsiflexion/radial deviation short arm thumb spica. Usually will need pinning.
Triquetrum fracture: Second most common carpal fracture. Dorsal tenderness distal to ulnar styloid. Avulsion (resisted twisting) has excellent prognosis and if minimally tender, early ROM is fine. Stable body fractures (direct trauma) require cast for 6 weeks.
Lunate fracture: usually associated with other fractures. Distal blood supply as well (Kienbock disease – avascular necrosis of lunate). Treatment: short arm thumb spica splint.
Trapezium fracture: saddle shaped bone articulates with thumb metacarpal. Painful thumb movement and weak pinch. Best viewed on oblique view xray. Treatment: short arm thumb spica splint.
Pisiform fracture: sesamoid bone in flexor carpi ulnar tendon. Both pisiform and hook of hamate form Guyon canal (contains ulnar artery/nerve). Last bone to ossify (12yo). Treatment: 30 degree flexion/ulnar deviation.
Hamate fracture: most are hook of hamate fractures – interrupted swing with club. Hypothenar pain and gripping pain. Hook of Hamate pull test: supinated, ulnar deviated wrist, resisted flexion of 4th-5th fingers. Best view with carpal tunnel view. Look for Guyon canal injury. Treatment: splint.
Capitate fracture: Usually associated with scaphoid fracture – scaphocapitate syndrome. Best viewed on lateral view. Treatment: splint.
Trapezoid fracture: extremely rare.
Colles fracture: distal radius metaphysis fracture with dorsal angulation. Outstretched hand, wrist extended. Dinner-fork deformity. Unstable fracture > 20 degrees. Treatment: Reduce by push fracture distal and palmarly. Splint 15 degree flexion/ulnar in sugar tong. F?u 7-10 days. Complications: median nerve compression, extensor pollicus longus (EPL) rupture (long term, due to blood supply).
Smith fracture: reverse Colles fracture. volar angulated fracture. Treatment: same as Colles.
Barton fracture: Colles or Smith fracture (more common of the two) with intraarticular involvement. Treatment: sugar tong, unstable fractures require ORIF.
Radial styloid fracture: usually associated with lunate dislocation.
Distal Radioulnar Joint Disruption (DRUJ): associated with intraarticular or distal radius shaft fractures (Galeazzi). Lateral view shows volar (most common) /dorsal ulna displacement. Can occur in isolation, though rare. Pronation limited. Treatment: splint, may require reconstructive surgery.
Q1. Whats the difference between a Colles fracture and a Barton fracture?
A1. Barton’s has intra-articular involvement. Other wrong answers: reverse colles (volar angulation), scaphoid involvement, Galleazzi fracture, etc.
Q2. What other carpal bone is fractured with a captitate fracture?
A2. Scaphoid. Other wrong answers: lunatate, hamate, trapezius, 3rd metacarpal.
Q3. What carpal fractures are best viewed with a carpal tunnel view xray?
A3. Pisiform and hook of hamate. Other wrong answers: Scaphoid and lunate, scaphoid and capitate, colles fracture, etc.
Q4. Which fracture occurs with resisted twisting on the wrist and has excellent prognosis?
A4. Triquetrum avulsion fracture. Other wrong answers: hook of hamate, pisiform, trapezium fracture.
Q5. Whats the most common carpal bone fractured?
A5. Scaphoid. Other wrong answers: Lunate, capitate, hook of hamate, etc.
Q6. What type of injury is this?
A6. Lunate dislocation. Other wrong answer: perilunate dislocation, capitate dislocation, normal wrist, etc.
References / Resources
Tintinalli, Seventh Edition, Chapter 266: Wrist Injuries