Wrist Injuries

1. THE 2-MINUTE KINEMATICS

The predominant mechanism of injury for catastrophic wrist trauma—including scaphoid fractures, distal radius fractures, and carpal dislocations—is a fall onto an outstretched hand (FOOSH).

• Carpal Dislocations: These injuries specifically result from forceful dorsiflexion and impact on the outstretched hand with immense kinetic energy, typically from falls from a height or motor vehicle collisions.
• Biomechanical Failure: In a perilunate dislocation, the lunoradial articulation remains intact, but the surrounding carpal bones (such as the capitate) dislocate dorsally relative to the lunate. Conversely, a lunate dislocation represents a complete disruption of the normal lunoradial relationship, where the lunate is displaced relative to the other carpals, shifting anteriorly and rotating so its concave surface faces the palm rather than distally.

2. THE BEDSIDE ACTION PLAN

• Immediate Stabilization & Reduction: Any grossly displaced fracture-dislocation or carpal dislocation with vascular compromise or acute carpal tunnel syndrome (ACTS) requires immediate closed reduction in the ED to restore alignment and prevent ongoing neurovascular injury.
• Pain Control: Provide appropriate systemic analgesia or regional anesthesia (such as targeted radial, ulnar, or median nerve blocks at the wrist) prior to any manipulation.
• Splinting Applications:
• Suspected Scaphoid Fracture: Immobilize using a thumb spica splint (placing the 1st MCP in a "wine glass position") with the wrist in dorsiflexion and radial deviation.
• Distal Radius/Ulna Fracture: Apply a sugar-tong forearm splint, which biomechanically prevents forearm pronation and supination.

3. THE DIAGNOSTIC GRID

• Targeted Physical Exam: Inspect the wrist for symmetry and pinpoint tenderness. Specifically palpate the anatomic snuffbox—the triangle formed by the radial styloid, extensor pollicis brevis, and extensor pollicis longus—as well as the scaphoid tubercle. Exquisite tenderness here is the hallmark of a scaphoid fracture.
• Mandatory Neurovascular Checks: You must evaluate the median, ulnar, and radial nerves before and after any reduction or splinting.
• Median Nerve: Test motor function via thumb opposition or the "OK sign" against resistance, and check sensory function via 2-point discrimination on the volar tip of the index finger. Median nerve paresthesias are a critical clinical clue for an underlying lunate dislocation or distal radius fracture with acute carpal tunnel syndrome.
• Ulnar Nerve: Test motor function via finger abduction (spread) against resistance, and check sensory function on the volar/dorsal 5th digit.
• Radial Nerve: Test motor function via wrist/finger extension ("thumbs-up" sign), and check sensory function over the dorsal first web space.

4. THE VISUAL BOARD

• Explicit X-Ray Interpretation: A routine evaluation must include posteroanterior (PA), lateral, and oblique views free of overlying splint material, plus a dedicated scaphoid view if a scaphoid injury is suspected.
• Lunate vs. Perilunate Differentiation:
• Lunate Dislocation: On the lateral view, the lunate tilts anteriorly into the palm, creating the classic "spilled teacup sign". On the PA view, the rotated lunate overlaps abnormally, creating a pathognomonic triangular "piece-of-pie sign".
• Perilunate Dislocation: On the lateral view, the lunate remains seated in the radial fossa, but the capitate is visibly displaced dorsally to the lunate.
• Named Radiographic Angles: In a normal wrist, the scapholunate angle should measure between 30 and 60 degrees, and the capitolunate angle should measure between 0 and 30 degrees.
• Signs of Occult Fractures: Standard plain radiographs have a high miss rate for acute scaphoid fractures. A normal X-ray does not rule out a scaphoid fracture if snuffbox tenderness is present.

5. THE CLASSIFICATION MATRIX

• Sequential Stages of Carpal Dislocation: Carpal instability progresses through four sequential stages (Stages I–IV), representing a progressive circle of intercarpal ligament injury proceeding around the lunate.
• Fracture Description Convention: When describing distal radius and wrist fractures to consultants, use precise anatomical terminology; displacement and angulation must be described as "volar" (palmar) or "dorsal," and occasionally as "radial" or "ulnar".

6. THE DANGER ZONE

• Risk of Avascular Necrosis (AVN): The scaphoid bone relies on a tenuous blood supply. Discharging a patient with snuffbox tenderness without placing them in a thumb spica splint—even if initial X-rays are perfectly normal—is a massive cognitive error that directly leads to occult fracture displacement, nonunion, and AVN.
• The Benign AP View Trap: Lunate dislocations are notoriously missed because the PA/AP view of the wrist may look relatively normal to an untrained eye. The emergency physician must critically scrutinize the lateral radiograph for the "spilled teacup". Missed dislocations result in permanent median neuropathy and early degenerative arthritis.
• Missed Acute Carpal Tunnel Syndrome (ACTS): Distal radius fractures and lunate dislocations can cause severe compression of the median nerve within the carpal tunnel. Failure to recognize median nerve paresthesias requires emergent operative decompression to prevent permanent hand disability.

7. MCQ MASTERCLASS

• Buzzword: "Spilled teacup sign" on a lateral wrist radiograph = Lunate dislocation.
• Buzzword: "Piece-of-pie sign" on a PA wrist radiograph = Lunate dislocation.
• Buzzword: Exquisite "snuffbox tenderness" after a FOOSH with normal X-rays = Occult scaphoid fracture requiring immediate thumb spica splinting.
• Associated Nerve Injury: A volar lunate dislocation or a severely displaced distal radius fracture classically compresses the median nerve.
• Exam Distractor: Recommending a "removable wrist splint" or "reassurance" for a patient with normal radiographs but persistent snuffbox tenderness. This is incorrect; a thumb spica splint and orthopedic follow-up in 1 week is mandatory.

8. THE BOARDROOM SCRIPT

"I am consulting you for a [Patient Age]-year-old [Right/Left]-hand dominant patient who sustained a high-energy FOOSH mechanism resulting in a [Diagnosis, e.g., perilunate dislocation / severely displaced distal radius fracture]. On examination, there is gross deformity with [dorsal displacement and volar angulation]. My mandatory neurovascular check reveals [intact/compromised] median nerve function, with [presence/absence] of paresthesias at the volar index finger concerning for acute carpal tunnel syndrome. I have provided procedural sedation, performed an immediate closed reduction to relieve tension on the neurovascular bundle, and secured the wrist in a [sugar tong / thumb spica] splint. Post-reduction radiographs show improved anatomic alignment and the capitate is relocated over the lunate, with capillary refill remaining under 2 seconds. The patient requires your emergent evaluation."