42.1 Distal Radius, Scaphoid & Common Upper Extremity Fractures

Fall on Outstretched Hand (FOOSH) Injury Spectrum & Biomechanics

The fall on an outstretched hand (FOOSH) represents the single most common traumatic mechanism of upper extremity injury presenting to ambulatory primary care and urgent care settings. Biomechanically, impact forces are transmitted through the hand and carpus into the forearm bones, elbow, and shoulder girdle. The exact anatomical injury pattern depends on the patient's age, bone mineral density, vector of applied force, and degree of wrist extension at impact:

• Wrist Hyperextension (>90°) & Pronation: Transmits peak compressive forces directly to the metaphysis of the distal radius and carpal scaphoid waist. In older osteoporotic adults (>50 years, particularly postmenopausal females), low-energy falls from standing height characteristically produce extra-articular or intra-articular distal radius fractures (Colles fractures). In young athletic adults (15 to 40 years), the dense subchondral bone of the radius resists fracture, shifting mechanical failure to the carpal scaphoid.
• Wrist Flexion: A direct fall onto the dorsum of a flexed wrist or a direct blow to the dorsal carpus drives the distal radius fragment volarly, creating a Smith fracture ("reverse Colles").
• Forearm Rotation & High Energy: High-velocity impacts with axial load and rotational shear generate intra-articular fracture-dislocations (Barton fractures) or radial styloid avulsions (Chauffeur / Hutchinson fractures).

                          FOOSH INJURY SPECTRUM

             ┌─────────────────── FOOSH ───────────────────┐
             │                                             │
             ▼                                             ▼
     [Wrist Extended]                              [Wrist Flexed]
             │                                             │
      ┌──────┴──────┐                                      ▼
      ▼             ▼                               [Smith Fracture]
[Older / Osteo]  [Young / High Energy]             • Volar displacement
• Colles Frx     • Scaphoid Fracture               • Volar angulation
• Dorsal tilt    • Waist / Proximal pole           • "Garden spade"
• "Dinner fork"  • AVN / Nonunion risk

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Distal Radius Fractures: Colles vs. Smith vs. Barton

Distal radius fractures represent approximately 17% of all fractures evaluated in adult emergency and family medicine clinics. Accurate radiographic and clinical differentiation dictates immobilization strategies and operative referral.

1. Colles Fracture

• Definition: An extra-articular fracture of the distal radius metaphysis located within 2 to 3 cm of the radiocarpal articular surface, featuring dorsal displacement, dorsal angulation (loss of normal volar tilt), and radial shortening.
• Classic Deformity: "Dinner fork deformity"—the prominent dorsal displacement of the distal radial fragment and carpus produces an abrupt dorsal step-off resembling an upside-down fork.
• Associated Injuries: Ulnar styloid avulsion fractures occur in 50% to 60% of cases, reflecting tearing or strain of the triangular fibrocartilage complex (TFCC). Extensive comminution of the dorsal cortex is common in osteoporotic bone.

2. Smith Fracture ("Reverse Colles")

• Definition: A fracture of the distal radius metaphysis featuring volar displacement and volar angulation of the distal fragment.
• Classic Deformity: "Garden spade deformity"—the distal fragment and carpus are displaced anteriorly (volarly), creating a prominent step-off on the palmar aspect of the wrist.
• Clinical Significance: Smith fractures are inherently far more unstable than Colles fractures. The deforming pull of the flexor tendons causes high rates of secondary displacement following closed reduction. In addition, the volarly displaced bone fragments directly encroach upon the carpal tunnel, placing the median nerve under severe acute compressive strain.

3. Barton Fracture

• Definition: A fracture-dislocation of the radiocarpal joint with intra-articular involvement and subluxation of the carpus along with the fractured radial articular rim. Barton fractures can be dorsal (dorsal rim avulsion with dorsal carpal subluxation) or volar (volar rim avulsion with volar carpal subluxation; much more common and unstable).
• Management: Barton fractures represent high-energy, highly unstable intra-articular injuries that cannot be successfully maintained with cast immobilization; they uniformly require open reduction and internal fixation (ORIF) with a buttress plate.

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Acute Carpal Tunnel Syndrome & Median Nerve Evaluation

Acute median nerve compression—manifesting as acute carpal tunnel syndrome (ACTS)—is the most critical, limb-threatening soft-tissue complication associated with acute distal radius fractures. ACTS results from acute mechanical impingement by volarly displaced bony fragments, elevated interstitial pressure from fracture hematoma, post-injury soft-tissue edema, or iatrogenic excessive wrist flexion during splint application.

[!WARNING] RED FLAG: ACUTE CARPAL TUNNEL SYNDROME

• Presentation: Progressive, intractable burning pain out of proportion to exam, accompanied by progressive paresthesias, numbness, or tingling in the median nerve sensory distribution.
• Mandatory Physical Examination:
  1. Sensory Assessment: Light touch and two-point discrimination over the palmar aspect of the index finger (the most isolated median nerve sensory territory), thumb, long finger, and radial half of the ring finger.
  2. Motor Assessment: Test the Abductor Pollicis Brevis (APB) by instructing the patient to raise the thumb perpendicular to the palm ("point thumb to ceiling") against downward resistance. (Note: Thenar motor loss is a late, severe finding).
• Immediate Action: Acute carpal tunnel syndrome is an orthopedic emergency! If the wrist is immobilized in flexion, immediately release all splinting/bandages and place the wrist in neutral. If symptoms fail to resolve rapidly, emergent surgical decompression (carpal tunnel release) and fracture stabilization are required to prevent permanent ischemic axonal death and irreversible thenar atrophy.

                  MEDIAN NERVE CLINICAL EVALUATION

   Domain         Testing Maneuver                  Normal Finding
   ─────────────────────────────────────────────────────────────────────────
   Sensory        Two-point discrimination & light  Intact sensation (<5-6 mm)
                  touch at palmar tip of INDEX      over volar thumb, index,
                  finger and thumb                  long, radial ring finger

   Motor (APB)    Palmar abduction of thumb         Full strength against
                  (thumb elevated perpendicular     resistance; strong thenar
                  to palm toward ceiling)           muscle contraction

   Vascular       Radial & ulnar artery pulses;     Capillary refill <2 seconds;
                  palmar capillary refill           symmetric bounding pulses
   ─────────────────────────────────────────────────────────────────────────

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Radiographic Assessment & Acceptable Closed Reduction Criteria

Initial diagnostic evaluation of suspected distal radius fractures requires a standard 3-view wrist radiographic series: Posteroanterior (PA), true Lateral, and Oblique views. Precise quantitative measurements must be made to assess fracture stability and determine whether closed reduction is appropriate or surgical intervention is indicated.

Quantitative Radiographic Parameters

1. Radial Inclination (PA View):
   • Measurement: The angle formed between a line perpendicular to the long axis of the radial shaft and a line drawn from the tip of the radial styloid to the ulnar corner of the lunate fossa.
   • Normal: 21° to 25°.
   • Acceptable Closed Reduction: >=15°.
2. Radial Height / Length (PA View):
   • Measurement: The vertical distance between two parallel lines drawn perpendicular to the radial shaft: one at the tip of the radial styloid and one at the articular surface of the ulnar head.
   • Normal: 11 to 12 mm.
   • Acceptable Closed Reduction: Shortening <3 mm compared to the contralateral uninjured wrist (or absolute height >=8-10 mm).
3. Volar (Palmar) Tilt (True Lateral View):
   • Measurement: The angle between a line perpendicular to the long axis of the radial shaft and a line drawn between the dorsal and volar articular lips of the distal radius.
   • Normal: 11° volar tilt (normal articular surface slopes palmarward).
   • Acceptable Closed Reduction: Volar tilt >0° (neutral to normal volar tilt; dorsal tilt <10° is tolerated only in low-demand, elderly osteoporotic patients; young active individuals require neutral or positive volar tilt).
4. Intra-Articular Step-off & Gap (PA and Lateral Views):
   • Measurement: Incongruity of the radiocarpal articular surface (scaphoid and lunate fossae).
   • Normal: 0 mm (completely anatomical and smooth).
   • Acceptable Closed Reduction: <2 mm (<1 mm in young, high-demand individuals). Any step-off >=2 mm dramatically increases contact stresses and accelerates post-traumatic radiocarpal osteoarthritis.

Summary of Radiographic Reduction Thresholds

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Closed Reduction & Splinting Protocols

Hematoma Block Procedure

Closed reduction in the clinic or urgent care is optimally performed under local hematoma block:

• Cleanse the dorsal wrist using sterile chlorhexidine technique.
• Palpate the dorsal fracture depression approximately 2 cm proximal to the radiocarpal joint line.
• Advance a 20- to 22-gauge, 1.5-inch needle into the dorsal fracture site at a 45° angle.
• Aspirate to confirm dark, non-clotting fracture hematoma (confirming intra-fracture location).
• Inject 5 to 10 mL of 1% or 2% plain lidocaine (or 0.5% bupivacaine) into the hematoma. Allow 10 to 15 minutes for complete regional periosteal anesthesia.

Reduction Technique

1. Apply longitudinal traction along the forearm axis, either using finger traps (thumb and index finger) with 10 lbs of counterweight or an assistant providing firm countertraction at the flexed elbow.
2. Exaggerate the initial deformity slightly (dorsal extension) to disimpact the locked dorsal cortical fragments.
3. While maintaining continuous longitudinal traction, translate the distal fragment volarly with firm pressure from the examiner's thumbs while simultaneously bringing the wrist into slight flexion (15°-20°) and ulnar deviation.
4. Avoid the "Cotton-Loder" Position: Extreme wrist flexion combined with extreme ulnar deviation is strictly contraindicated because it dramatically elevates carpal tunnel pressure, compresses the median nerve, and stretches the extensor tendons, leading to acute median neuropathy and complex regional pain syndrome (CRPS).

Splinting Principles: Sugar-Tong Splint

• Acute Immobilization Choice: A Sugar-Tong Splint (or volar-dorsal plaster sandwich splint) is the mandatory standard of care in the acute setting.
• Application: The sugar-tong splint wraps around the distal elbow from the dorsal MCP joints, around the olecranon, to the volar palmar crease. This restricts forearm pronation and supination (which disrupt distal radioulnar alignment) while leaving the splint open on the radial and ulnar sides.
• CRITICAL WARNING ON CASTING: Circumferential casting is strictly contraindicated in acute distal radius fractures! Acute post-reduction tissue edema peaked over 48 to 72 hours within an unyielding circumferential fiberglass cast produces acute compartment syndrome, ischemic skin necrosis, and severe nerve injury. Convert to a circumferential cast only after 7 to 10 days once swelling has fully resolved.
• Repeat post-reduction PA and lateral radiographs and repeat neurovascular checks are mandatory prior to clinic discharge.

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Scaphoid (Navicular) Fractures: Anatomy, Blood Supply & AVN Risk

The scaphoid is the most commonly fractured carpal bone, accounting for 70% to 80% of all carpal fractures. It links the proximal and distal carpal rows, acting as a crucial mechanical bridge during wrist flexion, extension, and radial-ulnar deviation.

                  SCAPHOID VASCULAR ARTERIAL SUPPLY

            [Radial Artery] ──► Dorsal Scaphoid Branches
                                        │
                                        ▼ (Enters at Distal Pole & Waist)
                       ┌─────────────────────────────────┐
                       │  DISTAL POLE (10-15% of frx)    │ ── Excellent Supply
                       │  • Rapid healing (4-6 weeks)    │
                       ├─────────────────────────────────┤
                       │  WAIST (65-70% of frx)          │ ── Moderate AVN Risk
                       │  • Healing: 10-12 weeks         │    (10-30%)
                       ├─────────────────────────────────┤
                       │  PROXIMAL POLE (15-20% of frx)  │ ── RETROGRADE FLOW!
                       │  • Zero direct vessels          │    AVN Risk 50-100%
                       │  • Nonunion rate: 30-50%        │
                       └─────────────────────────────────┘

Retrograde Vascular Supply & Fracture Location Prognosis

• Arterial Anatomy: The scaphoid receives its arterial blood supply predominantly (70% to 80%) from the dorsal scaphoid branches of the radial artery, which penetrate the scaphoid ridge at the waist and distal pole. Intraosseous microvessels then course retrogradely from distal to proximal to supply the proximal pole. The remaining 20% to 30% enters via the volar branches at the distal tubercle.
• Vascular Vulnerability: Because no direct arterial branches enter the proximal pole, any transverse fracture traversing the waist or proximal pole severs the intraosseous nutrient vessels feeding the proximal segment:
  • Distal Pole Fractures (10% to 15%): Excellent blood supply; rapid union in 4 to 6 weeks; low risk of complications.
  • Waist Fractures (65% to 70%): Moderate risk of avascular necrosis (10% to 30%) and delayed union/nonunion (5% to 15%); requires 10 to 12 weeks of immobilization.
  • Proximal Pole Fractures (15% to 20%): Highest risk of avascular necrosis (50% to 100%) and nonunion (30% to 50%). Fractures of the proximal pole require prolonged casting (12 to 24 weeks) and frequently warrant early orthopedic surgical referral for percutaneous headless compression screw fixation (Herbert screw).
• Long-term Complication: Untreated nonunion progresses inevitably to Scaphoid Nonunion Advanced Collapse (SNAC)—a predictable pattern of wrist arthritis starting at the radioscaphoid joint and advancing across the midcarpal joints, producing chronic wrist pain and permanent functional impairment.

Clinical Examination: The Scaphoid Diagnostic Triad

Three physical examination maneuvers should be routinely performed in every patient presenting with wrist pain following a FOOSH:

1. Anatomical Snuffbox Tenderness:
   • Anatomy: Bounded medially (ulnar border) by the tendon of the Extensor Pollicis Longus (EPL) and laterally (radial border) by the tendons of the Abductor Pollicis Longus (APL) and Extensor Pollicis Brevis (EPB).
   • Maneuver: Palpate the floor of the snuffbox with the wrist in slight ulnar deviation.
   • Sensitivity: Exceptionally high (90% to 95%), but specificity is only moderate (approx. 40% to 50%); tenderness rules out fracture when absent, but false positives occur from superficial radial nerve irritation or radial collateral ligament sprains.
2. Scaphoid Tubercle Tenderness:
   • Maneuver: Palpate the volar-radial wrist over the bony prominence at the base of the thenar eminence just proximal to the flexor carpi radialis tendon.
   • Significance: High specificity (approx. 85%) for scaphoid injury.
3. Pain with Axial Compression of the Thumb:
   • Maneuver: Grasp the patient's thumb and apply direct longitudinal compressive force through the first metacarpal shaft into the trapezium and scaphoid ("telescoping the thumb").
   • Significance: Elicits sharp pain directly over the scaphoid.

Radiographic Protocol & The Occult Scaphoid Fracture Protocol

• Dedicated 4-View Scaphoid Series: Standard wrist radiographs are inadequate. A complete scaphoid evaluation requires:
  1. Posteroanterior (PA) view;
  2. True Lateral view;
  3. 45° Semi-pronated Oblique view;
  4. Dedicated Scaphoid View: PA view taken with the wrist in 30° of extension and 20° of ulnar deviation. Ulnar deviation straightens the long axis of the scaphoid parallel to the cassette, preventing foreshortening and exposing subtle waist fracture lines.

[!IMPORTANT] CLINICAL PEARL: THE SUSPECTED OCCULT SCAPHOID FRACTURE

• Diagnostic Reality: Up to 10% to 20% of acute scaphoid fractures are radiographically invisible on initial plain radiographs taken on the day of injury due to non-displaced trabecular microfractures.
• Mandatory Protocol: In any patient with a suggestive mechanism of injury (FOOSH) and localized tenderness in the anatomical snuffbox, scaphoid tubercle, or with axial thumb compression whose initial 4-view radiographs are completely negative:
  1. Do NOT diagnose a simple wrist sprain!
  2. Immobilize immediately in a short-arm Thumb Spica splint (or cast) with the thumb immobilized to the interphalangeal joint.
  3. Schedule repeat 4-view scaphoid radiographs in 10 to 14 days. Over this interval, osteoclastic bone resorption at the fracture margins widens the fracture gap, making occult fractures easily visible on plain films.
  4. Alternative Modern Pathway: Obtain an early non-contrast MRI of the wrist within 24 to 72 hours of injury. MRI boasts 100% sensitivity and specificity, identifies scaphoid trabecular bone marrow edema immediately, and prevents unnecessary immobilization in patients with simple ligamentous sprains.

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Boxer's Fracture (Metacarpal Neck)

A Boxer's fracture is a fracture of the neck of the 5th metacarpal (and occasionally 4th metacarpal), typically resulting from direct axial impact sustained when a clenched fist strikes a hard, unyielding surface (e.g., a wall, door, or another person's jaw).

                    BOXER'S FRACTURE BIOMECHANICS

                  Interossei / Lumbricals
                         (Pull Volarly)
                              │
                              ▼
           Metacarpal Shaft ─────► /  ◄───── Metacarpal Head
                                  /          (Volarly Angulated)
                                 /
                 [5th Metacarpal: Accepts up to 30°-40°]
                 [2nd/3rd Metacarpal: Accepts <10°-15°]

Biomechanics & Angulation Tolerances

During fracture, the metacarpal head displaces volarly due to the downward vector of the intrinsic interosseous and lumbrical muscles. The degree of acceptable residual volar angulation is directly determined by the mobility of the corresponding carpometacarpal (CMC) joint:

• 2nd and 3rd Metacarpals: The 2nd and 3rd CMC joints are rigid, stable mortise joints with virtually 0° of motion. As a result, compensatory adaptation is impossible; acceptable volar angulation is <10° to 15°. Any greater angulation causes functional clawing and painful palmar grip prominence.
• 4th Metacarpal: Possesses approximately 10° to 15° of sagittal CMC motion; accepts up to 20° to 30° of volar angulation.
• 5th Metacarpal: The 5th CMC joint possesses remarkable compensatory mobility, with 25° to 30° of anteroposterior motion. Because the mobile 5th ray can adapt during grip, the 5th metacarpal neck tolerates up to 30° to 40° of volar angulation (some clinical guidelines accept up to 45°-50° in non-laborers) without causing long-term grip weakness or functional impairment.
• ROTATIONAL DEFORMITY IS NEVER ACCEPTABLE: While sagittal plane angulation is well tolerated in the 5th ray, rotational malalignment has ZERO tolerance! Even 5° of metacarpal rotation results in 1.5 cm of digital overlap ("scissoring") when making a fist. On physical examination, when the patient flexes the fingers, the fingernails must align in the same plane and all digits must point directly toward the scaphoid tubercle.

Splinting Protocol: Ulnar Gutter in "Intrinsic Plus" Position

• Splint: Ulnar Gutter Splint covering the 4th and 5th digits and ulnar forearm.
• The "Intrinsic Plus" (Edinburgh) Position:
  • Wrist: 20° to 30° extension.
  • Metacarpophalangeal (MCP) joints: Flexed to 70° to 90°.
  • Interphalangeal (PIP and DIP) joints: Extended (0° to 10° flexion).
  • Biomechanical Rationale: At 70° to 90° of flexion, the MCP collateral ligaments are stretched to their maximal anatomical length (cam effect of metacarpal head). Immobilizing MCPs in extension allows collateral ligaments to slacken, contract, and fibrose, causing permanent joint stiffness and extension contractures!

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"Fight Bite" Knuckle Wounds & Eikenella corrodens

A small laceration (even 2 to 3 mm) over the dorsal aspect of the 3rd, 4th, or 5th MCP joint sustained during a fist fight is termed a "fight bite" or clenched-fist injury.

[!CAUTION] THE CRITICAL FIGHT BITE TRAP

• Mechanism: When the punch strikes human teeth, the tooth penetrates the skin, the extensor tendon expansion, and frequently the synovial capsule of the MCP joint. When the hand is subsequently opened and fingers extended, the skin, extensor tendon, and joint capsule shift into different planes, sealing aggressive oral pathogens deep inside the joint space and subaponeurotic compartment.
• Microbiology: Classic polymicrobial infection dominated by Eikenella corrodens (a fastidious Gram-negative facultative anaerobe unique to human dental plaque), Streptococcus viridans, Staphylococcus aureus, and oral anaerobes (Fusobacterium, Peptostreptococcus).
• MANAGEMENT RULES:
  1. NEVER CLOSE A FIGHT BITE PRIMARILY! Suturing a fight bite seals virulent oral anaerobes within an enclosed space, virtually guaranteeing septic tenosynovitis, purulent arthritis, and osteomyelitis.
  2. Perform copious bedside wound irrigation with sterile normal saline (at least 200-500 mL) and careful exploration through a full arc of motion.
  3. First-Line Antibiotic: Oral Amoxicillin-clavulanate 875/125 mg PO BID for 7 to 10 days (covers Eikenella, Staph, Strep, and anaerobes).
  4. PENICILLIN ALLERGY WARNING: Eikenella corrodens is intrinsically RESISTANT to cephalexin, clindamycin, erythromycin, and vancomycin! If the patient has a severe penicillin allergy, prescribe Moxifloxacin 400 mg PO daily OR Ciprofloxacin 500 mg PO BID PLUS Clindamycin 300 mg PO TID.
  5. Evaluate for Kanavel's Four Cardinal Signs of Flexor Tenosynovitis (symmetric sausage digit swelling, held in slight flexion, tenderness along flexor sheath, severe pain on passive extension). Immediate hand surgery consultation for operative I&D is required if tenosynovitis or septic arthritis is present.