SCAPHOID FRACTURES

 

Introduction

The scaphoid is the most commonly injured bone in the carpus, accounting for 60-70% of all carpal fractures. Only distal radius fractures are more common. 90 to 95% will go on to union if treated adequately (thus, 5-10% non-union may occur, in spite of treatment.)

 

Anatomy

 

The scaphoid is the most complex carpal bone, making up the base of the lateral (mobile) column of the wrist (Navarro). It lies obliquely at about 45 degrees to the longitudinal axis of the two carpal rows. Most of its surface is made up of articular cartilage. Distally, it articulates with the trapezium and trapezoid in a gliding motion, The articulation with the trapezium forms a base for independent movement of the thumb. On the ulnar side, it articulates distally with the capitate, and proximally with the lunate in a rotary motion. Proximally, its large, biconvex surface allows articulation with the radius.

 VOLAR (top) and DORSAL (bottom)

LIGAMENTS of the scaphoid and wrist

The dorsal radiocarpal ligament inserts obliquely across the dorsal surface. The waist, or central indentation, provides a path for the palmar radiocarpal ligament to the capitate. The scaphoid tuberosity acts as a pivot for the tendon of the flexor carpi radialis. The scaphoid is bound to the radius and carpal bones by a complex ligament system. Since the scaphoid spans the proximal and distal carpal rows, it acts as a fink, or structural strut between them and its integrity is necessary for wrist stability. Because of these complex articulations, the scaphoid moves in nearly all carpal motions, especially in volar flexion. Any alteration to the integrity of the joint surfaces (fracture) or to the ligamentous stability (dislocation) may ad to degenerative changes and cause a great deal of morbidity.

 

Blood Supply

 

The scaphoid receives its blood supply from the radial artery primarily, via lateral (volar, dorsal) and distal branches. This blood supply tenuous. Approximately 67% of individuals have 2 or more vascular foramina proximal to the waist, 20% have only one foramina proximally and 13% were found to have no proximal vessel foramina (Obletz.) Thus, in one third of waist (mid) fractures, there will be diminished blood supply to the proximal fracture fragment This may produce a non-union and avascular necrosis may ensue.

 

Diagnosis/Mechanism of Fracture

During dorsiflexion, the scaphoid bears the compressive stresses passing through the capitate as well as those from the thumb axis on its dorsal side. Since the scaphoid crosses the two carpal rows, it also acts as the principal bony block to excessive dorsiflexion at which point the scaphoid is under high tension loading palmarly. At 95 - 100% dorsiflexion, the proximal pole of the scaphoid is fixed in place by the radius (proximally, dorsally and radially), by the capitate and lunate (ulnarly), and by the radiolunate triquetrum and radioscaphocapitate ligaments volarly. When the distal carpal row translates on the distal pole of the scaphoid, this makes the scaphoid particularly susceptible to fracture, especially at the waist. The palmar aspect fails in tension and the dorsal aspect fails in compression. Rockwood and Greene found that a classic waist fracture could be incurred in a position of greater than 97 degrees dorsiflexion and 7- 10 degrees radial deviation.

Patients usually present with a history of wrist dorsiflexion injury. On physical exam, tenderness is elicited on palpation of the dorsal scaphoid in the anatomic snuffbox. Swelling may be minimal. There may be palpable abnormalities just distal to the radial styloid. Pain is elicited with dorsiflexion and radial deviation of the wrist, as well as with longitudinal compression or tension applied to the thumb metacarpal.

Radiographic evaluation should include PA, lateral, 45 degree pronation PA, and scaphoid view (PA with ulnar deviation.) The latter view places distraction across the fracture site, making it more readily visible. However, occasionally fractures may be difficult or impossible to see by plain films. If clinically indicated, these should be treated as non-displaced fractures, or further studies may be performed (bone scan, CT, NM.) "...all patients with an appropriate stress or injury to the wrist and tenderness in the region of the scaphoid should be treated as if they had a fracture until a fracture has been disproved by negative x-rays at 2 and 4 weeks." (R&G)

 

Classification

 Time Since Injury
  • Acute/Fresh Fracture - < 3 weeks - better prognosis
  • Delayed Union - 4-6 months
  • Non-Union - > 4-6 months - worse prognosis

 Anatomic

 Transverse Fractures

  • Proximal-third - Extremely high rate of decreased blood flow (90- 100%) - AVN.
  • Mddle-third ("waist") - Most frequent fracture. 30% risk decreased blood flow.
  • Distal-third -AVN rare.
  • Tuberosity fracture
  • Osteochondral fracture (distal articular surface)
 Oblique Fractures
 Comminuted Fractures
 Associated Ligamentous Injury

 
 The Usual five sites of scaphoid fractures are denoted on the left.

Negative prognostic factors include late diagnosis, proximal fractures, displacement, angulation, and obliquity.

 

Treatment

Undisplaced, Stable Scaphoid Fractures

Prognosis is excellent in undisplaced, stable fractures if diagnosed and immobilized early (90 % with x-ray evidence of beginning consolidation at 6 weeks (R&G).) After one week of splinting, either a short or long arm thumb spica cast should be applied to the base of the thumbnail and the proximal palmar crease with the wrist in slight radial deviation and neutral flexion. The thumb is thus maintained in a functional position and the fingers are free to move at the MCP joints. X-rays are taken at 6 weeks, and if union is delayed, a short arm cast is placed for an additional 4 weeks. Length of immobilization until union can range from 4 weeks for distal fractures to 12 weeks for proximal fractures. If stiff without union, some recommend electrical stimulation (Osterman), but data remains inconclusive.

Displaced, Unstable Fractures

Reduction may be attempted by longitudinal traction along the thumb and compression of the carpus, followed by splinting and casting. Fractures with > I mm stepoff (AP or Oblique view), lunocapitate angulation > 15 degrees (Lateral), or scapholunate angulation > 70% (Lateral view) indicate instability, as does inability to maintain reduction with immobilization, In these cases, surgical intervention may be warranted.

Surgical Options

Closed Reduction with Percutaneous Pinning

Useful if reduction cannot be maintained by casting. Rate of union is less than with bone grafting, and time for union may be prolonged.

Open Reduction with Bone Grafting

Indications include failure of non-operative immobilization, displaced fracture which is non-reducible, established non-unions, and AVN of proximal fragments.

Matti-Rouse - Excavation of proximal and distal fragments with volar or dorsal inlay cancerous or corticocancellous bone grafting. Because of limited vascularity, it is important to curret the fragments until bone bleeding is noted or subchondral bone is uncovered. 85% success rates have been reported with this technique (Jupiter),

Murray - Dorsal peg bone grafting. Some report lower rates of union.

Fisk-Fernandez - Anterior wedge grafting, particularly useful for dorsal intercalated segmental instability.

Internal Fixation

Indications are displaced fractures, dislocations, associated transscaphoidperilunate fractures, or delayed/non-union in spite of adequate immobilization.

Kirschner Wires - do not provide compression of fragments.

AO Cannulated Screws - more easily placed over guide pin with flouroscopy.

Herbert Scow - Countersunk, smooth shaft screw with differential pitch threads to provide compression (proximal threads are finer than distal threads.) Advantages include compression, internal fixation and less time for immobilization (4 weeks.) However, it is technically difficult and the scaphotrapezial joint is traumatized during jig placement. This is also not useful for very small proximal or distal fragments. Herbert reported a 80% success rate with documented non-unions (comparable to bone grafting in many cases.)

 

Non-Union of Scaphoid Fractures

Influenced by delayed diagnosis, severe displacement/dislocation, more proximal fractures (impaired blood supply), and associated carpus injuries. Many non-unions display minimal symptoms and can be tolerated well in the low demand wrist (older age, sedentary lifestyle.) Degenerative arthritic changes are probably inevitable, but may not occur for years.

 

Salvage procedures are generally reserved for painful non-unions. These include excision of small fragments, styloidectomy (more commonly used as a source for bone graft and to improve exposure), interposition of a dorsal soft tissue flap to create a painless pseudoarthrosis (Bentzon's Procedure), vascularized radial graft, proximal row carpectomy, silicone implant arthroplasty, and partial or total arthrodesis of the wrist.



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