Percutaneous Fixation of Acute Scaphoid Fractures

Peter J.L. Jebson

Jane S. Tan

Andrew Wong

DEFINITION

Located in the proximal carpal row, the scaphoid serves as an important link between the proximal and distal carpal rows. It is the most commonly fractured carpal bone, accounting for about 1 in every 100,000 emergency room visits.¹⁷
Scaphoid fractures typically result from a fall on an outstretched hand or less commonly following forced palmar flexion of the wrist¹⁶ or axial loading of the flexed wrist such as in punching.¹⁴^, ²⁶
- There are about 345,000 scaphoid fractures annually in the United States.

ANATOMY

The scaphoid has a complex three-dimensional geometry that has been described as a “twisted peanut.”⁸ Anatomically, the scaphoid is organized into proximal pole, waist, and distal pole regions.
Scaphoid dimensions vary between genders; the male scaphoid is usually longer and wider than the females. In addition, the diameter of most commercially available standard screws are larger than the proximal pole of the female scaphoid.¹³
The scaphoid articulates with the radius, lunate, capitate, trapezium, and trapezoid; thus, its surface is almost completely covered with hyaline cartilage. This feature has several important implications, including articular disruption during wire or screw insertion, paucity of vascular supply, and the absence of periosteum.
- Lacking periosteum, the scaphoid heals almost completely by primary bone healing, resulting in minimal callus and a biomechanically weak early union.²³
- Blood supply comes from branches of the radial artery that enter the scaphoid via two main routes⁷:
  - A dorsal branch, which enters the scaphoid via the dorsal ridge, provides the primary supply and 70% to 80% of the overall vascularity, including the entire proximal pole (via retrograde endosteal branches).
  - A volar branch, which enters through the tubercle, supplies 20% to 30% of the internal vascularity, all in the distal pole.
The precarious blood supply contributes to the high incidence of nonunion after a fracture at the scaphoid waist or proximal pole. It also places the proximal pole at risk for the development of avascular necrosis.

PATHOGENESIS

A scaphoid fracture classically occurs in a young, active adult most commonly following a fall onto an outstretched hand.
- Studies have demonstrated that wrist extension of more than 95 degrees combined with more than 10 degrees of radial deviation is required for a scaphoid fracture to occur. In this position, the scaphoid abuts the distal radius, resulting in fracture.
- The scaphoid can also be fractured following a forced palmar flexion of the wrist injury such as punching an object.¹⁴^, ²⁶
Seventy percent to 80% of scaphoid fractures occur at the waist region, whereas 10% to 20% involve the proximal pole and 5% occur at the distal pole and tuberosity.
In children, the most common location for a scaphoid fracture is the distal pole.²
- Although rare, scapholunate ligament injuries can occur in association with a scaphoid fracture.¹⁵^, ²²^, ²⁸^, ³¹

NATURAL HISTORY

The true natural history of an untreated scaphoid fracture is unknown due to limitations in the existing literature, particularly with respect to study design.¹⁶ However, several retrospective studies have suggested that if a nonunion occurs, a predictable pattern of wrist arthritis develops, usually within 10 years of the injury.¹⁹^, ²¹
Unrecognized, untreated, or inadequately treated scaphoid fractures have an increased likelihood of nonunion and secondary carpal instability.
A fracture through the proximal pole has the highest likelihood of nonunion, followed by a fracture of the scaphoid waist.
If the scaphoid fracture is unstable, extension forces exerted on the proximal fragment (via the long radiolunate and the radioscaphocapitate ligaments) and flexion forces at the distal fragment result in a flexion (“humpback”) deformity of the scaphoid.
- This deformity and loss of scaphoid support results in carpal instability, most frequently a dorsal intercalated segment instability (DISI) pattern, which eventually leads to arthritis as previously described.
The overall incidence of nonunion after fracture at the scaphoid waist region is about 5% to 10%.¹⁸

PATIENT HISTORY AND PHYSICAL FINDINGS

A patient with an acute or subacute scaphoid fracture presents with radial-sided wrist pain, swelling, and loss of motion, particularly with dorsiflexion.
Classic physical examination findings include the following:
- Edema over the dorsoradial aspect of the wrist
- Tenderness to palpation between the first and third dorsal compartments (the “anatomic snuffbox”)
- Tenderness with palpation volarly over the distal tubercle
- Pain with axial compression of the wrist (scaphoid compression test)
- Acutely, swelling and ecchymosis over the volar radial wrist

IMAGING AND OTHER DIAGNOSTIC STUDIES

The following plain radiographs should routinely be ordered in the patient with a suspected scaphoid fracture: posteroanterior (PA), oblique, lateral, and dedicated scaphoid views.
- The PA view allows visualization of the proximal pole of the scaphoid.
- The semipronated oblique view provides the best visualization of the waist and distal pole regions.
- The semisupinated oblique view provides the best visualization of the dorsal ridge.
- The lateral view permits an assessment of fracture angulation, carpal alignment, and carpal instability.
- The dedicated scaphoid view is a PA view with the wrist in ulnar deviation. This results in scaphoid extension, allowing visualization of the scaphoid in profile.
Displaced and unstable fractures are defined by the following criteria:
- At least 1 mm of displacement
- More than 10 degrees of angular displacement
- Fracture comminution
- Radiolunate angle of more than 15 degrees
- Scapholunate angle of more than 60 degrees
- Intrascaphoid angle of more than 35 degrees
Computed tomography (CT) scan is helpful in identifying and characterizing an acute fracture and evaluating for a nonunion. Thin 1-mm cuts are obtained in the sagittal and coronal planes.
Magnetic resonance imaging (MRI) is useful for diagnosing an occult fracture and, when combined with gadolinium administration, can be used to assess the vascularity of the proximal pole and the presence of avascular necrosis. Bone bruising without a fracture detected on MRI may eventually be found to be the result of an occult fracture in 2% of cases.²⁷
Technetium bone scan has been shown to be up to 100% sensitive in identifying occult fractures but lacks specificity. It is optimally used 48 hours after injury.

NONOPERATIVE MANAGEMENT

Nonoperative management, specifically cast immobilization, is indicated for a nondisplaced, acute (<4 weeks from injury) fracture of the distal pole. For a nondisplaced, acute waist fracture, there is debate regarding the preferred treatment approach—cast immobilization or surgical stabilization.
With cast immobilization, there is no consensus regarding the preferred position of the wrist, the need to immobilize other joints besides the wrist, and the duration of immobilization.⁴
- Clinical studies have demonstrated no benefit with thumb immobilization nor any influence of wrist position on the rate of union.
- Studies have also demonstrated no difference in union rates with use of a long-arm versus short-arm cast; however, a small randomized prospective study by Gellman et al⁹ demonstrated a shorter time to union and fewer nonunions and delayed unions with the initial use of a long-arm cast.
In general, cast immobilization is required for 6 weeks after a distal pole fracture and 10 to 12 weeks following a nondisplaced waist fracture.
- Confirmation of fracture union requires serial plain radiographs demonstrating progressive obliteration of the fracture line and clear trabeculation across the fracture site.⁶
If there is any question regarding fracture union, particularly if the patient is returning to a contact sport, a CT scan should be obtained.