Scaphoid Fractures Diagnosis & Management

 
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Scaphoid Fractures Diagnosis & Management

Introduction. Scaphoid fractures are the most commonly fractured carpal bone, accounting for 2-3% of all fractures and ~10% of all hand fractures (Duckworth, 2012). They account for approximately 60% of all carpal fractures (Hove, 1999). There is a male predominance with low-energy falls being the most common etiology although men are more likely to sustain their fracture after a high-energy injury. Approximately 65% of injuries occur at the waist, with another 25% occuring in the proximal third.

The major blood supply of scaphoid is provided by the dorsal carpal branch of the radial artery which provides retrograde flow to the proximal 80% of scaphoid via an intraosseous supply. The superficial palmar arch supplies the distal 20%. This intraosseous retrograde flow makes the scaphoid particular susceptible to avascular necrosis, which can lead to scaphoid nonunion and eventual collapse (termed SNAC: scaphoid nonunion advanced collapse). Avascular necrosis, sometimes termed Preiser’s disease, is reported to occur anywhere from 13-50% of scaphoid fractures, with the highest incidence in the proximal 1/5th of the scaphoid (Herbert, 1984). Missed scaphoid fractures have a high risk of nonunion or malunion. Nonunion occurs in up to 12% of patients if an occult fracture is not detected and treated (Steinmann, 2006). For these reasons, early detection and appropriate treatment is critical in avoiding chronic, debilitating wrist problems associated with missed scaphoid fractures.

History and Physical. Scaphoid fractures tend to occur in young and middle aged men. As patients age, the distal radial metaphysis is much more likely to fail than the scaphoid. The typical mechanism involves falling onto a hyperextended wrist with radial deviation (Ring, 2000). The hand and wrist should be observed for any signs of soft tissue swelling, effusion, ecchymosis or deformities. Strength, range of motion and a thorough neurovascular exam should be performed. Comparison should be made to the unaffected wrist.

There are several clinical tests that can aid in evaluation of a potential scaphoid fracture. The scaphoid compression test involves using the thumb metacarpal to provide an axial load on the scaphoid. Anatomic snuffbox tenderness appears to be the most sensitive with rates reported from 87-100% (Mallee, 2014). Palpation of the volar (distal tuberosity or scaphoid tubercle) is estimated to be 87% sensitive and 57% specific (Freeland, 1989). In combination, these three exam findings are thought to be up to 100% sensitive and 74% specific in the first 24 hours of injury (Parvizi, 1998).

Watson test or scaphoid shift test is designed to evaluate for scapholunate instability but may also be positive in patients presenting with scaphoid fractures. The clamp sign involves using the thumb and index finger to form a “clamp” over the volar and dorsal aspects of the scaphoid respectively.  The variables of male sex, sports injury, scaphoid tubercle tenderness, and anatomic snuffbox pain with wrist ulnar deviation have been shown to be independently significant positive factors for scaphoid fracture and all 4 combined factors are 91% predictive of fracture (Duckworth, 2012). Patients may also have pain with resisted pronation.  Range of motion is neither sensitive nor specific for scaphoid injuries.

Imaging. The initial imaging modality of choice remain radiographs. Standard wrist xrays include AP, lateral and oblique views. Dedicated scaphoid series can also be obtained if clinical concern is high enough (Cheung, 2006). A PA view in ulnar deviation will give the so-called ‘scaphoid view’. A 45० pronation view can also be obtained. Overall, plain radiographs are about 70% sensitive for scaphoid fractures (Gabler, 2001). If the clinical suspicion is high enough despite normal appearing initial radiographs, a thumb spica splint or cast is usually administered. Repeat radiographs at approximately 2 weeks are usually recommended. Ultrasound has a growing but largely undefined role in the initial evaluation of potential scaphoid fractures. In one chinese study, ultrasound was 80% sensitive and specific compared to 36% and 40% respectively for xrays (Jain, 2018).

Image 1. AP wrist radiograph demonstrating a chronic scaphoid waist fracture.

Image 2. Oblique radiograph of the wrist showing acute, displaced scaphoid waist fracture.

Because of the economic implications of immobilization and repeat imaging, some orthopedists have suggested early utilization of advanced imaging (Dorsay, 2001). There is no clear consensus on optimal advanced imaging modality for suspected scaphoid fractures, however MRI is most commonly used. MRI is 90-100% sensitive and specific for scaphoid fractures (Raby, 2001). MRI loses sensitivity on proximal pole injuries, which can be improved with gadolinium-enhanced MRI (Cerazal, 2000). CT is less sensitive than MRI with greater than 90% specificity for scaphoid fractures, which improves if a CT-scaphoid protocol is used (Mallee, 2014). The role of CT may be greatest in patients with negative radiographs and high clinical suspicion due its relative availability and quick access compared to MRI. CT may also aid in evaluation of location of fracture, size of fragments, extend of collapse and progression after surgery. Bone scintigraphy has demonstrated 92% to 95% sensitivity and 60% to 95% specificity for scaphoid fractures (Beeres, 2007).

Image 3. CT of wrist demonstrating chronic, displaced non-union scaphoid fracture.

Classification. The Herbert and Fisher classification is commonly used to describe scaphoid fractures. Herbert classification B2 is the most common at 36.4% (Duckworth, 2012).

Figure 1: Herbert and Fisher classification for scaphoid fractures.

Management. The majority of scaphoid fractures are nondisplaced or minimally displaced and can be treated with immobilization for 8-12 weeks in a thumb spica cast (Kawamura, 2008). The healing rate of nondisplaced waist scaphoid fractures with cast immobilization is 88% to 95%, provided that treatment is started within 3 weeks after injury (Cooney, 1980). There is no consensus on long arm vs short arm casting. In patients with normal radiographs, but a high degree of clinical suspicion, patients should be placed in a thumb spica splint with repeat radiographs in roughly 2 weeks. Some surgeons recommend early ORIF even for nondisplaced fractures to avoid complications such as more frequent office visits to check whether the cast fits properly, more frequent radiographs to assess fracture alignment, potential skin breakdown, prolonged immobilization until complete healing has occurred, stiffness of immobilized joints, and a longer time to healing.

Internal fixation is indicated for displaced waist and proximal pole scaphoid fractures because they have a high risk of delayed union, nonunion, or avascular necrosis. More than 1 mm of displacement of the fracture fragment in any view is considered unstable. Nonunion scaphoid fractures can lead to scaphoid nonunion advanced collapse and subsequent osteoarthritis and management is directed at preventing these degenerative changes. Patients can also develop dorsal intercalated segment instability (DISI). Bone grafting plays a role in managing nonunion.

Figure 2: Proposed Algorithm from Kawamura for Suspected Scaphoid Fracture

Summary. Scaphoid fractures are the most common carpal bone fracture and they tend to occur in young men. A careful clinical exam, including anatomic snuff box tenderness, axial compression and volar palpation of the scaphoid tubercle are very sensitive in evaluating for a scaphoid fracture. Radiographs are the initial imaging study of choice, however only 70% sensitive. MRI and CT are utilized in the appropriate patient and the role of ultrasound remains unclear. In the acute setting in which initial radiographs are unremarkable but clinical suspicion is high, the patient should be placed in a thumb spica splint with repeat radiographs in approximately 2 weeks. Management of nondisplaced scaphoid fractures is generally nonoperative, although consultation with a hand or orthopedic surgeon is recommended. In patients with displaced fractures, proximal pole fractures or non-union, surgical management is indicated.

References

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