The scaphoid is the most commonly fractured bone of the eight carpal bones.1 Despite this, it is one of the most difficult fractures to accurately diagnose. Timely diagnosis is important because a delay can lead to various unwanted outcomes such as delayed union, non-union, limited range of motion, and osteoarthritis. Also, due to the shape and retrograde blood supply of the scaphoid, it is highly susceptible to avascular necrosis (AVN).2-3
The scaphoid has a unique, boat-like shape. The term scaphoid is actually derived from the Greek word “scaphos” which means boat.3 It consists of four main parts, the proximal pole, the waist, and the distal pole which contains the tubercle.4 Because of its shape it articulates with five surrounding bones: the radius, lunate, capitate, trapezoid, and trapezium.5 Many ligaments attach to the scaphoid such as: volar radiocarpal, raidioscaphoid, radioscapholunate, and radioscaphocapitate ligaments on the palmar side, and dorsal radiocarpal, dorsal transverse intercarpal, scapholunate, scaphocapitite, and scaphotrapezium-trapezoid ligaments on the dorsal side.4 There are other ligaments that have an association with, but do not attach to, the scaphoid.
Figure 1 - Scaphoid and Surrounding Carpal Bones
The scaphoid can be palpated on the dorsal surface in the anatomical snuffbox, a triangular region formed by the tendons of the extensor pollicis brevis and abductor pollicis longus muscles. The distal tubercle can also be palpated on the palmar surface at the base of the thenar eminence.4
Figure 2 - Surface Anatomy of Anatomical Snuff Box
Rhemrev et al states that 80% of the scaphoid surface is cartilage, thus leaving a small area for arterial blood supply to enter the bone. Most of the blood supply comes from the dorsal carpal branch of the radial artery. It enters the bone at, or distal to, the waist. In a retrograde fashion, this branch of the radial artery supplies blood to the proximal end.5 According to Wheeless, the blood supply enters proximal to the waist only 7% of the time. A second source of supply comes from the palmar and superficial palmar branches of the radial artery. This branch enters the bone at the distal tubercle and accounts for only 20-30% of the total supply, which does not reach the proximal pole.4 Alternately, Gray’s Anatomy states that in approximately 10% of the population the blood supply comes exclusively from the radial artery and enters through the distal pole. Individuals with this configuration are very vulnerable to AVN after a waist or proximal pole fracture; however, it is impossible to know who will have this blood supply.6
Figure 3 - Blood Supply of Scaphoid
The scaphoid is unique in that it crosses both proximal and distal rows of the carpal bones, thus serving as a type of link between the rows. Also, as stated above, there are many ligaments associated with the scaphoid, of which the scapholunate is the strongest stabilizer.7 Due to these aspects, the scaphoid is important in maintaining normal biomechanics of the wrist. All biomechanical movements within the wrist and hand complex occur as a series of rolls and glides between concave and convex surfaces.8
At the carpometacarpal joint of the thumb, abduction and adduction occur in the sagittal plane, while flexion and extension take place in the frontal plane. The abduction and adduction movements occur as the convex surface of the thumb metacarpal moves on the concave surface of the trapezium. When abducting the thumb, the convex surface of the metacarpal rolls palmarly while it slides dorsally on the trapezium.8 Conversely, during adduction, the convex surface of the metacarpal rolls dorsally while it slides palmarly on the trapezium.
Unlike the abduction and adduction, the movements of flexion and extension occur in conjunction with axial rotations of the metacarpal. The biomechanics of these motions occur as the concave surface of the metacarpal moves transversely on the trapezium. During flexion, the metacarpal medially rotates as the concave metacarpal rolls and slides ulnarly. As the thumb begins to extend the metacarpal will laterally rotate and the metacarpal will roll and slide radially.8
Opposition is the unique movement that combines all primary motions of the thumb allowing the thumb to reach the tips of the fingers. The full movement of opposition can be separated into two distinct phases. In the first phase, the metacarpal begins to abduct as the base of the metacarpal moves palmarly on the trapezium. In the second phase, the metacarpal flexes and medially rotates toward the other fingers.8 It is important to note that during opposition, the trapezium medially rotates on the scaphoid and the trapezoid contributing to further rotation at the metacarpal. As the thumb progresses back into reposition this motion involves adduction and extension-lateral rotation at the thumb.8
Figure 4 - Movement of the Thumb
The following motions of the scaphoid are also important to note when examining the biomechanics of the thumb. When the wrist flexes the scaphoid flexes, and when the wrist extends the scaphoid extends. Also, when the wrist ulnarly deviates the scaphoid extends, and when the wrist radially deviates the scaphoid flexes. It is important to note, however, that when the wrist extends the scaphoid is compressed between the dorsal lip of the radius and the radiocapitate ligament.8 These various movements are important when understanding the mechanism of injury of scaphoid fractures, which will be discussed below.
All authors agree that scaphoid fracture is the most common fracture of the carpal bones, occurring in approximately 80% of all carpal fractures.1,2,3,4,9,10 Young men, usually between the ages of 10-29, have the highest rate of injury.2,11 Van Tassel et al estimate the incidence rate to be quite low at 1.47/100,000 people/year.11 This is in contrast with other authors that suggest a much higher rate around 30/100,000 and even one study showing 121/100,000 in a population of military members.
The following table from an article by Schubert lists the different types of scaphoid fractures and the prevalence of each.
Figure 5 - Types of Scaphoid Fractures
*Includes tuberculum fractures.
A patient with a scaphoid fracture will present with deep, dull pain in the radial side of the wrist that usually worsens with gripping or squeezing.1 Swelling is typically present and bruising is often visible, but if it has been more than four days since injury, swelling is not always noted. The most suggestive sign is tenderness to palpation of the anatomical snuffbox or the distal tubercle.1 Most clinicians will treat for scaphoid fracture solely based on anatomical snuffbox tenderness.
The most common mechanism of injury for scaphoid fracture is from a fall on an outstretched hand (FOOSH).2 In a FOOSH injury the wrist is usually positioned in extension and radial deviation.5 As discussed above, when the wrist is in extreme extension the scaphoid is compressed against the radius. This compression combined with the force from the fall causes the fracture, most commonly near the waist. Also, fractures can occur from an axial force applied down the hand, through the scaphoid, to the radius.5
Other causes of patient symptoms must be ruled out before a diagnosis of scaphoid fracture is made. The following list for differential diagnosis comes from the Phillips, et al.1
Figure 6 - Differential Diagnosis of Scaphoid Fracture
- more common after scaphoid fracture because blood supply to the scaphoid is poor; less than optimal healing environment
- abnormal motion and collapse of the bone fragments may lead to mal-alignment within the wrist and subsequent arthritis
- in the event that the bone fails to heal, surgery to apply a bone graft may be indicated
- commonly seen when fragments have moved apart and the blood supply to these fragments is disrupted
- blood supply may be so poor that the piece does not get enough nutrients and the cells in the fragment die and may collapse
- proximal 2/3 of the scaphoid is most vulnerable
- most effectively treated with a vascularized bone graft
- may be caused by nonunion and avascular necrosis of the scaphoid
- symptoms may include: aching in the wrist, decreased range of motion in the wrist, pain with lifting or gripping
The most common diagnostic exam performed for suspected scaphoid fracture is anatomical snuffbox palpation for tenderness. This diagnostic test has a sensitivity of 90% and a specificity of 40% as an indicator of a scaphoid fracture12. Such results allow us to recognize that the absence of tenderness in the anatomical snuffbox is a good indicator that there is no fracture of the scaphoid1. Scaphoid tubercle palpation is also a common test performed along with anatomical snuffbox palpation. Schubert states that tubercle tenderness strongly supports scaphoid fracture diagnosis because it applies more direct pressure to the bone itself, whereas anatomical snuffbox palpation is not as direct2. Scaphoid tubercle palpation has a sensitivity of 87% and a specificity of 57% as an indicator of a scaphoid fracture12. There is no statistically significant difference in sensitivity of the two tests; however, the scaphoid tubercle test has a significantly higher specificity than anatomical snuffbox palpation for tenderness12. The presence of tenderness with either test should be used to aid in the diagnosis of a scaphoid fracture and can be a good indicator as to whether or not imaging is necessary13. Absence of tenderness in both areas will essentially exclude a fracture diagnosis.
Figure 7 - Palpation on the Palmer Surface
Another test that may be performed is the Scaphoid Compression Test, where the thumb is compressed against the scaphoid2. The sensitivity of the scaphoid compression test is 70.5% but the specificity is only 21.8%14. Although the specificity of this test has been questioned, it may aid in differential diagnosis due to greater sensitivity for radial side fractures.
Figure 8 - Palpation of Scaphoid and Axial Compression Test
Imaging tests are also performed with the most common being plain radiographs. X-rays are usually taken in four views: posteroanterior, lateral, semipronated oblique, and “scaphoid view” with the wrist pronated in ulnar deviation and the beam directed proximally with an angle of 25 degrees from vertical2. There is varying evidence on the reliability of radiographs on first examination, with an 86% specifity in a prospective trial by Tiel-van et al.15 This leads most physicians to cast a suspected fracture and re-evaluate approximately two weeks later, even if a fracture is not visible on radiographs. Other imaging tests performed are MRI, CT, and bone scintigraphy (bone scan). Yin et al reported these tests to have sensitivity/specificity of 96/99%, 93/99%, and 97/89%, respectively9.
Figure 9 - Radiological Diagnosis
Typical treatment for acute fractures consists of a below-elbow cast with immobilization of the thumb10. If there is only suspicion of a fracture, the cast is removed after two weeks and new radiographs taken10. In the event of a nondisplaced fracture, it has been recommended to cast for eight weeks, with follow-up radiographs taken upon removal of the cast5. If anatomical snuffbox tenderness is present and radiographs are unclear at this time, the patient is usually casted for another six weeks5.
Figure 10 - Below-elbow Cast with Immobilization of the Thumb
Unstable fractures, fracture dislocations, and displaced fractures, as well as conservatively treated fractures that progress to non-unions are treated with surgery3. The most typical surgical intervention for scaphoid fracture is internal fixation16. Wheeless describes Herbert Screw fixation as being indicated for unstable fractures as well as delayed or non-union fractures, and Cannulated Screw fixation as being indicated for delayed or non-union fractures4. In the past few years percutaneous screw fixation has become more widely used. This type of surgery is indicated for non-displaced waist fractures, acute unstable waist fractures, and proximal pole fractures. It should not be used when reduction and alignment cannot be achieved with a closed approach16. Recently, the development of percutaneous arthroscopic techniques of scaphoid stabilization that minimize surgical morbidity have surfaced, as well as marked improvements in the use of vascularized bone grafts for complicated scaphoid nonunions12. Evidence shows that surgical intervention is more appropriate for fractures and nonunions of the scaphoid proximal pole5. Overall, research shows that surgical intervention is more effective in relation to short term functional outcomes, patient satisfaction scores, grip strength, decreased duration to union, and earlier return to work17. No significant differences were found with post surgical pain, range of motion, non-union rates, infection, complications, or total treatment costs compared to conservative treatments17.
Video 1 - Garcia-Elias Approach for Volar Scaphoid (link)
Video 2 - Percutaneous Scaphoid Fixation with Kompressor Screw (link)
Video 3 - Minimal Incision Surgery for Scaphoid Fracture via Dorsal Approach (link)
Additional Web Based Resources
Video 5 - Scaphoid Fracture Overview (link)