Scaphoid Fractures

Relevant Anatomy

The scaphoid bone functions as a link between the proximal and the distal carpal rows through ligamentous attachments and articular mechanics. It has a fairly complex and certainly unique anatomy. It is often described as having a peanut shell shape. The scaphoid articulates with the distal radius proximally and the lunate ulnarly. It also articulates with the trapezium, trapezoid, and capitate of the distal carpal row. While it is one of the four bones of the proximal carpal row, it acts as the linkage between the proximal and distal row and is therefore integral to wrist biomechanics in creating motion and stability of the wrist. When this linkage is damaged, as with fracture or scapholunate ligament disruption, carpal instability ensues. One of the fairly unique features of the scaphoid is the relatively large surface area covered by articular cartilage reported to be approximately 80%. This leads to multiple articulating forces being applied to the bone as well as the fact that joint fluid almost always interacts with the fracture, possibly washing away hematoma critical to fracture healing.

Traditionally, scaphoid fractures are divided into three distinct categories based on anatomic fracture location: proximal pole, waist, and distal pole. One of the greatest challenges in treating scaphoid fractures lies in its tenuous and somewhat variable blood supply, leading to a relatively significant risk of nonunion. The classic study performed by Gelberman in 1980 outlined the vascular supply to the scaphoid to stem from the radial artery, wherein 70%–80% of intraosseous vascularity, including the entire proximal pole, comes from branches entering through the dorsal ridge ( Fig. 70.1 ).

Pathoanatomy

The scaphoid is the most commonly fractured carpal bone, accounting for 60%–70% of all carpal fractures. Acute scaphoid fractures are most commonly the result of a fall on an outstretched hand in slight pronation. In one cadaveric study, scaphoid fractures were reproduced by loading the wrist in extension. The severity of pain and disability is variable after these injuries, and so any patient presenting with pain on the radial side of the wrist should be ruled out for scaphoid fracture as part of the initial workup. However, a large number of scaphoid fractures go unrecognized, or are initially diagnosed as a sprain. Any patient with radial-sided wrist pain, even with normal imaging, should be immobilized until evaluation by an orthopedic surgeon can be arranged and repeat imaging can be obtained. Failure to follow this protocol continues to lead to missed fractures and scaphoid nonunions.

Classification

There are two popular classification systems for scaphoid fractures. These are the Herbert and Russe classifications. They vary in that the Herbert classification is based upon fracture stability, whereas the Russe classification is based upon fracture pattern. ^, In the Herbert classification ( Fig. 70.2 ), type A fractures are considered stable whereas type B fractures are considered unstable. Type C and D fractures are related to healing, with type C fractures indicating delayed union and type D fractures being established nonunions.

In the Russe classification ( Fig. 70.3 ), the plane of the fracture pattern is considered. There are three separate patterns, characterized by abbreviations of their pattern, with “HO” representing horizontal oblique fractures, “T” representing transverse fractures, and “VO” representing vertical oblique fractures.

In 2012, the concept of classification by displacement versus instability was evaluated with arthroscopic assessment. While not developing a traditional classification scheme, the authors challenged the equality often used for the terms “displaced” and “unstable,” evaluating 58 consecutive patients with scaphoid fracture assessed arthroscopically. They found that of 31 nondisplaced fractures, 11 were actually unstable upon arthroscopic evaluation, indicating a relatively high percentage of arthroscopically unstable fracture in contrast to those traditionally considered to be stable based on nondisplaced radiographs.

Most commonly, scaphoid fractures are categorized based on the location of the fracture. These are broken down into distal pole, waist, or proximal pole fractures. Based on anatomical considerations discussed above and blood supply, this type of classification does have prognostic value, as proximal fractures are very prone to nonunion, while distal pole fractures have a much lower rate of nonunion. This suggestion is supported by a prospective multicenter study of 1052 patients, wherein proximal pole fractures were found in only 5% of fractures, but accounted for 23% of nonunions.