Peter J. L. Jebson, Jane S. Tan, and 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.12
There are about 345,000 scaphoid fractures annually in the United States.
A scaphoid fracture classically occurs in a young, active adult due to a fall onto an outstretched hand.
The Herbert classification categorizes scaphoid fractures into acute stable, acute unstable, delayed union, and established nonunion patterns.
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.
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.17
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
The typical mechanism of injury involves a fall onto the wrist. 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.
Seventy to 80% of scaphoid fractures occur at the waist region, while 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
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.11 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.14,16
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 at the proximal fragment (via the lunate and scapholunate ligament) and flexion forces at the distal fragment result in a flexion (“humpback”) deformity of the scaphoid.
This 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 of the scaphoid waist region is about 5% to 10%.13
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:
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 ecchymoses over the volar radial wrist
IMAGING AND OTHER DIAGNOSTIC STUDIES
Initial imaging studies for a suspected scaphoid fracture should include a posteroanterior (PA) view with the wrist in ulnar deviation, semipronated and semisupinated 45-degree oblique views, and a lateral view.
The PA ulnar deviation view produces scaphoid extension, permitting visualization of the entire scaphoid.
The semipronated view permits visualization of the waist and distal-third regions.
The semisupinated view provides visualization of the dorsal ridge.
The lateral view can demonstrate a waist fracture, fracture displacement and angulation, and overall carpal alignment.
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
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.
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.
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.
DIFFERENTIAL DIAGNOSIS
Scapholunate injury
Wrist sprain
Wrist contusion
Fracture of other carpal bones
Distal radius fracture
NONOPERATIVE MANAGEMENT
Nonoperative management, specifically cast immobilization, is indicated for a nondisplaced, acute (less than 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, a CT scan should be obtained.
SURGICAL MANAGEMENT
Operative treatment is advocated for fractures that are unstable or displaced (see above criteria) and following a significant treatment delay.
Percutaneous fixation is indicated for:
Nondisplaced fractures of the scaphoid waist
Displaced fractures of the scaphoid waist
Proximal pole fractures
Percutaneous stabilization of scaphoid fractures may be performed using either the dorsal arthroscopically assisted reduction and fixation (AARF) approach17–19 or the volar approach.3,10
Regardless of the technique used, the screw must be inserted in the middle third or central axis of the scaphoid, as this provides the greatest stability and stiffness, improves fracture alignment, and decreases time to union.1,20,21
Preoperative Planning
All imaging studies should be reviewed to identify the location of the fracture and the size of the scaphoid, both of which influence implant selection.
Plain radiographs should be templated to determine the approximate screw length.
Required equipment:
Portable mini-fluoroscopy unit
Kirschner wires
Cannulated headless compression screw system
Wrist arthroscopy equipment for AARF
Positioning
The patient is positioned supine on the operating table, with the shoulder abducted 90 degrees and the arm on a radiolucent hand table.
A pneumatic tourniquet is applied to the upper arm.
The portable fluoroscopy unit is positioned at the end of the hand table.
TECHNIQUES
DORSAL ARTHROSCOPY-ASSISTED REDUCTION AND FIXATION
Nondisplaced Fracture of the Scaphoid Waist or Proximal Pole
Position the wrist to obtain a PA view of the wrist.
Under fluoroscopic guidance, gently pronate the wrist until the scaphoid appears as an oblong cylinder, indicating that the proximal and distal poles are aligned.
Flex the wrist about 45 degrees until the cylinder rotates into the plane of imaging, forming a “ring” sign. The center of the ring indicates the central axis of the scaphoid (TECH FIG 1).
Using a 14-gauge angiocatheter as a guide for wire insertion, place the tip of a 0.045-inch guidewire through the catheter and onto the proximal pole of the scaphoid, at the center of the scaphoid ring. Confirm correct positioning with fluoroscopy.
Insert the guidewire down the central axis of the scaphoid using a wire-driver. Keep the wrist flexed to avoid bending the wire.
Insert the guidewire through the trapezium and advance it until the proximal tip of the guidewire clears the radiocarpal joint such that the wrist can be extended for arthroscopic examination.
TECH FIG 1 • The scaphoid ring sign indicates the central axis of the scaphoid, which is critical for accurate insertion of the cannulated compression screw. The wrist is positioned in flexion and pronation until the scaphoid appears as a “ring” (arrow) on fluoroscopic imaging. A 0.045-inch guidewire is inserted through the center of the ring.
Confirm correct wire position with fluoroscopy.
The radial midcarpal portal is used to evaluate the accuracy of fracture reduction.
The 3-4 and 4-5 portals are used to assess the integrity of the radiocarpal and intercarpal ligaments.
Suspend the hand vertically in finger traps and apply 10 lb of traction to the upper arm to distract the radiocarpal and midcarpal articulations.
Create a small longitudinal incision over each portal site, and bluntly dissect down to the capsule with a hemostat. Enter the capsule with a blunt trocar.
Perform a diagnostic arthroscopy to assess for any associated injuries and to evaluate the fracture reduction.
Remove the hand from traction for screw insertion.
Position the wrist again to obtain the “ring” sign, and maintain the wrist in flexion.
Drive the guidewire from dorsal to volar, perpendicular to the fracture line, until the distal tip lies just within the distal pole of the scaphoid (TECH FIG 2A–C).
Place a second guidewire of equal length against the tip of the proximal pole, parallel and next to the first guidewire. The difference between lengths of the protruding wires represents the length of the scaphoid.
Subtract at least 4 mm from the length of the scaphoid to obtain the desired screw length.
Make a small longitudinal incision around the guidewire, and bluntly dissect down to the joint capsule. Carefully retract the extensor pollicis longus and extensor digitorum communis tendons away from the surgical site.
Use the cannulated reamer to ream to 2 mm short of the distal articular. It is critical not to ream closer than 2 mm, as this may cause loss of fracture compression during screw insertion.
Insert an Acutrak or mini-Acutrak screw (Acumed, Beaverton, OR) of appropriate length (at least 4 mm shorter than the measured scaphoid length) to within 1 to 2 mm of the distal surface.
The tip of the screw should not penetrate the distal surface, and the proximal end of the screw should rest 2 mm deep to the proximal articular cartilage (TECH FIG 2D,E).
Confirm satisfactory screw position and fracture reduction with fluoroscopy. The screw should be inserted down the central axis of the scaphoid. If any doubt exists, use the arthroscopic portals to confirm that the screw is buried in the scaphoid.
TECH FIG 2 • A–C. Before screw insertion, the position of the Kirschner wire must be changed from its position used for arthroscopy. The Kirschner wire should be driven from volar to dorsal until the distal end lies just beneath the articular surface of the scaphoid. (continued)
TECH FIG 2 • (continued) D,E. Screw fixation of minimally displaced scaphoid fracture via the dorsal percutaneous technique. The screw tip should rest within 1 to 2 mm of the distal cortex. Excellent compression should be obtained with this technique.
The 3-4 portal and the radial midcarpal portals provide the best view to ensure that the fracture is adequately reduced and that there is no violation of the midcarpal joint.
Displaced Scaphoid Waist Fracture
Insert two percutaneous 0.062-inch smooth Kirschner wires dorsally into each fragment perpendicular to the long axis of the scaphoid to be used as joysticks to reduce the fracture (TECH FIG 3A,B).
Position the wrist as previously described.
The guidewire from the Acutrak system is inserted from proximal to distal, starting dorsally and aiming for the central axis of the distal fragment.
The guidewire is driven through the distal fragment and out through the volar skin of the hand. The protruding tip is then pulled volarly until the wire is only in the distal fragment (TECH FIG 3C).
The proximal fragment, which is now freely mobile, is reduced manually using the Kirschner wire joysticks.
Once the fracture is reduced, the central guidewire is driven from volar to dorsal into the proximal fragment, securing it in place (TECH FIG 3D).
TECH FIG 3 • A. Reduction of a displaced scaphoid waist fracture using Kirschner wire joysticks. B. The Kirschner wire joystick technique for fracture reduction. C. The guidewire is pulled volarly until it remains only in the distal fragment. (continued)
The guidewire is further advanced from volar to dorsal until its distal tip is just within the subchondral bone of the distal articular surface. This allows for measurement of the screw length as previously described.
An additional 0.045-inch Kirschner wire is inserted parallel to the guidewire to prevent rotation of the scaphoid fragments during reaming and screw implantation.
Maintenance of reduction during and after screw insertion is confirmed with fluoroscopy, and all wires are subsequently removed.
TECH FIG 3 • (continued) D. The guidewire is driven from volar to dorsal, transfixing the proximal fragment.
VOLAR PERCUTANEOUS APPROACH
Position the patient in a supine position with the shoulder abducted and the forearm in supination. The wrist is placed into an extended and ulnarly deviated position over a rolled towel to gain access to the distal pole of the scaphoid.
Position the portable fluoroscopy unit such that PA and lateral views of the wrist can be obtained. Image intensification is used to locate the distal scaphoid tuberosity.
A small longitudinal stab incision is made at this point, and the soft tissues are bluntly dissected down to the scaphotrapezial articulation.
Introduce the guidewire on the distal scaphoid tuberosity. Under image guidance, the wire is advanced toward the center of the proximal pole, aiming for the tubercle of Lister (TECH FIG 4).
The volar prominence of the trapezium may be partially excised to facilitate the correct starting point and trajectory for the guidewire.
Alternatively, the guidewire may be placed directly through the trapezium into the scaphoid distal pole. We do not prefer this approach due to concerns about the development of scaphotrapezial arthritis.
Advance the guidewire to the subchondral bone of the proximal pole.
Place a second guidewire of equal length against the surface of the distal scaphoid, adjacent and parallel to the first guidewire. The difference between the lengths of the wires represents the length of the scaphoid.
Subtract 4 mm from the length of the scaphoid to obtain the desired screw length.
Use the cannulated reamer to ream to within 2 mm of the proximal cortex. It is critical not to ream closer than 2 mm from the proximal cortex, as this may result in a lack of compression during screw insertion.
Insert an Acutrak or mini-Acutrak screw of appropriate length, remove the guidewire, and confirm satisfactory screw position and fracture reduction with fluoroscopy.
TECH FIG 4 • In the percutaneous volar approach, the guidewire is inserted into the scaphoid at the scaphotrapezial joint, and into the center of the proximal pole. The wire should be inserted aiming for the tubercle of Lister.
POSTOPERATIVE CARE
Dressings are applied and the limb is immobilized in a forearm-based splint, immobilizing only the wrist. The thumb and fingers remain free for range-of-motion exercises.
The patient is instructed in the importance of limb elevation and finger range-of-motion exercises.
At 2 weeks postoperatively, the sutures are removed, a removable wrist splint is applied, and a wrist range-of-motion exercise program is initiated.
If the patient is noncompliant, the fracture is deemed unstable, or the fixation is less than ideal, then a short-arm cast is applied for at least 6 weeks.
Plain radiographs are obtained at 2, 6, 12, and 24 weeks postoperatively.
The splint (or cast) is discontinued when union is confirmed on serial plain radiographs. If there is any question regarding fracture union, a CT scan is obtained.
Unprotected strenuous activity or contact sports are not permitted until 3 months postoperatively.
OUTCOMES
Results of contemporary techniques of percutaneous fixation are excellent; it has been shown to allow for earlier mobilization and return to activity and high satisfaction rates compared to nonoperative measures.5,17,22
Earlier mobilization avoids complications such as muscle atrophy and joint stiffness.
Percutaneous techniques result in decreased soft tissue damage compared to conventional open techniques.22
In a recent series of 27 consecutive patients, the union rate (confirmed by CT) was 100%. The average time to union was 12 weeks, with a prolonged time to union noted in patients with a proximal pole fracture.18
COMPLICATIONS
Complications are rare with percutaneous fixation techniques. The risks associated with open reduction and internal fixation, such as damage to the ligamentous support of the carpus and disruption of the dorsal blood supply, are minimized.
Possible complications include15,19 :
Nonunion
Malunion
Injury to the dorsal sensory branch of the radial nerve
Extensor tendon injury
Infection
Technical problems: screw protrusion, screw malposition, bending or breakage of guidewire
Erosion of the trapezium and discomfort from the head of the screw has been reported with the use of a percutaneous cannulated screw inserted via the volar approach.22
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