Treatment of Scaphoid Fracture and Nonunions

                                   Dr. KS Dhillon

Introduction

Scaphoid fracture is the most common carpal bone fracture. It accounts for 90% of carpal fractures [1-3]. The scaphoid fracture is prone to nonunion because of its complex geometry and poor blood supply [4]. Zura et al [5]  performed epidemiological research on fracture nonunion in 18 human bones and they found that the site with the highest nonunion was the scaphoid (15.5%), followed by the tibia and fibula (14%) and femur (13.9%). The treatment of scaphoid fractures has improved a lot since the 1950s, but nonunion of scaphoid fractures is still a difficult problem. Duppe et al [6] found osteoarthritis in 56% of the patients with scaphoid nonunion after 36 years compared with 2% in patients with healed fractures. Nonunion of scaphoid fracture can decrease the function of the wrist and greatly affect the patient's life quality [7-9]. In the literature, the nonunion rate of scaphoid fracture is between 10%–40% [10,11].

There are several risk factors for scaphoid nonunion. Failure to seek medical attention after a fracture is considered a risk factor for scaphoid nonunion [12]. Wong and von Schroeder [13] studied 96 patients with 99 scaphoid fracture nonunions and they found that more than half of them did not receive initial treatment for acute injuries and presented late for initial treatment. Initially, many minimally displaced fractures are not visible on radiographs [14,15] and these ignored fractures can be a risk for nonunion [16]. Proximal pole fractures are at a higher risk of nonunion and avascular necrosis (AVN) due to a decreased arterial supply to the proximal pole [17]. 

Classification

Russe [18] classified scaphoid fractures as transverse, horizontal oblique, or vertical oblique, depending on the obliquity of the fracture line. Vertical oblique fractures account for only 5% and are more likely to be displaced by shear forces, whereas horizontal oblique and transverse fractures have greater compressive forces and are less likely to be displaced. Herbert and Fisher [19] defined scaphoid fractures as stable or unstable, as well as delayed union or nonunion (Table 1).

Herbert and Fisher Classification of Scaphoid Fractures (Table 1).

Type A: Stable acute fractures

  A1: Tubercle fracture

  A2: Incomplete waist fracture

Type B: Unstable acute fractures

  B1: Distal oblique fracture

  B2: Complete or displaced waist fracture

  B3: Proximal pole fracture

  B4: Transscaphoid perilunate dislocation fracture

  B5: Comminuted fracture

Type C: Delayed union

Type D: Established nonunion

  D1: Fibrous union

  D2: Pseudarthrosis

Type A fractures are stable acute fractures. Type B fractures are unstable acute fractures. Type A fractures can be treated non-operatively. Other types of fractures usually require surgical treatment. Type A fractures include tubercle fractures (A1) and incomplete waist fractures (A2). Type B fractures include distal oblique fractures (B1), complete waist fractures (B2), proximal pole fractures (B3), trans scaphoid perilunate dislocation fractures (B4), and comminuted fractures (B5). Type C fractures are delayed unions, and type D fractures are established nonunions, either fibrous (D1) or sclerotic (D2). Based on this classification, type A fractures are stable fractures. All other types are considered unstable and require surgical treatment.

Prosser et al [20] expanded the classification of distal pole fractures. Type I fractures are tuberosity fractures, type II are distal intra-articular fractures, and type III are osteochondral fractures.

About 70% to 80% of scaphoid fractures occur at the waist, 10% to 20% at the proximal pole, and the remainder at the distal pole [21]. Fractures occurring at the distal pole are more common in children than in adults.

Diagnosis

Scaphoid fractures usually occur in young adult men between the ages of 15 to 40 years. They are rare under the age of 10 years. The mechanism of injury is usually a fall on a hyperextended and radially deviated wrist. Examination will show tenderness in the anatomic snuff box or on the scaphoid tubercle. The wrist’s range of motion will be reduced and thumb movement may be painful. The grip strength is usually reduced. However, not all patients with scaphoid fractures have pain in the wrist. The diagnostic sensitivity is high for clinical examination, but specificity approaches only upto 74% to 80% [22,23].

The initial wrist radiographs include standard posteroanterior (PA), lateral, 45° pronated oblique, and 45° supinated oblique views, as well as a PA view in ulnar deviation (scaphoid view) [24]. The scaphoid view can pick up the fracture because the ulnar deviation of the wrist distracts the unstable fracture fragments. The sensitivity of plain radiographs is about 70% for scaphoid fractures [25].

If there is a high clinical suspicion of a scaphoid fracture but the x-rays are normal, a short arm thumb spica cast is usually applied [26]. Follow-up x-rays may show bone resorption or early callus formation adjacent to the fracture site if an occult fracture did exist. This traditional treatment with repeat x-rays and immobilization can lead to a loss of work and has economic implications. It has been reported that 75% to 80% of patients who had clinical suspicion of scaphoid fractures would be immobilized unnecessarily if they underwent such traditional treatment [27].

Occult scaphoid fractures can now be detected by early definitive evaluation with bone scintigraphy, magnetic resonance imaging (MRI), or computed tomography (CT). Bone scintigraphy has demonstrated a 92% to 95% sensitivity and a 60% to 95% specificity for scaphoid fractures [28]. MRI has shown a 95% to 100% sensitivity and specificity for scaphoid fractures [29]. MRI is superior to bone scintigraphy due to fewer false positive results and the ability to identify other causes of wrist pain, such as ligamentous injury. 

In patients with scaphoid nonunion, preoperative MRI is recommended to assess the vascularity of the proximal pole. Standard MRI shows only 68% accuracy for assessing proximal pole vascularity, while gadolinium-enhanced MRI has 83% accuracy [30].

Treatment

Undisplaced or minimally displaced scaphoid fractures can be treated by immobilization with a thumb spica cast for 8 to 12 weeks. An above-elbow cast to avoid motion of the scaphoid by eliminating forearm rotation may be preferred for the initial immobilization period of 4 to 6 weeks, followed by a short-arm cast. Provided that treatment is started within 3 weeks following injury the healing rate of nondisplaced waist scaphoid fractures with cast immobilization is 88% to 95% [31]. The main disadvantages of cast immobilization are more frequent office visits to check whether the cast fits properly, more frequent x-rays to assess fracture alignment, potential skin breakdown, prolonged immobilization until complete healing has occurred, stiffness of immobilized joints, and a longer time to healing. Some surgeons recommend early internal fixation even for non-displaced fractures to avoid such complications. Percutaneous cannulated screw fixation of undisplaced or minimally displaced scaphoid fractures has demonstrated promising results [32,33]. The role, benefits, and risks associated with internal fixation of undisplaced or minimally-displaced scaphoid fractures remain controversial and have not been established.

Dias et al [32] in a prospective randomized trial of 88 patients with acute nondisplaced or minimally-displaced fractures of the waist of the scaphoid, reported that an early return of grip strength and range of motion after open reduction and internal fixation was transient, and the complication rate related to surgery was high. Postoperative complications included wound infection (1 case), scar problems (10 cases), nerve injury (1 case), and algodystrophy (1 case). They were of the opinion that there was no clear overall benefit of early internal fixation compared with cast immobilization for acute nondisplaced or minimally-displaced fractures.

A prospective randomized trial conducted by Bond et al [33], which compared percutaneous internal fixation (11 patients) with cast immobilization (14 patients) for nondisplaced scaphoid fractures, showed an earlier time to union (7 weeks versus 12 weeks with casting) and earlier return to work (8 weeks versus 15 weeks with casting) with internal fixation, with no functional differences between the two groups after two years. They found no increase in the surgical complication rate.  McQueen et al [34] in a prospective randomized trial of 60 patients with acute fractures of the waist of the scaphoid reported a faster radiological union and a more rapid return of function, sports, and full work activities after percutaneous screw fixation compared with cast immobilization.

There is no consensus concerning the best treatment for nondisplaced or minimally-displaced scaphoid fractures. Prolonged cast immobilization is becoming less well tolerated, especially by younger patients who want to return to work and sports early. Patient expectations are now accelerating the trend to fix undisplaced scaphoid fractures, although the long-term outcomes do not seem to differ between internal fixation and cast immobilization. Economic analyses have shown that early internal fixation is superior from a social perspective, by returning people back to their duties earlier [35,36]. 

The percutaneous technique is more challenging than the open technique but it has the advantages that the carpal ligaments are not divided (thereby preserving the ligament support of the wrist), the blood supply to the scaphoid is not interrupted and there is less scarring that can limit wrist motion. Percutaneous fixation performed by experienced surgeons may be recommended for active patients with a nondisplaced or minimally displaced scaphoid fracture.

Internal fixation is indicated for displaced waist and proximal pole scaphoid fractures because they have a high risk of nonunion, delayed union, or AVN. Displacement of the fractured fragments by more than 1 mm in any view is defined as an unstable scaphoid fracture. Fractures that have progressively displaced during cast immobilization are also considered as unstable fractures, even if there was no initial displacement. Proximal pole fractures are more likely to progress to nonunion or AVN because of the tenuous blood supply to the proximal pole of the scaphoid. Internal fixation for such fractures is strongly recommended.

Herbert and Fisher introduced a headless compression screw called Herbert screw in 1984. Internal fixation with a headless screw has become the accepted standard surgical technique for the treatment of scaphoid fractures [37]. The headless screw can be recessed below the articular cartilage that covers 80% of the scaphoid surface. The screw can be inserted through both the dorsal and palmar approaches. The palmar approach preserves the important dorsal blood supply and provides access to distal pole and waist fractures. It, however, disrupts the carpal ligaments and gives poor exposure of the proximal pole. The dorsal approach provides good exposure of the proximal pole and allows easier screw placement, but can disrupt the tenuous blood supply. The choice of approach depends on an individual surgeon’s preference and experience. The dorsal approach is strongly recommended for the fixation of proximal pole fractures because it is technically easier to insert the screw into a small fractured fragment of the proximal pole [38]. When using a headless screw the screw should be placed within the center of the scaphoid. A successful union rate of approximately 95% can be achieved following adequate screw fixation of acute scaphoid fractures with both palmar and dorsal approaches. Screw malpositioning can result in nonunion of scaphoid fractures. In recent years, several cannulated headless compression screws have been developed. These cannulated devices have enabled surgeons to insert the screw percutaneously through both palmar and dorsal approaches. The percutaneous technique is used only for nondisplaced or minimally-displaced scaphoid fractures. This technique has recently been used for displaced scaphoid fractures, with reduction of fracture displacement using fluoroscopic or arthroscopic control [39,40]. Reported union rates with the percutaneous technique ranged from 94% to 100% and complication rates from 0% to 30%, which seem to be comparable to those with the open technique [41]. 

The disadvantages of surgery include the potential for infection, wound complications, injury to nerves, tendons, or ligaments, injury to the vascular supply to the scaphoid, hardware failure, and other associated risks such as anesthesia complications. Nonunion and delayed union after internal fixation are unusual but can occur if there is a loss of rigid fixation caused by screw malpositioning, inadequate reduction, or AVN of the proximal pole. 

Scaphoid Malunion and Nonunion

Nonunion by conventional terms is a non-healed scaphoid 6 months after injury, whereas a delayed union is a time frame that is less than 6 months. Nonunion of scaphoid fractures can produce scaphoid nonunion advanced collapse (SNAC). SNAC can lead to degenerative osteoarthritis of the wrist. Humpback malunion deformity of the scaphoid can result from volar angulation of the proximal and distal poles of the scaphoid in the setting of scaphoid fracture through the waist. The dorsal component forms a 'humpback' which can be palpated. The lateral intrascaphoid angle is increased because of a shortening of the palmar cortical length. The humpback deformity can cause dorsal intercalated segment instability (DISI) because of the dorsal rotation of the lunate together with the proximal scaphoid fragment. 

The aim of treatment for scaphoid nonunions and malunions is to achieve healing and to correct any carpal deformities to prevent arthritis of the wrist [42]. 

Nonoperative treatment of scaphoid nonunions includes electrical or ultrasound bone stimulation combined with cast immobilization. A nondisplaced scaphoid nonunion can be treated nonoperatively but a very long period of cast immobilization (4 to 6 months) is required. Surgical treatments are more effective than bone stimulation for the treatment of scaphoid nonunions. Nonoperative treatment is restricted to patients who cannot have surgery for any reason.

The surgical techniques for the treatment of scaphoid nonunions include nonvascularized or vascularized bone grafting, with or without internal fixation. Sometimes salvage procedures may be necessary for scaphoid nonunions when advanced degenerative arthritis is present in the wrist. Salvage procedures include proximal row carpectomy, scaphoid excision, limited intercarpal fusion, four-corner fusion, total wrist arthroplasty, and total wrist fusion.

Nonvascularized bone grafting

Russe [18] reported that healing of scaphoid nonunions could be achieved by placing iliac cancellous bone grafts into an egg-shaped cavity created within both fractured fragments. Russe subsequently modified his technique where he inserted two iliac corticocancellous bone grafts into the excavated scaphoid, with their cancellous sides facing each other, while the remainder of the cavity is filled with cancellous chips. Union rates of approximately 90% can be achieved by this Russe procedure [18,43].

Most of the failed cases are due to AVN of the proximal pole. The Russe procedure is now not recommended for this type of fracture. It is difficult to correct the humpback deformity using this technique. 

Such a deformity can be corrected by performing an intercalated wedge bone graft. The wedge bone graft can be fixed to the scaphoid fragments with Kirchner wires (K-wires) or screws. 

A meta-analysis found that screw fixation with wedge grafting had markedly better results (94% union) than K-wire and wedge grafting (77% union) [44]. Although screw fixation with wedge grafting can provide highly successful union rates, this technique is technically quite difficult. 

Stark et al [45] introduced an alternative technique to correct the humpback deformity and to heal nonunion by temporary K-wire fixation and bone chip grafting. The humpback deformity is corrected by forcefully extending the wrist dorsally before the fragments are fixed with K-wires. Cancellous bone chips are packed tightly into the defect. Stark et al reported successful union in 97% of 151 scaphoid nonunions.

Finsen et al [46] demonstrated success in 90% of 39 nonunions with the same technique. The results were also excellent for proximal pole nonunions in both studies. In the Stark et al study, only one of 32 proximal pole nonunions failed to heal. Finsen et al showed that all the 14 proximal pole nonunions healed. There has been limited information for cases in which AVN was associated with proximal pole nonunions. Union rates of 40% to 67% have been reported with nonvascularized bone grafting and internal fixation [47].

Although there are many reports in the literature, treatment strategies for scaphoid nonunions remain controversial. Factors that adversely affect the outcome in scaphoid nonunions include a long duration of nonunion, AVN of the proximal pole, and failed previous surgery [48]. Nonvascularized bone grafting is usually sufficient for most waist fracture nonunions without AVN. Vascularized bone grafting is needed in cases with a long duration of nonunion, AVN of the proximal pole, and failed previous surgery.

Vascularized bone grafting

In recent years, vascularized bone grafting for the treatment of scaphoid nonunions has gained considerable popularity. The principal advantage of vascularized bone grafting is that there is potential for a more reliable union after grafting. There are several methods of transferring a vascularized bone graft to the scaphoid [48,49]. These include: 

• The pronator quadratus pedicled bone graft

• Pedicled grafts based on the ulnar artery or the palmar carpal artery

• The radial styloid fasciosteal graft

• Pedicled grafts from the index finger metacarpal and the thumb metacarpal.

Free vascularized bone grafts from the iliac crest and the medial femoral supracondylar region have also been reported in the literature. Zaidemberg et al [50] described a vascularized bone graft derived from the dorsal radial aspect of the distal radius, which is nourished by the intercompartmental supraretinacular artery. Most of the published studies on vascularized bone grafting for scaphoid nonunions have reported union rates of between 80% to 100%. Only some of the nonunions in these studies had AVN [48,49]. A recent meta-analysis found that vascularized bone grafting achieved an 88% union rate compared with a 47% union rate with screw and intercalated wedge fixation in scaphoid nonunions with AVN [44].

In some reported series, the means of assessing the vascularity of the proximal pole were not described. In others, it was only assessed by the presence of increased density of the proximal fragment on the preoperative radiographs.

Perlik and Guildford [51] reported that increased density on the preoperative radiographs has only 40% accuracy for detecting proximal fragment avascularity. 

In the study by Boyer et al [52], 6 of 10 proximal pole nonunions healed with the distal radius vascularized bone graft. This study included only patients with AVN of the proximal pole, as proven by the absence of punctuate bleeding from the proximal pole during surgery. 

Straw et al [53] reported discouraging results in that only 2 of 16 nonunions with AVN united with the distal radius vascularized bone graft.

Chang et al [54] evaluated a large series of distal radius vascularized bone grafts that were performed for scaphoid nonunions and they showed that 71% of 48 nonunions healed and the union rate was 91% in the absence of AVN and 63% in the presence of AVN. Overall, the balance of evidence suggests that vascularized bone grafting may improve healing of scaphoid nonunions, particularly in the presence of AVN of the proximal pole. It is important to note that a successful outcome is not universal and depends on careful patient and fracture selection and the use of appropriate surgical techniques. 

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