Nonunion of the Scaphoid

Susanne Roberts, Scott W. Wolfe

Abstract

Scaphoid nonunion refers to a spectrum of failed healing, each of which requires a tailored approach. Rigid internal fixation is key to achieving good outcomes, regardless of nonunion type. However, dorsal or volar approaches may be used depending on the fracture location. Autogenous bone grafting is used in most cases of scaphoid nonunion. Correction of deformity should be addressed during the same surgical procedure. Dysvascular nonunions are often treated with vascularized bone grafts. If traditional treatments fail, a number of salvage treatment options still remain.

Keywords: proximal pole, scaphoid waist, humpback deformity, vascularized bone graft, scaphoid, nonunion, internal fixation

26.1 Trauma Mechanism

The oft-quoted definition of scaphoid nonunion is a scaphoid fracture that has failed to heal radiographically 6 months after cast immobilization or surgical intervention. However, delay in diagnosis is a leading cause of scaphoid nonunion. Many scaphoid fractures are either dismissed by the patient or family as a sprain or may be missed on early evaluation and radiographs by the primary care provider. Adequate radiographs and thorough examination may be insufficient to diagnose an acute scaphoid fracture. Many of these missed scaphoid fractures present as nonunions months to years after injury. Initial providers should have a high index of suspicion in patients with a fall on an outstretched hand or, less commonly, a high impact to a closed fist.

The unusual vascularity of the scaphoid has been investigated as a primary cause of nonunion. The proximal 70 to 80% of scaphoid vascularity is based on retrograde blood flow from radial artery branches entering through the narrow, oblique dorsal ridge. The distal portion of the blood supply comes from direct radial artery branches entering the volar tubercle. The volar and dorsal branches of the anterior interosseous artery anastomose with the radial artery branches to provide collateral blood flow. The proximal pole of the scaphoid is covered almost entirely with articular cartilage and few perforating vessels. Therefore, it is not surprising that, while only 30% of middle third fractures have been associated with avascular necrosis, nearly 100% of proximal pole fractures are rendered avascular as a result of poor retrograde blood flow.1

Fracture displacement, angulation, and comminution also increase the likelihood of scaphoid nonunion. Scaphoid fractures with ≥1.0 mm of displacement, intrascaphoid angle of greater than 45 degrees, or height-to-length ratio of greater than 0.65 have been shown to have higher incidence of malunion and nonunion.²

Even among nondisplaced fractures, inadequate immobilization or poor compliance has also been cited as an important but difficult-to-quantify cause of scaphoid union. Some fracture patterns such as distal pole and tubercle fractures have excellent vascularity and are highly amenable to a short period of casting. In nondisplaced proximal pole and waist fractures, the precise method of immobilization has not been shown to influence outcomes.³ However, young, active patients are less likely to tolerate prolonged immobilization and may have better outcomes with early surgical management.⁴

26.1.1 Natural History of Scaphoid Nonunion

In a long-term study of nonoperatively treated scaphoid fractures, the rate of nonunion was found to be 10%.5 In its early stages, scaphoid nonunion is often asymptomatic.⁶ Because the scaphoid serves as a critical link between the proximal and distal rows of the carpus, a disruption of this link can be expected to have a profound effect on carpal mechanics. Under normal circumstances, the scapholunate interosseous ligament pulls the lunate into flexion as the wrist and hand move from ulnar to radial deviation. However, with loss of scaphoid integrity, the scaphoid is rendered incapable of coordinating proximal row mechanics ( Fig. 26.1). With time, the volar waist of the scaphoid erodes, the distal scaphoid collapses into flexion, and the proximal scaphoid extends, resulting in a “humpback deformity” of the scaphoid. This frequent collapse pattern of scaphoid nonunion is usually associated with lunate instability and dorsal intercalated segment instability (DISI; Fig. 26.2).⁷ The natural history of untreated scaphoid nonunions is continued carpal collapse and osteoarthritis.⁸ In a 30-year study of scaphoid fractures, osteoarthritis was seen in 56% of patients with nonunion as compared to 2% of healed scaphoid fractures.⁵

The characteristic pattern of posttraumatic arthritis is known as scaphoid nonunion advanced collapse (SNAC). Arthritic changes originate in the radial styloid articulation and are followed by a degenerative cascade into the midcarpal joint, first at the distal scaphocapitate joint, and subsequently at the capitolunate joint.⁹ The radiolunate joint is relatively spared until late in the disease, given the nearly perfect concentricity of the proximal lunate articular surface and the lunate facet of the distal radius.

Fig. 26.1 Disruption of the link between the scaphoid and lunate through the nonunion site results in altered carpal mechanics and instability whereby the distal portion of the scaphoid collapses into flexion as the proximal portion extends with the lunate.

Fig. 26.2 (a) Characteristic humpback deformity with resorption of the scaphoid waist and collapse. (b) Corresponding dorsal intercalated segment instability deformity with dorsal tilt of the lunate. (Copyright © Scott W. Wolfe, MD.)

26.1.2 Classification

Both Herbert and Fisher 10 and Slade and Geissler¹¹ advanced classification systems intended to guide treatment of scaphoid fractures and nonunion, but it is difficult to build consensus around a classification system given the wide variety of anatomy, chronicity, and vascularity. For the purposes of intervention, four main characteristics of scaphoid nonunion guide treatment; within these broad categories, there is variation of fragment size and fracture orientation. Some nonunions may have more than one factor to consider. The most straightforward group are non-unions without deformity. Such fractures appear to have some element of stability and may be fibrous nonunions. They do not have evidence of bone loss, by either resorption or cyst formation that portends mechanical instability and can be managed with a more limited approach. The second class relates to those that have lost inherent stability as demonstrated by humpback or DISI deformity, which is the result of displacement and bone loss. Treatment of these fractures focuses on correction of mechanical malalignment, restoration of deficient bone, and provision of stability. The third class of scaphoid nonunions are those with impaired poor blood supply as determined by imaging or by direct operative inspection. Restoration of vascular flow to the proximal pole is critical to healing. The final characteristic is the presence of degenerative arthritis, which may redirect treatment toward a salvage procedure.

26.2 Diagnostic Techniques and Criteria

26.2.1 Clinical Signs and Tests

When evaluating a patient with scaphoid nonunion, it is important to keep in mind that the term scaphoid nonunion actually applies to a spectrum of failed healing, each of which requires a different approach to treatment. The primary patient factors that should be considered in evaluation of a scaphoid nonunion include time from injury, patient age, patient activity level, and amount of pain or disability. Not surprisingly, increased time from injury is associated with increased incidence and severity of osteoarthritis.8 Younger patients with higher activity levels and minimal arthritic change may be amenable to more aggressive treatment, while older or low-demand patients may favor nonoperative treatment until more severe functional impairment demands a salvage procedure. Other patient factors that should be considered include tobacco use and an assessment of compliance, which can derail even the best efforts at treatment. Patient comorbidities such as inflammatory arthritis or steroid dependency will also pose challenges to healing.

As an acute fracture may be missed, and early scaphoid nonunions may be asymptomatic, patients may present with an insidious onset of pain and without a recollection of trauma. Most commonly, patients complain of vague wrist discomfort and loss of motion. On examination, there is often localized swelling on the dorsoradial aspect of the wrist. Tenderness is usually localized to the anatomic snuffbox, and pressure over the scaphoid tubercle or performance of a “scaphoid shift” test is generally painful. Depending on the degree of arthritis that may be present, sharp radial deviation may elicit pain, and there may be tenderness, swelling, or synovitis at the midcarpal joint.

26.2.2 Imaging

If history and physical examination suggests scaphoid nonunion, diagnostic radiographs should include the following: posteroanterior (PA), lateral, and scaphoid views (partly supinated PA in ulnar deviation), and oblique pronation views. The primary goal is to identify the location of the fracture and to note displacement. Most non-unions occur either in the scaphoid waist or in the proximal pole, and the optimal approach differs depending on location. Deformity such as the characteristic “humpback” should be noted, as this will need to be corrected surgically. Any comminution or cyst formation will require additional bone grafting. Attention should be paid to overall carpal alignment and the presence of DISI deformity, as defined by a radiolunate angle of greater than 15 degrees and generally accompanied by scaphoid collapse and humpback. If carpal malalignment is present and is long-standing, it is important to note the presence of SNAC osteoarthritis at the radiocarpal and/or midcarpal joints.

When plain radiographs are equivocal, and especially when planning surgery, advanced imaging with computed tomography (CT) should be obtained. CT provides more precise visualization of osseous anatomy. This allows not only confirmation of suspected scaphoid nonunion, but also more exact determination of bone loss and precise measurement of intrascaphoid angles. Carpal collapse can be quantified using either the intrascaphoid angle or the height-to-length ratio on sagittal CT. An intrascaphoid angle of greater than 45 degrees is associated with an increased rate of functional impairment.7 Height-to-length ratio of greater than 0.65 correlates with increased carpal collapse. While the latter measurement has excellent interobserver reliability, it has yet to be correlated to outcomes.² CT is ideal for visualizing the degree of comminution or cavitation present. This aids in determining the type and location of bone graft, and the type of fixation, implant size, approach, and screw trajectory can also be planned ( Fig. 26.3).² It is important to obtain high-resolution, thin-slice, and contiguous axial and coronal scans that can be reformatted into long-axis sagittal and coronal views for operative planning. Finally, CT is considered the gold standard for assessment of healing, and can be used to quantify cortical bridging and provide guidelines for initiation of rehabilitation and return to activities.¹²

While CT scans can show the characteristic sclerosis, cysts, and fragmentation that are consistent with impaired vascularity, magnetic resonance imaging (MRI) is considered more informative in assessing fragment viability. MRI, however, is extremely operator dependent, and there is considerable controversy on the ideal sequencing algorithms and the role of contrast enhancement or perfusion studies.^13,14 MRI should be strongly considered in proximal third scaphoid nonunions. In one study, proximal fracture fragments with low T1 signal correlated with histologic evidence of osteonecrosis and poor uptake of tetracycline, whereas retention of proximal pole signal on T1 showed histologic viability. In this study, the investigators showed that nonunions with low signal on both T1- and T2-weighted sequences had the greatest compromise of vascularity and poor healing after nonvascularized bone grafting.¹⁵ However, a more recent study demonstrated lack of correlation between MRI findings, presence or absence of intraoperative bleeding, histologic evidence of osteonecrosis, healing, or time to union.¹⁶

26.3 Treatment Options

26.3.1 Indications for Treatment

Fibrous Nonunion without Deformity

Scaphoid nonunions with delayed presentation (> 6 months) are unlikely to heal with casting alone, as the repair process has ceased. Electrical stimulation may be used as an adjunct to surgical intervention or casting.17,18 In patients with delayed presentation, the success rate of casting combined with electrical stimulation has been reported to be only 69%.19 Therefore, rigid internal fixation with or without bone grafting is indicated for even nondisplaced scaphoid nonunions, unless medically contraindicated.

Fig. 26.3 (a) Three-dimensional CT surgical planning for optimal screw placement in a proximal pole fracture (Copyright © Joseph Lipman, PhD). (b) Intraoperative and postoperative imaging resulting from this preoperative plan (Copyright © Scott W. Wolfe, MD).

Historically, even in nondisplaced fractures, thorough debridement of the nonunion site was recommended prior to grafting and/or fixation. However, McInnes and Giuffre demonstrated that a more limited debridement (average 50%) achieved equivalent results, and therefore these authors concluded that full debridement is not necessary for healing.20 Select stable scaphoid fractures without bone loss or deformity, an intact cartilaginous envelope, and with minimal sclerosis may be amenable to open, percutaneous, or arthroscopic-assisted screw fixation without need for autogenous graft.^21–23 Even in patients with significant bone resorption (> 2mm) but without humpback deformity, Mahmoud and Koptan reported 100% union with screw fixation without bone grafting after a mean of 11.6 weeks. The authors found time to union to be more related to delay in fixation rather than gap size.²⁴ However, controlled studies comparing stable fixation with more extensive debridement and grafting as compared to more limited techniques in stable nonunions have not yet been performed.

Scaphoid Waist Nonunion and Humpback Deformity

This is the most common type of nonunion faced by hand surgeons, with varying degrees of bone loss and deformity. Nonvascularized bone graft is most commonly indicated in cases with good vascularity of the proximal fragment. Graft can be obtained locally either from the distal radius or from the iliac crest. Matti originally described the process of removing all necrotic bone and fibrous tissue through a dorsal approach and packing the debrided nonunion site with a cancellous bone plugs.²⁵ Russe later described a method using a volar approach and two oblong corticocancellous grafts from the iliac crest as inlayed struts, in addition to packed cancellous graft ( Fig. 26.4). This volar approach was believed to cause less damage to the dorsal blood supply.²⁶ Green later modified this procedure to use the volar aspect of the distal radius as the graft donor site.²⁷

Fisk first proposed the technique of using a wedge graft taken from the distal radius to restore scaphoid length and simultaneously correct flexion deformity and DISI. However, his technique used a graft osteotomized from the styloid of the distal radius without internal fixation.²⁸ In 1984, Fernandez described use of a corticocancellous, trapezoidal wedge from the iliac crest through a volar approach with Kirschner’s wire fixation.29 Iliac crest graft was preferred to radial styloid graft as it was felt that the former resists compression forces better. Cohen et al reported treating scaphoid waist fractures with humpback deformity with purely cancellous bone graft and screw fixation. The authors proposed that screw fixation served as an internal strut without the need for corticocancellous interposition graft. However, this method is dependent on having proximal and distal fragments of sufficient size to support screw fixation, and the authors did not report the ability to correct DISI with this technique.³⁰

Fig. 26.4 Russe’s technique with two corticocancellous inlayed struts with cortical side facing out is used to restore height and correct flexion deformity.

26.3.2 Proximal Pole Nonunion

As long as the proximal fragment has good vascularity and size, surgical indications do not differ substantially for proximal pole fractures as compared to scaphoid waist fractures. Volar approaches for fixation result in less adequate reduction and union rates in both acute proximal pole fractures and nonunions.31 Proximal pole fractures are most amenable to a dorsal approach, and in those with cavitation or cyst formation, cancellous bone graft from the dorsal distal radius or the iliac crest is generally recommended. Slade and Gillon recommended arthroscopically assisted percutaneous bone grafting from the distal radius, followed by rigid screw fixation for proximal pole nonunion, and his series demonstrated a 96% union rate by 9 months.²³

Dysvascular Nonunions

Due to the tenuous retrograde blood supply of the scaphoid, proximal pole and even occasionally scaphoid waist nonunions may present with signs of poor vascularity either on preoperative imaging or with intraoperative inspection of punctate bleeding. Vascularized bone grafting has been recommended in the absence of punctate bleeding of the proximal pole. Initially described techniques by Kuhlmann et al and others used vascularized pedicle grafts based on the pronator quadratus or the volar carpal artery.^32–35 The volar carpal artery pedicle lies between the palmar periosteum of the radius and the distal part of the superficial aponeurosis of the pronator quadratus and is harvested along with a 5-mm-wide strip of fascia and periosteum. In cases of humpback deformity, the harvested vascularized bone can be fashioned into a trapezoidal graft and wedged into the volar defect.³⁴

However, many dysvascular nonunions involve the proximal pole, where a dorsal approach is preferred. In response to this, Zaidemberg et al³⁶ in 1991 described an anatomical and clinical study of a vascularized pedicle graft from the dorsal distal radius based on the 1,2 intercompartmental supraretinacular artery (1,2 ICSRA), a consistent branch of the radial artery.³⁷ In 2006, Sotereanos et al reported a dorsal capsular-based graft from the distal radius, which is supplied by the artery of the fourth extensor compartment and can be used as an inlay graft.³⁸ Criticism of dorsal vascularized grafts centers on their potential for disruption of the dorsal scaphoid blood supply. Bertelli et al described a thumb metacarpal graft based on the first dorsal metacarpal artery to be used as a volar interposition graft that does not require crossing the wrist joint.³⁹

More recently, there has been enthusiasm for free vascularized grafts, particularly as there is concern that radial grafts are structurally inadequate for correction of humpback deformity. Sakai et al⁴⁰ first described the medial femoral condyle graft based on the articular branch of the descending genicular artery in 1991 and Gabl et al⁴¹ described free iliac crest graft based on the deep circumflex iliac vascular pedicle in 1999. The medial femoral condyle graft technique has been further popularized by Bishop and Shin, and Jones et al reported superior results with free medial femoral condyle graft as compared to the 1,2 ICSRA graft.^42–44 Bürger et al⁴⁵ and Higgins and Bürger⁴⁶ demonstrated successful use of a free osteoarticular medial femoral trochlear graft to replace unsalvageable avascular and fragmented proximal poles. Disadvantages of free grafts include the potential for donor site morbidity. Current commonly used vascularized graft choices include 1,2 ICSRA pedicle, pedicled volar carpal artery, and free medial femoral condyle. Less commonly used options include dorsal capsular pedicle, thumb metacarpal graft, and free iliac crest or osteoarticular grafts.

As a sort of middle ground between nonvascularized and vascularized bone grafting, Hori et al originally described the transplantation of a vascular bundle in 1979. In this technique, a vascular pedicle (consisting of a peripheral artery, venae comitantes, and perivascular tissue) is transplanted and anchored directly into the nonviable bone fragment.47 Fernandez and Eggli later described a similar procedure using a vascular pedicle from the second dorsal intermetacarpal artery with an iliac crest corticocancellous inlay graft. In this small series, 10 of the 11 healed at an average of 10 weeks, but further studies on this or similar techniques have not yet been performed.⁴⁸

Considerable controversy remains as to the need for vascular grafting of dysvascular scaphoid nonunions, and the optimal means to determine the vascularity of the proximal pole. Neither MRI nor punctate bleeding has been validated as predictive of histologic trabecular viability, time to union, or union itself.¹⁶ Robbins et al showed successful healing of scaphoid nonunions without punctate bleeding when treated with interposition iliac crest corticocancellous bone graft and rigid screw fixation, though the majority of cases in this study were waist or distal pole fractures.⁴⁹ A recent meta-analysis by Pinder et al on 1,602 patients in 48 publications demonstrated no benefit of vascular grafts over nonvascular grafts in the treatment of scaphoid nonunion.⁵⁰

26.3.3 Surgical Techniques

Percutaneous Fixation and Bone Grafting

In select stable, nondisplaced scaphoid nonunions, a percutaneous approach may be appropriate, particularly in proximal pole fractures. Many surgeons prefer a mini-incision over the 3–4 portal to quickly expose the ideal screw starting point and avoid potential injury to the extensor tendons. For the mini-incision approach, the extensor pollicis longus (EPL) tendon is identified and retracted radially in order to make a small capsular incision to expose the proximal pole. If there is some displacement, 0.062-inch Kirschner’s wires may be used as joysticks to aid in reduction prior to guide wire placement. The guide wire for the cannulated screw is passed from its starting point at the proximal pole, down the scaphoid axis, radially and distally, in line with the thumb under fluoroscopy. This is done with the wrist in slight flexion. Once reduction and wire placement are verified on fluoroscopy and the screw length is measured, the wire tip can be driven out through the volar skin and clamped. This is an important step, should the guide wire break during reaming or screw insertion. Reaming over the guide wire is then performed, being careful not to violate the most distal cortex. The volar aspect of the guide wire is then withdrawn into the distal fragment, and a curette is inserted through the dorsal portal to debride the nonunion site. Care must be taken not to violate the outer fibrocartilaginous shell that maintains stability of the scaphoid. If the fragment is loose, a small cortical window is created just distal to the fracture site for cancellous grafting.

Bone graft may be obtained from the iliac crest or distal radius. For distal radius graft, a small incision and blunt dissection are used to expose the cortex over Lister’s tubercle. For large amounts of graft, the tubercle is removed and abundant cancellous graft is harvested with curettes. Luchetti et al prefers to pack the graft in a small syringe, for ease of placement into the nonunion defect.51 Alternatively, the cortex is opened and an 8-gauge bone biopsy cannula is inserted to obtain multiple cancellous bone plugs. Bone plugs are then passed into the nonunion site via the bone biopsy cannula, and packed into the nonunion defect with a trocar or curette. The scaphoid guide wire is then retrograde drilled back out the dorsal cortex. Prior to screw insertion, the hand reamer may be passed over the guide wire to gently pack the bone graft and advance it into the distal pole. The screw is inserted and final radiographs are obtained. The amount and type of postoperative immobilization varies in these cases, but nonetheless should be maintained until union is confirmed on CT scan.⁵²

Surgical Fixation with Nonvascularized Bone Graft

Author’s Favored Treatment Option: Local Bone Graft from Radius

The original Matti–Russe procedure with Green’s modification utilized a volar approach to first excavate the nonunion site and remove all necrotic bone, cartilage, and fibrous tissues. This technique then includes inlay of two corticocancellous strut grafts from the distal radius with the cortical surfaces facing outward into the nonunion site to restore height and correct flexion deformity. The remaining cavity is then packed with cancellous bone graft. The author’s preferred treatment is a further modification of this technique, or hybrid Russe, using a single cortical strut and cancellous graft packing in combination with rigid screw fixation.⁵³

Under tourniquet control, a 4-cm volar incision is made along the flexor carpi radialis (FCR) tendon and extending another 2 cm along the glabrous border of the thenar eminence distally. After dividing its sheath, the FCR tendon is retracted ulnarly and the superficial branch of the radial artery is retracted radially or divided between sutures. The floor of the FCR tendon sheath is next incised longitudinally to expose extrinsic volar carpal ligaments. These capsular flaps should be carefully divided to expose the proximal and distal poles of the scaphoid, tagged, and preserved for later closure at the end of the case. The nonunion site is then wedged open using small osteotomes and the site is debrided using curettes to reach healthy bone with punctate bleeding. Small hooks or 0.062-inch Kirschner’s wire joysticks can be used to keep the nonunion site open. Care is taken not to disrupt the dorsal cortex to maintain stability and preserve the blood supply.

Once the nonunion site is thoroughly debrided, the pronator quadratus is incised from its radial attachment to expose the radial metaphysis. A 20-mm-long by 8-mm-wide oval cortical window is marked out on the distal radial cortex ( Fig. 26.5). A 0.045-inch Kirschner wire is used to make multiple holes along the marked line and the cortex is lifted using a small osteotome ( Fig. 26.6). This cortical graft is sculpted using a rongeur to form a “matchstick” strut appropriately sized to the defect and deformity of the scaphoid ( Fig. 26.7). Abundant cancellous bone graft is harvested using curettes. The defect is then packed with thrombin-soaked Gelfoam and the pronator quadratus is repaired over the defect.