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Minimally Invasive Management of Scaphoid Nonunions

Slade, Joseph, F, III; Dodds, Seth, D

Section Editor(s): Meals, Roy A MD, Guest Editor; Harness, Neil G MD, Guest Editor

Clinical Orthopaedics and Related Research: April 2006 - Volume 445 - Issue - p 108-119
doi: 10.1097/01.blo.0000205886.66081.9d
SECTION I: SYMPOSIUM: Problem Fractures of the Hand and Wrist
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Not all proximal pole scaphoid nonunions with avascular necrosis require vascularized bone graft or a formal open incision. If the distal scaphoid is well perfused and the proximal pole can be secured rigidly after percutaneous bone grafting, then nonunion repair and healing can proceed. We describe minimally invasive techniques that permit fracture site débridement, establishment of distal perfusion by central axis reaming, arthroscopic assessment of perfusion, percutaneous bone grafting, and rigid internal fixation. As surgeons develop new minimally invasive techniques, it is still imperative to continue to base treatment on scaphoid nonunion pathology and the key principles in the treatment of any non-union.

Level of Evidence: Level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.

One or more authors (XXX) received benefits for personal of professional use from a commercial party related indirectly to the subject of this article. In addition, benefits have been directed to a research fund with which one or more of the authors (XXX) is associated.

Correspondence to: Joseph F. Slade, III, MD, Associate Professor, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 73 Faulkner Drive, Guilford, CT 06437. Phone: 203-458-0718; Fax: 203-785-7132; E-mail: joseph.slade@yale.edu.

Scaphoid nonunions have reported treatment failure rates of 25% to 45% and continue to challenge surgeons to think out of the box.4,47 These fractures are difficult to treat because their unique anatomy limits potential repair. The predisposing factors that prevent successful osteogenesis include a tenuous vascular supply, high shear stress at the fracture site, the inability of cartilaginous bone to form stabilizing callus, and joint fluid that dilutes the necessary local hormone and bone stimulants. The viable bone at the nonunion site is increasingly replaced with mechanically weak fibrous tissue. The difficulty in healing scaphoid nonunions is challenged further by the dynamic, unstable nature of the fracture-fragment interface, which can result in changes in bone density and biomaterial stiffness as time passes.5,6,35,54 Failure to recognize the heterogeneous nature of these nonunions can result in incorrect treatment or limit any chances for successful bone mending.

We reviewed selected literature pertinent to fracture healing, the natural history of scaphoid fractures, original techniques in the history of scaphoid nonunion repair, and recent trends in the treatment of scaphoid fracture non-unions. Although the scientific level of evidence of the papers reviewed is mixed, each referenced study imparts a unique element to the treatment of scaphoid fractures and nonunions. We also present new approaches to scaphoid fixation and arthroscopic and percutaneous techniques that can be used in addition to or in place of traditional formal open exposures for these challenging fracture nonunions. We sought to identify the causes for failed healing, to categorize scaphoid nonunions by their potential for restoration, and to propose minimally invasive strategies that assist in nonunion evaluation and repair.

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Scaphoid Fracture Healing: Understanding the Problem

Scaphoid fractures are inherently unstable. The scaphoid is subjected to complex rotatory and bending forces throughout the wide range of wrist motion. This bone acts as a long lever arm connecting the distal and proximal carpal row. It is restrained proximally by the stiff scapholunate ligament and distally by stout volar ligamentous and capsular attachments. In cadaveric wrists with scaphoid waist osteotomies, interfragmentary flexion averaged 36° with wrist flexion and 22° with wrist extension.54 Although rotation, compression, or distraction did occur, the primary forces acting on the distal scaphoid were bending forces resulting in a displaced scaphoid fracture in a flexed and pronated position.54 If left untreated, such displacement results in a flexed and pronated humpback deformity of the scaphoid (Fig 1).5,6,35,45,54 Scaphoid healing is influenced by fracture biology and mechanical stimulation. The scaphoid heals by primary bone healing as the surface of scaphoid is composed almost entirely of cartilage with minimal soft tissue attachments. Without periosteum and subsequent periosteal reaction, this intra-articular bone must rely on cutting cones to bridge the fracture gap and strengthen by bone remodeling. As a consequence of its inability to make stabilizing peripheral fracture callus, early scaphoid unions are structurally weaker. Without callus to resist bending and shear forces at the fracture site, micromotion occurs and disrupts the healing process. Prolonged periods of protection for up to 4 months or structural augmentation (ie, internal fixation) are required before normal wrist loading can be resumed.61

Fig 1

Fig 1

The vascular supply to the scaphoid also plays a critical role in its fracture healing. Apart from radial artery's small dorsal scaphoid branch, the blood supply to the proximal pole enters endosteally from the distal pole and is disrupted by waist and proximal pole fractures.30 Despite the retrograde perfusion, an ischemic acute proximal pole fracture will heal. With rigid fixation an avascular proximal pole can revitalize from vascular ingrowth provided by the well-perfused distal scaphoid.

Ultimately, scaphoid fracture healing only occurs if there is adequate blood supply, local hormonal bone stimulants and modulators, and continuous viable bone contact of rigidly secured bone fragments.12 Scaphoid nonunion or delayed healing that occurs after acute fracture treatment, is a direct result of a compromise in establishing these contingencies for primary bone healing. The mechanical effectiveness of internal fixation for any fracture is determined by five independent variables: bone quality, fragment geometry, reduction, choice of implant, and implant placement.36 At the time of definitive treatment, a surgeon only can control fracture reduction, choice of implant, and implant placement. Careful preoperative planning, anatomic reduction, fracture-specific hardware selection, and accurate implant placement are necessary. The goals of scaphoid fixation must reflect an awareness of the forces acting on the proximal and distal scaphoid fracture fragments.

The primary tools to establish scaphoid fracture stability are intramedullary implants that can resist the bending and shear. Bone graft, Kirschner wires (K wires) and compression screws continue to be the mainstays for scaphoid fixation. Cancellous bone graft, a biomaterial rich in viable osteoblasts and local hormonal osteogenic stimulants, affords only limited structural strength in a fixation construct.37 Although cortical bone graft can be used in a structural fashion, we think a tricortical piece of iliac crest remodels slowly and reluctantly. Regardless of choice of grafting material, additional rigid fixation should supplement the construct. Despite the current popularity of headless cannulated compression screws, healing has been shown in selected nonunions using multiple K wires alone.20 Although multiple stacked K wires may resist bending forces and incite bony bleeding sufficiently, they do not compress the fracture site and have been shown to have ⅓ the strength of a compression screw.13

Scaphoid screws also have been tested extensively in simulated cadaveric fracture models regarding compression and pullout strength.7,26,42,63 These compression testing models have not addressed the forces that lead to fracture displacement including bending and shear. In bio-mechanical research that includes bending forces, Herbert-Whipple and Acutrak screws have withstood twice as many loading cycles (compared with standard Herbert screws) before fracture displacement.59 The advantage of a cannulated, headless implant includes ease of placement over a guide wire with no prominence at the articular surface.

After an implant has been selected for fracture repair, one must consider the optimal implant position. Clinically, centrally placed screws have lead to shorter healing times.1,44,60 Centrally placed scaphoid screws have been shown to improve construct stiffness compared with eccentrically placed scaphoid screws in biomechanical research.40 In addition to screw position, screw length has been shown to enhance biomechanical rigidity.24 Longer screws distribute forces along their shafts, resulting in an increased ability to resist displacement from shear forces.24 From these biomechanical studies, it can be concluded that long, centrally placed screws optimize stability at the fracture site.

Augmentation of the central screw fixation construct with an additional implant increases stability.24 This can be accomplished by stiffening the fixation with a parallel K wire or even a second scaphoid screw (Fig 2). An alternative strategy is to reduce the forces applied to the scaphoid's long lever arm with a tie rod effect, which can be accomplished by shifting the forces applied to the distal scaphoid pole away from the fracture site to another carpal bone. For instance, a K wire or a second implant can be placed from the distal scaphoid pole fracture fragment into the capitate. This type of construct reduces bending forces that usually would be transmitted to the fracture site (Fig 3).24 Another stability augmenting configuration includes pinning the lunate to the capitate: blocking midcarpal motion. This type of temporary fixation reduces the moment arm forces exerted on the distal scaphoid pole and reduces shear at the scaphoid healing site. Intercarpal fixation constructs that lock the midcarpal joint remain until bone healing has occurred.

Fig 2

Fig 2

Fig 3A

Fig 3A

Although these strategies increase the stability of scaphoid waist fractures, they do not apply to fractures of the extreme proximal pole. Obtaining stable fracture fixation of these fractures is challenging because very proximal fractures of the scaphoid are subjected to extreme forces of a very long lever arm. Only a few screw threads compress the proximal fragment; the forces transmitted through these threads required to maintain stable fixation are substantial. A solution to this difficult situation include locking the midcarpal joint as previously described to decrease the strain on these few screw threads and diminish bending at the fracture site. Another helpful construct previously not reported involves compressing the proximal pole between the distal scaphoid and the lunate with a temporary compression screw (Fig 4).

Fig 4

Fig 4

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The Healing of Nonunions: Other Factors

The challenges to scaphoid healing are compounded by the dynamic nature of nonunions, which reduce their healing potential as time passes.47 For example, if a proximal scaphoid fragment fails to unite, vascular perforators gradually recede from the fracture site. With increased cell death and micromotion the bone matrix is absorbed and replaced by avascular bone cysts. This results in a widening avascular zone at the fracture site. When shear is present, fibrous tissue becomes dominant in this anoxic zone.17 Healing declines markedly with increased gapping, fragment separation from the original fracture site, gradual cyst formation, and bone loss.2,16,17 The focus of successful bone union must prioritize the fracture site, not just the proximal pole ischemia. Three problems must be solved: (1) the reestablishment of local perfusion; (2) the replacement of necrotic tissue with an osteoconductive and osteoinductive matrix; and (3) the rigid fixation of the healing bones. Rigid fixation is critical because it provides continuous bone contact and, by preventing shear at the healing site, allows vascular ingrowth and penetrating cutting cones.

The reduction of scaphoid bone density as fracture site resorption occurs leads to in increased difficulty in obtaining rigid fixation. Bones are dynamic physiologic structures and nonunions will continue to deteriorate unless an appropriate intervention is crafted. One dynamic concern is the exposure of the bone-healing front to joint fluid. Synovial fluid washes across this surface as the fracture site is subjected to repetitive micromotion. This fluid dilutes local osteogenic stimulants, encourages a fibrous tissue response at the fracture site, and ultimately reduces the potential for bone union.

Proximal pole ischemia after injury is another difficult problem. Ischemia can be transient (Type 1) or permanent (Type 2) and result in cell death and avascular necrosis (AVN).11 Although perfusion is critical to healing, the presence of an ischemic proximal pole does not always result in nonunion. Healing has been documented in cases of early bone ischemia11,21 and rigidly fixed allografts.14 Early in AVN, an ischemic scaphoid fracture fragment will revascularize and heal if interfaced and rigidly secured to a well-perfused bone. Perfusion can be reestablished in these early nonunions by reaming the distal bone fragment until viable bone is breached and bleeding initiated. With large zones of necrosis (> 1 mm) it is not enough to simply reestablish perfusion. The necrotic tissue must be excised and replaced with an active bone matrix. The scaphoid can be reamed through its proximal pole, debrided, implanted with bone graft, and fixed rigidly.

If vascular perfusion cannot be re-established by bone reaming, then a new blood supply must be established. This is done by the transplantation of a vascularized bone graft directly to the nonunion site. Experimentally, this has been shown to rapidly heal bone.58 Clinically, it has resulted in a high rate of union.49,56,64 The transfer of a vascular pedicle bone graft decreases the distance and time required for revitalization of ischemic bone. However, the transfer of a vascular pedicle bone graft alone does not guarantee healing of a scaphoid nonunion, and at best provides only two of the three requirements for bone healing (perfusion and viable bone), not rigid fixation.57

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Scaphoid Fracture and Nonunion Evaluation

Scaphoid nonunions are not easy to categorize. They have been described by their anatomic location or with clinically specific terms such as stable, fibrous, sclerotic, unstable, humpback, synovial, cystic, pseudarthrosis, or avascular.33,47 These descriptions frequently dictate specific treatment strategies. In an effort to match the healing potential of a nonunion to a specific treatment algorithm, we propose a revised classification of scaphoid nonunions. Our new classification focuses on the width of the devitalized scaphoid zone and circumstances that complicate the healing process when additional structural or biologic enhancements are needed. Our grading system reflects the natural degradation that occurs at a scaphoid nonunion site with time and the difficulties these changes pose to healing. Scaphoid nonunions can be divided roughly into two groups: early nonunions without substantial bone resorption, and older nonunions with substantial bone resorption. Complicating efforts to treat these nonunions are perfusion, deformity, and instability (bony or ligamentous). The treatment algorithm assumes there is no (or minimal) arthrosis. Wrists with substantial degenerative changes of a scaphoid nonunion advance collapse (SNAC) are treated with a salvage reconstruction based on the degree of joint involvement. This adapted algorithm relies on radio-graphs, computed tomography (CT) scans, magnetic resonance imaging (MRI), and arthroscopy for grading and treatment tactics (Table 1).53

TABLE 1

TABLE 1

Preoperatively, we use CT scans with 1-mm slices to observe bony anatomy and MRI to help evaluate proximal pole vascularity.15,62 Additional information is gathered in the operation theater using minifluoroscopy and wrist arthroscopy. Green reported the direct examination of the scaphoid for punctate bleeding predicted healing.31 It is our preference to inspect the cancellous bone of the proximal pole arthroscopically after percutaneously reaming the proximal fragment, placing a 1.9-mm small joint arthroscope into the base of the scaphoid and deflating the tourniquet. A viable proximal pole fragment is confirmed if there is punctate bleeding from the cancellous bone exposed by the reamer (Fig 5). At the same time, small-joint wrist arthroscopy can provide a direct view of the articular surfaces and intrinsic ligaments to rule out associated arthritis or injury. A compilation of these sensitive tools are used to grade and classify scaphoid nonunions and to plan definitive care.

Fig 5

Fig 5

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Scaphoid Nonunion Repair

Scaphoid Nonunions without Substantial Bone Loss: Grades I-III

Scaphoid nonunions without substantial bone loss require only rigid fixation to heal if there is adequate perfusion.50 These include fractures with delayed presentation, fibrous unions, and minimal sclerosis (< 1 mm). Stable scaphoid fractures presenting for treatment after 1 month have already developed bone resorption at the fracture site from shearing. Early bony resorption typically is not detected by standard radiographs. These Grade I injuries have a poorer union rate with immobilization than those presenting earlier.38 They require reduction and rigid fixation without bone grafting for successful but often slower healing.38

Fibrous unions (Grade II) appear solidly healed, but insufficient bone remodeling has occurred to resist the stresses of bending and torque. Barton3 studied a group of fibrous unions treated with immobilization and determined there was solid union between the fracture fragments, but at followup only ½ went on to full healing based on physical examination and radiographs. Fibrous unions stabilized with a compression screw and without a bone graft typically heal.48 Therefore, fibrous unions require only rigid fixation to prevent micromotion to permit bone healing to continue.

Early scaphoid nonunions have only minimal bone resorption of the anterior cortical bone, and there is still potential for healing these early stages (Grade III). Correctly aligned scaphoid nonunions with minimal fracture sclerosis (< 1 mm confirmed by CT scan) also require only rigid fixation for osteogenesis to resume. Multiple stacked K wires along the central scaphoid axis stiffen the scaphoid to resist bending forces of displacement at the fracture site allowing healing in nearly 80% of nonunions.20 Several authors have treated aligned nonunions successfully without bone loss using screw fixation alone.10,29,39,48 A Matti-Russe graft or a screw alone achieve similar outcomes regardless of nonunion subtype.43 The senior author (JS) previously has had success by percutaneously reducing and internally fixing scaphoid fractures and selected fibrous nonunions.50-53 All 15 patients in one case series healed at an average of 14 weeks and showed bridging cortical bone on CT scans.50

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Correctly Aligned and Perfused Scaphoid Nonunions with Substantial Bone Loss: Grades IV-VI

If the scaphoid nonunion fragment is well perfused but there is substantial bone loss (2-10 mm) without substantial flexion deformity (Grades IV and V), then bone grafting is essential to achieving union. Although fracture healing may occur with a minimal gap (1-2 mm), the likelihood of bridging greater distances is marginal and may require bone grafting.2,16 If these nonunions go through anatomic reduction, rigid internal fixation, and bone grafting they will heal by vascular penetration from a viable bone fragment into bone graft, creeping substitution with cutting cones, and bridging bone trabeculae. Computed tomography scans provide critical architectural information on the scaphoid alignment, and size and position of bone cysts to be grafted. Magnetic resonance imaging determines fragment vascularity and the width of the zone of necrosis that must be penetrated to permit perfusion of the healing site. Arthroscopic examination of the joint confirms the presence of fibrous scar tissue at the scaphoid nonunion site. Peripheral fibrocartilaginous scar tissue permits the percutaneous implantation of bone graft into a centrally reamed scaphoid without loss the graft material from the nonunion site into the radiocarpal joint. This fibrous tissue acts as a net and screw implantation impacts and compresses percutaneously placed bone graft at the nonunion site.

In our experience, a waist or proximal pole nonunion with no peripheral fibrocartilaginous scar tissue proceeds to synovial pseudarthrosis (Grade VI). These nonunions are unable to prevent joint fluid from diluting essential local osteogenic factors, and they are unable buttress percutaneously inserted cancellous bone graft. These scaphoid nonunions require open débridement, interpositional corticocancellous bone graft that provides structural support, viable bone matrix, and rigid fixation.25,27 Such non-unions may also candidates for vascularized bone graft assuming rigid fixation can also be accomplished.

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Special Circumstances for Scaphoid Nonunion: Avascular Necrosis, Proximal Pole Fractures, and Deformity

Scaphoid nonunions with substantial deformity require open débridement, correction of the deformity, and rigid fixation. The technique for volar correction of a typical humpback deformity includes an open approach, harvesting and fashioning a tricortical iliac crest bone graft for volar interposition, and rigid fixation.27 This type of volar-wedge bone grafting typically requires 6 months to heal and may result in reduced wrist function.19 In avascular cases volar-wedge grafting with autologous iliac crest has been documented to have poor results.34 But, radical débridement of long-standing necrotic bone and cancellous bone grafting of the entire proximal pole shell followed by structural wedge graft has been reported to heal avascular cases.46 Despite the débridement necessary for the placement of a Matti-Russe-type bone graft, this treatment has been associated with poor results in the presence of an avascular proximal pole.31,55 Many authors advocate vascularized bone graft to provide a blood supply and increased healing potential to the proximal pole fracture fragment, which often becomes avascular as the nonunion progresses.9,28,41 Although the benefit of vascularized bone grafting is improved perfusion, the downside is the surgical dissection, including exposure of the bone graft and vascular supply, a generous capsulotomy, open scaphoid nonunion débridement, and vascularized bone graft insertion with inadequate internal stabilization.32,57

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Arthroscopic and Percutaneous Techniques

Not all proximal pole scaphoid nonunions with AVN require vascularized bone graft! If the distal scaphoid is well perfused and the proximal pole can be secured rigidly after bone grafting, then healing can proceed. Percutaneous techniques permit fracture-site débridement, establishment of distal perfusion by central axis reaming, percutaneous bone grafting, and rigid fixation. Critical steps in treating scaphoid nonunions using minimally-invasive techniques include establishment of vascular channels, alignment of scaphoid fracture fragments, débridement of devitalized tissue from the healing front, preservation of peripheral fibrocartilaginous tissue surrounding the nonunion site, percutaneous implantation cancellous bone graft, and augmented rigid fixation (Fig 6).

Fig 6

Fig 6

The required surgical equipment includes a headless cannulated compression screw, a fluoroscopy unit (preferably a mini-imaging unit), 0.045-inch and 0.062-inch double-cut K wires; a wire driver, and a small joint arthroscopy setup including a traction tower. We prefer screws of standard size with their larger core shaft because of their increased ability to resist bending forces.

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Step 1 - Imaging

A minifluoroscopy imaging unit is placed in a horizontal position so the imaging beam is perpendicular to the wrist. A fluoroscopic survey of the nonunion is performed to evaluate the scaphoid alignment, fragment mobility, and the presence of cysts including location, size, and number. The central axis of the scaphoid is located after completion of the survey. This is accomplished by obtaining a posteroanterior (PA) view of the scaphoid. The wrist is pronated and flexed until the scaphoid poles are aligned in the radiographic beam. The scaphoid assumes a ring shape and the center of the circle is the central axis of the scaphoid. This position is critical because in a reduced scaphoid it is the longest straight path in the scaphoid bone. The percutaneous placement of a central axis guide wire along this trajectory permits a multitude of tasks to be accomplished through minimal incisions.

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Step 2 - Dorsal Guide Wire Placement in an Aligned Scaphoid Nonunion

A guide wire is placed along the scaphoid central axis which can be done using a percutaneous technique and fluoroscopy (Fig 3).50,52 First, the tip of the guide wire is inserted percutaneously into the proximal pole of the scaphoid. The wrist is maintained in a flexed position to avoid bending the guide wire, and its position is periodically checked using fluoroscopy. The leading edge of the wire exits the volar radial base of the thumb at the trapezium, which is a safe zone. The wrist is extended once the trailing end of the wire clears the radiocarpal joint. Imaging is used to confirm scaphoid alignment and the correct positioning of the guide wire.

If preoperative CT or MRI scans, arthroscopy, or intraoperative imaging detect fragment malalignment, reduction can be accomplished in some nonunions without major disruption to any partial healing. A small curved hemostat can be introduced percutaneously under fluoroscopic control into the nonunion site and an osteoclasis can be performed. This maneuver requires withdrawing the central axis guide wire across the nonunion site and percutaneously placing stout wires into the bone fragments to use as joysticks. If the lunate is rotated dorsally with respect to the longitudinal axis of the radius, it can be reduced in a similar manner with a joystick and provisionally fixed to the distal radius with an additional K wire. After alignment of the nonunion fragments is achieved, the longitudinal central wire again is driven distally to capture and hold the reduction. If a substantial correction is required then the central axis of the scaphoid has changed. This circumstance requires the placement of a second longitudinal scaphoid wire that will now be the true central axis wire. The first wire can remain as an antirotation wire during reaming, débridement, bone grafting, and screw implantation.

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Step 3 - Arthroscopy and Soft Tissue Injuries

After fluoroscopy confirms the scaphoid fragments are aligned anatomically and the guide wire is in the correct position along the scaphoid central axis, longitudinal traction is applied for safe entry of the small joint arthroscope and instruments. The midcarpal and radiocarpal portals are located using minifluoroscopy, and 19-gauge needles mark these portal sites. An angled, small-joint arthroscope is placed in the radiocarpal and midcarpal joints. It is used to inspect the scaphoid nonunion site for peripheral fibrocartilaginous tissue and the absence of carpal joint arthritis. Intraarticular scaphoid alignment is confirmed and the joint is inspected for associated soft tissue or bony injuries.

The carpal joints of long-standing nonunions often have capsular adhesion and arthrofibrosis. These conditions must be treated before nonunion repair. Untreated wrist stiffness can lead to increased bending forces at the repair site. Small adhesions can be disrupted percutaneously by inserting a small, curved hemostat into the radiocarpal joint. This lysis of adhesions is followed with an arthroscopic shaver or radiofrequency wand to achieve a thorough capsular release. Finally, a 1.9-mm angled scope can be placed into the proximal scaphoid pole after reaming and imaging can confirm the position of the small joint scope within the scaphoid. The arm tourniquet can be deflated, and the proximal pole fragment can be assessed for viability by direct visualization of the amount and location of active bone bleeding (Fig 5). Débridement of nonviable bone is guided by the arthroscopic observation of the location of viable bone that is present.

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Step 4 - Scaphoid Length, Reaming, and Perfusion

The scaphoid length is determined after scaphoid fracture reduction and guide wire position are confirmed. The scaphoid central axis guide wire is adjusted until the distal end is in contact with the distal cortex. A second identical wire is placed parallel to the first wire so that the tip touches the cortex of the proximal pole. The difference in length is the exact length of the scaphoid along its central axis. A preventable complication of percutaneous screw implantation is the selection of a screw that is too short or too long.8 A screw 4 mm shorter than the scaphoid length provides 2-mm clearance between the screw end and scaphoid cortex, proximally and distally. A standard screw most commonly is used for implantation because the widest screws provide the strongest fixation and are best suited to resist bending and shear.59

In Grades I, II, and III scaphoid nonunions, healing can be achieved with standard reaming followed by screw implantation, compressing the aligned scaphoid fragments. With the wrist flexed, blunt dissection along the guide wire exposes a tract to the dorsal wrist capsule and scaphoid base. Before reaming, the guide wire is adjusted so both ends are exposed equally. This is done so the wire will not become dislodged during reaming. A path is reamed ≥ 2 mm to the opposite scaphoid cortex with a cannulated hand reamer. This will provides fresh perfusion to the nonunion site and prepares the scaphoid for screw implantation. It is critical to use fluoroscopy to confirm the position and depth of the reamer. Overreaming the scaphoid reduces fracture compression and increases the risk of motion at the nonunion site. The scaphoid never should be reamed up to the opposite cortex.

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Step 5 - Nonunion Débridement and Percutaneous Bone Grafting

In Grades IV to VI scaphoid nonunions, it is not enough to ream the distal scaphoid to a level of viable bone and to implant a headless compression screw because there is a large zone of devitalized bone. These nonunions require débridement, bone grafting, and complex rigid fixation, all of which can be performed with a minimally-invasive approach. Before percutaneous scaphoid nonunion débridement, an antirotation wire is placed parallel to the central axis wire along the scaphoid longitudinal axis before reaming. This dorsally placed antirotation wire is adjusted so the trailing end rests within the proximal scaphoid pole. It anchors the distal fragment during scaphoid reaming, bone grafting, and screw fixation. It also offers an opportunity to place a second parallel screw if that fixation strategy is used.

Using fluoroscopic imaging, the wrist is maintained in a flexed position, the central axis wire is adjusted so its ends are exposed from the dorsal and volar wrist, and the scaphoid is hand reamed using a cannulated reamer starting at the proximal pole. Next, the central axis wire is withdrawn volarly past the scaphoid nonunion site. A small curette is placed through the scaphoid proximal pole to the nonunion site using the scaphoid reamer portal. This narrow curette is used to debride centrally devitalized tissue from the nonunion site reaching distally into the distal scaphoid pole until viable bone is penetrated (Fig 7). It is important not to disturb the peripheral fibrocartilaginous tissue because it serves as a barrier to joint fluid when new bleeding is established. It also acts as a buttress for cancellous bone placed through the scaphoid proximal pole to the vacant nonunion site. The progress of débridement is monitored using fluoroscopy. After completion the wrist is flexed, and central axis wire is advanced proximal until it exits the dorsal skin through the previously established scaphoid portal.

Fig 7

Fig 7

An 8-gauge bone biopsy cannula is placed over the central wire and is advanced until firmly seated on the scaphoid proximal pole. The central axis wire is withdrawn volarly into the distal scaphoid, and the second parallel antirotation wire maintains the scaphoid reduction. Cancellous bone (Fig 8) is then introduced into the trailing end of the biopsy cannula, and the cannula's central trocar is used to advance the bone into the nonunion site (Figs 9, 10). Fluoroscopic imaging is used to monitor this process. The radiolucent zone of the nonunion soon becomes radio-opaque (Fig 11). Bone is careful packed with increasing firmness into nonunion site and proximal pole. Once the grafting is complete, the central axis wire is advanced proximally and dorsally through the bone and into the bone grafting cannula. The cannula is removed, the hand drill is replaced, and gentle reaming is performed. This tends to advance the bone graft distally into the nonunion site. Once the bone grafting has been accomplished, the nonunion repair is completed with rigid fixation.

Fig 8

Fig 8

Fig 9

Fig 9

Fig 10

Fig 10

Fig 11A

Fig 11A

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Step 6 - Rigid Fixation of Scaphoid Nonunion

Rigid fixation requires understanding the forces that displace the scaphoid. Although a series of complex forces act at the fracture site, the most important forces are bending and shear forces that result in micromotion at the healing front. To resist these forces, modern methods require the implantation of the longest and widest headless compression screw. This fixation works well for central fractures. Proximal pole fractures tend to shift the fulcrum, and the neutralizing forces required at this site are increased by the long lever arm. Stiffness decreases at the nonunion site over time, and the implantation of cancellous bone graft reduces any chance for rigid fixation using a traditional headless compression screw alone. If instability is noted on fluoroscopic stress views, then addition forms of fixation need to be considered.

For instance, the axial loading and bending forces to the scaphoid can shifted to the capitate by a stout K wire or a screw from the distal scaphoid to the capitate (Fig 3). This configuration locks the midcarpal but not the radiocarpal joint and is usually our first choice in augmenting scaphoid fracture fragment stability.24 A stout K wire inserted between the II or III web space into the capitate and lunate also blocks midcarpal motion and provides enhanced stability at the scaphoid healing site. Another construct includes the compression of the proximal pole, usually ischemic between the distal scaphoid and lunate after percutaneous bone graft, using a headless compression screw (Fig 4). This temporarily crosses the scapholunate joint, but violation of the joint is more desirable than a SNAC wrist reconstruction. These additional implants are removed percutaneously once bridging bone is observed on CT scans. Any residual joint stiffness can be treated effectively with an arthroscopic release as described earlier.

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Postoperative Treatment and Scaphoid Nonunion Healing

Immediate postoperative care includes a bulky compressive hand dressing and splint. Early finger exercises are encouraged to reduce swelling. We immobilize scaphoid nonunions with a short-arm cast or splint the wrist for 4 weeks but encourage functional exercises and strengthening. Avascular nonunions and small proximal pole fragments are protected for 6 to 8 weeks in a short-arm cast until CT scans show bridging bone. Scaphoid healing will proceed for these nonunions, but at a slower rate than fresh fractures, especially when avascular bone must be revitalized.

Thereafter, a therapist makes a removable volar splint that holds the wrist and hand in a functional position. All patients then are started on an active strengthening program that axially loads the fracture site (secured with an intramedullary screw) to stimulate healing. Postoperative radiographs are obtained at the first postoperative visit and then at 6-week intervals. Our protocol includes at 6-week serial CT scans of the scaphoid with 1-mm slices and coronal and sagittal reformatting to evaluate the progress of fracture healing. This is repeated every 6 to 8 weeks until final union. If healing stalls, repeat percutaneous bone grafting should be considered. With cannulated implants, the percutaneous process is straightforward and requires minimal operative time. It is not necessary to wait many months to confirm a lack of bridging bone clearly observed on reformatted CT scan images perpendicular to the fracture site. Prolonged waiting only increases an unfavorable result. Patients often do not have pain before evidence of bridging cortical bone on three-dimensional imaging. Therefore, clinical symptoms alone are not always a reliable guide to healing. Contact sports and heavy labor are restricted until bridging cortical bone is confirmed by CT scan.

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DISCUSSION

The impact of a formal open exposure on the treatment of scaphoid nonunions is unclear. The senior author has developed a percutaneous approach for the treatment of scaphoid nonunions with minimal bone resorption by rigid fixation these nonunions without bone grafting.50 Minimally invasive approaches to more advanced nonunions as described in this review also have been clinically successful. We think a minimally invasive approach to scaphoid nonunions using wrist arthroscopy and percutaneous non-union débridement, bone grafting, and internal fixation has the potential to minimize postoperative stiffness and maximize functional outcome. Current techniques such as cortical iliac crest wedge grafts or vascularized bone grafts necessitate formal open approaches with dissection of wrist capsule and ligaments. Although a comparative study has not been done, it seems intuitive that the dissection required to place these grafts would lead to greater postoperative morbidity than small percutaneous stab incisions. As surgeons develop new minimally invasive techniques, it is still essential not to forget the basic science concepts and key principles in the treatment of scaphoid nonunions.

Scaphoid nonunions present a difficult clinical challenge for even the most experienced wrist surgeons. The treatment for scaphoid nonunions varies, but maintaining blood supply, nonunion débridement, fracture reduction, bone grafting, and rigid internal stabilization are critical requirements.18,41 Although vascularized bone grafting for avascular scaphoid nonunions may provide a solution for this very difficult orthopaedic problem, understanding the biomechanical forces within the carpus and applying rigid internal fixation to counteract bending forces and shear will optimize the environment for that vascularized graft to succeed. Minimally invasive techniques can be used to satisfy the critical requirements for healing a scaphoid nonunions as long as those requirements are not compromised.

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References

1. Adams BD, Blair WF, Reagan DS, Grundberg AB. Technical factors related to Herbert screw fixation. J Hand Surg. 1988;13:893-899.
2. Augat P, Margevicius K, Simon J, Wolf S, Suger G, Claes L. Local tissue properties in bone healing: influence of size and stability of the osteotomy gap. J Orthop Res. 1998;16:475-481.
3. Barton NJ. Apparent and partial nonunion of the scaphoid. J Hand Surg [Br]. 1996;21:496-500.
4. Barton NJ. Experience with scaphoid grafting. J Hand Surg [Br]. 1997;22:153-160.
5. Barton NJ. Natural history of scaphoid nonunion. J Hand Surg [Br]. 1993;18:545.
6. Barton NJ. Twenty questions about scaphoid fractures. J Hand Surg [Br]. 1992;17:289-310.
7. Beadel GP, Ferreira L, Johnson JA, King GJ. Interfragmentary compression across a simulated scaphoid fracture-analysis of 3 screws. J Hand Surg. 2004;29:273-278.
8. Bond CD, Shin AY, McBride MT, Dao KD. Percutaneous screw fixation or cast immobilization for nondisplaced scaphoid fractures. J Bone Joint Surg. 2001;83:483-488.
9. Boyer MI, von Schroeder HP, Axelrod TS. Scaphoid nonunion with avascular necrosis of the proximal pole. Treatment with a vascularized bone graft from the dorsum of the distal radius. J Hand Surg [Br]. 1998;23:686-690.
10. Brostrom LA, Stark A, Svartengren G. Nonunion of the scaphoid treated with styloidectomy and compression screw fixation. Scand J Plast Reconstr Surg. 1986;20:289-291.
11. Buchler U, Nagy L. The issue of vascularity in fractures and non-union of the scaphoid. J Hand Surg [Br]. 1995;20:726-735.
12. Buckwalter JA, Einhorn TA, Simon SR, eds. Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System. 2nd ed. Rosemont, IL: American Academy of Orthopaedic Surgeons, 2000.
13. Carter FM II, Zimmerman MC, DiPaola DM, Mackessy RP, Parsons JR. Biomechanical comparison of fixation devices in experimental scaphoid osteotomies. J Hand Surg. 1991;16:907-912.
14. Carter PR, Malinin TI, Abbey PA, Sommerkamp TG. The scaphoid allograft: a new operation for treatment of the very proximal scaphoid nonunion or for the necrotic, fragmented scaphoid proximal pole. J Hand Surg. 1989;14:1-12.
15. Cerezal L, Abascal F, Canga A, Garcia-Valtuille R, Bustamante M, del Pinal F. Usefulness of gadolinium-enhanced MR imaging in the evaluation of the vascularity of scaphoid nonunions. AJR Am J Roentgenol. 2000;174:141-149.
16. Claes L, Eckert-Hubner K, Augat P. The fracture gap size influences the local vascularization and tissue differentiation in callus healing. Langenbecks Arch Surg. 2003;388:316-322.
17. Claes LE, Heigele CA, Neidlinger-Wilke C, Kaspar D, Seidl W, Margevicius KJ, Augat P. Effects of mechanical factors on the fracture healing process. Clin Orthop Relat Res. 1998;355 (Suppl): S132-S147.
18. Cooney WP III, Dobyns JH, Linscheid RL. Nonunion of the scaphoid: analysis of the results from bone grafting. J Hand Surg. 1980;5:343-354.
19. Cooney WP, Linscheid RL, Dobyns JH, Wood MB. Scaphoid non-union: role of anterior interpositional bone grafts. J Hand Surg. 1988;13:635-650.
20. Cosio MQ, Camp RA. Percutaneous pinning of symptomatic scaphoid nonunions. J Hand Surg. 1986;11:350-355.
21. Dawson JS, Martel AL, Davis TR. Scaphoid blood flow and acute fracture healing. A dynamic MRI study with enhancement with gadolinium. J Bone Joint Surg. 2001;83:809-814.
22. Dias JJ, Taylor M, Thompson J, Brenkel IJ, Gregg PJ. Radiographic signs of union of scaphoid fractures. An analysis of inter-observer agreement and reproducibility. J Bone Joint Surg. 1988;70:299-301.
    23. Dias JJ, Thompson J, Barton NJ, Gregg PJ. Suspected scaphoid fractures. The value of radiographs. J Bone Joint Surg. 1990;72: 98-101.
      24. Dodds SD, Panjabi MP,Slade JF III. Percutaneous Treatment of Scaphoid Fractures: A biomechanical assessment of screw size and screw augmentation. In: American Society for Surgery of the Hand: Residents and Fellows Conference, New York, NY, 2004.
      25. Eggli S, Fernandez DL, Beck T. Unstable scaphoid fracture non-union: a medium-term study of anterior wedge grafting procedures. J Hand Surg [Br]. 2002;27:36-41.
      26. Faran KJ, Ichioka N, Trzeciak MA, Han S, Medige J, Moy OJ. Effect of bone quality on the forces generated by compression screws. J Biomech. 1999;32:861-864.
      27. Fernandez DL. Anterior bone grafting and conventional lag screw fixation to treat scaphoid nonunions. J Hand Surg. 1990;15:140-147.
      28. Gabl M, Reinhart C, Lutz M, Bodner G, Rudisch A, Hussl H, Pechlaner S. Vascularized bone graft from the iliac crest for the treatment of nonunion of the proximal part of the scaphoid with an avascular fragment. J Bone Joint Surg. 1999;81:1414-1428.
      29. Gasser H. Delayed Union and Pseudarthrosis of the Carpal Navicular: Treatment by Compression-Screw Osteosynthesis; a Preliminary Report on Twenty Fractures. J Bone Joint Surg. 1965;47:249-266.
      30. Gelberman RH, Menon J. The vascularity of the scaphoid bone. J Hand Surg. 1980;5:508-513.
      31. Green DP. The effect of avascular necrosis on Russe bone grafting for scaphoid nonunion. J Hand Surg. 1985;10:597-605.
      32. Harpf C, Gabl M, Reinhart C, Schoeller T, Bodner G, Pechlaner S, Piza-Katzer H, Hussl H. Small free vascularized iliac crest bone grafts in reconstruction of the scaphoid bone: a retrospective study in 60 cases. Plast Reconstr Surg. 2001;108:664-674.
      33. Herbert TJ. The Fractured Scaphoid. St Louis, MO: Quality Medical Publishing, 1990.
      34. Inoue G, Kuwahata Y. Repeat screw stabilization with bone grafting after a failed Herbert screw fixation for acute scaphoid fractures and nonunions. J Hand Surg. 1997;22:413-418.
      35. Inoue G, Sakuma M. The natural history of scaphoid non-union. Radiographical and clinical analysis in 102 cases. Arch Orthop Trauma Surg. 1996;115:1-4.
      36. Kaufer H. Mechanics of the treatment of hip injuries. Clin Orthop Relat Res. 1980;146:53-61.
      37. Khan SN, Cammisa FP Jr, Sandhu HS, Diwan AD, Girardi FP, Lane JM. The biology of bone grafting. J Am Acad Orthop Surg. 2005;13:77-86.
      38. Langhoff O, Andersen JL. Consequences of late immobilization of scaphoid fractures. J Hand Surg [Br]. 1988;13:77-79.
      39. Leyshon A, Ireland J, Trickey EL. The treatment of delayed union and nonunion of the carpal scaphoid by screw fixation. J Bone Joint Surg. 1984;66:124-127.
      40. McCallister WV, Knight J, Kaliappan R, Trumble TE. Central placement of the screw in simulated fractures of the scaphoid waist: a biomechanical study. J Bone Joint Surg. 2003;85:72-77.
      41. Merrell GA, Wolfe SW, Slade JF III. Treatment of scaphoid non-unions: quantitative meta-analysis of the literature. J Hand Surg. 2002;27:685-691.
      42. Newport ML, Williams CD, Bradley WD. Mechanical strength of scaphoid fixation. J Hand Surg [Br]. 1996;21:99.
      43. Parkinson RW, Hodgkinson JP, Hargadon EJ. Symptomatic non-union of the carpal scaphoid: Matti-Russe bone grafting versus Herbert screw fixation. Injury. 1989;20:164-166.
      44. Pring DJ, Hartley EB, Williams DJ. Scaphoid osteosynthesis: early experience with the Herbert bone screw. J Hand Surg [Br]. 1987;12:46-49.
      45. Prosser GH, Isbister ES. The presentation of scaphoid non-union. Injury. 2003;34:65-67.
      46. Richards RR, Regan WD. Treatment of scaphoid nonunion by radical curettage, trapezoidal iliac crest bone graft, and internal fixation with a Herbert screw. Clin Orthop Relat Res. 1991;262:148-158.
      47. Schuind F, Haentjens P, Van Innis F, Vander Maren C, Garcia-Elias M, Sennwald G. Prognostic factors in the treatment of carpal scaphoid nonunions. J Hand Surg. 1999;24:761-776.
      48. Shah J, Jones WA. Factors affecting the outcome in 50 cases of scaphoid nonunion treated with Herbert screw fixation. J Hand Surg [Br]. 1998;23:680-685.
      49. Shin AY, Bishop AT. Pedicled vascularized bone grafts for disorders of the carpus: scaphoid nonunion and Kienbock's disease. J Am Acad Orthop Surg. 2002;10:210-216.
      50. Slade JF III, Geissler WB, Gutow AP, Merrell GA. Percutaneous internal fixation of selected scaphoid nonunions with an arthroscopically assisted dorsal approach. J Bone Joint Surg. 2003;85 (Suppl 4): 20-32.
      51. Slade JF III, Grauer JN, Mahoney JD. Arthroscopic reduction and percutaneous fixation of scaphoid fractures with a novel dorsal technique. Orthop Clin North Am. 2001;32:247-261.
      52. Slade JF III, Gutow AP, Geissler WB. Percutaneous internal fixation of scaphoid fractures via an arthroscopically assisted dorsal approach. J Bone Joint Surg. 2002;84 (Suppl 2): 21-36.
      53. Slade JF III, Merrell GA, Geissler WB. Fixation of Acute and Selected Nonunion Scaphoid Fractures. In: Geissler WB, ed. Wrist Arthroscopy. New York, NY: Springer; 2005:112-124.
      54. Smith DK, An KN, Cooney WP III, Linscheid RL, Chao EY. Effects of a scaphoid waist osteotomy on carpal kinematics. J Orthop Res. 1989;7:590-598.
      55. Stark A, Brostrom LA, Svartengren G. Scaphoid nonunion treated with the Matti-Russe technique. Long-term results. Clin Orthop Relat Res. 1987;214:175-180.
      56. Steinmann SP, Bishop AT, Berger RA. Use of the 1,2 intercom-partmental supraretinacular artery as a vascularized pedicle bone graft for difficult scaphoid nonunion. J Hand Surg. 2002;27:391-401.
      57. Straw RG, Davis TR, Dias JJ. Scaphoid nonunion: treatment with a pedicled vascularized bone graft based on the 1,2 intercompartmental supraretinacular branch of the radial artery. J Hand Surg [Br]. 2002;27:413-416.
      58. Sunagawa T, Bishop AT, Muramatsu K. Role of conventional and vascularized bone grafts in scaphoid nonunion with avascular necrosis: A canine experimental study. J Hand Surg. 2000;25:849-859.
      59. Toby EB, Butler TE, McCormack TJ, Jayaraman G. A comparison of fixation screws for the scaphoid during application of cyclical bending loads. J Bone Joint Surg. 1997;79:1190-1197.
      60. Trumble TE, Clarke T, Kreder HJ. Nonunion of the scaphoid. Treatment with cannulated screws compared with treatment with Herbert screws. J Bone Joint Surg. 1996;78:1829-1837.
      61. Trumble TE, Gilbert M, Murray LW, Smith J, Rafijah G, McCallister WV. Displaced scaphoid fractures treated with open reduction and internal fixation with a cannulated screw. J Bone Joint Surg. 2000;82:633-641.
      62. Trumble TE. Avascular necrosis after scaphoid fracture: a correlation of magnetic resonance imaging and histology. J Hand Surg. 1990;15:557-564.
      63. Wheeler DL, McLoughlin SW. Biomechanical assessment of compression screws. Clin Orthop Relat Res. 1998;350:237-245.
      64. Zaidemberg C, Siebert JW, Angrigiani C. A new vascularized bone graft for scaphoid nonunion. J Hand Surg. 1991;16:474-478.
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