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).
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
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
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.
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
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.
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
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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