22 Percutaneous Fixation of Scaphoid Fibrous/Nonunion With and Without Percutaneous Bone Graft
Why do scaphoid fractures fail to heal? The scaphoid, like other bones, heals in stages, which include inflammation, repair, and remodeling.1 A disruption in the early stages of healing can result in delayed or failed healing. The reasons for failure of progression to heal are multifactorial. Scaphoid nonunions, a heterogeneous group, require a careful evaluation of the “causes” prior to the execution of a treatment plan ( Fig. 22.1 ).2 , 3 The scaphoid is more challenged in healing because it is covered mostly by cartilage and cannot be stabilized from external shearing forces by an external collar of fracture callus bone like other bones (“secondary” bone healing) ( Fig. 22.2 ).4 For this bone to heal, viable bone fragments with a blood supply must be held in apposition with minimal motion during the early stages of “primary bone” healing, as vascular channels with “osteoclastic-osteoblastic cutting cones” cross the fracture site. The early stages of healing can be influenced by both local and system factors that can result in failure. Nonunions require both perfusion and viable bone cells to heal; these conditions may be diminished over time. This environment must be carefully examined and if deficient reinvigorated. Other local factors at the fracture site include mechanical forces of stress and strain.5 Significant micromotion or shearing at the healing site results in fibrous tissue formation ( Fig. 22.3 ).6 All unstable scaphoid fractures and nonunions require rigid fixation to prevent micromotion. To achieve bony stability, an evaluation of the fracture for its location, its plane, and bone integrity must be made to determine the best implant and its position to achieve rigid fixation. This chapter presents an algorithm for evaluation and healing of scaphoid nonunions.
▪ Nonunion—Evaluation and Planning
Successful planning requires the use of several imaging tools, including standard radiographs, minifluoroscopy, computed tomographic (CT) or magnetic resonance imaging (MRI) scans, and arthroscopy. The injured wrist is imaged with standard radiographs and minifluoroscopy to identify fracture displacement and ligament injury. Imaging is used to identify the fracture plane and position. This may impact the location and size of the implant. Minifluoroscopy may also identify other carpal injuries or radius fractures that require treatment, which may not be appreciated using standard radiographs. Also, excessive gapping between the carpal bones is suggestive of ligament injuries and will guide the arthroscopic inspection. Scaphoid displacement can be seen either as lateral displacement visualized as a step-off on a posteroanterior (PA) view, or as flexion of the distal fragment creating a V-shaped separation or humpback deformity of the dorsal cortex on a lateral or oblique view. On the PA view this displacement appears as a foreshortened scaphoid. Preoperatively, we use CT scans with 1 mm slices to visualize the bony anatomy and MRI to help evaluate the proximal pole vascularity ( Fig. 22.4 ).7 , 8 Green reported that a direct examination of the scaphoid for punctate bleeding was a good predictor of healing.9 It is our preference to directly inspect the cancellous bone of the proximal pole arthroscopically after percutaneously reaming the proximal fragment, by 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. 22.5 ). At the same time, small-joint wrist arthroscopy can provide direct visualization of the articular surfaces and intrinsic intercarpal ligaments to rule out associated injury or arthritis.
▪ Scaphoid Nonunion Classification
Scaphoid nonunions are not easily categorized, but a fracture that has failed to unite by CT scan as defined by 100% bridging at the fracture site by 3 months can be diagnosed as either a partial union or a nonunion ( Fig. 22.6 ).10
Nonunions have been described by their anatomical location or with clinically specific terms such as stable, fibrous, sclerotic, unstable, humpback, synovial, cystic, pseudarthrosis, or avascular.2 , 11 , 12 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 the circumstances that complicate the healing process when additional structural or biological enhancements are needed ( Table 22.1 ). Our grading system reflects the natural degradation that occurs at a scaphoid nonunion site over time, and the difficulties these changes pose to healing. Scaphoid nonunions can be roughly divided into two groups: early nonunions without substantial bone resorption, and older nonunions with substantial bone resorption.
Scaphoid Nonunions without Substantial Bone Loss: Grades I–III
Grade I scaphoid nonunions without substantial bone loss require only rigid fixation to heal if there is adequate perfusion.13 These include fractures with a delayed presentation, fibrous unions, and nonunions with 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 is not typically detected by standard radiographs. These grade I injuries have a poorer union rate with immobilization than those presenting earlier.14 They can be treated with reduction and rigid fixation without bone grafting for successful though often slower healing.
Grade II fibrous unions appear solidly healed, but insufficient bone remodeling has occurred to resist the stresses of bending and torque. Barton explored 10 patients with radiological nonunion of the scaphoid and four patients with a suspected nonunion. Intraoperatively, 10 scaphoids appeared healed but only five went on to union. The other five went on to nonunion, despite Herbert screw (Zimmer Inc., Warsaw, IN) fixation in one patient. Another four patients appeared to have a partial union at surgery, and all went on to unite.15 Fibrous unions stabilized with a compression screw and without a bone graft typically heal. Shah and Jones examined 50 scaphoid nonunions treated with open Herbert screw fixation and noted that those scaphoid nonunions that had an intact cartilaginous envelope or a stable fibrous union healed with screw fixation alone, without bone grafting.3 Therefore, fibrous unions require only rigid fixation to prevent micromotion to permit bone healing to continue.
Grade III scaphoid nonunions have minimal bone resorption of the anterior cortical bone and, with minimal fracture sclerosis (<2 mm confirmed by CT scan), still have the potential for healing in the early stages. Correctly aligned scaphoid nonunions also require only rigid fixation for osteogenesis to resume. Cosio and Camp achieved union in 13/18 patients treated with two to four K-wires along the central scaphoid axis and cast immobilization.16 Several authors have successfully treated aligned nonunions without bone loss using screw fixation alone.3 , 17 – 19 The senior author (JS) has previously reported success by percutaneously reducing and internally fixing scaphoid fractures and selected fibrous nonunions.13 All 15 patients in one case series healed at an average of 14 weeks and showed bridging cortical bone on CT scans.
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 to 10 mm) without substantial flexion deformity (Grade IV), then bone grafting is essential to achieving union ( Fig. 22.7 ). Although fracture healing may occur with a minimal gap (1 to 2 mm), the likelihood of bridging greater distances is marginal; hence bone grafting is necessary.6 , 20 If these nonunions undergo anatomical reduction, rigid internal fixation, and bone grafting they will heal by vascular ingrowth from a viable bone fragment into the bone graft, followed by creeping substitution with cutting cones, and bridging bone trabeculae ( Fig. 22.2 ). CT scans provide critical architectural information on the scaphoid alignment and the size and position of bone cysts to be grafted. MRI allows one to assess the vascularity of the fragments and the width of the zone of necrosis that must be revascularized. An arthroscopic examination of the joint confirms the presence of fibrous scar tissue at the scaphoid nonunion site and early arthritis. This peripheral fibrocartilaginous scar tissue acts as a net that prevents any percutaneously placed bone graft at the nonunion site from leaking into the radiocarpal joint. Percutaneous screw implantation then impacts and compresses the bone graft ( Fig. 22.7 ).
In our experience, a waist or proximal pole nonunion with no peripheral fibrocartilaginous scar tissue proceeds to a synovial pseudarthrosis (Grade V). 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 debridement, inter-positional corticocancellous bone graft that provides structural support as well as viable bone matrix, and rigid fixation.21 , 22 Such nonunions may also be candidates for vascularized bone graft, assuming rigid fixation can also be accomplished.