18 Arthroscopic Bone Grafting in Scaphoid Nonunion and Delayed Union
Problematic nonunion of the scaphoid continues to present a unique clinical challenge to hand surgeons. Natural history studies by Mack et al,1 Ruby et al,2 and Lindström and Nyström3 noted that radiographic signs of wrist arthritis occurred in almost 100% of the symptomatic patients between 5 to 20 years after the onset of the scaphoid nonunion. Anatomical restoration of a stable scaphoid architecture and its linkage to the surrounding carpal and forearm bones should be the goal of treatment before arthritis sets in.
▪ Conventional Bone Grafting
Various techniques have been described for the treatment of a scaphoid nonunion. Nagle4 has summarized the essence of the surgical principles: correction of scaphoid malalignment; debridement of necrotic bone and scar tissue; exposure of healthy, well-vascularized cancellous scaphoid bone (if available); bone grafting (either cancellous or corticocancellous); and stabilization of the scaphoid with internal fixation or an intrinsically stable corticocancellous bone graft. Conventional techniques utilize either corticocancellous5 or cancellous bone graft such as the inlay grafting by Russe6 for scaphoid nonunion. In the last decade, various techniques for vascularized bone grafting have also been introduced, mainly as a salvage procedure for the failed surgical treatment of a scaphoid nonunion. These grafts were designed based on a variety of vascular pedicles found within the pronator quadratus,7 second metacarpal bone,8 and dorsal distal radius.9 Although the literature has reported variable but somewhat favorable results with open bone grafting procedures, with union rates ranging from 55 to 95%,10 – 12 potential problems do exist. In 2004, Munk and Larsen13 conducted a systematic review of bone grafting for scaphoid nonunion in 147 publications, from 1928 to 2003. The outcomes of 5246 scaphoid nonunions were evaluated in three treatment groups. In the first group involving nonvascularized bone grafting without internal fixation, they found a union rate of 80% after an average immobilization period of 15 weeks. In the second group involving nonvascularized bone grafting with internal fixation, the figures were 84% and 7 weeks, respectively. In the last group involving vascularized bone grafting with or without internal fixation, the figures were 91% and 10 weeks, respectively. The authors concluded that there was still a need for improvement in the treatment of scaphoid nonunion. In a recent retrospective study evaluating the outcomes and complications of the 1,2-intercompartmental supraretinacular artery pedicled vascularized bone graft in 50 scaphoid nonunions, Chang and Bishop and colleagues14 noted that only 34 scaphoid nonunions (68%) went on to union at an average of 15.6 weeks after surgery. They concluded that a successful outcome was not universal, and it depended on careful patient and fracture selection and appropriate surgical techniques.
▪ Principle of Arthroscopic Bone Grafting
An arthroscopic approach can reduce potential morbidity associated with open arthrotomy such as pain and stiffness, maximally preserve blood supply to the carpal bone for improved healing, and create minimal disturbance to the ligamentous structures. A comprehensive assessment of the wrist joint and evaluation of any concomitant intraarticular pathology and associated degenerative changes can also be performed prior to the definitive treatment of the nonunion at the same setting. The latter changes can significantly affect the logical choice of treatment for the nonunion, its prognosis, and the surgical outcome. Moreover in arthroscopic surgery, the use of a tourniquet to maintain a bloodless field is often not necessary during most of the surgical procedure. It thus renders the assessment of the vascularity of the scaphoid nonunion fragments more accurate and reliable. Thanks to the growing enthusiasm and the rapid progression of technical proficiency in fixing acute scaphoid fractures with percutaneous screw techniques over the last decade,15 – 17 similar techniques can be applied in the treatment of a scaphoid nonunion.
Since 1997, we have developed a new technique of arthroscopic bone grafting and percutaneous fixation for the treatment of missed scaphoid fractures, delayed union, as well as nonunion. It is our treatment of choice in all noncomplicated missed primary scaphoid fractures and nonunion with or without a reducible dorsal intercalated segmental instability (DISI) deformity, as well as persistent nonunion following stable internal fixation.
Contraindications to this method include a longstanding scaphoid nonunion with significant carpal collapse that cannot be adequately corrected with a closed percutaneous method. Severe scaphoid nonunion advanced collapse (SNAC) changes will likely preclude a good outcome from bone grafting. Avascular necrosis is not by itself a contraindication in our opinion, though the chance of persistent nonunion may be higher. Significant radiocarpal and midcarpal arthrofibrosis may preclude an arthroscopic approach and constitutes a relative contraindication.
Adequate preoperative imaging is a prerequisite for the successful planning of surgical treatment. The minimal requirements are radiographic imaging including a posteroanterior (PA), lateral, semipronated PA, and scaphoid view with the wrist in ulnar deviation and extension. Measurement of the scapholunate angle, intrascaphoid angle [anteroposterior (AP) and lateral], and capitolunate angle is mandatory to evaluate the presence and degree of carpal collapse. Computed tomography with or without reconstruction is important to establish the degree of scaphoid displacement and resorption at the nonunion site. When the vascularity of a scaphoid fragment is of concern, the use of magnetic resonance imaging with gadolinium contrast enhancement is effective in evaluating the blood flow of each nonunion fragment before the operation.
▪ Surgical Technique
The procedure is performed under regional or general anesthesia and fluoroscopic control. The patient is placed in the supine position while the operated hand is suspended with a wrist traction tower on a hand table. Vertical traction of 4 to 6 kg force is applied through plastic finger trap devices to the middle three fingers for joint distraction. An arm tourniquet is applied but needs not be inflated for most of the procedure. Adrenaline solution of 1:200,000 dilution injected into the portal site skin and capsule can help to reduce bleeding and hence the need or a tourniquet. Either side of the iliac crest region is draped for bone graft harvesting depending on the patient’s preference. Bone graft from the ipsilateral distal radius is not preferred because the quality of cancellous bone is usually not sufficient to fill up the typical pseudarthrosis site.
A routine arthroscopic assessment is performed through the ¾ portal and the midcarpal portals, with particular attention to the articular cartilage, the scapholunate interosseous ligament, and the scaphotrapezialtrapezoid (STT) joint. The fracture site is usually not visible from the radiocarpal portals except with very proximal fractures. The bone grafting is performed through the midcarpal joint portals in all cases because it provides the most convenient and direct approach to the nonunion site.
Bone Grafting in the Presence of Previous Internal Fixation
The arthroscope is inserted in the midcarpal ulnar (MCU) portal, whereas the midcarpal radial portal (MCR) is used for instrumentation. Two accessory portals may also be used. The triquetrohamate (TH) portal is useful for outflow and is located in the axilla between the extensor carpi ulnaris (ECU) tendon and the hamate. The STT portal is situated ∼1 cm radial and slightly distal to the MCR portal just ulnar to the extensor pollicis longus (EPL) tendon, at the junction between the scaphoid, trapezoid, and trapezium. Care should be taken in avoiding injury to the radial artery, which is radial to the EPL tendon. The nonunion site can often be identified by the presence of a cleavage line in the scaphoid articular surface or with frank disruption of the articular cartilage and fibrous tissue interposition ( Fig. 18.1 ). The stability at the nonunion site can be assessed by direction palpation with a small probe inserted in the MCR portal. Any interposed fibrous tissue is debrided with a shaver. If bridging bone is encountered, grafting may not be necessary because this may represent an ongoing healing process of the fracture. If a frank bony defect is encountered, the nonunion site is enlarged with a 2.9 to 3.5 mm burr and small angled curettes to expose the implant. Care is taken to preserve any intact cartilage or pseudocapsule over the nonunion site to avoid subsequent graft protrusion into the radiocarpal joint. The shaving and burring procedure can usually be accomplished without a tourniquet. Bleeding encountered can be controlled readily with a radio frequency coagulator. Both ends of the nonunion site are burred until healthy-looking cancellous bone with punctate bleeding can be seen ( Fig. 18.2 ). A better view of the proximal fragment can be obtained with the scope in the MCR while inserting a curette in the STT portal. The stability of the implant is then assessed visually with manipulation and, if necessary, using a C-arm image intensifier. If it is found to be unstable and loose, it can be exchanged with a larger screw or by converting to multiple pins using percutaneous techniques.
An arthroscopic cannula is introduced through the appropriate portal, which is directly opposite the bone defect ( Fig. 18.3 ). Cancellous bone graft is harvested from the iliac crest using either a trephine technique or an open approach through a small incision. The volume of the harvested bone graft has to be at least three to five times that of the defect because the graft needs to be tightly compressed into the defect to increase the strength of the graft. The bone graft is then cut into small chips and delivered through the cannula into the bone defect cavity and impacted with a slightly undersized trocar with a flat end, such as a bone biopsy trocar, until a satisfactory volume of graft is achieved ( Fig. 18.4 ). The most proximal and dorsal part of the defect first needs to be meticulously packed with graft so as to reduce subsequent void formation in this area. A small impactor can be employed intermittently to mold the graft to match the contours of the wall of the defect ( Fig. 18.5 ). Fluoroscopy is used to confirm the obliteration of the cavity as well as to ensure satisfactory scaphoid alignment. At the end of the procedure, blood clot taken from the iliac crest can be injected into the graft cavity to add an osteogenic element for better bone healing. We routinely inject 1 mL of fibrin glue onto the surface of the graft substance after suctioning any excess fluid to contain the graft in place and to prevent adherence of the graft to the capitate articular surface, which in some cases may lead to loss of motion at the midcarpal joint. The midcarpal and radiocarpal joints are then inspected to remove any excess graft and debris. The traction is then released, which allows the natural compression effect of the capitate to stabilize the graft in situ ( Figs. 18.6 and 18.7 ).