28 The Use of a Vascularized Graft from the Dorsal Radius for Scaphoid Nonumion
Scaphoid proximal pole fractures, which represent ∼10 to 20% of all scaphoid fractures, present with particular challenges.1 Proximal-pole fractures have a slower rate of healing than more distal fractures.1 – 3 Moreover, the proximal pole, with its tenuous blood supply, is the part of the scaphoid that is most susceptible to avascular necrosis, which further impairs healing.2 – 4 According to a univariate risk analysis by Chang et al,5 risk factors for failure following nonvascularized grafting for scaphoid nonunion included older age, proximal pole avascular necrosis, preoperative humpback deformity of the scaphoid, techniques that did not use screw fixation, tobacco use, and female gender.
Vascularized bone grafting has recently changed the treatment of scaphoid nonunion. It can lead to a faster rate of union and improve the viability of the proximal pole. It can also provide an alternative to a salvage procedure with previously failed conventional bone grafting.6 – 11 Pedicled grafts from the dorsal and volar12 , 13 aspects of the distal radius have been described, although the dorsal pedicles are currently favored.5 , 9 – 11 , 14 – 16
Zaidemberg et al17 utilized a pedicled vascularized bone graft (VBG) source from the dorsoradial aspect of the radius and reported a 100% union rate in 11 cases of scaphoid nonunion, with an average time to union of 6.2 weeks. The benefit of this technique is the constant nature of the dorsal vascular network. The VBG derived from the dorsoradial aspect of the distal radius is nourished by the 1,2 intercompartmental supraretinacular artery (1,2-ICSRA) as described by Sheetz et al.18 Union rates of 100% using the 1,2-ICSRA pedicled VBG have been reported by several authors.9 , 10 , 19 , 20 Others, however, have reported less favorable results with the same technique.14 , 21 Recently, Chang et al5 concluded that a successful outcome with VBG based on the 1,2-ICSRA is not universal and depends on careful patient and fracture selection and appropriate surgical techniques.
Harvesting a VBG based on the 1,2-ICSRA can, on the other hand, be challenging because it involves the dissection of small vessels (the mean diameter of the 1,2-ICSRA artery is 0.3 mm), and the need for rotation of the graft on its pedicle may compromise the long-term patency18
Free VBGs such as that from the medial femoral condyle22 require a microsurgical anastomosis.
Sotereanos et al15 proposed an alternative pedicled VBG from the dorsum of the distal radius to overcome these difficulties. This novel VBG is obtained from the dorsal aspect of the distal radius (just ulnar and distal to the Lister tubercle), and it is attached to a wide distally based strip of the dorsal wrist capsule. This graft is in close proximity to the proximal pole nonunion site, thus permitting graft insertion with minimal rotation. The vascular supply is derived from the strip of dorsal capsule without the need for dissection of a pedicle. The capsular-based distal radius bone graft is based on the fourth extensor compartment artery (ECA), which runs under the dorsal retinaculum.15 , 23 The fourth ECA extends between the anterior or posterior interosseous artery proximally and the dorsal carpal (radiocarpal or intercarpal) arch or the fifth ECA distally ( Fig. 28.1 ).18 , 23 , 24 The pedicle diameter is less than 1 mm, and the length ranges between 1 and 2 cm.23 The pedicle easily reaches the proximal one third of the scaphoid by rotation of the graft on the capsular pedicle between 10 and 30 degrees Advantages of the capsular-based VBG for scaphoid nonunions include a simple and expedient harvesting technique without the need for dissection of small-caliber vessels (as in pedicled grafts) or microsurgical anastomoses (as in free grafts). Furthermore the short arc of rotation lessens the risk for vascular impairment caused by kinking of the nutrient vessel.15
▪ Indications and Contraindications
Indications for vascularized bone grafting to the scaphoid include the following:
Avascular necrosis of the proximal pole
Symptomatic proximal pole nonunion
Displaced proximal pole fractures
Failed traditional bone grafting
Absolute contraindications for the procedure include the following:
The presence of severe arthrosis [scaphoid nonunion advanced collapse (SNAC) wrist, stage II or greater]
Carpal collapse (i.e., a collapsed scaphoid with a humpback deformity)25
In cases with a humpback deformity of the scaphoid, alternative VBGs such as a free iliac crest or free medial femoral condyle graft, or a pedicled vascularized graft from the volar radius or thumb metacarpal should be considered.22 , 26 , 27
Relative contraindications to the procedure include previous surgery or injury to the dorsal aspect of the wrist or distal radius, which might impair the blood supply to the dorsal capsule.15
▪ Surgical Technique
The patient is positioned supine with the affected upper extremity placed on an arm board. After the administration of either a general or a regional anesthetic, a nonsterile tourniquet is applied. After prepping and sterile draping, the extremity is exsanguinated with a sterile Esmarch wrap from the wrist proximal. The tourniquet is inflated to 250 mm Hg. Loupe magnification is used for the procedure.
A 4 cm straight dorsal incision centered just ulnar to the Lister tubercle is performed ( Fig. 28.2 ). Dissection is carried through the subcutaneous tissue. The fourth dorsal compartment is partially released to expose the wrist capsule and the distal radius. The extensor pollicis longus tendon is identified and retracted radially, and the extensor digitorum communis tendons are retracted ulnarly. Next the capsular-based vascularized distal radius graft is outlined with a skin marker on the dorsal wrist capsule ( Fig. 28.3A ). The flap is trapezoidal in shape: The flap is trapezoidal in shape: the length is ∼2 cm and it widens from 1 cm at the bone block to 1.5 cm at its distal base ( Fig. 28.3B ). The bone block for the graft measures ∼1 × 1 cm and is harvested from the distal aspect of the dorsal radius just ulnar and distal to the Lister tubercle. The depth of the bone graft is ∼7 mm, and it includes the dorsal ridge of the distal radius. Two to three mm of the distal radius cortex is left intact to minimize the risk of propagation onto the aricular cartilage of the radiocarpal joint. The bone graft is outlined on the distal radius cortex with multiple drill holes by using a 1.0 mm side-cutting drill bit. A thin osteotome is then used to gently elevate the bone graft, with care not to violate the joint articular cartilage. The capsular flap is outlined sharply with a knife and elevated along with the bone graft from the underlying tissues in a proximal-to-distal direction. Care should be taken to prevent detachment of the dorsal scapholunate ligament. In the past, the tourniquet was released to verify the vascularity of the bone graft. We have found, however, that the graft has perfused in all cases, and hence we no longer release the tourniquet because the blood often obscures the surgical field despite reinflation of the tourniquet.
Once the flap is elevated ( Fig. 28.4 ), attention is directed toward the scaphoid nonunion for fracture site preparation. Wrist flexion is often necessary to expose a proximal pole nonunion that may be obscured by the dorsal lip of the radius. If a pseudarthrosis is present with disruption of the cartilage shell, the nonunion is cleaned with a dental pick and small curettes. It is important not to destabilize the nonunion site before scaphoid fixation because taking down the nonunion site can make fixation extremely challenging. If the cartilage shell is not grossly disrupted then the nonunion site is not violated. Fixation of the nonunion is performed under fluoroscopic control. Two 1 mm smooth Kirschner wires are inserted from the proximal pole of the scaphoid oriented toward the base of the thumb, with the wrist in extreme flexion. One of these serves as a guide wire for a cannulated screw and the other as an antirotation wire. Care is taken to place the guide wire for the screw perpendicular to the fracture site and as volar as possible, while maintaining sufficient purchase of the proximal and distal fragments. This guide wire should be also in a slight ulnar position so there is enough space for a bone anchor. The length of the screw is determined by measuring it next to an intact K-wire, followed by drilling and insertion of a cannulated screw ( Fig. 28.5 ). The screw (cannulated Herbert-Whipple screw, standard size, Zimmer Inc., Warsaw, IN) is buried underneath the articular surface by ∼2 mm, and the antirotation wire is removed. In the case of a very small proximal pole fragment, it is not possible to obtain adequate fixation with a cannulated screw, and fixation with two Kirschner wires is recommended.
Once the fracture nonunion is secured, the nonunion site is debrided with a small curette, and a dorsal trough is created across the nonunion site with a side-cutting burr ( Fig. 28.6 ). The size of the trough is determined by the size of the VBG. At this point, the proximal pole fragment should be assessed to determine its vascularity. When the proximal pole fragment is too small to accommodate a trough, it is possible to position the graft in the excavated cavity of the proximal fragment. We secure the VBG with the placement of a small bone suture anchor, nonabsorbable (micro Quickanchor Plus, DePuy Mitek, Inc., Raynham, MA) or absorbable (Microfix Quickanchor Plus, DePuy Mitek, Inc., Raynham, MA) ( Fig. 28.7 ). This bone anchor, which is loaded with two absorbable 3–0 sutures, is placed at the floor of the trough and radial to the cannulated screw ( Fig. 28.8 ). The VBG is then gently inserted into the scaphoid trough and is secured with a mattress stitch. This must be tied over the graft in such a way so as not to compress the pedicle. Due to the close proximity of the graft donor only minimal rotation (10 to 30 degrees) of the flap is needed for the graft to be inserted into the trough ( Fig. 28.9 ).
Hemostasis is obtained, the wound is irrigated, and the incision is closed with 3–0 nylon sutures. A short-arm thumb spica splint with the wrist in neutral position is applied for the first 2 weeks, followed by a short-arm cast for another 4 weeks. Radiographs are obtained with the cast removed in 6 weeks and monthly thereafter to assess union progression. A removable forearm-based thumb spica splint may be used for protection in patients who have delay in union. Return to full activities is permitted only after solid union occurs.