The Capsular-Based Vascularized Bone Graft from the Dorsal Distal Radius

10.1055/b-0034-78115

The Capsular-Based Vascularized Bone Graft from the Dorsal Distal Radius

Aaron Venouziou and Dean G. Sotereanos

Most scaphoid fractures can be successfully treated nonoperatively or with open reduction and rigid internal fixation with or without conventional bone grafting. However, scaphoid fractures result in an overall nonunion rate of 5% to 15% despite treatment. Numerous bone grafting techniques have been used for the treatment of scaphoid nonunions. The reported union rate with the use of conventional bone graft ranges from 80% to 94%, dropping to 47% when proximal pole osteonecrosis is present.1,2

Vascularized bone grafts (VBG) have demonstrated superior biologic and mechanical properties in experimental studies. Animal models have shown that VBGs are incorporated in a faster, more predictable manner, especially when placed in a poorly vascularized bed. Currently, several authors have achieved high union rates with the use of VBGs for the treatment of scaphoid nonunions.1,2 Zaidemberg et al have described the use of a VBG based on the first recurrent branch of the radial artery (1,2 intercompartmental supraretinacular artery, or 1,2-ICSRA).3 This graft has been used with high success rate by numerous authors. However, harvesting the 1,2-ICSRA graft can be challenging because it involves the dissection of small vessels (the mean diameter of the 1,2-ICSRA is 0.3 mm). On the other hand, the course and characteristics of the vascular pedicle make it vulnerable to kinking and impingement, occasionally necessitating a styloidectomy.4

Sotereanos et al have reported good results with a dorsal capsular-based VBG from the distal radius for proximal pole scaphoid nonunions.5 This graft is nourished by the fourth extensor compartmental artery, and it is harvested from a position that allows easy access to the proximal scaphoid pole. Advantages of the capsular-based VBG include a simple and expedient harvesting technique without the need for dissection of small-caliber vessels or microsurgical anastomoses. Furthermore, the short arc of rotation lessens the risk for vascular impairment caused by kinking of the nutrient vessel.

Indications

The ideal candidates for this procedure are young or middle-aged healthy patients with an established scaphoid non-union, with avascular necrosis (AVN) of the proximal pole and without carpal collapse. The following conditions are indications:

Symptomatic proximal pole nonunion
Displaced proximal pole fractures
Failed traditional bone grafting

Contraindications

Absolute

The presence of advanced arthrosis (scaphoid non-union advanced collapse (SNAC) wrist, stage II or greater)
Scaphoid collapse, as in the case of a humpback deformity
Vascular disease

Relative

Damaged blood supply to the dorsal capsule from a previous surgery or injury
Children and adolescents with remaining growth potential from the distal radial physis
Tobacco use

Imaging

The standard radiographic evaluation of the scaphoid includes four views: a postero-anterior (PA), a lateral, a semipronated oblique, and a PA grip view with the wrist in ulnar deviation (scaphoid view).
Comparison views of the opposite uninjured wrist allow determination of the scaphoid length and the alignment of the carpus, although computed tomography (CT) scanning of the scaphoid in the longitudinal axis is the preferred technique to determine the presence of a humpback deformity and to evaluate carpal alignment.
In established nonunions, we do not order magnetic resonance imaging (MRI) scans, because we routinely treat those cases with VBGs. We assess the vascular status of the proximal pole intraoperatively by releasing the tourniquet and evaluating bone bleeding from the proximal pole.

Relevant Anatomy

Latex-injection studies of wrist vascular anatomy demonstrated reliable vascularization of this bone graft by the fourth extensor compartmental artery (4 ECA).5
This artery runs along the floor of the fourth compartment radial to the posterior interosseous nerve (70% of cases) or within the 3,4 intercompartmental septum (30%), provides numerous nutrient arteries, and anastomoses distally with the dorsal intercarpal arch, the dorsal radiocarpal arch, and other compartmental arteries ( Fig. 28.1 ).
The pedicle diameter is less than 1 mm, and the length ranges between 1 and 2 cm.
It easily reaches the proximal third of the scaphoid by rotation of the graft on the capsular pedicle between 10 and 30 degrees. Therefore this graft may be viewed as an axial flap (based on 4 ECA) and is harvested with the ease of a random flap.

The graft harvest site and the dorsal vascular supply of the wrist. The blood supply to the capsular-based bone graft is based on the artery of the fourth extensor compartment. *Abbreviations:* RA, radial artery; UA, ulnar artery; AIA, anterior interosseous artery; PIA, posterior interosseous artery; ODUA, oblique dorsal ulnar artery; 1,2, 1,2 intercompartmental supraretinacular artery; 2,3, 2,3 intercompartmental supraretinacular artery; 4, fourth extensor compartment artery; 5, fifth extensor compartment artery.

Pearls

The scaphoid proximal pole is exposed with elevation of the capsular graft.
Full wrist flexion facilitates proximal pole exposure.
Insert two K-wires from the proximal pole aiming toward the base of the thumb. One serves as an antirotational wire.
Consider a mini Herbert screw in cases with a very small fragment of the proximal pole.
Position the graft in the excavated cavity of the proximal pole in cases with a very small fragment.
Secure the graft with a mini bone suture anchor to avoid extrusion in the early postoperative period.

Pitfalls

Leave 2–3 mm of the distal radius cortex intact to minimize the risk of an intraarticular fracture.
Elevate the capsular flap gently, taking care to prevent detachment of the dorsal scapholunate ligament.
Destabilizing the nonunion can make the fixation extremely challenging.
Place a screw that is 4 mm shorter than measured, to prevent penetration of the distal articular surface.