Upper limb bone defectindications for vascularized bone transfer

In general, most authors suggest that the strongest indications for the use of vascularized bone graft include situations that are prone to failure or complications with technically less demanding techniques such as nonvascularized bone autografts or allografts. These situations include massive defects and/or an unfavorable surrounding soft tissue milieu related to prior failure of conventional bone grafting failure, infection, radiation, or other causes of extensive scarring.

Specific indications

1. Recipient site considerations. In the upper limb, reconstruction of the humerus probably represents the most compelling indication for the use of vascularized fibula transfer. This is because, other than massive allo-grafts, there are few techniques available to reconstruct a large missing segment of the humeral shaft. Although large defects of the radius and ulna may also be excellent indications for reconstruction by vascularized bone transfer, the option of forearm salvage by a one-bone forearm conversion always merits consideration (Fig. 1) [28]. Moreover, more limited defects of the proximal radius or distal ulna may be consistent with an acceptable level of upper limb function.

2. Large bone defects. The precise length of a bony defect that would lead one to select a vascularized bone graft for reconstruction is not particularly well established. Many authors [6,11,14,17,19,20,22,24,27] have suggested that a 6-cm gap is the point where vascularized bone reconstruction should be chosen in place of a nonvascularized auto-graft. However, it is important to recognize that with sufficient mechanical protection over several months, and when dealing with a well-vascularized surrounding soft tissue milieu, bone defects exceeding 10 cm may be healed with cancellous autograft [29] or non-vascularized cortical bone segments [30]. Moreover, massive allografts may be a suitable option for reconstructing very lengthy defects [31,32]. However, it should be recognized that massive allografts have limited ability to be

Fig. 1. Radiograph depicting one-bone forearm construct for proximal radius defect.

revascularized and hence a limited capacity to be replaced by ''creeping substitution'' of host osteoprogenitor cells [33]. In general, the authors believe that a defect as short as 6 cm in the presence of a poor surrounding soft tissue bed and for all defects greater than 10 cm, the selection of vascularized bone transfer for reconstitution is justifiable.

3. Prior bone reconstruction failures. Bone defects in the upper limb, without regard to length, that have failed to heal with nonvascu-larized autograft may be candidates for a vas-cularized bone graft. This is particularly the case when there is no readily apparent explanation for the initial failure (ie, inadequate bone graft material, inadequate stabilization, use of allograft or xenograft, and so forth).

4. Infected bone defects. The use of vascular-ized bone grafts for reconstructing infected bone defects is particularly attractive for a number of reasons. Probably of most importance is that such bone grafts are inherently a vehicle for local blood supply [13,25]. However, also of importance is that a vascularized fibula is a generous source of bone length and it makes little difference from the technical perspective if one transfers a 6- or 16-cm graft segment. Thus, a more aggressive debridement of infected bone ends may be performed with less regard to concerns about creating a larger bone defect than can be reconstructed (Fig. 2A, B).

5. Bone nonunions associated with osteo radio-necrosis. Bone nonunion that is associated with radiation osteonecrosis is a particularly challenging problem that responds poorly to conventional bone-grafting techniques [34]. This is because three adverse circumstances exist in the presence of localized radiation changes: (1) impaired intraosseous blood supply; (2) impaired blood supply of the surrounding soft tissue; and (3) periosteal and intraosseous cell death. These adverse circumstances are directly addressed by the transfer of a vascularized bone segment obtained from a site well distant to the irradiated field (Fig. 3A-C).

Donor sites

The focus of this article is repair of large bone defects of the upper limb. For all practical purposes, for these types of defects, the fibula is the preferred donor bone. Rarely is the fibula unavailable—for example, if both were previously harvested for bone grafting or in unique patients with osteogenesis imperfecta. The technique of dissection of a vascularized fibula has been well described [15,31] and will not be repeated in this article. In the rare patient where the fibula is unavailable, one can consider other vascularized bone donor sites, for example, iliac crest, scapula, rib, radius, metatarsal, or any bone segment from a paralyzed or useless limb.

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