Pathogenesis
Reduced viability of the graft results from a combination of prolonged time between harvesting and implantation of the graft, dehydration or compaction of the graft, or exposure of the graft to air, saline‐soaked sponges, or antibiotics prior to implantation. Reduced cell survival is attributed to a combination of mechanical damage, desiccation, or osmotic challenge, depending upon the circumstances [10, 11].
Prevention
Cell survival may be maximized by several techniques during harvesting and implantation. A separate surgical team in addition to the surgeons repairing the fracture is advantageous, in order to harvest the cancellous bone graft while the surgical procedure is begun to reduce lag time between harvesting and implantation.
It is recommended to have blood‐soaked sponges ready to store the harvested bone or marrow following collection and prior to implantation (Figure 10.1). Blood may be obtained via intravenous catheter from the jugular or cephalic vein. Exposure of graft tissue to air, coverage with saline‐soaked sponges, or exposure of the graft tissues to antibiotics during harvesting should be avoided. Aseptic technique during implantation is essential for successful incorporation of the graft.
Figure 10.1 Loosely arranged cancellous bone graft in blood‐soaked sponge following collection from tuber coxae.
The bone graft material should be lightly packed into the recipient site to allow for appropriate oxygenation of the graft and to reduce mechanical damage to the cells [1, 10]. Osteogenesis occurs as a result of the activity of viable osteoblasts on the surface of the bone graft. Loosely arranged bone grafts are more desirable due to the greater surface area created, with more living cells available resulting in greater osteogenic activity. Avoiding dehydration and compaction of the bone graft results in a greater number of surviving cells and improved viability of the graft [8].
Diagnosis
Reduced viability of the bone graft may contribute to lack of incorporation of the graft into host tissue, resulting in prolonged fracture repair or increased rate of fracture repair failure. However, lack of viability of the graft itself may not be apparent unless infection of the recipient site occurs or fracture repair failure occurs postoperatively as a result of implant fatigue. Diagnostic imaging (e.g. radiography, ultrasonography or CT) may be utilized to recognize infection or fracture repair failure earlier if indicated based upon clinical signs.
Monitoring
Monitoring for host acceptance of the graft involves monitoring for morbidity at the recipient site (e.g. infection) as well as clinical and radiographic evidence of bone healing. Radiographic signs consistent with infection or lack of incorporation of the graft include evidence of malunion of the fracture site or lucency around the implants. Complete integration of the bone graft into host tissue may take years [9]. Autogenous cancellous bone grafting enhances and stimulates bone healing, and utilization of bone grafts in long bone fracture repair should decrease fracture healing time and fracture repair failure as a result of implant fatigue.
Treatment
Treatment following reduced viability of a bone graft is typically not necessary unless infection of the recipient site occurs due to lack of adherence to aseptic technique. Aggressive treatment of infection of the graft bed or fracture site is recommended, typically with a combination of local and systemic antibiotic therapy. In addition, revision of the fracture repair and local lavage may be performed.
Expected outcome
Lack of incorporation of the bone graft may contribute to prolonged fracture repair as well as infection of the recipient site if aseptic technique is not followed appropriately. In the event of persistent infection, removal of orthopedic implants may be necessary following fracture repair and bone healing.
Early Postoperative Complications
Morbidity Associated with Incision at Donor Site
Definition
The most common complications associated with the incision for bone graft harvest include incisional infection, seroma, and drainage with peri‐incisional edema [3, ]. Incisional dehiscence may result in osteomyelitis, particularly when the sternum and proximal tibia are used as donor sites [13].
Risk factors
Harvest site location
Pathogenesis
Case selection in the bone graft harvest site is important in minimizing complications. Several donor sites for cancellous bone grafts in the horse have been described, principally the tuber coxae, sternum, rib, proximal medial aspect of the tibia, and proximal humerus, each with its advantages and disadvantages, which are summarized in Table 10.1 [3, 12, 14–17]. Similar amounts of cancellous bone may be obtained from the sternum, tuber coxae, tibia and humerus, while the rib yields smaller quantities in comparison [2, 17].
Case‐specific factors dictate intraoperative access to the donor site, amount of graft material required, as well as other case‐specific factors including pre‐existing soft tissue trauma or decubital ulcers [12, 16, 17].
Utilization of the sternum as a graft donor site is associated with minor complications, including peri‐incisional edema, serum exudate, and wound dehiscence due to the ventral location and tension [16].
Incisional dehiscence, which may result in osteomyelitis, is reported, particularly when the sternum and proximal tibia are used as donor sites due to tension and location [13].
Prevention
Location of the donor site is selected based upon the location of the surgical site and therefore anesthetic recumbency selected, which dictates intraoperative access to the site and amount of graft material required. While multiple donor sites may supply an adequate quantity of bone graft material, each donor site carries its own risks and benefits in terms of early postoperative sequellae. Donor site selection is made after taking into account the known risks associated with each site as well as case specific factors such as location of the lesion, soft tissue trauma or presence of decubital ulcers. Whenever possible, avoiding sites at greatest risk of complication is recommended (Table 10.1 ).
Adherence to aseptic technique is advised to reduce morbidity associated with the bone graft donor site incision. The sternum and tibia have also been reported to be more prone to dehiscence due to tension in these areas during anesthetic recovery, and so avoidance of these sites as donor sites for bone graft harvest may reduce incisional site complications.
Diagnosis
Incisional infection, seroma, or edema is diagnosed by clinical
