with evidence of drainage or swelling at the incision site.
Monitoring
Monitor the graft donor incision site for increased drainage, swelling or dehiscence that may indicate seroma formation or infection. 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 repair failure as a result of implant fatigue.
Treatment
Incisional infection or seroma at the donor site may be treated successfully with facilitated drainage of the incision site and antimicrobial therapy.
Expected outcome
Incisional complications, such as incisional infection, seroma, and drainage with peri‐incisional edema or superficial incisional infection, are usually self‐limited and carry a good prognosis [3, 12, 13]. Osteomyelitis is a more serious condition but usually responds well to local debridement and antimicrobial therapy.
Table 10.1 Summary of bone graft donor sites
| Donor Site | Advantages | Disadvantages |
|---|---|---|
| Tuber coxae [2, 23, 17] | Provide ample grafting materialGood visualization for surgical approachLow rate of postoperative incisional complicationsRemains the most commonly used donor site | Time‐consumingRequires patient in lateral recumbencyDecubital ulcers or soft tissue trauma over the tuber coxae may preclude its use |
| Sternum [16, 21, 37, 38, 39] | Use in cases where patient in dorsal recumbencyReduces risk of pathological fracture associated with harvesting from the tibia and humerusAbsence of skin tension and dependency of this location facilitates drainage if incisional infection or dehiscence occurCancellous bone obtained is equivalent in amount and microscopic appearance to that obtained from other sites such as the tuber coxae, proximal tibia, and ribNo instability or fractures of the sternum have been reported, even when more than one sternebra is accessed in order to obtain the desired amount of cancellous bone | Risk of puncturing thoracic or pericardial cavities exists |
| Tibia [12, 19] | May be accessed with patient in dorsal or lateral recumbencyUseful in cases where smaller amounts of graft material (<50 ml) are required, such as in arthrodeses, bone cysts or acute fractures | Risk of pathologic fracture on anesthetic recovery has been recognized |
| Humerus [3] | Greater soft tissue coverage and muscular support may reduce potential for incisional complications and help to dissipate torsional forces exerted on the bone during recovery from general anesthesia | Catastrophic fracture during recovery from anesthesiaMild to moderate incisional swelling and edema |
| Rib [25] | Bone obtained from transcortical rib biopsies was reported to be superior in quality to unicortical biopsies in terms of histomorphometry | Pneumothorax or hemothorax |
| Fourth coccygeal vertebra [15] | Provides large quantity of cancellous boneAccessible with the patient in dorsal or lateral recumbency | Use of this site requires tail amputation |
| Periosteum [15] | Transplantation of periosteum as a source of osteoprogenitor cells may enhance bone healing as donor tissue with good osteogenic propertiesEquine tibial periosteum was examined in vitro for its osteogenic and osteoprogenitor characteristicsUse of autogenous tibial periosteum in human cartilage repair techniques reportedly did not result in morbidity associated with donor site | Periosteum as an alternative donor source in bone grafting warrants further investigation in vivo in the equine patient. |
Fracture at Donor Site
Definition
Catastrophic fracture during anesthetic recovery has been reported when the graft is obtained from the tibia or humerus [3, 12, 18, 19].
Risk factors
Utilization of the humerus or tibia as graft donor sites [3, 12, 18, 19]
Young horses are more at risk for tibial fracture [2]
Pathogenesis
Fracture of the humerus or tibia following bone graft harvest is attributed to inappropriate torsional forces exerted on the bone during recovery from general anesthesia [3].
Prevention
The risk of pathologic fracture of the tibia on anesthetic recovery has been recognized [19], and may be minimized with careful drill placement upon entering the medullary cavity [12]. It has been suggested to use an alternative donor site to the tibia, particularly in immature horses [2]. However, Boero et al. demonstrated that an approximately 1 cm diameter hole could be made in the proximal medial aspect of the tibia at a point midway between the distal end of the groove for the middle patellar ligament and the caudal border of the bone from horses weighing 350 to 450 kg [12]. Two adjacent 4.5‐mm holes were drilled, and the holes were joined and enlarged to approximately 1 cm in diameter to accommodate an 8.0‐mm bone curette. This technique allowed for up to 55 ml of cancellous bone to be removed from the tibia without significant decrease in the strength of the tibia, without altering torsional load capacity, or increasing risk of pathological fracture [12].
It is not recommended to utilize the humerus as a graft donor site due to concern that a defect of this size may create a stress riser resulting in catastrophic fracture of the humerus, which occurred in 1 out of 8 cases where a 12‐mm cortical defect was created using a drill in the lateral proximal humerus [3].
Instability or pathologic fractures have not been reported following bone graft harvest from the tuber coxae or sternum, and these donor sites may be used preferentially.
Diagnosis
Catastrophic fracture of the humerus and tibia secondary to bone graft harvest from these sites would typically be apparent following anesthetic recovery from general anesthesia with significant lameness of the affected limb. Radiographic evaluation would confirm diagnosis of catastrophic fracture of humerus or tibia following bone graft harvest.
Monitoring
Monitor for catastrophic breakdown or significant lameness of the affected limb following anesthetic recovery if the humerus or tibia were elected as donor sites. Radiographic or ultrasonic evaluation would confirm diagnosis of fracture.
Treatment
Pathological fracture of the humerus and tibia following bone graft harvest would typically necessitate euthanasia, depending on the age of the patient and fracture
