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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 configuration.

Expected Outcome

Euthanasia