Complications in Equine Surgery. Группа авторов

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 configuration.

       Expected Outcome

      Euthanasia

      Pneumothorax/Hemothorax

       Definition

      Pneumothorax and hemothorax has been reported when the sternum and ribs are used as donor sites [20].

       Risk factors

       Selection of rib or sternum as donor site for bone graft

       Lack of familiarity with anatomy of region of donor site

       Pathogenesis

      Inadvertent puncture of the thoracic or pericardial cavities during bone marrow graft harvest from the sternum or rib may result in hemothorax or pneumothorax, leading to pulmonary collapse or catastrophic cardiovascular event.

       Prevention

      Examination upon necropsy has revealed that the sternum of the equine patient contains between six and eight sternebrae. The preferred biopsy sites are the fourth or fifth sternebrae of adult horses [21]. It is recommended to use the more caudal sternebrae for several reasons [16].

      The caudal sternebrae are covered by less muscle and have a thinner cartilaginous covering, are closer together, and contain more cancellous bone per sternebra in comparison with the more cranial sternebrae. Familiarization with the anatomy of this region is essential if sternum and ribs are to be used as donor sites for bone graft harvest. Utilization of a different donor site may result in less morbidity to the patient.

       Diagnosis

      Clinical signs result from damage to thoracic structures, which may include pneumothorax, hemothorax, as well as injury to the lungs, heart, or blood vessels, with resultant respiratory distress. Clinical signs of pneumothorax include dyspnea, tachypnea, increased respiratory effort and cyanotic mucous membranes [22]. Clinical signs of hemothorax are referable to hypovolemic shock, and include tachycardia, tachypnea, weak arterial pulses, pale mucous membranes, cold extremities, respiratory distress, trembling, weakness, and sweating.

      Auscultation and percussion of the chest wall allow the clinician to distinguish pneumothorax from hemothorax. In patients with pneumothorax, lung sounds are absent with increased resonance percussed dorsally, while reduced lung sounds ventrally and percussion of a fluid line