Use of an Autologous Bone Graft Derived from Three Caudal Vertebrae for Reconstruction in a Dog with Radioulnar Atrophic Nonunion and Osteomyelitis

This case report describes the case of a 4-year-old toy poodle who underwent reconstruction using an autologous caudal vertebral graft for nonunion and osteomyelitis of a left radioulnar fracture. Radial reconstruction was performed 14 days after the removal of existing implants. Three autologous caudal vertebrae mounted onto a titanium T-plate were used to ﬁ ll the radial bone defect. Rehabilitation was initiated 3 weeks after surgery. By the ﬁ fth week after surgery, the dog showed weight bearing on the affected limb. One year after the reconstruction surgery, revision surgery for replacing all implants was performed due to increased radiolucency of the graft. The dog remained clinically stable, and radiographic bone union was complete 3 years and 2 months after the ﬁ rst surgery. An autologous caudal vertebral graft was successfully used for the treatment of a large radial defect in a dog suffering from atrophic nonunion. Clinical improvement was prompt, and the long-term functional outcome was satisfactory.


Introduction
Nonunion is a serious complication of bone fracture management and is caused by inappropriate reduction, inadequate stability, insufficient blood supply, infection, and bone defects. 1 Radioulnar nonunion is more common in toy breeds than in large breed dogs, likely due to reduced intraosseous blood supply at the distal radius. 2 Although amputation may be considered in such cases of uncontrollable infection or extensive bone resorption, bone grafting is a valid treatment option to preserve the limb and to achieve reduction and healing. Cortical bone grafting provides mechanical support and contributes to structural stability and thus might be necessary to bridge larger bone defects. 3 In small-animal surgery, the ilium and ribs are generally used as autologous cortical bone grafts. 3 However, disadvantages associated with the use of autografts include limitations of donor sites and bone mass. We performed and reported autologous bone grafting using vertebrae harvested from the dog's tail for bridging of a large radioulnar bone defect as a consequence of nonunion in a toy-breed dog.

Implant Removal and Bacterial Culture
Infection and osteomyelitis were suspected based on the radiographic findings and blood test results; therefore, the implants were removed, and the affected area was thoroughly cleansed under general anesthesia on first presentation (►Fig. 1B). Bacterial culture and antibiotic susceptibility testing revealed methicillin-resistant coagulase-negative staphylococcus infection; therefore, Fosfomycin (23 mg/kg, orally, twice a day) was administered for 2 weeks.

Autologous Bone Grafting Procedure
Surgery with grafting was performed 2 weeks after implant removal. The dog was anaesthetized using a routine protocol with endotracheal intubation and isoflurane in oxygen. The tail was docked and the sixth to eighth caudal vertebrae were aseptically collected and prepared for implantation (►Fig. 2A, B). Soft tissue and cartilaginous tissue surrounding the vertebrae were trimmed using a rongeur and a No. 11 blade. The cancellous bone on each epiphysis of the vertebra  was partially exposed using a round burr (Stryker TPS System, Stryker, Kalamazoo, Michigan, United States). The bone specimen was packed and protected in saline-soaked sponges until implantation. A craniolateral approach was performed on the left forelimb to expose the gaping radial lesion. The stumps of the atrophic bone ends were excised, and the adjacent medullary cavity was reamed. A 1.5-mm titanium T-shaped conventional plate (Radius Reduction Plate TH type, Platon Japan, Japan) was placed over the bone defect whereby two screws each were applied to purchase and transfix each caudal vertebra transplant (►Fig. 2B). Only three caudal vertebrae (the total length was 3 cm) could be fitted into the gap, because of the shortening effect of chronic muscle contracture at the fracture site. Four screws were placed in the distal radius fragment, and three in proximal (►Fig. 2C). Cancellous bone was harvested from the ipsilateral greater tubercle and implanted at the radial fracture ends and around the autologous caudal vertebrae graft. Additionally, an autologous iliac wing bone graft was also transplanted at the medial site of the vertebral graft. A long limb cylinder cast was kept in place for 2 weeks postoperatively. Buprenorphine (Buprenorphine Inj., NISSIN, Japan, 0.01 mg/kg IV, every 12 hours) was administered as an analgesic for 3 days, followed by tramadol (2 mg/kg, orally, every 12 hours) administration for 7 days. Fosfomycin (23 mg/kg, orally, twice a day) was given during the 14-day postoperative period. Rehabilitation using an underwater treadmill was started 3 weeks after surgery. Radiographic follow-up examination was performed until 1 year postoperatively.

Outcome
The limb length discrepancy between the left and right forelimbs was improved from 48 to 20% after vertebral grafting surgery. The numeric lameness score was two-fifths, and the Colorado State University pain scale score was onefourth at 3 weeks. At 5 weeks postoperatively, there was stable weight bearing on the affected limb and no pain on palpation, and lameness was not apparent. The range of motion of the left elbow joint was 100 degrees (normal range of motion: 130 degrees [flexion 36 degrees and extension 165 degrees]) 1 month after surgery due to muscle contracture. 6 The range of motion improved to 120 degrees by the end of the 2-week rehabilitation period (that is, 5 weeks after surgery). There was no obvious implant loosening or refracture on radiographs until 3 months postoperatively. The 5-month postoperative radiographic examination revealed a progressive increase in the radiolucency of the fracture gap (►Fig. 3B). The implants were stable, and periosteal callus formation was noted.

Revision Surgery
Radiographic examination 1 year after surgery revealed further increase of radiolucency of the vertebral grafts (►Fig. 3C). Therefore, revision surgery was performed to avoid stress concentration. During screw removal, a slight plate bending toward medial was observed, and replating was done. A soft bandage was applied postoperatively and was maintained for 1 week. During the first week, the dog was kept on activity restriction After revision surgery, the dog remained clinically well. Three years and 2 months after the first surgery, radiographs and computed tomography images revealed complete bone healing and no implant loosening (►Figs . 3D and 4). There was no apparent lameness at this point.

Discussion
The transplanted tail vertebrae were suitable spacers for the plate fixation of a large radial bone defect in this case because of their size and bone mass. Apparently, several caudal vertebrae could be placed to reach the length required to fill the bone defect. Caudal vertebrae contain cortical bone that provides structural support. The ratio of cortical to cancellous bone in canine caudal vertebra has not been reported. Although difficult to compare, in humans, approximately 70% of a lumbar vertebra is cancellous bone. 7 Therefore, caudal vertebra may be considered useful as grafts for long bone defects because of the structural support, osteoconductivity, and osteoinductivity.
Increased radiolucency of the grafts suggesting incomplete bone healing was a major complication 1 year after the initial surgery. It may have been caused by creeping bone substitution. Also, it may have been better to place the second bridging plate on the lateral side of the radius to avoid plate bending.
According to one report, dogs can compensate forelimb length deficits up to 15% by extending the joints. 8 In our case, the discrepancy was approximately 20% after reconstructive surgery and might have contributed to initially observed lameness. The positive result of gap healing with plate and vertebral spacers may have been due, in part, to the dog's small size. In addition, it was possible that some lameness was masked by short and rapid successive strides.
The surgical result achieved in this single case demonstrates the feasibility of using tail vertebrae as autologous bone graft and may encourage further evaluation when treating large bone gaps in radioulnar nonunions, especially in canine toy breeds.

Note
This case report was presented in 2018 at the conference of the Japanese Society of Veterinary Anesthesia and Surgery in Omiya, Japan.
Authors' Contribution M.G. and H.I. performed the surgery described in this case report. M.G. drafted and revised the manuscript. Both the authors approved the submitted manuscript.