Treatment of a nonunion, secondary to gunshot fracture, of the distal radius with circular external fixation and rhBMP-2 in a cat

Case Report: Treatment of Femoral Non-union With Rib and Iliac Crest Autografts and rhBMP-2 in a Cat

A 5-year-old, intact male Bengal cat weighing 5.2 kg was referred for the fixation failure of a right femoral fracture. Multiple surgical revisions failed, and atrophic non-union was diagnosed. The cat was then admitted for a final revision surgery using locking plate fixation in conjunction with rib and iliac crest autografts and recombinant human bone morphogenetic protein 2 (rhBMP-2). The fracture site was debrided and stabilized before filling the defect with 1.8 cm of rib bone autograft. The residual space in the defect was then filled with an iliac crest autograft. Finally, a 3 ×5 cm absorbable collagen sponge soaked with 0.5 mL of 0.2 mg/mL rhBMP-2 solution was placed around the defect. No significant complications were noted postoperatively. Bone healing was noted 2 months postoperatively, and it continued for 12 months. Although mild lameness remained, the cat's ambulatory function and quality of life were good. To the authors' knowledge, this is the first case report of a clinical transplantation of a rib segment as an autograft in combination with rhBMP-2 in a cat with a large bone defect.

Outcomes and Complications Associated with Acute Gunshot Fractures in Cats and Dogs

OBJECTIVE

 The aim of this study was to summarize outcomes and complications of gunshot fracture management in small animals.

STUDY DESIGN

 Review of cats and dogs with radiographically confirmed acute gunshot fractures, presenting data on signalment, fracture location, fracture management (surgical vs. non-surgical, type of surgical repair), fracture comminution, extent of soft tissue trauma, postoperative complication and overall outcome. A poor outcome was defined as patient death, major postoperative complication or limb amputation (both as primary treatment or secondary to postoperative complications).

RESULTS

 Ninety-seven animals with 137 acute gunshot-induced fractures were identified. There were 21 (15.3%) maxillofacial, 16 (11.7%) vertebral column, 8 (5.8%) rib, 56 (40.9%) distal long bone (below stifle/cubital joint) and 36 (26.3%) proximal long bone (at or above stifle/cubital joint) fractures. Overall, 20/37 cases with sufficient follow-up details incurred a poor fracture outcome. Extensive soft tissue trauma at the fracture site was associated with an increased likelihood of poor outcome. The most common poor outcomes were primary limb amputations (7 cases) and postoperative complications (3 osteomyelitis/surgical site infections, 4 delayed/non-unions).

CONCLUSIONS

 Gunshot fractures overall have high likelihood of poor outcome. Severe soft tissue injury is associated with complications. Mitigating poor outcome likely requires early aggressive wound management.

Case Report: Trans-Articular External Skeletal Fixation of the Hip for a Highly Comminuted Juxta-Articular Fracture of the Proximal Femur Caused by Gunshot Injury in a Cat

This report describes a novel surgical technique for trans-articular external skeletal fixation (TA-ESF) of the hip to stabilize a rare, highly comminuted juxta-articular fracture of the proximal femoral segment involving the metaphysis and diaphysis in a cat. A 2-year-old, castrated male, Korean shorthair cat was admitted for a left femoral fracture caused by gunshot injury. Radiographs and computed tomography (CT) scans revealed a highly comminuted proximal femoral diaphyseal fracture that involved the femoral neck and the greater trochanter. The left femoral head was intact on CT. Under fluoroscopic guidance, an intramedullary Steinmann pin was placed to align the femur, and five positive-profile, end-threaded pins were placed in the left hemipelvis and distal femur. A triangulated frame of connecting bars was constructed using Steinmann pins and epoxy resin for TA-ESF. This secured the pins placed in the pelvis and femur as well as the intramedullary pin, providing proximal femoral stabilization by trans-articular fixation of the hip. The cat began placing weight on the left pelvic limb 4 days postoperatively, and progressively obtained near-normal limb function by day 112. The TA-ESF was partially dismantled to a linear tie-in construct on day 64 and was completely removed on day 161. Final radiographs on day 161 revealed lack of bone healing in the proximal segment, especially femoral head and neck, despite functional recovery of the injured leg. At one year postoperatively, the cat had normal limb function without any noticeable complications. On follow-up 29 months after surgery, the owner reported that the cat had normal limb function without any noticeable complications. Despite insufficient bone healing in the cat, TA-ESF of the hip allowed for satisfactory functional recovery of this challenging juxta-articular fracture of the proximal femur, which was not amenable to stabilization with a traditional non-load-sharing fixation system.

BMP-2 delivered from a self-cross-linkable CaP/hydrogel construct promotes bone regeneration in a critical-size segmental defect model of non-union in dogs

Objectives: To determine whether the addition of recombinant human bone morphogenetic protein (rhBMP-2) to a self-crosslinkable cellulosic hydrogel/biphasic calcium phosphate (BCP) granules construct promotes bone healing in critical-size ulnar defects in dogs.

Methods: A standardized 2 cm long ulnar ostectomy was performed bilaterally in five dogs to compare bone healing with hydrogel/BCP constructs associated with or without rhBMP-2. Cancellous-bone autografts were used as positive controls in unilateral ulnar defects in five additional dogs. Radiographically, bone healing was evaluated at four, eight, 12, 16 and 20 weeks postoperatively. Histological qualitative analysis with microCT imaging and light and scanning electron microscopy were performed 20 weeks after implantation.

Results: All rhBMP-2-loaded constructs induced the formation of well-differentiated mineralized lamellar bone surrounding the BCP granules and bridging bone/implant interfaces as early as eight weeks after surgery. Bone regeneration appeared to develop earlier with the rhBMP-2 constructs than with the cancellous-bone autografts while similar results were obtained at 20 weeks. Constructs without any rhBMP-2 showed osteoconductive properties limited to the bone junctions and a lack of osteoinduction without bone ingrowth within the implantation site. In one dog, the leakage of the hydrogel loaded with rhBMP-2 induced an extensive heterotopic bone formation.

Clinical significance: The addition of rhBMP-2 to a self-crosslinkable hydrogel/BCP construct could promote bone regeneration in a critical-size-defect model with similar performance to autologous bone grafts.