Defect nonunion fractures are managed in 1 stage when teeth are not present.
If the teeth are present a two-stage approach is performed:
Stage 1: full-mouth dental radiographs, periodontal treatment and extractions of periodontally affected teeth. Periodontally affected teeth are common in the fracture area, especially in small breed dogs and cats.
Stage 2: approximately four weeks later, mandibular reconstruction using a regenerative approach is performed.
Note: a staged approach allows the soft tissue inflammation to subside before definitive repair of the nonunion
Restoration of occlusion and normal anatomy is crucial to avoid long term complications such as malocclusion, malunion, continued nonunion, refracture, facial asymmetry and loss of function.
2. Single stage approach
When a single stage approach is used, debridement and reconstruction are performed at the same time.
The incision should expose enough intact bone to place at least two screws on both sides of the fracture.
Fracture reduction is accomplished with 1-2 periosteal elevators placed at the fracture site to lever the caudal fragment into reduction to restore the normal anatomy. Bone holding forceps and sometimes digital reduction can be used.
Plate selection and preparation
The first choice is a 2.0mm titanium locking plate (a and b in the illustration).
If this is not available, for a medium or large breed dog, a single 2.4/3mm titanium locking mandibular reconstruction plate can be used (c). For small breed dogs and cats, a 2.0mm titanium mandibular reconstruction plate is used (d).
If the locking plate is used, it is minimally contoured using bending pliers.
If the mandibular reconstruction plate is used, it is anatomically contoured in 3 dimensions using the appropriate bending pliers.
Note: 3D printed models of the skulls based on CT can be used to precontour the plates prior to surgery. Precontouring the plates saves time in the operating room and ensures the appropriate plate is available for surgery.
The length of the plate should allow for 2-3 bicortical locking screws on both sides of the fracture.
The plate is applied to span the fracture site and screw placement must avoid the mandibular tooth roots. The plate is placed ventral to the tooth roots and above the mandibular canal. A single plate is sufficient to stabilize the mandible.
Note: In small dogs and cats, due to limited bone stock, the screws often penetrate the mandibular canal.
The plate is held in place using bone holding forceps. A locking drill guide is screwed into the plate to allow precise drilling of the hole.
The rostral screw closest to the fracture site should be inserted first alternating as illustrated until all screws are inserted.
The screw length is determined by a depth gauge measurement. Preoperative CT measurements can be used to estimate the screw length for planning purposes.
The defect is filled with a Compression Resistant Matrix (CRM) or similar scaffold infused with rhBMP2 at a dose of 0.5mg/ml at a soak volume of 50%.
The infused scaffold is placed to fit snugly at the defect site.
If rhBMP2 is not available, cancellous autograft can be used instead.
After handling rhBMP2 it is important to change surgical gloves and not reuse any instruments that touched the rhBMP2.
The soft tissues are closed in 3 layers.
The first layer includes all the surrounding muscles, known as the soft tissue envelope, which will recruit progenitor cells that are critical for bone regeneration. The second layer is the subcutaneous tissue and the last layer is the skin.
7. Case example 1
Defect nonunion fracture in a small breed dog. The fracture gap is bridged with a 2.0mm titanium locking plate.
Defect nonunion fracture in a small breed dog. The fracture gap has been filled with compression resistant matrix soaked with rhBMP2.
8. Case example 2
2.4 reconstruction plate with cancellous autograft repair of a defect nonunion in a Labrador retriever.
Multimodal analgesia is recommended. Non-steroidal medication for 10-14 days and opioids for the first 5 days post-surgery as needed. Antibiotic therapy is prescribed for a period of 10-14 days following surgery.
Soft food should be fed for the first 14 days, followed by a gradual return to eating kibble over 2 weeks. Rough play (i.e., tug of war) should be avoided for the first 3 months after surgery.
Suture removal is performed 10-14 days after surgery.
A radiographic recheck is performed every 6 weeks until the fracture is healed. The plate is not removed after the fracture is healed.