Prior to any oral surgery or reconstruction familiarization with local nerve blocks is essential. Unlike some other areas of the body, good options exist for local analgesia. Local anaesthetics include:
- 0.5% bupivacaine (up to 2 mg/kg, onset within 30 minutes—effective for 6–10 hours)
- Lidocaine 2% (up to 5 mg/kg in dogs and 1 mg/kg in cats, onset within 5 minutes—effective for < 2 h)
The infraorbital nerve bock is applied at the infraorbital foramen or inside of the infraorbital canal and will block tissues rostral to the infraorbital foramen. The inferior alveolar nerve block is injected around the mandibular foramen situated on the ventromedial aspect of the mandibular ramus. The area blocked includes the mandibular body, mandibular dentition and adjacent soft tissues. The middle mental nerve block is applied at the middle mental foramen ventral to the mesial root of the second premolar in the dog or halfway between the canine and third premolar in the cat. This will block the rostral mandibular body, the dentition, and adjacent soft tissues. The major palatine nerve block is applied to the palatal mucosa just rostral to the major palatine foramen and will block the palatine shelf of the maxilla. The maxillary nerve block is given just caudal to the last molar tooth as the maxillary nerve enters the maxillary foramen. This will bock the incisive bone, maxilla and palatine bone as well as maxillary dentition.
Many smaller upper lip excisions can be performed in an inverted “V” shape and reconstructed directly. The upper lip in most dogs has significant mobility to allow both cosmetic and function reconstruction in this manner. A two to three-layer closure can be used depending on patient size. In cases where larger quantities of tissue require excision a direct unipedicle advancement flap may still facilitate closure. For more extensive defects or significant defects of the lower lip an angularis oris axial pattern flap or caudal cervical flap may be used to bring additional tissue into the reconstruction.
Soft Tissue Reconstruction Following Mandibulectomy
In most cases mandibulectomy is being performed to remove an oral malignancy. Gingival margins can be assessed visually however infiltration into adjacent bone and soft tissues is best conducted on CT. Margins of at least 1 cm (more when feasible) should be achieved when performing excisions. Caudal mandibulectomies can usually be closed by direct intraoral mucosal apposition. In these instances, there is often no need to excise skin, allowing relatively straight forward if slightly awkward closure. Four tissue surfaces must be considered when excising central or cranial portions of the mandible: the oral sublingual mucosal, gingival, labial mucosa and skin. Excision should be performed to remove the desired bone and soft tissue margins. Additional bone often needs to be resected as transaction should be performed between dentition and still leave enough soft tissue to cover the bone ends (i.e., the bone excision must extend beyond the soft tissue excision). Edges of bone that are excised should be rounded off or filled where possible to avoid focal pressure on the overlying mucosa. Priority should be given to complete neoplastic excision and it is not uncommon that the cutaneous tissues of the skin must be sutured directly to the sublingual mucosa.
Although osseous reconstruction has been described with the use of BMP impregnated scaffolds, most large excisions will be performed without structural replacement. As such mandibular drift should be expected or managed at the time of the original surgery with elastic trainers. Subsequent application of elastic trainers following drift is less likely to be successful.
When preforming a maxillectomy the palatine and infraorbital arteries may need to be transected and ligated. A combination approach, both intraoral and through a lateral skin incision can be used to perform these procedures. Closure is typically accomplished by direct apposition of the labial mucosa to the palatine mucosa. A single pedicle advancement flap can be generated from the labial mucosa to allow improved closure. It is not uncommon to need to drill holes in the palate to allow placement of the sutures as the palatine mucosa can be friable. In situations where the palatine resection passes midline, complete closure with a labial flap can be difficult. A superficial cervical axial pattern flap or angularis oris flap can be used.
Many patients with congenital palatine defects are euthanized at birth by the breeder. Those that are candidates for reconstruction need to reach at least 3–7 months of age before surgery. Premature correction can result in tearing of tissues or damage to the periosteum which can hamper further development. Waiting until adult dentition has erupted will also allow extraction, freeing more soft tissues to allow closure. Waiting too long can result in larger defects and often the pet will require a tube feeding until definitive repair which can place a burden on the owner.
The defects are a result of incomplete fusion of the maxillofacial structures:
- Cleft lip, rostral hard palate
- Midline of hard and soft palate
- Lateral area of the soft palate
- Hypoplastic soft palate
Attempts should be made to have the repair supported by underlying bone. This is where a CT is of value in preoperative assessment. The oral fistula may appear relatively small, however the defect in the supportive bone shelf can be much larger. Flaps should be 1.5 x larger than the required defect, electrosurgical equipment or lasers should be avoided, and closure should take place with no significant tension.
Congenital defects of the primary palate (rostral to the incisive papilla) require flaps of oral and nasal soft tissue. Advancement, rotation, transposition or overlapping flaps are followed by reconstruction of the cutaneous tissues.
Overlapping Flap Technique for Hard Palate Repair
An incision is made in the mucoperiosteum 1–2 mm away from the dentition on one side of the defect laterally. The second incision is made in the mucoperiosteum at the defect. Elevation of the tissues is performed bilaterally while attempting to preserve the major palatine artery. The first flap is then rotated medially across midline and under the second flap before being secured.
Medially Positioned Flap Technique for the Hard Palate
Bipedicle flaps are directly elevated from each side of the oral mucosa and centrally apposed. This is used only for minor reconstructions as there is no underlying bone to support the closure. In cases of trauma the bone apposition can sometimes be improved by direct digital pressure on each side of the maxilla or twisting orthopaedic wire between the maxillary canines (and then covering in a self-curing composite).
Medially Positioned Flap Technique for Soft Palate Repair
Incisions should be made along the medial margins of the defect to the level of the caudal end of the tonsils. By cutting the margins of the defect two separate sets of flaps are created, one in the nasopharynx and one in the oropharynx. A separate closure of the two flaps creates a double layered closure.
Labial Based Mucoperiosteal Flap for Repair of Oronasal Fistula
Either a single (labial based only) or double (labial based over a reflected palatine mucosal flap) repair can be used to close these defects.
Elongated Soft Palate
Elongated soft palates are typically resected with laser, blade or vessel sealing device to the level of the caudal tonsils.