Surgery of Exotic Animals. Группа авторов

Healing

Epithelialization, wound contraction, and tissue remodeling takes place in amphibians similar to in mammals (Poll 2009). In immature amphibians, skin healing involves contraction and regeneration of the skin, while postmetamorphic amphibians will form scar tissue devoid of dermal mucous and granular glands (Yannas et al. 1996).

      During the inflammatory phase of wound healing, wet‐to‐dry bandages are contraindicated in amphibians because they may result in desiccation of the tissue surrounding the wound (Poll 2009). During the proliferative phase, becaplermin (Regranex^®, 0.01% gel, Ortho‐McNeil Pharmaceutical Inc., Raritan, NJ, USA), recombinant human platelet‐derived growth factor has been suggested to accelerate healing (Walker and Whitaker 2003; Poll 2009). Apply the gel to the wound for 60 seconds every three weeks (Fleming et al. 2008). Before applying the gel, irrigate the wound with saline to loosen external debris, necrotic skin and exudates. Gently debride the area until a small amount of hemorrhage is observed and then rinse the wound again before applying a thin layer of gel (Poll 2009). After a contact time of 60–120 seconds, rinse the gel off or leave it on the wound. The use of hydrogel has also been recommended to accelerate wound granulation (Poll 2009).

Skin Surgery

There are a number of indications for skin biopsy. Perform a local anesthesia block with lidocaine 2 mg/kg and obtain the biopsy with a sterile punch biopsy instrument or scissors. Use hand‐held electrocautery to achieve hemostasis, if needed. For skin closure, use a cutaneous everting pattern (Figure 6.3), appositional sutures, and/or cyanoacrylate tissue adhesive (Tuttle et al. 2006; Gentz 2007; Van Bonn 2009; Baitchman and Herman 2015; Chai 2015a). Appositional sutures are preferred by the authors. Take care to minimize suture tension as amphibian cutaneous tissue is less elastic than mammalian skin (Chai 2015a). This is not always possible when large margins are needed for excising neoplasms. To relieve tension, use silicone rubber tubing as stents on each side of the incision (Wright and Whitaker 2001a).

Figure 6.3 Cutaneous everting suture pattern with monofilament absorbable suture material on the right forelimb of a cane toad (Bufo marinus).

      Source: Photo courtesy: Zoological Medicine Service, Université de Montréal.

      Cryosurgery and laser surgery have been used in amphibians for mass ablation (Wright and Whitaker 2001a). These modalities improve hemostasis, but do not enable histologic analysis of the mass. A protocol of three freeze‐thaw cycles over 30 seconds for each phase using a thermocouple has been described. If cryosurgery is elected and histopathology is needed, first collect an incisional biopsy of the mass. Chemical cauterization, such as with formalin and metacresolsulfonic acid (Lotagen TM, Schering Plough Animal Health), has been used to remove cutaneous masses in amphibians (Chai 2015a); however, controlled studies are needed to evaluate tissue healing, adverse effects, and pain associated with this technique.

Orthopedic Surgery

      Surgical stabilization is indicated for traumatic fractures as the moist environment precludes the use of bandages unless they are frequently assessed and changed. Bone healing is typically slower in amphibians than in mammals and reptiles (Pritchard and Ruzicka 1950). Cartilaginous union of the fracture fragments may appear after a month, but bony union may not occur until after 80 days, and callous remodeling may take more than seven months at the POTZ (Pritchard and Ruzicka 1950; Johnson 2003).

      External fixators may be difficult to place in amphibians to achieve appropriate compression and alignment without movement due to the normal limb angulation as hind limbs are positioned in close contact with the body and other limb segments in the resting position and external fixators can cause cutaneous abrasions of the adjacent skin (Wright and Whitaker 2001a; Royal et al. 2007). Stabilization of tibiofibular fractures with type I external fixators has been reported (Johnson 2003). Insert at least two transcortical Kirschner wires on each side of the fracture. When using nonthreaded pins, vary the angle of insertion into the bone in case lateral traction is applied to the fixator. Form the connecting bar by bending the transcortical pins and joining them with epoxy putty in a ventrolateral plane compared to the tibiofibula. While bending the Kirschner wires, hold the insertion site of the pin with a wire twister applying counter pressure while bending the pin over with a second wire twister to avoid iatrogenic fracture of the bone.

Successful stabilization of a simple closed mid‐diaphysis femoral fracture with an internal fixator has been reported (Royal et al. 2007). Make a dorsolateral skin incision and dissect the underlying tissues with care to not damage the sciatic nerve. After approaching the fracture site, place at least two transcortical Kirschner wires on each side of the fracture. Place a threaded pin alongside the femur on its caudal surface and secure it to the femur with polyglyconate suture. Place cerclage wires as needed. Mold sterile polymethylmethacrylate (PMMA) over the threaded pin and the protruding transcortical pins to secure the apparatus. The PMMA device will remain internal and should not be too voluminous to close soft tissue without tension. Suture the muscular and cutaneous planes with monofilament suture. The advantage of this internal fixator is the amphibian can return in water quickly postoperatively.

      A surgical technique to stabilize the stifle joint was performed in an American bullfrog (Lithobates catesbeiana) after a suspected cranial cruciate ligament tear (Van Bonn 2009). A tourniquet was applied at the level of the proximal femur to reduce the risk of hemorrhage. A curved incision was made over the craniomedial aspect of the stifle joint. Two extraarticular 3‐0 monofilament nylon sutures were placed in a cruciate pattern along the cranial aspect of the joint capsule. The skin was closed with 5‐0 monofilament nylon in a Ford interlocking pattern which was removed two weeks postoperatively. The joint remained stable with no complication.

      A dorsal laminectomy was performed in a salamander to manage scoliosis (Waffa et al. 2012). Perform a 1.5 cm dorsal incision over the affected vertebrae. Use blunt and sharp dissection to expose dorsal spinous processes and laminae. Excise the dorsal laminae and facets with rongeurs. Lavage the surgical site with sterile saline. Place a hemostatic absorbable gelatin sponge (Gelfoam^®, Pfizer, New York, NY) over the laminectomy site. Close the incision with subcutaneous and subcuticular suture patterns. Unfortunately, three weeks postoperatively, the patient self‐mutilated caudal to the surgery site and was euthanized. Focal osteonecrosis and vertebral fractures at the laminectomy site were detected on post mortem examination. It is unknown whether the surgical technique or postoperative antinociceptive management should be modified to avoid this complication.

      Mandibular fractures can be stabilized with external coaptation using bone cement, orthopedic wire, an external skeletal fixator or by gluing the mouth closed with tissue adhesive for species with limited gular respiration (Wright and Whitaker 2001a). Bilateral mandibular fractures may be stabilized more efficiently by gluing the mouth closed and placing a feeding tube to provide nutrition. Placing and maintaining a feeding tube can be challenging in small amphibian species (Wright and Whitaker 2001a), and the prognosis is guarded in most amphibians with mandibular fractures.

Larval forms and neotenic amphibians have the ability to regenerate limbs (Pearl et al. 2008; Aguilar and Gardiner 2015) and even the spinal cord after complete transection (Diaz Quiroz et al. 2014). Thus, surgery may not be indicated in cases of traumatic amputation (Baitchman and Herman 2015). Limb, toe, and tail amputations are frequently performed (Figures 6.4 and 6.5) (Pizzi and Miller 2005) especially for very comminuted, articular, infected, or pathologic fractures (Dombrowski et al. 2016). It is advisable to amputate the limb proximally by disarticulation of the humerus or at the proximal third of the femur,