The anatomy of reptiles varies among orders, families, and species. A knowledge of the basic features of reptilian anatomy is therefore vital to surgeons.
Cardiovascular System - Chelonians and squamates are considered to have a 3 chambered heart because the ventricular septum is incomplete. Reptiles have 2 aortic arches that spiral on each other. The left aortic arch receives part of its blood from the oxygen-poor right ventricle and the right aortic arch mainly receives oxygenated blood from the left ventricle. Crocodilians are considered to have a 4 chambered heart, although the foramen of Panizza is present within the septum and allows some mixing of ventricular blood. Reptiles have a renal portal system that receives venous blood from the pelvis, the rear legs, and the caudal part of the abdomen. The system carries blood to the renal arterial circulation.
Digestive System - Except for most snakes, reptiles have a cecum. The stomach of crocodilians has 2 compartments. The first is very muscular and frequently contains stones. The second is similar to the glandular stomach of mammals. All reptiles have a gall bladder. The liver of many reptiles contains melanin and can have black spots or streaks. Reptiles generally have little subcutaneous fat and store fat in discrete masses (called fat bodies) in the caudal abdomen.
Urinary System - The metanephric kidneys of reptiles are lobulated. One or more renal arteries can be present to receive blood from the renal portal system. The nitrogenous wastes of reptiles are in the form of ammonia, urea, uric acid, or a combination of these. Crocodilians, snakes, and some lizards do not have a urinary bladder. In chelonians and those lizards with a bladder, it is connected to the cloaca by a short urethra. Urine passes into the cloaca and then into the urinary bladder, if present, or into the distal colon where water resorption occurs.
Cloaca - The cloaca typically consists of 3 chambers. The coprodeum is the most cranial and receives fecal material and urinary wastes. The urodeum is the middle section and receives genital secretions and urinary wastes from the urogenital ducts. The caudal proctodeum acts as a reservoir for fecal and urinary wastes before they are excreted. This is also the location of the openings of the musk glands.
Integument - The skin of reptiles is dry and virtually devoid of glands. Many lizards have femoral glands, which open on the medial aspects of the thighs. Crocodilians have a pair of scent glands in the medial aspects of the lower jaw and another pair within the cloaca. In proposing sites for incisions, these glandular areas should be avoided. The skin of most reptiles is made up of scales and scutes. Soft shelled turtles and some lizards do not have scales but have a leathery, smooth skin. Crocodilians and some lizards have calcific plates, called osteoderms, located within the dermis designed for protection. Incisions can usually be made between osteoderms. The shells of chelonians are composed of bony dermal plates covered with keratinized epidermal shields. The carapace contains 10 fused thoracic, lumbar, and sacral vertebrae as well as the ribs. The plastron and the carapace are joined at the so-called bridge.
Histologically, the epidermis is composed of 3 layers. The outer stratum corneum is heavily keratinized, acellular, and has a serrated surface. The middle intermediate zone is composed of daughter cells of the stratum germinativum in various stages of differentiation. These 3 layers are present during the skin's resting phase. As ecdysis begins, the cells of the stratum germinativum undergo synchronous mitosis to form a new intermediate zone and stratum corneum under the old generation. The action of enzymes breaks down the cells of the base of the old intermediate zone, and the subsequent influx of lymph causes separation between the old intermediate zone and the new stratum corneum. Blood vessels and sinuses in the head become engorged and cause it to swell. The old skin splits and ecdysis is completed by the animal rubbing off the old skin. In squamates, this process occurs simultaneously over the entire body. In chelonians and crocodilians, proliferation and keratinization are continuous and shedding occurs only at the flexible regions of the body. This produces growth rings between these scales as they grow and the previous, smaller layers are not lost. The frequency of ecdysis is proportional to the growth and metabolic rates of the animal. Age, environmental temperature, availability of food, and space can influence the frequency. In squamates, the cells of the epidermis are mitotically active only during ecdysis.
Skin wounds of reptiles undergo phases of healing similar to those observed in mammals. Wounds strengthen slowly and skin sutures are generally not removed until at least 4-6 wk. Many factors influence wound healing in reptiles. Maintenance of the environmental temperature at the high end of the optimum range promotes healing. In snakes, cranial to caudal wounds heal faster than dorsal to ventral wounds. Open wounds heal well by second intention with a low incidence of infection.
Ideally, laboratory data should be obtained before induction of anesthesia. Because of the small size of many patients and the inaccessibility of most peripheral veins, blood samples are often difficult to obtain. Environmental conditions, time of day, and laboratory variations can influence blood cell counts and biochemistry data making interpretation difficult. If blood samples can be obtained repeatedly, trends provide valuable information. The hydration and nutritional status of patients is assessed as it would be for mammalian patients. Balanced electrolyte solutions can be given IV or IP.
Reptiles are susceptible to a variety of microbial infections. It is imperative that aseptic technique be used. Many cutaneous infections result in septicemia and lead to visceral granuloma formation. Perioperative antibiotic therapy is more appropriate if intraoperative contamination is anticipated. It has been suggested that amikacin be used in snakes at a loading dose of 5 mg/kg followed by 2.5 mg/kg every 72 hr. Gentamicin at 2.5 mg/kg every 72 hr maintains adequate therapeutic plasma concentrations in gopher snakes and red eared slider turtles. In view of the long plasma half life of these antibiotics, one dose prior to surgery should provide perioperative coverage.
Patient positioning is a challenge especially for legless and small reptiles. For snakes, a sterile stockinette can be rolled over the surgically prepared patient. The snake can then be placed on a sterile drape providing an aseptic field. The dome shape of the carapace of chelonians makes it difficult to position a patient in dorsal recumbency. A towel can be rolled into a ring such that the carapace will fit into the ring and prevent the patient from rolling. Clear plastic adhesive drapes are very useful in reptiles. The entire patient remains visible under the sterile drape allowing for proper anesthetic monitoring. Sterile spray adhesives can also be used to allow paper or cloth drapes to stick to the patient avoiding the use of towel clamps.
With a few exceptions, the instruments needed for surgery on reptiles are found in a general surgical pack. Most abscesses in reptiles contain caseous, inspissated pus. Dental curettes and cerumen loops help in removing this material. Eyelid retractors work well as abdominal retractors for small patients. With most chelonians, some type of saw or drill is needed to approach the coelomic cavity and a restorative material should be available for repair of shell defects and celiotomies.
The edges of incised reptilian skin have a tendency to invert. An everting suture pattern, such as a horizontal or vertical mattress, achieves accurate skin edge apposition. The relatively tough reptile skin and scales help prevent sutures from tearing through. The break down of absorbable materials appears to be prolonged in reptiles and if used in the skin, removal is recommended after the incision has healed. Chromic catgut was still present in a rhinoceros viper 12 weeks after the material was used in the pleuroperitoneum and SQ tissue. It appears to be best to use materials which are absorbed by hydrolysis rather than proteolysis in reptiles. In squamates, suture removal should be performed after the ecdysis subsequent to surgery. The shed skin usually sticks in the sutured area for several ecdyses postoperatively, but can be gently peeled away.
Anesthetic recovery in reptiles can be prolonged and difficult to monitor. Increasing the environmental temperature to the upper end of the optimal range (30-36o C) will increase the rate of metabolism of anesthetic agents. Once the patient is awake and responsive, it should be placed in a warm, dark, quiet place to complete its recovery. Clean paper should be provided in the recovery area to prevent contamination. Hibernation should be delayed for at least 6 mo as it delays healing. Swimming should be prevented for 7-14 days after surgery. Fluid therapy may be administered IV or IP as needed to maintain hydration. Many reptiles become anorectic after surgery. Force feeding or tube feeding might be necessary.
Indications for celiotomy in reptiles include egg binding, egg peritonitis, gastrointestinal obstruction, ovariohysterectomy, colopexy for colon prolapse, cystotomy for calculi, and exploration for biopsy. The technique varies depending on the family to which the patient belongs.
In snakes, abdominal incisions can be made at the lateral margin of the scutes or between the first 2 rows of lateral scales. Incisions should be made between rather than through scales if possible. The tips of the ribs should be avoided at the junction of the scutes and scales. The lateral approach is generally preferred over a ventral midline approach as it is easier to keep clean. The suture line is not in direct contact with the substrate and is not stressed by rectilinear motion. Three layers are encountered: skin, muscle, and pleuroperitoneum. When separate layers are not identifiable, a single-layer closure is adequate.
Paralumbar and midline incisions have been recommended for approaching the coelomic cavity of lizards and crocodilians. The ventral abdominal vein is a very large vein located inside the body wall on the ventral midline. It should be avoided during celiotomy by using a paramedian approach.
In chelonians with a small plastron, the majority of abdominal structures can be approached through an incision between the plastron and the femur in the flank region. In other chelonians it is necessary to perform an osteotomy of the plastron. The pelvic bones should be avoided and can be identified using radiography. Usually the femoral and abdominal shields are osteotomized for the approach. A high-speed burr or an orthopedic saw is used to cut the plastron. Irrigation is used to dissipate heat and to remove dust. The bone is elevated from the underlying abdominal musculature using a periosteal elevator. The incision into the abdominal wall can be performed using a flap technique or a ventral midline incision. There are venous sinuses on each side of the midline approximately midway between the midline and the bridge. These sinuses should be avoided but can be ligated if necessary. The bone is replaced using restorative material as is described below.
Small defects or cracks in the shell of chelonians can be maintained in reduction with wires, external bandages, or acrylic materials. Acrylic materials, such as those used for hoof reconstruction and dental repairs, can be used to hold fragments in apposition. The fracture should be maintained in reduction for 3-7 days without exposure to water so that a seal can form. The fixation should not be removed until there is radiographic evidence of union. Large defects should be repaired using prostheses. Various restorative materials have been used, including hoof or dental acrylics, boat or auto body fiberglass, and epoxy resin. Patches of fiberglass cloth can be autoclaved. The fiberglass provides a matrix to enable the resin to bridge the defect. The patch should be large enough to extend beyond the margin of the defect. The shell should be cleaned with acetone, ether, or similar degreaser. During application, care must be taken to keep epoxy from the edge of the defect as its presence will delay healing. The fiberglass patch is stretched over the defect and held in place, allowing the resin to penetrate the cloth and bond to the shell surface. When this layer has cured, a light coat of epoxy is applied to the fiberglass cloth over the defect. After this layer has cured, several more thin layers of epoxy should be applied to strengthen and seal the defect.
If a large fragment is to be replaced, as in the case of closing a celiotomy, the piece should be bonded to the center of the cloth patch with epoxy before the patch is applied to the defect. Healing of bone in reptiles takes at least 6-18 mo. In growing chelonians, the patch should be removed from the growth rings after healing is complete to allow the shell to continue to grow. Epoxy dust can be toxic and carcinogenic to humans. Copious irrigation should be used to prevent aerosolization, and a face mask should be worn.
Clinical signs of dystocia include anorexia, regurgitation, straining, cloacal discharge that is often malodorous, paresis, respiratory distress, and edema of the cranial extremities. Noninvasive procedures should be attempted before surgical intervention. Intramuscular oxytocin at 1-10 IU/kg and IM or SQ 1% calcium borogluconate at 10 ml/kg have been successful to relieve dystocia when manipulation was not. In species that produce soft and leathery eggs, percutaneous ovocentesis can collapse the eggs and allow them to pass more easily. Salpingotomy is indicated if noninvasive techniques fail or if there is radiographic evidence that natural passage is not possible. In snakes, it might be necessary to make more than one incision to access all eggs or fetuses. The incision in the salpinx and uterus should be repaired with an inverting suture pattern of an absorbable material. Salpingohysterectomy should be considered if dystocia recurs, if the patient is not being maintained for breeding purposes, or if bacterial salpingitis is present. The ovaries of many reptiles are not pedunculated making them difficult to remove. Removal of the ovaries may not be necessary. During salpingohysterectomy the oviduct should be pulled free from the ovary and the uterus should be ligated as close to the cloaca as possible.
The presence of egg yolk within the coelomic cavity produces severe inflammation. Fibrin deposition and serosal thickening are typical. Surgical removal of the yolk material and lavage are indicated, however, the prognosis in such cases is grave.
Cloacal Organ Prolapse
The cloaca has openings from the colon, uterus, urinary bladder, and reproductive tract. Ureteral prolapse has not been reported in reptiles.
Squamates have paired copulatory organs called hemipenes which lie inverted within the tail. Chelonians have a single penis which is everted during copulation. Although prolapse of the penis or hemipenes has been reported as a sequel to constipation and neurological dysfunction, it is most frequently the result of infection, forced separation during copulation, or swelling secondary to probing for sex determination. The organ should be cleaned, gently lubricated and replaced. A purse string suture is placed in the cloaca tight enough to prevent prolapse but to allow voiding. The suture should be left in place for 3-4 weeks. If the prolapse cannot be reduced, the cloacal opening can be enlarged by incision. Surgery is indicated in cases in which the organ is severely swollen and damaged. Amputation is performed after mattress sutures are placed at the base of the organ to prevent hemorrhage. Snakes and lizards with one hemipenis are considered fertile.
Prolapse of the uterus is rare but does occur. Replacement should be attempted. If reduction is not possible, celiotomy and salpingohysterectomy should be considered.
Colon prolapse can result from straining because of constipation or bacterial or parasitic enteritis. Conservative management should be attempted before surgical therapy. Often colon prolapse is reducible and successfully managed by treating the primary cause while maintaining a purse-string suture in the cloaca. Frequently the venous return from the prolapsed colon is severely compromised and it becomes engorged and friable. Celiotomy and colopexy are recommended in such cases. An area of healthy colon should be selected and sutured to the body wall. If the colon is severely compromised, it can be resected and anastomosis can be performed.
Principles of gastrointestinal surgery in reptiles are similar to those in mammals. The intestines of most reptiles are thin walled, and the use of fine sutures and an atraumatic needle is recommended. Such sutures as polydioxanone are strong and maintain their tensile strength for several months in mammals which can be advantageous in slow healing reptiles. If the affected section cannot be adequately exteriorized, it should be well packed off before enterotomy. Copious coelomic lavage with saline should be performed before closure.
Cystic calculi can occur in those reptiles with a bladder but desert tortoises seem to have the highest incidence. Clinical signs associated with cystic calculi are nonspecific and include anorexia, lethargy, and depression. The urinary bladder is generally very mobile within the coelomic cavity and is easily isolated during surgery. A 2 layer closure using an inverting pattern of absorbable suture is preferred.
Long bone fractures in reptiles are usually the result of trauma or metabolic bone disease. Most fractures occur after relatively low impact trauma making the incidence of comminuted fractures low and because most reptiles have tough skin they are usually not open fractures. Little information is available regarding bone healing in reptiles; however, it appears that it occurs at a significantly slower rate compared with birds and mammals. Healing time for traumatic fractures is generally 6-18 mo. Pathologic fractures from nutritional secondary hyperparathyroidism seem to heal much quicker (6-8 wk).
General principles of fracture fixation apply to reptile patients - rigid stabilization and anatomic alignment with minimal disruption of callus and soft tissues. Many factors must be considered when deciding on the method of fixation to be used. The forces exerted on the fracture (bending, compression, rotation, and shear) must be neutralized to promote healing. The more forces that must be neutralized by the fixation, the higher the incidence of complications and failure. Practical consideration include the cost of the materials, ease of application, availability of equipment, and the surgeon's level of experience with various fixation devices. In many cases some degree of malalignment may be acceptable. The patient's size and conformation may influence the type of device used and how it is applied. The patient's metabolic status may preclude a surgical procedure for orthopedic repair. Finally, financial concerns are often the major factor to be considered.
External coaptation involves the use of splints, slings, and other bandages. This is probably the most commonly used method of fixation in reptile orthopedics because it is simple, requires little equipment, takes only a short time to apply and a brief anesthesia period, and generally is the least expensive. Additionally, when dealing with pathologic fractures secondary to metabolic bone disease, external coaptation is usually the treatment of choice.
These fractures are difficult to stabilize using internal fixation because the bone is too soft to support implants. Steinmann pins frequently do not stay within the medullary canal. When inserted, if they contact a cortex, they penetrate the cortex instead of "bouncing off" and continuing down the canal. Cerclage, hemicerclage, and interfragmentary wires collapse the soft bone. Bone screws have minimal resistance to pull out when placed in such soft bone. Similarly, external skeletal fixation does not function well due to the limited ability of the fixation pins to gain purchase in the bone. In some cases, with careful placement, IM pins may be used to provide axial alignment and some bending stability; however, external coaptation should be applied in addition to the pin as cortical purchase will be minimal. Fortunately, once the patient's calcium homeostasis has been reestablished, fracture healing progresses rapidly with a fibrous union providing stability as early as 3-4 wk.
A wide variety of splinting and casting techniques have been used successfully. Anesthesia is recommended during the application of external coaptation. All forms of external coaptation should be monitored closely for signs of vascular compromise, soiling, slippage, or other problems which may require splint replacement. Soft, conforming cast padding (Specialist Cast Padding, Johnson & Johnson, New Brunswick, NJ; Webril, Kendall Co., Boston, MA) and conforming roll gauze (Conform, Kendall Co., Boston, MA) work well for the initial padding layers. These materials should be cut to an appropriate width for the size of the patient. Using a roll that is too wide will result in a lumpy bandage. The bandage may be reinforced with wood applicator sticks, tongue depressors, aluminum rod, light weight casting material, or other substance that will add bending stability. Most of these do not conform to the normal angles of a reptile limb. Orthoplast (Johnson & Johnson, New Brunswick, NJ) and Hexcelite (Hexcel Medical, Dublin, CA) are firm at room temperature but when heated in water become malleable. This allows the material to conform closely to the configuration of the limb. Orthoplast is a solid sheet while Hexcelite is a webbing available in roll or sheet form. The Hexcelite is much easier to conform but is not as rigid when cool.
Tubular traction splints may be used to treat fractures of the crus, antebrachium, distal humerus, and distal femur. A tube such as a syringe case of a diameter appropriate to the size of the patient's limb is padded at its proximal end which will be tightly pushed into the inguinal or axillary region. Tape stirrups are applied to the limb and secured to it. Padding is added to the limb to limit movement within the tube. The tape is then pulled through the tube such that the padded end is forced into the inguinal/axillary area and the limb is in traction. The tape is secured to the outside of the tube maintaining the leg in extension and traction. The disadvantage of this type of splint is that it maintains the limb in complete extension predisposing to fracture disease.
The bone involved and the conformation of the patient will influence the type of coaptation used. For example, it would not be possible to stabilize a humerus fracture in a chelonian with a traditional splint as the joint proximal to the fracture would not be immobilized. In chelonians with a fractured humerus or femur, the limb may be folded into the cavity created between the plastron and the carapace and taped in place preventing movement. Unfortunately, this does not address fracture alignment. In lacerta, fractures of the humerus or femur may be stabilized with a modified spica splint which will cross over the pelvic or pectoral girdle to the opposite limb, thereby stabilizing the hip or shoulder joint1. Most lacerta stand relatively flat and use abdominal undulation as an aid to locomotion allowing them the ability to ambulate even with this type of device. With fractures of the pelvic limb the splint crosses dorsally to allow normal voiding, while with fractures of the pelvic limb the splint crosses ventrally.
All methods for internal fracture fixation have been used successfully in reptiles. Bone plating requires a relatively large patient; however, with the recent availability of the veterinary cuttable plates (Synthes, Paoli, PA) with screws as small as 1.5 mm diameter (1.1 mm core diameter) bones as small as 3 mm diameter may be plated. Of course, bone plating is expensive and requires specific expertise. This is often the treatment of choice for stabilizing femur and humerus fractures in chelonians.
External skeletal fixation (ESF) may be used for stabilizing a variety of fractures in reptiles. In fracture management with ESF pin loosening will occur for a variety of reasons. Their success relies on the ability of the bone to heal before the fixation pins loosen and the device fails. Because reptile bones heal slowly, the pins may loosen before the fracture is stable. Pin purchase can be maximized by using threaded pins (preferably with the threads applied onto the pin, not cut into it) and inserting the fixation pins at the proper angle. Biphasic ESF devices use various size Kirschner wires, Steinmann pins, or hypodermic needles as fixation pins but the connecting bar and clamps are replaced by acrylic polymer or other rigid material. ESF may be used in very small patients. These devices provide good stability without interfering with joints. They are most often applied in a cranial to caudal plane in reptiles rather than a medial to lateral plane as in mammals.
Intramedullary Steinmann pins and orthopedic wires are very familiar to most veterinarians. They are inexpensive, provide axial alignment and bending stability, and require minimal tissue exposure for insertion. Kirschner wires are available in sizes as small as 0.028 in. Spinal needles are available as small as 25 ga x 3.5 in and may be used as IM pins.
Limb amputation in snakes will not be discussed. In most animals it is recommended that amputation be performed as proximal as possible to prevent the patient from traumatizing the stump on their substrate. Most reptiles have very tough skin which is resistant to such trauma. Their scar tissue, however, is delicate and easily abraded. Further, because most lacerta stand flat even a short stump may aid in locomotion. When a limb must be amputated in a lizard, if the patient may be able to use the stump, it should be amputated as far distal as possible. The skin should be incised to create a flap of skin on the ventral surface which will be placed over the end of the stump and sutured dorsally. This will place healthy, normal skin in contact with the substrate and the incision/scar tissue dorsal and lateral. The end of the bone should be padded with viable soft tissues prior to skin closure.
In chelonians, it is best to amputate as proximal as possible as they are more upright and more likely to traumatize their stump. A prosthesis may be provided by securing a wood block on the plastron ventral to the shoulder or hip joint. The block can be secured using an acrylic cement. This will elevate the affected corner of the shell allowing easier ambulation.
1. Jenkins JR: A coaptive device for repair of fractures in the Iguana. J Sm Exotic Anim Med 1(4): 154-155, 1992.
2. Bennett RA. 1989. Reptilian surgery, parts I and II. Comp Cont Ed Pract Vet, vol 11 (1 & 2).
3. Bennett RA. 1996. Fracture management. In: Mader D (ed), Reptile Medicine and Surgery, Philadelphia, WB Saunders Co. Pp 281-287.
4. Bennett RA, Mader D. 1996. Soft tissue surgery, In: Mader D (ed), Reptile Medicine and Surgery, Philadelphia, WB Saunders Co. Pp 287-289.
5. Bennett RA. 1996. Cloacal prolapse. In: Mader D (ed), Reptile Medicine and Surgery, Philadelphia, WB Saunders Co. Pp 335-359.