Avian Orthopedics

As avian veterinarians, we are often called upon to treat avian orthopedic problems. Some occur as the result of trauma (ceiling fan injuries, flying into a window or mirror, or getting stepped on), others occur from nutritional imbalances, and others may occur as a result of genetic or developmental problems. Fortunately, our training in mammalian orthopedics will give us a good base for approaching correction of orthopedic problems, as the main principles are the same. Most of the orthopedic techniques developed for mammals can be applied to birds, taking into account the anatomical differences in avian species, and whether or not the bird can have flight restored.

Anatomy and Physiology

The bones of flighted birds are unique in that they have evolved some pneumatic bones that are hollow and contribute to the bird being light enough to fly. The bones of the pelvic girdle, some ribs, the humerus and the femur all are pneumatic, and contain large air-filled medullary canals that are involved with the respiratory cycle during flight. The bones of birds are relatively brittle and have thin cortices. They also contain more calcium than mammalian bone, which tends to make them more brittle and prone to developing multiple fractures at one site. The distal portion of the leg, below the tibiotarsus, has very little soft tissue covering bone, and the proximal half of the humerus also has little soft tissue covering bone, so fractures in these areas are often open and comminuted. When a pneumatic bone is fractured, often subcutaneous emphysema occurs, but it usually resolves within a day, without treatment.

Avian orthopedic techniques have advanced remarkably over the last years. Orthopedic techniques developed for other species have all been proved to be applicable in avian fracture stabilization. The principles of fracture stabilization are the same as those defined for mammals. Deciding on a method of fracture repair will depend on several factors, including what the bird's function will be. Wild birds destined to be released must be able to fly, catch prey and perch normally. Breeder birds must have enough limb function to successfully copulate. Pet birds may do well after limb amputation as a salvage procedure.

Primary or secondary bone healing may occur. Primary bone healing can occur with rigid stabilization and minimal fracture gap, however most avian fractures heal by secondary or callus healing. This occurs because of larger fracture gaps or micromotion across the fracture site. Endosteal callus production provides major and early support for fracture healing.

Avian bones usually heal faster than mammalian bones. Simple, closed fractures, such as a midshaft tibiotarsal fracture, when properly splinted, will be clinically stable within two to three weeks, however a callus may not be visible radiographically for three to six weeks. If a fracture site feels stable on palpation, it may be advisable to remove fixation devices, if warranted, even if a callus is not visible on radiographs.

Non-unions may occur in birds, and the principles for treatment are the same as for mammals. Other complications may interfere with healing, including osteomyelitis. Birds with osteomyelitis may not show clinical signs of systemic disease, however, the white blood cell count is usually elevated. Non-unions may benefit from autogenous bone grafting.

Methods of Fracture Repair

There are many factors to consider when choosing a method of fixation to repair a fracture. The patient's role (pet, breeder, wild bird), the function required of the injured limb, the type of injury, the location of the injury and the age and weight of the bird all should be considered when choosing a method of repair. The anatomy of the injured area should be studied, including review of the surgical approaches, with special attention paid to the arteries, veins, nerves, tendons, ligaments and muscles in the area. Fractures to the wing require special attention, as flight feathers are attached to the periosteum of the ulna and major metacarpus. If the periosteum is elevated during surgical manipulation, the follicles may become damaged, resulting in deformed feathers or feather cysts.

Pneumatic bones require special care, as well. During surgery, it is very important that no fluid be allowed to enter the proximal fracture segment, as this may result in aspiration pneumonia, air sacculitis or asphyxiation.

If there is any evidence of injury to the skin near a fracture site, the fracture should be considered open, even if no evidence of infection is present.

Young birds may be presented with healing or healed folding fractures as a result of nutritional deficiencies, most commonly metabolic bone disease. This is most often observed in African grey parrot babies, Psittacus erithacus erithacus, that are from the second, third or fourth clutches of the breeding season. If the hen is on a nutritionally marginal diet, she will become depleted of her calcium stores in her bones, and will be unable to pass adequate calcium to her eggs. As these baby birds grow, their leg bones will not be able to support their body weight and folding fractures and bowing of long bones may occur. If a baby bird tries to support itself partially by leaning on a wing, the wing may also become deformed. Healed fractures in baby birds may be better off left alone, as significant bone remodeling may occur as weight bearing occurs, and the leg may be quite functional as is. If tendons are incorporated into the callus, some loss of mobility of joints distal to the fracture may occur. However, attempting surgical correction in these cases is often unrewarding and is unlikely to restore normal mobility. Young, rapidly growing baby birds heal very quickly, regardless of the method of fixation employed.

External Coaptation

The use of bandages, splints or slings often work well for fracture fixation, and is the least expensive way to stabilize fractures. Splints work very well for tibiotarsal fractures in birds that weigh less than 200 grams, and are particularly well suited to stabilize fractures in small birds where tiny bones make internal fixation almost impossible. Splints also are indicated to stabilize fractures due to metabolic bone disease, since soft bone may not hold internal fixation devices. Splints can also be used when the risk of anesthesia or surgical correction is too great, in certain cases.

Splints can often be applied using manual restraint, if the bones do not need to be manipulated extensively, although general anesthesia will allow for greater muscle relaxation and will prevent pain sensation.

The different techniques for splinting bones of the pelvic and thoracic girdles have been well described in the avian literature. As in other species, the joints above and below the fracture must be immobilized for adequate stabilization. White cloth tape works well for tibiotarsus fractures, however since the hip joint cannot be immobilized adequately, splints are ineffective for femoral fractures. In small birds, less than 200 grams, tape alone, crimped after application with a hemostat along the caudal surface, will be sufficient to immobilize fractures. Larger birds will benefit by having wooden applicator sticks, tongue depressors, aluminum rods or other material incorporated into the splint to add support. SAM splints also work well to make a strong, lightweight support to immobilize fractures. Splints must be as light in weight as possible. White tape can be used to immobilize the entire wing, so tape splints work very well for most fractures of the thoracic limb, especially in the smaller birds. By immobilizing the wing in its normal anatomical resting position, the bones will usually be pulled into proper alignment, resulting in adequate healing for most pet birds. Care must be taken when applying a splint to the body to immobilize the wings, as the bandage must not prevent normal respiration, nor can it impede normal crop function.

The use of splints may result in poor alignment, joint ankylosis, tendon contracture or entrapment within the callus or shortening of the bone may occur. For pet birds, splinting will often result in adequate fracture repair for those sites amenable to external coaptation.

Internal Fixation

When function is of utmost importance, internal fixation will provide the best chance for proper anatomic alignment. Internal fixation requires general anesthesia, so the patient must be stabilized, hydrated and able to withstand the procedures.

Intramedullary pins are the most common type of internal fixation. Pins do not counteract rotational forces or shear forces, and the cortices of avian bones are quite thin so they don't provide much purchase to hold IM pins. Additional methods of internal fixation may be utilized in addition to the IM pin to help counteract rotation and shear forces. Cerclage and hemicerclage wires, external fixators or stack pinning may all be employed. Cross pins may be used to stabilize metaphyseal fractures.

Orthopedic wires may be used, especially in small birds, however, they must not be used as a sole method of fixation because they are not stable against bending forces.

In place of stainless steel IM pins, other materials have been utilized. Polydioxanone (PDS) pins are absorbable and have been used to stabilize fractures in birds. External coaptation is recommended as an adjunct method of support, because the PDS pins are not as rigid as stainless steel pins. One advantage to PDS pins is that they do not need to be removed. Polypropylene welding rods are also used in place of stainless steel IM pins. These rods are very inexpensive, easy to sterilize in an autoclave, are biologically inactive and are lighter than stainless steel pins. However, they only are available in larger diameters, so they cannot be used in very small patients (less than 75 grams). As with PDS pins, they are not as rigid as stainless steel, and micromotion at the fracture site usually occurs, so additional methods of fixation may also be required. These pins are usually inserted via shuttle techniques. To assist in providing rotational stability when using pins, Kirschner wires, small pins, or external fixators may be added, and intramedullary polymethylmethacrylate (PMM) may be used to fill the medullary interstices.

The shuttle technique requires more skill than that needed in placing IM pins. To employ the shuttle technique, a hole is drilled into the center of the rod once the rod has been cut to size, using a small K wire or hypodermic needle. Suture material is passed through the hole and the rod is then inserted into the longer segment of the fractured bone. Traction is then applied to the suture to pull the rod into the shorter segment. Threaded stainless steel IM pins can be used as shuttle pins when the rigidity of steel is required.

Polymethylmethacrylate bone cement can be used alone for fracture stabilization or in concert with other methods of internal fixation. Strict asepsis must be followed when using PMM because once placed into the medullary canal, it cannot be removed. If osteomyelitis develops, it can act as a nidus of infection. For this reason, the addition of cephalothin to the PMM mixture is recommended.

External Skeletal Fixation (ESF)

The Kirschner-Ehmer splint is the most well known ESF, however, many types of K-E type biphasic fixators have been devised, using acrylic cement columns in place of the stainless steel connecting bars and clamps utilized by the Kirschner-Ehmer splint. K-wires, Steinmann pins, hypodermic needles, spinal needles, threaded fixation pins and half-pins have all been employed to transect both cortices of the fractured segments of bone. ESF devices are usually well tolerated by birds, and do not interfere with joint function, which allows for early return to function. This is very important, especially in birds that are destined to be released back to the wild. Latex tubing, drinking straws and Penrose drains may be used to hold pins in place. The hollow tubes are filled with non-sterile PMM or dental acrylic cement, and the pins are stabilized once the cement has cured. Hexcelite or epoxy resin may also be used for the connecting system, especially in small birds. K-wires can also be used for the connecting system, with each fixation pin glued to the K-wire connecting bar, using epoxy.

According to Dr. Susan Orosz, an avian specialist at the University of Tennessee, who will be teaching an advanced MasterClass on orthopedics at the Association of Avian Veterinarians Annual Conference and Expo in August with Dr. Pat Reddig, of the Raptor Center, Dr. Reddig has been refining and developing new techniques to repair wing fractures in wild raptors, to best return full function. When an injured bird of prey is presented, once the bird is hydrated, stabilized and treated appropriately for the injuries, he will apply a K-E type apparatus as soon as possible. This prevents contracture of the muscles and maintains the proper bone length. When the humerus is fractured the biceps and triceps muscles contract, which can severely complicate surgical correction. By applying an external fixator as soon as possible, the chance of a wild bird returning to full functional flight is greater. In addition to applying a K-E type external fixator as quickly as possible, Dr. Reddig has developed a tie-in procedure that incorporates the IM pin into the K-E type apparatus. After approximately five days (depending on the individual bird's injuries), Dr. Reddig will insert a stainless steel IM pin into the fractured bone, bending it to become one of the K-wires used in the connecting bar. This provides additional rotational stability to the fracture site. As healing occurs, portions of the apparatus are removed, so that physical therapy can begin as soon as possible. In all cases of bone repair, especially when restoring function is imperative, physical therapy is a very important part of the recovery process. Early physical therapy means that there is less chance of joint mobility loss. The sooner a bird can begin using an injured wing, the greater the chance of successful return to function, which keeps joints flexing and extending through the full range of motion.

Bone plates can be used in birds, and are best utilized to repair fractures in ratites or the larger flighted birds. Screws used in conjunction with plates must be inserted in a different manner than that used in mammals, due to the thin cortices of avian bone. IM PPM may be used to improve screw purchase in the bone. Some form of external coaptation must be used for at least 24 hours after bone plate application to help reduce soft tissue swelling. Plates need not be removed.

The Doyle technique was developed to apply compression pressure at the fracture site, which aids in bone healing. This technique combines IM support of the Rush technique with external fixation. Dental impact rubber bands are used to apply compression at the fracture site and to improve rotational stability. This is a lighter system than traditional ESF devices, as K-wires are adequate for most avian fractures. This technique can also be applied to repair of the beak and fractures of the mandible, when combined with acrylics.

Luxations

Luxations usually occur as the result of trauma, and coxofemoral luxations are one of the more commonly seen injuries. Elbow luxations usually occur in raptors from trauma during flight. To successfully correct a luxation, reduction should take place as quickly as possible to minimize the formation of periarticular fibrosis.

Limb Deformities

Baby birds may develop spraddle or splay leg. This may occur as a result of parents sitting too tightly on the babies, from inadequate substrate in the nestbox or brooder or as a result of genetic or nutritional problems. As soon as a problem is discovered, correction should be attempted. Small, heavy bodied babies, such as rose-breasted cockatoos, tend to develop spraddle leg, and should be placed in a small, deep container that will keep the legs underneath the baby. Hobbles, foam saddles, braces, splints and other methods of support may be employed to correct splay legs. Placing the baby in a deep cup with a rough surface that allows a foot hold is important. In some cases, the digital flexor tendons may be displaced, and correction of these cases is more challenging. Osteotomies may be used in some cases to correct angular bone deformities.

Beak Repair

Birds may suffer from traumatic injury to the beak and underlying structures, or they may develop mandibular prognathism or lateral deviation of the rhinotheca (scissors beak), which may be congenital defects. The application of rhamphorthotic devices, using wire mesh, wires and dental acrylic may be used to redirect the growth of abnormal beaks. Mandibular fractures may be repaired using stainless steel wires, mesh splints or dental acrylic. These fractures are difficult to manage, as osteomyelitis, non-union, tissue avulsion or avascular necrosis may occur.

Physical Therapy

Regardless of the method of repair employed, it is very important that the avian patient begin some type of physical therapy as soon as possible, to prevent joints from freezing and loss of range of motion. When a bird is to be re-released into the wild, the sooner that some exercise can be begun, the better.

Pain Management

There is no doubt that birds that have suffered bone or joint injuries will be suffering from some degree of pain. The use of non-steroidal anti-inflammatories or opiods should be considered routine therapy both pre-operatively and post-op, for the well being of the patient. For severe pain, morphine or hydrocodone can be used, and for moderate pain, butorphanol has proved effective.

Conclusions

Avian orthopedics present a unique challenge to the avian practitioner, but with a good knowledge of bone repair techniques in mammals and an understanding of the anatomical and physiological differences in avian patients, repairs can be rewarding and successful.

Cadeusus
Copyright 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
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