Abstract

Introduction

Degenerative joint disease (arthritis) occurs secondary to various disease processes such as trauma, infection, immune-mediated disease, and congenital abnormalities. Primary arthritis is uncommon in animals. Medical management of arthritis centers around the use of antiinflammatory medications to help decrease the pain associated with arthritis. Surgical management involves either an excision arthroplasty (such as femoral head and neck excision arthroplasty for hip dysplasia) or joint replacement using prosthetic implants. In human medicine, artificial joints are available for most joints including the digits. In veterinary medicine, joint replacement surgery has primarily involved the use of total hip replacement for the management of arthritis secondary to hip dysplasia in dogs. Other joint replacements have been used with limited success.

This report describes the use of a silastic human finger joint prosthesis for the management of severe degenerative joint disease in the hock of a Siberian crane (Grus leucogeranus).

Case Report

A 20-yr-old, 4-kg male Siberian crane was evaluated for severe degenerative joint disease of both tarsal joints. The bird was hatched from an imported egg at the International Crane Foundation in Baraboo, WI. The arthritis was progressive over a period of approximately 5 yr, involving first the tarsus of the right leg, and later the left tarsus was noted to be affected. Both joints were enlarged and firm on digital palpation. There was a 2x3 cm scab on the plantar surface of the right hock, apparently related to the bird hock sitting for extended periods of time. For 3 mo, the bird had been barely able to rise and stand, requiring its wings to balance itself while rising from a sternal position. As a result, the skin over both carpal joints was eroded. Treatment had consisted of 2 mg/kg methylprednisolone IM, as needed, for several weeks prior to presentation. Because of concerns regarding the potential effects of the glucocorticoid on wound healing, the methylprednisolone was discontinued 2 wk prior to presentation. The arthritis pain was then managed using butorphanol at 1.25 mg/kg IM as needed.

A preoperative CBC and plasma chemistry profile revealed an anemia (PCV=25%). Other values were within ISIS normal ranges. Radiographs of both tarsi showed severe degenerative joint disease with the right being slightly more severely affected than the left. A total hock joint replacement using a human silastic finger joint prosthesis (Wright Medical Technology, Arlington, TN, 901-867-9971) was performed on the right tarsus because it was clinically and radiographically most severely affected.

The crane was anesthetized with isoflurane in oxygen through an endotracheal tube and given 20 mg/kg cefazolin IV every 2 h during the procedure. A 20-cm incision was made along the cranial aspect of the distal tibiotarsus, across the tarsal joint and down the proximal tarsometatarsus. Care was taken to avoid major blood vessels. There was concern that significant vascular injury might result in avascular necrosis of the distal extremity. The joint capsule was very thick (approximately 1 cm) and numerous osteophytes were encountered. Large osteophytes were removed with rongeurs to allow access to the joint. Both medial and lateral collateral ligaments were elevated off their attachments to the tarsometatarsus to allow the joint to be opened enough to insert the bone saw. Extensor tendons were retracted rather than being transected. Stay sutures were placed in the common digital extensor tendon and it was incised. This tendon courses along the cranial aspect of the tarsus interfering with the saw used for the osteotomies. It passes through an osseous tunnel which prevents it from being retracted enough to expose the joint. At this point, the joint could be opened in a direction opposite to the normal flexion of the tarsus. This hyperextension allowed access to the distal tibiotarsus and proximal tarsometatarsus. An oscillating bone saw was used to cut the articular surfaces off the distal tibiotarsus and proximal tarsometatarsus leaving a 1-cm gap between the cut ends to accommodate the prosthesis.

The medullary canals of the proximal tarsometatarsus and the distal tibiotarsus were reamed with a broach manufactured to create a hole to precisely accept the stems of the prosthesis. The prosthesis was inserted and the joint flexed into a normal position. The tarsus was put through several flexion-extension cycles to ensure the prosthesis fit and functioned well. A Kirschner wire was used to create a small hole from cranial to caudal in both the lateral and medial aspects of the proximal tarsometatarsus. The collateral ligaments were secured to the proximal tarsometatarsus by passing 2-0 polypropylene suture through the collateral, through the hole, then exiting out the collateral ligament. The joint capsule was closed using 3-0 polydioxanone suture in a simple interrupted pattern. The common digital extensor tendon was repaired using 2-0 polypropylene in a three-loop pulley pattern. Subcutaneous tissue and skin were closed routinely. During recovery, a lateral thermoplastic splint was applied from the proximal tibiotarsus to the distal tarsometatarsus. A Doppler flow probe confirmed the presence of arterial perfusion of the digits. Recovery was uneventful.

The bird was given butorphanol at 1.25 mg/kg every 4–6 h postoperative for pain. The day after surgery, the foot was warm to the touch; however, the bird was not able to stand. A sling was created to keep the bird off the ground, but keep it from bearing weight. Physical therapy consisted of taking the bird out of the sling and encouraging controlled weight-bearing. On the third postoperative day, it was noted that there was external rotation at the tarsus. Ten days after surgery, the splint was removed and it was determined that the external rotation was a result of medial collateral instability. The splint was replaced in a manner to decrease tension on the medial aspect of the joint in an effort to encourage the insertion of the ligament to attach to the proximal tarsometatarsus. Eighteen days later, there was still medial instability and it was decided that surgical intervention was necessary.

An incision was made through the scar of the previous incision. The skin was elevated exposing the medial aspect of the joint. Tissues were bluntly dissected to expose the medial aspects of the distal tibiotarsus and proximal tarsometatarsus. A 3.5-mm bone screw was placed in the medial cortex of each bone. The screws were not placed through to the lateral cortex as they would have damaged the stems of the prosthesis. Nylon (60# test sterile fishing line) was passed in a figure eight pattern around the screws to reconstruct the medial collateral. The incision was closed routinely and the leg placed in a lateral splint again. Prior to closure, the site was cultured and the bird was placed on enrofloxacin at 10 mg/kg every 12 h. Aerobic and anaerobic cultures were negative.

One week after the second surgery, upper respiratory noises were observed and a CBC and plasma chemistry profile were evaluated. The crane had a WBC count of 35,200/mm³ with a mature heterophilia, lymphopenia, and monocytosis. Radiographs of the body were made and were within normal limits. A tracheal wash yielded no bacterial or fungal growth and normal cytology. Blood cultures were positive for an Enterococcus sp. During the examination it was determined that the medial joint compartment was again unstable. The bird was started on amoxicillin+clavulanic acid at 150 mg/kg and itraconazole at 10 mg/kg orally. One week later, a third surgery was performed in an effort to reconstruct the medial collateral ligament.

The screws placed during the previous surgery had failed resulting in laxity of the medial joint compartment. A Kirschner wire was used to create a hole from cranial to caudal in both the distal tibiotarsus and proximal tarsometatarsus. Nylon (60# test sterile fishing line) was passed through these holes in a figure eight pattern and tightened to stabilize the medial compartment. A transarticular external skeletal fixation device was placed to immobilize the hock joint allowing the medial collateral to heal without stress. Two pins were placed in both the tibiotarsus and tarsometatarsus. The site was cultured again and this time was positive for Enterococcus sp. which was sensitive to amoxicillin+clavulanic acid.

The bird was still maintained in a sling but was taken out three times daily for physical therapy consisting of walking with the body supported in a sling. After the fixator was applied, the crane was able to bear weight on the leg with the prosthesis, but was no longer able to bear weight on the left (unoperated) leg. Because of the bird’s inability to use the left leg and the protracted course of the recuperation, a poor prognosis was offered for regaining the ability to stand and walk again. Euthanasia was being considered when the crane was found dead in his enclosure.

Gross and microscopic evaluation fail to reveal a specific cause of death for this Siberian crane. He had moderate to severe muscle atrophy as well as hepatic lipidosis; however, his weight had maintained between 4–5 kg for the duration of his hospitalization.

Discussion

In the management of arthritis, surgery is indicated to eliminate pain by removing the articular surfaces of the bones involved and either allowing a pseudoarthrosis to form or implanting a prosthetic joint for a better functional outcome. Because of the endangered status of Siberian cranes, the long life span (up to 70 yr), and the value of this bird as a breeding animal, a joint replacement was considered. The advanced state of the degenerative joint disease was considered to be a contraindication for surgery, but a decision had been made to manage the bird medically until it was refractory to medical management. It is likely the outcome would have been better if the surgery were performed before both legs were severely arthritic. Following the surgery, this crane did not have a good leg on which to stand; consequently, the morbidity associated with managing a crane in a sling for an extended period of time became an issue.

Another factor in this case was the failure of the medial collateral repair. This resulted in severe external rotation at the tarsal joint and two additional surgeries were required to attempt to repair the medial collateral ligament. It appears the lateral splint did not provide adequate stability to allow the ligaments to heal appropriately. Based on this case, it would seem more appropriate to place a transarticular external fixation device during the initial joint replacement surgery as there does not appear to be a way to avoid damaging the collateral ligaments during the approach.

The prosthetic joint appeared to function well during range of motion physical therapy. Unlike the tarsal joint of mammals, that of birds is a simple hinge joint between the distal tibiotarsus and the proximal tarsometatarsus similar in size and function to a human interphalangeal joint. The collateral ligaments provide medial and lateral support. The digital extensor tendons course along the cranial aspect of the joint and the digital flexor tendons travel along the plantar surface of the joint. Blood supply is provided by a single artery (dorsal metatarsal artery) and a single vein (medial metatarsal vein). Damage to one or both of these vessels can result in avascular necrosis of the distal extremity. It would be ideal to be able to implant the prosthesis without damaging any ligaments, tendon, or blood vessels. Based on preoperative dissections using Siberian crane cadaver legs, the surgical approach used in this case appears to be the best for allowing the articular surfaces of the bones to be cut off with minimal damage to support structures. The prosthesis used in this crane was the largest finger joint prosthesis made.

The cause of the degenerative joint disease in this crane was not definitively determined. It was suspected to be due to a less aquatic captive environment than they live in naturally. It is thought that their buoyancy in water results in less impact on the tarsal joints, and when they are in a more dry environment the impact associated with walking results in cartilage damage over time and subsequent degenerative joint disease. This syndrome appears to be unique to Siberian cranes which are more aquatic in their natural habitat than most other species of cranes.