An 11-month-old 8.5-kg (18.7-lb) sexually intact male red kangaroo (Macropus rufus) was examined because of a left forelimb fracture sustained 4 hours earlier when the animal became entangled in new fencing that had recently been placed around its enclosure. Previously, the kangaroo had been healthy and raised in captivity since leaving the pouch.
On examination, the kangaroo was ambulatory with its hind limbs and tail and was slightly thin. There was a visually apparent open fracture of the left antebrachium (Gustilo-Anderson grade 21) just distal to the elbow joint. Palpation of the right forelimb revealed obvious instability of the antebrachium, with fractures in the proximal aspects of the radius and ulna. There were no neurologic deficits affecting either forelimb, and results of the remainder of the physical examination was unremarkable. Antimicrobial treatment with enrofloxacin (8.0 mg/kg [3.6 mg/lb], PO, q 24 h) was started, and the kangaroo was sedated with buprenorphine hydrochloride (0.010 mg/kg [0.005 mg/lb], IM), dexmedetomidine (20.0 μg/kg [9.1 mg/lb], IM), and ketamine hydrochloride (4.0 mg/kg [1.8 mg/lb], IM) for wound care and radiography.
Orthogonal radiographs of both antebrachii were obtained, and findings confirmed short oblique fractures of the proximal aspects of both radii and ulnae and indicated mild comminution of the left ulnar fracture (Figure 1). Bone fragments were overriding and moderately displaced, caudolaterally in the left forelimb and caudomedially in the right forelimb. Wider than expected gaps were noted in the humeroulnar and humeroradial joints bilaterally. The importance of these radiographic findings in the elbow joints of such a young red kangaroo was unknown; possibilities included clinically normal development, bilateral elbow joint incongruity, or, less likely, bilateral traumatic luxation.
Mediolateral (A and C) and craniocaudal (B and D) radiographic images of the left (A and B) and right (C and D) antebrachia of a sedated 11-month-old 8.5-kg (18.7-lb) sexually intact male red kangaroo (Macropus rufus) examined because of a left forelimb open fracture sustained 8 hours earlier when the animal became entangled in new fencing placed around its enclosure. Bilaterally, the radii (long arrows; A through D) and ulnae (short arrows; A through D) have short oblique fractures that are overriding and moderately displaced, wider gaps than expected appear at the humeroradial and humeroulnar joints (arrowheads; A through D), and there is no evidence of proximal radial physes.
Citation: Journal of the American Veterinary Medical Association 255, 8; 10.2460/javma.255.8.942
The proximal radial physes were interpreted as being closed because neither was radiographically evident.
The open fracture wound in the left forelimb was lavaged with sterile saline (0.9% NaCl) solution, and a sterile dressing was secured. The forelimb fractures were stabilized with splints (a lateral splint placed on the left and a bivalved cast of polyurethane resin impregnated fiberglass tape on the right), and surgical stabilization was recommended to facilitate a prompt return to function. Administration of meloxicam (0.1 mg/kg [0.05 mg/lb], PO, q 24 h) for analgesia was initiated, and vaccinationa against tetanus and enterotoxemia was recommended but declined by the owner.
The kangaroo was hospitalized overnight in preparation for surgical stabilization of the fractures the following day. Food, but not water, was withheld overnight.
On the day of surgery, the kangaroo was pre-medicated with midazolam hydrochloride (0.4 mg/kg [0.18 mg/lb], IM) and methadone hydrochloride (0.5 mg/kg [0.23 mg/lb], IM). Afterward, general anesthesia was induced with alfaxalone (5 mg/kg [2.3 mg/lb], IV to effect), the kangaroo was intubated, and general anesthesia was maintained with isoflurane delivered in oxygen. A standard hanging limb preparation was performed on each forelimb with the kangaroo in dorsal recumbency.
In the left forelimb, a craniolateral approach to the radius and ulna centered over the fractures was made between the common digital extensor and the extensor carpi radialis muscles. An open but do-not-touch approach was elected, and the fracture hematoma was maintained. The left radial fracture was reduced and stabilized with a 6-hole 2.0-mm locking compression plate on the cranial surface of the bone, with 2 locking screws proximal to the fracture and 4 distal to it (Figure 2). The left ulnar fracture had reduced indirectly during reduction and stabilization of the radial fracture, and a 7-hole, 2.0-mm, limited-contact dynamic compression plate was placed on the lateral surface of the ulna, with 4 cortical screws proximal to the fracture and 3 distal to it. During reduction of the left radial fracture, a dynamic luxation of the radial head was noted. Therefore, the initial surgical incision was extended proximally, and a positional screw was placed across the radius and ulna just distal to the elbow joint articulation. There was no gross evidence of a proximal physis in the left radius or of nonmineralized bone in the radiographic gap of the humeroradial joint.
Immediate postoperative mediolateral (A and C) and craniocaudal (B and D) radiographic images of the left (A and B) and right (C and D) antebrachia of the kangaroo in Figure 1. Dual bone fixation was performed with plating of the radii and ulnae. A positional screw (arrow; A and B) is visible spanning the left radius and ulna to stabilize dynamic luxation of the left radial head noted during surgery.
Citation: Journal of the American Veterinary Medical Association 255, 8; 10.2460/javma.255.8.942
A similar surgical approach was used in the right forelimb, and the radial and ulnar fractures were reduced. The right radius was stabilized with a 7-hole, 2.0-mm, locking compression plate secured on the craniolateral surface of the bone with 2 locking screws and 1 cortical screw proximal to the fracture, combined with 3 locking screws and 1 cortical screw distal to the fracture (Figure 2). The right ulna was stabilized with a 9-hole 2.0-mm limited-contact dynamic compression plate secured to the lateral surface of the ulna with 2 cortical screws proximal to the fracture and 3 distal to it.
Both surgical incisions were closed routinely in 3 layers. Interrupted skin sutures were placed, with removal advised at 10 to 14 days after surgery. Postoperative radiography revealed satisfactory alignment, apposition, and implant placement bilaterally (Figure 2). The kangaroo recovered from anesthesia smoothly without complications and was discharged the following day. Enrofloxacin and meloxicam were continued as prescribed. Exercise restriction was advised for the following 8 weeks, with the kangaroo being housed separately indoors and allowed outside only when directly supervised.
On follow-up examination 8 weeks after surgery, the kangaroo's left forelimb appeared to have clinically normal function. It was used well in feeding and grooming, and there was no sign of lameness when bearing weight. Mild lameness was evident in the right forelimb; however, it was used normally for other functions. The range of motion in the left elbow joint was unremarkable. The range of supination of the right elbow joint, however, was mildly decreased, compared with the contralateral limb. The kangaroo received sedatives as before and underwent radiographic examination. Radiography revealed that the right radius had an irregularly margined lucency in the medullary and cortical bone at the level of the most proximal screw (Figure 3). Bilaterally, there was no evidence of implant-associated complications, the fractures had healed, synostosis formation was evident, and the gaps in the humeroulnar and humeroradial joint remained unchanged. A surgery to remove the positional screw between the radius and ulna on the left was advised; however, the client declined.
Mediolateral (A and C) and craniocaudal (B and D) radiographic images of the left (A and B) and right (C and D) antebrachia of the kangaroo in Figures 1 and 2 obtained 8 weeks after surgery. Synostosis formation (asterisks; A and C) is evident bilaterally, and the gaps in the humeroulnar and humeroradial joints (arrowheads; A through D) remain unchanged.
Citation: Journal of the American Veterinary Medical Association 255, 8; 10.2460/javma.255.8.942
Twenty-four months later (26 months after surgery), the kangaroo was returned for a follow-up examination. The client reported that the kangaroo had been healthy since the surgery. On physical examination, the 3.1-year-old 20.4-kg (44.9-lb) sexually intact male kangaroo appeared to have grown normally. No functional abnormality was detected in the kangaroo's left forelimb; however, although the right forelimb was consistently weight bearing during pentapedal motion, a mild gait abnormality with positioning of the right forelimb to bear weight predominantly over the lateral aspect of the manus was identified. In addition, a small callus had developed over the lateral aspect of the manus. No abnormality was noticed in the kangaroo's use of the right forelimb in grooming or grasping. The range of motion of both elbow joints was smooth, with no associated crepitus or signs of pain. Both elbow joints flexed to just beyond 90° and extended to 180°. However, the range of motion in pronation and supination was less in the right antebrachium, compared with the left. In addition, when the positions of the carpi in relation to the elbow joints were evaluated, the right carpus had an abnormal internal rotation of approximately 45°, whereas the left carpus had no abnormal rotation. The kangaroo received sedatives as before and underwent radiographic examination, which revealed no evidence of implant-associated complications but confirmed a torsional deformity in the right forelimb with internal rotation of the carpus (Figure 4). In addition, the synostosis had increased in the right forelimb since the previous radiographic examination but appeared unchanged in the left. The wider than anticipated gaps in the humeroulnar and humeroradial joints noted on previous radiographic examinations had closed bilaterally, and all imaged physes of the humeri and antebrachia, including the proximal radial physes, were radiographically apparent.
Mediolateral (A and C) and craniocaudal (B and D) radiographic images of the left (A and B) and right (C and D) antebrachia of the kangaroo in Figures 1 to 3 obtained 26 months after surgery. The proximal radial physes (narrow arrows; A through D) are evident. The fractures have remodeled (wide arrow; A through D), and synostosis (asterisks; A and C) is more extensive in the right forelimb (C and D) but unchanged in the left forelimb (A and B), compared with radiographic findings at 8 weeks after surgery. The gaps in the humeroulnar and humeroradial joints (arrowheads; A through D) have closed. There is a torsional antebrachial deformity on the right, as evidenced with the right carpus (dotted circle; C and D) having an internal rotation of approximately 45° in relation to the right elbow joint.
Citation: Journal of the American Veterinary Medical Association 255, 8; 10.2460/javma.255.8.942
Discussion
Unlike most terrestrial animals, kangaroos are bipedal and use their forelimbs minimally for weight bearing at high speeds during the bipedal hop.2 Aside from providing partial support during pentapedal locomotion, the forelimbs are primarily used for grooming, pouch manipulation, grasping food, and fighting.3–5 Kangaroos need dexterous forelimbs for survival and assertion of intersex dominance; therefore, maintenance of antebrachial dexterity, including range of motion from pronation to supination, is critical. In captive kangaroos, fractures are commonly caused by fighting, collisions between animals, poor enclosure design, or inappropriate nutrition6,7; however, literature describing fracture management in kangaroos is scarce. Standard orthopedic principles of fracture repair can be applied, yet prognosis following hind limb fracture stabilization in adult macropods is poor because of the unique anatomy and large forces placed on their bones when ambulating.8
Because of the bilateral nature of the fractures in the kangaroo of the present report and the scarcity of information describing skeletal anatomy, physeal closure sequence, and fracture repair in immature red kangaroos, radiographic interpretation and surgical planning were complicated. Additionally, the unexpected intraoperative finding of a dynamic luxation of the radial head in the left forelimb necessitated supplementary forms of fixation. Furthermore, although information regarding osteogenesis in marsupials up to 60 days after birth has been reported,9 information beyond this time frame is scarce. Therefore, our goal was to describe the radiographic, intraoperative, and postoperative findings in the kangaroo of the present report to facilitate management of similarly injured kangaroos in the future.
On the basis of radiographic examinations, the kangaroo of the present report was considered to have had wider gaps than expected in the humeroradial and humeroulnar joints and closed proximal radial physes at 11 and 13 months of age. Interestingly, at 3.1 years of age, the gaps in the humeroradial and humeroulnar joints had closed and the proximal radial physes were radiographically apparent, as were all other physes in the region of the elbow joints.
Historically, the sequence of union of various physes was originally considered to be consistent among all mammals10–12; however, it has become clear that there is more variation in the age and order of physeal union than was originally supposed, and many marsupials maintain open physes to advanced age.13,14 For instance, a study14 in 3 genera of opossums shows that their proximal radial physes remain open until at least 24 months of age and close later in life than do the proximal ulnar, distal humeral, and medial epicondylar physes. When the results of that study14 were generalized on the basis of groups of physes considered, physes of the acetabulum and the coracoid process of the scapula could be anticipated to unite near the end of the first year after birth, physes in the feet and in regions of bones comprising the elbow joints during the second year, and the remainder of the physes of the extremities in the third year. Similarly, a study15 of the union sequence of 15 different physes in the limbs of approximately 400 specimens representing 58 mammalian species (34 placentals, 23 marsupials [including 22 kangaroos, wallaroos, and wallabies], and 1 monotreme) shows that the anticipated sequence of physeal closure is the acetabulum and coracoid process first, followed by physes at the elbow joint, then physes in the hind limb. On the basis of this information, we extrapolated that the kangaroo of the present report was not skeletally mature at 11 months of age and that its radial and ulnar physes, although not radiographically evident, would not have been closed. Skeletal immaturity could also likely explain the gaps in the humeroulnar and humeroradial joints noted radiographically.
A comparison between dissection findings for a young kangaroo taken from the pouch and an apparently fully grown, yet orthopedically immature, kangaroo skeleton (age unknown) indicates that a proximal radial physis is not evident in the younger specimen but is evident in the older specimen.16 It was possible that at 11 months of age, the kangaroo of the present report was similar to the younger animal in the previous report,16 with no radial physis evident. Our intraoperative findings also supported this because when a positional screw was placed just distal to the articular surface of the radius to stabilize the radial luxation, there was no evidence of nonmineralized bone proximal to this.
Although most mammals have cartilage canals, which function during the maintenance of epiphyseal and physeal cartilage17–19 and the development of epiphyseal ossification centers,20 cartilage canals are absent in the marsupial specimens that have been examined.21,22 This absence may explain the lack of epiphyseal ossification centers in some otherwise expected anatomic sites in marsupials such as koalas and ringtail possums.22 No epiphyseal ossification was evident in the bones comprising the elbow joints in the kangaroo of the present report, and it was unknown whether the lack of such was because of the kangaroo's young age or because the ossification process is different in kangaroos. The absence of radiographic evidence of obvious epiphyses and physes complicated our radiographic interpretation. Further, had the physiologic importance of the gaps in the humeroradial and humeroulnar joints been definitively discerned and the potential for continued growth appreciated, alternative approaches for maintaining reduction of the radial luxation, including a primary annular ligament repair or use of sutures,23 may have been considered. Alternatively, the positional screw as placed could have been used but with earlier removal recommended to avoid iatrogenically induced incongruency with the continued growth of the kangaroo anticipated.
Our intraoperative finding of luxation of the radial head in the kangaroo's left forelimb was an unanticipated complicating factor. Kangaroos may be at increased risk for this injury, and a study24 of natural disarticulation of skeletal remains shows that kangaroo skeletons had significantly earlier disarticulation of forelimb joints than did African ungulates. This is likely related to the general body structure of kangaroos, including the limited weight-bearing function of the forelimbs and the size difference between the forelimbs and hind limbs.25 Kangaroos use their forelimbs primarily for grooming and for support during slow pentapedal motion,26 whereas forelimbs in more commonly treated animals, such as cats and dogs, have more vital roles in weight bearing and locomotion and are proportionally heavily muscled. The forelimb joints in cats and dogs are strongly ligamentous, with mobility being largely restricted, at least in dogs, to the sagittal plane; thus, these species may have a comparatively lower risk of elbow joint luxations than do kangaroos. Careful assessment for evidence of elbow joint luxation may be warranted in kangaroos with traumatic forelimb injury.
Despite the surgical techniques used to treat the fractures in the kangaroo of the present report, synostoses developed. Radial and ulnar fractures present a higher risk of such complications than other long bone fractures because of the complex paired bone system. Similar to cats, kangaroos may present additional complexity owing to their increased ability to supinate and pronate the antebrachium.27 Therefore, given the importance of pronation and supination in forelimb function of kangaroos, the recommendations made for treatment of radial and ulnar fractures in cats may also apply to kangaroos. The ability of cats to supinate and pronate the antebrachium may render fixation of the radius or ulna alone less likely to result in stable fixation of the adjacent bone,27 and the same may be true for kangaroos. Dual bone fixation is recommended for cats to reduce complications, including limiting synostosis formation and maintaining pronation and supination.28 Similarly, dual bone fixation was performed in the kangaroo of the present report, and an open but do-not-touch approach was used to limit further damage to the periosteum and thereby minimize proliferative new bone formation. In addition, surgical injury to the tissues around the fractured bone fragments was minimized, with the small fragments and surrounding hematoma disturbed as little as possible. Nonetheless, synostoses formed bilaterally and may have contributed to the persistent right forelimb lameness in the kangaroo of the present report. To mitigate this in the future, we recommend the use of shorter screws and potentially a minimally invasive approach to achieve and maintain accurate fragment apposition. Synostoses, however, may be unavoidable in skeletally immature kangaroos with radial and ulnar fractures because the body may favor fracture healing by callus formation regardless of the stabilization technique performed. In contrast, we anticipate that synostoses should be avoidable in skeletally mature kangaroos and that dual bone fixation may be preferable to optimize the future function of affected forelimbs and to reduce risks of postoperative complications.
The underlying cause of the torsional deformity that developed in the right forelimb of the kangaroo was difficult to determine. Potential contributing factors included the development of the synostosis,28 physeal injury at the time of the original trauma, or physeal injury during the surgery itself. However, synostosis formation following antebrachial fracture typically results in signs similar to those seen after premature closure of distal ulnar physes in dogs, including humeroulnar separation and subluxation,29 that were not noted in the kangaroo reported here. Premature closure of the distal radial physis could produce clinical signs similar to those of the treated kangaroo; symmetric premature closure of the distal radial physes has led to varus angulation with internal rotation of the manus.30 However, there was no obvious radiographic evidence of premature closure of the distal radial physis on follow-up radiographic examinations, making this cause less likely. Further, the percentage of growth that each physis causes is unknown for kangaroos. In dogs, however, the proximal and distal radial physes contribute 40% and 60%, respectively, of longitudinal growth of the radius, whereas the proximal and distal ulnar physes contribute 10% to 15% and 80% to 85%, respectively, of longitudinal growth of the ulna.31 Given the sequential radiographic findings and clinical development of the kangaroo of the present report, it is possible that percentages of bone length contribution from physes may differ between dogs and kangaroos and that the potential difference may influence which deformities develop following synostosis formation in kangaroos. Veterinarians treating kangaroos should be aware of difficulties in determining skeletal maturity and planning fracture stabilization in kangaroos because of potential differences in skeletal growth and fracture healing, compared with other species.
Acknowledgments
Procedures were performed at the Michigan State University Veterinary Medical Center.
The authors declare that there were no conflicts of interest.
Footnotes
Bar Vac CD-T, Boehringer Ingelheim Vetmedica Inc, St Joseph, Mo.
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