Abstract

Pelvic limb injuries involving the long bones are common in cranes, and are frequently associated with traumatic injury.³ The basis for the injury is often unknown, but is suspected to frequently involve collision with enclosure materials during direct attacks from conspecifics, or reaction to outside disturbances such as automobile, aircraft, predator, or human voice noise. Capture and restraint episodes may also induce iatrogenic injury to the pelvic limbs of cranes, including fractures. In 1996, the Whooping Crane Health Advisory Team identified musculoskeletal problems, specifically pelvic limb fractures, as a significant source of morbidity and mortality for the captive population of whooping crane (Grus americana) chicks used in reintroduction efforts. Among cases of pelvic limb fracture, we have identified seven cases of tibiotarsal cnemial crest fracture with varying degrees of patellar ligament rupture in whooping crane chicks from records of the International Crane Foundation (ICF, n=4), Calgary Zoo (n=1), and a release project conducted at Grays Lake, Idaho² (n=2) between 1993–2000.

All cases occurred in whooping crane chicks being reared in isolation from human contact for reintroduction efforts. The relevant history for each case is summarized in Table 1. All cases occurred in hatch-year birds, with ages ranging from 62–138 days. All weights were considered normal for the chick’s stage of development, except for Case #6 which experienced developmental limb abnormalities that required treatment prior to the injury. All chicks were captured and restrained for transport crate loading, pen transfer, or medical examination within the previous 24 hours of injury.

Each injury was characterized by one or more of the following lesions:

1.  Patellar ligament rupture with patellar luxation

2.  Avulsion fracture(s) of the cnemial crest of the tibiotarsus

3.  Severe muscle and joint capsule trauma

4.  Extensive subcutaneous and intra-articular hemorrhage

Table 1. Characteristics of whooping crane chicks with patellar ligament ruptures (1995–2000)

Surgical repair was attempted in four of the six cases. Each surgery was successful in achieving an anatomic restoration, but two chicks died during anesthetic recovery with severe lymphoid necrosis attributed to excessive stress. Case #2 died 68 days post-surgery during transport to a new release site. This bird had originally sustained a minimally displaced right tibiotarsal crest fracture with little patellar ligament trauma; the fracture of the tibiotarsal crest had healed normally by the time of death. Case #7 survived to 18 days post-surgery, including 11 days in a modified sling to diminish weight bearing on the repaired leg, but was ultimately euthanatized due to additional muscle trauma and wound healing complications.¹ Thus, the mortality associated with this type of injury in captive reared whooping crane chicks is 86%. A similar case in a female 120-day-old Brolga crane (Grus rubicunda) chick from ICF in 1997 survived surgical repair and postoperative therapy; she eventually died from visceral gout and systemic amyloidosis 10.5 months post-surgery possibly due to chronic inflammation at the surgical site. At necropsy, a severe and chronic synosteoarthritis in the repaired joint was noted, suggesting complete rehabilitation was not achieved in this case.

The underlying risk factors in these cases are difficult to identify. To date, some form of handling by husbandry or veterinary staff preceded each injury, but there were four or more different handlers involved in the seven cases. Case #1 died in its transport crate from severe hemorrhage and shock due to bilateral patellar ligament rupture and tibiotarsal crest fracture. Upon release of the remaining cases, each bird was noted to be lame or non-weight bearing on the affected limb, but handlers did not perceive a significant injury during the preceding restraint. Whooping crane chicks do not appear to be predisposed to this type of injury compared to chicks of other crane species fledged during the same period at ICF (4/72 vs. 1/79, respectively; Χ²₁=2.15, p=0.14). Hatching date, age, sex, diet, weight gain curves, long bone growth (specifically tibiotarsal length), body weight at injury, rearing method, social status when in cohorts, pen types, and concurrent health problems were also not associated with the development of this injury in whooping crane chicks. None of the chicks appeared to have primary morphologic or histologic abnormalities in the affected structures postmortem.

We believe the basis of these injuries was due to increased biomechanic stress from the femorotibialis/iliotibialis muscles on the insertion at the cnemial crest. In particular, the restraint method chosen by the handler may have compounded this stress. To our knowledge, each bird was restrained with the pelvic limbs folded under the crane’s body. This common handling method, an alternative technique to keeping the legs in an extended position, is used only when the pelvic limbs are easily folded with little resistance.⁴ Based on goniometry performed during several recent handling events using whooping cranes at ICF, the stifle joint remains in a moderately flexed state in either restraint position, suggesting the femorotibialis/iliotibialis mechanism is not in a neutral position and may experience loading with muscle contraction. However, with the limbs folded, resistance to extension (isometric loading) is likely to be extreme during struggling, whereas minimal loading should occur with the legs held extended. We believe it may have been the resistance to movement that created conditions favorable for the development of forces sufficient to fracture the cnemial crest in these cases.

Future investigations will include biomechanic stress testing on archived specimens and simulation modeling to support or refute our hypotheses.

Literature Cited

1.  Businga NK. Guidelines for the medical management of cranes in slings. In: Proceedings of the Association of Zoo Veterinary Technicians. 1998:81–84.

2.  Drewien RC, Munroe WL, Klegg KR, Brown WM. Use of cross-fostered whooping cranes as guide birds. Proc North Am. Crane Workshop. 1994;7:86–95.

3.  Olsen GH, Langenberg JA, Carpenter JW. Medicine and surgery. In: Cranes: Their Biology, Husbandry, and Conservation. Blaine, WA: Hancock House Publishers; 1996:137–174.

4.  Swengel SR, Carpenter JW. Medicine and surgery. In: Cranes: Their Biology, Husbandry, and Conservation. Blaine, WA: Hancock House Publishers; 1996:31–44.