Pelvic limb lameness in a ferret

The owner of a 4-year-old neutered female ferret (Fig. 1) presented her for lameness of the left hind leg. The ferret had fallen from the owner's shoulder 3 weeks earlier and since then showed variable lameness. The owner was not initially concerned, as the lameness appeared to improve with rest. But over the past 3 weeks, the owner had noticed that the lameness became worse when the ferret played or exercised. The lameness also seemed to be worse in the morning after the ferret woke up and seemed to improve slightly with movement.

Figure 1

A 4-year-old neutered female ferret that presented for lameness of the left hind leg.

The ferret had no previous history of disease, and the owner described her as active and playful. On clinical examination, we found the ferret was bright, alert and responsive. Her vital parameters were within normal limits. When placed on the floor of the examination room, the ferret showed unilateral weight-bearing lameness, characterized by holding up her left hind leg when she moved. Examination of the hind limb musculature was unremarkable; we did not detect any swelling, atrophy, pain or asymmetry. Palpation of the hind limb joints for swelling, thickening, crepitus and pain was also unremarkable.

Because the ferret had a loss of ability to support weight, we conducted a neurological examination, paying particular attention to gait, postural reactions and spinal reflexes. There was no incoordination when the ferret walked. However, it was difficult to establish a normal postural reaction by examining the hopping response (the weight is borne on the limb to be tested and the animal is moved laterally on that limb) of the left hind leg. We were able to elicit a patellar reflex in both hind limbs. Gentle compression of the base of the claw in each paw of the hind legs with a forceps showed a normal withdrawal-flexor reflex. Because the neurological examination did not show any major abnormalities, we then carried out an orthopedic examination.

We conducted an Ortolani maneuver for hip joint laxity and found no suggestion of hip laxity. We then carried out a cranial drawer sign test for knee joint instability on the left hind limb. This involved placing a finger and thumb of one hand on the patella and lateral fabella proximal to the left knee joint, and placing the finger and thumb of the other hand on the fibular head and tibial crest distal to the left knee joint. We were able to elicit a positive drawer sign by moving the tibia cranial relative to the femur.

We then took radiographs of the left knee (Fig. 2). A left lateral recumbency view of the flexed left knee showed a caudal displacement of the tibia. We did not see any sign of inflammation of the left knee joint or periosteal reaction of the left tibia or femur.

Figure 2: A left lateral recumbent view of the flexed left knee of the ferret shown in Figure 1.

The position of the tibia relative to the femur is abnormal: it is caudally displaced.

For what condition is the cranial drawer sign pathognomonic? How would you treat this ferret for its lameness?

What's your diagnosis?