Causation. Working on rough, irregular, rocky ground, or on roads with deep ruts, is the commonest cause of this condition. When the animal moves on irregular surfaces the two claws do not bear an equal share of weight; sometimes the whole weight is for a moment thrown on one claw.
The phalanges, therefore, are displaced inwards or outwards, or are twisted around their vertical axis, causing the fetlock joint and its supporting ligaments to be more or less severely strained. The internal or external ligaments of the joint or the suspensory ligament or flexor tendons may even be lacerated.
The fetlock may also be strained by the animal making violent efforts to free the claws or pastern which have become fixed in a hole in the ground, in bogging, in hobbling, or in leaping a fence.
Symptoms. Lameness is noticeable from the beginning, but is unaccompanied by any visible lesion. On examination of the limb, the entire region from the fetlock downwards is found to be sensitive to pressure, and painful when forcibly extended or flexed from side to side. This sensitiveness is particularly marked when the phalanges are rotated on the shank. A few days later the entire fetlock becomes the seat of diffused swelling.
Diagnosis is facilitated by the fact that the fetlock has an entirely different appearance from that seen when tendon sheaths or the synovial capsules of joints are distended.
Prognosis. The prognosis varies considerably, according to the extent to which deep-seated structures are involved, and the gravity of the lesions is usually proportioned to the intensity of the symptoms.
Treatment. Frequent cold applications, cold foot baths for an hour or two night and morning, and even cold poultices are useful. When the pain has somewhat diminished, which usually occurs in from three to four days, vesicants may be employed, and, at a later stage, massage. Failing improvement by these methods, the injured region may be fired in points.
Strain of the hind fetlock occurs under precisely similar conditions to those above described in the case of front limbs.
STRAIN OF THE STIFLE JOINT.
Strain of the stifle joint results from over-extension of ligaments without displacement of the patella, and also (and probably more frequently) from injuries to the aponeurosis and tendons of insertion of the abductor muscles of the femur and tibia.