Causes of Lameness
Sudden causes of lameness are generally more easy to define. If your dog was completely normal before taking exercise and suddenly comes up lame, obviously something happened that created a gait abnormality. Trauma of some type is most likely, although this can be extremely variable. A thorn in a foot-pad can produce a sudden onset profound lameness and pain.
An insect sting or bite on an affected leg may prove more subtle and difficult to find, but can be equally affective at producing lameness.
A boisterous young dog chasing over uneven terrain in a woodland area could suddenly pull up with a non-weight bearing lameness due to an acute tear of a cranial cruciate ligament of the knee.
An over weight dog might jump down from a deck, landing awkwardly and damaging the ligaments supporting its carpus (wrist).
In all of these examples, the pet has gone from normal to abnormal within a short period of time, but this does not necessarily mean that defining the lameness is always easy. In some cases it is possible to hone in on the correct area, for example the knee, and from there, try to define the problem more accurately.
Sometimes dogs will develop sudden onset lameness when the underlying problem has actually been around for some time. A dog with a low grade, partially torn cruciate ligament may suddenly progress to a full blown tear, but there can be chronic arthritis and soft tissue thickening of the joint suggestive of a more long standing problem. Some pets with bone tumors of the limbs can suddenly develop a severe lameness associated with a fracture of a bone at the site of the tumor. These fractures are often associated with more minor trauma, such as slipping on a kitchen floor, an incident that would not normally be thought of as causing a broken bone.
Sudden onset lameness may be the initial presentation associated with a variety of spinal disorders. Extruded disk material in the neck region can causes a profound, single front leg lameness, a so-called root signature, as can disk problems in the lumbo-sacral region of the spine. Disk disease and fibrocartilaginous emboli (FCE) can produce rapid onset weakness and clumsiness that can be misinterpreted as lameness.
Many lameness problems are noted in young and growing animals. These problems often improve with rest and get worse during exercise, such as elbow dysplasia. They start out as low grade and become progressively more severe over a period of a few weeks.
Overt lameness of one or more legs may not be what an owner initially notices. It may be a reluctance to go up or down stairs, not eager to exercise, or just not acting as lively and bouncy as one might expect for a puppy. This often occurs in hip dysplasia in dogs, causing gait abnormality rather than causing specific limb lameness.
Some owners may pick up on subtle gait abnormalities, such as swinging a limb rather than flexing specific joints. Agility, endurance and working dogs may present with more mild and challenging sports injuries that affect performance but produce only minor problems in one or more limb.
Sometimes lameness due to an orthopedic disorder can be misinterpreted as a neurological disease. Dogs with cruciate injuries to both stifles can find it extremely difficult to walk and when they do can appear to be weak and clumsy on their back legs, similar to dogs with disk disease.