Clinical Vignette
Max, a 6-year-old male Rottweiler, is presented for vague right forelimb lameness. Your physical examination reveals grade 2 lameness in the right forelimb but no other obvious abnormalities. You elect to treat with NSAIDS for 2 weeks. The owner does not return for 4 weeks at which time the history reveals a persistent and worsening lameness, which at times, is a non-weight-bearing lameness. Your examination now reveals that there is (1) muscle atrophy of all extensors of the right forelimb, (2) the right pupil is 4 mm in diameter compared to a left pupil that is 8 mm (in normal examination room light), (3) the right third eyelid is slightly protruded, (4) the right palpebral fissure is narrow compared to the left, and (5) the triceps and extensor carpi radialis reflexes are weaker on the right side compared to left side. What is your assessment of the history? What category of disease does the history support? What is your neurologic examination assessment, that is, where do you localize the lesion? If you were not sure whether the muscle atrophy was due to disuse atrophy or truly due to neurologic disease, what test would you recommend to separate these two mechanisms of atrophy? On the basis of the case presentation what are your thoughts regarding prognosis? What diagnostics would you recommend to the client? What is the most likely therapeutic approach that will be needed to manage Max’s problem?
Problem Recognition and Definition
Lameness is simply defined as a deviation from the normal gait. Although it is common for pain to be the cause, the term “lameness” does not unequivocally include pain. It is manifested clinically as a visual variation in movement of a limb or limbs secondary to disease, damage, or dysfunction of one or more of the tissues responsible for locomotion (see “Pathophysiology” section). Readers should consult Chapter 39 for related information.
Pathophysiology
Lameness is most commonly secondary to and associated with pain, but it may also result from nonpainful mechanical abnormalities such as skeletal deformities, muscle contractures, or muscle rigidity (e.g., focal tetanus). At times a combination of both pain and instability of the skeleton or a mechanical problem may result in lameness.
If pain is the reason for the lameness, the source will usually be one of the tissues necessary for locomotion such as bone, muscle, joint, or nervous system. Soft tissue inflammation in the digits due to minor trauma, localized infection, or a foreign body (thorn in the foot) can cause lameness without affecting one of the four systems above. Pure mechanical causes of lameness result in improper positioning or placement of the limb(s) during the gait.
Classification
Origin
Once lameness is identified as a problem, the next step is to define its origin. Lameness may originate from (1) skeletal (osseous), (2) muscle, (3) joint, (4) neurogenic, or (5) soft tissues (see Table 38-1 for examples of diseases for these various locations). Many times this is easily answered from a detailed physical examination and history (see subsection “Diagnostic Procedures”). The age, breed, and sex may also assist with the differential diagnosis (see Table 38-2).
Severity
The severity of lameness can assist with establishing the “seriousness” of the disease process and/or to help establish a list of rule-outs. Over the years, the authors have not found this scheme to have useful diagnostic value. Due to the considerable overlap between the etiologies of lameness and the severity of the lameness associated with each, this classification is more helpful as a method to monitor lameness over time. On the basis of severity, the four levels of lameness are described as follows:
Grade I—Barely perceptible lameness.
Grade II—Noticeable lameness, but weight bearing most of the time. This is more typical of a disease in the developing stage, for example, degenerative joint disease or panosteitis; or recovery state, for example, healing traumatic injury.
Grade III—Severe lameness, with use limited to touching of paw to the ground for balance.
Grade IV—No weight bearing; the limb is carried.
Diagnosis
History
The clinical course of lameness may help define its cause. Acute onset lameness is typical of traumatic, inflammatory, and infectious etiologies. Examples would include foot/footpad lacerations and foreign bodies, blunt trauma, fractures, muscle strains/tears/disease, joint or ligament sprains/tears such as rupture of the cranial cruciate ligament, infectious arthropathies, and immune-mediated polyarthropathies. The history of a patient presenting with chronic lameness must be scrutinized for the possibility of a previous acute onset, which may indicate one of the aforementioned problems which is in a static or resolving stage. A good example of this is the patient which presents with a chronic lameness associated with infraspinatus contracture. In this condition, a key diagnostic feature is an acute onset lameness 4—5 weeks (which resolved spontaneously in 48 hours) prior to the onset of the chronic lameness problem.
TABLE 38-1. Differential diagnosis for lameness on the basis of the body system involved
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