Testing for Lameness

By Ryan Llera, BSc, DVM; Tammy Hunter, DVM; Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DVM, DVSc

What might be causing my pet’s lameness?

The most common cause of lameness is trauma or injury to joints, ligaments, tendons, muscles, or bones. Other causes of lameness include developmental diseases in young animals, degenerative joint disease in older pets, immune-mediated joint disease, infectious joint diseases, neurological disorders, and cancer of the bones or joints.

How is the cause of a pet’s lameness determined?

Finding the cause of a pet's lameness usually starts with a complete history and physical examination. Your pet's history includes details such as whether the lameness occurred suddenly or came on gradually, whether trauma was involved, whether more than one limb is affected, whether the lameness is constant or comes and goes, and whether there are other signs of illness. The physical examination includes assessment of the pet's overall health as well as close inspection of the affected limb(s) or joint(s). Your veterinarian is looking for evidence of trauma such as bruising or wounds, as well as signs of soreness such as swelling, heat, redness, pain, or reduced ability to move a joint or limb.

What diagnostic tests are commonly done in a pet with lameness?

  • If a pet appears to be healthy except for lameness, the first diagnostic test will likely be to take X-rays of the sore area. If there is joint pain, then joint fluid analysis may also be recommended.
  • If pain is found only in the knee of the hind leg, a ruptured or torn cranial or anterior cruciate ligament (ACL) may be the cause. When the ACL is damaged, the knee joint becomes loose and moves in an abnormal way called a drawer sign. The drawer sign is more easily detected when the leg is completely relaxed and therefore the test is often done with the pet under sedation or light general anesthesia.
  • If the pet has additional signs of illness, such as fever, poor appetite, lethargy, or weight loss, then underlying systemic illness may be present and screening tests may be recommended. Screening tests are a series of simple tests that assess the overall health of a pet. The most common screening tests include a complete blood count (CBC), a serum biochemistry profile, and a urinalysis.

How is joint fluid obtained?

Before collecting joint fluid, the skin over the joint is shaved and carefully scrubbed as if for surgery. Joint fluid (also called synovial fluid) is collected by passing a fine sterile needle through the skin into the joint space, then attaching a small syringe and pulling out, or aspirating, a small amount of synovial fluid. Immediately after collection, a small amount of synovial fluid is spread thinly on one or more microscope slides and quickly air-dried. Any remaining fluid is placed in a sterile sample tube and sent along with the slides to the laboratory for analysis.

How does joint fluid analysis help?

Joint fluid analysis can be very helpful in identifying the cause of lameness. At the laboratory, the amount of protein in the fluid is measured. The fluid is also examined microscopically by a veterinary pathologist to see how many cells are present and to identify what types of cells are there. If the protein content of the joint fluid is higher than normal or there are too many cells in the fluid, then joint inflammation is likely present. The types of cells found may explain the cause of the inflammation. For example, high numbers of neutrophils (a type of white blood cell) suggest either bacterial infection of the joint or immune-mediated joint disease, and increased numbers of mononuclear cells (white blood cells seen in longstanding inflammation) are associated with degenerative joint disease. Occasionally, there may be evidence of damaged cartilage or previous bleeding in the joint; sometimes infectious organisms or tumor cells may be seen.

What additional diagnostic tests might be done on joint fluid?

If bacterial infection is suspected, culture and sensitivity of the joint fluid may be recommended. This test helps to identify bacteria that might be causing lameness and indicates which antibiotic should be used to treat the infection.

What other diagnostic tests might be done?

Depending on the results of the history, physical exam, and screening tests, specific blood tests may be recommended to diagnose infectious diseases (e.g., Lyme disease, ehrlichiosis, or fungal infection) that cause lameness. There are also specific antibody tests, such as the rheumatoid factor test that can help to confirm a diagnosis of immune-mediated joint disease.

If X-rays reveal a mass or an area of abnormal-looking bone, then fine needle aspiration or surgical biopsy of the area may be recommended to determine if there is inflammation, infection, or cancer.

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