By Dr. Laura Hady
You call your dog in from the backyard and see that they aren’t using one of their back legs and can’t jump up on the bed. Living in New Mexico, you immediately check the paw for a goat head but do not find one. You rub the leg, looking for pain in the muscles or bones, but don’t find any swelling or bumps. In a few days, your dog begins to use the leg again but still seems uncomfortable on it. While dogs can shift weight to their other three limbs, they should still see a veterinarian for diagnosis and treatment options when this type of activity is noticed. This article will discuss the function and structure of the knee and about two issues that can arise if there is a problem with that critical joint.
- The knee is the joint between the thigh (femur) and shin bones (tibia) that helps the leg bear weight and move properly. The cranial (front) and caudal (back) cruciate ligaments connect the two bones in a cross-like fashion. Between the femur and the tibia are two C-shaped pieces of spongy cartilage that act as a cushion. On the outer and inner knee are collateral ligaments that act as stabilizers. The quadriceps muscles on the front of the thigh allow for knee extension, while the hamstring muscles on the back of the thigh work to perform flexion. Issues can occur when the angle of the knee joint or bones are not properly aligned, or if parts of the knee are not shaped properly.
- The cranial cruciate ligament (CCL) blocks the tibia from sliding in front of the femur, stops hyperextension of the knee, and prevents internal rotation of the tibia, which keeps the foot from toeing inwards. Injuries usually occur during hyperextension (running fast or jumping), coupled with a quick turn, like when retrieving a ball. Damage to the ligament can be compared to a rope that unwinds over time. It typically occurs in medium- to large-breed dogs that have a straighter leg conformation. All cranial cruciate ligaments with a partial tear will continue to degenerate and progress to a full tear. At the same time, or shortly after the tear, there can also be a tear on the inside meniscus, which tends to cause more pain. Ways that your veterinarian can test for a cranial cruciate tear includes testing how much the tibia can move forward in relation to the femur (cranial drawer test), an X-ray looking for swelling in the knee, feeling the knee for a thick joint capsule, and/or seeing how the dog sits. Dogs with torn CCLs tend to sit with the affected knee facing outward more than usual instead of having a square sit. Most dogs tend to improve by two weeks as the body begins to lay down more bone and tissue to stabilize the joint. Due to the instability, arthritis will form within two months. Surgery will likely be recommended to decrease the amount of arthritis that forms.
- The patella (kneecap) is a small bone that sits in a groove and helps to improve flexion (bending) and extension (straightening) of the leg by acting as a lever when the large patellar tendon arising from the quadriceps muscles glides over it during movement. Issues occur in smaller breed dogs because the trochlear groove is not deep enough to keep the patella in it during leg extension. The patella tends to pop out to the inside of the leg (medially) in smaller breeds and to the outside (laterally in larger breeds). Pups present as having a “hitch” in their gait that resolves when shaking or extending the leg. Dogs that have luxating knees (usually both knees are involved) require surgery if the patella stays out of the groove most or all of the time and cannot be replaced in the groove. If not treated, dogs and cats with patellar luxations can tear their cranial cruciate ligaments due to abnormal use of the knee to compensate.
Next month, I will discuss ways to treat these knee conditions with surgery, medications, regenerative medicine with stem cells, and physical rehabilitation. Pets can tend to compensate by shifting weight to their other legs but still need help. The key is to talk with your family veterinarian for a confirmed diagnosis and the best ways to help your pet have comfortable movement in the leg after an issue occurs.
