An Overview of a Dog’s Joints & Ligaments
Because there are variables amongst the many breeds, the anatomy of dogs varies. However, there are physical characteristics that all dogs have in common, from the small Pomeranian to the large Afghan Hound.
This article will provide an overview of the structure and function of the canine joints and ligaments. It will outline the general structure of joints and ligaments, how they work, some common diseases that affect joints and ligaments and common diagnostic tests used to evaluate these joints and ligaments.
THE FUNCTIONS OF JOINTS AND LIGAMENTS
Joints are found throughout the body wherever two bones meet. A joint is formed when two bones come together and are held in place by supporting tissues. The joints provide motion and flexibility to the skeletal frame and act as shock absorbers.
A ligament (slightly elastic tissue) is a short band of tough, flexible fibrous connective tissue which connects two bones or cartilages or holds together a joint. Ligaments prevent dislocation and excessive movement that might cause breakage. They typically stretch over joints, connecting bones.
THREE DIFFERENT TYPES OF JOINTS
Joints may have large ranges of movement such as the shoulder and hip joints, or have very little movement, such as the joints between the bones in the skull.
These three different types of joints are:
- Synovial: They allow free movement, such as knees, elbows and wrists. Synovial joints are the most numerous in the body and the most susceptible to inflammatory disease. Examples of synovial joints include the joints in the legs and the temporomandibular joint which joins the skull to the lower jaw (mandible).
- Cartilaginous: As the name suggests, these are between cartilage, for example the vertebrae. There is some movement. An example of cartilaginous joints are the joints where the ribs meet the sternum.
- Fibrous: Since these are connected with fibrous tissues, the length of the fibers will determine movement capabilities. Typically, movement is none or very limited. Fibrous joints include those that join the bones of the skull together. The canine skull is actually made up of over 40 different bones, all tightly held together by this fibrous tissue.
WHAT MAKES UP A SYNOVIAL JOINT?
The synovial joints are the most common type of joint, and they provide free movement between the bones they link. They are typical of nearly all limb joints, such as the knee, elbow and wrist. Their name is derived from the synovial fluid (lubricating substance within the joint cavity).
Synovial joints are the most susceptible to inflammatory disease.
A synovial joint consists of:
- Such as the upper thigh (femur) and humerus bone
- Sheets, cords or bands of fibrous connective tissue that connect bones or cartilage
- Can be found either inside or outside the joint capsule
- Bound by a tough fibrous capsule, which contributes to the mechanical stability of the joint
- Lined inside by a very thin synovial membrane that functions to supply nutrients, joint fluid and to mediate immune or inflammatory processes
- Both the fibrous capsule and the synovial membrane have nerve and blood supply
Synovial (lubricating) fluid:
- Transparent, viscous fluid which bathes the joint
- Lubricates the joint, reducing friction between articulating surfaces
- Also supplies nutrients and removes waste from cartilage, which has very poor blood supply of its own
- Lines and protects the articular surfaces of bones in a joint
- Flexible, compressible type of connective tissue that is more resilient than bone
- Reduces friction between articulating bones
- Cushions the bones by acting as a shock absorber
FUNCTIONS OF JOINTS
The skeletal frame on its own is not flexible and needs help to move and absorb shock. Joints connect bones within the body, bear weight and enable movement. Without the right support, bone ends are prone to breakage caused by dislocation and excessive movement. Fortunately, bone ends are bound by ligaments.
JOINT AND LIGAMENT DISEASES IN DOGS
Some common diseases of joints and ligaments in dogs are:
- Dislocation of the hip, usually caused by trauma, causing lameness.
- Osteoarthritis (OA) or degenerative joint disease (DJD) is a common condition in which the joints become inflamed, swollen and painful. Symptoms can range from slight stiffness to loss of mobility.
- A collapse of the wrist can result from carpal hyperextension injuries, for example, jumping from an unnatural height and landing on the front legs.
- Hip dysplasia is an abnormal hip joint development that causes progressive lameness, stiffness and pain (more common in larger and giant breeds).
- Rupture of the cruciate ligament in the knee.
- Septic arthritis, a bacterial infection within a joint, can lead to systemic illness.
EVALUATION OF JOINTS AND LIGAMENTS
Diagnostic tests used to evaluate joints may include:
- Routine lab tests including blood and urine tests as well as immune tests.
- Orthopedic examination: simply use arms and hands to test motion capabilities.
- Regular X-rays can pick up dislocation, arthritis, hip dysplasia, joint effusion and other joint abnormalities.
- Arthrography, a type of contrast X-ray, relies on injected dye for enhanced assessment.
- Arthroscopy: typically, a knee or shoulder examination via a small scope inserted into joint.
- Arthrocentesis: a microscopic examination and bacterial culturing of fluid drained from the joint.
- MRI and CT scans as well as surgical exploration are other (more costly) options to help diagnose abnormalities.
HELP MAKE YOUR DOG MORE COMFORTABLE
When pets are happy, pet owners are happier too, so don’t ignore canine joint or ligament abnormalities, even if they seem minor. If you are concerned about your dog’s joints and movement, seek the advice of your veterinarian.