The joints are where two or more bones meet, their function is to enable movement of the skeleton. There are several types of joints including:
Fibrous (fixed) joints – These joints are connected by connective tissue, the skull bones are fibrous joints.
Cartilaginous joints – The bones of the spine are cartilaginous joints, which are connected with cartilage.
Synovial joints – The most common form of joint, these joints pivot in different directions (depending on the joint). The ends of the bones are covered with slippery cartilage to reduce friction between the bones. They are surrounded by a capsule made of a tough connective tissue that is lined with a membrane (synovial membrane). This membrane produces synovial fluid to lubricate the joint. There are several types of synovial joints including hinge (jaw, elbow, and knee), saddle (hip and shoulder) and ball and socket (shoulder and rear legs).
Additionally, joints are classified by how they allow movement to occur:
Synarthrosis – This type of joint has no movement, such as the joints in the skull.
Amphiarthrosis – Slight movement occurs with these types of joints, the vertebrae, and the pelvis are this type of joint.
Diarthroses – This joint has the highest range of movement and includes the elbows, knees, shoulders, and wrists.
Joints allow bones to move against each other (articulate), allowing for movement. Ligaments hold the bones together, and tendons attach bones to muscles.
What is a joint dislocation?
A joint dislocation is when bones in a joint pull apart and out of position. Any joint can dislocate, however, mobile joints have the highest incidence.
Common joint dislocations in cats include:
Luxating patella: The knee joint consists of the shin bone, fibula and the femur (thigh bone), the kneecap (patella) sits in a cartilage groove at the end of the femur. The patella can slip (or luxate) from its position shifting either to the outside or the inside of the leg.
Hip dislocation: The hip is a ball and socket type joint. The round head of the humerus fits snugly into the ball (known as acetabulum). A dislocation occurs if the humerus slips out of the ball socket.
Shoulder dislocation: This type of dislocation is uncommon in cats.
Elbow luxation: The elbow is located in the upper portion of your cat’s forelimbs and is made up of a hinged joint and three bones.
Tail dislocation: The tail is made up of between 20-23 vertebrae, if enough force is applied, these can be pulled apart resulting in a dislocation.
Once a dislocation has occurred, the ligaments and muscles become weaker, which makes it easier for a dislocation to happen again.
Causes of joint dislocation in cats
Dislocations most commonly occur due to trauma such as falling from a height, tail pulling, limb pulling (usually by a child), having the tail trapped in a door, being stepped on (foot or tail), or a motor vehicle accident or in some cases congenital disorders such as hip dysplasia where there is an abnormality of the joint which is present from birth.
Symptoms of a dislocation depend on the severity and location. For example, a cat will feel pain as the kneecap slides out of position, but not once it has moved out of the groove it sits in. Common symptoms of dislocation can include:
- Pain in and around the joint
- Abnormal movement
- A decrease in muscle mass around the affected joint
- Refusal to place the affected limb on the ground, hind limbs may be held upwards parallel to the cat’s body
- Elbow dislocations may involve the front limb being held out and away from the body
- Loss of motion
- Skipping of the affected limb
- Deformity of the joint area
- Pain upon manipulation
Your veterinarian will perform a complete physical examination of your cat and carefully evaluate the joint. If he suspects there is a dislocation he will perform x-rays.
If the cat has been in a trauma, additional x-rays or ultrasound will be necessary to evaluate for internal injuries.
Treatment depends on the severity of the dislocation as well as the joint affected.
- Manipulation of the joint: The veterinarian will manipulate the joint back into place while the cat is under anesthesia. Once the joint has been put back in place, follow up X-rays can determine that the joint is back in its correct position. Do not put the joint back into place yourself. A skilled veterinarian must perform this to avoid further damage to the area.
- Surgery: For severe dislocations and/or hip dysplasia. Read here for more detailed information.
- Immobilisation: After the joint is back in position, the veterinarian may immobilise the joint with a bandage to prevent further damage.
- Cage rest: Confine the cat to a large cage or small room while the joint heals.
- NSAIDs: To reduce inflammation and antibiotics if the cat has had a surgical repair of the joint.
- Analgesics: To relieve pain, once the joint is back in place pain will resolve.
- Ice packs: Apply to the area to reduce swelling.
- Soft diet: If the jaw has been dislocated, this can make it easier for the cat to eat.
- Physiotherapy: In some cases, the veterinarian will recommend physiotherapy once the joint has started to heal to help strengthen the joint and surrounding muscles.
Keep the cat indoors and confine it to a small area until fully healed. Weight loss will be necessary for overweight cats to relieve pressure on the joints.