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 a slippery cartilage which reduces friction between the bones and are surrounded by a capsule made of a tough connective tissue which is lined with a membrane. Known as the synovial membrane, this produces synovial fluid which lubricates 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. The joints are held together by ligaments holding the bones together, tendons attaching the bones to muscles, the joint capsule in the synovial joints, which adds stability to the joint, the synovial fluid.
What is a joint dislocation?
A joint dislocation is when bones in a joint pull apart and out of position. Any joint can be affected but the most mobile joints are at greater risk of dislocation. If surrounding tendons and ligaments are damaged it is known as a 'luxation', if the joint is dislocated but surrounding tissues undamaged, it is a 'subluxation'.
Common 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 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). 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
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 are weakened making it easier for a dislocation to happen again.
How to joint dislocations occur?
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.
What are the symptoms of joint dislocations?
Symptoms of a dislocation depend on the severity and location. For example, a cat will feel pain as the knee cap slides out of position, but not once it has moved out of the groove it sits in. Common symptoms of dislocation can include:
- Pain on and around the joint
- Abnormal movement
- 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
How are joint dislocations diagnosed?
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.
Further testing such as routine blood work (complete blood profile, biochemical profile, and urinalysis) and/or ultrasound may be required if additional trauma has occurred to assess the overall health of your cat and look for signs of internal injuries.
How are joint dislocations treated?
Treatment depends on the severity of the dislocation as well as the joint affected.
- Manipulation of the joint back into its proper location. Your veterinarian may attempt to manipulate the joint back, this will be performed under anaesthesia. Once the joint has been put back in place X-rays will be taken to make sure it is where it should be. Please do not try to put the joint back into place yourself, this needs to be performed by a skilled professional to avoid further damage to the area.
- Immobilisation. After the joint is manipulated back into position, your veterinarian may immobilise the joint with a bandage.
- Cage rest may be recommended to heal a dislocated hip.
- Surgery may be required for severe dislocations and/or hip dysplasia. Read here for more detailed information.
- NSAIDs to reduce inflammation and antibiotics may both be prescribed if your cat has had a dislocation surgically repaired.
- Painkillers may be prescribed although once the joint is back in place pain should be greatly reduced.
- Ice packs may be applied to the area to reduce swelling.
- If the jaw has been dislocated, your cat will need to be fed a soft diet for a few weeks while the jaw heals.
- Physiotherapy may be necessary once the joint has started to heal to help strengthen the joint and surrounding muscles.
- All cats who have had a dislocation will need to be kept indoors and usually confined to a cage until they are fully healed.
- Overweight cats may need to be put on a diet as obesity will place additional pressure on the joints.