Joints and Ligaments

Cats have three very different kinds of joints: fibrous, cartilaginous, and synovial. Each of these has a different level of flexibility, and each of them performs a different function.

The joints at the suture lines between the fused bones that form the skull are made of hard fiber. These joints have no flexibility at all. The mandible or jawbone, for example, is really made up of two bones, with a fibrous joint at the midline between the incisor teeth.

If a cat lands heavily on its jawbone in a fall, this hard fibrous joint may split: technically, the cat has not actually broken its jaw, although that is the apparent effect, but has torn this fibrous joint.

Other joints, like the thick discs between the spinal vertebrae, are made from tough cartilage. These cartilaginous joints are looser and more supple than similar joints in other species, such as humans and dogs, providing the cat with a far greater degree of flexibility in its torso. 

During growth, the growth plates at the end of the long bones are temporarily cartilaginous joints, and as such they are less sturdy and more prone to damage than in adulthood.

Synovial joints are found where the greatest degree of movement is needed. They are hinged or ball-and-socket joints, with pearly, smooth, articulating cartilage on their contact surfaces, and surroudded by a joint capsule filled wich synovial fluid. This construction is found in the highly flexible joints of the legs and the jaw.

Synovial joints sometimes suffer from excess production of lubricating synovial fluid or inflammation due to arthritis or synovitis through injury, disease, or allergic reaction.

Ligaments, the tough bands that hold bones together, are important in all joints, but vital in synovial joints, which inherently lack stability. The feline hip joint, in particular, is prone to dislocation; this is often, although not always, prevented by the ligament that holds the ball of the femur firmly in the socket of the pelvis.