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How does ankylosis limit joint movement?
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Ankylosis limits joint movement by causing stiffness or complete fixation of a joint due to injury or disease. This restriction occurs through two primary mechanisms:12
- Extrinsic factors: Inflammation of the tendinous or muscular structures surrounding the joint can cause rigidity, a condition sometimes referred to as false ankylosis.1
- Intrinsic factors: In true ankylosis, the disease process occurs within the joint itself. In conditions like rheumatoid arthritis, the destruction of joint cartilage leads to the formation of adhesions between articular surfaces. When these adhesions transform into mature fibrous or bony connective tissue, they create a firm union between the bony surfaces.13
When the joint ends of the bones are fused together by this process, it is known as osseous or complete ankylosis, which can render the joint totally immobile. In the case of ankylosing spondylitis, structures in the spine become bridged by bone, resulting in a rigid spine.13