Atlantoaxial instability is a condition where the first two vertebrae in the neck, known as the atlas and axis, are not properly aligned. This misalignment can lead to excessive movement between these vertebrae, which may cause pain, neurological issues, or even spinal cord compression. It is often seen in individuals with certain conditions, such as Down syndrome or rheumatoid arthritis. Diagnosis typically involves imaging studies like X-rays or MRIs to assess the alignment and stability of the cervical spine. Treatment options may include physical therapy, bracing, or, in severe cases, surgical intervention to stabilize the vertebrae and prevent further complications.