Spinal instability: the orthopedic approach

The determination of spinal stability remains an important task of the spine surgeon, as treatment strategies rely heavily on this assessment. However, a clinically useful definition of spine stability remains elusive. Numerous classification systems have been proposed: White and Panjabi proposed a checklist point system to assess spinal stability for each of the cervical, thoracic, and lumbar spines. This remains one of the best recognized systems to date. Denis proposed that spinal integrity depended on the three-column system (anterior, middle, and posterior) and used it to describe thoracolumbar fractures. The spine is considered unstable when any two of the three columns are disrupted. These two classification systems are designed for traumatic injuries and do not explain other causes of instability. In the end, numerous factors must be taken into account when determining spinal stability. These include the disease process causing the injury, the medical and neurologic status of the patient, the anatomic site, and findings on imaging studies.