Segmental Instability of the Lumbar Spine

Low back pain (LBP) is a pervasive problem in modern societies, but identifying a specific pathoanatomical cause is not possible in a majority of cases.1 Patients for whom a specific pathoanatomical diagnosis cannot be made are often described as having “mechanical” LBP. Many researchers and clinicians suggest that segmental instability of the lumbar spine is a possible pathomechanical mechanism underlying mechanical LBP.1–3 Segmental instability of the lumbar spine, however, remains a controversial and poorly understood topic.4 The purpose of this update is to review the current literature on segmental instability of the lumbar spine, with special emphasis on Panjabi's theory of the “neutral zone” and how that relates to physical therapy.