The challenge of diagnosing lumbar segmental instability

Abstract

Abstract Background Lumbar spinal instability is very commonly discussed in research studies and is routinely used in clinical practice to make treatment decisions. That practice must be reconciled with expert consensus in the peer-reviewed literature: there is currently no validated diagnostic test for spinal instability. Some treatments for instability can have serious complications, so correct diagnosis is important. Biomechanically rational and clinically effective diagnostic tests for instability are needed, where instability is defined as incompetence of the intervertebral motion restraints forming the passive part of the motion control system.Methods This study critically examines and identifies deficiencies in previously employed metrics and criteria for diagnosing spinal instability. New metrics are described that account for the deficiencies. The new metrics were retrospectively applied to 7621 lumbar spine flexion-extension studies to document the prevalence of abnormalities in different patient populations.Results Traditional measurements, such as intervertebral rotation or translation, may fail to find abnormalities in intervertebral motion due to factors such as inconsistent patient effort and radiographic magnification. The proposed biomechanically grounded metrics for lumbar spine sagittal plane shear and vertical instability appear more adept at finding abnormalities in patient populations where abnormalities might be expected and not in patients where instability would not be expected.Discussion New approaches to detecting abnormal sagittal plane intervertebral motion may lead to enhanced and standardized diagnosis of lumbar spine instability. Further clinical research is imperative to validate the efficacy of these metrics in diagnosis and treatment algorithms.