Changes in quantitative elastography assessment of the adjacent lumbar disc after segmental fixation of the spine: a case description of a burst fracture of L4

Abstract

Vertebral burst fractures are usually due to traumatic high-energy distraction of the vertebra. They often require pedicle screw fixation to stabilize the spine during the healing process but once the fusion of the fractured vertebra has occurred, the posterior fixation can be removed or shortened to restore part of the spinal mobility. The importance of sparing fusion levels to ensure optimal functional results has been demonstrated. In surgical planning, the rule is therefore to ensure the osteosynthesis stability while limiting the number of levels included. Immobilization or fixation of a vertebral segment may be responsible for degeneration of the intervertebral disc and in case of surgical treatment the adjacent disc. Therefore, we can ask whether removal of a vertebral fixation could decrease the stress on adjacent segments. Ultrasound shearwave elastography is a new innovative and non-invasive technique allowing evaluation of soft tissue’s elastic modulus through the measurement of shear wave speed (SWS). This non-invasive imaging method has shown its added value in breast or in liver oncology and, more recently, in musculoskeletal pathologies assessment. In particular, Langlais et al. found that SWS measured in annulus fibrosus was significantly higher in progressive adolescent idiopathic scoliosis than in asymptomatic population, which is associated with a stiffer tissue. The same authors defined a corridor of normality (2.3–3.7 m/s) for the asymptomatic population and observed that annulus SWS tended to normalize 1 year after fusion surgery in severe adolescent idiopathic scoliosis. The aim of this case was to analyze the effect of removing the posterior fixation in a case of burst fracture on the mechanical properties of the bridged and adjacent intervertebral discs.