Pedicle shifting or migration as one of the causes of curve progression after posterior fusion: an interesting case report and review of literature

Abstract

The aim of this retrospective study was to explain a previously undescribed mechanism of 'pedicle migration or shift' with longitudinal growth of the spine owing to biological remodeling of plastic posterior fusion mass as well as pedicles which may explain at least a few cases of deformity recurrence after posterior fusion in scoliosis surgery. Progressive loss of deformity correction after scoliosis surgery in growing children has been variously described. The various mechanisms described have been 'crankshaft effect', pseudoarthrosis, implant failure (loosening/breakage), biological plasticity, choosing wrong levels, excessive apical translation causing decompensation by unfused segments, progressive etiology, inadequate anchorage provided by some older instrumentation systems, etc. Though there have been claims that segmental pedicle instrumentation might prevent crankshaft phenomenon by providing a more rigid fixation, numerous studies have shown progressive loss of correction even after segmental pedicle instrumentation. A 10.6-year-old girl was fused posteriorly before her prepubertal growth spurt using segmental screw rod instrumentation. The index case in our study showed progressive loss of operative correction during subsequent follow-up at 2 years. This probably occurred because of longitudinal growth of the spine and posterior fusion mass because of its biological plasticity during the period of rapid growth spurt. In conclusion, despite the recent trend towards the use of segmental pedicle instrumented correction and fusion and claims that by providing rigid, tri-column fixation, it enhances fusion and controls growth of the vertebral body anteriorly; caution must be taken in children with high remaining growth and high growth velocity.