Distraction Forces on the Spine in Early-onset Scoliosis: A Systematic Review and Meta-analysis of Clinical and Biomechanical Literature

Distraction-based growing rods are frequently used to treat Early-Onset Scoliosis. These use intermittent spinal distractions to maintain correction and allow for growth. It is unknown how much spinal distraction can be applied safely. We performed a systematic review and meta-analysis of clinical and biomechanical literature to identify such safety limits for the pediatric spine. This systematic review and meta-analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Three systematic searches were performed including in-vivo, ex-vivo and in-silico literature. Study quality was assessed in all studies and data including patient- or specimen characteristics, distraction magnitude and spinal failure location and ultimate force at failure were collected. Twelve studies were included, 6 in-vivo, 4 ex-vivo and 2 in-silico studies. Mean in-vivo distraction forces ranged between 242 and 621 N with maxima of 422-981 N, without structural failures when using pedicle screw constructs. In the ex-vivo studies (only cervical spines), segment C0-C2 was strongest, with decreasing strength in more distal segments. Meta-regression analysis demonstrated that ultimate force at birth is 300-350 N, which increases approximately 100 N each year until adulthood. Ex-vivo and in-silico studies showed that yielding occurs at 70-90% of ultimate force, failure starts at the junction between endplate and intervertebral disc, after which the posterior- and anterior long ligament rupture. While data on safety of distraction forces is limited, this systematic review and meta-analysis may aid in the development of guidelines on spinal distraction and may benefit the development and optimization of contemporary and future distraction-based technologies.