Biomechanical comparison of different anchors (foundations) for the pediatric dual growing rod technique.
BACKGROUND
Children with early onset scoliosis benefit from early operative treatment with dual growing rods as they provide an "internal brace" for the spine and allow curve correction and sequential lengthenings to maximize thoracic cage development. The foundations that provide anchor points for the dual growing rods may incorporate hooks, screws, or a hybrid construct. It is unclear how stable different types of foundation constructs are with regard to pullout.


OBJECTIVE
This study was to determine the differences in stability between four foundation configurations used in the pediatric dual growing rod technique. Eight porcine spines were sectioned and randomly assigned to one of four foundation groups: 1) hook-hook with cross-link; 2) hook-screw with cross-link; 3) screw-screw with cross-link; and 4) screw-screw without cross-link. After instrumentation, biomechanical pullout tests were conducted. Ultimate failure loads, modes of failure, and level of instrumentation were analyzed.


METHODS
Controlled in vitro laboratory investigation.


RESULTS
Screw-screw with cross-link constructs demonstrated the greatest failure load but this was not statistically significant compared with the screw-screw without cross-link constructs. Both screw-screw constructs were statistically stronger than either construct containing hooks. There was no difference between the hook-screw and hook-hook constructs that was statistically significant. Hook-containing constructs sustained higher failure loads in lumbar versus thoracic vertebrae.


CONCLUSIONS
A foundation composed of four pedicle screws implanted in two adjacent vertebral bodies provides the strongest construct in pullout testing. A cross-link does not seem to enhance fixation. Hook constructs are stronger in lumbar versus thoracic laminae.
Mahar
Andrew Todd
AT
Department of Orthopedics, Rady Children's Hospital San Diego, San Diego, CA, USA. amahar@chsd.org
Bagheri
Ramin
R
Oka
Richard
R
Kostial
Patricia
P
Akbarnia
Behrooz A
BA
D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws; D001864:Bone Wires; D002648:Child; D019544:Equipment Failure Analysis; D006801:Humans; D066298:In Vitro Techniques; D008159:Lumbar Vertebrae / Q000254:growth & development / Q000502:physiology / Q000601:surgery; D012600:Scoliosis / Q000503:physiopathology* / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D013552:Swine; D013904:Thoracic Vertebrae / Q000254:growth & development / Q000502:physiology / Q000601:surgery