General Session: Biomechanics
Presented by: B. Bucklen - View Audio/Video Presentation (Members Only)
I. Cheng(1), F. Lamarca(2), J. Pirolo(3), C. Farley(2), S. Yandamuri(4), E. Matheis(5), B. Bucklen(4)
(1) Stanford University, Orthopaedic Surgery, Palo Alto, CA, United States
(2) University of Michigan, Ann Arbor, MI, United States
(3) Stanford University, Palo Alto, CA, United States
(4) Globus Medical, Audubon, PA, United States
(5) Globus Medical, Musculoskeletal Education and Research Center, Audubon, PA, United States
Objectives: Long pedicle screw constructs have been associated with a high incidence of proximal junctional kyphosis (PJK) in both adults and adolescents, in which an abrupt change from rigidity to complete motion occurs in unfused spinal segments. Semi-rigid constructs have been used to bridge free-motion and completely rigid segments to achieve gradual motion restoration.
Methods: Eleven T8-L2 human specimens were tested on a six-degrees-of-freedom machine with a motion capture system that monitored the most proximal fixed segments in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) motion. Specimens were instrumented from T10-L2 with pedicle screws at T12-L2 and were tested in two groups with varying instrumentation at proximal levels (T10-T11). Group 1: (1) intact; (2) bilateral pedicle screws (PS); (3) one-level sublaminar 6mm polyethylene terephthalate (PET) band (SL-1); and (4) two-level sublaminar 6mm PET band (SL-2); Group 2: (1) intact; (2) bilateral pedicle screws (PS); (3) one-level bilateral dynamic stabilization (T1); and (4) two-level bilateral dynamic stabilization (T2).
Results: The general trend in ROM was PS < one-level semi-rigid constructs < two-level semi-rigid constructs, across all loading modes with very few exceptions
Conclusions: PET bands and dynamic stabilization show similar flexibility, providing a less rigid option than pedicle screws for gradual stabilization of the spine. Two-level semi-rigid constructs showed a similar increase in ROM with either PET bands or dynamic stabilization across all loading modes. Gradual stabilization may be clinically relevant as a potential prophylactic treatment for PJK. (Figure). At T11-T12, the increase in ROM from the PS construct with SL-1/SL-2 and T1/T2 constructs showed analogous trends across all bending modes, with two-level treatment (SL-2, T2) yielding the greatest increase. However, at T10-T11, subtle differences in FE and LB were seen across both groups.