P12. Does posterior ligamentous complex disruption following lumbar pedicle screw and rod instrumentation affect the upper adjacent level

BACKGROUND CONTEXT The lumbar level above the fusion segment is the most common level for the development of adjacent level instability. The posterior ligamentous complex (PLC), (eg, interspinous ligament, and supraspinous ligament) a posterior tension band that stabilizes the spine, is usually removed for laminectomy during lumbar fusion and decompression surgery. The removal of the posterior complex may jeopardize upper adjacent level stability. PURPOSE To compare mobility and principal disc strains at the upper adjacent level to L4-5 pedicel screw-rod fixation (PSR) between L4-5 PSR, L4-5 PSR+ bilateral laminotomy (PLC preservation), and L4-5 PSR+ conventional laminectomy, in cadaveric specimens. The disc strain was studied with a new optical technique of soft tissue strain analysis (3D digital image correlation (DIC) technique). STUDY DESIGN/SETTING Biomechanic testing in human cadaveric spine specimens. PATIENT SAMPLE Human cadaveric lumbar spine. OUTCOME MEASURES 1. Adjacent segment range of motion, 2. Disc surface strains. METHODS Seven human cadaveric L3-S1 specimens were instrumented with L4-5 PSR. All specimens were tested multi-directionally under pure moment loading (7.5Nm) following: 1) L4-5 PSR, 2) L4-5 PSR+bilateral L4 laminotomy while preserving PLC and 3) L4-5 PSR +L4 conventional laminectomy. DIC was performed with cameras positioned laterally (left side) to capture the change in disc principal strain (Pmax and Pmin) at upper adjacent level (L3-4) under peak load. Optical motion tracking was simultaneously performed on the right side. The disc region was divided into four similar sized quarters and included upper and lower endplates. Analysis of variance of upper adjacent level (L3-4) range of motion (ROM) and disc strain between the groups was performed. Statistically significant was set at p≤0.05. RESULTS ROM of the upper adjacent (L3-4) level was significantly greater with L4-5 PSR+laminectomy (6.26 degree) versus L4-5 PSR+ bilateral laminotomy (5.94 degree, p=0.006), and L4-5 PSR (5.20 degree, p CONCLUSIONS The posterior ligamentous complex disruption during lumbar fusion surgery was associated with significant increases in upper adjacent level instability and principle (Pmax) intervertebral disc stress/strain. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.