P4. In vitro assessment of adjustable lordotic expandable lateral interbody spacers on endplate loading and lordosis correction

BACKGROUND CONTEXT Anterior column realignment is a minimally invasive technique that uses a lateral transpsoas interbody approach with anterior longitudinal ligament (ALL) release, which aims to restore sagittal alignment. Resection of the ALL enables use of expandable lateral lumbar interbody fusion (LLIF) spacers with larger implant heights and lordosis, increasing focal lordosis correction and minimizing endplate mismatch. The relationship between implant height and lordosis selection, and their effect on segmental lordosis correction and anterior-posterior endplate loading, is poorly understood. PURPOSE The aim of this study is to quantify lordosis correction and endplate force distribution using an adjustable-lordosis expandable LLIF spacer. STUDY DESIGN/SETTING In vitro human cadaveric study. PATIENT SAMPLE A total of seven cadaveric specimens. OUTCOME MEASURES Lordosis and anterior-posterior endplate forces. METHODS Seven L4–L5 cadaveric segments were used. A 55 lb axial load was applied to L4 to simulate intraoperative loads. Segments were instrumented with bilateral pedicle screws and a sequence of expandable spacers with anterior fixation at varied heights and implant lordosis (ten constructs), including (A) 0°, 6°, and 20° lordosis with intact ALL; B) 20° and 30° lordosis following ALL resection. Segmental lordosis and endplate force-maps were collected. An equivalent loading ratio (ELR=anterior load/total load*100%) was calculated; ELR=80% refers to 80% anterior and 20% posterior edge loading. ELR was statistically compared to 50%, which is equivalent anterior-posterior loading. RESULTS The mean intact L4–L5 lordosis was 11.5°±3.0°. With the ALL intact, the 20° spacer without expansion increased lordosis to 11.9°±3.6° (p\u003e0.05). Following ALL resection, use of 20° spacer with largest expansions (14.7 and 17.4 mm) significantly increased lordosis to 19.4°±4.5° (p=0.036 and 22.5°±4.9° (p CONCLUSIONS This study suggests that expandable spacers may help to balance anterior-posterior endplate loading while maximizing lordosis correction. Following ALL release, hyperlordotic spacers do not increase anterior loading, therefore, spacers may be selected for maximum lordosis. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.