LAUSR

EUROSPINE Meetings 2018: Abstracts, 19–21 September ADULT DEFORMITY/GROWING SPINE QF1 COMPENSATORY MECHANISMS OF LOWER LIMB IN ADULT SPINAL DEFORMITY—IS THE ANKLE DORSIFLEXED OR PLANTER-FLEXED?Mitsuru Takemoto, Takayoshi Shimizu Dept of Orthopaedic and Spine Surgery, Kyoto City Hospital, Kyoto, Japan Introduction: Patients with adult spinal deformity (ASD) compensate their spinal using their lower-limb compensatory mechanisms (LCMs). When a patient has a decreased lumbar lordosis (LL), the center of gravity (COG) shifts anteriorly. Anteriorly shifted COG is corrected backward and its vertical position is kept on the feet by LCMs (such as hip extension and knee flexion). As for LCMs by ankle, planter flexion also induces posterior translation of COG (Barrey, et al, 2011). However, recent studies based on the full-body (head to toe) radiographic evaluation indicate that ASD patients dorsiflex their ankle. The aim of this study is to clarify the detail of LCMs to explain this contradiction using a simple mathematical model. Methods: This full-body mathematical model consists of 15 segments (i.e., head, upper trunk, lower trunk, upper arms, anterior arms, hands, thighs, lower legs, and feet), which were connected by 14 joints. We defined the base of the feet (12 cm anterior from heels) as the coordinates of the origin of sagittal plane [ (y, z) = (0 cm, 0 cm)]. The coordinates of the COG were calculated based on the weight and the relative location of each segment, which were determined based on the previous literatures and our original data. First, we developed a healthy model (model-H, PI = 52, LL = 60), second a lumbar kyphosis model (model-LK, PI = 52, LL = 0), and finally compensated lumbar kyphosis models. In compensated models, at first, the degrees of hip extension (He = 0, 10, 20) and ankle dorsiflexion (Ad = 5, 0, 5, 15) were determined. Then, in each model, the vertical position of COG is corrected backwards and restored on the feet (y = 0 cm) by knee flexion, and the degree were recorded. We also calculated each of sagittal parameters and the moments of forces (MOFs) at the posterior corner of sacrum, hip, and knee joint. Results: Representative results are shown in Fig. 1. Five-degree ankle dorsiflexion causes 8-degree increase in knee flexion, resulting in 3-degree PT increase, 2 cm SVA decrease and 50–70 cm*kg decrease in MOF at sacrum and hip joints. Ten degree hip extension causes 3-degree decrease in knee flexion, resulting in 7-degree PT increase, 4 cm SVA decrease, and 80–150 cm*kg decrease in MOF at sacrum and hip joints. More than 5-degree ankle dorsiflexion shifts knee joints anteriorly to COG, resulting in increased MOF at knee joints. Conclusion: Ankle dorsiflexion causes additional knee flexion, resulting in increased PT and decreased SVA and MOF at sacrum and hip joints. Disclosures: Author 1: none; author 2: none. Fig. 1 Representative results. Model-LK: lumbar kyphosis model. In compensated models, ‘‘He’’ indicates degree of hip extension, and ‘‘Ad’’ indicates degree of ankle dorsiflexion. Moment (sum): sum of moments of forces at sacrum, hip and knee joints 123 European Spine Journal https://doi.org/10.1007/s00586-018-5692-z