General Session: Biomechanics - Hall F

Presented by: P. Passias


P. Passias(1), S. Horn(1), G. Poorman(1), J. Moon(1), P. Zhou(1), J. Tishelman(1), L. Steinmetz(1), C. Bortz(1), F. Segreto(1), D. Ge(1), B. Beaubrun(1), C. Jalai(1), M. Gerling(1), A. Buckland(1), V. Lafage(2)

(1) New York University Langone Orthopedic Hospital, Division of Spinal Surgery, New York, NY, United States
(2) Hospital for Special Surgery, Department of Orthopaedic Surgery, New York, NY, United States


Introduction: Few studies have investigated the impact of cervical deformity (CD) on lower limb compensation. Previous reports show that thoracolumbar deformity (TLD) affects lower limb compensation and cervical spine alignment. The aim of this study was to assess patients with radiographically defined CD with and without concurrent TLD to identify differences in pelvic and lower limb compensation.

Methods: Single center retrospective review of patients with full body stereoradiographic x-rays ages≥18 years with radiographic CD defined as at least one of the following: cervical sagittal vertical axis (cSVA)>4cm, C2-C7 lordosis (CL)>10º, T1 slope - CL (TS-CL)>20 º, or chin brow vertical angle (CBVA)>25 º. TLD was defined as at least one of the following: SVA>4cm, PI-LL>10°, or PT>20°. Patients were grouped on the basis of TLD presence into two groups: CD-only or CD with concomitant TLD(CD-TLD). Patients were propensity score matched for age, gender, and BMI and were then evaluated for regional, global, and lower limb compensation: cSVA, CL, TS-CL, CBVA, thoracic kyphosis(TK), T1 pelvic angle(TPA), T1 slope(T1S), sagittal vertical axis(SVA), lumbar lordosis(LL), spino-pelvic mismatch(PI-LL), and pelvic tilt(PT); C0-C2, C0, C1, C2 slope, slope of line of sight(SLS), sacrofemoral angle(SFA), knee flexion(KA), ankle flexion(AA), pelvic shift(PS), global sagittal angle(GSA). Clinical

Outcomes: Neck Disability Index(NDI), Oswestry Disability Index(ODI), Visual Analog Scale(VAS). Alignment and clinical outcome differences between the groups were assessed with independent t-tests.

Results: Of 1360 included patients, 680 had CD-only and 680 had CD with concurrent TLD. Relative to an unaffected population, CD-only patients were within the normal ranges for TK, LL, and CBVA, though their TPA was lower than an unaffected population. Additionally, CD-only patients had similar knee flexion compensation as unaffected patients, but CD-only patients recruit more pelvic shift than unaffected individuals. In comparing CD patients with and without concurrent TLD, TK and CTPA were higher in the CD-only cohort (p< 0.001). In looking at the patients' upper cervical and cranial parameters, CD-only patients had a smaller C1 slope and SLS than CD-TLD but a larger CBVA (all p< 0.05). CD-only and CD-TLD patients showed significantly different lower limb compensation: SFA, KA, AA, Pelvic Shift, and GSA were all significantly greater in the CD-TLD cohort (all p< 0.001), suggesting that CD patients with concomitant TLD recruit more lower limb compensation for their malalignment. In a sub-analysis of patients with HRQLs, Vas Neck and Leg scores were significantly different between the groups: CD-only patients had higher VAS Neck scores (2.54 vs 2.0, p=0.026) and lower VAS Leg scores (3.2 vs 4.14, p=0.001) than the CD-TLD group and CD patients without severe TLD had a higher NDI score than patients with concurrent severe TLD (28.5 vs 23.8, p=0.028).

Conclusions: Patients with only cervical deformity have similar lower limb compensation to an unaffected population, though they have slightly lower TPA and recruit more pelvic shift. Cervical deformity patients with concurrent thoracolumbar deformity recruited more lower limb compensation for their malalignment than patients with only cervical deformity, as shown by an increase in knee and ankle flexion, pelvic shift as well as SFA and GSA. CD-only patients had higher neck pain scores and lower leg pain scores than patients with concurrent TLD.