Spine Surgeon NYU School of Medicine New Canaan, CT, US
Introduction: Full body radiographs allow for the assessment of lower limb compensation and global alignment in adult spinal deformity(ASD) patients, although little work has been done looking at how these mechanisms affect age-adjusted realignment by two years. We sought to determine if ASD patients displaying lower extremity(LE) compensation after ASD surgery demonstrate malalignment in age-adjusted parameters.
Methods: Retrospective cohort study of ASD patients with two-year data. Age-adjusted values assessed for PI-LL, pelvic tilt(PT), T1-pelvic angle(T1PA), and Sagittal Age-Adjusted Score(SAAS) based on published formulas. Patients who matched(‘Match’) age-adjusted targets were compared to unmatched cases(‘Undercorrected/Under’ or ‘Overcorrected/Over’). Compensatory mechanisms tested: Knee Angle(KA), sacrofemoral angle(SFA), Ankle Angle(AA), Pelvic Shift(PS), Global Spinal Angle(GSA). Each parameter was ranked at early follow-up and highest tertile was deemed ‘compensating’. Multivariable regression analysis controlling for age, gender, and baseline deformity assessed likelihood of maintaining alignment when compensating.
Results: 225 ASD patients improved in each parameter at early follow-up and 2Y(all p< 0.001). 64.8% were compensating at baseline(32% hip,39% knee,39% ankle,47% global; 20% TKA/THA). At early follow-up, patients improved in KA, PS, and GSA(all p< 0.001). From early-2Y, patients recruited knee flexion and pelvic shift(p < 0.05) while GSA increased(p=0.001). At early follow-up, age-adjusted corrections were: 40% ‘Under’,25% ‘Over’,35% ‘Match’. Patients compensating at baseline were more likely to be undercorrected by early follow-up(OR:8.2,[3.0-22.4];p < .001). Adjusted analysis revealed those undercorrected were more likely to be compensating by early follow-up(OR:5.1;[1.8-14.3];p=.002). Patients undercorrected increased hip extension by early follow-up(p=.001). When examining ‘Match’ patients, those unmatched by 2Y were more likely to be compensating at early follow-up(OR:32.7,[1.04-1026.7];p=.047).
Conclusion : Patients improved in alignment by early follow-up, while recruiting compensatory mechanisms by two years. Lower extremity compensation proved to be a product of undercorrection, plays a role in disrupting age-adjusted alignment over time, and, should be considered during surgical planning and postoperative management to conserve spinopelvic realignment.
