Postoperative lower limb compensation in patient with adult spinal deformity

The objective of this study was to determine whether inadequate decompensation of spine and pelvis would lead to persistent compensatory action of lower extremity. Patients who underwent adult spinal deformity from January 2014 to December 2016 were included. Postoperatively, patients who showed persistent lower extremity compensation (femur obliquity angle/FOA ≥ 5°) were classified into compensated lower extremity (CLE) group and decompensated lower extremity (DLE) group with FOA < 5°. Sagittal vertical axis (SVA), T1 spinopelvic inclination, TPA (T1 pelvic angle), thoracic kyphosis, lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt, sacral slope and FOA were measured and compared between two groups. The lack of lumbar lordosis was assessed by PI-LL mismatch and multivariate analysis were used to investigate correlation in changes of parameters. 115 patients were classified into CLE group (23 patients) and DLE group (92 patients). Thoracic compensations were more prevalent in the CLE group while pelvic compensation was more prominent in the DLE group. Both postoperative TPA and PI-LL in the CLE group were greater than those in the DLE group while postoperative SVA was similar. At 1 year postoperatively, SVA was increased in the CB group with persistent lower extremity compensation. Changes in FOA had moderate correlation with changes in SVA and strong correlation with changes in TPA. In conclusion, postoperative persistent lower limb compensation can be interpreted into surgical undercorrection. TPA rather than SVA is a useful parameter to assess global alignment and compensatory action of the lower extremity.