Cranial Center of Mass Compared to C7 Plumb Line Alignment in Adult Spinal Deformity

To report the cranial center of mass (CCOM) progression in surgically treated patients for adult spinal deformity (ASD). The C7 plumb line/sagittal vertical axis (SVA) has important relationships with patient-reported outcomes; however, this has not yet been defined for CCOM.

Patients with consecutive ASD who were undergoing surgery greater than 5 levels of fusion between 2007 and 2012 and had radiographic, clinical, and outcomes data spanning ≥2 years were analyzed, retrospectively. Radiographic parameters were obtained preoperatively and at 6 weeks, 1 year, and 2 years postoperatively. Statistical analysis included descriptives (measures of central tendency, dispersion, frequencies), independent Student t tests, χ(2) square, Pearson correlation, and Kaplan-Meyer curve.

Fifty-eight patients (10 male, 48 female) with a mean age of 60.5 years (range, 27-81 years) were reviewed. The mean preoperative SVA was 7.40 cm (SD = 5.51; 37/58 [63.8%] malalignment), and mean CCOM was 10.0 cm (SD = 6.58; 47/58 [81%] malalignment). Six-week postoperative SVA and CCOM was -0.17 cm (SD = 3.3) and 2.5 cm (SD = 4.11), respectively. SVA malalignment was 12.7% and CCOM malalignment was 38.2% at 6 weeks postop. Six week (absolute), 6-week change, and patient number at 6 weeks who were CCOM malaligned was significant compared with SVA (P = 0.003, P < 0.001, P < 0.001, respectively). SRS appearance worsened as preoperative SVA and CCOM increased (P < 0.05), and 2-year SRS appearance and mental health was worsened as 2-year SVA and CCOM increased (P < 0.05). SVA malalignment was 8 and 10 at 1 and 2 years, respectively, and CCOM malalignment was 24 and 32, respectively. Kaplan-Meier curve demonstrates persistent malalignment of CCOM at 6 weeks if not corrected.

CCOM alignment restoration is an important parameter in ASD, and malalignment is consistent over time.