The Coronal Plane Matters: An Evaluation of Primary Coronal Cobb Correction for Adult Spinal Deformity using Pre-Bent Sagittal Contoured Rods

Introduction: Patient specific rods (PSR) are pre-bent to post-spinal fusion sagittal alignment goals. Adult idiopathic and degenerative scoliosis can cause large, multiplanar, and rigid coronal deformities. It is unknown to whether a sagittaly-derived PSR detracts from coronal correction.

Methods: Patients > 18 years-old with adult idiopathic or degenerative scoliosis who received posterior instrumented fusion from a single surgeon/single institution were reviewed. Patients with prior fusions > 2 levels were excluded. Those fused >6 levels using PSRs with a UIV and LIV greater than T1 and L1, respectively, were included. All patients had at least one coronal Cobb angle > 20°. Demographics, operative/inpatient variables were recorded. Post-operative versus pre-operative primary Cobb angle were compared; post-operative sagittal alignment versus pre-and planned alignment goals were compared. Restoration of primary coronal Cobb was evaluated in a multivariable regression model, including scoliosis type, primary curve apex PCOs, and final sagittal alignment deviation from the plan.

Results: 33 patients were included. The average age was 61.1 ± 16.7; 25 were female (25/33, 75.8%). BMI averaged 26.5 ± 4.3kg/m2. Degenerative scoliosis was more common than idiopathic (22/33, 66.7%). The average pre-op PI, lumbar lordosis (LL), and pelvic tilt (PT) were 56.0 ± 13.7°, -48.1 ± 16.0°, and 21.6 ± 9.5°, respectively. T5-T12 kyphosis was 33.3 ± 17.0°. The most frequent primary Cobb angle was thoracolumbar (38.1 ± 10.5°, 30/33, 90.9%.). 9.7 ± 3.1 levels were fused per case; coronal apex PCOs were performed 29/33 patients (87.8%). Post-operative primary Cobb angle was reduced 58.8± 27.7% to 15.0 ± 9.7°. Final LL was slightly less than planned (mean 4.3°, 95% CI[.91 -7.7], p = 0.01); PT and T5-T12 kyphosis were similar to the plan (mean 4.9°, 95% CI[-.95 -10.7], p = 0.9; mean 2.5°, 95% CI[-1.0-6.0], p = 0.16). On multivariable analysis, primary Cobb angle change was significantly correlated with starting Cobb magnitude (p = .01); PCO location/number and nearness of final sagittal parameters to goal were not significant (overall model r2 = .48, p = .01).

Conclusion : Significant primary coronal Cobb restoration from PSRs is achieved in tandem with sagittal realignment. Research evaluating whether predictive analytics could include coronal parameters is warranted.