258. The pelvic tilt response to ASD correction depends on PI, age and alignment

Abstract

BACKGROUND CONTEXT Increasing pelvic tilt (PT) is the main compensatory mechanism in sagittal spinal deformity. Traditionally PT>25° has been considered pathologically high. Some adult spinal deformity (ASD) patients do not seem to improve their PT following ASD correction. However, the driving forces behind this lack of PT-response are not well defined. Previous studies have demonstrated a significant relationship between pelvic incidence (PI), age and alignment. PURPOSE To investigate PT response following ASD surgery and its relationship to PI, age and alignment. STUDY DESIGN/SETTING Retrospective review of a prospectively-collected ASD database. PATIENT SAMPLE A total of 772 operative ASD patients with positive sagittal balance and 1-year follow up. OUTCOME MEASURES Postoperative spinal alignment and SF36-PCS. METHODS A prospective database of operative ASD was analyzed. Patients with a baseline TPA >5° from optimal were included. Regression models were developed to calculate optimal TPA (TPAo) and PT (PTo) for age and alignment. Similarly, the PT and TPA changes (MCIC) corresponding to the SF-36 PCS MCID were calculated. Two definitions for PT nonresponse were used: (1) Traditional: PT>25 at baseline and 1 year; (2) PT>PTo by 1 MCIC and PT change 20°). PT responders were compared to non-responders in terms of PI and PCS offset (difference between actual and age-ideal PCS). RESULTS A total of 772 patients met inclusion criteria (mean 64y, 75%F). 71% (n=548) had a pre-PT>25°, 25% had a PI >65°. PTo for each patient was calculated using the formula: PT=3.91-.01*Age+.101*PI+.701*TPA(R2=.82). Using the new PT definition, 45% had appropriate PT(PT=PTo) (PT>PTo: 22%).The MCIC for TPA and PT were 4.1° and 2.9°, respectively. At 1 year, 30% had a PT>25. 91 did not have MCIC for TPA and 34 had sPJK. Analysis of the remaining 103 nonresponders showed that 48% had a PI>65, 45% had a PT=PTo (PT>PTo: 51%). For patients with pre-PT>25 and 1 year PT>PTo (n=136), 27% had a PI>65, 26% had insufficient TPA correction, 27% had sPJK and 50% were >65y old. A total of 184 patients(24%) had a PT change 25 vs PTo groups (-16.7 vs -14.8 vs -13.4, p PTo group had worse PCS offset compared to the PT=PTo group (-9.5 vs .59, p CONCLUSIONS PT response in ASD surgery depends on change in spinal alignment but also age and PI and so it is patient specific. A PT within 2.9° of optimal was considered appropriate. Nearly half of the 45% of patients traditionally considered to be PT nonresponders had an appropriate PT for age and alignment. A postoperative PT greater than optimal was associated with worse HRQL. This study's novel patient-specific method for defining PT response reveals that PT is not a one-size-fits-all parameter; it is imperative to consider the patient's PI, age and alignment. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.