179. Correcting ASD patients to normative alignment results in no functional benefit but more PJK and PJF

BACKGROUND CONTEXT

A previous study utilized normative alignment to determine overcorrections and predict mechanical complications in adult spinal deformity (ASD) surgery. Other studies have recommended alignment targets that optimize age-appropriate physical function. The difference in functional outcomes and mechanical complications between these prescribed alignment targets has not been explored. This study utilizes a component angle of the T1 pelvic angle (TPA) within the fusion to compare normative and age-pelvic incidence (PI) optimal alignment in terms of proximal junctional kyphosis (PJK), proximal junctional failure (PJF) and health related quality of life measures (HRQL). Using the component of TPA within the fusion, the T4-pelvic angle (T4PA), allows for the measurement spinopelvic alignment separate from that of the unfused thoracic spine and any PJK that may occur postoperatively.

PURPOSE

To compare ASD patients corrected to normative alignment vs age-PI optimal alignment in terms of PJK/PJF and outcomes.

STUDY DESIGN/SETTING

Retrospective analysis of a prospective multicenter ASD database and a database of asymptomatic subjects.

PATIENT SAMPLE

This study included 1,916 ASD patients and 118 asymptomatic subjects for formula development; 288 ASD patients with 2-year X-ray and HRQL follow-up.

OUTCOME MEASURES

SF36-PCS, ODI, SRS-22, NRS back/leg, PJK (change in UIV to UIV+2 >10°), PJF (defined as severe PJK with change >21.6°, or UIV olisthesis, or proximal junctional fracture).

METHODS

Baseline relationships between age, PI and T4PA, were analyzed in the ASD patients and compared to the asymptomatic subjects. Linear regression modeling was used to determine alignment based on PI and age in asymptomatic subjects (normative alignment), and in ASD patients, alignment corresponding to age-appropriate functional status (optimal alignment). ASD patients with UIV above T4 were grouped based on their corrections: normative vs optimal. Extreme over or under corrected patients were excluded (greater than or less than 2SD from mean postop T4PA). For each group, the rate of PJK and PJF were determined.

RESULTS

In the multilinear regression analysis of the 119 asymptomatic subjects, T4PA correlated with age and PI, r=.713, p<.0001. 1916 ASD patients were included in the optimal formula development. In the 288 ASD patients included in the pre- to postop analysis (137 normative, 151 optimal), there was no difference in baseline alignment or HRQL between the groups. At 6 weeks, the normative aligned group had smaller T4PA (4.45 vs 14.1) and PI-LL (-7.24 vs 7.4), all p<.0001. Normative aligned patients had the higher PJK rate (40% vs 27.2%, p=.03) compared with optimal; and a higher PJF rate (17% vs 6.8%, p=.008). PJF patients had -1.2°of T4PA offset from normative alignment and -5.2°of offset from optimal alignment. By contrast, no PJF patients had 3.8° of T4PA offset from normative alignment and -0.42° of offset from optimal alignment. There was a trend toward worse 2-year SF36-PCS in patients who suffered PJF (37.7 vs 41.6, p=.09). Both the Normative and Optimal groups improved in outcomes from baseline to 2-year (p<.001) with no difference in 2-year HRQL.

CONCLUSIONS

Correcting ASD patients to normative alignment resulted in higher rates of PJK and PJF without improvements in HRQL. ASD patients should not be corrected to match the alignment of their asymptomatic unfused peers, rather they should be realigned optimally to match age-appropriate physical function.

FDA DEVICE/DRUG STATUS

This abstract does not discuss or include any applicable devices or drugs.