54. PMMA augmentation is not protective against proximal junctional kyphosis in adult spinal deformity correction bridging the thoracolumbar junction

Abstract

<h3>BACKGROUND CONTEXT</h3> Proximal junctional kyphosis (PJK) is a relatively common complication following adult spinal deformity surgery. Some studies have demonstrated cement augmentation of the upper instrumented vertebra (UIV) decreases development of acute PJK, while others have been inconclusive. This study quantifies the radiographic progression of PJK in patients undergoing instrumented spinal fusion for adult deformity crossing the thoracolumbar junction with and without polymethylmethacrylate (PMMA) vertebroplasty. <h3>PURPOSE</h3> Determine whether polymethylmethacrylate (PMMA) vertebroplasty is protective against development of proximal junctional kyphosis. <h3>STUDY DESIGN/SETTING</h3> Single center, retrospective. <h3>PATIENT SAMPLE</h3> One hundred patients who underwent thoracolumbar fusion between 2013 and 2020. <h3>OUTCOME MEASURES</h3> Development of proximal junctional kyphosis at 6 weeks, 6 months, 12 months and 24 months postoperative. <h3>METHODS</h3> A retrospective cohort of 100 patients who underwent thoracolumbar fusion between 2013 and 2020 was identified. PMMA augmentation at the UIV and UIV+1 was performed at the discretion of the treating surgeon. Degree of PJK was measured from preoperative scoliosis, immediate postoperative, 6-week, 6-month, 12-month, and 24-month radiographs. Osteoporosis and osteopenia were defined as a DEXA T score ≤ -2.5 and ≤ -1, respectively. Differences in PJK and reoperation rates between PMMA and non-PMMA groups were assessed with stratified Kaplan-Meier survival curves and 95% confidence intervals with log-rank tests. Other categorical variables were assessed with chi-square and Fisher's exact tests while continuous variables were assessed with Mann Whitney U tests. Bonferroni correction was used to adjust the error rate for the multiple time points when appropriate. Multivariable Cox proportional hazard models adjusted for osteoporosis, degenerative disc disease, number of levels fused, pain medications taken, osteoporosis medications taken, age, sex and PI-LL mismatch > ± 9. All analyses were performed with SAS vs 9.4 with a two-sided level of significance of α = 0.05. <h3>RESULTS</h3> One hundred patients were included. The median age was 68 (interquartile range (IQR) 64-73) and median follow up was 43 months (IQR 34 - 54). Of the cohort, 56% received PMMA, and this group was significantly older (p=0.021), more often female (p=0.04), and had a higher rate of osteopenia (p < 0.01) and osteoporosis (p=0.038), took more preoperative pain medications (p=0.02), and more often underwent concurrent decompression (p < 0.01). Patients augmented with PMMA had significantly lower DEXA scores (p=0.024). Of PMMA patients, 55.4% developed PJK compared to 44.6% of Non-PMMA patients (p=0.097). Patients augmented with PMMA had higher rates of PJK at 6 months, but there was no difference at any further time point. The rate of all cause reoperation was 7.1% in the PMMA group compared to 11.4% in the Non-PMMA group (p=0.501). In multivariable models, PJK risk was significantly predicted by the presence of osteopenia (p=0.002) and presence of osteoporosis (p < 0.03). After risk adjustment, there was no difference in PJK rates attributable to PMMA use (HR 0.77, 95% CI 0.38-1.6, p = 0.47). <h3>CONCLUSIONS</h3> In long thoracolumbar fusions for adult spinal deformity, PMMA augmentation was not protective against PJK. Osteopenia and osteoporosis were significantly associated with higher rates of PJK. This suggests a complex interplay of surgical, biomechanical and patient factors in achieving an optimal outcome. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.