Paraspinal muscle size as an independent risk factor for proximal junctional kyphosis in patients undergoing thoracolumbar fusion
Presented at the 2019 AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves
OBJECTIVE
Proximal junctional kyphosis (PJK) is a structural complication of spinal fusion in 5%–61% of patients treated for adult spinal deformity. In nearly one-third of these cases, PJK is progressive and requires costly surgical revision. Previous studies have suggested that patient body habitus may predict risk for PJK. Here, the authors sought to investigate abdominal girth and paraspinal muscle size as risk factors for PJK.
METHODS
All patients undergoing thoracolumbosacral fusion greater than 2 levels at a single institution over a 5-year period with ≥ 6 months of radiographic follow-up were considered for inclusion. PJK was defined as kyphosis ≥ 20° between the upper instrumented vertebra (UIV) and two supra-adjacent vertebrae. Operative and radiographic parameters were recorded, including pre- and postoperative sagittal vertical axis (SVA), sacral slope (SS), lumbar lordosis (LL), pelvic tilt, pelvic incidence (PI), and absolute value of the pelvic incidence–lumbar lordosis mismatch (|PI-LL|), as well as changes in LL, |PI-LL|, and SVA. The authors also considered relative abdominal girth and the size of the paraspinal muscles at the UIV.
RESULTS
One hundred sixty-nine patients met inclusion criteria. On univariate analysis, PJK was associated with a larger preoperative SVA (p < 0.001) and |PI-LL| (p = 0.01), and smaller SS (p = 0.004) and LL (p = 0.001). PJK was also associated with more positive postoperative SVA (p = 0.01), ΔSVA (p = 0.01), Δ|PI-LL| (p < 0.001), and ΔLL (p < 0.001); longer construct length (p = 0.005); larger abdominal girth–to-muscle ratio (p = 0.007); and smaller paraspinal muscles at the UIV (p < 0.001). Higher postoperative SVA (OR 1.1 per cm), smaller paraspinal muscles at the UIV (OR 2.11), and more aggressive reduction in |PI-LL| (OR 1.03) were independent predictors of radiographic PJK on multivariate logistic regression.
CONCLUSIONS
A more positive postoperative global sagittal alignment and smaller paraspinal musculature at the UIV most strongly predicted PJK following thoracolumbosacral fusion.
ABBREVIATIONS
AP = anteroposterior; BMD = bone mineral density; BMP = bone morphogenetic protein; CCI = Charlson Comorbidity Index; DEXA = dual energy x-ray absorptiometry; LL = lumbar lordosis; |PI-LL| = absolute value of PI-LL mismatch; PJK = proximal junctional kyphosis; ROC = receiver operating characteristic; SS = sacral slope; SVA = sagittal vertical axis; UIV = upper instrumented vertebra.
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