Association between lower Hounsfield units and proximal junctional kyphosis and failure at the upper thoracic spine

Abstract

OBJECTIVE The aim of this study was to analyze risk factors and avoidance techniques for proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) in the upper thoracic spine with an emphasis on bone mineral density (BMD) as estimated by Hounsfield units (HU). METHODS A retrospective chart review identified patients at least 50 years of age who underwent instrumented fusion extending from the pelvis to an upper instrumented vertebra (UIV) between T1 and T6 and had a preoperative CT, pre- and postoperative radiographs, and a minimum follow-up of 12 months. HU were measured in the UIV, the vertebral body cephalad to the UIV (UIV+1), and the L3 and L4 vertebral bodies. Numerous perioperative variables were collected, including basic demographics, smoking and steroid use, preoperative osteoporosis treatment, multiple frailty indices, use of a proximal junctional tether, UIV soft landing, preoperative dual-energy x-ray absorptiometry, spinopelvic parameters, UIV screw tip distance to the superior endplate, UIV pedicle screw/pedicle diameter ratio, lumbar lordosis distribution, and postoperative spinopelvic parameters compared with age-adjusted normal values. RESULTS Eighty-one patients were included in the study (21 men and 60 women) with a mean (SD) age of 66 years (6.9 years), BMI of 29 (5.5), and follow-up of 38 months (25 months). Spinal fusion constructs at the time of surgery extended from the pelvis to a UIV of T1 (5%), T2 (15%), T3 (25%), T4 (33%), T5 (21%), and T6 (1%). Twenty-seven patients (33%) developed PJK and/or PJF; 21 (26%) had PJK and 15 (19%) had PJF. Variables associated with PJK/PJF with p < 0.05 were included in the multivariable analysis, including HU at the UIV/UIV+1, HU at L3/L4, DXA femoral neck T-score, UIV screw tip distance to the superior endplate, UIV pedicle screw/pedicle diameter ratio, and postoperative lumbar lordosis distribution. Multivariable analysis (area under the curve = 0.77) demonstrated HU at the UIV/UIV+1 to be the only independent predictor of PJK and PJF with an OR of 0.96 (p = 0.005). Patients with < 147 HU (n = 27), 147–195 HU (n = 27), and > 195 HU (n = 27) at the UIV/UIV+1 had PJK/PJF rates of 59%, 33%, and 7%, respectively. CONCLUSIONS In patients with upper thoracic–to-pelvis spinal reconstruction, lower HU at the UIV and UIV+1 were independently associated with PJK and PJF, with an optimal cutoff of 159 HU that maximizes sensitivity and specificity.

Lower Hounsfield Units and Severe Multifidus Sarcopenia Are Independent Predictors of Increased Risk for Proximal Junctional Kyphosis and Failure Following Thoracolumbar Fusion

“…1,4 In an effort to reduce the risk of PJK and PJF, many studies have sought to identify risk factors for the development of these complications. 1,[5][6][7][8][9] In their study of patients undergoing thoracolumbar fusions that terminated proximally near the thoracolumbar junction for degenerative indications, Mikula et al 7 identified diminished HU at the UIV as a risk factor for PJK. A subsequent study by the same authors revealed that lower HU at the UIV was also associated with an increased risk of PJK and PJF in patients undergoing long-construct thoracolumbar fusions that terminated proximally in the upper thoracic spine.…”

“…A subsequent study by the same authors revealed that lower HU at the UIV was also associated with an increased risk of PJK and PJF in patients undergoing long-construct thoracolumbar fusions that terminated proximally in the upper thoracic spine. 8 However, while these studies did consider demographic variables, sagittal alignment parameters, and DEXA measurements in their multivariate analyses, they did not include other potentially important risk factors such as frailty indices and paraspinal fatty degeneration. Consequently, the impact of evidence-based frailty indices and sarcopenia on proximal junctional complications has remained unknown.…”

“…Complications at the proximal junction of long thoracolumbar and lumbar fusion constructs are both common and burdensome to patients and health care systems 1,4. In an effort to reduce the risk of PJK and PJF, many studies have sought to identify risk factors for the development of these complications 1,5–9. In their study of patients undergoing thoracolumbar fusions that terminated proximally near the thoracolumbar junction for degenerative indications, Mikula et al 7 identified diminished HU at the UIV as a risk factor for PJK.…”

Characteristics and Comparisons of Morphometric Measurements and Computed Tomography Hounsfield Unit Values of C2 Laminae for Translaminar Screw Placement Between Patients With and Without Basilar Invagination

“…The Hounsfield unit (HU) obtained from computed tomography (CT) has been widely used for the calculation of bone mineral density (BMD) and the estimation of bone strength. [20][21][22] Moreover, HU measured at a region of interest (ROI) of the screw trajectory presents the approximate BMD and correlates strongly with insertion torque and implant stability in vitro and in vivo studies. [23][24][25][26] Furthermore, Han et al 27 demonstrated that HU values on C2-3 segments indicate a more reliable BMD level than those on C4-7 segments, and HU values of cervical CT provided reliable information regardless of measured sections, age, sex, and degree of degeneration.…”

“…The Hounsfield unit (HU) obtained from computed tomography (CT) has been widely used for the calculation of bone mineral density (BMD) and the estimation of bone strength [ 20 - 22 ]. Moreover, HU measured at a region of interest (ROI) of the screw trajectory presents the approximate BMD and correlates strongly with insertion torque and implant stability in vitro and in vivo studies [ 23 - 26 ].…”