Poster Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

INTRODUCTION

While dual-energy X-ray absorptiometry (DXA) is widely regarded as the gold standard for osteoporosis diagnosis, its tendency is to overestimate degenerative changes, particularly in adult spinal deformity (ASD) patients. The Hounsfield unit (HU) values from computed tomography (CT), and magnetic resonance imaging (MRI)-based vertebral bone quality (VBQ) score are useful as an adjunct to the diagnosis of osteoporosis^{1), 2)}. This study aims to investigate the correlation among intraoperative pedicle screw (PS) insertion torque, BMD measured by DXA scan, HU values, and VBQ score in patients with adult spinal deformity.

METHODS

A prospective study was conducted at our hospital, involving patients who underwent spinal long fusion surgery from the thoracic spine to the pelvis between May 2022 and April 2023. The inclusion criteria were: (1) age >60 years, (2) diagnosis of ASD, (3) >5 levels posterior instrumented fusion to the pelvis. The CT HU value was calculated as the average of three slices covering the T10, T11, and T12 vertebrae. Regions of interest were identified in axial CT images of the vertebra at three specific points. The averaged measurements of these axial slices provided a mean HU value. The vertebral body quality (VBQ) score was derived from mean values observed across the L1-4 vertebrae in T1-weighted MRI images. These values were then divided by the signal intensity of the adjacent cerebrospinal fluid (CSF) to obtain a relative vertebral body signal intensity. PS insertion torque was measured using a torque meter (DTC-CN500REV). Pearson correlation coefficients were calculated to assess the relationships between insertional torque and BMD, HU values, and the VBQ score.

RESULTS

The study enrolled 31 patients, with a mean age of 75.1 years, including 10 males and 21 females. Preoperative diagnosis of osteoporosis based on DXA (YAM <70%) and CT HU (HU <120) was 30% and 64.5%, respectively. We assessed the insertion torques of 177 PSs. A positive correlation was observed between the pedicle screw insertion torque and BMD of the lumbar spine (T10: r = 0.58, p < 0.01; T11: r = 0.61, p < 0.01; T12: r = 0.69, p < 0.01), BMD of the femoral neck (T10: r = 0.61, p < 0.01; T11: r = 0.62, p < 0.01; T12: r = 0.58, p < 0.01), and HU (T10: r = 0.61, p < 0.01; T11: r = 0.62, p < 0.01; T12: r = 0.58, p < 0.01). However, no significant correlation was found between screw insertion torque and VBQ score. Moreover, a strong correlation was observed between screw insertional torque with a screw diameter of 6.5 mm and T10 HU (r = 0.68, p < 0.01), T11 HU (r=0.71, p < 0.01) as well as T12 HU (r = 0.74, p < 0.01) (figure 1).

DISCUSSION

The HU values obtained from the lower thoracic spine demonstrated minimal influence from lumbar spine degeneration and displayed a more pronounced association with PS insertion torque, surpassing that of lumbar spine and femoral neck BMD. Preoperative evaluation of HU is useful for adjunctive diagnosis of osteoporosis.