Teriparatide Treatment Increases Hounsfield Units in the Thoracic Spine, Lumbar Spine, Sacrum, and Ilium Out of Proportion to the Cervical Spine

Osteoporosis Evaluation and Management in Spine Surgery

Osteoporosis is a global health problem affecting over 200 million people worldwide and 54 million adults in the United States. Approximately half of all postmenopausal women will have an osteoporosis-related fracture during their lifetime. In the United States, the direct medical cost related to osteoporosis is expected to exceed $25 billion by 2025. Management of osteoporosis in vertebral fractures and elective spine surgery is of the utmost concern, given the high prevalence of osteoporosis in the general population and the increased risk of complication in this population. New pharmacologic treatment options such as anabolic medications and diagnostic tools including Hounsfield unit measurements on routine computed tomography scans are available to orthopaedic and spinal surgeons to help best manage this condition. This review serves as an update to diagnosis, management, and treatment of patients with osteoporosis undergoing spinal surgery.

Using advanced imaging to measure bone density, compression fracture risk, and risk for construct failure after spine surgery

Low bone mineral density (BMD) can predispose to vertebral body compression fractures and postoperative instrumentation failure. DEXA is considered the gold standard for measurement of BMD, however it is not obtained for all spine surgery patients preoperatively. There is a growing body of evidence suggesting that more routinely acquired spine imaging studies such as computed tomography (CT) and magnetic resonance imaging (MRI) can be opportunistically used to measure BMD. Here we review available studies that assess the validity of opportunistic screening with CT-derived Hounsfield Units (HU) and MRI-derived vertebral vone quality (VBQ) to measure BMD of the spine as well the utility of these measures in predicting postoperative outcomes. Additionally, we provide screening thresholds based on HU and VBQ for prediction of osteopenia/ osteoporosis and postoperative outcomes such as cage subsidence, screw loosening, proximal junctional kyphosis, and implant failure.

Sarcopenia and osteopenia are independent risk factors for proximal junctional disease after posterior lumbar fusion: Results of a retrospective study

Study Design

This was a retrospective study.

Objective

Since a better understanding of modifiable risk factors for proximal junctional disease (PJD) may lead to improved postoperative outcomes and less need of revision surgery, the aim of the present study is to determine whether sarcopenia and osteopenia are independent risk factors for PJD in patients undergoing lumbar fusion.

Summary of Background Data

PJD is one of the most frequent complications following posterior instrumented spinal fusion. It is characterized by a spectrum of pathologies ranging from proximal junctional kyphosis (PJK) to proximal junctional failure (PJF). The etiology of PJD is multifactorial and currently not fully understood. Patient-specific factors, such as age, body mass index, osteoporosis, sarcopenia, and the presence of other comorbidities, can represent potential risk factors.

Materials and Methods

A retrospective review of patients, aging 50-85 years, who underwent a short (≤3 levels) posterior lumbar fusion for degenerative diseases was performed. Through magnetic resonance imaging (MRI), central sarcopenia and osteopenia were evaluated, measuring the psoas-to-lumbar vertebral index (PLVI) and the M-score. A multivariate analysis was performed to determine the independent risk factors for PJD, PJK, and PJF.

Results

A total of 308 patients (mean age at surgery 63.8 ± 6.2 years) were included. Ten patients (3.2%) developed a PJD and all required revision surgery. Multivariate regression identified PLVI (P = 0.02) and M-score (P = 0.04) as independent risk factors for both PJK (P = 0.02 and P = 0.04, respectively) and PJF (P = 0.04 and P = 0.01, respectively).

Conclusions

Sarcopenia and osteopenia, as measured by PLVI and M-score, proved to be independent risk factors for PJD in patients who undergo lumbar fusion for degenerative diseases.

Clinical Trial Registration

The present study was approved by the Institutional Review Board, CE AVEC 208/2022/OSS/IOR.

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

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.