P9. Analysis of risk factors of adjacent vertebral fracture after balloon kyphoplasty including trunk muscles

Background Context

Balloon kyphoplasty (BKP) is a low invasive and effective treatment for pseudarthrosis in the vertebral body after osteoporotic vertebral fracture. However, a major problem in many cases is adjacent vertebral fracture (AVF). The cause of AVF is still unclear.

Purpose

The aim of this study was to analyze the risk factors of AVF after BKP.

Study Design/Setting

Retrospective study.

Patient Sample

Eighty-seven patients had BKP for pseudarthrosis after vertebral body fracture in our institution from 2015 May to 2023 June. We retrospectively investigated 68 patients (23 males, 45 females) who had only single-level BKP for levels >L2 and were followed up for >6 months after surgery. We excluded patients who had BKP with other surgery and BKP of <L3. The average age at surgery was 77.5 years old, and the average follow-up period was 13.4 months.

Outcome Measures

Data were analyzed using the Mann-Whitney U test.

Methods

We divided the patients into two groups: Group A (n = 23) had AVF after BKP during follow-up, and Group B (n = 45) had no additional AVF after BKP. We compared the risk factors between groups. Before BKP, we investigated duration from onset to BKP, body mass index (BMI), young adult mean (YAM) in the lumbar spine and femoral neck. As preoperative radiographic findings, we investigated the area of intra-vertebral cleft, the intravertebral body instability and the height of vertebral body. The area ratio of the major psoas muscle/vertebral body, back muscles (multifidus muscle, longissimus muscle, iliocostal muscle)/vertebral body was investigated. The area ratios were measured at the craniad L4 vertebral body end-plate level in axial CT images and regarded the ratio as the amount of each muscle. The area of fat and muscle in the major psoas and back muscles were investigated to clarify the quality of the trunk muscle. The area in which Hounsfield Unit was -100 to -50 and 30 to 120 were regarded as the area of fat and muscle in the major psoas and back muscles at L4 vertebral body end-plate level in axial CT images. The amount of PMMA used for BKP and difference of vertebral body height after BKP were also investigated.

Results

Significant difference was observed only in the area ratio of the back muscles/L4 vertebral body (average: 1.40 in Group A and 1.95 in Group B; p<.01). However, other factors, including the area ratio of the major psoas muscle /L4 vertebral body, have no significant difference between groups. In Group A, the area of fat in major psoas and back muscles were increased compared with Group B, and two patients who had AVF despite the higher area ratio of back muscles had low muscle quality. In Group B, 6 patients who had no additional AVF despite the lower area ratio of muscle had high muscle quality.

CONCLUSIONS

Trunk muscles are reported to be related to vertebral body fractures and spinal deformities. But, no study has investigated the relationship between AVF and trunk muscles. The amount of back muscles was lower in the AVF after BKP group than in the non-AVF group. And some patients who had AVF despite the higher area ratio of muscle had low muscle quality. This is the first study to determine the relationship between AVF after BKP and preoperative amount and quality of trunk muscles. The pathogenesis of AVF after BKP may be related to trunk muscles before BKP, especially back muscles. Patients with a lesser amount and lower quality of back muscles tended to suffer from AVF after BKP.

FDA Device/Drug Status

This abstract does not discuss or include any applicable devices or drugs.