1. Participants and methods

This retrospective cohort study was approved by the Institutional Review Board of Fukuoka University Hospital (approval no., U21-11-019). Informed consent was obtained from all individual participants included in the study.

Surgical outcomes of 72 patients who underwent BKP for VCFs between 2015 and 2021 were assessed. All patients had a minimum follow-up of 12 months. BKP was indicated for VCFs in patients whose pain did not improve after conservative treatment. BKP was performed only for fractures with an AO classification of A; fractures with a classification of B or higher were treated with fixation. Radiography and magnetic resonance imaging were used to diagnose VCFs, and computed tomography was used to evaluate AO classification. According to the definition provided by Resnick et al. [¹], DISH was defined as continuous anterior or lateral vertebral cross-linking and fusion of three or more intervertebral discs observed by radiography and computed tomography. Patients who had VCFs with DISH were assigned to group D, whereas those who had VCFs without DISH were assigned to group ND. The exclusion criteria were as follows: <12 months of follow-up, metastatic malignancy or multiple myeloma, treatment with surgical fusion, treatment with BKP performed simultaneously at multiple vertebrae, VCFs that are further apart than the adjacent vertebra of fused segments, and poor image quality (Fig. 1). All patients underwent surgery using the bilateral transpedicular approach. The patients were allowed to wear a rigid orthosis and began walking the day after surgery. Preoperative and postoperative images are shown in Fig. 2. Bone density measurements were taken preoperatively at the lumbar vertebra and proximal femur. Parathyroid hormone (PTH) was the primary recommendation for osteoporosis treatment; however, alternative treatments, such as denosumab or bisphosphonates, were considered for patients with side effects from PTH or who opted out of PTH. Each patient’s age, sex, follow-up period, time from injury to surgery, bone density at the lumbar vertebra, proximal femur, and fracture site were recorded. In group D, the positions of the fused vertebrae and fracture site (distal end or adjacent vertebra of the fused segments) were recorded. Back pain was investigated preoperatively, 3 months postoperatively, and at the final follow-up using a Numeric Rating Scale (NRS); subsequent adjacent fractures and reoperation at the final follow-up; and local kyphosis preoperatively, immediately postoperatively, and at the final follow-up. These factors were compared between groups D and ND. Subsequent adjacent fractures were confirmed by a 15% loss of height on radiography and bone signal intensity changes on magnetic resonance imaging. Local kyphosis was measured as the angle between the higher endplate of the upper vertebral body and the lower endplate of the lower vertebral body of the fractured vertebra (Fig. 3), including kyphosis of the adjacent fracture [^7,8]. The progression of kyphosis from the immediate postoperative period to the final follow-up was also assessed.

Study flowchart. BKP, balloon kyphoplasty; VCFs, vertebral compression fractures.

Radiographic imaging findings in the lateral view. (A) Preoperative image, (B) image immediately after surgery, and (C) image at the last follow-up in group ND. (D) Preoperative image, (E) image immediately after surgery, and (F) image at the last follow-up in group D (distal end of the fused segments). (G) Preoperative image, (H) image immediately after surgery, and (I) image at the last follow-up in group D (adjacent vertebra of the fused segments). Group D: patients with diffuse idiopathic skeletal hyperostosis; Group ND: patients without diffuse idiopathic skeletal hyperostosis.

Local kyphosis, measured as the angle between the higher endplate of the upper vertebral body and the lower endplate of the lower vertebral body of the fractured vertebra (☆).