Introduction: It is well known that future incidence of osteoporotic vertebral fracture (OVF) increases with age, low bone mineral density (BMD), and fracture history. Neuromuscular function of the trunk muscles and spinopelvic alignment could play an important role in the etiology and they are important but poorly understood. In this study, potential risk factors associated with the development of OVF, namely, poor muscle strength and spinopelvic alignment, were prospectively investigated in the middle-aged and older adult women.

Methods: We enrolled 197 female patients aged ≥50 years who were scheduled to undergo surgery for lower extremities degenerative diseases at our hospital. Preoperatively, patient’s anthropometric and muscle strength measurements, BMD measurement of the lumbar spine (L-BMD), and full-spine standing radiographs were obtained. Muscle strengths measured in this study included grip power, knee extensor muscle strength, and abdominal trunk muscle strength (ATMS) using an exercise device designed for abdominal trunk muscles (RECORE: presented in Figure). Based on full-spine standing radiographic findings, sagittal vertical axis, lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), and PI-LL were measured, and the presence of OVF were determined. This study evaluated a total of 141 patients who performed another full-spine standing radiography three years postoperatively to identify new non-traumatic OVFs after 54 without the second examination and two with new traumatic OVFs were excluded. To identify factors associated with the occurrence of new OVFs, univariate and multivariate analyses were performed. Finally, the receiver operating characteristic (ROC) curve analysis was used to determine the optimal cutoff of the occurrence of OVF.

Results: Ten (7.1%) patients had new non-traumatic OVFs during the three-year study period (the fracture group). The remaining 131 patients did not have new OVFs (non-fracture group). The fracture group had lower ATMS and L-BMD, smaller SS, and larger PT than the non-fracture group. The fracture group had a higher prevalence of old OVFs than the non-OVF group. In a multivariate analysis, weak ATMS (p = 0.037), low L-BMD (p = 0.011), and the presence of old OVFs (p = 0.023) were significant risk factors for the occurrence of new OVFs for the three years. ROC analyses showed that AMTS ≤4.0 kPa (95% confidence interval 0.643-0.909, P = 0.004, area under curve 0.776) and L-BMD ≤1.11 g/cm2 (95% confidence interval 0.575-0.833, P = 0.032, area under curve 0.704) best predicted the occurrence of OVF in the study cohort.

Discussion: Abdominal trunk muscle weakness in the middle-aged or older women was associated with future OVF. One previous study showed that the device used in this study can quantify ATMS and abdominal trunk muscles-strengthening exercise using the device increased ATMS and activated the abdominals, diaphragm, and pelvic floor muscles. Coordinated and isometric muscle contraction of these muscles creates a semirigid cylinder surrounding the spinal column with an increase in intra-abdominal pressure, which can reduce some of the imposed stress on the vertebral column in the lower thoracic or lumbar spine. ATMS measurement can be used to assess the risk of OVF occurrence.