Peripheral cortical bone density predicts vertebral bone mineral properties in spine fusion surgery patients

Abstract

Spine fusion surgery is one of the most common orthopedic procedures, with over 400,000 performed annually to correct deformities and pain. However, complications occur in approximately one third of cases. While many of these complications may be related to poor bone quality, it is difficult to detect bone abnormalities prior to surgery. Areal BMD (aBMD) assessed by DXA may be artifactually high in patients with spine pathology, leading to missed diagnosis of deficits. In this study, we related preoperative imaging characteristics of both central and peripheral sites to direct measurements of bone quality in vertebral biopsies. We hypothesized that pre-operative imaging outcomes would relate to vertebral bone mineralization and collagen properties. Pre-operative assessments included DXA measurements of aBMD of the spine, hip, and forearm, central quantitative computed tomography (QCT) of volumetric BMD (vBMD) at the lumbar spine, and high resolution peripheral quantitative computed tomography (HRpQCT; Xtreme CT2) measurements of vBMD and microarchitecture at the distal radius and tibia. Bone samples were collected intraoperatively from the lumbar vertebrae and analyzed using Fourier-transform Infrared (FTIR) spectroscopy. Bone samples were obtained from 23 postmenopausal women (mean age 67 ± 7 years, BMI 28 ± 8 kg/m²). We found that patients with more mature bone by FTIR, measured as lower acid phosphate content and carbonate to phosphate ratio, and greater collagen maturity and mineral maturity/crystallinity (MMC), had greater cortical vBMD at the tibia and greater aBMD at the lumbar spine and one-third radius. Our data suggests that bone quality at peripheral sites may predict bone quality at the spine. As bone quality at the spine is challenging to assess prior to surgery, there is a great need for additional screening tools. Pre-operative peripheral bone imaging may provide important insight into vertebral bone quality and may foster identification of patients with bone quality deficits.

Keywords: Bone quality; Dual-energy X-ray absorptiometry (DXA); Fourier-transform infrared (FTIR) spectroscopy; High resolution peripheral quantitative computed tomography (HRpQCT); Post menopause; Quantitative computed tomography (QCT); Spine fusion surgery.

Figure 1.

Representative FTIR spectra of cortical bone showing characteristic mineral and organic matrix peaks.

Figure 2.

Association between FTIR metrics and cortical vBMD at the tibia by HRpQCT. Correlation between Ct vBMD at the tibia, measured by HRpQCT with (a) collagen maturity (r = 0.45, p = 0.032), (b) acid phosphate content (r = −0.55, p = 0.0073), (c) mineral maturity/crystallinity (MMC) (r = 0.45, p = 0.034), and (d) carbonate to phosphate ratio (r = −0.42, p = 0.049). Shaded area represents the 95% confidence interval. Patients currently using bisphosphonates (BP) and teriparatide (TP) are indicated. Patients who developed post-operative complications are denoted by circles, and patients who did not develop complications are denoted by triangles.

Figure 3.

Association between FTIR metrics and aBMD by DXA. Correlation between acid phosphate content with (a) LS (r = −0.55, p = 0.013) and (b) 1/3R (r = −0.54, p = 0.010). Shaded area represents the 95% confidence interval. Patients currently on bisphosphonates (BP) and teriparatide (TP) are indicated. Patients who developed post-operative complications are denoted by circles, and patients who did not develop complications are denoted by triangles.