Compromised bone microarchitecture and estimated bone strength in young adults with cystic fibrosis

Abstract

Context: Young adults with cystic fibrosis (CF) are at risk for low bone density and fractures, but the underlying alterations in bone microarchitecture that may contribute to their increased fracture risk are currently unknown.

Objective: The main goal of this study was to use high-resolution peripheral quantitative computed tomography (HR-pQCT) to characterize the bone microarchitecture, volumetric bone mineral density (vBMD), and estimated strength of the radius and tibia in young adults with CF compared with healthy volunteers.

Design and setting: This was a cross-sectional study at an outpatient clinical research center within a tertiary academic medical center.

Participants: Thirty young adults with CF, 18 to 40 years of age, were evaluated and compared with 60 healthy volunteers matched by age (±2 years), gender, and race.

Main outcome measures: The primary outcomes were HR-pQCT-derived cortical and trabecular vBMD, bone microarchitecture, and estimates of bone strength.

Results: At the radius and tibia, young adults with CF had smaller bone cross-sectional area and lower vBMD. Cortical and trabecular microarchitecture were compromised at both sites, most notably involving the trabecular bone of the tibia. These differences translated into lower estimated bone strength both at the radius and tibia. After accounting for body mass index differences, young adults with CF had lower bone area and estimated bone strength at the radius and had compromised trabecular microarchitecture and lower total and trabecular vBMD and estimated bone strength at the tibia. Alterations in trabecular bone density and microarchitecture and estimated strength measures of the tibia were also greater than expected based on dual-energy x-ray absorptiometry-derived areal BMD differences.

Conclusions: Young adults with CF have compromised bone microarchitecture and lower estimated bone strength at both the radius and tibia, even after accounting for their smaller body size. These skeletal deficits likely explain the higher fracture risk observed in young adults with CF.

Figure 1.

HR-pQCT scans of the tibia in a representative young woman with CF (A) and female healthy volunteer (B).

Figure 2.

μFEA results. A and B, Stiffness (A) and failure load (B) of the radius and tibia in young adults with CF (black bars) and age-, gender-, and race-matched healthy volunteers (gray bars). Data are expressed as mean ± SE and are presented for the unadjusted analysis, the BMI-adjusted analysis, and the BMI- and total hip areal BMD-adjusted analysis. *, P < .05.

Figure 3.

Correlations with FEV1. A–D, Scatter plots correlating percent predicted FEV1 with total vBMD of the radius (A) and tibia (B) and failure load of the radius (C) and tibia (D).