A new study led by the Columbia University showed that patients with cystic fibrosis (CF) have decreased bone mineral density (vBMD) and stiffness in the distal tibia, compared with healthy individuals.

Fracture rates are higher among individuals with CF than in the general population, but the reasons, likely multifactorial, remain unclear. Studies have reported lower BMD ( aBMD ) in CF patients, but this may be related to the limited ability of dual-energy x-ray absorptiometry (DXA) to distinguish between low BMD and small bone size, which is also more common in CF patients

Dr. Kyle K. Nishiyama and colleagues from Columbia University, in New York City, used high-resolution quantitative computed tomography ( HR-pQCT ), which measures true three-dimensional vBMD, at both the standard DXA scan sites and at the distal tibia to compare aBMD, vBMD, bone structure and estimated bone strength in 29 adults with CF and 29 matched healthy controls of similar size.

CF patients had significantly lower HBMD, compared with healthy controls, at the lumbar spine, total hip, femoral neck and whole body, but not at the one-third or ultradistal radius, the reports in Bone .

By HR-pQCT, both CF patients and controls had larger total and trabecular bone area and smaller cortical area at the relative site (4% of the current proximal limb to its distal end) than at the fixed site (9.5 mm proximal to the distal radius and 22.5 mm proximal to the distal tibia).

At the radius, CF patients had significantly lower total bone area at the relative site, whereas total, cortical, and trabecular, vBMD, cortical thickness, and porosity did not differ between the groups. Torsional stiffness was lower in CF patients at the relative and fixed radius sites.

Total bone area at the tibia did not differ significantly between CF patients and healthy controls, but total, cortical, and trabecular vBMD were all significantly lower in CF participants at the fixed and relative sites.

Trabecular number was lower and separation was higher among CF patients, especially at the relative tibia site; plate trabecular number, rod-plate and plate-plate junction densities were lower at both sites, compared with healthy controls. Axial and torsional stiffness were also significantly lower at both distal tibial sites in CF participants than in healthy controls.

"The pathogenesis of these differences in bone density and strength at the tibia appear to be related to trabecular drop-out and reduced trabecular connectivity and to be independent of differences in limb length, as assessed by scanning participants at both standard and relative sites," the noted researchers

"These results suggest that bone structure is compromised and strength is lower in individuals with CF even when there are minor differences in weight and bone size, but further investigation is required to determine the preferred scan site," the conclusion concluded.