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Open Access Research article

Bone microarchitecture in ankylosing spondylitis and the association with bone mineral density, fractures, and syndesmophytes

Eva Klingberg1*, Mattias Lorentzon2, Jan Göthlin3, Dan Mellström2, Mats Geijer4, Claes Ohlsson2, Elizabeth J Atkinson5, Sundeep Khosla6, Hans Carlsten1 and Helena Forsblad-d’Elia1

Author Affiliations

1 Department of Rheumatology and Inflammation Research, Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden

2 Centre for Bone and Arthritis Research, Institute of Medicine, Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden

3 Department of Radiology, Sahlgrenska Hospital/Mölndal, Sahlgrenska Academy at the University Hospital/Mölndal, Gothenburg, Sweden

4 Centre for Medical Imaging and Physiology, Skåne University Hospital, Lund, Lund University, Lund, Sweden

5 College of Medicine, Mayo Clinic, Rochester, MN, USA

6 College of Physiology and Medicine, Mayo Clinic, Rochester, MN, USA

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Arthritis Research & Therapy 2013, 15:R179  doi:10.1186/ar4368

Published: 5 November 2013

Abstract

Introduction

Osteoporosis of the axial skeleton is a known complication of ankylosing spondylitis (AS), but bone loss affecting the peripheral skeleton is less studied. This study on volumetric bone mineral density (vBMD) and bone microarchitecture in AS was conducted to compare peripheral vBMD in AS patients with that in healthy controls, to study vBMD in axial compared with peripheral bone, and to explore the relation between vertebral fractures, spinal osteoproliferation, and peripheral bone microarchitecture and density.

Methods

High-resolution peripheral quantitative computed tomography (HRpQCT) of ultradistal radius and tibia and QCT and dual-energy x-ray absorptiometry (DXA) of lumbar spine were performed in 69 male AS patients (NY criteria). Spinal radiographs were assessed for vertebral fractures and syndesmophyte formation (mSASSS). The HRpQCT measurements were compared with the measurements of healthy controls.

Results

The AS patients had lower cortical vBMD in radius (P = 0.004) and lower trabecular vBMD in tibia (P = 0.033), than did the controls. Strong correlations were found between trabecular vBMD in lumbar spine, radius (rS = 0.762; P < 0.001), and tibia (rS = 0.712; P < 0.001).

When compared with age-matched AS controls, patients with vertebral fractures had lower lumbar cortical vBMD (-22%; P = 0.019), lower cortical cross-sectional area in radius (-28.3%; P = 0.001) and tibia (-24.0%; P = 0.013), and thinner cortical bone in radius (-28.3%; P = 0.001) and tibia (-26.9%; P = 0.016).

mSASSS correlated negatively with trabecular vBMD in lumbar spine (rS = -0.620; P < 0.001), radius (rS = -0.400; p = 0.001) and tibia (rS = -0.475; p < 0.001) and also with trabecular thickness in radius (rS = -0.528; P < 0.001) and tibia (rS = -0.488; P < 0.001).

Adjusted for age, syndesmophytes were significantly associated with decreasing trabecular vBMD, but increasing cortical vBMD in lumbar spine, but not with increasing cortical thickness or density in peripheral bone. Estimated lumbar vBMD by DXA correlated with trabecular vBMD measured by QCT (rS = 0.636; P < 0.001).

Conclusions

Lumbar osteoporosis, syndesmophytes, and vertebral fractures were associated with both lower vBMD and deteriorated microarchitecture in peripheral bone. The results indicate that trabecular bone loss is general, whereas osteoproliferation is local in AS.