Microdamage and altered vascularity at the enthesis-bone interface provides an anatomic explanation for bone involvement in the HLA-B27-associated spondylarthritides and allied disorders

Arthritis Rheum. 2007 Jan;56(1):224-33. doi: 10.1002/art.22290.


Objective: To describe the basis for entheseal-associated bone disease in the spondylarthritides, by analyzing microanatomic and histopathologic relationships between soft tissue, bone cortex, and adjacent trabeculae.

Methods: Serial sections from 52 entheses were examined; these entheses encompassed small and large insertions in the upper limb (n = 21), lower limb (n = 27), and spine (n = 4) from 60 cadavers. Enthesis microdamage (fissuring) as well as vascular and reparative changes were evaluated. Contact radiographs were used to ascertain the relationship between entheses and the trabecular network.

Results: At virtually all fibrocartilaginous entheses, the deep cortical boundary was extremely thin (typically 50-600 microm) or indistinguishable, and 96% of entheses had small holes in the cortical shell (typically 100-400 microm wide). Such regions were frequent sites of bone formation and renewal (96%) and microdamage (31%); these changes were more common in the lower limb. The presence of blood vessels near holes in the cortical shell was common; in 85% of attachments, blood vessels were present on the soft tissue side of the enthesis. Highly orientated trabeculae were more obvious in the lower limb than the upper limb (59% versus 29%).

Conclusion: The trabecular network supporting the cortical shell is an integral part of the enthesis, transferring load to an extensive skeletal region. In many cases, tendons/ligaments are anchored directly to such networks. This functional integration is associated with microdamage and repair at the hard tissue-soft tissue interface. These findings have implications for understanding bone involvement in SpA and for the SpA concept in general, especially the hypothesis that enthesis-bone architecture may be important in disease initiation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Bone and Bones / diagnostic imaging
  • Bone and Bones / pathology*
  • Cadaver
  • Female
  • HLA-B27 Antigen / genetics*
  • Humans
  • Ligaments, Articular / diagnostic imaging
  • Ligaments, Articular / pathology*
  • Male
  • Middle Aged
  • Radiography
  • Spondylarthropathies / genetics*
  • Tendons / diagnostic imaging
  • Tendons / pathology*


  • HLA-B27 Antigen