What is an Enthesophyte?
An enthesophyte is a bony projection (spur) that develops at the site where tendons, ligaments, or joint capsules insert into bone (the enthesis). 1
Anatomical Definition
- The enthesis is the anatomic location where tendon, ligament, or joint capsule fibers insert into the bone 1
- Enthesophytes represent calcific overgrowth or ossification at these insertion sites 2
- They are analogous to osteophytes seen in osteoarthritis but occur specifically at tendon/ligament attachment points 3
Common Locations
Enthesophytes may occur at any enthesial site, but are most frequently found at: 1
- Plantar fascia insertion (heel)
- Achilles tendon insertion (posterior calcaneus)
- Ligamentous attachments to the ribs, spine, and pelvis
- Patellar tendon insertions
- Iliac crest
- External occipital protuberance (skull base)
Clinical Associations
Spondyloarthropathies
Bone proliferation in the form of enthesophytes is a hallmark feature of the seronegative spondyloarthropathies, including: 1
- Psoriatic arthritis
- Ankylosing spondylitis
- Reactive arthritis
- Inflammatory bowel disease-associated arthritis
Other Conditions
Enthesophytes can also develop in: 3, 2, 4
- Gout (crystals of monosodium urate monohydrate provoke inflammatory reaction leading to ossification)
- Diffuse idiopathic skeletal hyperostosis (DISH)
- Calcium pyrophosphate deposition disease
Age-Related Changes
Enthesophytes are predominantly a phenomenon of aging in the general population, unrelated to inflammatory arthritis: 2
- Frequency increases with age independent of sex or site examined
- Plateaus in frequency after age 60
- Mechanical factors appear to outweigh the "enthesis calcifying" impact of underlying disorders at most sites
- Enthesophytes in individuals under age 60 are usually unrelated to any underlying disorder
Imaging Characteristics
- Radiography effectively demonstrates enthesophytes as bony projections at tendon/ligament insertion sites 1
- CT can show cortical irregularity and bone proliferation at entheses 1
- MRI can detect early enthesitis (inflammation at the enthesis) before ossification occurs, showing cortical irregularity and increased fluid signal in adjacent bone marrow 1
- Ultrasound can identify enthesophytes and associated soft tissue changes 1
Clinical Pitfalls
- Do not confuse enthesophytes with erosions - enthesophytes represent new bone formation, while erosions represent bone destruction 1
- In rheumatoid arthritis, enthesophytes are typically absent unless there is coexisting hyperostosis, as RA is characterized by minimal reactive new bone formation 4
- The presence of enthesophytes alone does not confirm inflammatory arthritis, as they commonly occur with aging and mechanical stress 2, 5