Enthesitis at Onset of Ankylosing Spondylitis


Although AS typically starts in the low back it can start at other sites throughout the body. This page explains why that is the case and is especially important for the early disease detection in first degree relatives of Ankylosing Spondylitis patients.

The unifying concept for AS is that skeletal disease localises to sites of high mechanical stressing. Such sites can be identified by the presence of a stress resisting tissue called fibrocartilage. The sacroiliac joint has abundant fibrocartilage due to the high levels of physical stressing at that site. However, many other sites outside the spine have abundant fibrocartilage.

Lower limb enthesitis as first AS manifestation

The large insertions of the lower limbs including the patellar tendon and Achilles tendon and plantar fascia are sites where the initial inflammatory symptoms may occur. The patellar tendon origin or insertion also sites where disease may start.

Some patients may get symptoms around the pelvis such as the pubic symphysis or higher up the spine.

These conditions are characterised by at least 30 minutes joint stiffness in the morning which improves with activity. Due to the anatomy of the enthesis the doctor may not be able to detect swelling even though the structures are inflamed.

In young people and especially those in sports academies or other elite level sport there may be an initial wrong diagnosis of mechanical enthesopathy or tendonitis.

Lower limb joint inflammation

Patients with AS may present with joint swelling in the knee and ankle that is linked to inflammation in structures termed synoivo-entheseal complexes. So the original manifestation of disease may be isolated joint swelling.

Isolated hip disease may also be an early presentation. This is poorly recognised due to the severity of inflammation as detected by MRI and may be mis-diagnosed as hip infections.

Other early enthesitis manifestations

Chest wall pain due to enthesitis at that site may be an initial presentation also and may be misdiagnosed as other cardiac or lung problems.

Eye involvement or uveitis is another type of pathology that may be related to micro-enthesitis.


The first bout of inflammation in Ankylosing Spondylitis may occur outside the sacroiliac joint. This is especially the case in Juvenile Spondyloarthropathy which may later evolve into Ankylosing Spondylitis but it can occur in any subject in the evolution of disease.


Spondylitis Association of America JUVENILE SPONDYLOARTHRITIS

NHS choices Ankylosing spondylitis - Symptoms