The Foot and Ankle in Ankylosing Spondylitis
Introduction
Patients with AS may experience easily recognised types of enthesitis of the foot. These most typically include Achilles Enthesitis and Plantar fasciitis. The foot and ankle are also sites of unrecognised pain and inflammation in AS. Enthesitis of the foot and ankle is a major problem in the Juvenile Spondyloarthropathies some of which may evolve into AS. This page summarises foot and ankle problems in AS.
Enthesitis in the Foot
Achilles Enthesitis- this is usually characterised by fluctuations in severity but in a few cases may be chronic and persistent.
Plantar fasciitis-pain on the bottom of the heel.
Patients may also experience enthesitis at several other sites but this is poorly recognised and includes the following regions.
Enthesitis of the peroneus brevis insertion which manifests as pain on the outside of the foot.
Tibialis anterior enthesitis may manifest as ankle pain and swelling on the top of the foot.
Enthesitis of the small intrinsic muscles of the foot or the small ligaments in the foot is much harder to recognise. It may also manifest as soft tissue swelling or bone pain.
Functional Enthesis or wrap around tendon pain
Pain around the ankle may be due to functional entheses disease. This includes peroneus longus and peroneus brevis inflammation where the tendons wrap around the bony pulleys on the outside of the ankle joint.
On the opposite side of the ankle the tibialis posterior tendon functional entheses may also be subject to inflammation.
Disease of these wrap around tendons typically manifests as soft tissue swelling or tendonitis but it has the same underlying mechanism as enthesitis.
Diagnosis
Ultrasound or Magnetic Resonance Imaging or both may be needed to recognise deep seated enthesitis which may be the cause of foot pain in AS or Spondyloarthropathy.
Management of foot enthesitis in AS
This site gives information about all aspects of enthesitis including foot disease.
First it is important to confirm that the foot pain is due to inflammatory enthesitis rather than mechanical enthesopathy. Identification of mechanical factors that could be driving or exacerbating inflammatory disease including flat feet and obesity should be addressed. Specialised input from a podiatrist may therefore be very useful even if the pain is primarily coming from inflammation in the foot.
Footwear should be assessed with insole provision if needed.
Analgesia strategies including paracetamol or codene are not generally very effective but may help some patients.
Non-steroidal anti-inflammatory strategies may help.
Corticosteroid injection may be used used and depending on the site of enthesitis may be injected adjacent to the inflamed enthesis (for Achilles) or directly into it (for plantar fascia).
If the enthesitis is very disabling then more potent disease modifying or biological drugs could be considered. However, in the UK and other countries these are not licenced for isolated disabling foot enthesitis and a special case for their use in this setting would need to be made. The literature in the past 3 decades shows how therapy for resistant enthesitis including foot enthesitis has dramatically improved, especially since the arrival of biological drugs.
References
Resources
National Ankylosing Sponylitis Society AS and feet
Arthritis Research UK Feet and footwear for ankylosing spondylitis (AS)