Foot pain is a common component of Ankylosing Spondylitis (AS) & other seronegative spondyloarthropathies (SpA- psoriatic arthritis, reactive arthritis). In AS/ SpA, the inflammation is predominantly at two locations- within the joints- synovitis & at the attachment of ligaments/ tendons to a bone (enthesitis)
Let us have a look at the various causes of foot pain—
Heel pain– also known as plantar fasciitis. The foot has a bone called calcaneum located at the heel region. A muscular structure ‘plantar fascia’ is attached at the lower end of this bone.
There is inflammation at the attachment of this fascia to the bone (enthesitis) & causes pain that is generally maximal in the morning & after periods of rest.
Use of soft footwear & heel cushion/ cup in footwear helps reduce the pain. A simple exercise involving rolling of the foot on top of a bottle in the morning before walking does a lot good in many.
Pain at the backside of the foot– this is commonly due to Achilles enthesitis.
Achilles tendon is the thick band like structure at the backside of the foot. This is attached to the calcaneum bone below.
Achilles enthesitis is a telltale sign of active AS/ SpA & mandates better control with DMARDs/ biologics.
Toe pain—At times, the entire toe may be swollen & painful. This is known as dactylitis & is a feature of AS.
This is suggestive of ongoing active inflammation.
Pain & swelling at the base of the toe can be due to inflammation of the joint & DMARDs/ steroid injection in the joint/ biologics are used to control it.
Mid foot pain– is generally due to inflammation of the underlying joints especially if associated with swelling. This would require better control of AS.
Ankle & midfoot pain can also be due to a flat foot.
This would require foot analysis & an insole to correct the flat foot.
All in all, understand your foot pain & discuss with your rheumatologist.
Understanding the reason can help you take better decisions to take control of your AS.