Ankylosing spondylitis (AS) notably affects the foot in several important ways, leading to pain, disability, and reduced quality of life for many patients. Its impact extends beyond the spine, often involving the joints, tendons, and ligaments of the foot through inflammatory and degenerative processes. The following essay explores how AS affects the foot, considering pathophysiology, symptoms, clinical significance, diagnosis, and treatment options.
Pathophysiology: How AS Targets the Foot
Ankylosing spondylitis predominantly affects the axial skeleton, but up to 80% of patients can experience peripheral involvement, most commonly enthesitis—where tendons and ligaments attach to bone. In the foot, the primary sites are the Achilles tendon and plantar fascia. Inflammation at these sites leads to pain, swelling, and impaired mobility.
Enthesitis is the hallmark of AS’s effect on the foot. The heel (Achilles tendon insertion) and the arch (plantar fascia origin) experience chronic inflammation, causing tenderness and stiffness, especially after periods of rest or on waking up. Advanced disease may end in abnormal bone growth (enthesophytes) and local ankylosis—where bones fuse together—impacting the biomechanics of gait.
Tarsal arthritis is another manifestation, with inflammation of mid-foot joints resulting in pain, swelling, and sometimes structural deformity. Severe, chronic inflammation can produce “ankylosing tarsitis,” marked by pronounced swelling, diffuse osteopenia, joint space narrowing, and bone ankylosis visible on radiographs. Over time, persistent inflammation may lead to erosions and enthesophyte formation at bone attachments.
Clinical Symptoms: Pain, Disability, and Deformity
Foot pain in AS is highly prevalent; studies indicate that only about 20% of AS patients have no foot complaints, with pain, swelling, and stiffness being the leading issues. Pain typically centers on the heels, ankles, and arches, sometimes radiating to the toes. The most common conditions in the foot are:
- Achilles enthesitis: Pain and swelling at the back of the heel due to inflamed Achilles tendon insertion.
- Plantar fasciitis: Pain in the arch or heel resulting from plantar fascia inflammation, making walking or standing difficult.
- Tarsal arthritis/tarsitis: Pain, swelling, and reduced mobility in the mid-foot due to inflamed tarsal bones and joints.
- Dactylitis: Swelling and tenderness of toes, sometimes referred to as “sausage digits” due to the characteristic appearance.
Morning stiffness, pain upon waking, and exacerbation after periods of inactivity are classic AS features in both the spine and the foot.
Functional limitations are prominent, with more severe disability correlated with higher disease activity. Patients report difficulty in ambulation, climbing stairs, and even basic movements, all associated with pain and reduced foot function.
Deformities can develop, such as flat foot due to arch involvement, or joint fusion (ankylosis) in severe cases. Imaging studies occasionally show “boot sign” on ankle radiographs due to bony fusion.
Diagnosis and Assessment
Diagnosis of AS foot involvement combines clinical history, physical examination, and imaging. Tenderness at the entheses (Achilles, plantar fascia) is a key clinical finding. Patient-reported outcome measures, like the Foot Function Index (FFI), track pain and disability, while disease activity scores such as ASDAS and BASDAI help assess severity.
Imaging includes radiographs, which may show erosions, joint space narrowing, enthesophytes, and ankylosis. MRI can detect soft tissue edema, synovial swelling, and bone inflammation even in early disease.
Management: Relieving Symptoms and Improving Function
Treatment of AS-related foot problems focuses on reducing pain and inflammation, restoring function, and preventing deformity. Main interventions include:
- Medications: Nonsteroidal anti-inflammatory drugs (NSAIDs) are first-line for pain and stiffness. Disease-modifying antirheumatic drugs (DMARDs) and biologics (TNF inhibitors) are reserved for more severe or persistent cases; these agents target systemic inflammation and have shown benefit for enthesitis and arthritis.
- Physical therapy: Stretching and strengthening exercises for the ankle, Achilles tendon, and plantar fascia improve mobility and reduce pain.
- Footwear modifications: Supportive shoes, custom orthotics, and heel pads can reduce stress on inflamed areas and improve comfort.
- Local interventions: In refractory cases, corticosteroid injections at the Achilles or plantar fascia may help reduce local inflammation.medicalnewstoday
- Surgical intervention: Rarely, surgery may be necessary for severe deformities or intractable pain, such as tendon release or correction of fused joints.
Education and self-care are also important, as patients must learn how to manage exacerbations and avoid activities that worsen symptoms.
Quality of Life and Long-Term Impact
Foot problems significantly affect quality of life in AS. Pain and disability can limit walking, exercise, and even work. Studies report that those with higher disease activity have worse foot function and greater impairment in daily living. Chronic foot pain may contribute to fatigue, depression, and reduced participation in social and recreational activities.
Ankylosing spondylitis exerts a profound effect on the feet by inducing pain, stiffness, swelling, and deformity through enthesitis, arthritis, and abnormal bone growth. Foot involvement in AS is common and correlates with disease activity, leading to substantial disability and lowering quality of life. Early recognition and targeted management—including medication, physical therapy, and supportive footwear—are essential to alleviate symptoms and preserve function. Comprehensive care should address both the physical and psychological impacts to optimize outcomes for those living with AS.