Ankylosing spondylitis (AS) is a chronic, progressive inflammatory disease that primarily affects the axial skeleton, especially the spine and sacroiliac joints. However, its impact is not confined to these regions. Peripheral manifestations, particularly in the lower limbs and feet, are common and can significantly affect mobility, quality of life, and foot function.
Pathophysiology of Ankylosing Spondylitis
Ankylosing Spondylitis is classified as a seronegative spondyloarthropathy, characterized by inflammation at sites where ligaments and tendons attach to bone (entheses). The disease is strongly associated with the HLA-B27 gene, and its pathogenesis involves a complex interplay of genetic, immunological, and environmental factors. Chronic inflammation leads to pain, stiffness, and, over time, new bone formation and joint fusion. While the axial skeleton is the hallmark site of involvement, peripheral joints and entheses, including those in the feet, are frequently affected.
Clinical Manifestations in the Feet
- Enthesitis: The most common foot manifestation in AS is enthesitis—inflammation of the entheses. The plantar fascia (at the heel), Achilles tendon insertion, and the metatarsal heads are frequently involved. Patients often report heel pain (plantar fasciitis) or posterior heel pain (Achilles enthesitis), which can be severe and disabling.
- Peripheral Arthritis: AS can cause swelling, pain, and stiffness in the joints of the feet, particularly the metatarsophalangeal (MTP) and interphalangeal (IP) joints. This can lead to difficulty walking, altered gait, and secondary complications such as callus formation or ulceration.
- Dactylitis: Sometimes referred to as “sausage toe,” dactylitis is the diffuse swelling of an entire digit. It results from a combination of synovitis, tenosynovitis, and enthesitis, and is a distinguishing feature of spondyloarthropathies.
- Structural Changes: Chronic inflammation can lead to joint erosion, deformity, and in severe cases, ankylosis (fusion), reducing the range of motion and flexibility in the feet. These changes can contribute to abnormal foot biomechanics, increasing the risk of secondary musculoskeletal problems.
Impact on Function and Quality of Life
The effects of Ankylosing Spondylitis on the feet can be profound. Heel and midfoot pain may limit mobility, reduce exercise tolerance, and impair daily activities such as walking, standing, or working. Persistent pain and deformity can also lead to compensatory gait patterns, which may further stress the knees, hips, and lower back. In severe cases, patients may become housebound or require assistive devices for ambulation. The psychological impact, including depression and reduced self-esteem, should not be underestimated.
Diagnostic Considerations
- Clinical Assessment: Diagnosis is based on a combination of patient history, clinical examination, and imaging. Key features include chronic heel pain, swelling, and tenderness at the entheses, as well as a history of back pain or stiffness. A family history of spondyloarthropathy and the presence of extra-articular features (such as uveitis or psoriasis) may support the diagnosis.
- Imaging: Plain radiographs may reveal erosions, periostitis, or new bone formation at the insertion sites. MRI is more sensitive for detecting early inflammatory changes and is particularly useful for assessing enthesitis and soft tissue involvement.
- Laboratory Tests: While there is no definitive blood test for AS, the presence of HLA-B27, elevated inflammatory markers (ESR, CRP), and the exclusion of other causes of foot pain are important diagnostic steps.
- Pharmacological Treatments: Nonsteroidal anti-inflammatory drugs (NSAIDs) are the first-line treatment for pain and inflammation. In more severe cases, disease-modifying antirheumatic drugs (DMARDs) or biologic agents (such as TNF inhibitors) may be indicated to control systemic and peripheral manifestations.
- Podiatric Interventions: Custom orthoses, heel cups, and appropriate footwear can help redistribute pressure, support the foot, and alleviate pain. Padding and offloading devices may be necessary for patients with significant deformity or ulceration.
- Physical Therapy: Stretching and strengthening exercises, along with manual therapy, can improve flexibility, maintain joint function, and reduce stiffness. Patient education on home exercise programs is essential for long-term management.
- Multidisciplinary Care: Optimal management of AS involves collaboration between rheumatologists, podiatrists, physiotherapists, and sometimes orthopedic surgeons. Early intervention and regular monitoring are key to preventing irreversible damage and maintaining mobility.
Prognosis and Long-Term Outlook
With advances in diagnosis and treatment, the long-term outlook for patients with Ankylosing Spondylitis has improved. Early recognition of foot involvement and a proactive, multidisciplinary approach can minimize disability and enhance quality of life. However, AS remains a lifelong condition, and ongoing management is essential to address both axial and peripheral manifestations.
Ankylosing spondylitis, while classically associated with the spine, frequently affects the feet through enthesitis, arthritis, dactylitis, and structural changes. These manifestations can be debilitating, impacting mobility, independence, and psychological well-being. Clinicians and patients should be vigilant for early signs of foot involvement, and management should be tailored to address pain, preserve function, and improve overall quality of life.
