Introduction

Ankylosing spondylitis (AS) and knee osteoarthritis (KOA) might seem unrelated at first—they are, after all, two distinct and common joint conditions. However, both can profoundly impact how people move, function, and experience daily life.

AS is a chronic inflammatory disease that primarily targets the spine and the joints connecting the spine to the pelvis, causing stiffness, pain, and, over time, the potential fusion of spinal bones. In contrast, KOA is traditionally thought of as a “wear-and-tear” disorder, in which the cartilage cushioning the knee bones wears away, leading to pain, swelling, and reduced mobility.

Recent research reveals these two conditions are more connected than they appear—particularly through shared pathways of inflammation and joint stress. This article unpacks how AS and KOA can overlap, why that matters for both diagnosis and treatment, and what emerging research means for people navigating both conditions. We’ll dive into what’s happening inside the joints, explore effective treatments, and look toward future advances.

How Inflammation Bridges Ankylosing Spondylitis and Knee Osteoarthritis

Inflammation is the body’s natural defense against injury or infection, but when it becomes chronic—as in AS—it can disrupt and damage joints well beyond the spine. Scientists have discovered that inflammation in AS isn’t limited to the back; it can also affect other joints, including the knees. Inflammatory proteins called cytokines circulate throughout the body in AS, raising the risk of joint damage far from the spine.

Medical imaging has shown that people with AS sometimes develop changes in their knees that resemble those seen in osteoarthritis. This suggests that ongoing inflammation in AS may speed up cartilage loss and trigger abnormal bone growth within the knee—essentially accelerating the process of osteoarthritis. Traditionally, doctors thought knee osteoarthritis was mostly caused by aging or long-term mechanical stress, but new findings make it clear that inflammation can play a major role as well, especially for those with AS.

Recognizing that inflammation links these two conditions can help healthcare providers diagnose and manage joint problems more effectively, treating not just the symptoms but one of the root causes.

What’s Happening Inside the Joints?

To really understand how AS and KOA can overlap, it’s helpful to peek into what’s happening at the microscopic level. In AS, the immune system mistakenly targets healthy tissues, releasing high levels of inflammatory messengers like tumor necrosis factor-alpha (TNF-α) and interleukin-17 (IL-17). These chemicals keep the body in a near-constant inflammatory state.

While the spine is their main target, these messengers don’t stop there. They can break down cartilage in the knees and encourage the growth of abnormal bone, causing the joint pain and stiffness seen in both AS and KOA.

The overlap in symptoms can make it challenging for doctors to pinpoint the source of a patient’s knee pain—whether it’s due to osteoarthritis, AS-related inflammation, or both. This is why diagnosis usually relies on a combination of physical exams, imaging tests like MRI or X-rays, and bloodwork to check for signs of inflammation and cartilage breakdown.

Recent studies also reveal how widespread KOA can be in certain populations, underscoring the need for accurate diagnosis and early intervention.

Treating Both Conditions: A Comprehensive Approach

When someone is living with both AS and KOA, treatment has to tackle two problems: inflammation and joint breakdown. For AS, common therapies include nonsteroidal anti-inflammatory drugs (NSAIDs) and biologics that target specific inflammatory messengers such as TNF-α or IL-17. Physical therapy is also crucial for preserving spinal flexibility and easing discomfort.

On the KOA side, treatment focuses on reducing pain and protecting the knee. This often includes weight management, muscle-strengthening exercises, activity modifications, and—only in severe cases—surgery. Knee braces and supportive devices can also help reduce joint strain.

Because both inflammation and joint stress contribute to symptoms, an integrated treatment plan that combines medication, physical therapy, and lifestyle changes works best. This holistic approach not only addresses immediate pain but helps preserve long-term joint health and mobility.

Looking Ahead: Promising Advances and Ongoing Questions

Our understanding of how ankylosing spondylitis and knee osteoarthritis interact is still evolving. Researchers are now following patients over many years to see how knee issues progress in those with AS and to evaluate which treatment strategies work best for people with overlapping conditions.

Emerging technologies, like advanced MRI and the search for new blood markers, could lead to earlier, more precise diagnoses. There’s also ongoing research into new medications that target the specific inflammatory pathways involved in both diseases.

The best care happens when experts from different specialties—rheumatology, orthopedics, and rehabilitation—work together. This team-based approach makes it possible to create personalized plans that address the unique challenges facing each patient.

Conclusion

The connection between ankylosing spondylitis and knee osteoarthritis illustrates how deeply intertwined inflammation and joint health truly are. By understanding this relationship, doctors can better diagnose and treat both conditions, offering patients improved relief and mobility.

With ongoing research and a collaborative approach, the outlook for people living with both AS and KOA is brighter than ever. Advances in science and care mean we’re moving toward more effective treatments and a better quality of life for everyone affected by these complex joint issues.

References

Magnusson, K., Kumm, J., Turkiewicz, A., & Englund, M. (2018). Early knee osteoarthritis or healthy ageing? [Journal/Conference name if available].