Ankylosing Spondylitis vs. Osteoarthritis: What Are the Differences?

Ankylosing spondylitis (AS) and osteoarthritis (OA) are two types of arthritis—conditions that cause inflammation and swelling of one or more joints. Both diseases cause joint pain and stiffness and eventually damage joints, but their underlying processes and causes are very different.

This article discusses the similarities and differences between ankylosing spondylitis and osteoarthritis, including the symptoms, causes, and treatment.

Symptoms  

Both AS and OA can cause pain, stiffness, and swelling of the joints. In some cases, these conditions can lead to loss of joint function and disability.

Ankylosing Spondylitis

Ankylosing spondylitis belongs to a group of inflammatory arthritis conditions called spondyloarthritis (SpA) or spondyloarthropathies. These conditions have distinct features. They affect the spine and other joints, including the fingers, arms, and legs. They also affect the areas where ligaments and tendons attach to bone (entheses) and the peripheral joints. 

With AS, the immune system targets the spine's joints as well as the ligaments and tendons attached to the bone at the joints. Ongoing inflammation eventually leads to bone erosion, and the body will respond by forming new bone tissue.

The new bone growth causes the spine to grow together (fuse) and become stiff, painful, and inflexible. Even at the sites where there is new bone growth, the original bone becomes thin, which increases the risk of spinal fractures.

Symptoms of AS include:

• Neck pain, hip and buttock pain, and low back pain: The pain is usually felt on both sides of the back
• Back stiffness: The stiffness gets better with activity and is worse in the morning or after periods of inactivity
• Chronic fatigue: Fatigue is a primary symptom of AS, affecting up to 70% of people with the condition. It is also linked to poor treatment response, decreased quality of life, and disability. 
• Enthesitis or swelling at the entheses, especially in the spine: Among people with AS and non-radiologic axial spondylitis (nr-axSpA), enthesitis is reported in about 34% to 74% of people with the condition. Nr-axSpA is considered a precursor to AS.
• Skin rash: SpA conditions are commonly linked to chronic skin diseases, including psoriasis. 
• Bowel inflammation and gastrointestinal symptoms: Bloating, nausea, and other GI symptoms can occur with AS.
• Eye inflammation: Inflammation of the colored ring around the eye's pupil (iritis) and inflammation of the middle layer of the eye wall (uveitis) are often seen in people with AS and can cause eye pain, redness, blurry vision, and sensitivity to light.
• Chest pain or trouble breathing: Some people with AS have severe chest pain and breathing trouble. These symptoms occur when the upper body curves forward and the chest wall stiffens. AS can also cause lung scarring and an increased risk of lung infections.
  

Osteoarthritis 

According to the Centers for Disease Control and Prevention (CDC), an estimated 27 million Americans have OA. The condition occurs when the protective cartilage that cushions the ends of bones starts to break down. 

The symptoms of OA develop slowly over the years or decades and get worse with time.

Symptoms of OA include:

• Pain in affected joints: Especially with movement 
• Stiffness: Most noticeable after inactivity
• Tenderness: Affected joints will feel tender when pressure is applied on or near the joint
• Swelling: Soft tissue inflammation around the joint
• Flexibility loss: Cannot move an affected joint to its full range of motion
• Grating sensation, popping, or cracking: Feeling a grating sensation when moving the affected joint or hearing popping or cracking noises with movement
• Bone spurs: Can be felt as lumps below the skin can form around an OA-affected joint
  

People who have OA of the spine might have the following symptoms: 

• Pain in the back or neck that is more noticeable when bending or twisting the back or neck
• Stiffness of the back and spine joints, especially in the morning and after periods of inactivity 
• Crunching or grating noises with the movement of the back or neck
• Headaches
• Pain in the shoulders and arms
  

Causes 

AS and OA occur because of different underlying processes. AS is an autoimmune disease where the immune system malfunctions and attacks healthy tissues. OA happens over time because of aging and joint wear and tear. 

Ankylosing Spondylitis

AS is an autoimmune disease where the body malfunctions and attacks healthy tissues—mainly the spine and the sacroiliac joints attaching the pelvis to the base of the spine. It can also occur in the large joints of the arms and legs (peripheral joints).

AS affects 1 in 200 people, according to a 2021 report. The cause of AS is still unclear, but it does seem to run in families. It is also linked to specific genetic and environmental risk factors. 

Having a family history of AS increases your risk for AS. Research has also shown that up to 90% of people with AS express the HLA-B27 gene. Fewer than 8% of people in the general population have this gene.

Carrying the HLA-B27 gene does not necessarily mean you will eventually develop AS. Instead, it means you are at an increased risk for AS—especially when environmental factors or other unknown factors also come into play.

Other risk factors for AS include:

• Age: A diagnosis of AS typically occurs before age 45, but children and teens can also be diagnosed with the condition.
• Sex: HLA-B27 gene prevalence is equal for people of any sex, but people assigned male at birth are more likely to be diagnosed with AS. Male sex is also considered a risk factor for nr-axSpA progression to AS.
• Having another autoimmune disease: If you have another autoimmune disease, your risk for AS is higher.
• Gut bacteria: Alterations in gut bacteria and gut inflammation might be linked to AS risk.
• Infections like Klebsiella pneumoniae, respiratory tract infections, and tonsillitis (especially in childhood) may increase AS risk.
• Mechanical stress: Stress that occurs in body tissues and leads to musculoskeletal diseases may contribute to AS.
• Smoking: Research has found that smoking can increase your risk for AS. Smoking might also worsen AS and hasten disease progression, eventually leading to joint and bone damage.
  

Osteoarthritis 

OA occurs when there is a breakdown or damage to the joint cartilage. OA is linked to several risk factors, including:

• Age: Your risk for OA increases as you get older.
• Sex: People born female have a higher risk for OA, especially after the age of 50.
• Being overweight: Extra weight puts more stress on joints, especially weight-bearing ones like the hips and knees. Obesity also causes metabolic effects, which can increase OA risk.
• Joint injuries and overuse: Bone fractures and damage to cartilage and ligaments can lead to OA. Using the same joints repeatedly on the job or when playing a sport can also lead to OA. In both cases, OA can rapidly progress and appear in younger people. 
  
• Genetics: OA tends to run in families and is often linked to joint defects. You are more likely to have OA, especially before age 50, if your parents or grandparents have OA.
• Race/ethnicity: In the United States, OA is more commonly diagnosed in White people than in people of other racial/ethnic backgrounds, especially spine OA.
  

Diagnosis 

Some methods used for diagnosing AS are also used to diagnose OA. However, AS will require more testing, especially bloodwork. If bloodwork is done in OA, it is to rule out other conditions. 

Ankylosing Spondylitis

Diagnosing AS typically starts with a physical exam. Your healthcare provider may test your spine's range of motion as you are asked to move in different ways. They might also press on parts of your pelvis or have you move your legs to see if you feel pain.

By having you take deep breaths, they can look for any problems you have expanding your chest or breathing. Additional testing for AS includes imaging and blood tests. 

X-rays can help your provider look for any changes in your joints and bones. Magnetic resonance imaging (MRI) studies can give them more detailed images of bones and soft tissues. MRI scans can show evidence of AS earlier in the disease process.

No specific lab tests can confirm a diagnosis of AS. However, your provider can request blood work to check for inflammatory markers and the HLA-B27 gene.

Osteoarthritis 

Much like AS, diagnosing OA starts with a physical examination. Your provider will check the affected joints for tenderness, swelling, and redness. They will also ask you to move the affected joints to look at your flexibility and range of motion.

X-rays can help your provider identify the narrowing of the spaces between the bones in a joint, indicating cartilage loss. X-rays can show bone spurs around a joint.

Bloodwork might be done to rule out other conditions that cause similar symptoms, such as AS and rheumatoid arthritis (another type of autoimmune arthritis).

Joint fluid testing can also rule out other inflammatory arthritis conditions like gout. With this test, your provider will use a needle to take fluid out of an affected joint, then send it off for testing.

Treatment 

Arthritis conditions generally are not curable, but they are treatable and manageable. Treatment focuses on managing your symptoms, protecting your joints, preventing damage, and improving your quality of life. Some treatments for AS and OA will overlap, but certain medicines work better to treat each condition.

Ankylosing Spondylitis 

Treating AS is aimed at relieving symptoms and delaying complications like spine deformity. This includes a combination of medicines, physical therapy, and lifestyle modifications. 

Medications

The earliest treatment options for AS are nonsteroidal anti-inflammatory drugs (NSAIDs) like Advil (ibuprofen) and Aleve (naproxen). They can treat pain and reduce inflammation.

NSAIDs should be taken cautiously because they can lead to stomach symptoms, cardiovascular conditions, bleeding problems, and kidney damage. Topical NSAIDs are safer pain relief alternatives with fewer side effects.

If NSAIDs aren't helpful, your healthcare provider might suggest you try a biologic drug. Biologics used to treat AS include Cosentyx (secukinumab) and Taltz (ixekizumab). These medicines are injected under your skin or given intravenously (IV) directly into a vein. However, these medicines have side effects—for example, they can make you more prone to infections.

Physical Therapy 

Physical therapy is a key part of treating AS. It can offer pain relief and improve your strength and flexibility. 

A physical therapist can make an exercise plan to help you manage pain and improve your posture. An exercise plan for AS might include doing range of motion and strengthening exercises, as well as education on proper sleep, walking, sitting, and lifting positions. 

Surgery

It is unlikely that you will need surgery to manage AS. Surgery might be recommended if you are experiencing severe hip or back pain or if you have a damaged joint that needs repair or replacement. 

Lifestyle Changes

Some lifestyle modifications might help you manage AS and slow the disease's effects:

• Staying active: Exercise can ease pain and help you improve and maintain your posture.
• Not smoking: If you smoke, quitting can reduce AS symptoms and keep your treatments working effectively. 
• Practicing good posture: Practicing good posture can help you to avoid spine problems linked to AS and reduce pain and stiffness.
  

Osteoarthritis 

OA cannot be reversed, but treatment can ease pain and help you move better. Treatments for OA include pain relief medicines, at-home remedies, physical and occupational therapies, and as a last resort, surgery.

Medicines 

Medicines that treat OA symptoms include prescription and over-the-counter (OTC) pain relievers. 

Treatments include:

• Tylenol (acetaminophen): Acetaminophen can help relieve mild to moderate OA pain. Do not take more than the recommended dose because acetaminophen can cause liver damage.
• NSAIDs: OTC NSAIDs can ease OA pain. Your provider can prescribe a stronger NSAID to manage more severe OA pain if you need it.
• Cymbalta (duloxetine): Duloxetine can help to relieve OA pain.
• Corticosteroid injections: Steroid injections may provide pain relief for several weeks.  

Home Remedies 

Home remedies will not replace medical treatment, but they can help you manage OA pain with fewer side effects.

Home remedies for OA include:

• Hot and cold compresses: Heat therapy can soothe stiff joints and relax muscles. Cold treatment can numb OA pain and ease inflammation.  
• Epsom salt baths: An Epsom salt bath can offer all-over pain relief. You can add Epsom salt to warm bath water and soak for up to 30 minutes.
• Support and assistive devices: Various support and assistive devices can take pressure off affected joints. Examples include braces, canes, grabbing and gripping tools, taping (a physical therapist can show you how to tape an affected joint), and dressing tools.
  

Physical and Occupational Therapies 

A physical therapist can show you how to do exercises to improve pain and stiffness and strengthen the muscles around your joints. You can also exercise regularly with activities like swimming and walking to manage OA symptoms.

An occupational therapist can help you find ways to do everyday activities without putting stress on painful joints. They can also offer information about assistive devices that can make your life easier. 

Surgery 

If other therapies have not helped to treat OA pain or you have joint damage, your provider might recommend surgery. 

The most commonly performed surgeries in people with OA are knee osteotomy and joint replacement. With knee osteotomy, the surgeon removes or adds a wedge of bone to shift weight away from the worn-out part of the knee. With joint replacement surgery, the surgeon takes out the damaged joint surfaces and replaces them with plastic and metal parts.

Surgery is not without risks, including blood clots and infections. Also, artificial joints can wear away, come loose, and eventually need replacement.

Prevention 

Arthritis conditions are generally not preventable. If you have a family history of AS or OA, ask your provider to help you identify your risk factors.

While it is not always possible to prevent OA, you might be able to minimize your risk by avoiding injury to joints, maintaining a weight that's healthy for you, controlling your blood sugar, and staying active.

Summary 

Ankylosing spondylitis and osteoarthritis are arthritis conditions. Both cause joint pain and stiffness. While these conditions have some similarities, they are different diseases. 

AS is an autoimmune disease where the immune system affects healthy tissues—mainly the small joints of the spine. On the other hand, OA is a "wear and tear" arthritis that occurs with age and is linked to injuries and genetics. 

Some treatments for AS and OA might overlap. Both are treated with OTC pain relievers, physical therapy, lifestyle changes, and surgery. AS is also treated with biologics. OA can be managed with home remedies and medications like Cymbalta. 

AS and OA are not preventable. It is possible to reduce some risk factors for OA by avoiding joint injuries and leading an active, healthy life.