by Tracey Kellett, Online Health Advisor

An enthesis is a site where the tendons, which anchor muscles to bone, and ligaments, which join bones together, connect with bone via a specialised fibrous tissue. Enthesitis is a medical condition in which the enthesis becomes inflamed, resulting in swelling, pain, and stiffness in the nearby joint and muscle. Entheses enable the proper transfer of force from muscle to the skeleton for you to move, as well as moving the force away from the joint and enthesis itself. Common orthopaedic injuries that athletes tend to get, such as tendonitis and rotator cuff injuries, may involve enthesitis. For them, symptoms will eventually disappear with appropriate treatment and rest, but for people with inflammatory types of arthritis, the symptoms will persist for much longer and need different treatment approaches.  

As well as causing pain, persistent enthesitis can cause structural changes, including bone erosion, bone spurs, and bone growth that can result in joint fusion. 

The enthesitis and arthritis link 

Associate Professor Andrew Harrison, Wellington Rheumatologist, says “Enthesitis is inflammation in the specialised tissue that forms the junction between bone and tendons, ligaments and joint capsules. It is commonly seen in patients with spondyloarthritis.”  

Types of spondyloarthritis are Psoriatic Arthritis, Ankylosing Spondylitis, arthritis related to inflammatory bowel disease, Reactive Arthritis, and a subgroup of Juvenile Idiopathic Arthritis (enthesitis-related arthritis).  

Prof. Harrison says “patients with Ankylosing Spondylitis often have enthesitis in the ligaments that run along the vertebral column and around the pelvis and chest wall.”  

For Psoriatic Arthritis, enthesitis is a hallmark feature which adds substantial amounts of pain, stiffness, and swelling. One study found 50% of their participants with Psoriatic Arthritis had clinical enthesitis, with another in Canada finding 35% prevalence. Studies have shown that subclinical (which means not quite bad enough to make it to a clinical diagnosis or typically have symptoms) enthesitis could predict the future development of Psoriatic Arthritis in people with psoriasis.  

The most common sites of enthesitis in people with Psoriatic Arthritis are the Achilles tendon, plantar fascia (the strong tissue that runs under the sole of the foot from the heel to the base of the toes), and the bony bump on the outside of the elbow (tennis elbow). 

Enthesitis can coexist with other joint and tendon problems like Osteoarthritis and overuse/injuries, but with spondyloarthritis, it is one of the main features. 

Fibromyalgia 

Differentiating enthesitis from fibromyalgia can be difficult in a clinical examination, but there are criteria for this, and the vast majority of fibromyalgia patients don’t have enthesitis. One study identified a 15% crossover of people with fibromyalgia, psoriatic arthritis and enthesitis diagnoses. 

Rheumatologist Doug White says “this confusion mostly relates to the previous reliance on counter tender points to make a fibromyalgia diagnosis. Diagnostic thinking has changed and we now recognise the key concept of central sensitisation in fibromyalgia. To put it bluntly, people with enthesitis have regional pain; people with fibromyalgia are sensitive everywhere.”  

What causes enthesitis?

Risk factors for developing enthesitis are overuse, injury, being diagnosed with spondyloarthritis, younger age of diagnosis, and higher BMI.  

Psoriatic Arthritis Online Support Group member Wendy knew that there was something else going on in addition to joint pain and talked to her rheumatologist: “I asked if my joints are the problem then why does this hurt- pointing to just below my shoulder joint. That’s when he explained that enthesitis was where the muscle attaches to the bone is also inflamed. This really helped me understand my pain and the strangeness of it when PsA is supposed to be joints.” 

Sue says “It’s a dragging pain for me (like period pain in your arms lol). It’s nasty and I get it a lot.” 
 

How is enthesitis diagnosed? 

Enthesitis is usually diagnosed clinically based on the symptoms and by the finding of tenderness over the tendon or ligament insertion. 

According to Associate Professor Harrison, radiological investigations can be helpful, e.g. demonstrating thickening of the tendon insertion and abnormal blood flow by ultrasound or by thickening and oedema in the tendon and adjacent bone by MRI. 

Treatment for enthesitis 

The treatment for enthesitis typically involves reducing inflammation, relieving pain, and improving joint function. The specific treatment plan will depend on the severity of the enthesitis and any underlying conditions contributing to the inflammation. Options for treatment involve controlling underlying arthritis. Some common treatments include: 

Non-steroidal anti-inflammatory drugs (NSAIDs) can help reduce pain and swelling. 

Corticosteroids: These medications can be taken orally or injected directly into the affected joint to reduce inflammation. 

Biologic medications: These target specific parts of molecules in the immune system to reduce inflammation. In particular, anti-tumour necrosis factor (anti-TNF) agents are recommended for treating spondyloarthritis. 

Movement: An exercise professional can give you gentle movement and stretches to help strengthen the surrounding area and relieve some pain and stress. A recent review of movement and spondyloarthritis said that the trials consistently demonstrated the beneficial effect of a combination of anti-TNF therapy and axial spondylitis-specific exercise programmes, compared with either anti-TNF treatment or exercise alone. Research also says that individual home exercises are better than nothing, but supervised group exercises are more effective, and a combination of inpatient exercise therapy followed by group physiotherapy sessions was better than the group sessions alone. Exercise can produce systemic anti-inflammatory effects, but high-intensity exercise may worsen enthesitis and inflammation, so work with a health professional for personalised movement and exercise advice. 

Other treatments that may help 

• Gel or foam inserts in your shoes can help relieve some of the discomfort caused by plantar fasciitis, you can see a podiatrist for this if you can’t find something over the counter that works for you
• Anti-inflammatory gels/creams
• Massage  
• Rest the area and get enough sleep 
• Hot and cold therapy 
• A healthy, anti-inflammatory way of eating to maintain a healthy weight 
• Support with K-tape, compression socks/sleeves
• Other pain-relieving medications, such as paracetamol 

It is important to work with a healthcare provider to determine the most appropriate treatment plan for enthesitis and the type of arthritis you have. More often than not, a combination of treatments is needed for optimal relief. 

This article was medically reviewed by Andrew Harrison, Associate Professor of Medicine and Dr Doug White, Rheumatologist. 2023.