article written by dr. Pop Cristina
Medical specialist in rheumatology
WHAT IS ENTHESIS?
An enthesis is a fibrocartilaginous structure defined as the site where ligaments, tendons, aponeuroses, and the joint capsule attach to bone. This type of tissue does not retain water, which makes it difficult—though not impossible—to examine using magnetic resonance imaging (MRI), unlike musculoskeletal ultrasound—a more user-friendly modality that allows for a satisfactory evaluation of this structure.
The enthesis represents the transition—or, more vividly put, the “bond”—between a soft structure (tendinous collagenous tissue) and a hard one (bone), playing a fundamental role in facilitating mobility by enabling the movement of tendons and ligaments relative to the joint and protecting joint structures from mechanical stress.
From an anatomical standpoint, the enthesis was initially described as consisting of several structures, such as the distal fibers of the tendon (the part of the tendon that inserts into the bone), the subchondral bone, and the bursa—an anatomical structure that forms between the bone and the tendon (a small sac filled with fluid that cushions and lubricates the area where the structures overlap to facilitate their sliding and, consequently, their movement, thereby reducing friction).
The new concept, which focuses on the dynamics of mechanisms and sequences involved in enthesal injury, was developed within the synovio-enthesal context and encompasses, under the umbrella term “enthesal organ,” several structures that explain the functional interrelationship with the synovial membrane, specifically: fibrocartilage, the adjacent bursa, structures of the synovial membrane, the periarticular fat pad, the deep fascia, and the adjacent bony structure—namely, the cortical bone.
Normally, entheses are not vascularized, with the exception of the bone-supplying vessels.
ENTEZOPATHY
Entheses are subjected to extreme mechanical stress during their active life. In general, enthesal damage can be degenerative (due to wear and tear, given the mechanical stress to which these structures are exposed) or inflammatory in nature—in the context of inflammatory rheumatic diseases.
Damage to the synovial membrane at the joint level can be primary or secondary. In enthesitis, we are referring to secondary inflammatory synovitis, whereas in other inflammatory conditions, such as rheumatoid arthritis, we are referring to primary synovitis.
Degenerative or mechanical enthesopathy occurs primarily in the elderly, but has also been frequently observed among elite athletes (due to overuse).
Inflammatory enthesopathy (also known as enthesitis) is most commonly described in the context of spondyloarthropathies. Given that, approximately 40 years ago, enthesitis led to the reclassification of inflammatory rheumatic diseases into rheumatoid arthritis and seronegative spondyloarthritis, we can assess the important role of enthesitis as a “cornerstone” of spondyloarthropathies. This category of inflammatory diseases known as spondyloarthropathies includes: ankylosing spondylitis, psoriatic arthritis, reactive arthritis, arthritis associated with inflammatory bowel diseases (Crohn’s disease and ulcerative colitis), and undifferentiated spondyloarthropathy.
Although there are major differences in both causation and progression between the two types of conditions—inflammatory enthesopathy (enthesitis) versus degenerative enthesopathy—their ultrasound findings may be similar; therefore, it is important for a specialized healthcare professional to evaluate symptoms in context. Currently, with the emergence of new biologic therapies available for the treatment of spondyloarthropathies, musculoskeletal ultrasound plays an important role in quantifying the level of inflammation as well as in monitoring its progression during treatment, especially in psoriatic arthritis, and serves as a good indicator of treatment response. From an ultrasound perspective (although there is not yet a consensus unanimously accepted by experts in the field regarding the interpretation of the Doppler signal in enthesitis), the presence of a vascular Doppler signal within 2 mm of the bone surface is considered an important indicator to monitor over time, as it provides insight into both the progression of inflammation during treatment and the ability to distinguish between enthesitis and tendinitis.
Among rheumatic inflammatory diseases, enthesitis is the most common symptom in patients with psoriatic arthritis or ankylosing spondylitis. When discussing psoriatic arthritis, we are referring to an autoimmune disease that affects the skin and joint structures and occurs most frequently in people between the ages of 35 and 55; and when we refer to ankylosing spondylitis, we are referring to chronic inflammation affecting the spine, leading to its gradual stiffening and complete immobilization over time, as well as other peripheral joints, with onset in young people under the age of 40, most commonly in males.
Because it is a strictly localized injury, enthesopathy is very painful in most cases. Typically, the pain occurs in the heel—either at the back or on the bottom (on the sole)—as a result of inflammation in the Achilles tendon or the plantar fascia. Sometimes, when standing, a slight swelling may be observed at the site of the inflamed Achilles tendon. The pain most often occurs in the morning when the patient puts their foot on the floor and improves slightly with movement. Heel enthesitis is not painful at night but can be difficult to tolerate and is sometimes resistant to standard anti-rheumatic treatment. The pain may worsen when climbing stairs or while running.
It is important to note that the bony growths or deposits on the calcaneus, known as osteophytes (commonly referred to as “bone spurs” or “spikes”), do not occur in the context of enthesopathy (although they may coexist) and are not specific to inflammatory rheumatic diseases; they can occur and be detected even in clinically healthy individuals who show no signs of inflammation. It is also important to distinguish between an osteophyte (a bony outgrowth originating from the bone) and an enthesophyte—a calcification that can occur at the site of the enthesis following an inflammatory process.
Painful tenderness associated with enthesitis can also occur in other anatomical structures, such as the elbows, knees, hips, or calves (on the front of the calves).
Because pain causes discomfort and affects the quality of life of the person affected, the early detection and proper treatment of enthesitis are very important. In cases of enthesitis associated with inflammatory rheumatic diseases, treatment overlaps with that of the underlying autoimmune disease. In other situations, treatment may include both medication and physical rehabilitation, depending on the severity of the symptoms. In the case of plantar fasciitis, it is important to avoid walking barefoot on hard or sloped surfaces, walking or running on uneven surfaces, and strenuous (excessive) physical activity for individuals without physical training or exercise endurance. Any type of training should be started gradually, with the intensity of the workouts increasing over time. For obese individuals, gradual weight loss is recommended. Light stretching exercises for the calf or foot may also be performed, and in cases of severe pain accompanied by swelling, ice and/or a topical anti-inflammatory ointment may be applied (intermittently) until you see a doctor. It is recommended to wear high-quality footwear or even special shoes designed to cushion the heels, as well as to use heel lifts for people with flat feet.
Anti-inflammatory medication may be administered in varying doses and for varying durations, depending on the individual case. It is not recommended to take anti-inflammatory medications without the advice or recommendation of a healthcare professional, given their side effects and contraindications in certain situations or in the presence of associated medical conditions.
Bibliography:
Johannes WJ Bijlsma, Eric Hachulla and Co-editors José Antonio P da Silva, Frank Buttgereit, Marco A Cimmino, Frédéric Lioté, Terence O’Neill, „EULAR – Textbook on Rheumatic Diseases”, Third Edition, , BMJ Publishing Group Ltd, London, 2018
Daniela Fodor, “Ecografie musculo-scheletală – Semiologia normală și patologică a
structurilor musculoscheletale”, Vol I, Librex Publishing, București, 2017