Concepts of Entheseal Pain

Enthesopathies - Mechanical, inflammatory or both?

Entheses have the challenging task of transferring biomechanical forces between tendon and bone, two tissues that differ greatly in composition and mechanical properties. Consequently, entheses are adapted to withstand these forces through continuous repair mechanisms. Locally specialized cells (mechanosensitive tenocytes) are crucial in the repair, physiologically triggering biochemical processes to maintain hemostasis. When repetitive forces cause "material fatigue," or trauma exceeds the entheses' repair capacity, structural changes occur, and patients become symptomatic. Clinical assessment of enthesopathies mainly depends on subjective reports by the patient and lacks specificity, especially in patients with central sensitization syndromes. Ultrasonography has been increasingly used to improve the diagnosis of enthesopathies. In this article, the literature on how biomechanical forces lead to entheseal inflammation, including factors contributing to differentiation into a "clinical enthesitis" state and the value of ultrasound to diagnose enthesopathies will be reviewed, as well as providing clues to overcome the pitfalls of imaging.

Entheseal surface (Sharpey's fiber insertion) alterations identify past trauma; bone base robusticity, level of routine activity

Sharpey's fiber alterations, referred to as entheseal reaction or enthesopathy, have long been considered an indicator of daily activities. Such semantic transformation seems to conflate processes which alter the characteristics of tendonous and ligamentous attachments to bone with the rugosity and extent of their base/footprint. Rather than reflecting normal activities, it is suggested that surface reactions are actually the response to the application of sudden or unconditioned repetitive stresses-analogous to stress fractures. Thus, they are distinct from enlargement of the base/footprint, the bone remodeling process responsible for the robusticity of the area to which the enthesis attaches, which is actually a measure of actual muscle activity. Surface reactions in attachment areas represent injury, be it mechanical stress fracture-equivalents or inflammation-derived. Bone base/footprint is the reaction of the enthesis to stresses of routine physical activities. The character of underlying bone supporting Sharpey's fibers may be augmented by applied stress, but there is neither a physiologic mechanism nor is there evidence for significant addition of Sharpey's fibers beyond ontogeny. Behavior is responsible for the physiologic response of robusticity; spiculation, pathology.

The relationship between clinical parameters and ultrasonographic enthesitis assessment in patients with spondyloarthritis

Objectives

The study aimed to evaluate the role of ultrasonographic assessment of enthesitis in patients with spondyloarthritis (SpA) in terms of disease activity, functionality, and quality of life.

Patients and methods

Ninety SpA patients (57 males, 33 females; mean age: 37.5±9.7 years; range, 18 to 60 years) were included in cross-sectional study between November 2016 and January 2017. Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Ankylosing Spondylitis Disease Activity Score (ASDAS), Bath Ankylosing Spondylitis Functional Index (BASFI), Short Form-12 (SF-12), and Ankylosing Spondylitis Quality of Life (ASQoL) were utilized for clinical evaluation. The clinical evaluation of enthesitis was performed with the Spondyloarthritis Research Consortium of Canada (SPARCC) and Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) via an algometer calibrated to 4 kg/cm2 of pressure. Ultrasound evaluation was performed according to Madrid Sonographic Enthesitis Index (MASEI). A total of 2,610 entheseal sites were examined clinically, and 1,080 were assessed ultrasonographically.

Results

A significant proportion of enthesitis (463/1,080) was detected on ultrasonographic evaluation but not with clinical enthesitis score (MASES and SPARCC). Although ultrasonographic entheseal evaluation detected enthesitis in at least one enthesis of all patients, 35 of the patients had no enthesitis with clinical examination. The sites most frequently involved in the entheses were the proximal patellar tendon and Achilles tendon. The MASEI score did not correlate with the MASES, SPARCC, BASDAI, SF-12, and ASQoL but moderately correlated with the C-reactive protein (CRP) level (r=0.348), ASDAS-CRP (r=0.294), and BASFI score (r=0.244).

Conclusion

The association of ultrasonography scores with CRP levels and ASDAS-CRP indicates that ultrasonography is effective in detecting inflammation. The MASEI score weakly correlates with functionality but not with quality of life. Ultrasonographic evaluation is invaluable and merits to be incorporated into SpA disease scoring system.

Compositional, Structural, and Biomechanical Properties of Three Different Soft Tissue-Hard Tissue Insertions: A Comparative Review

Connective tissue attaches to bone across an insertion with spatial gradients in components, microstructure, and biomechanics. Due to regional stress concentrations between two mechanically dissimilar materials, the insertion is vulnerable to mechanical damage during joint movements and difficult to repair completely, which remains a significant clinical challenge. Despite interface stress concentrations, the native insertion physiologically functions as the effective load-transfer device between soft tissue and bone. This review summarizes tendon, ligament, and meniscus insertions cross-sectionally, which is novel in this field. Herein, the similarities and differences between the three kinds of insertions in terms of components, microstructure, and biomechanics are compared in great detail. This review begins with describing the basic components existing in the four zones (original soft tissue, uncalcified fibrocartilage, calcified fibrocartilage, and bone) of each kind of insertion, respectively. It then discusses the microstructure constructed from collagen, glycosaminoglycans (GAGs), minerals and others, which provides key support for the biomechanical properties and affects its physiological functions. Finally, the review continues by describing variations in mechanical properties at the millimeter, micrometer, and nanometer scale, which minimize stress concentrations and control stretch at the insertion. In summary, investigating the contrasts between the three has enlightening significance for future directions of repair strategies of insertion diseases and for bioinspired approaches to effective soft-hard interfaces and other tough and robust materials in medicine and engineering.

Enthesitis in Spondyloarthritis Including Psoriatic Arthritis-To Inject or Not To Inject?: A Narrative Review

PURPOSE

Enthesitis is a key manifestation of psoriatic arthritis (PsA) and spondyloarthritis (SpA) and is considered to be the tissue where the disease initiates. Enthesitis leads to pain and substantial limitations in patients with PsA. Treatment is key in achieving remission or minimal disease activity. Whether it is safe to apply injections to entheseal tissue is unknown. This narrative review aimed to summarize the literature on the efficacy and tolerability of entheseal corticosteroid (CS) injections.

METHODS

The published literature was searched through PubMed as well as identifying relevant articles from their citations,  for articles on the anatomic location of the injection, tissue characteristics (eg, whether there is a tendon sheath), blind versus imaging-guided and entheseal versus perientheseal injections, and related studies in animals. Given that articles on SpA are limited, those on mechanical enthesopathies were also included.

FINDINGS

The literature on the efficacy and tolerability of entheseal CS injection in SpA and PsA are limited. In most articles on entheseal injection, the entheseal tissue has not actually been targeted. The decision of entheseal injection should be made on an individual basis, with consideration of the use of CS injection as the last treatment option following more conservative measures such as NSAIDs, physiotherapy, rest, and lifestyle modifications. Entheseal injection should be avoided in high-risk patients, such as those who have rupture at the enthesis. Diagnostic ultrasound is advised to ensure the presence of inflammation that can potentially benefit from corticosteroid injection, as well as the absence of rupture. In the authors' perspective, perientheseal injections should be tried before intraentheseal injections. Finally, ultrasound guidance for needle placement is strongly encouraged.

IMPLICATIONS

The literature on the efficacy and tolerability of entheseal CS injection in SpA and PsA is limited. With the lack of quality data, recommendations on entheseal corticosteroid injection remain expert opinion.