Glenohumeral Joint Synovitis

Definition

Synovitis, or Synovialitis, is an inflammation of the lining of the joint capsule in synovial joints. The main characteristic of these joints is the presence of a joint cavity, in which synovial cells secrete the so-called synovial fluid. Macroscopically, synovitis impresses as a local synovial inflammation with hyperaemia and hypertrophy of the synovial villi [1].

Aetiology

Synovitides are an expression of inflammatory processes in the joint. Therefore, most inflammatory arthritides may be responsible in developing synovitis. However, certain diseases are accompanied by synovial inflammation more often such as:

• Rheumatoid arthritis (RA)

• Crystal arthropathies

• Frozen shoulder

• Infection

A compilation of underlying inflammatory diseases can be found in the table below. Practically all of these diseases can lead to inflammation in the glenohumeral joint.

Inflammation also occurs in the joint in the case of underlying degenerative diseases or in the context of a chronic or acute rupture of the rotator cuff. Analysis of the synovial fluid helps to differentiate between inflammatory and mechanical affection of the joint.

To this day, unclarity remains, whether synovitis is a process that further progresses chronic shoulder pathologies or is a result of chronic shoulder diseases [1]. However, studying pathological processes in RA has led to the discovery of increased inflammatory mediator production in inflamed synovial cells such as prostaglandins, bradykinin, TNF-α, interleukin-1, and interleukin-6 [2]. Hence, direct activation of afferent nerves and their sensitisation led to increased pain levels and lowered thresholds for otherwise harmless stimuli [2]. These and other mediators were also found in higher quantities in other chronic diseases mentioned above and were shown to recruit leukocytes [3]. Therefore, inactivation of these mediators depicts a potential target for treatment to prevent progression of synovitis. Specific treatment of the underlying disease, or synovitis, also prevents joint damage or cartilage damage and later secondary arthrosis.

Epidemiology

As synovitis is widely regarded as an epiphenomenon rather than its own entity, literature about prevalence of synovitis is scarce. In a study with 167 patients suffering from different chronic shoulder diseases, 87.6% showed signs of microscopic synovitis [1].

History

As a whole range of different diagnosis may coincide with synovitis, so that a comprehensive internal and rheumatological anamnesis is necessary.

Disease specific diagnosis

Clinically, the diagnosis of glenohumeral synovitis is almost impossible because the joint is virtually impalpable. Patients usually report deep-seated pain and there is a limitation of movement for both external rotation and internal rotation. Although recently, a macroscopic assessment system has been proposed, where 3 parameters including villous hypertrophy, hyperaemia, and density were graded during arthroscopy [4]. Other authors attempted to further optimise criteria, yet some objectivity remains [5]. In rheumatoid arthritis, additional symptoms may include proliferation of the synovial membrane, imposing as an almost pathognomonic pannus [6].

Gold standard in verifying synovitis is a histopathological assessment [1]. In order to verify synovitis, synovial fluid analysis, rarely histopathological assessment, or imaging technologies are used.

Ultrasonography is used in questionable synovitis [6]. Particularly useful is the Doppler signal in the detection of synovial hyperaemia [6]. MRI with intravenous gadolinium-based contrast is used in a similar matter, where it can help identify and characterise synovitis with high sensitivity [6].

Differential Diagnosis

• Enthesitis

• Tendinitis

• Other glenohumeral diseases

The prognosis and further course depends on the underlying disease or the response to the specific therapy.