SC joint instability

Definition

Sternoclavicular joint instability (SCJI) is a non-physiological translation of the clavicula in the sternoclavicular joint (SCJ) associated with pain or discomfort in the SCJ area.

Aetiology

Several different mechanisms can lead to a development of instability in the sternoclavicular joint.

• Traumatic dislocations

• Collagen deficiency disorders

  • Although, ligamentous structures supporting the SC joint are remarkably stable, weakend ligaments might lead to subluxation and instability

• Aberrant muscle patterning

  • M. pectoralis major

• Clavicular shape

  • Short clavicula increases torque stress on the SC joint [1]

• Infection

• Inflammatory and degenerative arthritis

  • Up to 31% of patients with rheumatoid diseases suffer from SCJ involvement [1]

According to the Stanmore-Triangle-System (originally used for glenohumeral instability), SCJI can be divided by different causative factors as followed [1]:

• Type I: Traumatic structural

  • Dislocations, medial clavicula fractures

• Type II: Atraumatic structural

  • Capsular laxity due to collagen disorders (e.g. Ehlers-Danlos- & Marfan-Syndrome), Clavicular shape, degenerative osteoarthritis, inflammatory arthritis, infection

• Type III: Muscle patterning, non-structural

  • Abnormal pectoralis major activity

Note that these are not definite categories as patients can move from one type to another in the course of the disease.

Epidemiology

As SCJI is a rare condition so is literature on the prevalence of the topic. It should be noted however, that injuries to the sternoclavicular joint account for only 5% of injuries to the shoulder girdle [2]. Although uncommon, instability in the SCJ may have a negative impact on the quality of life of people affected and should therefore be included in one’s differential diagnosis.

History

When taking the patients history regarding SCJI, one should prioritise on traumatic high-energy collisions in the past or ask about hypermobility of other joints or inquire about family members with collagen disorders. Other things indicating instability might be pain during overhead activities (work- or sports-related) or occasional bony prominences during certain movements. A targeted medical history taking into account all the differential diagnoses mentioned below is indispensable.

Disease specific diagnosis

Detailed information on the clinical assessment of acute dislocations can be acquired under SC Dislocations

Type II of the Stanmore-Classification is a group of several different pathomechanisms that lead to instability in the sternoclavicular joint. Patients with capsular laxity due to collagen deficiencies have generalised joint hypermobility and should be assessed accordingly. Clavicular shape plays a role in patients under the age of 25 as the clavicular epiphysis is the last to fuse at the age of 23 to 25 [1, 2]. Medial segments are often straighter and therefore have higher torque stress on the sternoclavicular joint [1]. Degenerative osteoarthritis in the SCJ can be detected by performing a cross-body-adduction test in which pain worsens and clicking due to crepitus can be felt by the patient [1]. It should be noted that osteoarthritis can be the cause of instability or that instability may cause osteoarthritis. Inflammatory or infectious aetiologies can be diagnosed by synovial fluid aspiration where certain laboratory parameters are elevated (C-reactive-protein, blood sedimentation rate, leukocytes, rheumatoid factors etc.)

In order to diagnose type III instability, an electromyography is performed [1]. It will show inappropriate pectoralis major recruitment [1]. In fact, patients suffering from SCJI with absence of arthritis should be screened for abnormal muscle patterning [1].

In every case a series of imaging methods may help diagnosing or rule out different pathologies that might be responsible for instability in the SCJ. X-rays in ap and serendipity view as well as computed tomography may provide clarity in unusual cases [2].

Differential Diagnosis

Possible differential diagnoses in unilateral SCJ swelling

• Mechanical enthesopathy

  • Overuse syndromes

  • Trauma

• Inflammatory enthesitis

  • Peripheral spondyloarthritides (e.g. psoriatic arthritis, SAPHO syndrome, reactive arthritis)

  • Endocrinopathies (e.g. diabetes, hypothyroidism)

  • Crystal arthropathies (e.g. gout, CPPD)

• Arthritis

  • Septic

  • Inflammatory rheumatic diseases (e.g. rheumatoid arthritis, peripheral spondyloarthritis)

  • Crystal arthritis (e.g. gout, CPPD)

• Osteitis/ osteomyelitis

  • Septic

  • Aseptic (e.g. SAPHO syndrome, CRMO)

  • Osteitis clavicularis condensans

• Subluxation

  • Traumatic with ligamentous lesions

  • Benign subluxation (especially women, dominant side)

  • Articular hyperlaxicity

• Osteoarthritis

  • Primary (rare)

  • Secondary (in all other diseases mentioned), with or without subluxation

In most cases, patients suffer from an unstable SC joint after closed reduction with recurrent dislocations or subluxations [2]. However, literature about surgical outcomes of type I still remains scarce.

In a study about non-operative treatment of type II instability, 90% suffered from recurrent subluxations and 21% still complained about pain [1]. Yet, all patients undergoing surgical treatment reported unsatisfactory results [1].