Sternoclavicular Joint

Fig. 9.1

Sternoclavicular joint

Table 9.1

Stabilisers of the SCJ

Static stabilisers	Dynamic stabilisers
Capsule Intrinsic stabilisers Intra-articular disc ligament Anterior sternoclavicular ligament Posterior sternoclavicular ligament Extrinsic stabilizers Interclavicular Costoclavicular	Subclavius muscle Sternocleidomastoid muscle Pectoralis major muscle

Static stabilisers

Dynamic stabilisers

Capsule

Intrinsic stabilisers

Intra-articular disc ligament

Anterior sternoclavicular ligament

Posterior sternoclavicular ligament

Extrinsic stabilizers

Interclavicular

Costoclavicular

Subclavius muscle

Sternocleidomastoid muscle

Pectoralis major muscle

The anterior and posterior sternoclavicular ligaments are formed by thickenings in the capsule and are the most important contributors to antero-posterior stability [5]. The intra-articular fibrocartilagenous disc resists medial translation of the clavicle [4]. As a result, the disc can be prone to shearing injury, usually as a degenerate tear but occasionally as an acute incident.

The interclavicular ligament passes between the medial ends of both clavicles via the posterior aspect of the sternal notch and resists clavicular superior translation from gravity or forceful depression of the upper limb [4, 6]. The costoclavicular ligament passes from the inferior aspect of the medial clavicle to the first rib and/or first costal cartilage [7]. It is an important restraint when the clavicle is elevated.

The dynamic stabilisers form a musculo-tendinous envelope around the joint. The sternocleidomastoid and pectoralis major tendons lie anterior to the SCJ and play a role in anterior and posterior stability, whilst the subclavius passes from the inferior aspect of the clavicle to the first rib providing superior stability as well as an additional anterior/superior component.

A number of vital structures lie posterior to the SCJ including the great vessels of the neck, oesophagus and the trachea. These are at potential risk following posterior dislocations. A layer formed by the sternothyroid and sternohyoid muscles lies between these structures and the joint capsule [1, 2].

The epiphysis of the medial end of the clavicle is the first epiphysis to appear in utero and the last to close (25–31 years) [8, 9]. This is of relevance because the physis at the medial end of the clavicle is weaker than the SCJ ligaments. Significant traumatic injuries before physeal closure, under the age of 25 years, may result in fracture through the physis rather than a true SCJ dislocation.

The SCJ moves in three planes: retraction/protraction, elevation/depression and rotation [10]. Movement at the SCJ and ACJ allows the scapula to move around the thorax to position the glenoid in the optimal location to maintain glenohumeral joint congruency for upper limb positioning.

9.2 History and Examination

As with any upper limb complaint, it is important to consider the age, handedness, sport, aspirations and occupation of the patient. An acute injury typically involves a high-energy mechanism and an SCJ injury may be missed in the presence of more dramatic components. Details of the exact mechanism of injury including direction of impact should be sought. Up to 30% of acute posterior dislocations develop mediastinal compromise, concerning features include dyspnoea, dysphonia, dysphagia, coughing and venous congestion of the ipsilateral arm and should be considered as a medical emergency. Patients usually present with pain over the SCJ in the presence of a deformity, a prominence of the medial clavicle in anterior dislocations and a defect lateral to the sternum in a posterior dislocation.

In patients presenting with more chronic problems a history of previous trauma or a change of activity preceding the onset of symptoms may be relevant. In younger patients, complaints of pain, clicking, a feeling of instability or even recurrent dislocation in the absence of injury may suggest an atraumatic instability. A history of connective tissue disorders such as Ehlers-Danlos Syndrome maybe relevant. Older patients may present with a pain and restriction of movement associated with a swelling over the medial end of the clavicle.

SCJ examination is predominantly based on comparison and any asymmetry between sides. This requires exposure of the upper trunk to allow for comparison of both shoulder girdles including the clavicles, glenohumeral joints and scapulothoracic movements. There may be obvious asymmetry between the patient’s SCJs with a lump present on the affected side. It is important to determine whether this is soft, representing an effusion or synovitis secondary to an inflammatory arthropathy or infection, or hard, which could represent either a chronic anterior dislocation of the medial end of the clavicle or an osteophyte secondary to osteoarthritis.

Movements at the SCJ are intimately related to the rest of the shoulder girdle, so that assessment of the ACJ, glenohumeral joint and scapulothoracic movements are essential to identify any confounding pathology. Both the SCJs should be examined and compared in 3 planes of movement. Protraction/retraction with the arms in full extension, elevation with the arms extended in maximal abduction. Rotation with the arms at 90°, abduction and the elbows flexed to 90° moves in 3 planes (Fig. 9.2).

../images/473070_1_En_9_Chapter/473070_1_En_9_Fig2_HTML.png — Fig. 9.2

Examination of the sternoclavicular joint—3 planes of movement. (a) Superior and inferior elevation. (b) Anterior and posterior (protraction and retraction). (c) Rotation

It is important to also place a hand over the anterior joint to feel for any abnormal movement and clicking through the range of motion. Clicking, popping, or crepitus at the joint during movement may suggest degenerative changes or, in a younger patient, a disc tear. The medial end of the clavicle may sublux or even dislocate anteriorly in patients with instability. In this instance broader assessment of the stabilising soft tissue envelope, particularly looking at sternocleidomastoid and the sternal part of Pectoralis Major, for muscle sequencing over activity.

9.3 Sterno-Clavicular Joint Pathophysiology

9.3.1 Instability

Sterno-clavicular joint (SCJ) instability can be classified by direction (anterior or posterior), by severity (sprain, subluxation or dislocation—often referred to as type 1, 2 or 3) or by whether it is acute, recurrent or persistent (chronic/unreduced). Whilst these classifications are descriptive, none of them are able to take into account the traumatic or atraumatic nature of the instability. However, a classification system, that is a direct derivation of the Stanmore tri-polar instability triangle for the glenohumeral joint, has recently been described for the SCJ. In the Stanmore SCJ instability classification there are three polar groups: type I traumatic structural, type II atraumatic structural and type III muscle patterning (neuromuscular) (Fig. 9.3).

../images/473070_1_En_9_Chapter/473070_1_En_9_Fig3_HTML.png — Fig. 9.3

Stanmore triangle

The type I traumatic structural group comprises traumatic subluxations and dislocations of the SCJ, as well as medial physeal fracture displacements. The type II atraumatic structural group comprises conditions that lead to laxity of the restraining ligaments, and includes connective tissue disorders (Marfan’s, Ehlers Danlos), degenerative arthritis, inflammatory arthritis, infection and clavicular shortening secondary to previous malunion. The type III muscle patterning group can occur in isolation and is most commonly due to an over active or aberrant pectoralis major muscle but it can also develop secondary to a type I or type II disorder.

A continuum exists between the groups. Therefore, a patient with an initial type II cause of instability can develop secondary muscle patterning (type III) over time; this patient would be then classified as type II/III. The effect of any treatment can also be monitored using the Stanmore SCJ instability classification system. Patients ‘migrate’ around the triangle, depending on the presenting pathology, and how that changes over time as their treatment progresses.

9.3.1.1 Type I Traumatic Structural

Traumatic SCJ dislocations are rare, accounting for less than 1% of upper limb injuries, and usually occur as the result of a high-energy impact. The force is usually indirect and follows an impact either to the front or the back of the humeral head [11]. The force vector is then transferred along the clavicle resulting in disruption of the SCJ’s restraining soft tissues. If the scapula is protracted at the time of impact a posterior dislocation is more likely and if the scapula is retracted it is more likely to dislocate anteriorly (Fig. 9.4). Less frequently a direct anterior blow to the clavicle can drive the medial end posteriorly into the mediastinum [12]. Biomechanical studies have shown that the force required to dislocate the SCJ posteriorly is 50% greater than that required to cause an anterior displacement [13].

../images/473070_1_En_9_Chapter/473070_1_En_9_Fig4_HTML.png — Fig. 9.4

Mechanism of injury. (a) Posterior dislocation: the scapula is protracted with an indirect force to the posterior shoulder. (b) Anterior dislocation: the scapula is retracted with an indirect force to the anterior shoulder

A meta-analysis of 140 adolescents with posterior SCJ dislocations reported that 71% occurred during sporting activities [14]. Although still rare, this requires particular vigilance by pitch-side sports physicians and physiotherapists as over 30% of patients following an acute posterior SCJ dislocation develop mediastinal pressure symptoms. Acute symptoms include dyspnoea (14%) and dysphagia (22.5%) due to pressure on the trachea and oesophagus and venous congestion or oedema of the ipsilateral arm due to compression of the vessels (14%) [14]. Less common complications of posterior dislocations include mediastinal hematoma, vessel laceration (leading to death), stroke, pneumomediastinum, pneumohemothorax, and venous thromboembolism (0.72–2.90%) [14]. As a result, an acute posterior SCJ dislocation should be treated as a medical emergency.

Patients presenting more chronically often complain of pain and deformity over the SCJ. In certain patients, as the medial clavicle has been pushed posteriorly, the whole of the shoulder girdle has rotated anteriorly and superiorly. As a result, the scapular tends to sit in a more superior and protracted position. Patients may complain of problems with glenohumeral function and of asymmetrical scapular protraction which, for example, can make sitting in high-backed chairs uncomfortable as the medial scapula adopts a winged position (Fig. 9.5).

../images/473070_1_En_9_Chapter/473070_1_En_9_Fig5_HTML.png — Fig. 9.5

Posterior dislocation. A 16-year-old boy referred 4 weeks after sustaining a left posterior SCJ dislocation in a tobogganing accident. His CT scan confirmed an SCJ dislocation rather than an expected medial clavicular physeal injury. (a) Anterior view: note the asymmetry and loss of clavicular contour on the left. (b) Posterior view. Note the elevated and winged scapula on the left hand side. 3 months following open reduction and stabilisation using a figure of eight gracilis graft. (c) Anterior view: clavicular symmetry has been returned. (d) Posterior view: the left scapula has now returned to its normal position

On examination an anterior SCJ dislocation presents with an obvious forward displacement of the clavicle, while a posterior dislocation demonstrates asymmetry compared with the contralateral side, with diminution of the entire clavicular contour on the affected side. However, there is often significant soft-tissue swelling in the days after an acute posterior dislocation, which may make this less obvious. It can also be difficult to clinically distinguish a medial clavicular physis fracture-dislocation from a true SCJ dislocation. A high clinical suspicion for medial clavicle physeal injury should remain for anyone under 25 years.

Traditionally initial investigations following an SCJ injury include plain radiography using either a Serendipity or Heinig view. However, these are often difficult to interpret. A plain chest X-ray may be considered following an acute injury to check for an associated pneumothorax secondary to rib fractures. Currently the investigation of choice is a CT scan or, in the case of a posterior dislocation, a CT angiogram, this should be undertaken as a matter of urgency in the acute situation should there be any concern with regards to mediastinal compromise [15]. A CT scan can accurately assess the position of the medial end of the clavicle with regards to the sternum and the contralateral SCJ. It can also differentiate between a dislocation and a medial physeal injury. A CT angiogram additionally shows the arch of the aorta and great vessels in relation to the medial clavicle (Fig. 9.6). An MRI scan has poorer bony resolution than a CT scan but is able to more effectively demonstrate the ligamentous structures following subluxation and recurrent dislocation. It is also able to assess the intra-articular disc for injury and the condition of adjacent neurovascular anatomy.