Introduction
Diagnostic ultrasound (US) has been described as the most practical, rapid, cost effective method of obtaining images of the musculoskeletal (MSK) system. The use of diagnostic US has been used for imaging structures involved with the diagnosis of inflammatory rheumatological diseases as well as MSK diseases (Patil and Dasgupta, 2012).
Tendon Appearance and Tendon Pathology At Shoulder
When scanning all tendinous structures, using diagnostic US, a normal tendon appearance is hyper-echoic with a regular fibrillar pattern. The long head biceps brachii (LHB) tendon in short section (SS) can be identified sitting in the bicipital groove. If the LHB tendon appears hypo-echoic in SS there is a possible absence of the tendon, or it is anisotropy artefact. If this occurs the tendon should be assessed in long section (LS). The LHB tendon may demonstrate anechoic clefts or an irregular superficial surface. This may represent a partial thickness tear. Buck et al. (2011) stated that in the absence of the LHB tendon placed in the bicipital groove, medal subluxation/dislocation must be considered. To assess for subluxation/dislocation of the LHB, external rotation of the humerus should be performed (Farin, Jaroma, Harju et al., 1995). The subscapularis tendon in SS should appear to have a normal multipennate structure. It is very rare to have an isolated tear of the subscapularis tendon (Morag et al., 2011). Jacobson (2018) stated that full thickness tears (FTT) are represented by a hypo-echoic discontinuity of the tendon most commonly at the lesser tuberosity of the humeral head. Teefey et al. (2000) stated that the accuracy of identifying FTT in the shoulder girdle can achieve 100%. Dinnes, Loveman and McIntyre et al. (2003) argued that the use of diagnostic ultrasound when investigating FTT of the RTC was found to have a pooled sensitivity of 0.87 as well as a specificity of 0.96. This was, again, found to decrease in the detection of PTT with sensitivity being found to be 0.67, although, specificity remained high. Despite this they stated that US is as effective as MRI for the identification of full thickness RTC tears and may be better at picking up PTT.
Schaeffeler et al. (2011) states that the supraspiatus tendon is most commonly injured, with the anterior aspect of the distal tendon at the rotator interval the most likely site of injury. However, Kim et al. (2010) argues that in degenerative tears the posterior supra-infraspinatus junction is more commonly affect. Jacobson (2018) stated that alternative signs of tears include tendon thinning. Tendon thinning is essential to differentiate between tears and tendinosis. Tendinosis is characterised on ultrasound by an ill-defined, hypo-echoic, heterogeneous tendon with the absence of a definitive defect and possible tendon thickening (Jacobson et al., 2004). Other signs of RTC tear is joint effusion and bursal fluid as well as the cartilage interface sign. Joint effusion has been shown to have a positive predictor value of 95% and can be evaluated by assessing the anechoic appearance around the LHB tendon in SS, whereas Jacobson (2018) stated that the cartilage interface sign described by van Holsbeeck et al. (1994) is indicative of an abnormal tendon that extends to the articular surface.
Tendon Pathology at Elbow
Downey et al. (2011) states that imaging the biceps tendon at the elbow can offer difficulty due to its oblique nature, resulting in anisotropy, making it particularly difficult to make a diagnosis of tendinosis or PTT. Smith et al. (2010) stated that imaging via a medial approach can reduce the effects of anisotropy when scanning this structure. Jacobson (2018) states that despite its possible hypo-echoic appearance, if the tendon is uniform in size and structure, it is unlikely to present with any pathology. Imaging of the tendon structures at lateral elbow consists of the common extensor origin, an abnormal hypo-echogenicity at this site coupled with a tendon enlargement (>4.2mm) confirms the likely diagnosis of tendinosis. However, Hyperaemia and neovascular changes on Doppler investigation has been described as variable (Jacobson, 2018). Tricep Brachii tendon tears and avulsions at the olecranon process are possible and visible via US, PTT most commonly involve the superficial layers of the tendon, which involves the lateral and long head attachments (Downey et al., 2011). Jacobson (2018) stated that the medial head, which is a predominantly muscle with a short tendon attachment, often remains intact preventing FTT. Avulsion of the tendon at the site of the olecranon can result in a possible 4cm retraction. In the absence of tendon retraction, but the presence of an ill defined osteophyte with an adjacent hypo-echoic tendon and hyperaemia on Doppler, may be indicative of an active enthesopathy. Draghi et al. (2007) concluded that diagnostic US is effective in identifying degenerative changes associated with tendon overuse syndromes with Dones et al. (2014) stating a sensitivity and specificity of 64% and 82% respectively in identification on Lateral epidcondylalgia.
Tendon Calcification
The supraspinatus tendon is also the most common site for calcification (Leow et al., 1995). Jacobson (2018) stated there are 2 types of calcifications, a degenerative calcification can be identified as a thin, linear hyper-echoic line along the axis of the tendon fibers at the enthesis. Uhthoff and Loehr (1999) stated that the second form of calcification is that a hydroxyapatite deposition. The stages of which are shown below (image 1). From a diagnostic US perspective, Beccionlini, Bonachhi and Galletti (2016) described three types of calcification appearances. The formative phase of calcification appears as a hyper-echoic region within the tendon with a well defined acoustic shadow. The resting and formative phases however appear hyper-echoic, with a faint acoustic shadow and no acoustic shadows shown respectively. These findings are important when it comes to the management of the condition, as in the acute formative stages of calcification development aspiration is the preferred management.
Posterior Shoulder Labrum and Capsulitis
The posterior labrum can also be visualised with diagnostic US. A normal posterior labrum sonographic appearance is hyper-echoic, triangular in shape and attached to the glenoid (Taljanovic et al., 2000). Sonographic findings of a degenerative labrum as heterogeneous hypo-echogenicity, whereas the presence of a well defined hypo-echoic or anechoic cleft indicates a tear (Jacobson, 2018). He also stated that one limitation of US when assessing the posterior labrum is the inability to visualise the entire structure. Despite this, Taljanovic et al. (2000) reported a 98% accuracy in identifying the type of abnormality, as well as an 88% accuracy of identifying an abnormal posterior labrum. This compared to reported accuracies of Magnetic Resonance Arthrogram (MRA) of between 83% and 94%. Adhesive capsulitis can be identified during assessment of the RTC interval. Sonographic signs of adhesive caspsulitis can be demonstrated by hypo-echogenicity, hyperaemia on Doppler and thickening of the coracohumeral ligament (Homsi, Bordalo-Rodrigues, da Silva et al., 2006). This has clinical significance as hydrodilatation could be considered should the time frame of symptoms persevere (Rymaruk and Peach, 2017). However, often clinical evaluation is enough to confirm a diagnosis.
Ligamentous Structures
The coracoacromial ligament (CAL) can be visualised well with US. Dietrich et al. (2016) suggested that although thickness of CAL is similar in asymptomatic patients compared to those with shoulder impingement (SI), the anterior convex shape is significantly more prominent in patients with SI. Evaluation of both the medial and lateral ligament complex is possible with US. Both usually appear as hyper-echoic with compact fibers. Jacobson (2018) stated a partial tear or sprain may appear as hypo-echoic and thickened, with a chronic injury may be intact, but lax on active assessment. During active assessment of the medial ligament complex, a shift of >1mm compared to the asymptomatic side provides an 87% accuracy of the diagnosis, a threshold of >2.5mm difference is used as a FTT (Roedl et al., 2016). In static assessment of the ligaments FTT may appear with a variable anechoic, hypo-echoic and iso-echoic fluid and haemorrhage (Miller, Adler and Friedman, 2014).
Nerve
Yoon et al. (2008) state that compression of a peripheral nerve has an hourglass appearance with proximal swelling, compression with resumption of their normal calibre. Klauser et al. (2009) state that the most common upper extremity nerve compression is the median nerve at the level of the wrist or carpal tunnel syndrome (CTS). Jacobson (2018) described CTS’s sonographic appearance as hypo-echoic and enlarged at the proximal carpal tunnel. It has been identified that a 2mm increase in size comparing proximal to distal can diagnose CTS with 99% accuracy (Klauser et al., 2009) with changes in 6mm and 9mm indicating moderate and severe CTS respectively (Klauser et al, 2015). However US investigations are shown to be far less sensitive and specific than nerve conduction studes (NCS) showing 29.4% and 47% respectively, compared to 100% for both on NCS (Roll et al., 2011).
Ganglion
US appearance of ganglion cysts at the wrist most commonly appear as multilocular, hypo-echoic or anechoic and non compressible (Cardinal et al. 1994). Jacobson (2018) states that most ganglion cysts appear on the dorsal surface of the wrist adjacent to the scapholunate ligament. It is essential to differentiate a ganglion from a joint recess, with the key finding that a joint recess collapses with compression. Freire et al. (2012) stated that US plays a significant role in the assessment of cyst formation at the wrist due to its simplicity and cost. They went onto conclude, MRI should be considered in deep seated cysts that show atypical features or in a specific post operative setting.
Rheumatology
Jacobson (2018) stated that each articulation of the hand and wrist should be assessed for joint abnormalities. He went onto state that anechoic distension of a joint recess typically represents simple fluid, although possible ethologies include degenerative, reactive, inflammatory causes, with joint aspiration being considered in the risk of infection. Synovial hypertrophy is also visible with US and appears as a hypo-echoic, non-compressible distension of a joint recess (Wakefield et al., 2005). If this is change shows hyperaemia on Doppler, it is suggestive of an active inflammatory synovitis (Jacobson, 2018). One of the key techniques when using Doppler is to ensure that minimal pressure is used as this may show up false negatives. Synovial hypertrophy without hyperaemia is not suggestive of a particular diagnosis but may indicate osteoarthritis, however evaluation of further joints is required (Witt et al., 2003). Osseous erosions are also visible on US and appear as an irregular bony cortex that is visible on LS and SS (Wakefield et al., 2005). If rheumatoid arthritis (RA) is suspected, evaluation of the extensor carpi ulnaris should be carried out, as hyperaemia and synovitis here can indicate early signs of RA. Zayat et al. (2015) states that although it is impossible to confirm a diagnosis with US alone, large erosions at the second or fifth metacarpal head or the distal ulnar is also suggestive of RA however further ESR blood investigations should be carried out.
Conclusion
The use of US plays an effective role in the assessment of MSK conditions. Some evidence suggests that it is as accurate as MRI in the identification of FTT of the RTC and possibly more accurate in the identification of PTT. Imaging of the posterior labrum of the shoulder is possible, with limitations based on the size of the patient and inability to view all of the structure, MRA investigations are shown to be more accurate for labral injuries. US is essential during the diagnostic process of calcific tendinitis, as in plain film imaging does not provide the clinician with enough information of the stage of the calcification which can drive your intervention decision process. Nerves are visible via US with more recent advances in technology and pathology can be observed, however NCS are more specific and sensitive. From a rheumatological perspective, US is effective at identifying the possibility of an inflammatory rheumatological condition, however US alone is not sufficient in gaining a specific diagnosis.
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