Digital, computed or conventional radiographs

Radiographic imaging is the first-line investigation of many elbow pathologies as it provides a cost-effective, reliable, easily accessible, quick and safe method of assessing acute and chronic elbow conditions. Frontal and lateral views are considered standard and further imaging with oblique radiographs is now rarely requested, as CT, US or MRI is usually better placed to provide further insight.¹

Sensitivity of elbow radiographs to bone injury and pathology is relatively high, although sensitivity falls when the clinician reviewing the film is inexperienced.² While most of the information available from radiographs relates to bone, the value of the soft tissue signs visible on many radiographs should not be underestimated. Elevation of the anterior and posterior fat pads may indicate a joint effusion or haemarthrosis, which in turn may predict the presence of an occult fracture in the context of trauma. Alternatively, the elevated fat pad may indicate an effusion or synovitis secondary to an erosive arthropathy, infection or loose intra-articular bodies. Periarticular mineralization is often present in crystal arthropathies, hydroxyapatite deposition or in relation to ligaments and muscle following trauma.

Radiographic imaging is often the only imaging that is required in the follow-up of fractures, dislocation and after surgical intervention (Fig. 5.1).

Figure 5.1 Tension band and K-wire fixation of an olecranon fracture with a Mason type II fracture of the radial head, AP radiograph.

Ultrasound examination (ultrasonography)

Ultrasonography (US) provides a useful method for investigation of soft tissue pathology at the elbow, and has several advantages over MRI and CT. The superior spatial resolution inherent in US allows detailed examination of fine structures, such as nerves, tendons and ligaments, and gives more detail about the internal architecture of muscles, masses and cysts. In order to maximize spatial resolution a transverse high-frequency probe with a narrow footprint should be used. US of tendons and muscle is prone to artefact and also requires a sound understanding of normal anatomy to avoid diagnostic pitfalls.

US allows face-to-face contact during imaging, providing correlation between the ultrasound appearances and the history and clinical findings such as tenderness or swelling. Comparison can easily be made with the ‘normal’ contralateral side (with caution, as pathology may be bilateral) and dynamic assessment of the elbow joint is possible during scanning. Imaging can be performed in any plane, in line with, perpendicular to, or oblique to any superficial structure. Coupled with the fact that it is widely available, relatively inexpensive, well tolerated and harmless to the patient, US is a good first-line investigation of elbow pathology.

US can provide excellent detail about the surface of bone, particularly with regard to enthesial and joint margin pathology, including erosions. However, the high-frequency ultrasound used in medical imaging does not penetrate bone beyond the cortex and US has limited resolution of deep structures. In addition, US has relatively poor anatomical resolution, is highly user dependent and US images are less readily interpreted by a third party than CT or MRI. A good working relationship between the radiologist performing the ultrasound examination and his/her clinical colleague is therefore essential.

Magnetic resonance imaging

In many ways magnetic resonance imaging (MRI) provides the ideal modality for investigating the elbow, where it gives excellent anatomical resolution, particularly of ligaments,³ tendons, articular cartilage and subchondral bone and neurovascular structures.⁴ Multi-planar imaging allows these structures to be clearly identified from several ‘viewpoints’, usually the axial, coronal or sagittal plane. MRI holds the greatest advantage over ultrasound where multiple structures are thought to be abnormal and where the suspected pathology is deep within the joint, rather than superficial.

Where possible the elbow should be imaged using a surface or circular coil with the joint extended and forearm supinated, although in practice this may not be possible because of pain or deformity. In order to maximize MR image quality, the patient should be as comfortable as possible. Careful positioning of the upper limb and elbow during MRI may be used to better demonstrate structures that present an imaging challenge, such as the distal biceps tendon,⁵ where the elbow is flexed, the arm abducted and the forearm supinated (FABS). Oblique structures may be better visualized by additional imaging with a microscopy coil applied close to the ligament or joint region in question and acquiring thin-slice (1–2 mm) volume data with a T2* gradient echo (GRE), STIR or PD FS TSE sequence, although image acquisition time is significantly increased with this technique.³

Standard sequences are acquired in the axial, sagittal and coronal planes using a combination of T1 and T2 turbo/fast spin echo (TSE) and proton density (PD) TSE or PD with fat saturation (FS). Pathology is often best demonstrated with fluid-sensitive imaging, such as short tau inversion recovery (STIR), PD FS TSE or T2 FS TSE sequences. However, it should be noted that these fluid-sensitive sequences have reduced anatomical resolution, as ligaments, tendons and muscles are less clearly demarcated from the adjacent fat. There is no such thing as the perfect series of sequences, as the MRI scanner, coils, available scan time and personal preferences of the reporting radiologist will vary greatly from site to site. Where sequences are described they are intended only as a guide, taken from the sequences reported in the scientific literature or from my personal experience.

MRI imaging using 3-tesla (3T) field strength scanning is becoming more widespread. Detailed imaging of articular cartilage and fine structures such as ligaments is generally better when 3T imaging is possible, although there may be an increase in chemical shift artefact and susceptibility artefact from metal, both of which can reduce image quality. Furthermore, image quality may suffer when imaging large anatomical regions as a result of dielectric artefact.

Computed tomography

Computed tomography (CT) is used in the preoperative assessment of the elbow, to define bone anatomy and pathology. In the context of acute trauma, CT shows the extent of fractures and joint dislocation. With long-term morbidity, it is used for the investigation of suspected loose bodies, restricted range of movement and other pathology related to bone.

In simplistic terms the elbow is a hinge joint, but when rotation at the proximal radio ulnar joint during supination–pronation is considered, the elbow joint is demonstrably more complex and may present difficulty in assessing bone and soft tissue anatomy. Multi-detector CT (MDCT) allows sub-millimetre fine-slice axial images to be ‘reconstructed’ in any plane or volume rendered to provide 3-D imaging of the bony anatomy of the elbow.

CT arthrography, usually performed with a posterolateral intra-articular injection of dilute iodinated contrast, is particularly useful in detecting unstable osteochondral fragments, loose bodies and osteophytes/defects in the articular surface of the elbow joint. However, MR arthrography is more frequently utilized as it also demonstrates soft tissue pathology in addition to bone and articular cartilage.

Bone scintigraphy

Bone scintigraphy (or a bone scan) may be used to identify metabolically active bone lesions in the elbow, particularly where MRI, CT, plain films and radiographs have not produced a definitive diagnosis, or where one or more of these modalities cannot be utilized. The bone scan uses a radioactive tracer (technetium 99m) attached to methylene diphosphonate (MDP); the MDP is taken up by osteoblasts and is therefore a marker of physiological bone activity. The gamma radiation emitted by decay of technetium 99m is used by a gamma camera to form an image. Single-positron emission computed tomography (SPECT) produces a CT image of the joint, allowing more exact anatomical resolution of pathology. While bone scanning involves the injection of radioactive material into the body, it produces a relatively low effective radiation dose of the order of 0.008 mSv in an adult and 0.025 mSv in a child,⁶ compared with 2 mSv for a standard appendicular CT scan.

Three-phase imaging allows immediate blood flow, 10-minute blood pooling and delayed bone uptake to be assessed, which provides further information regarding physiological activity around the elbow. Bone scanning is useful in confirming arthritides, neoplasia, osteomyelitis, stress fractures/reaction, avascular necrosis or bone infarction and reflex sympathetic dystrophy. It is particularly helpful when trying to confirm or refute loosening of an elbow joint replacement, particularly where infection is suspected, or to identify occult or non-united fractures. It should be noted, however, that bone scanning is rarely a first-choice investigation and the marker of bone physiology that it provides should be used as a problem-solving tool in conjunction with primary imaging.

Elbow arthrography

Arthrography may be used in conjunction with CT, MRI and US in the investigation of elbow disorders.^7–9 While there are several approaches to intra-articular injection, I find that a posterolateral approach into the radiocapitellar joint, immediately posterior to the radial collateral ligament, is the most reliable method of safely accessing the joint space.

In CT arthrography 2–3 mL of dilute low osmolar contrast medium (LOCM), followed by 5–10 mL of air, as tolerated by the patient, may be injected under ultrasound, fluoroscopic or CT guidance to produce a double-contrast CT arthrogram. Alternatively, 8–15 mL of dilute LOCM (50 : 50 mix with 0.9% saline solution) may be injected to produce a single-contrast CT arthrogram. Axial slices are acquired, preferably with ultra-thin multi-slice CT, and then reconstructed in the coronal and sagittal plane (or any plane required). CT arthrography is most useful when looking for loose bodies and osteophyte impingement, although it may be used to demonstrate chondral and osteochondral fractures.⁷

MR arthrography is a useful adjunct to conventional MRI, particularly in the assessment of the collateral ligaments, synovial and capsular pathology, and articular cartilage and osteochondral injuries.^7,8 Direct arthrography involves injection of LOCM under ultrasound or fluoroscopic guidance, followed by 8–15 mL of either saline or, more commonly, a 1 : 200 solution (2 mmol/L) of gadolinium DTPA, into the elbow joint, followed by MRI.

Indirect MR arthrography does not involve any joint injection. An intravenous injection of gadolinium DTPA is given and, after a period of exercise during which the gadolinium diffuses from the elbow joint synovium into the synovial fluid, MRI is undertaken. Standard sequences for both direct and indirect arthrography will include T1 TSE with fat suppression in two (usually sagittal and coronal) or three planes, together with coronal PD or T2 imaging, usually with fat suppression, and further imaging in the axial or sagittal plane. The indirect technique allows examination of intra-articular pathology and has the added advantage of highlighting inflammatory tissue and hypervascularity.

US arthrography is mainly used to look for the presence of osteochondral loose bodies and involves the injection of 8–15 mL of saline into the joint under US guidance.⁹

Anterior muscle group

The biceps brachii and brachialis muscles are found anteriorly and insert into the radial and ulnar tuberosities, respectively. The distal biceps tendon is made up of a weak aponeurosis, the lacertus fibrosus, which inserts into the antebrachial fascia of the ulnar aspect of the proximal forearm, and a strong lateral tendon that passes through the deep part of the antecubital fossa to insert into the medial aspect of the radial tuberosity. The lacertus fibrosus and the lateral tendon components of the distal biceps tendon correspond to the short and long head of the biceps muscle and may be found as separate bifurcated muscles in a significant minority of normal individuals.¹⁰

While the majority of biceps injuries involve the proximal, long head of the biceps tendon, the distal tendon is also prone to injury and accounts for approximately 5% of biceps injuries. US provides a good first-line investigation of the biceps tendon.^11,12 Complete tendon rupture can be confirmed with US, which will also define the extent of tendon retraction (Fig. 5.2). When looking at the tendon in longitudinal section, the US probe should be oriented with inferolateral angulation, with the elbow flexed and the forearm supinated. When looking at the tendon in transverse section, the probe is held at right angles to the long axis of the forearm. If the heel of the probe is gently pressed into the interosseous groove towards the radial tuberosity, better imaging of the tendon insertion is possible.

Figure 5.2 Distal biceps brachii tendon rupture. Ultrasound (A) and sagittal T2 TSE MRI scan (B) of the distal biceps tendon, showing a complete tear and a thickened, retracted tendon (white arrows).

Partial tears of the distal biceps tendon may be diagnosed by identifying thickening of the tendon close to the radial tuberosity, together with a wavy appearance of the distal tendon on longitudinal scanning.¹³ The tendon is most prone to tendinosis and tears close to the radial tuberosity as a result of distal tendon impingement between the radius and ulna and relative hypovascularity of the tendon in this region (Fig. 5.3). Unfortunately, it is also this region of the tendon that is most difficult to visualize with US and most prone to anisotropic artefact as a result of its oblique route. If there is doubt about the US findings, further imaging with MRI is advised.

Figure 5.3 Partial tear of the distal biceps tendon. Sagittal oblique ultrasound showing a thickened, hypervascular tendon with a small partial tear (white arrows) close to the radial tuberosity.

MRI of the distal biceps tendon is best performed with axial and sagittal imaging. However, the oblique course of the tendon often makes standard MRI imaging less than satisfactory. Improved visualization of the distal tendon and insertion can be achieved with the FABS view, where the elbow is flexed, the arm abducted and the forearm supinated.⁵ The images are acquired in the coronal plane of the elbow, perpendicular to the radius, with proton density with and without fat suppression, or T1 SE and T2 TSE with fat suppression, in addition to standard elbow sequences. This method of imaging the biceps tendon is particularly useful in detecting partial tears of the tendon (Fig. 5.4).⁵

Figure 5.4 Partial tear distal biceps tendon (white arrow). MRI, coronal T2 TSE (FABS view).

Lateral muscle group

Lateral epicondylitis or tennis elbow is the most frequent cause of elbow discomfort.¹⁴ The diagnosis is often made from the history and clinical examination alone. Activities that may lead to overuse injury include throwing and racket sports and occupations involving repetitive forearm movement. It is most common in people aged 30–50, smokers and weekend warriors, who undertake intermittent bursts of high activity. Where there is clinical doubt about the diagnosis, or where the patient is not responding to treatment, the diagnosis may be confirmed with ultrasound or MRI. US will show a thickened common extensor origin, often with areas of hypoechoic change or hypervascularity on Doppler imaging (Fig. 5.5).¹⁵

Figure 5.5 Lateral epicondylitis. Colour Doppler ultrasound showing hypervascularity (white arrow) within the common extensor origin.

US has been shown to be less sensitive than MRI in demonstrating epicondylitis, but has a similar specificity.¹⁶ However, US has a number of advantages over MRI. The tendon origin is often tender to US probe pressure, allowing a degree of clinical correlation with the imaging findings. Comparison can be made with the contralateral elbow, particularly where the findings are subtle. Gentle valgus stress during US imaging may demonstrate gaping of partial- or full-thickness tears.

MRI will demonstrate ill-defined, increased T2 signal on fluid-sensitive sequences, (STIR or fat saturation), within the common extensor origin, often with oedema surrounding the tendon or within the lateral epicondyle. Partial or complete tears may show a better-defined focus of high T2 signal within the tear, with partial or complete disruption of muscle fibres (Fig. 5.6). Partial tears can show both a thickened or thinned appearance. MRI may also be used to assess an associated lateral ulnar collateral ligament injury.¹⁷

Figure 5.6 Partial tear of the common extensor origin (white arrow). MRI, coronal T2 FS.

Medial muscle group

Injuries of the medial muscle group are less common, with lateral epicondylitis occurring 10 times more frequently than medial epicondylitis (tendinosis of the common flexor origin). Medial epicondylitis or golfer’s elbow usually involves the pronator teres, flexor carpi radialis and palmaris longus muscle origins. Precipitating factors include an acute injury with valgus strain and sudden deceleration, such as when a golf club hits a tree root, and chronic repetitive valgus strain in racket sport, golf and during throwing activities. Ultrasound examination will show a thickened, hypoechoic tendon origin with increased vascularity on Doppler imaging. There may be enthesial change within the cortex of the medial epicondyle, particularly where the injury is chronic or where there is a history of long-term overuse or valgus stress (Fig. 5.7).

Figure 5.7 Medial epicondylitis. Ultrasound of the common flexor origin, showing a thickened hypoechoic tendon with cortical irregularity of the medial epicondyle (white arrow).

MRI holds the advantage where a more extensive injury is suspected. MRI provides additional information about adjacent structures, particularly the radiocapitellar joint, which may be injured by recurrent lateral compression during valgus stress. This injury is particularly likely in the little league elbow syndrome, where capitellar osteochondrosis or Panner’s disease occurs in younger children aged 5–12, and osteochondritis dissecans in adolescents and young adults.

If an associated injury to the ulnar collateral ligament is suspected, both ultrasound and MRI can assess ligament integrity. The advantage of US in this situation is that the elbow may be stressed to open up the ligament, and comparison may again be made with the contralateral elbow.

Posterior muscle group

Injury to the triceps muscle is relatively infrequent and usually follows a fall onto an outstretched arm or a direct blow to the muscle.¹⁸ The diagnosis of triceps rupture can be made with US, with the probe oriented in the sagittal plane. The tendon appears corrugated and is often outlined by fluid, with haematoma and debris in the rupture defect. Triceps rupture is often associated with bony avulsion of the insertion and in this situation the retracted bony avulsion fragment can be easily identified with US. In addition, the presence of a large haematoma that may lead to compartment syndrome and radial nerve compression¹⁹ can be identified quickly and easily. Compression of the ulnar nerve has also been reported,^20,21 and fluid or haematoma within the cubital tunnel is visible with US.

Triceps tendinosis shows US changes identical to those seen in epicondylitis. The difficulty lies in differentiating a partial tendon tear from tendinosis, as both may have a similar appearance on US, with hypoechoic change within a thickened tendon. Disruption of the usual striated, fibrillar pattern indicates a tear rather than tendinosis.^18,22 If doubt persists, sagittal T2 FS MRI will show a better-defined focus of altered T2 signal change within a partial tear and ill-defined or diffuse oedema with tendinosis.

A snapping triceps tendon, caused by subluxation of the medial head of triceps over the medial malleolus, may be demonstrated with US if the probe is held over the distal triceps while the elbow is flexed.²³ This may be associated with a swollen ulnar nerve indicating neuropathy, or occasionally with coexistent subluxation of the ulnar nerve.²³

Ulnar nerve

Ulnar nerve compression is relatively common, with the incidence of ulnar nerve entrapment at the elbow second only to entrapment of the median nerve in the carpal tunnel.²⁴ The ulnar nerve lies immediately posterior to the medial malleolus and reaches the forearm through the cubital tunnel. From proximal to distal the nerve courses through the condylar groove and then deep to the tunnel retinaculum and arcuate ligament, before passing between the ulnar and humeral heads of flexor carpi ulnaris. Compression of the ulnar nerve is most common at two points in the cubital tunnel: proximally, within the condylar groove; and distally, at the point where the nerve reaches the flexor carpi ulnaris.

US examination of the ulnar nerve is best performed with the arm abducted and externally rotated. A high-frequency probe with a narrow footprint should be held at right angles to the long axis of the arm, allowing the ulnar nerve to be identified in cross-section posterior to the medial malleolus before it enters the cubital tunnel. Ulnar nerve dislocation may be demonstrated if the probe is held over the ulnar nerve at the cubital tunnel while the patient moves the elbow from extension to flexion.²³

If US shows a thickened nerve proximal to the cubital tunnel,²⁵ with a cross-sectional area greater than 7.5 mm² (0.075 cm²) at the level of the medial epicondyle this is diagnostic of entrapment neuropathy (Fig. 5.8).²⁶ It is helpful to compare the cross-sectional diameter with the normal, contralateral ulnar nerve to confirm that the nerve is swollen. US may also be used to look for extrinsic causes of compression such as an accessory medial anconeus muscle, the anconeus epitrochlearis, ganglion cysts, synovial thickening and osteophytes arising from the posteromedial margin of the ulnar trochlear joint.²⁷

Figure 5.8 (A) Ulnar nerve entrapment neuropathy. Ultrasound shows a normal cross-sectional area of the proximal ulnar nerve above the level of the medial epicondyle. Markers indicate the following dimensions: major, 0.400 cm; minor, 0.144 cm; area, 0.045 cm². (B) Ulnar nerve entrapment neuropathy. Dilatation of the ulnar nerve immediately proximal to the cubital tunnel, with the cross-sectional area of the nerve greater than 7.5 mm². Markers indicate the following dimensions: major, 0.419 cm; minor, 0.259 cm; area, 0.085 cm².

When MRI is used to examine the ulnar nerve, the nerve is most easily identified with axial T1 SE or PD sequences. The ulnar nerve will appear enlarged at the level of the cubital tunnel, with increased T2 signal in the nerve on T2 FSE or T2 FSE with fat suppression imaging.²⁴