Abstract
Musculoskeletal regional pain syndromes often lead to patient referrals in general and rheumatological practice. Detailed history taking and clinical examination can in most cases reveal the cause for pain and direct the subsequent management of the conditions. Yet, when in doubt, imaging methods have to support the clinical assessment.
This paper presents the underlying pathologies of the most frequently encountered regional pain syndromes and the role of musculoskeletal ultrasonography and magnetic resonance imaging in their visualization. It presents data, where available, on diagnostic accuracy and comparisons with gold standards.
The article stresses the advantages and disadvantages of the analyzed imaging modalities and suggests the future research agenda.
Introduction
Musculoskeletal regional pain syndromes (RPS) are some of the most frequent reasons for referral in both general and rheumatological practice.
Although of a different origin, the degenerative disorders show the highest prevalence due to overuse, previous trauma, and underlying or previous hypermobility.
The anatomical structures involved are the muscles, fasciae, tendons, ligaments, bursae, joint capsules, and nerves.
Detailed history taking and clinical examination in every case are and will hopefully remain the basis of the tentative diagnosis. The proper use of imaging methods depends on the initial assessment and allows for more optimal decisions for the management of RPS.
In the recent years, musculoskeletal ultrasonography (MSUS) has become a routine tool of assessment for rheumatologists to visualize many of the involved anatomical structures and their pathologies in real time. This modality is used as the assessment at the time of consultation, with immediate correlation of data from history and the clinical findings that is probably the greatest advantage of the method. Moreover, MSUS enables superior dynamic evaluation of the assessed structures than other imaging modalities. The method is yet perceived as operator-dependent, and the assessment, because of its physical limitations, is not complete.
Magnetic resonance imaging (MRI) is increasingly used for the assessment of musculoskeletal structures offering visualization of all the tissues in the analyzed anatomical region, but is still limited by cost and availability.
Soft-tissue traumatic lesions, referred pain syndromes, and complex RPS can also cause pain in different anatomical locations. They are, however, not the subject of this study.
In the present study, the assessment of the most frequent RPS is analyzed using MSUS and MRI, and the role of the two imaging modalities for the management of the syndromes is presented.
Upper extremity
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Shoulder
Pain in the shoulder is only second to low back pain as the most frequent musculoskeletal complaint leading to referral to general practice and subsequently rheumatological assessment.
It may be due to an array of soft-tissue lesions, affecting mostly the structures of the rotator cuff and the adjacent bursae ( Fig. 1 ). Joints, nerves, and muscles may also be involved. Referred pain caused by cervical nerve roots, intrathoracic tumors, liver and gallbladder diseases, or acute coronary syndrome should also be considered.
Careful history taking, physical examination, and specific physical tests lead to the accurate diagnosis and management of the disorder.
The specific and exact diagnosis with visualization of the affected structure can only be established with imaging.
In tendinopathy of the rotator cuff, a typical heterogeneous hypoechogenic appearance of the tendon on MSUS, often accompanied by a difference in thickness (1.5–2.5 mm) between the contralateral tendons or a swelling of the affected tendon (between 5.5 and 8 mm) provides the diagnosis. Few studies have addressed this issue, and the data are based on measurements published in textbooks on ultrasonography (US). Only MSUS studies allow the estimation of diagnostic accuracy of imaging of the rotator cuff tendinopathy, with sensitivity and specificity of 79% and 94%, respectively .
Full-thickness rotator cuff tears are characterized by effusion, retraction, or discontinuation of the tendon fibers; herniation of the deltoid muscle, sometimes, in a massive tear; and complete disappearance of the tendinous structure ( Fig. 2 ). In a study by Teefey et al., where US was correlated to arthroscopy, 100% sensitivity and 85% specificity, with positive predictive value of 96% and negative predictive value of 100%, were achieved for diagnosing full-thickness rotator cuff tears . Compared with arthroscopy, MRI arthrography showed full-thickness tears, with sensitivity, specificity, and accuracy of 96%, 99%, and 98%, respectively . Conflicting data are available concerning the necessary level of experience of the ultrasound examiner, with high-level experience and top-quality equipment described as the prerequisite for correct diagnosis . Comparison between MRI and MSUS showing similar accuracy for the detection of full-thickness tears was also described for highly experienced ultrasound assessors . MRI of the shoulders of 90 patients in comparison with subsequent arthroscopy for rotator cuff injury showed sensitivity and specificity of 67% and 98%, respectively, for the detection of complete tears of the long head of the biceps tendon .
In the case of partial rotator cuff tears, the detection of localized intratendinous defect on US not affecting the full breadth of the tendon is diagnostic. Correlation of the ultrasound findings with arthroscopy shows sensitivity of 67–93%, specificity of 85–94%, positive predictive value of 77–82%, and negative predictive value of 77–98% . The best results are achieved by correlation of MRI arthrography with arthroscopy. In a series of 44 tears, both partial and complete, MRI arthrography detected 43 tears, while the sensitivity of MSUS declined with the decreasing size of the tears . In a later study, MRI arthrography detected partial thickness tears, in comparison with arthroscopy, with sensitivity, specificity, and accuracy of 80%, 97%, and 95%, respectively .
Symmetrical shoulder pain suggestive of rheumatic polymyalgia (PMR) can also be subject to imaging assessment. A systematic review by Mackie et al. analyzed both MSUS and MRI data and revealed that subacromial bursitis on US is the only imaging characteristic of PMR that had enough number of control persons to allow the assessment of diagnostic accuracy with specificity of 89% and specificity of 66% . Jimenez et al. described the effects of PMR treatment with glucocorticosteroids with normalizing the US finding after 4 weeks and the normalization persisting until 6 months . The only prognostic MSUS feature identified in a study by Macchioni et al. was power Doppler signal in the articular/periarticular structures that predicted PMR relapse after 6 months .
Swelling of the acromioclavicular or glenohumeral joint makes the diagnosis easy, and description of synovial thickening with or without Doppler may indicate a more specific inflammatory condition. An unspecific swelling of the shoulder or unexplained pain in the shoulder ( Fig. 3 ) is also an indication for an imaging assessment.
While searching for the cause of pain, erosive lesions of the bones and muscles may also be detected, suggestive of either inflammatory joint disease or an underlying neoplastic bone or muscle process. Suspicion of especially the latter conditions on US must lead to further assessment with MRI and computed tomography (CT).
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Elbow
Pain in the elbow is a common complaint affecting mostly 1–3% of the population, with pain experience in the lateral epicondyle region and less frequently in the region of medial epicondyle and caused by overuse and trauma. Other conditions of pain in the elbow are inflammatory arthritis; bursitis; fractures; and ligament, muscle, and nerve lesions/entrapments.
MSUS and MRI can be used for identifying elementary lesions and establishing the diagnosis in lateral elbow pain. The clinical diagnosis in lateral epicondyle pain (LEP) is usually sufficient and use of imaging methods should be reserved for doubtful or refractory cases. Both MSUS and MRI can help differentiate the elementary lesions of LEP such as tendinosis and/or enthesopathy and partial tears from other conditions affecting the elbow: joint effusions, synovitis, nerve compression syndromes, and lesions of the collateral ligaments .
A comparison of MSUS and MRI in the assessment of LEP by Miller et al. in a series of 11 patients with suspected epicondylitis showed similar specificities of both imaging methods (67–100% for US and 83–100% for MRI) for diagnosis with lower sensitivity of the former (64–82% for US and 90–100% for MRI) . A pure MSUS study of symptomatic cases of LEP by Levin et al. suggested high sensitivity of US for the detection of the condition (72–88%) with lower specificity of the method (36–48.5%) .
Cubital tunnel syndrome is the second most frequent nerve entrapment condition after the carpal tunnel syndrome (CTS) that can be assessed by both MSUS and MRI . Characteristic features of abrupt narrowing and displacement in the cubital tunnel, proximal increased nerve area (>7.5–7.9 mm 2 ), space occupying lesions, and bone abnormalities can be assessed with imaging .
Distal biceps tears were analyzed in a study by Lobo et al. (2013), where 45 patients with this suspected condition underwent MSUS and a subsequent elbow surgical procedure . US showed 95% sensitivity, 71% specificity, and 91% accuracy of diagnosing complete versus partial tears of the distal biceps tendon. The posterior acoustic shadowing of the distal biceps tendon had sensitivity of 97% and accuracy of 91% in differentiating the complete from the partial tears and sensitivity of 97% with accuracy of 100% in indicating complete versus normal tendons.
Although not a method of choice in unexplained unilateral overarm pain, especially in small children, both MSUS and MRI may enable diagnosis of humeral fractures. In a study by Supakul et al., children with pain in the distal overarm were assessed with MSUS, which revealed distal humeral epiphyseal separation in all 12 radiographically confirmed cases .
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Wrist
Wrist pain mostly leads to rheumatologic assessment, because of overuse, tenosynovitis, synovitis, CTS, or previous trauma. Similar to other pain conditions, the value of careful history taking and detailed clinical examination cannot be underestimated. When in doubt, imaging can be helpful in diagnosing specific conditions.
CTS is responsible for almost 90% of all nerve entrapments ( Fig. 4 ). Causes of CTS are overuse, local trauma, inflammation, thickening of the transverse carpal ligament, bone fracture, or osteoarthritic changes. The syndrome is mostly diagnosed clinically with Phalen and Tinnel’s tests, tourniquet test, and hand elevation and provocation tests. The gold standard for diagnosis is the nerve conduction study. Yet, in the recent years, there has been a growing evidence of use of imaging in the assessment of CTS. Cross-sectional area of the median nerve is probably one of the most studied parameters on MSUS, but it did not yield unequivocal results. The normal cross-sectional area in the studies ranges from below 9–15 mm 2 , and the sensitivity of the MSUS assessment lies between 48% and 89% with specificity between 47% and 100%. Additional characteristic features of the assessment may be added to increase the sensitivity, like proximal increase in the cross-sectional area, flattening of the distal nerve, nerve displacement, and the nerve’s uniform hypoechogenicity. Moreover, a significant proportion of abnormal MSUS examinations exist when conduction studies show negative results . MSUS is an excellent method to visualize the causes of compression of the median nerve. MRI adds other aspects of assessment: it can detect intracarpal ganglia and signs of osteoarthritis undetectable with conduction and ultrasound studies. Both MSUS and MRI can visualize inflammation, as synovitis or tenosynovitis of the flexor tendons, in the wrist as the causes of CTS.
Wrist ganglia are a frequent cause of pain in the wrist, although a significant proportion also remains clinically “silent.” The initial clinical evaluation can be extended with the MSUS examination, which provides information on its characteristic, location, and size, as well as a specific diagnosis. Moreover, MSUS enables differentiation of the wrist ganglia from pseudo-aneurysms of the branches of the radial artery. Yet, it is not infrequent that the first MRI provides the complete picture of the tissues in the wrist, which enables the final decisive evaluation .
Synovitis, specific or unspecific for a rheumatological systemic disease, is also a frequent cause of pain in the wrist. The differentiation between fluid collection and synovial hypertrophy is not always obvious on MSUS, with compression of the fluid and lack of Doppler signal being the characteristic differentiation parameters. Chronic synovial hypertrophy may also present without hyperemia. In MRI, signal enhancement on water-dependent sequences or after intravenous contrast administration may face the same difficulties when assessing synovial hypertrophy of a longer duration ( Fig. 5 ).
Involvement of all wrist tendons by tenosynovitis can produce pain symptoms. The best-known syndrome is de Quervain tenosynovitis affecting tendons of the first wrist extensor compartment. MSUS and MRI can be used to confirm the clinical diagnosis and exclude other causes affecting the tendons . Like in many other musculoskeletal pathologies, MSUS can be used to guide therapeutic injections ( Fig. 6 ).
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Fingers
Pain in the fingers is a symptom associated with many musculoskeletal conditions. Differentiation of the causes of pain can be decisive for diagnosis and the subsequent management of the conditions ( Fig. 7 ).
Synovitis in the finger joints is a frequent finding. Signs of incompressible hypoechoic thickening with or without Doppler signal allow diagnosis of the condition. It is well known that MSUS and MRI are more sensitive and specific for the detection of synovitis than clinical examination .
Trigger finger or stenosing flexor finger tenosynovitis can be differentiated from Dupuytren’s contracture both clinically and with imaging. A precise treatment guidance can only be achieved with MSUS.
“Sausage fingers” or dactylitis, as visualized by both MSUS and MRI, can be better characterized as either flexor tendon tenosynovitis or psoriatic arthritis with simultaneous involvement of all three finger joint regions .
Upper extremity
- –
Shoulder
Pain in the shoulder is only second to low back pain as the most frequent musculoskeletal complaint leading to referral to general practice and subsequently rheumatological assessment.
It may be due to an array of soft-tissue lesions, affecting mostly the structures of the rotator cuff and the adjacent bursae ( Fig. 1 ). Joints, nerves, and muscles may also be involved. Referred pain caused by cervical nerve roots, intrathoracic tumors, liver and gallbladder diseases, or acute coronary syndrome should also be considered.
Careful history taking, physical examination, and specific physical tests lead to the accurate diagnosis and management of the disorder.
The specific and exact diagnosis with visualization of the affected structure can only be established with imaging.
In tendinopathy of the rotator cuff, a typical heterogeneous hypoechogenic appearance of the tendon on MSUS, often accompanied by a difference in thickness (1.5–2.5 mm) between the contralateral tendons or a swelling of the affected tendon (between 5.5 and 8 mm) provides the diagnosis. Few studies have addressed this issue, and the data are based on measurements published in textbooks on ultrasonography (US). Only MSUS studies allow the estimation of diagnostic accuracy of imaging of the rotator cuff tendinopathy, with sensitivity and specificity of 79% and 94%, respectively .
Full-thickness rotator cuff tears are characterized by effusion, retraction, or discontinuation of the tendon fibers; herniation of the deltoid muscle, sometimes, in a massive tear; and complete disappearance of the tendinous structure ( Fig. 2 ). In a study by Teefey et al., where US was correlated to arthroscopy, 100% sensitivity and 85% specificity, with positive predictive value of 96% and negative predictive value of 100%, were achieved for diagnosing full-thickness rotator cuff tears . Compared with arthroscopy, MRI arthrography showed full-thickness tears, with sensitivity, specificity, and accuracy of 96%, 99%, and 98%, respectively . Conflicting data are available concerning the necessary level of experience of the ultrasound examiner, with high-level experience and top-quality equipment described as the prerequisite for correct diagnosis . Comparison between MRI and MSUS showing similar accuracy for the detection of full-thickness tears was also described for highly experienced ultrasound assessors . MRI of the shoulders of 90 patients in comparison with subsequent arthroscopy for rotator cuff injury showed sensitivity and specificity of 67% and 98%, respectively, for the detection of complete tears of the long head of the biceps tendon .
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