Musculoskeletal infections: US manifestations.

One of the most important prognostic factors in patients with musculoskeletal infections is the delay in establishing therapy. Early diagnosis of septic arthritis requires analysis of joint fluid. Ultrasonography (US) is a rapid, portable, sensitive technique for confirming the presence of joint effusions. The study can be easily repeated for follow-up of lesions. US allows real-time guidance of fluid aspiration and can reduce the risk of contaminating other anatomic compartments, especially in the hands, wrists, and feet. Radiography provides complementary information and should be performed in conjunction with US. US is the imaging modality of choice for diagnosis of superficial abscesses. Dynamic compression with the US probe and color Doppler imaging can facilitate detection of superficial abscesses. US may help in the early diagnosis of osteomyelitis by demonstrating subperiosteal or juxtacortical fluid collections and by providing guidance for aspiration of these collections. Evaluation of osseous involvement requires additional imaging; a US examination with normal results does not allow exclusion of bone infection. US is not degraded by metallic artifact and may be useful in cases of osteomyelitis complicating metallic fixation in an extremity. After initial radiography, US can play an important role in the management of musculoskeletal infections.     

Ultrasonography of hip joint effusions

In order to evaluate ultrasonography in patients with suspected hip joint effusions, 123 consecutive patients were examined prospectively. Twenty healthy subjects were used as a control group. The normal sonoanatomy, the recommended scanning approach, and the diagnostic features of intra-articular joint effusions are presented. Even minor fluid collections of 1 or 2 ml could be accurately detected. Transient synovitis and fresh hemorrhagic effusions proved to be echofree, whereas clotted hemorrhagic collections or septic arthritis showed non-echofree effusions. Based on intraoperative and computed tomography (CT) data, ultrasonography is clearly superior to X-ray films in detecting joint effusions. A negative sonogram will exclude a fluid collection; the depiction of an echofree effusion with virtually rule out septic arthritis. The use of additional imaging techniques can be reduced greatly, as ultrasonography seems to be an improved method for the early diagnosis of septic arthritis.     

Transient synovitis of the hip in children: role of US

Transient synovitis of the hip remains a common diagnostic problem for the clinician. The physical signs are not pathognomonic of the condition, and the classic technical examinations are of little help. Therefore, the authors retrospectively studied the value of hip arthrosonography in 46 children with clinical symptoms suggesting pathologic hip conditions. In 20 of the 21 patients with a final diagnosis of transient synovitis, articular effusion was detected on ultrasound (US). Conventional radiography showed an increased medial joint space in only eight of these patients. Increased echogenicity of the articular fluid was found in both transient synovitis and septic arthritis. The high sensitivity of US in detecting intraarticular fluid was demonstrated by cadaver studies.     

Hip ultrasound

In newborns, US has an established role in the detection and management of developmental dysplasia of the hip. Later in childhood, when the limping child is a major diagnostic dilemma, US is extremely helpful in the identification of the varied disease processes underlying this condition, as transient synovitis, septic arthritis, Perthes disease and slipped femoral capital epiphysis. In adolescent practicing sporting activities, US is an excellent means to identify apophyseal injures about the pelvic ring, especially when avulsions are undisplaced and difficult-to-see radiographically. Later on, in the adulthood, US is an effective modality to diagnose tendon and muscle injuries about the hip and pelvis, identify effusion or synovitis within the hip joint or its adjacent bursae and guide the treatment of these findings. The aim of this article is to provide a comprehensive review of the most common pathologic conditions about the hip, in which the contribution of US is relevant for the diagnostic work-up.     

Septic arthritis versus transient synovitis at MR imaging: preliminary assessment with signal intensity alterations in bone marrow

PURPOSE: To find any differential magnetic resonance (MR) imaging findings between septic arthritis and transient synovitis in pediatric patients. MATERIALS AND METHODS: The MR imaging findings in nine pediatric patients with septic arthritis and 14 with transient synovitis were retrospectively studied. The diagnoses were made by means of joint aspiration with bacteriologic study, arthrotomy, and clinical evaluation. MR imaging findings were analyzed with emphasis on the grade of joint effusion and alterations in signal intensity in the soft tissue and bone marrow of the affected hip joint. RESULTS: Signal intensity alterations in bone marrow (i.e., low signal intensity on fat-suppressed gadolinium-enhanced T1-weighted spin-echo images and high signal intensity on fat-suppressed T2-weighted fast spin-echo images) were seen in eight of nine patients with septic arthritis. These signal intensity alterations consisted of mild juxtaarticular changes in six patients without osteomyelitis and extensive changes in the femoral head and neck in two patients with coexistent osteomyelitis. Signal intensity alterations in bone marrow were not seen in the 14 patients with transient synovitis. CONCLUSION: Signal intensity alterations in the bone marrow of the affected hip joint are useful in the differentiation of septic arthritis from transient synovitis.     

Radionuclide joint imaging

Modern radionuclide techniques of joint imaging involve the use of either 99mTc-pertechnetate or 99mTc-phosphate compounds in conjunction with the Anger camera. In general, images obtained with both types of radiocompound are nonspecific--although increased uptake of 99mTc-pertechnetate usually denotes the presence of synovitis. The most popular uses of the technique are in documenting the extent and severity of inflammatory joint disease, assessing the effect of therapy, and establishing the diagnoses of Legg-Perthes disease and septic arthritis. The method is also useful in judging the extent of involvement in osteoarthritis of the knee prior to surgical intervention. Radionuclide joint imaging is more sensitive than clinical or radiographic techniques in detecting early joint involvement but usually it must be supplemented by other techniques to establish a specific diagnosis.     

US assessment of hip joint synovitis in rheumatic diseases. A comparison with MR imaging

PURPOSE: To assess the significance of ultrasonography (US) in detecting hip joint synovitis in patients with rheumatic diseases. MATERIAL AND METHODS: Forty patients with rheumatic disease and suspected hip joint synovitis underwent MRI and US of the hip joint. In addition to the throughout MRI evaluation, the anterior collum-capsule distance (CCD) was determined by both MRI and US. Thirteen healthy volunteers were examined with MRI to establish the criteria for normal findings in MRI when classifying hip joints to those with synovitis and those without. MRI was used as a gold standard. RESULTS: Synovitis was found using MRI in 31 hips of 22 patients (9 patients had bilateral synovitis). The intraclass correlation was 0.61 between MRI and US in measuring CCD. In classifying hip joint synovitis with US, the sensitivity of the method was 87% and specificity 42%, when the CCD criterion for synovitis was determined to be > or = 7 mm. If the cut-off point was raised to 9 mm, the sensitivity decreased to 61% while specificity increased to 94%. A difference in CCD of > or = 1 mm between the hips as an additional criterion for synovitis increased the number of false-positive findings. CONCLUSION: Measurement of CCD with US proved to be a rather inaccurate method to point out synovitis in rheumatic patients when using MRI as a reference. The main reason for this result was the thickened capsule, which US could not differentiate from a thickened synovium.     

Imaging of bone erosion in rheumatoid arthritis

Rheumatoid arthritis (RA) is the most common type of inflammatory arthritis, with a prevalence of 1% in the United States. Recently introduced disease-modifying antirheumatic drugs have been extremely successful in preventing irreversible joint damage, particularly if initiated early. Accordingly, accurate and early diagnosis of RA has become imperative. This shift places increased demands on imaging to identify even the slightest traces of erosive joint damage and predict future structural and functional deterioration. Unfortunately, conventional radiography has been shown to be insensitive for bone erosions, particularly in early stages of the disease. Computed tomography (CT) is rarely used, but its tomographic perspective offers advantages over projectional radiography. Ultrasound (US) detects more erosions than radiography does and also can evaluate synovitis. Scintigraphy also can detect inflammation and bone turnover at sites of active erosion. It lacks spatial resolution but offers greater anatomical coverage, making whole-body assessments possible. Of all imaging modalities, however, magnetic resonance imaging (MRI) shows the greatest sensitivity for detecting and monitoring bone erosions and also can detect and follow pre-erosive features of RA, such as synovitis, bone marrow edema or osteitis, and tendinous and ligamentous abnormalities. In this article, we review the appearance of bone erosions on conventional radiography and alternative imaging modalities including MRI, CT, US, and scintigraphy. We also review alternative acquisition techniques for MRI in RA and discuss the utility of fat suppression and contrast enhancement.     

MRI features of tuberculosis of peripheral joints

The aim of this article is to present the magnetic resonance imaging (MRI) features of peripheral tubercular arthritis. The clinical presentation of peripheral tubercular arthritis is variable and simulates other chronic inflammatory arthritic disorders. MRI is a highly sensitive technique which demonstrates fine anatomical details and identifies the early changes of arthritis, which are not visible on radiographs. The MRI features of tubercular arthritis include synovitis, effusion, central and peripheral erosions, active and chronic pannus, abscess, bone chips and hypo-intense synovium. These imaging features in an appropriate clinical setting may help in the diagnosis of tubercular arthritis. Early diagnosis and treatment can effectively eliminate the long-term morbidity of joints affected by tuberculosis.     

Anterior joint capsule of the normal hip and in children with transient synovitis: US study with anatomic and histologic correlation

PURPOSE: To study the anatomic components of the anterior joint capsule of the normal hip and in children with transient synovitis. MATERIALS AND METHODS: Six cadaveric specimens were imaged with ultrasonography (US) with special attention to the anterior joint capsule. Subsequently, two specimens were analyzed histologically. These anatomic findings were correlated with the US findings in 58 healthy children and 105 children with unilateral transient synovitis. RESULTS: The anterior joint capsule comprises an anterior and posterior layer, mainly composed of fibrous tissue, lined by only a minute synovial membrane. Both fibrous layers were identified separately at US in 98 of 116 (84%) hips of healthy subjects and in all hips with transient synovitis. Overall, the anterior layer was thicker than the posterior layer. In transient synovitis compared with normal hips, no significant thickening of both layers was present (P = .24 and .57 for the anterior and posterior layers, respectively). Normal variants include plicae, local thickening of the capsule, and pseudodiverticula. CONCLUSION: Increased thickness of the anterior joint capsule in transient synovitis is caused entirely by effusion. There is no US evidence for additional capsule swelling or synovial hypertrophy.     

Perfluoroctylbromide as a contrast agent for computed tomographic imaging of septic and aseptic arthritis

Perfluoroctylbromide (PFOB), a perfluorocarbon macrophage-labeling contrast agent, was applied to computed tomographic imaging of septic and aseptic arthritis models in rabbits. Marked enhancement of induced pyarthrosis was observed in both the knee and the sacroiliac joint. Moderate enhancement was noted in tetracycline-induced synovitis of the knee. Sterile synovitis of the sacroiliac joint and simple knee joint effusion showed no enhancement. These results suggest that PFOB is a useful contrast medium for the diagnosis of and distinction between septic and sterile arthritis.     

Ultrasound of Musculoskeletal Infections

Ultrasound (US) can play an important role in differentiating infectious processes from other musculoskeletal diseases. US is the imaging modality of choice to diagnose superficial abscesses. These abscesses may have variable echogenicity and their detection can be facilitated by ultrasonographic dynamic evaluation and color Doppler imaging. Septic arthritis either in a native or prosthetic joint may have devastating complications on the joint function. Early diagnosis requires joint fluid analysis. US is very sensitive in the detection of joint effusions and is helpful to guide the arthrocentesis. US may help in the early diagnosis of osteomyelitis, although one must always remember that a normal US never excludes bone infection. This article also reviews the role of US in the diagnosis of necrotizing fasciitis, tenosynovitis, bursitis, and pyomyositis. After initial radiographs, along with nuclear medicine studies, US should be considered as the next imaging step in the investigation of musculoskeletal infections.     

The role of ultrasound and isotope scanning in the management of irritable hips.

Patients (n = 181) with the irritable hip syndrome were reviewed. Four of these were found to have Perthes disease and 3 cases had septic arthritis. Ultrasonography provides accurate information as to the presence or absence of an effusion in children with an irritable hip syndrome. The likelihood of a positive result is higher in the early course of the disease process (i.e. within 3 days). Bone scanning, if done routinely will help in the early diagnosis of Perthes disease. Recurrence of the symptoms occurred in 18% of patients and most of them were within 12 months of the first onset of symptoms.     

The 'cold hip' sign on bone scan. A retrospective review

The "cold hip" sign on bone scan is often seen in patients referred with irritable hip. This sign is due to fluid in the hip joint under pressure causing impaired perfusion of the structures within the joint capsule. In a retrospective review, 22% of patients with this sign on bone scan were found to have septic arthritis at surgery. This fact would appear to justify surgical drainage or aspiration of any hip showing this sign on scan. An attempted follow-up study through the medical records was incomplete because of the short follow-up on most patients. The possibility that temporary impairment of blood supply to the head of the femur causes long-term damage to the hip is unanswered on this study, and a long-term recall follow-up study is underway.     

MRI and ultrasound in children with juvenile chronic arthritis

In this era of advancing imaging technology, a knowledge of the relative values of available imaging techniques is necessary to optimize the management of children with juvenile chronic arthritis (JCA). After clinical examination, plain films remain the initial investigation. The need for radiation protection must be a priority in children with JCA. Conventional radiographs allow grouping of the various arthritides (on the base of the distribution and pattern of joint space changes) and staging of disease progression. Ultrasound (US) is very sensitive in the detection of joint effusions, especially in the hip, and guides fluid aspiration. US and Doppler can be used for the evaluation of synovial hypertrophy and activity. Arthrography and to a certain extent nuclear studies have been replaced by magnetic resonance imaging (MRI). MRI can demonstrate articular cartilage, joint effusion, synovial hypertrophy, cortical and medullary bone, cartilage and bone perfusion, and fibrocartilaginous structures (menisci and ligaments). Contrast enhanced MRI is the most sensitive modality to determine whether an arthritic condition is present. However, it does not assist in establishing a specific diagnosis. MRI determines accurately the activity and the extent of the disease and is particularly useful in the early detection of articular damage. Finally, MRI is of major importance in the evaluation of response to local therapy (especially steroids) and the detection of complications.     

Atypical findings of the combined scintigraphy of bone marrow and labeled leukocytes in osteonecrosis of the hip secondary to infection

Avascular osteonecrosis can be associated with septic arthritis and osteomyelitis. Combined labeled leukocyte-marrow imaging scintigraphy has demonstrated excellent accuracy for the detection of infection since both tracers accumulate in the bone marrow and only leukocytes accumulate in infection. We report an unusual total absence of 99mTc HMPAO leukocytes/9mTc-sulfur colloid tracer accumulation, not only in the femoral head but also in the acetabulum and hip in hip osteonecrosis secondary to septic arthritis and osteomyelitis.     

Magnetic resonance imaging of the wrist in early rheumatoid arthritis: a pictorial essay

This pictorial essay describes the changes seen in the wrist in early rheumatoid arthritis (RA) on MRI. Magnetic resonance imaging can demonstrate bone erosions, bone marrow signal changes, synovitis and tenosynovitis in early rheumatoid arthritis. Magnetic resonance imaging of the wrist can identify erosions in RA earlier than plain radiographs and can detect more erosions. Common sites include the capitate, lunate and scaphoid. Bone marrow signal changes occur frequently and are most common in the capitate, lunate and triquetrum. Synovial thickening and enhancement are clearly demonstrated with MRI and are most commonly seen in the radiocarpal joint (RCJ). Tenosynovitis can be seen in the wrist in more than half of patients presenting with RA. This most commonly involves the extensor carpi ulnaris tendon and is seen as sheath fluid, thickening and enhancement.     

Septic arthritis mimicking cellulitis: distinction using radionuclide bone imaging.

Two patients originally diagnosed as having cellulitis involving the dorsum of the foot actually had bacterial arthritis of an underlying joint. In both patients, even after pyarthrosis was suspected, the wrong joint was aspirated. The arthropathies were located by subsequent 99mTc-phosphate bone imaging at a time when roentgenograms were normal. Early diagnosis and aggressive therapy of septic arthritis are essential to prevent joint destruction and osteomyelitis. Radionuclide bone imaging can identify inflammatory joint disease but it cannot specify etiology. In our patients, however, the differential diagnosis was between skin and joint infection. Radionuclide imaging was of great help in making this distinction.     

Tuberculosis of the hip as the presenting sign of HIV and simulating pigmented villonodular synovitis

A 36-year old man, with no prior known exposure to human immunodeficiency virus (HIV) or tuberculosis, presented with monoarticular pain and a decreased range of motion in his left hip. Radiography and magnetic resonance imaging revealed bony erosive lesions, juxta-articular cysts, a large effusion, and juxta-articular edema. The initial clinical and radiographic diagnosis was pigmented villonodular synovitis (PVNS) of the left hip. However, what was initially felt to be a chronic proliferative inflammatory process was later determined to be tuberculous arthritis. This case emphasizes the importance of including tuberculous arthritis in the differential diagnosis of patients with monoarticular destructive joint disease radiologically suggestive of PVNS.     

Neuroarthropathy of the extremities: magnetic resonance imaging features

The objective of this article was to review the magnetic resonance imaging (MRI) findings of four different neuroarthropathic extremities, and discuss the role of MRI in establishing a correct diagnosis. The shoulder, ankle, and knee had predominantly atrophic neuroarthropathic changes, whereas both atrophic and productive changes could be seen in the elbow. Bone marrow edema, suggesting a recent stress fracture, was detected in the elbow and knee. Osteochondral defects, or “detritic” synovitis with effusion, were extensive in all joints but exceptionally profound in the shoulder with amputation-like osteolysis and a total loss of the humeral head. Radiologists may encounter the joint manifestations of neuropathy, which may be confused with various pathologies, including tumor and septic arthritis, before the neurological diagnosis is established. MRI is helpful in detecting the extension of the disease as well as to differentiate chronic Charcot's arthropathy from septic arthritis before radiographic findings suggest the diagnosis.