US has been proposed for the early detection and follow-up of several chronic inflammatory disorders of joints, including rheumatoid arthritis (Wakefield et al. 2000; Keen et al. 2005; Scheel et al. 2006; Gibbon 2004) and seronegative arthropathies (Gibbon 2004; Milosavljevic et al. 2005; Kane 2005). Rheumatoid arthritis is a chronic systemic disease that affects approximately 0.5–1% of the population and has a definite prevalence (2:1 to 3:1) in women. The etiology of rheumatoid arthritis is unknown but it seems to be multifactorial, with any genetic susceptibility, expression of HLA-DR4 and environmental factors believed to play a role (Sommer et al. 2005). The diagnosis requires a spectrum of disease manifestations and can be made according to established clinical criteria, the description of which is, however, beyond the scope of this chapter (Arnett et al. 1988; Sommer et al. 2005). From the pathophysiologic point of view, synovial hyperemia is the first step of the inflammatory process in rheumatoid arthritis that can be identified with diagnostic imaging modalities, including power Doppler contrast-enhanced US (Sommer et al. 2005). Then, the immune response mediated by cytokines (TNFα and IL-1) and the subsequent infiltration by inflammatory cells lead to edema and swelling of the synovium. This causes widening of the joint space, which may be further expanded by effusion (Fig. 22a). It is assumed that the above stages of the disease may be fully reversible. Later, the inflammatory response leads to hypertrophy of the synovial membrane by invasive granulation tissue with proliferation of synoviocytes, macrophages, lymphocytes, plasma cells and mast cells. As synovial hypertrophy continues, the hypertrophied synovium—usually referred to as “pannus” (the Latin for “cloth”)—undergoes villous transformation and expands concentrically into the joint space leading to damage of the central portion of the articular cartilage and the subchondral bone (formation of subchondral cysts and erosions) (Fig. 22b). Tenosynovial sheath involvement coexists in many instances. From the clinical point of view, the above abnormalities are encountered not only in rheumatoid arthritis but also in other forms of chronic arthritis. The hallmark of rheumatoid arthritis is bilateral symmetrical involvement of more than three joints. Early in its course, the disease usually affects the small hand joints, the second and third metacarpophalangeal and the third proximal interphalangeal joints being the more typically affected (a characteristic finding of rheumatoid arthritis is sparing of the distal interphalangeal joints, which are commonly involved in osteoarthritis and psoriatic arthritis). In more advanced disease, synovitis involves the larger joints of the limbs and extremities. The destructive action of the pannus is responsible for progressive joint surface damage, ligament and capsule tearing and, finally, joint instability and deformities (Fig. 22c,d). When imaging rheumatoid arthritis, one should consider that the disease progresses in a nonlinear fashion and that joint involvement is non-uniform, particularly in the early stages. Although a consensus has not been reached on which joints must be systematically checked, the symptomatic ones and those typically involved in rheumatoid arthritis (i.e., wrist and hand joints) should be examined (Sommer et al. 2005). For follow-up purposes, wrist and hand joints are the preferred sites for assessing the efficacy of therapy (Sommer et al. 2005). In terms of treatment, among drugs that have an influence on the course of disease are the so-called biologic response modifiers (i.e., anti-TNFα drugs) that inhibit certain cytokines, thus reducing the inflammatory activity. These drugs are expensive, have important side effects and must be used in patients with erosive aggressive arthritis in whom conventional drugs (NSAIDs, steroids, analgesics, etc.) do not produce a positive response. Early diagnosis of synovitis is, therefore, required to start adequate aggressive therapy before occurrence of structural damage to the joint (Herburn 1988).

Figure 22. a–d. Rheumatoid arthritis. Schematic drawings showing progression of joint damage during the course of disease. a Early involvement is characterized by joint effusion and pannus formation (1) associated with marginal erosions (2), cartilage thinning (3) and loosening of the capsuloligamentous structures (4). b As the disease progresses, the erosions increase in size, subchondral cysts become evident (5) and the hyaline cartilage appears increasingly thinned (6). Partial tears of the para-articular structures (7) may occur leading to joint instability. c Later on, fibrous ankylosis (9) of the joint can take place with more evident destruction of the bone ends (10). d In some joints (carpal and tarsal joints) bone ankylosis (11) is the end stage. Inactive fibrous pannus (12) may replace active erosive pannus in the chronic phase.

Because early changes in rheumatoid arthritis are nonosseous in nature, US has proved superior to conventional radiography in terms of disease detection (Gibbon 2004; Clement et al. 2005: Keen et al. 2005). In patients with rheumatoid arthritis and other seronegative arthropathies, US is an effective means for detecting early signs of synovitis, thus allowing prompt institution of an appropriate treatment (Grassi et al. 1993, 2001; Brown et al. 2004). As stated before, US is able to detect joint effusion which accompanies acute inflammatory phases or exacerbation of disease – even in small synovial joints and can distinguish affected from adjacent normal joints. It can define synovial changes, allowing evaluation of pannus as hypoechoic vegetations protruding inside the synovial fluid or completely filling the articular space (Fig. 23a,b). Using MR imaging as the reference method, US has proved to have higher sensitivity and accuracy in detecting signs of inflammation in finger joints than do clinical and radiographic examinations, without loss of specificity (Szkudlarek et al. 2006). In other series, it was even more sensitive than MR imaging in detecting synovitis (Backhaus et al. 1999). The integrated use of Doppler imaging can help to distinguish hypervascular (active) from hypovascular (inactive) pannus, to monitor the response to therapy based on a decreased hyperemia (reflecting improvement in terms of symptoms and disease activity variables) and to differentiate active pannus from echogenic effusion (Fig. 23c–f) (Spiegel et al. 1987; Newman et al. 1996; Hau et al. 1999, 2002; Backhaus et al. 1999; Stone et al. 2001;  Szkudlarek et al. 2001; Klauser et al. 2002; Fiocco et al. 2005; Kiris et al. 2006). In addition, Doppler US may have value in distinguishing noninflammatory synovial proliferation in osteoarthritis from inflammatory arthritis (Breidahl et al. 1996). Similar to gadolinium-enhanced MR imaging, some attempts have been made with US to obtain a quantitative estimate of the synovial volume. Although a correlation among the histologic findings, clinical markers of disease activity and synovial volume seems to exist, such measurements are time-consuming and, therefore, not currently applicable in routine practice. More recently, microbubble-based US contrast agents seem to be a promising adjunct to assess the activity of the disease process (Magarelli et al. 2001; Klauser et al. 2002). There have been many reports in the literature on power Doppler rather than on color Doppler imaging to detect synovial hyperemia. Current US technology indicates, however, that the sensitivity of color Doppler systems to detect slow and low blood flow signals is now at least equal to or even superior to that of power Doppler imaging. The main limitations of both techniques are essentially related to the lack of standardized examination technique, reproducibility, operator experience and choice of the equipment (Cardinal et al. 1996; Koski et al. 2006).

Figure 23. a–f. Rheumatoid arthritis: spectrum of US appearances of synovitis in active disease. Different cases. a Longitudinal 12–5 MHz US image over the anterior femoral neck (Fneck) demonstrates a distended anterior recess (asterisk) with thickened synovial walls (arrowheads). The space of the recess is filled with effusion mixed with hypoechoic synovium. b Longitudinal 12–5 MHz US image over the suprapatellar recess (arrows) of the knee shows prominent synovial fronds (sf) within the effusion (asterisks), partially filling the articular space. The synovial fronds can be seen moving back and forward during alternate compression and release of the probe over the recess. c Transverse 12–5 MHz US image over the dorsal wrist with d fat-suppressed T2-weighted MR imaging correlation reveals marked distension of the dorsal carpal recesses by hypervascular (open arrowheads) active synovial pannus (white arrowheads). Note the multiple erosions (arrows) affecting the bone surfaces. e,f Longitudinal e gray-scale and f color Doppler 17–5 MHz US images over the dorsal midfoot in a patient complaining of pain and local swelling demonstrate the navicular-cuneiform (1) and the cuneiform-metatarsal (2) joint spaces. The first joint is characterized by hypoechoic distension of the joint space (asterisk) reflecting synovitis. Note the marked hyperemia around it on the color Doppler image. The second joint may appear normal on gray-scale US but shows increased blood flow (arrow) on color Doppler imaging. In this particular case, color Doppler increased the sensitivity of gray-scale US for detecting joint involvement at the midtarsal level.

In advanced disease, the inflammatory process may lead to massive erosions and extensive bone damage with disintegration of structures of and around joints, fibrosis, subluxation or dislocation and, at the end stage, bone ankylosis. Based on cartilage thickness measurements, US has proved able to estimate the amount of cartilage destroyed (Grassi et al. 1993; Grassi et al. 1999). US can also depict joint space abnormalities at an earlier stage than conventional radiography. A characteristic feature of rheumatoid arthritis is the release of a subset of loose bodies, called “rice bodies,” within the joint cavity. These particles are considered to be the result of sloughed fibrinogen-coated infarcted synovial tissue or aggregates of fibrin, fibronectin or multinuclear cells (McCarthy and Cheung 1982; Popert 1985). US may demonstrate rice bodies as hypoanechoic spherules measuring a few millimeters in size (Martini et al. 2003). In many instances, however, distinguishing them from hypertrophied synovium with US may be difficult (Fig. 24).

Among the seronegative (rheumatoid factor negative) arthropathies, US has proved useful to examine patients with psoriatic arthritis (Kane et al. 1999; Fiocco et al. 2005; Ory et al. 2005; Kane 2005). Like rheumatoid arthritis, psoriatic arthritis is a chronic disorder with significant joint damage at an early stage of the disease process (Husted et al. 2001). The distal interphalangeal joints are typically affected in an asymmetric pattern. Characteristic radiographic features include joint erosions, joint space narrowing, bony proliferation including periarticular and shaft periostitis, osteolysis with “pencil-in-cup” deformity and acro-osteolysis, ankylosis, spur formation and spondylitis. In psoriatic arthritis, synovitis, enthesitis and tenosynovitis can be reliably assessed with US (Barozzi et al. 1998; Kane et al. 1999; Fiocco et al. 2005; Ory et al. 2005; Kane 2005; Falsetti et al. 2003). In general, the US findings are nonspecific as they may also occur in patients with rheumatoid arthritis and osteoarthritis (Fiocco et al. 2005; Ory et al. 2005). In psoriatic dactylitis (sausage digit), US may show subcutaneous soft-tissue enlargement and, to a lesser extent, tenosynovitis and joint synovitis, the latter sign correlating with joint space narrowing and periostitis on plain films (Fig. 25) (Barozzi et al. 1998; Kane et al. 1999). In seronegative arthropathies, unenhanced and contrast-enhanced color Doppler imaging are able to demonstrate active sacroiliitis by showing a hypervascular pattern around the posterior aspect of the sacroiliac joints (Arslan et al. 1999; Klauser et al. 2005). In ankylosing spondylitis, there is predominant involvement of large joints, such as the knee, the shoulder and the hip, with uniform joint space narrowing and low-grade subchondral sclerosis and synovitis. Reiter arthritis is characterized by prevalent distal lower extremity involvement and conspicuous new bone deposition. Arthritis in inflammatory bowel disease is, for the most part, transitory and not destructive; the most commonly involved joints are the knee and the ankle. The features of juvenile idiopathic arthritis are discussed in detail elsewhere.

Figure 24. a,b. Rice bodies in rheumatoid arthritis. a Longitudinal 12–5 MHz US image over the anterior knee shows a distended suprapatellar recess (arrows) filled with heterogeneous solid tissue resembling synovial pannus. b Corresponding sagittal T2-weighted MR image reveals multiple hypoechoic dots (arrowheads) in the fluid related to rice bodies. The US appearance of rice bodies may be virtually indistinguishable from synovial pannus.

Figure 25. Psoriatic dactylitis. Longitudinal 17–5 MHz US image over the proximal interphalangeal joint of the middle finger in a 45-year-old woman with psoriatic arthritis shows extensive destruction of the articular surface (arrowheads) of the middle phalanx (MPh). Coexisting deformity (arrow) of the head of the proximal phalanx (PPh) and heterogeneous appearance of para-articular soft-tissues (asterisks) is found. The findings correspond to the radiographic sign referred to as the “pencil-in-cup” deformity.

16. SEPTIC ARTHRITIS

Septic arthritis is a serious condition leading to rapidly destructive joint disease (Goldenberg 1998; Mohana-Borges et al. 2004). This condition is most commonly caused by Staphylococcus aureus (in adults and children older than 2 years) and Neisseria gonorrheae (in young adults), which have a definite tropism for the synovium (Craig et al. 2003; Mohana-Borges et al. 2004). A variety of streptococci, including S. viridans and S. pneumoniae, group B, aerobic Gram-negative rods, viruses, mycobacteria and fungi may also produce joint infection in isolation or as a result of poly-microbial association (Jbara et al. 2006). Possible pathomechanisms of infection are: hematogenous seeding of the synovium from a distant focus or an adjacent area of osteomyelitis; spread from a contiguous infected site, such as the soft tissues in the diabetic foot; and inadvertent implantation during arthrocentesis or secondary to penetrating wounds and postoperative infection (Mohana-Borges et al. 2004). The most common pattern of presentation of septic arthritis is monoarticular. The most commonly involved joints are the hip, the knee, the shoulder, the elbow and the ankle (Mohana-Borges et al. 2004; Chau and Griffith 2005). Infection causes lysis of the articular cartilage, joint space narrowing and periarticular osteopenia. Late complications of arthritis include joint sub-luxation, premature osteoarthritis, osteonecrosis, fibrous or bony ankylosis, and limb shortening. In the acute setting, US is a reliable way to detect early septic arthritis before the occurrence of substantial cartilage lysis and when radiographs are still noncontributory (Bureau et al. 1999). The main US sign of septic arthritis is detection of a joint effusion in a patient with clinical signs of joint infection (pain, redness, heat, soft-tissue swelling about the involved joint). As regards fluid echotexture, septic effusions often contain a diffuse pattern of low-level echoes and are clearly demarcated from the thickened synovial walls (Chau and Griffith 2005). Highly hyperechoic effusions with debris and septations are often encountered. This appearance might confuse the inexperienced examiner as the collection appears to be solid on static scans; however, dynamic examination and probe compression may show swirling of echoes indicating fluid (Fig. 26). Gas bubbles may also be found in joint infection. On the other hand, completely anechoic collections of infected joint fluid are rare. However, these characteristics are too subtle to allow a definitive diagnosis and needle aspiration of fluid, possibly obtained under US guidance, is needed to confirm the infectious nature of the effusion (Bureau et al. 1999; Widman et al. 2001). Power Doppler imaging almost invariably shows a synovial hyperemic flow pattern of hypertrophied synovium and para-articular tissues. Even though the absence of fluid in a joint does not exclude adjacent osteomyelitis, a negative US and Doppler imaging examination makes diagnosis of septic arthritis unlikely (Zawin et al. 1993).

Figure 26. a–c. Septic arthritis. a Lateral radiograph of the knee in a newborn with fever and painful swollen knee suggesting an infection reveals diffuse soft-tissue swelling and an enlarged knee joint space. b,c Longitudinal 12–5 MHz US images obtained over b the patella and c the suprapatellar recess demonstrate the joint cavity filled with highly echogenic dense fluid (arrows) related to purulent material and debris. Note the hypoechoic appearance of the unossified patella and the epiphyseal cartilages of the femur (F) and tibia (T). e, ossification center of the distal femoral epiphysis. Aspiration of the joint fluid revealed Staphylococcus aureus infection.

 

17. TRAUMATIC INJURIES

When affecting joint portions that are amenable to US examination, osteochondrosis and osteochondral fractures can be detected as surface irregularities of the cartilage or nidus formation involving the cartilage and the subchondral bone (Takahara et al. 1988). In degenerative osteoarthritis, the cartilage may appear progressively thinner and irregular, or even completely disintegrated, whereas the hyperechoic line of the subchondral bone shows irregularities. At US, osteophytes are usually depicted at the joint margins as beak-shaped hyperechoic bone projections covered by cartilage. Following joint surface fractures or other conditions leading to progressive derangement of joints (i.e., osteoarthritis, osteo-chondromatosis, neuropathic joint disease), loose bodies can be released into the joint cavity, possibly leading to intermittent locking of the joint and early degenerative changes. Intra-articular loose bodies are osseous, chondral or osteochondral fragments. They often have a three-layered structure composed of a superficial bright echo due to an artifact at the interface with fluid, an intermediate hypoechoic band due to the cartilage, and a deep hypoechoic surface with posterior acoustic shadowing due to the bone component (Bianchi and Martinoli 2000). In many instances, US can give a better delineation of loose bodies than can plain films and MR imaging (Fig. 27). On the other hand, MR imaging is superior in detecting the nidus of the fragment. A monolaminar appearance is observed in old extensively calcified fragments, which appear as hyperechoic images like gallstones without a detectable rim of hypoechoic cartilage (Bianchi and  Martinoli 2000). During joint motion or while applying transducer pressure, loose bodies can be mobilized within joint recesses: this may be helpful for the differential diagnosis with either osteophytes or capsular and synovial calcifications.

Figure 27. a–d. Osteochondral fracture. a Longitudinal and b transverse 17–5 MHz US images of the anterior knee in a patient with onset of painful swelling and locking of the knee following an episode of patellar dislocation show a distended suprapatellar recess (asterisks) containing an osteochondral loose body (arrowhead). The fragment is characterized by a trilayered structure composed of: a superficial bright echo (1) due to the acoustic impedance mismatch at the solid-fluid interface; an intermediate hypoechoic layer (2) due to the cartilage; and a deep bright echogenic surface (3) with slight posterior attenuation due to the detached subchondral bone. c Lateral radiograph is unable to reveal the loose body except for a subtle radio-opaque linear image (arrows) reflecting its bony component. Qt, quadriceps tendon. d Gross operative view demonstrates the loose body (arrowhead) fixed into the patellar nidus.

The diagnosis of joint instability basically relies on plain films. In some instances, however, the complex anatomy of joints and surrounding structures may make detection of subluxation and dislocation of joints difficult on standard radiographs. If undetected, joint instability may lead to chronic local pain, secondary osteoarthritis and altered joint function. In specific clinical settings in which the physical examination may be inconclusive, US can contribute to the detection of occult positional joint abnormalities, including posterior shoulder dislocation and mild acromioclavicular joint instability (Hunter et al. 1998; Bianchi et al. 1994; Bize et al. 2004; Borsa et al. 2005).

Many joints contain fibrocartilaginous structures, including the meniscus in the knee, the labrum in the hip and the shoulder, the triangular fibrocartilage in the wrist, and the volar and plantar plates in the hand and foot. Because of their deep location and close contact with the bone, these structures can be evaluated with US only in part and not reliably. Although different authors have reported a high sensitivity and specificity of US in diagnosing knee meniscal and shoulder labral tears (Sohn et al. 1987a, b; Schydlowsky et al. 1998; Hammar et al. 2001), further evidence has demonstrated that US cannot be considered an accurate technique for diagnosing fibrocartilage tears (Azzoni and Cabitza 2002). In particular, distinguishing tears from degenerative states is problematic on the basis of the US findings due to a similar echotextural pattern. However, some conditions involving the superficial part of these structures, such as an extruded meniscus, a meniscocapsular detachment with fluid intervening between the capsule and the fibrocartilage or a meniscal ossicle can be inferred on US. Initial experience is also available in the literature on US investigation of the normal triangular fibrocartilage of the wrist and the volar plates  (Boutry et al. 2004; Chiou et al. 1988; Keogh et al. 2004). However, further studies are needed to establish the ultimate value of US in imaging pathologic conditions affecting these structures. In contrast to the results of fibrocartilage evaluation, US has proved to be an effective modality for diagnosing parameniscal and paralabral cysts  (Peetrons et al. 1990; Rutten et al. 1998; Seymour and Lloyd 1998). These cysts are believed to derive from tangential or compressive forces that lead to trauma, degeneration and tearing of the fibrocartilage. Synovial fluid is extruded through the tear toward the peripheral margin of the fibrocartilage, expanding it and dis-placing the capsule outward into the surrounding tissues (McCarthy and McNally 2004). Because these cysts are almost invariably associated with a fibrocartilage tear, the US diagnosis of an associated meniscal or labral rupture is straightforward even in cases of unclear or doubtful findings (Fig. 28a,b). The cyst can track some distance from the fibrocartilage before becoming clinically palpable and US may show a narrow pedicle connecting it to the tear. Parameniscal and paralabral cysts appear as space-occupying masses with sharply defined borders. They often exhibit mixed internal echotexture as a result of mucoid degeneration or appear as undefined softening and swelling of the connective spaces in which they expand (Fig. 28c,d). Even if small in size, labral-related cysts may lead to neuropathy of adjacent nerves, such as the suprascapular nerve (posterior glenoid labrum cysts), the axillary nerve (inferior glenoid labrum cysts) and the femoral nerve (anterior acetabular labrum cysts)  (Takagishi et al. 1991).

Figure 28. a–d. Cysts associated with fibrocartilage lesions. Spectrum of US appearances of parameniscal cysts in two different patients. a Oblique sagittal 17–5 MHz US image with b sagittal T1-weighted MR imaging correlation over the anterolateral knee shows a large cyst (white arrows) with internal septa lying adjacent to the anterior horn of the lateral meniscus (open arrows). A cleft (arrowheads) representing a horizontal meniscal tear is seen extending through the meniscus. F, femur; T, tibia. c Coronal 12–5 MHz US image obtained over the lateral knee with d fat-suppressed T2-weighted MR imaging correlation shows a horizontal degenerative tear (arrowheads) of the middle third of the lateral meniscus (open arrow) associated with extrusion of joint fluid in the adjacent soft tissues forming a irregularly shaped cyst (white arrows). Note the popliteal tendon (P) partially surrounded by fluid.

Ligament tears can be demonstrated with US at different sites, including the ankle and foot ( Campbell et al. 1994; Peetrons et al. 2004), the wrist and hand (Jones et al. 2000; Noszian et al. 1995; Finlay et al. 2004; Boutry et al. 2005), the knee (Ptasznik et al. 1995; Miller 2002; O’Reilly et al. 2003) and the elbow (Nazarian et al. 2003). The US features of a torn ligament vary depending on whether the lesion is acute or has healed. In acute phases, a partially torn ligament appears swollen and hypoechoic but continuous (Fig. 29a); an anechoic band over the superficial aspect of the ligament may be observed representing reactive soft-tissue edema (Peetrons et al. 2004). In complex ligaments, US can distinguish the abnormal hypoechoic portion of the ligament from the unaffected one retaining a normal appearance (Fig. 29b). In acute complete ruptures, a hypoechoic cleft reflecting the hematoma can be detected through the ligament substance and the free ends of the severed ligament may appear retracted and wavy (Fig. 30a,b). In doubtful cases, the ability to assess the ligament dynamically is a definite advantage of US: under stress, a normal ligament tightens preventing excessive widening of the joint space; if the ligament is torn, a paradoxical movement is obtained reflecting joint instability (Fig. 30) (De Smet et al. 2002; Brasseur et al. 2005). In chronic partial tears, the ligament always appears thicker than normal on US images. Calcifications within the ligament substance in old tears and irregularities of the bony insertions in avulsion injuries may be observed (Fig. 31) (Brasseur et al. 2005). A typical example is the Pellegrini-Stieda syndrome (calcification of the proximal end of the medial collateral ligament of the knee). In ligament lengthening following a partial tear, dynamic scanning during a stress maneuver obtained at rest and during stretching may be helpful to distinguish normal laxity from partial ligament tears based on widening of the joint space (Nazarian et al. 2003; Peetrons et al. 2004). The significance of these maneuvers has yet to be fully determined.

Figure 29. a,b. Partial ligament tear. a Long-axis 17–5 MHz US image over the anterior talofibular ligament (arrowheads) in a patient following an inversion injury of the ankle demonstrates a markedly thickened and hypoechoic but straight ligament without signs of macroscopic discontinuity. A hypoechoic band of fluid (asterisk) underlines the superficial aspect of the ligament representing reactive soft-tissue edema. LM, lateral malleolus. Arrow, articular cartilage of the talus. b Coronal 17–5 MHz US image over the medial aspect of the medial femoral condyle (MC) reveals diffuse hypoechoic thickening of the superficial component (arrows) of the proximal medial collateral ligament, whereas the deep meniscofemoral component (arrowheads) is unaffected. Asterisk, medial meniscus.

Figure 30. a–g. Complete ligament rupture. Spectrum of US appearances in a–d the anterior talofibular and e-g scapholunate ligaments. a Long-axis 17–5 MHz US image obtained at rest over the anterior talofibular ligament after an inversion injury with b schematic drawing correlation demonstrates the torn ends (1, 2) of the ligament in a wavy shape with hematoma insinuating between them. c,d While performing an anterior drawer test, there is opening (large arrows) of the joint space (asterisks) and the ligament ends are more clearly separated from each other. e Transverse 17–5 MHz US image over the dorsal aspect of the proximal carpal row shows a normal scapholunate ligament (arrows) joining the lunate (Lun) and the scaphoid (Scaph). f,g Transverse 17–5 MHz US images obtained in patient who underwent previous wrist injury. f In neutral position, there is absence of the scapholunate ligament with respect to the normal findings shown in e. The dashed lines demarcate the distance between
the scaphoid and the lunate. g During ulnar deviation of the wrist, widening (arrows) of the scapholunate distance can be seen: this can be considered a sign of ligament tear.

Figure 31. a–c. Avulsion injury of the ulnar collateral ligament of the thumb (gamekeeper thumb). a Coronal 15–7 MHz US image obtained over the ulnar aspect of the metacarpophalangeal joint of the thumb with b radiographic and c schematic drawing correlation shows a retracted ulnar collateral ligament (arrowheads) lying deep to the adductor pollicis aponeurosis (open straight arrow). Note a small distal hyperechoic fleck of bone (white straight arrow) corresponding to cortical avulsion (curved arrow) from the base of the proximal phalanx (Ph). The proximal ligament insertion onto the first metacarpal (M) appears normal.

 

18. DEGENERATIVE JOINT DISEASE (OSTEOARTHRITIS)

The term “osteoarthritis” (degenerative joint disease) includes a heterogeneous group of disorders which are characterized by defective integrity of the articular cartilage and related changes in the underlying bone and at the joint margins (Felson 2004; Gupta et al. 2004). Osteoarthritis is the most widespread form of joint disease in the Western world and can be divided into idiopathic and secondary forms (Gupta et al. 2004). The causes of osteoarthritis include various combinations of systemic risk factors (aging, inheritance, estrogen deficiency), local joint vulnerabilities (previous injuries, bone malalignment) and extrinsic factors acting on the joint (obesity, muscle weakness, occupational and sports-related repetitive overuse but also chronic underuse) (Felson et al. 2004). The initial abnormality of osteoarthritis occurs in the articular cartilage with edema followed by fibrillation and superficial and deep clefts possibly evolving toward ulcerations and production of new cartilage and bone. In severe forms, complete cartilage loss associated with pathologic changes of the subchondral bone (i.e., sclerosis, cysts) and marginal osteophytes can occur. Intra-articular loose bodies may develop as a result of detachment of small cartilage pieces or bone fragments which may activate new chondral or bone formation. The diagnosis of osteoarthritis is essentially based on clinical and radiographic data. US is able to detect joint surface and hyaline cartilage abnormalities (Grassi et al. 2005). Changes include progressive thinning and irregularity of the cartilage layer up to its complete disintegration and irregularities of the underlying subchondral bone (Fig. 32) (Grassi et al. 1999). One of the major limitations of US in evaluating osteoarthritis is the incomplete evaluation of the cartilage surface, which is, for the most part, masked by the ends of opposing bones. This is true for both tight and large joints. In the knee, for instance, articular cartilages that are vulnerable to tears and ulcerations are mainly located at the posteroinferior aspect of the femoral condyle and on the lateral facet of the patella: both surfaces are barely evaluated with US. Similarly, geodes (sub-chondral cysts) are not visible at US because they are completely surrounded by bone. On the other hand, osteophytes can be readily appreciated as beak-like bone projections covered by hypoechoic cartilage adjacent to the joint line (Fig. 33). They increase the surface area of the articular cartilage, thus lessening the stress and loading forces that are experienced by the joint and, at the same time, increasing its stability: typical locations of osteophytes are the posterior humeral head, the internal femorotibial and the anterior tibiotalar joints (Gupta et al. 2004). Finally, US can be useful in assessing para-articular soft-tissue abnormalities that can be responsible for pain in osteoarthritis and may help to guide intra-articular drug injection (Naredo et al. 2005; Migliore et al. 2005).

Figure 32. a–d. Degenerative osteoarthritis. Two different cases. a Transverse 12–5 MHz US image obtained over the trochlear cartilage with b proton density MR imaging correlation shows diffuse thinning (arrowheads) of the mid-third of the cartilage. Note the erosive changes (arrow) in the subchondral bone. c,d Loss of lateral compartment articular cartilage. c Transverse 12–5 MHz US image with d fat-suppressed proton-density MR imaging correlation shows a wide cartilage defect (black arrowhead) in the lateral facet of the trochlea. Note the normal-appearing cartilage of the medial trochlear compartment (white arrowheads).

Figure 33. a–c. Degenerative osteoarthritis. a Transverse 12–5 MHz US image obtained over the anterior aspect of the glenohumeral joint with b CT-arthrography and c standard radiographic correlation in a patient with advanced degenerative joint disease demonstrates a large marginal osteophyte of the humerus (H) as a beak-like bone projection (arrow) lying adjacent to the joint line, covered by hypoechoic cartilage (arrowheads). GL, bony glenoid.

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19. DEPOSITION DISEASES

The deposition of crystals of monosodium urate (gout), calcium pyrophosphate dehydrate (CPPD; chondrocalcinosis, pseudogout) and calcium hydroxyapatite (HADD; calcifying tendinitis) within synovium, articular cartilage, fibrocartilages and para-articular soft tissues may produce a spectrum of clinical conditions ranging from asymptomatic entities to severe rapidly destructive arthropathy (Steinbach 2004; Clement et al. 2005). The accumulation of crystals takes months to years to develop and leads to the establishment of a chronic synovitis with intermittent acute flares.

Gout is the most common form of microcrystalline arthropathy, with a peak incidence occurring in males between the third and fifth decades (Monu and Pope 2004). It results from a disturbance of urate metabolism and includes acute and chronic forms.  Acute gout typically affects the first metatarsophalangeal joint of the foot (podagra), but almost any other joint can be involved. The initial attacks are monoarticular and usually involve the lower limb. Following intermittent flare-ups or exacerbations over a period of years, the disease becomes chronic and tends to involve multiple joints. An inflamed joint shares the usual presentation with an acute synovitis, including joint effusion, para-articular edema and hyperemia. In general, gouty crystals are not depicted with US unless larger aggregates have calcified (Farina et al. 2002). Basically, the US findings are not disease-specific (Filippucci et al. 2003). US may be used for short-term monitoring of acute gouty attacks (Filippucci et al. 2003). US findings in chronic tophaceous gout are described elsewhere.

Calcium pyrophosphate dehydrate crystal deposition disease is widespread in the elderly and has multifaceted clinical presentations ranging from asymptomatic disease to severe painful destructive arthropathy, with symptoms that often confound clinicians (Steinbach 2004). Patients can complain of either chronic joint pain mimicking osteoarthritis or a swollen inflamed joint mimicking gout (pseudogout) or a septic joint. The knee is the most commonly affected joint (articular cartilage and menisci), followed by the hip (symphysis pubis), the wrist (triangular fibrocartilage, intrinsic ligaments), the glenohumeral joint, the elbow and the ankle. During pseudogout attacks, shedding of pyrophosphate crystals into the joint fluid occurs. In general, these attacks are self-limiting, less painful than gout attacks, and can last up to several weeks causing joint stiffness and restricted joint motion. Standard radiographs can demonstrate small calcified deposits within degenerating hyaline cartilage, synovium and para-articular structures, including ligaments, tendons and bursae (Abreu et al. 2004; Steinbach 2004). A conclusive diagnosis is based on detection of pyrophosphate crystals in the synovial fluid by means of a polarizing microscope. US can demonstrate crystal deposition in the articular cartilage as multiple hyperechoic dots in the mid-thickness of the cartilage forming a dense echogenic line that runs parallel to the articular margin, particularly at the level of the femoral condyles (Fig. 34) (Kellner et al. 1990; Coari et al. 1995; Foldes 2002; Sofka et al. 2002; Frediani et al. 2005). Three main patterns of calcified deposits have been described (Frediani et al. 2005): thin hyperechoic bands parallel to the surface of the hyaline cartilage (more frequent in the knee); a ”punctate” pattern, composed of several thin bright echogenic spots (commonly seen in fibrocartilage and tendons); and homogeneous hyperechoic nodular or oval deposits (found in bursae and articular recesses).

Figure 34. a–g. Calcium pyrophosphate deposition disease. a–c Transverse 12–5 MHz US images obtained over a the femoral trochlea, b the posterior aspect of the medial condyle and c the lateral meniscus in a patient with bilateral degenerative osteoarthritis of the knee reveal scattered hyperechoic foci (arrowheads) due to crystal deposition within the hyaline cartilage, the medial meniscus and the joint capsule (arrows). F, femur; T, tibia . Note that crystals tend to be deposited in the middle layer of the cartilage, parallel to the subchondral bone. d–f Radiographic correlation. g Schematic drawing illustrates the typical deposition pattern of pyrophosphate crystals within the cartilage.

The intra-articular involvement of calcium hydroxyapatite deposition disease—a condition more commonly referred to as “calcifying tendinitis” because of the involvement of tendons near to their osseous insertion—may produce an acute arthritis (chronic apatite arthropathy) possibly mimicking an infectious condition.

Amyloidosis is a major clinical complication with various subtypes that occur in association with multiple myeloma (primary disease), other chronic disorders (secondary disease) and in patients with chronic renal failure under long-term hemodialysis treatment (Jbara et al. 2006). Its prevalence increases with the duration of hemodialysis, ranging from approximately 20% of cases within 2 years of treatment to nearly all after 13 years (Dzido and Sprague 2003). This multiorgan disease is related to β2 microglobulin deposition in tissue. In the musculoskeletal system, amyloid deposition typically occurs on surfaces containing collagen, most often the synovium of joint and tendons. Such a predilection seems to be related to macrophage and cytokine activation, a process that might be involved both in the proteolytic processing of the molecule – a step that would enhance amyloid formation – and in the generation of pain, dysfunction and even destructive arthropathy (Bancroft et al. 2004). In its articular form, amyloidosis most often involves the hip, the knee and the wrist leading to development of large amyloid-filled subchondral cysts in the juxta-articular bone. The thickness of abnormal soft-tissue material measured with US in the anterior recess of the hip and the suprapatellar recess of the knee has been found to correlate positively with dialysis duration and radiological and histologic evidence of amyloidosis (Jadoul et al. 1993). Based on echotextural findings, amyloid deposits cannot be distinguished from other synovial pathology (Fig. 35a,b). MR imaging demonstrates amyloid with low to intermediate signal on T1- and T2-weighted sequences (Fig. 35c,d) (Cobby et al. 1991).

Figure 35. a–d. Amyloid arthropathy. a Transverse and b longitudinal 12–5 MHz US images obtained over the anterior hip in a patient affected by chronic renal failure demonstrate distension of the anterior joint recess (arrows) by solid homogeneously hypoechoic tissue. c,d Coronal c T1-weighted and d fat-suppressed T2-weighted MR imaging correlation confirm the presence of intra-articular amyloid (arrows), characterized by low signal intensities. Fneck, femoral neck.

 

20. POSTOPERATIVE COMPLICATIONS

Detection and localization of postoperative infection may be a challenging task. Septic arthritis complicating hip and knee joint replacement procedures is an important risk factor reported to involve approximately 2% of cases (Goldenberg 1998). Based on the clinical and radiographic findings, it may be impossible to distinguish mechanical loosening of a prosthesis from septic loosening (Bureau et al. 1999). Nuclear medicine, CT and MR imaging can be impaired around orthopaedic hardware by metallic shielding and artifact. US is less hindered in many of these respects and can be considered the first-line diagnostic modality in this setting, provided that an adequate probe access is available (Chau and Griffith 2005). In the postoperative hip, infection can be suspected with US by the presence of a large joint effusion (mean bone-to-pseudocapsule distance: normal, 3.2 mm; infected, 10.2 mm) associated with an extracapsular noncommunicating soft-tissue fluid collection and local inflammatory changes  (van Holsbeeck et al. 1994). More recently, however, a retrospective study revealed some limitations of US as an indicator of adult hip joint effusion, even in the postoperative setting (Weybright et al. 2003). When a collection is present around a postoperative hip, US can effectively guide arthrocentesis to obtain material for Gram staining and bacterial culture ( van Holsbeeck et al. 1994; Gibbon et al. 2002). Doppler US may also be used to rule out deep vein thrombosis after total hip or knee arthroplasty, especially if routine perioperative pharmacologic antithrombotic prophylaxis is not practised (Ko et al. 2003).

Granulomatous synovitis can be seen as a result of reaction to small particles of silicone polymers or other synthetic components of prostheses secondary to shedding, so-called “silastic synovitis” or “detritic synovitis”. Often encountered in wrist implants, this condition derives from a kind of foreign-body response, in which activated macrophages provoke bone resorption and dissection around the implant (Bancroft et al. 2004). Standard radiographs show well-defined subchondral lucency and erosions usually associated with fracture and/or dislocation of the prosthesis (Rosenthal et al. 1983; Schneider et al. 1987). MR imaging confirms the radiographic findings and demonstrates multiple small hypointense particles that represent silicone fragments resulting from implant breakage and disintegration (Chan et al. 1998). US can demonstrate the implant-derived debris as hyperechoic spots embedded within hypertrophied synovium: these fragments should be differentiated from calcifications based on the presence of posterior reverberation and ring-down artifact (Fig. 36).

Figure 36. a–d. Silastic synovitis. a Coronal and b transverse 12–5 MHz US images obtained over the lateral aspect of the sinus tarsi in a patient who was previously operated on for flatfoot show a hypoechoic solid mass (open arrowheads) containing multiple hyperechoic spots (open arrows) with posterior reverberation artifact (black arrowheads). A large hyperechoic structure (white arrow) is also found protruding outside the sinus tarsi. c Reformatted coronal CT and d transverse T1-weighted MR images identify extensive bone resorption and striking synovial hypertrophy around a loosened silicone prosthesis (white arrow). Some particles (open arrows) representing silicone fragments are also found.

 

21. SPACE-OCCUPYING MASSES

Bone Tumors

The role of US for the detection and assessment of bone tumors is obviously poor, given its inability to define intraosseous processes. US can only detect lesions associated with considerable cortical thinning and/or large extraosseous spread, such as large tumors eroding the cortex (Saifuddin et al. 1998). While evaluating bone tumors, US can be useful in two main clinical situations: the detection of an otherwise unsuspected tumor, or as guidance for a percutaneous biopsy of a bone tumor already investigated with standard radiographs, CT and MR imaging. It is not uncommon for patients with a bone tumor, either primary or metastatic, to complain of nonspecific regional pain and to undergo US examination for a suspected soft-tissue abnormality before a radiographic study. Therefore, careful assessment of the bone surface must be part of a standard US examination of soft tissues and the US signs suggesting a possible abnormality of bone – even if minimal – must be known by the examiner.

In osteolytic tumors with extraosseous extension, US shows a periosseous soft-tissue mass arising from a break or a deep defect in the hyperechoic bony cortex (Fig. 37). Direct continuity of the mass from the inner bone into adjacent soft tissues is a sign of the intraosseous origin of the tumor. Although US has limitations in assessing infiltration of periosseous tissue planes, the boundaries of the extraosseous component of the neoplasm are usually well circumscribed. In general, the tumor echotexture ranges from solid hypoechoic to a mixed heterogeneous appearance due to internal anechoic areas related to necrosis. In most cases, US is unable to suggest the histologic diagnosis as well as to differentiate malignant from locally aggressive benign tumors. Based on their fluid-filled appearance, US can diagnose intraosseous ganglia extruding into the paraosseous soft tissues (Bianchi et al. 1995). Occasionally, a presumptive diagnosis can be made, such as in the case of aneurysmal bone cysts presenting marked cortical thinning and multiple fluid-fluid levels (Fig. 38) (Haber et al. 1993; Gomez et al. 1998). In these instances, changing the patient’s positioning can show respective changes in the disposition of fluid layers within the tumor compartments (Fig. 38a-d). Recently, the US appearance of osteoid osteoma located in the proximal metaphysis of the right tibia and left femoral diaphysis of adolescents has been described (Gil-Sanchez et al. 1999). Color Doppler imaging may be useful for detection of the hypervascular nidus and to guide percutaneous localization and biopsy. Doppler imaging should always be performed when evaluating soft-tissue tumors. It can show internal vasculature, thus helping to differentiate viable from necrotic tissue. When a bone tumor exhibits a large extraosseous component at MR imaging, US can be effective and reliable to guide percutaneous needle biopsy (Civardi et al. 1994; Saifuddin et al. 1998, 2000; Konermann et al. 2000; Yeow et al. 2000; Gil-Sanchez et al. 2001; Torriani et al. 2002). Biopsy is a fundamental step in the investigation of suspected bone tumors and must be obtained in specialized centers to avoid inadequate tissue sampling, which is the most common reason for the inability to perform limb-salvage surgery (Skrzynski et al. 1996; Saifuddin et al. 2000). US-guided biopsy must be performed only in patients in whom the feasibility of the procedure has been previously checked on MR imaging or CT scan. The biopsy of a bone tumor must be performed in agreement with the referring orthopaedic surgeon in order to decide the most appropriate needle path by consensus: this helps to avoid seeding of tumor cells out of the involved compartment. As described in Chapter 18, 14–18 gauge Tru-cut type automatic devices are recommended to achieve better diagnostic yield for histologic diagnosis. Fine-needle aspiration biopsy seems to have definite limitations in this field, even in detection of tumor recurrence or diagnosis of metastasis of a known primary tumor. Compared with CT guidance, the main advantages of US-guided biopsies of bone tumors rely on the ability of US: to recognize viable tumor and adjacent vessels with Doppler imaging; to allow continuous real-time visualization of the needle to avoid necrotic areas and the risk of injury to adjacent structures; and to perform the procedure more rapidly, reducing patient discomfort (Torriani et al. 2002). If the US biopsy is performed in experienced hands, complications are rare (Torriani et al. 2002). In rib lesions, local pain and hematoma, infection and pneumothorax have been reported as complications.

Figure 37. a–c. Bone tumors. Two different cases. a Extended field-of-view 12–5 MHz US image over a slow-growing palpable pretibial mass in a patient with breast cancer shows a large well-circumscribed solid neoplasm causing osteolysis (straight arrows) and extending into the adjacent extraosseous spaces (white arrowheads). Dashed line indicates the level of destroyed tibial cortex. Residual small bone fragments (curved arrows) displaced by the growing neoplasm are seen. Biopsy revealed breast metastasis. b Longitudinal 12–5 MHz US image obtained over the shoulder in a patient with suspected rotator cuff disease reveals a large hypoechoic mass (asterisk) causing extensive osteolysis (white arrows) of the acromion (black arrow): some bone fragments are visible within the mass (arrowhead). c Anteroposterior radiograph confirms the osteolytic lesion (asterisk) and an associated pathologic fracture (black arrowhead). Biopsy revealed metastasis from lung cancer.

Figure 38. a–g. Aneurysmal bone cyst in a 12-year-old boy with a stiff slow-growing painless swelling over the fibular head and neck. a,b Coronal 12–5 MHz US images obtained over the fibular head a with the patient supine and b standing reveal a complex mass (arrows) which creates a bulge on the surface of the bone with cortical thinning (arrowheads) sufficient to allow US beam penetration. The mass is characterized by multiple dual fluid levels, an appearance fairly specific for an aneurysmal bone cyst. When the patient’s position is changed, fluid levels rearrange parallel to the floor according to gravity. c,d Diagrams show the disposition of fluid levels as seen in a and b. e Photograph shows focal bulging (curved arrow) over the fibular head. f Anteroposterior radiograph and g transverse T2-weighted MR imaging confirm the US diagnosis.

 

22. PIGMENTED VILLONODULAR SYNOVITIS

Pigmented villonodular synovitis is an uncommon benign proliferative disease of the synovium that affects joints, bursae or tendon sheaths (Dorwart et al. 1984; Yang et al. 1998; Bianchi et al. 1998; Lin et al. 1999; Middleton et al. 2004). From the pathogenetic point of view, the etiology of pigmented villonodular synovitis remains controversial. Of the two most widely accepted theories, one implicates a chronic inflammatory process, the other a benign neoplasm (Byers et al. 1968; Mukhopadhyay et al. 2006). The presence of histiocytes that contain fat or hemosiderin (a breakdown product of hemoglobin), multinucleated giant cells and plasma cells seems suggestive of inflammation, whereas the high cellularity, tendency for recurrence and recent cytogenetic studies revealing clonal cell proliferation favor a neoplastic process (Mukhopadhyay et al. 2006). The clinical presentation of articular pigmented villonodular synovitis depends on the morphologic form of disease, including a diffuse and nodular type. The more common diffuse pigmented villonodular synovitis grossly appears as a widespread proliferation of the synovium that shows fingers-like masses and villosities. It usually occurs in the third and fourth decades of life as a monoarticular arthritis affecting the knee (80% of cases) , the hip and the ankle. Patients’ complaints include insidious onset of progressive joint swelling, discomfort, pain, mechanical derangement and decreased range of motion. Focal pigmented villonodular synovitis more frequently occurs in the fifth and sixth decades, affecting joint, para-articular bursae and synovial tendon sheaths (giant cell tumor of tendon sheath), the latter being more common. It has a female predominance and affects the digits of the hand and foot, presenting as a slow-growing painless mass (Rao and Vigorita 1984).

Plain radiographs can be normal or show intra-articular effusion, an ill-defined para-articular soft-tissue mass and, in longstanding disease, juxta-articular bone erosions and subchondral cysts caused by pressure and hypertrophied synovium. CT shows hemosiderin and fat deposits, and is able to detect bone erosions that are not manifest on radiographs.

MR imaging shows synovial effusion and hypertrophied synovitis containing scattered areas of hemosiderin that exhibits low signal intensity on T1- and T2-weighted sequences—darker on T2* gradient-echo sequences due to susceptibility artifact (Fig. 39). Although similar appearances can be observed in hemophilic and rheumatoid arthritis in the proper clinical setting, these findings are often considered to be diagnostic of pigmented villonodular synovitis (Hughes et al. 1995; Jelinek et al. 1989; Narváez et al. 2001). The US appearance of diffuse pigmented villonodular synovitis is nonspecific as it appears either as an intra-articular area of hypoechoic synovial thickening or as an irregular mass located within the joint cavity usually associated with a joint effusion (Fig. 39a). In some cases, US can detect pressure erosions on the bone cortex as defects of the joint surfaces filled with hypertrophied synovium. Doppler imaging can show a hypervascular pattern within the synovial mass (Yang et al. 1998; Lin et al. 1999). A pattern of relatively increased flow in the periphery of the synovial capsule may be present (Lin et al. 1999). Local recurrence after surgical or arthroscopic synovectomy takes place in almost 50% of cases (Sheldon et al. 2005). The nodular type of pigmented villonodular synovitis  (Bianchi et al. 1998;  Middleton et al. 2004).

Figure 39. a–c. Pigmented villonodular synovitis: diffuse type. a Longitudinal 12–5 MHz US image obtained over the suprapatellar recess demonstrates hypoechoic thickening of the synovium (arrowheads), a fairly nonspecific appearance. P, patella. b Sagittal T2-weighted and c fat-suppressed postcontrast T1-weighted MR images confirm the US finding (arrowhead) and reveal additional lesions (arrows) lying in the anterior and posterior joint recesses. The hypointense pattern of these lesions on T2-weighted sequences strongly suggests pigmented villonodular synovitis.

 

23. LIPOMA ARBORESCENS

Lipoma arborescens, also referred to as diffuse synovial lipoma or villous proliferation of synovium, is a rare monoarticular reactive lesion giving rise to a focal fat-containing villous proliferation. It can be primary or, more frequently, associated with other joint disorders, such as degenerative joint disease, rheumatoid arthritis or previous trauma (Al-Ismail et al. 2002; Murphey et al. 2004; Davies and Blewitt 2005; Sheldon et al. 2005). Although occasionally reported in the hip, shoulder and elbow (Doyle et al. 2002; Nisolle et al. 1999; Bejia et al. 2005), lipoma arborescens most commonly occurs in the knee, particularly in the suprapatellar recess. From the clinical point of view, it presents with long-standing painless synovial thickening and intermittent joint effusions. US demonstrates lipoma arborescens as a mass with tree-like contours and villous projections related to replacement of subsynovial tissue by mature fat (Learch and Braaton 2000). In general, the mass is more echogenic than synovial tissue and is associated with joint effusion (Fig. 40a). During joint manipulation, dynamic examination allows real-time demonstration of to-and-fro bending and waving of villous projections (Learch and Braaton 2000; Sheldon et al. 2005). If lipoma arborescens is suspected, MR imaging should be obtained to confirm the diagnosis based on the frond-like architecture and signal intensity similar to that of fat in all pulse sequences (Fig. 40b,c) (Vilanova et al. 2003). Synovectomy is the definitive treatment.

Figure 40. a–c. Lipoma arborescens. a Transverse 12–5 MHz US image obtained over the lateral parapatellar recess of the knee shows an intra-articular relatively hyperechoic fronded mass (arrows) outlined by synovial effusion (asterisks). P, patella. b Transverse T1-weighted and c fat-suppressed T2-weighted MR imaging correlation confirm the fatty nature of the frond-like projections of the mass.

 

24. SYNOVIAL OSTEOCHONDROMATOSIS

Primary synovial osteochondromatosis (synovial chondromatosis) is a benign condition affecting the synovial membrane that leads to proliferation of intrasynovial chondral or osteochondral nodules. It most commonly affects the knee (50% of cases) of middle-aged men. In order of decreasing prevalence, other commonly involved joints are the elbow, the hip and the shoulder. In early disease (type 1), there is active synovial proliferation with cartilaginous masses embedded within the synovium; then (type 2), osteochondral nodules become pedunculated and are released within the joint cavity; finally (type 3), intra-articular bodies lie free with regression of synovial hypertrophy (Milgram 1977). Clinical symptoms include local pain and swelling, followed by stiffness, intermittent joint locking due to loose bodies trapped in between the joint surfaces, and premature degenerative joint changes. Synovial chondromatosis should not be confused with other causes of intra-articular osteocartilaginous bodies (secondary chondromatosis). US can detect thickened synovium containing hypoechoic chondral nodules that can or cannot undergo calcification. When mineralized, these nodules appear as bright hyper-echoic fragments with posterior acoustic shadowing and are better delineated with US (Fig. 41) (Pai and van Holsbeeck 1995; Leekam and Voorneveld 1996; Campeau and Lewis 1998; Cho et al. 2000). In conglomerate heavy calcified masses, the posterior acoustic shadowing from superficial calcified deposits can mask the rest of the synovial abnormality (Roberts et al. 2004). It is not uncommon that fragments migrate outside the joint space into communicating synovial bursae, such as the semi-membranosus-gastrocnemius bursa or the iliopsoas bursa (Moss and Dishuk 1984). When the diagnosis is suspected on US findings, standard radiographs must be obtained to confirm the presence of punctate or dense lobular calcifications, which occur in approximately two-thirds of cases. Treatment is surgical synovectomy; however, the recurrence rate is over 25% (Sheldon et al. 2005).

Figure 41. a–d. Synovial chondromatosis. a Plain lateral radiograph of the index finger shows a small soft-tissue calcified mass on the volar (white arrow) aspect of the first phalanx. Some calcifications are also visible on the dorsal aspect of the proximal phalangeal joint (void arrow). Lack of bone erosion and of periosteal reaction suggests excluding bone involvement. b Longitudinal 17-5 MHz US images obtained at the level of the proximal interphalangeal joint reveal a conglomerate of calcifications (arrows) filling the ventral joint recess (arrowheads) between the bone and the flexor tendons (ft). MPh, middle phalanx; PPh, proximal phalanx. c Axial CT imaging correlation. d Surgical specimen of the same case shows the loose bodies.

 

25. SYNOVIAL HEMANGIOMA

Synovial hemangioma is a rare intra-articular benign tumor arising from the synovium that is difficult to diagnose because of its nonspecific clinical presentation of nontraumatic recurrent swollen painful knee (Narváez et al. 2001; Okahashi et al. 2004). The knee of young adults and adolescents is usually affected. Clinical symptoms are related to the mass effect of the tumor, which leads to a decreased range of motion and repetitive episodes of bleeding causing joint pain and swelling and possibly mimicking other conditions, such as hemophilic arthropathy, arthritis or medial shelf syndrome. Hemangiomas arising from the synovium have a similar US appearance to other soft-tissue hemangiomas, but the presence of hypoechoic tissue with fluid-filled areas related to pooling of blood within vascular spaces may generate confusion with more common synovial conditions. Therefore, the examiner must be aware of this condition to avoid making a wrong diagnosis and wasting time for the patient. In the cavernous type of synovial hemangioma, slow-flowing blood can occasionally be appreciated within the anechoic spaces of the mass on gray-scale and color Doppler US (Fig. 42a–c). MR imaging of synovial hemangioma is pathognomonic, with intermediate T1-signal intensity and marked hyperintensity on T2-weighted images and after gadolinium administration (Fig. 42d,e). Intratumor fat overgrowth, low T2-signal vascular channels and phleboliths can also be found (Fig. 42e,f). Circumscribed masses can be resected on arthroscopy, whereas diffuse lesions need open surgery (Sheldon et al. 2005).

Figure 42. a–f. Synovial hemangioma. a,b Transverse 12–5 MHz US images obtained over the suprapatellar region a without and b with compression with the probe demonstrate a fluid-filled suprapatellar recess (arrows) containing slow-flowing swirling echoes that change their echogenicity depending on the pressure exerted over them. F, femur. c Color Doppler imaging displays venous flow filling the fluid-filled cavities contained in the recess. d Sagittal T2-weighted and e fat-suppressed postcontrast T1-weighted MR imaging correlation show a markedly hyperintense lesion (arrow) containing linear low-signal structures (arrowhead) representing fibrofatty septations and intratumor vascular channels. f Lateral radiograph reveals fullness of the suprapatellar recess and scattered phleboliths (arrowheads), a feature of value for the diagnosis of synovial hemangioma.