Radiographic Evaluation of Arthritis: - PDF Document

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  1. Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at REVIEWS AND COMMENTARY ? REVIEW FOR RESIDENTS Radiographic Evaluation of Arthritis: Inflammatory Conditions1 JonA.Jacobson,MD GandikotaGirish,MD YebinJiang,MD,PhD DonaldResnick,MD In the presence of joint space narrowing, it is important to differentiate inflammatory from degenerative conditions. Joint inflammation is characterized by bone erosions, os- teopenia, soft-tissue swelling, and uniform joint space loss. Inflammation of a single joint should raise concern for infection. Multiple joint inflammation in a proximal distri- bution in the hands or feet without bone proliferation suggests rheumatoid arthritis. Multiple joint inflammation in a distal distribution in the hands or feet with bone proliferation suggests a seronegative spondyloarthropa- thy, such as psoriatic arthritis, reactive arthritis, or anky- losing spondylitis. ? RSNA, 2008 1From the Department of Radiology, University of Michi- gan Medical Center, 1500 E Medical Center Dr, TC- 2910L, Ann Arbor, MI 48109-0326 (J.A.J., G.G., Y.J.); and Department of Radiology, University of California San Diego VA Hospital, La Jolla, Calif (D.R.). Received Decem- ber 11, 2006; revision requested February 7, 2007; revi- sion received July 25; accepted August 20; final version accepted November 1; final review by J.A.J. Address correspondence to J.A.J. (e-mail: ? RSNA, 2008 378 Radiology: Volume 248: Number 2—August 2008

  2. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal R cal assessment is differentiating inflam- matory arthritis from a degenerative process, because the treatment options are quite different. Identification of an inflammatory joint due to infection often requires diagnostic aspiration followed by administration of antibiotics and pos- sible surgical drainage and lavage. With regard to systemic arthritides, with early diagnosis there are several types of medications used to control joint in- flammation and even prevent or reduce subsequent joint destruction. The treat- ment options for a degenerative process include medication, joint injection, and, later, joint replacement. The objective of this review is to present a simplified approach to radio- graphic evaluation of arthritis (Fig 1). This is presented as an algorithm that uses joint space narrowing of the distal extremities as a starting point. While it is acknowledged that it is nearly impos- sible to include all types of arthritis in one simple algorithm, and that there are always exceptions and variations, this approach will encompass the most com- mon features of the frequently seen ar- thritides and can be viewed as a frame- work for radiographic evaluation. This algorithm does not include substantial detail of each topic but rather focuses on radiographic findings that, with the use of this algorithm, lead to a final and usually correct diagnosis. The first criti- cal step in the algorithm is to determine if joint space narrowing detected with radiography is related to an inflamma- tory or a degenerative condition. features of a degenerative joint, as well. In addition to lack of the findings de- scribed for inflammatory joint disease, degenerative findings include osteo- phyte formation and bone sclerosis (Fig 4). Although underlying cartilage damage is presumed, joint space nar- rowing does not involve the joint uni- formly, as is seen with inflammatory joint disease, and osteophytes are typi- cally present. As the joint space nar- rows, the osteophytes become larger, sclerosis increases, and subchondral cysts—or geodes—may be seen. If de- generative joint disease involves a syno- vial articulation, the term osteoarthro- sis or osteoarthritis is appropriate. adiography is typically the first imaging study in evaluation for ar- thritis. On radiographs, one criti- Inflammatory versus Degenerative Joint Disease There exist essential radiographic find- ings that are common to inflammatory arthritis due to any cause. The hallmark of joint inflammation is erosion of bone. This will initially appear as a focal dis- continuity of the thin, white, subchon- dral bone plate (Fig 2). Normally, this subchondral bone plate can be seen even in cases of severe osteopenia, whereas its discontinuity indicates ero- sion. Although it is true that periarticu- lar osteopenia and focal subchondral os- teopenia can appear prior to a true bone erosion, it is the presence of bone erosion that indicates definite joint in- flammation. As the bone erosion en- larges, osseous destruction extends into the trabeculae within the medullary space. One important feature of inflamma- tory arthritis relates to the concept of a marginal bone erosion. This term is given to bone erosion that is located at the margins of an inflamed synovial joint. This specific location represents that portion of the joint that is intraar- ticular but not covered by hyaline carti- lage; therefore, early joint inflammation will produce marginal erosions prior to erosions of the subchondral bone plate beneath the articular surface (Fig 3). When looking for bone erosions, multi- ple views of a joint are essential to pro- file the various bone surfaces. A second important characteristic of an inflammatory joint process is uni- form joint space narrowing. This occurs because destruction of the articular car- tilage is uniform throughout the intraar- ticular space. A third finding of inflam- matory joint disease is soft-tissue swell- ing. There are essential radiographic Inflammatory Arthritis Septic Arthritis Once joint space narrowing and fea- tures of inflammatory arthritis are iden- tified, the next step in the algorithm is to determine how many joints are in- volved. Multiple joints may be involved in as many as 20% of cases (1). If joint inflammation is limited to a single joint, infection must first be carefully ex- cluded (Fig 1). The cause of septic ar- thritis is usually related to hematoge- nous seeding owing to staphylococcal or streptococcal microorganisms. The radiographic features of a sep- tic joint encompass those of any inflam- matory arthritis—namely, periarticular osteopenia, uniform joint space narrow- ing, soft-tissue swelling, and bone ero- sions (Fig 5). Not all findings may be present simultaneously, and, acutely, bone erosions may not be evident. Fur- thermore, the joint space may be ini- tially widened owing to the effusion. Joint space widening may also be seen with more indolent and atypical infec- tions, such as those related to tubercu- losis and fungal agents; but, again, other inflammatory changes are typically present Essentials ? It is important to differentiate in- flammatory from degenerative causes of joint space narrowing. ? Inflammatory arthritis is charac- terized by bone erosions, osteope- nia, soft-tissue swelling, and uni- form joint space narrowing. ? With monoarticular joint inflam- mation, it is important to exclude infection. ? Inflammation that involves multi- ple joints in a proximal distribu- tion of the hands or feet without bone proliferation suggests rheu- matoid arthritis. ? Inflammation that involves multi- ples joints in a distal distribution of the hands or feet with bone proliferation suggests a seronega- tive spondyloarthropathy. Published online 10.1148/radiol.2482062110 Radiology 2008; 248:378–389 Authors stated no financial relationship to disclose. 379 Radiology: Volume 248: Number 2—August 2008

  3. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal to identify cortical discontinuity. If a round subchondral lucency does not interrupt the bone surface, possibili- ties include a subchondral cyst or an erosion viewed en face. In the feet, target sites of rheuma- toid arthritis include the metatarsopha- langeal, proximal interphalangeal (in- cluding the first interphalangeal), and intertarsal joints, and such involvement (Fig 6). The Phemister triad describes these findings classically seen in tuber- culous arthritis: juxtaarticular osteope- nia, peripheral bone erosions, and grad- ual narrowing of the joint space (2). Rheumatoid Arthritis If joint space narrowing and other ra- diographic findings of inflammatory ar- thritis involve multiple joints, a systemic arthritis must be considered. The next step in the algorithm is evaluation of the hands and feet. Proximal distribution at these sites and lack of bone prolifera- tion suggest the diagnosis of rheumatoid arthritis. Rheumatoid arthritis is most common in women aged 30–60 years. Serologic markers such as rheumatoid factor and antibodies to cyclic citrulli- nated peptide are important indicators of rheumatoid arthritis (3,4). The radiographic features of rheu- matoid arthritis are those of joint in- flammation and include periarticular osteopenia, uniform joint space loss, bone erosions, and soft-tissue swelling (Fig 7). Because of the chronic nature of the inflammation, additional findings such as joint subluxation and subchon- dral cysts may also be evident. Although the radiographic findings are not spe- cific for one condition, the proximal dis- tribution of joint involvement in the hands and feet and the lack of bone proliferation suggest rheumatoid arthri- tis. In the hands, target sites of rheu- matoid arthritis include the metacar- pophalangeal, proximal interphalan- geal, midcarpal, radiocarpal, and dis- tal radioulnar joints, with predilection for the ulnar styloid process (Figs 7, 8). Involvement is usually bilateral and fairly symmetric, although isolated carpal joint involvement may occur. Ulnar deviation occurs at the metacar- pophalangeal joints. Hyperextension at the proximal interphalangeal joints with flexion at the distal interphalan- geal joints results in a swan neck de- formity, while flexion at the proximal interphalangeal joint and hyperexten- sion at the distal interphalangeal joint results in a boutonnie `re deformity. It is important to profile the bone corti- ces with multiple radiographic views Figure 1 Flowchartshowsapproachtoradiographicevaluationofarthritis.Algorithmbeginswithjoint Figure1: spacenarrowingandinitiallyusesdifferentiationbetweeninflammatoryanddegenerativefindingstoreachthe finaldiagnosis. Figure 2 (a,b)Posteroanteriorwristradiographsshowdiscontinuityofbonecortexrepresentingerosion Figure2: (arrow)withdevelopmentofosteopenia.Noteprogressionofdiseasefromatob. 380 Radiology: Volume 248: Number 2—August 2008

  4. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal bursae such as the retrocalcaneal bursa. Loss of the normal radiolucent triangle between the posterosuperior margin of the calcaneus and the adjacent Achilles tendon suggests the presence of bursal fluid, with subjacent calcaneal erosions indicating inflammation (Fig 11). Other peripheral joints may also be involved in rheumatoid arthritis, with similar findings. Joint involvement in- cludes the knees (Fig 12), the hips (Fig 13), and the sacroiliac and glenohu- meral joints, with involvement of the last of these often associated with a high-riding humeral head related to a large rotator cuff tear. Spinal involve- ment is also possible. At the C1-C2 ar- ticulation, the odontoid process may be eroded, and the anterior atlantodens in- terval may be abnormally widened (?3 mm in adults), especially with neck flex- ion (Fig 14) (5). is commonly bilateral and nearly sym- metric in distribution (Fig 9). It is im- portant to closely evaluate the lateral aspect of the fifth metatarsal head, be- cause this is often the first site of a bone erosion in the foot and, at times, such involvement occurs prior to hand or wrist involvement (Fig 10). Because rheumatoid arthritis is a disease that affects synovium diffusely, other sites of involvement include tendon sheaths and Figure 3 (a)Illustrationofsynovialjointshowsjointfluid(f)andarticularcartilage(c).(b)Illustrationand(c)radiographshowinflammatoryarthritis,synovitis,and Figure3: pannus(P)causingcartilagedestruction.Marginalerosions(arrows)areseenwheresubchondralboneplateisexposedtointraarticularsynovitis.f?Fluid. Figure 4 Figure 5 Septic arthritis. Figure 5: (a)Posteroanteriorand (b)obliqueradiographsshowjoint spacenarrowing(arrows),os- teopenia,soft-tissueswelling,and aboneerosion(arrowhead). Osteoarthritis. Posteroanterior radio- Figure 4: graphshowsinterphalangealjointspacenarrow- ing,subchondralsclerosis,andosteophyteforma- tion(arrows). 381 Radiology: Volume 248: Number 2—August 2008

  5. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 6 Figure 7 Septicarthritis(tuberculosis).Mor- Figure6: tiseradiographofankleshowserosions(arrows) oftalusanddistaltibiawithosteopenia.Joint spacewideningisduetodiffusesynovitis. Figure 8 Rheumatoidarthritis.(a)Posteroanteriorand(b)obliquehandradiographsshowjointspace Figure7: narrowing,boneerosions,andosteopeniaofthemetacarpophalangeal,distalradioulnar,radiocarpal,and midcarpaljoints(arrows).Notesubluxationofproximalinterphalangealjoints. Figure 9 Rheumatoid arthritis. Posteroanterior Figure 8: wristradiographshowsosteopeniaandjointspace narrowingofthedistalradioulnar,radiocarpal,and midcarpaljointswitherosionsofthescaphoid (arrow)andtheulnarstyloidprocess(arrowhead). Seronegative Spondyloarthropathies Returningtotheproposedalgorithm,ifone observes joint space narrowing, signs of in- flammation,multiplejointinvolvement,and distal involvement in the hands and feet withaddedfeaturesofboneproliferation,a seronegative spondyloarthropathy is sug- gested. This category includes psoriatic ar- thritis, reactive arthritis, and ankylosing Rheumatoidarthritis.(a)Posteroanteriorradiographofrightfootand(b)obliqueradiographof Figure9: leftfootshowjointspacenarrowingandboneerosionsofbothmetatarsophalangealjointsandseveralinter- phalangealjoints(arrows).Notemostextensiveinvolvementoffifthmetatarsophalangealandfirstinterpha- langealjoints. 382 Radiology: Volume 248: Number 2—August 2008

  6. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 10 Figure 12 Rheumatoid arthri- Figure 10: tis.(a,b)Posteroanteriorradio- graphsintwopatientsshowsmall boneerosionaboutthefifthmeta- carpophalangealjointwithos- teopeniaina(arrow)andmore extensiveinvolvementinb(ar- rows)withalterationsofthefifth metatarsalheadandproximal phalanx. Rheumatoid arthritis. Anteroposte- Figure 12: riorkneeradiographshowsdiffuseanduniform jointspaceloss(arrows)withosteopenia. Figure 13 Figure 11 Rheumatoidarthritis.Lateralradio- Figure11: graphofcalcaneusshowsboneerosion(arrow) relatedtoinflammationoftheretrocalcanealbursa. spondylitis. Differentiation among these disorders largely relies on the distribution of radiographic abnormalities and clinical information.Inaddition,otherfindingsthat help differentiate the seronegative spondy- loarthropathies from rheumatoid arthritis are that cartilaginous joints and entheses are involved to a greater extent, the latter representing the osseous attachment sites of ligaments and tendons. Entheseal in- volvement leads to increased density and irregular bone proliferation. Psoriatic arthritis.—The cause of psoriaticarthritisisconsideredtobeacom- Rheumatoidarthritis.Anteroposteriorpelvisradiographshowsbilateralinvolvementofhips, Figure13: withuniformdiffusejointspacenarrowing,boneerosions,osteopenia,andacetabularprotrusion(arrows). Notebonesclerosisrelatedtoinvolvementofsacroiliacjoints(arrowheads). thoseoftheotherseronegativespondyloar- thropathies, are signs of inflammatory ar- thritis combined with bone proliferation, periostitis, enthesitis, and a distal joint dis- tribution in the extremities (Fig 15). In the hands, wrists, and feet, a dis- tal distribution is characteristic. Find- ings may be bilateral or unilateral and bination of environmental and hereditary factors, with as many as to 60% of patients beingHLA-B27positive(6).Approximately 10%–15% of patients with skin manifesta- tions of psoriasis will develop psoriatic ar- thritis (6). Usually such manifestations will precede the development of arthritis. The hallmarks of psoriatic arthritis, similar to 383 Radiology: Volume 248: Number 2—August 2008

  7. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 14 Figure 15 Psoriatic arthritis. Posteroanterior Figure 15: fingerradiographshowsmarginalboneerosions withadjacentirregularboneproliferation(arrows). Rheumatoidarthritis.(a)Lateralcervicalspineradiographshowserosionsofdens(straight Figure14: arrows)withnarrowingoffacetjoints(curvedarrow).(b)Lateralflexionradiographshowswideningofatlan- todensinterval(arrowheads). Figure 16 Figure 17 Psoriaticarthritis.(a)Obliquewristradiographshowsirregularboneproliferationandperiosti- Figure17: tisaboutradialandulnaraspectsofthewrist(arrows),witherosionoftheulnarstyloidprocess.(b)Contralat- eralwristradiographshowsboneerosionandirregularperiostitisofthescaphoid,withmoredistalperiostitis involvingthemetacarpalbase(arrows). Psoriatic arthritis. Posteroanterior Figure 16: fingerradiographshowsnarrowingofdistalinter- phalangealjoint.Noteboneproliferationandperi- ostitisthroughoutphalanges(arrows),which appearthickerthaninFigure15,withpartialincor- porationofnewboneintothecortex.Thereissoft- tissueswellingofentiredigit. joint, characterized as a “fuzzy” appear- ance or “whiskering” (Fig 17). Periostitis may take several forms: It may appear as a thin periosteal layer of new bone adjacent to the cortex, a thick irregular layer, or irregular thick- ening of the cortex itself (Fig 17). It may symmetric or asymmetric. Involvement of several joints in a single digit, with soft-tissue swelling, produces what ap- pears clinically as a “sausage digit” (Fig 16). The bone proliferation produces an irregular and indistinct appearance to the marginal bone about the involved be difficult to define where periostitis ends and bone erosion begins, as both may produce marked irregularity of the 384 Radiology: Volume 248: Number 2—August 2008

  8. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 18 Figure 19 Figure 20 Psoriaticarthritis.Lateralknee Figure18: radiographshowsirregularthickboneprolifera- tionandperiostitisofposterioraspectofthetibia (arrows). Psoriatic arthritis. Anteroposterior Figure 19: footradiographshowsinflammatoryanddestruc- tivechangesoffifthmetatarsophalangealand severalinterphalangealjoints(straightarrows). Notepencil-and-cupdeformity(arrowhead)and interphalangealjointfusion(curvedarrow). Psoriatic arthritis. Anteroposterior Figure 20: radiographshowsincreaseddensityandbone proliferationofdistalphalanx(ivoryphalanx)of thefirstdigit(arrows),withsoft-tissueswelling. Figure 21 Psoriaticarthritis.(a)Anteroposteriorsacrumradiographshowsboneerosionsandnarrowingofsacroiliacjointswithpartialfusion(arrows).(b)Antero- Figure21: posteriorlumbarspineradiographshowscomma-shapedparavertebralossifications(arrows). end of the joint forming a cup and the other a pencil that projects into this cup (Fig 19). This appearance is not specific for psoriatic arthritis or any of the sero- negative spondyloarthropathies, but it is most commonly seen in these condi- tions. One characteristic feature of pso- riatic arthritis in the foot is the “ivory phalanx,” which classically involves the distal phalanges (especially in the first digit) with sclerosis, enthesitis, periosti- tis, and soft-tissue swelling (Fig 20). Joint subluxation may also be present. Psoriatic arthritis may also involve the axial skeleton, a finding that occurs in 20%–40% of persons with peripheral osseous surface (Fig 18). It is important to note that periostitis may occur in an area without bone erosions; one such site is the radial aspect of the wrist ex- tending into the first metacarpal bone. Because of the degree of bone destruc- tion, an involved joint may take the ap- pearance of a “pencil and cup,” with one 385 Radiology: Volume 248: Number 2—August 2008

  9. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 22 Figure 23 quently) is a sterile inflammatory ar- thritis that follows an infection at a different site, commonly enteric or urogenital (6,7). An association with urethritis and conjunctivitis, as well as seropositivity for the HLA-B27 anti- gen, has been described (6). Reactive arthritis is most common in young men aged 25–35 years. The radio- graphic features of reactive arthritis are similar to those of psoriatic arthri- tis and include joint inflammation, bone proliferation, periostitis, and en- thesitis. The features allowing differ- entiation between reactive arthritis and psoriatic arthritis relate to clinical history, patient sex and age, and dis- tribution of joint involvement. Similar to psoriatic arthritis, the ra- diographic features seen in the hands, wrists, and feet in reactive arthritis in- clude joint inflammation, bone prolifer- ation, periostitis, and enthesitis, with a distribution that is unilateral or bilateral and symmetric or asymmetric (Fig 22); lower-extremity involvement is more common than upper-extremity involve- ment (6). Sausage digit and pencil-and- cup deformities may also occur (Fig 23). In the feet, an ivory phalanx may be seen (Fig 24). Axial involvement may also occur, leading to bilateral symmetric or asym- metric sacroiliitis. Large, comma- shaped, paravertebral ossification may also be seen. Other peripheral joints are less commonly involved. Ankylosing spondylitis.—Ankylos- ing spondylitis is an idiopathic inflam- matory arthritis, although a genetic contribution is noted as 96% of pa- tients are HLA-B27 positive (8). Men are affected three times more fre- quently than women, with the age of onset typically between 20 and 40 years (8). This is a disease that more commonly involves the axial skeleton, although peripheral joints may also be affected. Spine involvement is charac- terized by osteitis, syndesmophyte formation, facet inflammation, and eventual facet joint and vertebral body fusion. Sacroiliac joint disease is bilat- eral and symmetric. Other peripheral joints, such as the hips and glenohu- meral joints, may be involved. The ra- Reactivearthritis.Lateralradio- Figure22: graphofcalcaneusshowsbonesclerosisand irregularinflammatoryenthesopathy(arrow). Figure 24 Reactive arthritis. Posteroanterior Figure 23: fingerradiographshowsinvolvementofmultiple jointswithjointspacenarrowing,boneerosions, andboneproliferation(arrows). bone ankylosis (Fig 21a). Sacroiliac joint involvement in psoriatic arthritis is usually bilateral, either symmetric or asymmetric in distribution. The thora- columbar spine may show large comma- shaped paravertebral ossifications (Fig 21b); spondylitis is uncommon in the absence of sacroiliitis, however (6). The facet joints are relatively spared, and there is absence of vertebral body “squaring.” Other sites of joint involvement in psoriatic arthritis include the knees (Fig 18), elbows, ankles, and joints about the shoulders. Reactive arthritis.—Reactive ar- thritis (also called Reiter syndrome, which is currently being used less fre- Reactive arthritis. Anteroposterior Figure 24: radiographofgreattoeshowsbonesclerosis, marginalboneerosions,andboneproliferation (arrows)aboutinterphalangealjointanddistal phalanx,withsoft-tissueswelling. articular disease (6). The sacroiliac joints will show signs of inflammation, with an indistinct subchondral bone plate or os- seous erosions, joint space irregularity and mild widening, and eventual joint space narrowing and intraarticular 386 Radiology: Volume 248: Number 2—August 2008

  10. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 25 diographic appearance of spine and sacroiliac abnormalities in ankylosing spondylitis is identical to that found with inflammatory bowel diseases such as ulcerative colitis and Crohn disease. Sacroiliac involvement is typically bilateral and symmetric, and it usually precedes spinal involvement. Initially, there is indistinctness and discontinu- ity of the thin white subchondral bone plate about the sacroiliac joints. These changes can progress to gross bone erosions (Fig 25). Early erosions of the subchondral bone are often best seen in the inferior aspect of the joints because they are in profile in this re- gion on an anteroposterior pelvis ra- diograph. Along with the bone ero- sions, the adjacent bone is often scle- rotic and joint space narrowing and bone fusion eventually occur (Fig 26). Because the sacroiliac joints may be difficult to interpret on radiographs, magnetic resonance imaging can be useful in the diagnosis of sacroiliitis by showing joint fluid and marrow edema when radiographs are normal or equivocal. When radiographs are ab- normal, computed tomography may be used to differentiate bone erosions from osteophytes. The differential di- agnosis of bilateral sacroiliac joint erosions includes inflammatory bowel disease (Fig 27) and hyperparathy- roidism (Fig 28); however, in hyper- parathyroidism, sacroiliac joint space widening is more dramatic, and typi- cally there are other clinical and radio- graphic features of hyperparathyroid- ism. Spine involvement in ankylosing spondylitis is often centered at the thoracolumbar or lumbosacral junc- tion, and coned-down lateral radio- graphs at these sites optimally depict subtle and early abnormalities. Early radiographic findings are erosions at the anterior margins of the vertebral body at the discovertebral junction. These focal areas of osteitis become increasingly sclerotic, a finding termed the “shiny corner sign” (Fig 29). More extensive discovertebral erosions may also occur. Associated bone prolifera- tion leads to a “squared” appearance Ankylosing spon- Figure 25: dylitis.Anteroposteriorpelvis radiographshowsbilateralsym- metricboneerosions,sclerosis, andwideningofsacroiliacjoints (arrows). Figure 26 Ankylosing spon- Figure 26: dylitis.Anteroposteriorradio- graphofsacrumshowsfusionof sacroiliacjoints(arrows). Figure 27 Inflammatory bowel Figure 27: disease.Anteroposteriorradio- graphofsacrumshowsbilateral andsymmetricboneerosions, bonesclerosis,andwideningof sacroiliacjoints(arrows). of the vertebral body. Thin and slen- der syndesmophytes are generally ev- ident, representing ossification of the outer layer of the annulus fibrosis (Fig 30). The differential diagnosis for bone production at the vertebral mar- gins includes diffuse idiopathic ske- letal hyperostosis, or DISH, although 387 Radiology: Volume 248: Number 2—August 2008

  11. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 28 Figure 29 Hyperparathyroidism.Anteroposteriorradiographofsacrumshowsbilateralandsymmetric Figure28: bonesclerosisandirregularityofsacroiliacjoints(arrow).Notemarkedwideningofsacroiliacjointsandrenal dialysiscatheter. Ankylosing spondylitis. Lateral Figure 29: lumbarspineradiographshowssclerosisatante- rioraspectoftheendplate(shinycornersign) (arrow),withsquaringofanteriormarginofverte- bralbody. Figure 30 Figure 31 produces a dense radiopaque line, desig- nated the “dagger sign,” on anteroposte- rior radiographs of the lumbar spine (Fig 32). The combination of the fused facets and ossification of the interspi- nous ligaments produces the “trolley- track sign” (Fig 33). Disk calcification may also occur, possibly due to relative immobilization of the vertebral column. Other peripheral joints can be in- volved in ankylosing spondylitis. Hip in- volvement is usually bilateral in distri- bution (Fig 34). Uniform joint space loss in these joints is combined with acetab- ular protrusion, subchondral cysts, and a rim of osteophytes about the femoral neck. Bone erosions and remodeling in the lateral proximal aspect of the hu- merus produce a “hatchet” appearance. Ankylosing spondylitis. Lateral Figure 30: lumbarspineradiographshowsanteriorbridging syndesmophytes(arrows)andfacetjointfusion (arrowheads). Ankylosing spondylitis. Anteropos- Figure 31: teriorlumbarspineradiographshowsbridging syndesmophytes(bamboospine)(arrows). Conclusion Once joint space narrowing is recog- nized, the presence of bone erosions suggests an inflammatory arthritis, while osteophytes indicate a degenera- tive arthritis. The joint distribution and this latter condition more commonly reveals a flowing and undulating ap- pearance. As the syndesmophytes thicken and become continuous, the term bamboo spine is used to describe the appearance on anteroposterior lumbar spine radio- graphs (Fig 31). Facet joint inflammation leads to indistinctness and narrowing of the involved joint, and bone fusion of the joints appears later (Fig 30). Ossification of the posterior interspinous ligaments 388 Radiology: Volume 248: Number 2—August 2008

  12. REVIEWFORRESIDENTS:RadiographicEvaluationofArthritis Jacobsonetal Figure 33 the presence of bone proliferation allow distinction between septic arthritis, rheu- matoid arthritis, and the seronegative spondyloarthropathies. If inflammation involves a single joint, one must care- fully exclude infection. If inflammatory arthritis is diffuse and involves the prox- imal joints of the hands and feet without bone proliferation, rheumatoid arthritis is most likely. Distal joint involvement with bone proliferation suggests the presence of one of the seronegative spondyloarthropathies. Figure 32 References 1. Learch TJ. Imaging of infectious arthritis. Se- min Musculoskelet Radiol 2003;7:137–142. 2. Rutten MJ, van den Berg JC, van den Hoogen FH, Lemmens JA. Nontuberculous mycobac- terial bursitis and arthritis of the shoulder. Skeletal Radiol 1998;27:33–35. 3. Machold KP, Nell V, Stamm T, Aletaha D, Smolen JS. Early rheumatoid arthritis. Curr Opin Rheumatol 2006;18:282–288. 4. Tehranzadeh J, Ashikyan O, Dascalos J. Mag- netic resonance imaging in early detection of rheumatoid arthritis. Semin Musculoskelet Radiol 2003;7:79–94. 5. Monsey RD. Rheumatoid arthritis of the cer- vical spine. J Am Acad Orthop Surg 1997;5: 240–248. 6. Klecker RJ, Weissman BN. Imaging features of psoriatic arthritis and Reiter’s syndrome. Semin Musculoskelet Radiol 2003;7:115–126. Ankylosing spondylitis. Anteropos- Ankylosing spondylitis. Anteropos- Figure 32: teriorlumbarspineradiographshowsossification oftheinterspinousligament(daggersign) (arrows). Figure 33: teriorlumbarspineradiographshowsossification ofinterspinousligamentandfacetjointfusion (trolley-tracksign)(arrows). 7. Lu DW, Katz KA. Declining use of the eponym “Reiter’s syndrome” in the medical literature, 1998–2003. J Am Acad Dermatol 2005;53: 720–723. 8. Vinson EN, Major NM. MR imaging of anky- losing spondylitis. Semin Musculoskelet Ra- diol 2003;7:103–113. Figure 34 Ankylosing spon- Figure 34: dylitis.Anteroposteriorpelvis radiographshowsbilateraldiffuse jointspacenarrowingandbone erosionsofeachhipjoint(arrow- heads),withsacroiliacjointfusion (arrows). 389 Radiology: Volume 248: Number 2—August 2008