Arthritis

Osteoarthritis of Axial Skeleton

Anterior and lateral vertebral body osteophyte formation (spondylosis deformans) Facet joint narrowing and hypertrophy Uncovertebral (apophyseal) joint osteophytes Diagnosis made on radiographs Severity of canal/foraminal stenosis evaluated on MR Oblique sagittal MR images useful to evaluate foraminal stenosis Baastrup disease Shaggy bony production at spinous processes Sacroiliac (SI) joints: Generally 2 appearances Sclerosis along cortex of synovial portion Marginal osteophytes

Gout

Best clue: Dense tophi, juxtaarticular erosions with "overhanging edges" Location: 1st metatarsophalangeal (MTP) most frequent site 50% of patients have this as initial site 80-90% involve this site at some point in disease Radiographs usually normal 1st 7-10 years of disease Normal bone density maintained Cartilage damage occurs only late in disease Erosions are well circumscribed + sclerotic margins Erosions may have "overhanging edge" Tophi: Dense nodules MR: Synovial pannus: Thickened, low T1 & T2 signal with peripheral enhancement Adjacent soft tissue &/or bone marrow edema: Low signal T1, high signal T2 Gouty tophus has constant T1WI MR appearance: Intermediate homogeneous signal intensity Gouty tophus appears variably on T2 & other fluid sensitive sequences: Mixed low and high signal Gouty tophus enhances with contrast

Rheumatoid Arthritis of Hip

Bilaterally symmetric uniform cartilage narrowing Protrusio Osteoporosis Insufficiency fractures Femoral neck: Medial basicervical and midcervical Subtrochanteric region in patients taking bisphosphonates for osteoporosis Visualized as linear sclerosis adjacent to "bump" on lateral cortex in subtrochanteric region MR: Osteonecrosis (ON) 2° to steroid use MR T1WI: Soft tissue complications Ruptured and retracted gluteus tendon surrounded by high signal fat Fatty atrophy of gluteus muscle if tendon chronically torn MR fluid-sensitive sequences High signal marrow edema Thick low signal synovial thickening and pannus surrounded by high signal effusion Decompressed effusion shows high fluid signal in iliopsoas bursa With effusion, labral tear and cartilage thinning may be directly seen High signal tenosynovitis and tendon rupture

Psoriatic Arthritis

Diagnosis most frequently made on radiographs Peripheral arthropathy in hands/feet Row pattern Interphalangeal (IP) joints predominate Erosive; may progress to arthritis mutilans "Pencil-in-cup" deformities, "telescoping" fingers Ray pattern Productive, with enthesopathy, periostitis Soft tissue swelling, "sausage digit" Sacroiliitis: 35% of patients Usually begins asymmetrically, but bilaterally At any time in course, may appear symmetric Spondylitis: 30% of patients Bulky paravertebral ossifications More prominently seen on AP than lateral view Asymmetric with skipped levels Ankylosis is common feature Normal bone density Bilaterality and symmetry less frequent than in rheumatoid arthritis In early disease, MR shows abnormalities, though usually nonspecific Edema, synovitis in peripheral joints nonspecific Marrow edema Enthesopathy, periostitis

Rheumatoid Arthritis of Wrist and Hand

Erosions Earliest osseous pattern is loss of cortical distinctness, followed by dot-dash pattern of cortical loss Marginal erosions tend to occur early in portion of bone which is within capsule but not covered by cartilage Direct subchondral erosions Late aggressive disease: "Pencil-in-cup" appearance in phalanges Ulnar styloid may show "capping": Only site of productive change in RA Malalignment due to ligament/tendon disruption MR: Pannus: Thick, nodular low signal synovium outlined by effusion Marrow edema: Subchondral high signal Thickened, avidly enhancing synovium outlines low signal effusion and erosions Tenosynovitis may be earliest soft tissue abnormality, though nonspecific US: Excellent for early effusions in small joints Tenosynovitis and tendon rupture seen directly

Hydroxyapatite Deposition Disease

Homogeneous calcification located at site of tendon or bursa Generally monoarticular Shoulder most frequent (69%) External rotators of hip next most common Spine, elbow, knee, wrist, ankle Character of calcification changes over time Inhomogeneous, faintly seen initially Becomes more well defined and dense Eventually may disappear Rare cortical erosions "Tail" of calcifications extends from eroded surface MR: Globular focus of low signal on all sequences May have hyperintensity in adjacent soft tissues Bone marrow edema due to HA deposition in adjacent bone Gradient-echo imaging: "Blooming" of deposit Fusiform enlargement of affected tendon US: Hyperechoic foci within tendon showing other signs of tendinopathy

Pyrophosphate Arthropathy

Location is distinctive Chondrocalcinosis: Knee > symphysis pubis > wrist > hip (acetabular labrum) > shoulder > elbow Arthropathy: Knee > wrist > hand > shoulder, hip Knee: Patellofemoral shows isolated or greater involvement than medial or lateral compartments Wrist: Radiocarpal + 2nd and 3rd MCP Spine: Particularly at dens ("crowned dens") Radiographic appearance Chondrocalcinosis (not invariably present) Early arthropathy may be mixed or even purely erosive (1/8 will show erosion) Hook-like or "drooping" osteophytes at metacarpal heads are distinctive Subchondral cysts are common Scapholunate advanced collapse (SLAC) wrist deformity CT: Calcific densities may be more conspicuous than on radiograph or MR MR of chondrocalcinosis May not be conspicuous Meniscus may appear enlarged Chondrocalcinosis may be low or high signal on either T1WI or fluid-sensitive sequences Calcifications surrounding dens are low signal; can suggest pannus of rheumatoid arthritis

Ankylosing Spondylitis

MR shows earliest changes High signal enthesopathy may be earliest sign Romanus lesions: Inflammatory change (high signal) at vertebral body corners CT most useful in evaluating for subtle transverse fracture following trauma Radiographs show more advanced disease Osteopenia: Diffuse, especially with fusion Sacroiliitis: Usually bilaterally symmetric Osteitis at anterior corners of vertebral bodies Eventual long column fusion of bodies and facets "Bamboo spine" with "dagger" sign Erosions and eventual fusion: Sternoclavicular, costochondral, costovertebral, pubis Peripheral disease: Usually hip and shoulder

Osteoarthritis of Hip

Normal bone density, narrowed joint space Osseous productive change: Osteophytosis, femoral neck (calcar and lateral) buttressing Subchondral cyst formation (Egger cyst in acetabulum) Egger cyst may be isolated; may mimic tumor Subluxation femoral head: 80% superolateral, 20% medial (protrusio) Often associated with underlying FAI in young adults MR: Bone marrow edema Volume of edema correlates with severity of hip pain, severity of radiographic OA, and number of microfractures in subchondral bone Cartilage defects are seen if outlined by fluid Cartilage in hip is thin and capsule is tight, making cartilage more difficult to evaluate than in knee Labral tear or degeneration

OPLL

Ossification posterior longitudinal ligament (OPLL) Imaging Radiograph: Most frequent at 4th and 5th cervical levels May involve thoracic or lumbar spine (20%) May be seen at C1 level, posterior to dens CT to fully evaluate extent of ossification In patient with clinical signs of myelopathy, MR to evaluate spinal cord 44% of patients with OPLL have concomitant anterior hyperostosis If significant concomitant DISH and OPLL, may develop long column fusion

Rheumatoid Arthritis of Shoulder and Elbow

Purely erosive arthropathy Uniform cartilage narrowing Osteoporosis Glenohumeral joint Largest and earliest erosions at margin Eventually, erosions uniformly involve humeral head and glenoid Subchondral cysts may be large, but underlying osteoporosis may mask their size Elevation of humeral head due to rotator cuff tear Hatchet-like mechanical erosion at medial surgical neck of humerus Swelling of joint may be prominent due to decompression of synovial fluid through RCT into subacromial/subdeltoid bursa Elbow joint Effusion (elevated anterior and posterior fat pads) Olecranon bursitis common in RA Erosions uniform throughout joint MR in RA Thickened, low signal, avidly enhancing pannus and synovium Low signal "rice bodies" within effusion Subchondral marrow edema Rotator cuff tear, partial or complete Decompression of synovial effusion well seen

Rheumatoid Arthritis of Axial Skeleton

Purely erosive disease, most frequently involving C1-C2 articulation Radiographic findings Dens erosions Atlantoaxial subluxation Atlantoaxial impaction: May be unilateral or bilateral Subaxial subluxation Osteoporosis Radiographs must include lateral flexion-extension CT: Additive to radiographs Extent of erosive disease more apparent AA impaction well shown MR: Additive to radiographs Pannus, usually around odontoid, distinctly seen Cord compression and damage directly visualized

Rheumatoid Arthritis of Ankle and Foot

Radiograph: Effusions, especially tibiotalar and MTP Pre-Achilles bursitis Location of earliest erosions in foot is MTPs, particularly 5th Erosions posterior calcaneal tubercle Osteoporosis, increasing risk of insufficiency fracture (seen as linear sclerosis) MR T1WI: Low signal erosions, subchondral cysts Linear low signal insufficiency fractures MR fluid-sensitive sequences Thick low signal synovium bathed in high signal synovial fluid High signal marrow edema and erosions High signal bursitis (especially pre-Achilles) High signal tenosynovitis and abnormal morphology partial tendon tears Avid enhancement of synovium, with adjacent low signal fluid US: Confirm fluid collections and effusions Direct visualization of tendon ruptures

Osteoarthritis of Knee

Radiographic findings for OA Joint space narrowing, commonly medial Osteophytosis, marginal and subchondral Subchondral cysts Malalignment, varus > valgus MR findings predictive of early OA Cartilage defects or thinning Bone marrow edema: Thought to correlate with pain in many individuals Meniscal tears or degeneration Cruciate or medial/lateral supporting structure insufficiency High correlation of meniscal tears with adjacent cartilage damage, either focal or diffuse thinning Meniscal extrusion common in advanced OA and correlates with radiographic joint space narrowing

DISH

Radiographs make diagnosis Spine Flowing anterior ossification No significant facet arthropathy or ankylosis, minimal degenerative disc disease Normal bone density If bulky enough, marrow is seen within ossification Adjacent ligament ossification around cervical spine may result in pain &/or dysphagia May have associated ossification of posterior longitudinal ligament Sacroiliac (SI) joints Involves superior, nonsynovial portions Synovial portions of SI joints remain normal Often see nearby ligament ossification Extensive fluffy enthesopathy at tendon, ligament, or joint capsule insertions CT for evaluation of complications Transverse fractures following minor trauma Seen with long column fusion and osteoporosis (relatively rare in DISH compared with ankylosing spondylitis) If fractured may have progressive neurologic deficits and increased mortality rate MR: Evaluate cord following transverse fracture Displacement of critical structures in neck

Rheumatoid Arthritis of Knee

Radiographs: Osteopenia Effusion distorts suprapatellar recess, Hoffa fat pad Common decompression into popliteal cyst Uniform cartilage thinning, visualized as joint space narrowing, involving all 3 compartments Erosions initially marginal (tibial plateau, patella) Deformity, related to ligament and capsular laxity MR: T1WI Low signal linear insufficiency fracture lines MR: Fluid-sensitive sequences High signal effusion surrounded by low signal thickened synovium Cartilage seen directly, especially in fat-saturated sequences, which show different signal in cartilage relative to effusion High signal marrow edema Ligamentous injury well seen PD sequences show associated meniscal tears MR: T1WI FS + contrast Avid synovial enhancement, surrounding low signal effusion and popliteal cyst

Osteoarthritis of Shoulder and Elbow

Shoulder radiograph Osteophyte rings anatomic neck of humeral head (marginal) Osteophyte rings glenoid; often best seen on axillary lateral Subchondral sclerosis Normal bone density Subchondral cysts Intraarticular loose bodies Subluxation of glenohumeral joint may occur, based on underlying abnormality Superior subluxation humeral head if chronic rotator cuff tear Posterior subluxation of humeral head if chronic instability (seen on axillary lateral view) Elbow radiograph Osteophyte formation: Olecranon, coronoid, rings radial head/neck Intraarticular loose bodies CT or CT arthrography to search for loose bodies MR or MR arthrography to search for early cartilage damage prior to osteophyte formation Osteochondral defect Loose bodies Shoulder OA: Enhancement axillary nerve in quadrilateral space if huge osteophyte (rare) Elbow OA: Enhancement ulnar nerve in cubital tunnel (uncommon)

Osteoarthritis of Wrist and Hand

Terminology OA: Noninflammatory arthritis due to progressive loss of cartilage Resultant hypertrophic change in bone EOA: Inflammatory variant of OA Imaging Both OA and EOA are highly location specific OA: Cartilage narrowing + osteophytes EOA: Cartilage narrowing + erosions, ± osteophytes MR fluid-sensitive sequences ↑ signal inflammatory sites, early erosions ↑ signal marrow edema