approch to the foo-artrities radiology

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  • 62

    Approach to the FootA systematic assessment of foot radiographs for the manifestations of arthropathies is important, because the foot may be an early site of involvement in a systemic arthropathy such as rheumatoid arthritis, or it may be the only site of involvement in arthropathies such as gout or reactive arthritis. The foot, however, can be difficult to evaluate radiographically. Arches are present in the long and short axes of the foot that make assessment of articulations in more than one plane difficult. The wedge shape of the foot does not permit uniform exposure of the foot on a single radiograph. The hindfoot articulations are complex and often require either computed tomography (CT) or magnetic resonance (MR) imaging for accurate evaluation.

    A screening study of the foot should include anteroposterior (AP), lateral, and oblique radiographs. The AP radiograph of the foot permits evaluation of the interphalangeal (IP), metatarsophalangeal (MTP), and the first and second metatarsal-tarsal (MTT) joints. The oblique radiograph is necessary to observe abnormalities of the third through fifth MTT joints, the midfoot, and any early erosive changes on the lateral aspect of the fifth metatarsal. The oblique radiograph also permits evalu-ation of the lateral sesamoid at the first MTP joint. The lateral radiograph provides orthogonal assessment of the forefoot articulations, the mid- and hindfoot articulations, and the calcaneus. On rare occasions, a sesamoid view may be necessary to observe the sesamoidal articulation with the first metatarsal head.

    Successful assessment of the foot depends on systematically observing changes in four separate anatomic compartments: (1) the forefoot articulations (MTP, sesamoid-MTP, and IP joints), (2) the MTT joints, (3) the mid- and hindfoot articulations (tarsal joints), and (4) the ligamen-tous insertions about the calcaneus. As in the hand, the following radiographic changes should be assessed: soft tissue swelling, soft tissue calcification, bony mineralization, joint space narrowing, erosion, subluxation and dislocation, and bone production.

    FOREFOOT

    Arthropathies involving the IP joints and the MTP joints of the forefoot follow the same prin-ciples outlined in the chapter on the assessment of the hand. The sesamoid bones of the first MTP joint have a synovium-lined articulation with the plantar aspect of the first metatarsal head and, if involved, will demonstrate the manifestations of any of the arthropathies of the foot. This articula-tion should not be forgotten when assessing foot radiographs.

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  • Approach to the Foot 63

    Soft Tissue Swelling

    Symmetrical Swelling Around a Joint (Fig. 3-1)Symmetrical swelling about a joint is a manifestation of synovial proliferation, effusion, and periar-ticular soft tissue edema associated with inflammatory arthropathies. Soft tissue swelling is easier to appreciate with digital radiographic techniques than with a film screen system.

    FIGURE 3-1. Symmetrical swelling (arrows) of soft tissues around the first IP joint in inflammatory arthritis.

  • 64 Approach to Radiographic Changes Observed in a Specif ic Joint

    Fusiform Swelling of an Entire Digit (Fig. 3-2)The diffuse swelling of a digit resulting in a sausage or cocktail hot dog appearance is a manifestation of the spondyloarthropathies, trauma, and infection.

    FIGURE 3-2. Diffuse soft tissue swelling of the second digit giving a sausage appearance in a patient with psoriatic arthritis.

  • Approach to the Foot 65

    Lumpy, Bumpy Soft Tissue Swelling (Fig. 3-3)Soft tissue masses located eccentrically about a joint associated with cortical erosions are findings most commonly associated with gout, although these changes can be seen with amyloid, xanthomas, and sarcoid.

    FIGURE 3-3. Corticated erosion (arrowheads) at the medial aspect of the first metatarsal head, lateral aspect of the second metatarsal head and destruction fifth IP joint with associated soft tissue masses (arrows) in patient with gout.

  • 66 Approach to Radiographic Changes Observed in a Specif ic Joint

    Soft Tissue Calcification

    Mass (Fig. 3-4)Gouty tophi may or may not contain varying amounts of calcium. Regardless of calcium content, gouty tophi are more radiopaque than the surrounding soft tissues.

    FIGURE 3-4. Faintly calcified soft tissue mass overlying well-corticated ero-sions (arrows) on the medial aspect of the first MTP joint in patient with gout.

  • Approach to the Foot 67

    Tendinous or Ligamentous and Soft Tissue Calcification (Fig. 3-5)Idiopathic hydroxyapatite deposition disease may present as calcification of the tendons of the medial flexor group (flexor hallucis longus, flexor digitorum longus, and posterior tibialis) or around the first MTP joint. Because soft tissue calcifications can be associated with renal osteodystrophy and scleroderma, these diseases must be excluded before diagnosing idiopathic disease.

    FIGURE 3-5. Soft tissue calcification (arrows) medial to the first MTP joint in idiopathic hydroxyapatite deposition disease. There is no soft tissue mass outside the calcific deposit.

  • 68 Approach to Radiographic Changes Observed in a Specif ic Joint

    Mineralization

    NormalGenerally bone mineralization is maintained in the spondyloarthropathies, thus distinguishing these erosive arthropathies from rheumatoid arthritis.

    Juxta-Articular Osteoporosis (Fig. 3-6)Juxta-articular osteoporosis is a nonspecific finding that can be seen in nonarthropathic conditions. In an arthropathy it is most commonly associated with inflammatory disease. Juxta-articular osteo-porosis may be difficult to appreciate when the joints are diffusely involved. Resorption of sub-cortical bone in the medial aspect of the metatarsal head may be an indication of osteoporosis. Juxta-articular osteoporosis in acute reactive arthritis is the only feature that can radiographically distinguish this disease from psoriatic arthropathy.

    DIFFUSE OSTEOPOROSIS

    Generalized osteoporosis can be documented by assessing the cortical width in relation to the shaft width of the metatarsal bone. Generalized osteoporosis is usually seen in patients with rheumatoid arthritis.

    BA

    FIGURE 3-6. Juxta-articular osteoporosis in second through fourth MTP joints in right foot (A). This is better appreciated when nonaffected joints are available for comparison (B). There is loss of subchondral bone (arrowheads) when compared to normal in this patient with inflammatory arthritis.

  • Approach to the Foot 69

    Joint Space Change

    Widening of Joint Space (Fig. 3-7)Widening of a joint is often observed in acromegaly. Sometimes a joint involved by psoriatic arthrop-athy may appear widened secondary to fibrotic material replacing the joint.

    FIGURE 3-7. Widened joints, flaring of phalangeal ends, and new bone formation in patient with acromegaly.

  • 70 Approach to Radiographic Changes Observed in a Specif ic Joint

    Normal (Fig. 3-8)The joint space is typically maintained in gout in the face of periarticular well-corticated erosions with overhanging edges produced by tophaceous deposits.

    Uniform NarrowingUniform joint space narrowing reflects uniform loss of the cartilage and is associated with both inflammatory arthropathies and deposition diseases.

    Nonuniform NarrowingAsymmetrical loss of cartilage is associated with mechanical osteoarthritis. Osteoarthritis is most commonly seen at the first MTP joint.

    FIGURE 3-8. Sharply marginated erosions (arrowheads) associated with a soft tissue mass affecting the first MTP joint in patient with gout. Notice that the joint space is preserved.

  • Approach to the Foot 71

    Ankylosis (Fig. 3-9)Distal IP and PIP joint ankylosis is associated with the spondyloarthropathies. Ankylosis of the MTP joints is rare.

    Erosion

    Aggressive ErosionsAggressive erosions do not have corticated margins and are a manifestation of the inflamma-tory arthropathies. They tend to occur at the bare area of a bone, which is the area between where the synovial lining joins bone and the edge of the articular cartilage. Erosions are best seen on the AP view of the foot, which assesses the IP joints and the medial aspects of the second through fifth metatarsal heads (Fig.3-10). The lateral aspect of the fifth metatarsal head is the earliest site of erosive disease in rheumatoid arthritis of the foot and is best seen on the oblique view (Fig.3-11). The pencil-in-cup deformity is seen most frequently at the first IP joint and is most commonly associated with psoriatic arthritis, although it is also a manifestation of reactive arthritis (Fig.3-12). Erosion of the distal tuft (acro-osteolysis) may be seen with reactive arthri-tis and psoriatic arthropathy (Fig.3-13). Patients with acro-osteolysis in psoriasis may have nail changes that may be seen radiographically.

    FIGURE 3-9. Erosions and subluxations of MTP joints. Erosions at the first IP joint and ankylo-sis of the second and fourth DIPs and third and fourth PIPs joints in patient with psoriatic arthropathy.

  • 72 Approach to Radiographic Changes Observed in a Specif ic Joint

    FIGURE 3-10. Erosive changes involving third through fifth MTP joints in rheumatoid arthritis. Erosive changes are manifested by loss of the white cortical line (arrows) along the medial aspect of the third through fifth metatarsal heads. There are also erosions of the lateral metatarsal heads of the third through fifth toes.

    A B

    FIGURE 3-11. AP (A) and oblique (B) view of the foot. Erosion (arrows) along the lateral aspect of the fifth metatarsal head best seen in the oblique view of the foot.

  • Approach to the Foot 73

    Nonaggressive ErosionsAn erosi