Pathological conditions

Synovial inflammatory disease

 

A group of inflammatory diseases of connective tissue may cause bone and joint changes. These diseases, for discussion purposes, may be

Figure 72. Principal anatomy of the synovial joint. The inside of the joint capsule is covered by a synovial membrane. At the fold between the joint capsule and bone, the synovial membrane is in direct contact with bone, which is not covered with cartilage, the so-called "bare" areas (arrows).

divided into those associated with seropositivity forrheumatoid factor (i.e., rheumatoid arthritis) and those that are seronegative for rheumatoid factor (e.g., seronegative spondyloarthropathies (ankylosing spondylitis, psoriatic arthritis, Reiter's syndrome, and other types of reactive arthritis). All produce significant abnormalities in synovial joints.

General anatomy of the synovial joint

To understand the development of inflammatory joint changes, one must be familiar with the general anatomy of the synovial joint. It consists of two bone ends covered with articular cartilage. The joint is surrounded by a joint capsule, which is lined internally with a synovial membrane. At the edge between the joint capsule and bone a small area of the bone is bare (i.e., the synovial membrane has direct contact with bone without overlying cartilage) (Fig. 72).

Rheumatoid arthritis

Rheumatoid arthritis (RA) is a common type of arthritis. Its precise cause is unknown, but immunologic tissue damage is evident. No specific diagnostic test for RA exists. The diagnosis must be certified on the basis of clinical, laboratory, and radiologic criteria. Autoantibodies, the so-called rheumatoid factor, can be found in 75% of patients with RA.

Figure 73. Schematic development of joint changes in RA. a) Normal joint b) Synovial proliferation and pericapsular edema c) The inflammatory synovial tissue (pannus) has covered the surface of the hyaline cartilage and have caused erosions of the cartilage. d and e) Progressive destruction of joint cartilage and underlying bone. j) At the end-stage, fibrous ankylosis may occur.

 

Radiographic pattern of joint changes
At the early stage of RA, synovial proliferation occurs, which causes distention of the joint capsule and edema in the surrounding soft tissues (Fig. 73). This inflammation leads to hyperemia about the joint which is followed by periarticular osteoporosis. With continued synovial proliferation, bone erosions develop, particularly in the bare areas where the synovial membrane has direct contact with bone. These erosions have a characteristic distribution and appearance, especially in the fingers and toes (Fig. 74). The articular cartilage also is destroyed, leading to reduction of joint space. Finally, segments of the subcortical bone are destroyed and eventually a fibrous or bony ankylosis may ensue. Paralleling the changes in the joint are alterations in the ligaments and tendons. Such changes,

	Figure 74. Rheumatoid arthritis. Typical erosions adjacent to the metacarpophalangeal joints (arrows). Erosions also are present adjacent to the proximal interphalangeal joints. Note the soft tissue swelling adjacent to these joints.
	Figure 75. Ulnar drift. Advanced RA with ulnar subluxation at the metacarpophalangeal joints ("ulnar drift"). The erosions of the metacarpal heads are relatively small in comparison to the extensive de-rangement of the joints.

combined with muscle imbalance cause subluxation of the joints. One example of this is ulnar deviation at the metacarpophalangeal joints (Fig. 75).

Distribution of joint changes
RA usually develops symmetrically. Portions of joints that normally communicate with each other are affected simultaneously, for instance in the various compartments of the wrist, midfoot, and knee. Adjacent joints that normally are separate may develop communication because of soft tissue destruction (and then they too are affected) e.g., the distal radioulnar joint).

	Figure 76. RA in the foot with erosions in metatarsophalangeal joints and in the interphalangeal joint of the great toe (arrows).
	Figure 77. RA in the left hip joint. General cartilage destruction and cystlike changes are seen adjacent to the hip joint (arrow). Compare to the localized cartilage destruction in osteoarthritis (Fig. 67).

In the wrist and hands, the radiocarpal, distal radioulnar, metacarpophalangeal, and proximal interphalangeal (PIP) joints are affected, whereas the distal interphalangeal (DIP) joints are involved infrequently.

In the feet, involvement predominates in the metatarsophalangeal joint and the interphalangeal joint of the great toe (Fig. 76). The PIP and DIP joints rarely are involved. Of the large joints, the knees are affected predominantly (Fig. 77), and the hips, ankles, elbows and glenohumeral joints are affected less commonly. The temporomandibular joints are involved frequently. In the spine the cervical region is involved most typically (see Chapter 10).

Figure 78. RA with involvement of the retrocalcaneal bursa, which is filled with fluid. An erosion is present in the calcaneus adjacent to the bursa (arrow).

Changes in ligaments and bursae
Synovial membranes also are present in the bursae and ten don sheaths. Inflammation in these regions leads to soft tissue swelling and bone erosion (e.g., at the dorsal aspect of the calcaneus near the retrocalcaneal bursa) (Fig. 78). Laxity and rupture of ligaments cause subluxations and dislocations (Fig. 75). In the wrist, the ligament between the lunate and scaphoid bones often is eroded, resulting in scapholunate dissociation (i.e., the distance between the lunate and the scaphoid increases). Destruction of the supraspinatus tendon also may be evident; the deltoid muscle pulls the humerus in a cranial direction, with diminution of the distance between the humeral head and the acromion.

Seronegative spondyloarthropathies

These seronegative disorders consist of psoriatic arthropathy, ankylosing spondylitis, Reiter's syndrome, and reactive arthritis. The radiologic pattern of peripheral joint involvement in these disorders differs from that in RA. Less prominent periarticular osteoporoses and bony proliferation adjacent to sites of erosions are typical (Fig. 79). Ultimately, bony ankylosis is common. In Reiter's disease the feet are involved more often than the hands. In psoriatic arthropathy, the DIP joints or all the joints of one ray in the hand may be affected. Bone proliferation at the muscle and tendon insertions (i.e., enthesitis) often can be seen in the seronegative

Figure 79. Psoriatic arthropathy in the interphalangeal joint of the thumb. In addition to erosions, there also is new bone formation (arrows) that is characteristic of seronegative spondyloarthropathy. Soft tissue swelling is present adjacent to the joint.

arthritides. In ankylosing spondylitis, the sacroiliac joints are affected symmetrically, whereas in psoriasis and Reiter's syndrome involvement may be asymmetric.

Differential diagnosis
In both RA and the seronegative arthritides, cartilage destruction usually is diffuse, affecting all areas of a joint. In osteoarthrosis, often only the weightbearing part of the joint is affected and osteophytes are seen. In gout, the hands and feet are involved, most often the first metatarsophalangeal joint but also other joints, sometimes without involvement of the great toe. The joint space may be normal or reduced in width, and marginal bony erosions with a characteristic appearance are seen. Bone proliferation leads to overhanging edges about the eroded area. Lobulated soft tissue swelling may be evident adjacent to the bone erosion (Fig. 80).

Juvenile arthritis

Juvenile chronic arthritis (ICA) consists of a heterogeneous group of joint diseases affecting children. Seropositive arthritis simulating adult

	Figure 80. Gout in the first metatarsophalangeal joint. Soft tissue swelling (tophus) adjacent to the joint and erosions (arrows, arrowhead). The joint cartilage in the interphalangeal joint is preserved.
	Figure 81. Juvenile chronic arthritis. Thickening of the proximal and middle phalanges of the second to fifth fingers due to periostitis is seen. Irregularity of the carpal bones and general osteoporosis also are present.

type RA may affect children. This type is seen in 5 to 10% of all children with juvenile arthritis. The largest group, approximately 70%, consists of those with seronegative chronic arthritis. The disease usually starts before the age of 5 years. Most frequently the joints are involved symmetrically as in seropositive arthritis. Initially, the radiologic findings

Figure 82. Chondrocalcinosis with calcification in the medial and lateral menisci (arrow).

are identical (i.e., soft tissue swelling and osteoporosis). Because of hyperemia the epiphyses show increased growth and appear large in relation to the diaphyses. In the hip joint, coxa valga deformity, hypoplasia of the iliac bones, and acetabular protrusion may be evident. Joint space reduction and erosions are late manifestations. In the hand, periosteal reaction of the phalanges is identified (Fig. 81). The carpal bones often appear irregular (Fig. 81). In the cervical spine, erosions are seen in the apophyseal joints and bony ankylosis may develop (Chapter 10). Premature closure of the physes is common, causing shortening of stature. In certain types of juvenile arthritis, the joint findings are monoarticular.

Differential diagnosis
Radiologically it may be difficult to differentiate between JCA and hemophilia, especially if only a single joint is evaluated. Multiple epiphyseal dysplasia also may cause deformity and joint abnormalities that simulate those of JCA.

Other arthritides

Pyrophosphate synovitis (i.e., deposition of calcium pyrophosphate dihydrate [CPPD] crystals), is relatively common, especially in middle-aged and older patients. CPPD crystals are deposited in fibrous or hyaline cartilage (chondrocalcinosis) or in both (Fig. 82). Common sites of chondrocalcinosis are the pubic symphysis, knees, and wrists. As a rule, periarticular osteoporosis is not present, but reduction of the joint space is seen. Soft tissue swelling may be present during acute attacks of arthritis. Degenerative-like changes in certain joints, such as the metacarpophalangeal, radiocarpal, and patellofemoral articulations, suggest the

	Figure 83. Soft tissue calcifications in SLE with typical localization in the lower arm and at the back of the elbow.
	Figure 84. Acro-osteolysis (arrowhead).

diagnosis of CPPD crystal deposition disease.

Systemic lupus erythematosus (SLE) is an immunologic disease of connective tissue, often leading to polyarthritis. The synovitis may occur bilaterally and symmetrically with the same distribution as in RA. Soft tissue swelling and periarticular osteoporosis are seen, but joint space reduction and erosions are rare. Soft tissue involvement often causes subluxation, and periarticular or diffuse soft tissue calcifications may be evident (Fig. 83). Acro-osteolysis occurs in SLE but is more characteristic of scleroderma (Fig. 84). In rheumatic fever, migrating polyarthritis may occur, especially in the large joints. Nonerosive arthropathy of the hands (Jaccoud's arthropathy) also may be seen.

 

Niels Egund, Kjell Jonsson, Holger Pettersson and Donald Resnick