In the practice of rheumatology, rheumatoid arthritis is considered the everyday disease. It is a symmetrical arthritis of the appendicular skeleton, sparing the axial skeleton except for the cervical spine. The common radiographic findings are as follows:
- 1.
Periarticular soft tissue swelling
- 2.
Juxta-articular osteoporosis progressing to generalized osteoporosis
- 3.
Uniform loss of joint space
- 4.
Lack of bone formation
- 5.
Marginal erosions progressing to severe erosions of subchondral bone
- 6.
Synovial cyst formation
- 7.
Subluxations
- 8.
Bilateral symmetrical distribution
- 9.
Distribution in hands, feet, knees, hips, cervical spine, shoulders and elbows in decreasing order of frequency
Not all of these features are present at any one time, and no one abnormality is pathognomonic. However, combinations of many of these finding should lead to the correct diagnosis of rheumatoid arthritis. With the development of new drugs, many of these findings are becoming less frequent.
The hands and wrists
Radiographs of the hands are used by clinicians for two distinct purposes: (1) to help in early diagnosis and (2) to assess for disease progression. Therefore, the radiographic changes in the hands and wrists will be described in two separate categories: early changes, observed primarily for diagnosis, and late changes, observed primarily for disease state.
Early Changes
The plain film is still the first modality used for imaging for early changes. Though ultrasonography and magnetic resonance (MR) imaging are more sensitive for the detection of erosions, these modalities are more expensive, more time consuming, and not always available. The earliest changes seen radiographically are soft tissue swelling symmetrically around the joints involved and juxta-articular osteoporosis. These changes are nonspecific but help to confirm the clinical impression of an inflammatory problem. Erosive disease is an indication of the aggressiveness of the arthropathy. Early erosions are subtle radiographically, and one must specifically look for them. The first erosive changes occur before there is loss of joint space. Erosions occur in the bare areas of the bone or in the bone within the joint space capsule that is not covered by articular cartilage. Radiographically, one loses the continuity of the white cortical line. On the posteroanterior (PA) view, this is best observed in the heads of the metacarpals ( Fig. 9-1 ) and at the margins of the proximal interphalangeal (PIP) joints ( Fig. 9-2 ). However, erosions are often first observed on the radial aspect of the base of the proximal phalanges. These changes are best imaged on the Nørgaard, or semisupinated oblique view of the hands ( Fig. 9-3 ) (see Chapter 1 ).
In the wrist, early erosions must be looked for in specific locations. They commonly occur at the waist of the navicular, the waist of the capitate, the articulation of the hamate with the base of the fifth metacarpal, the articulation of the first metacarpal with the trapezium, the radial styloid, and the ulnar styloid. These can all be imaged on the PA view ( Fig. 9-4 A and B ). The Nørgaard view profiles the pisiform and triquetrum and often demonstrates erosive changes between these two bones before erosions are seen on the ulnar styloid ( Fig. 9-4 C) .
Late Changes
In the hand, the metacarpophalangeal (MCP) joints and/or the PIP joints are uniformly involved. In the wrist, all the carpals are affected as a unit. As the disease progresses, the cartilage and apparent joint space are lost uniformly ( Fig. 9-5 ). As the cartilage is lost, the soft tissue swelling caused by the rheumatoid synovitis decreases. Juxta-articular osteoporosis progresses to diffuse osteoporosis. The subtle marginal erosions continue to progress, involving more and more of the articular surface to become large subchondral erosions ( Fig. 9-6 ). Subluxations occur at the MCP joints, with the proximal phalanges subluxing ulnarly and palmarly in relationship to the metacarpal heads ( Fig. 9-7 ). Swan neck and boutonnière deformities develop in the distal phalanges. Ulnar subluxation (translocation) of the carpus can also be seen ( Fig. 9-8 ). Although the subluxations occur secondary to inflammation of the tendons and ligaments surrounding the joint, erosive disease is usually present when the subluxations occur.
In the late stages of the disease, there is actually soft tissue atrophy. Diffuse osteoporosis is present. Subcutaneous rheumatoid nodules may develop in 25 percent of patients ( Fig. 9-9 ). The nodules do not cause bone destruction. There is lack of recognizable joint spaces (see Fig. 9-7 ). Bone ankylosis of the carpals may occur ( Fig. 9-10 ). Although there may be fibrous ankylosis of the phalanges, there should be no radiographic evidence of bone ankylosis distal to the carpals unless there has been surgical fusion. Despite extensive involvement of the PIPs and MCPs, the distal interphalangeal joints (DIPs) are usually spared. If there are erosive changes involving the DIPs, a second arthropathy such as erosive osteoarthritis should be considered. The hand may eventually become an arthritis mutilans ( Fig. 9-11 ).
The feet
The feet are involved in 80 to 90 percent of patients with rheumatoid arthritis. Some observers state that in 10 to 20 percent of patients, the feet are involved before the hands. However, generally the changes in the feet accompany or lag somewhat behind the changes in the hands. The radiographic changes in the feet are evaluated through an anteroposterior (AP) and a lateral view. Early involvement of the feet again shows juxta-articular osteoporosis and erosion of the bare areas on the heads of the metatarsals. The first erosive change is seen in the lateral aspect of the head of the fifth metatarsal ( Fig. 9-12 ). There is loss of the white cortical line. The other metatarsal heads are eroded primarily medially and later laterally ( Fig. 9-13 ). As the disease progresses, there are uniform loss of the cartilage in the MTP joints, progressive erosive changes, and subluxations of the proximal phalanges in a fibular direction in relationship to the metatarsals ( Fig. 9-14 ). The metatarsal heads also subluxate in a plantar direction. There are dorsiflexion deformities of the PIP joints and a hallux valgus deformity of the big toe.
Like the carpal bones in the wrist, tarsal bones of the foot are involved as a unit, with uniform joint space loss ( Fig. 9-15 ). Bone ankylosis may occur in the tarsals but not distal to the tarsals ( Fig. 9-16 ). Erosive changes may be present in the calcaneus at the attachment of the plantar aponeurosis or superior to the attachment of the Achilles tendon ( Fig. 9-17 ).
