RA can affect any of the synovial joints. Most commonly, the disease starts in the MCP, PIP, and MTP joints followed by the wrists, knees, elbows, ankles, hips, and shoulders in roughly that order. Early treatment helps limit the number of joints involved. Of particular importance, RA almost always spares the distal interphalangeal (DIP) joints (in contrast, these joints are often involved in osteoarthritis and psoriatic arthritis).
Less commonly, and usually only in more advanced cases, RA may involve the temporomandibular, cricoarytenoid and sternoclavicular joints. RA may involve the upper part of the cervical spine, particularly the C1–C2 articulation, but unlike the spondyloarthropathies, rarely if ever involves the rest of the spine. Patients with RA are, however, at an increased risk for osteoporosis, and this risk should be considered and dealt with early.
The hands are a major site of involvement in almost all patients with RA; hand involvement is responsible for a significant portion of the disabilities caused by RA. Typical early disease is with the swelling of the PIP joints easily seen.
The DIP joints are almost always spared unless the patient also has osteoarthritis; both diseases are common and can coexist, particularly in elderly patients. Radiographs can detect evidence of articular damage early in the course of disease and long before the appearance of joint deformities. Late established disease all too commonly causes ulnar deviation of the fingers at the MCPs and swan-neck deformities (hyperextension of the PIP joints; Figure 15–2B). Boutonnière (or buttonhole) deformities of the fingers result from hyperextension of the MCP joints. If the clinical disease remains active, hand function will slowly deteriorate.
Wrists are involved in most patients with RA. Early in the course of the disease, synovial proliferation in and around the wrists can compress the median nerve, causing carpal tunnel syndrome. Chronic synovitis can lead to radial deviation of the wrist, and in severe cases, to volar subluxation. Synovial proliferation of the wrist can invade extensor tendons, leading to rupture and abrupt loss of function of individual fingers.
The feet, particularly the MTP joints, are involved early in almost all cases of RA and are second only to hand involvement in terms of the problems they cause. Radiographic erosions occur at least as early in the feet as in the hands. Subluxation of the toes at the MTP joints is common and leads to the dual problem of skin ulceration on the top of the toes and painful ambulation because of loss of the cushioning pads that protect the heads of the metatarsals. Symptoms from MTP subluxation can respond to orthotics but may require surgery.
Involvement of large joints (knees, ankles, elbows, hips, and shoulders) is common but generally occurs somewhat later than small joint involvement. Characteristically, the entire joint surface is involved in a symmetric fashion. Therefore RA is not only symmetric from one side of the body to the other, but is also symmetric within the individual joint. In the case of the knee the medial and lateral compartments are both severely narrowed in RA, whereas osteoarthritis usually involves only one compartment.
Total joint replacements of hips and knees can dramatically improve function and quality of life and should be considered in patients with severe mechanical damage.
Synovial cysts present as fluctuant masses around involved joints (large or small). Synovial cysts from the knee are perhaps the best examples of this phenomenon. The inflamed knee produces excess synovial fluid that can accumulate posteriorly because of a one-way valve effect between the knee joint and the popliteal space (popliteal or Baker cyst).
Baker cysts cause problems by compressing the popliteal nerve, artery, or veins; by dissecting into the tissues of the calf (usually posteriorly); and by rupturing into the calf. Dissection usually produces only minor symptoms such as a feeling of fullness. Rupture of a Baker cyst, however, leads to extravasation of the inflammatory contents into the calf, producing significant pain and swelling that may be confused with thrombophlebitis (the so-called pseudothrombophlebitis syndrome).
Ultrasonography of the popliteal fossa and calf is useful to confirm the diagnosis and to rule out thrombophlebitis, which may be precipitated by popliteal cysts. Short-term treatment of popliteal cysts usually involves injecting the knee with glucocorticoids to interrupt the inflammatory process.
Although most of the spine is spared in RA, the cervical spine (especially the C1–C2 articulation) is not. As with RA elsewhere, bony erosions and ligament damage can occur in this area and can lead to subluxation. Most often, subluxation is minor, and patients and caregivers need only be cautious and avoid forcing the neck into positions of flexion. Occasionally, C1–C2 subluxation is severe and requires complex surgical intervention in an attempt to prevent compromise of the cervical cord, and in some cases, death.
Wherever synovial tissue exists, RA may cause problems; the temporomandibular, cricoarytenoid, and sternoclavicular joints are examples. The cricoarytenoid joint is responsible for abduction and adduction of the vocal cords. Involvement of this joint may lead to a feeling of fullness in the throat, to hoarseness, or rarely to a syndrome of acute respiratory distress with or without stridor when the cords are essentially frozen in a closed position. In this latter situation, emergent tracheotomy may be life-saving.