Radiographs of the hands are probably the most informative part of any screening series for arthritis. It is suggested that two views be obtained for evaluation: a posteroanterior (PA) view and a Nørgaard view of both hands and wrists (see Chapter 1 ). The former is excellent for imaging mineralization and soft tissue swelling; the latter is necessary for imaging early erosive changes. Using these two views, a systematic approach to observation should be employed. One must observe (1) the radiographic changes occurring in a specific joint and (2) the distribution of these changes within the hand and wrist to make an accurate diagnosis.
Radiographic changes
The radiographic changes occurring around a specific joint to be evaluated are soft tissue swelling, subluxation and dislocation, mineralization, calcification, joint space narrowing, erosion, and bone production. Each arthropathy has its own characteristic set of changes.
Soft Tissue Swelling
Symmetrical Swelling Around an Involved Joint ( Fig. 2-1 )
Symmetrical soft tissue swelling around a joint is a manifestation of synovitis. Soft tissue swelling is more readily appreciated with digital radiographic techniques than with film screen systems. Symmetrical swelling is most easily evaluated around the interphalangeal (IP) joints and wrist but can also be appreciated around the metacarpal phalangeal joint with careful evaluation. This type of swelling may be seen in any of the inflammatory arthropathies but is most common in rheumatoid arthritis.
Asymmetrical Swelling Around an Involved Joint ( Fig. 2-2 )
Asymmetrical swelling may not be actual soft tissue swelling, but rather soft tissue asymmetry due to subluxation or an osteophyte. The osteophyte may have a nonopaque cartilage cap that distorts the soft tissue. This swelling is seen in osteoarthritis and erosive osteoarthritis. Such swellings around the distal interphalangeal (DIP) joints are called Heberden nodes and around the proximal interphalangeal (PIP) joints are called Bouchard nodes.
Diffuse Fusiform Swelling of an Entire Digit ( Fig. 2-3 )
This swollen digit is reminiscent of a sausage or a cocktail hot dog. This type of swelling is seen commonly in psoriatic and reactive arthritis when it involves the hands or feet. The cause of this pattern of soft tissue swelling is not clear but may be related to either enthesopathy or flexor tenosynovitis.
Lumpy, Bumpy Soft Tissue Swelling ( Fig. 2-4 )
Lumpy soft tissue swelling is produced by infiltration with a substance foreign to the normal tissues around the joint (i.e., urate crystals, xanthomatous tissue, or amyloid). An eccentric bump may be observed near or away from the joint. Such a swelling is most commonly seen in gout and rarely in xanthomatous or amyloid disease. Granulomatous involvement of the hand with sarcoid can also be associated with a soft tissue bump.
Subluxation
Subluxations may not be visualized on the PA view of the hands and wrists, because the technician will reduce any subluxation during positioning. Subluxations become apparent on the Nørgaard view, because the fingers are not supported in a fixed position. Subluxation is a prominent feature of rheumatoid arthritis and the arthritis of lupus. The proximal phalanges sublux in an ulnar and palmar direction in relationship to the adjacent metacarpals ( Fig. 2-5 ). One can distinguish the arthritis of lupus from rheumatoid arthritis in that erosive disease is not present in the former. Subluxations do occur in osteoarthritis. These are usually in a lateral direction, deviating either radially or ulnarly ( Fig. 2-6 ).
Mineralization
Overall mineralization is evaluated by observing the metacarpal shaft of the second or the third digit. The sum of the two cortices of the shaft should equal one half the width of the shaft in a normally mineralized digit ( Fig. 2-7 ). The degree of generalized osteoporosis can be accurately judged by the sum of the two cortices in relationship to the width of the shaft ( Fig. 2-8 ).
Normal Mineralization (see Fig. 2-7 )
Normal mineralization is typical of every arthropathy except rheumatoid arthritis. The maintenance of normal mineralization helps to distinguish the “rheumatoid variants”—psoriasis, reactive arthritis, and ankylosing spondylitis—from rheumatoid arthritis. The crystalline arthropathies and the osteoarthropathies maintain normal mineralization.
Diffuse Osteoporosis (see Fig. 2-8 )
This change is associated only with rheumatoid arthritis. It is seen in the advanced stages of this disease. All other arthropathies tend to maintain normal mineralization. If one observes osteoporosis in a patient with another arthropathy, such as gout, then the generalized osteoporosis may be secondary to disuse, to medication or to the normal aging process. It should not be blamed primarily on the arthropathy.
Juxta-Articular Demineralization ( Fig. 2-9 )
This change has no objective criteria but is more readily appreciated in bilateral but asymmetric arthropathies. The metaphyseal-epiphyseal part of the digit is always less dense than the diaphysis, for the cortical bone is thinner in the metaphysis and epiphysis. Dramatic differences are easy to see. However, juxta-articular osteoporosis is a nonspecific finding; it is observed in many abnormal conditions, including posttraumatic change. It may be present in any of the arthropathies at any time. Observation of its presence only helps to establish that something is abnormal in the hand.
Calcification
Soft Tissue Mass Calcification ( Fig. 2-10 )
The urate crystals of gout are not radiopaque. However, when the urate crystals deposit in the soft tissues to form a tophus, calcium is precipitated with the urate crystals to varying degrees. Therefore the tophus may be just slightly denser than the surrounding soft tissue structure or it may be very densely calcified. In either case, such a tophus is part of the radiographic picture of gout.
Cartilage Calcification (Chondrocalcinosis) ( Fig. 2-11 )
Calcium pyrophosphate dihydrate crystals deposit in hyaline and fibrous cartilage, producing a radiographic picture of calcified cartilage. When seen in two or more joints (meaning one knee and one wrist, not two knees), the radiographic diagnosis of calcium pyrophosphate dihydrate (CPPD) deposition disease can be made. In the older literature, “chondrocalcinosis” was associated with a long list of diseases. For example, it was listed as a manifestation of gout. However, it is now known that, although urate crystals deposited in soft tissues may precipitate calcium, urate crystals deposited in cartilage will not precipitate calcium. Therefore, a patient with known gout who demonstrates calcification of hyaline or fibrous cartilage must also have deposition of CPPD crystals in the cartilage; thus the patient has both gout and CPPD deposition. The only two diseases known to cause actual deposition of CPPD crystals in cartilage, other than idiopathic CPPD crystal deposition disease, are hyperparathyroidism and hemochromatosis.
Tendinous and Soft Tissue Calcification ( Fig. 2-12 )
Hydroxyapatite crystals deposit in tendons and bursae, producing the classic tendinitis or bursitis of the shoulder. The second most common location for this deposition is over the greater trochanter. It can also cause a problem around the elbow or the wrist. Hydroxyapatite is also known to deposit in soft tissues in various systemic diseases, such as scleroderma, dermatomyositis, and renal osteodystrophy. However, patients have presented recently with hydroxyapatite deposition in numerous tendinous and soft tissue sites without an underlying systemic disease. Associated with this deposition, one can see erosive changes of the small joints of the hands adjacent to the concretion ( Fig. 2-13 ). This disease entity has become known as hydroxyapatite deposition disease.
Joint Space Narrowing
Maintenance of Joint Space
Although urate crystals may deposit within the cartilage of a joint and cause secondary loss of the joint space, gout is one of the few arthropathies that can cause significant changes around the joint while maintaining the joint space itself. A tophus deposited on the extensor aspect of a joint may cause significant erosive change of the dorsal aspect of the joint while preserving the flexor aspect ( Fig. 2-14 ). Radiographically one may observe extensive erosion with a ghost of a joint space imaging through the erosion. In the rare instance of pigmented villonodular synovitis (PVNS) involving the wrist, the involved joint will usually be maintained.
Uniform Narrowing ( Fig. 2-15 )
All of the arthropathies except for osteoarthritis produce uniform narrowing of the joint space. This includes the inflammatory arthropathies that erode the cartilage and all other arthropathies that deposit extra substance into the cartilage (i.e., the crystalline arthropathies, acromegaly, and Wilson disease).
Nonuniform Narrowing ( Fig. 2-16 )
Nonuniform narrowing of the joint space is typical of osteoarthritis and erosive osteoarthritis.
Erosion
Aggressive Erosions
Aggressive erosions are actively changing while the radiograph is being taken. They have no sclerotic borders or evidence of reparative bone. In the inflammatory arthritides, early erosions are seen in the “bare” areas of bone. The bare area is located within the joint, between the edge of the articular cartilage and the attachment of the synovium. The very first radiographic change is a disruption of the white cortical line in the bare area, giving a “dot-dash” appearance ( Fig. 2-17 ). These early erosions are best seen in the metacarpal heads or on the Nørgaard view at the base of the proximal phalanges on the radial side ( Fig. 2-18 ). As these erosions progress, they involve more and more of the joint, ignoring the original barrier of cartilage ( Fig. 2-19 ). Eventually the entire joint may be destroyed. The end of the proximal bone may be eroded in such a fashion as to appear whittled or pointed, while the end of the adjacent distal bone becomes splayed or cup-like ( Fig. 2-20 ). This type of erosion has been called a “pencil-in-cup” deformity and is most commonly seen in patients with psoriatic arthritis.
