Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is a common disorder and the most common crystal arthropathy. In a typical hospital population, one to three patients per week will be observed with some manifestation of this disorder. It typically affects the middle-aged and elderly population. Some estimate the frequency to be 5 percent of this population. The clinical picture varies from the pseudogout syndrome to asymptomatic joint disease. The radiographic picture also varies from chondrocalcinosis without arthropathy to severe arthropathy.

Chondrocalcinosis is the deposition of CPPD crystals into fibrous or hyaline cartilage. Chondrocalcinosis has been associated in the past with many diseases, such as diabetes, degenerative joint disease, and gout. However, the only two diseases that have definite significant association with CPPD crystal deposition are primary hyperparathyroidism and hemochromatosis. If a patient with gout demonstrates chondrocalcinosis on the radiograph, then the chondrocalcinosis is not secondary to deposition of urate crystals but secondary to deposition of CPPD crystals. The patient should be diagnosed as having two separate diseases, gout and CPPD crystal deposition disease ( Fig. 17-1 ). In ochronosis, some patients have had CPPD crystals in the synovium but not in the cartilage.

Chondrocalcinosis is seen most frequently in the knee, pubic symphysis, and wrist ( Fig. 17-2 ). At least one of these areas is involved in a patient with CPPD deposition disease. Therefore, when screening a patient for this disorder, one should obtain radiographs of these areas. Radiographic diagnosis can be made when two or more areas in the skeleton demonstrate chondrocalcinosis. CPPD crystals may also deposit in synovium capsules, tendons, and ligaments.

The arthropathy of CPPD radiographically resembles osteoarthritis. How its distribution within the skeleton as well as within the individual joint is distinctive, allowing separation from primary or mechanical osteoarthritis. The following are the radiographic features of CPPD crystal deposition disease:

1.
Chondrocalcinosis
2.
Normal mineralization
3.
Uniform joint space loss
4.
Subchondral new bone formation
5.
Variable osteophyte formation
6.
Cysts—more prominent than in osteoarthritis
7.
Occasional neuropathic changes
8.
Bilateral distribution
9.
Distribution in knees, hands, and hips, in decreasing order of frequency; unlike osteoarthritis, the shoulder and elbow are involved

The knee

The knee is the most commonly involved joint in CPPD crystal deposition disease. Eighty percent of patients show chondrocalcinosis, and 75 percent show changes of an arthropathy. The chondrocalcinosis is seen as (1) wedge-shaped calcification in the fibrocartilaginous menisci and (2) thin linear calcification in hyaline cartilage paralleling the femoral condyles or tibial platen ( Fig. 17-3 ). Calcification may also be seen in the synovium, quadriceps tendon, or cruciate ligaments ( Fig. 17-4 ).

Figure 17-4, Lateral view of the knee shows chondrocalcinosis in the quadriceps and gastrocnemius tendons ( arrows ). Typical calcification is also present in the joint.

In the arthropathy, there is often preferential narrowing of the patellofemoral joint space with sparing of the medial and lateral tibiofemoral compartments ( Fig. 17-5 ). This patellofemoral narrowing is accompanied by subchondral bone sclerosis and osteophyte formation on the posterior aspect of the patella and the anterior aspect of the femoral condyles. There is often a scalloped defect seen in the femur proximal to the patella in the flexed knee. This scalloping is caused by abutment of the patella against the femur when the knee is in extension. Isolated patellofemoral involvement in the knee should always suggest CPPD crystal deposition disease.

Figure 17-5, Lateral view of the knee in the flexed position shows marked patellofemoral joint space narrowing with subchondral sclerosis and osteophyte formation. There is extensive remodelling of the anterior distal femur producing a notched appearance because of abnormal articulation of the patella with the femur in extension.

However, joint space narrowing may be seen in all three compartments, with the medial tibiofemoral compartment being involved more frequently than the lateral tibiofemoral compartment. In this case, the presence of chondrocalcinosis may be the only finding to distinguish this arthropathy from mechanical osteoarthritis. Occasionally the osteoarthritic changes become so severe that they resemble a neuropathic joint ( Fig. 17-6 ). Such excessive changes should suggest CPPD arthropathy, rather than mechanical osteoarthritis.

Figure 17-6, AP ( A ) and lateral ( B ) views of a knee in patient with CPPD arthropathy. There is loss of all compartments of the knee joint. There is extensive subchondral sclerosis and some cyst formation. There is fragmentation and bone debris in the joint. The findings resemble those of a neuropathic joint.

The hand

Chondrocalcinosis in the wrist is found in 65 percent of patients and the arthropathy in 70 percent of patients. Chondrocalcinosis is most frequently seen in the triangular fibrocartilage, hyaline cartilage, or ligament between the lunate and the triquetrum ( Fig. 17-7 ). The hyaline cartilage may calcify around any of the carpal bones but most frequently between the scaphoid and lunate. This may lead to disruption of the scapholunate ligament and the resulting instability may produce osteoarthritis of the radioscaphoid joint. In the fingers, pyrophosphate deposition tends to occur in the synovium and capsule around the metacarpophalangeal (MCP) joints ( Fig. 17-8 ).

Figure 17-7, The wrist in patient with CPPD arthropathy. There is chondrocalcinosis present in the triangular fibrocartilage ( arrowhead ) and in the hyaline cartilage between the lunate and triquetrum ( arrow ). There is also loss of the joint space between the navicular and the radius and between the lunate and capitate with subchondral bone formation.

Figure 17-8, MCP joints in patient with CPPD arthropathy. Calcification is present in the capsule.

The arthropathy in the hands is usually confined to the MCP joints. The interphalangeal (IP) joints are usually spared. The changes are those of osteoarthritis in the wrong distribution for primary osteoarthritis. There is joint space narrowing, subchondral bone formation, and variable osteophyte formation ( Fig. 17-9 ). Occasionally there is cyst formation and resultant bone collapse. The arthropathy of the wrist most commonly affects the radiocarpal joint. Again, there are osteoarthritic changes in a distribution different from that of primary osteoarthritis. There is joint space narrowing, subchondral bone formation, and cyst formation ( Fig. 17-10 ). The latter may dominate the radiographic picture. If there is dissociation between the scaphoid and lunate, there may be accompanying narrowing of the joint space between the lunate and capitate. The appearance has been described as a “stepladder” configuration ( Fig. 17-11 ). This pattern of radioscaphoid and capitolunate joint space narrowing is known as scapholunate advanced collapse or SLAC wrist.