394 Figure 2. C‘alc[jific.o/ion in the quadriceps mechanism. Patellar “Whiskering” To the Editor: This communication is written in response to an article by Turjeque et al. on Patellar “Whiskers” (Arthritis Rheum 20:1409-1412, 1977). Although I do not disagree with the authors that radiodensity along the superior surface of the patella on lateral radiographs is a frequent finding, particularly in elderly patients, one must be careful not to consider all such deposits as “calcification.” Several distinct radiographic findings may be apparent. Patellar Hyperostosis. Bony thickening or hyperostosis (Figure 1 ) on the anterior surface of the patella may occur on the superior and/or inferior surfaces of the bone. These ossific shadows extend into the adjacent tendon with visible bony trabeculae. These outgrowths may occur as an incidental finding in patients who are asymptomatic or whose symptoms relate to other findings. We have noted such deposits in one patient (5% of 21 men with an average age of 65 years) without any knee symptomatology ( I ) . Figure 1 in the article by Trujeque et al. indeed demonstrates such a deposit. I n fact, adjacent hyperostosis on the anteroinferior surface of the patella is just visible in this reproduction. An increased incidence of patellar hyperostosis is apparent in ankylosing hyperostosis of the spine (diffuse idiopathic skeletal hyperostosis-DISH). We have noted such ossification in 29% of 21 patients with this disorder. This finding is representative of a characteristic manifestation of the disease: hyperostosis at sites of tendon and ligament attachment to bone in both axial and extraaxial skeleton. Hyperostosis is observed at other extraspinal sites including the pelvis, calcaneus, and ulnar olecranon. Calcification in the Quadriceps Mechanism. Linear calcific radiodensities may be seen within the quad- 395 riceps at or separated from the superior margin of the patella (Figure 2). These densities are not common in the general population but are observed in approximately 4% of patients with calcium pyrophosphate deposition disease (2). In this condition, tendon calcification is not limited to the quadriceps mechanism but also occurs elsewhere, including the rotator cuff region of the shoulder, triceps, and achilles tendons in association with calcification of cartilage (chondrocolcinosis), synovium, ligaments, and soft tissue. A report has appeared that biopsy of a calcified achilles tendon in one such patient demonstrated calcium pyrophosphate dihydrate crystals (3). Patellar Osteophytes. If we reserve the term osteophyte in the current discussion to b.one formation occurring at the articular margins of the patella, these excrescences are seen at the posterior superior and posterior inferior margins of the patella (Figure 3). They are distinct from anterior hyperostosis and quadriceps calcification. Osteophytes may be seen in patellofemoral osteoarthritis and as part of the structural joint change which is characteristic of calcium pyrophosphate deposition disease (2). Each of these recognizable radiodensities-patellar hyperostosis, quadriceps tendon calcification, and patellar osteophytes-is associated with different clinical manifestations and may be the radiographic clue to an underlying disease process such as diffuse idiopathic skeletal hyperostosis, calcium pyrophosphate deposition disease, and osteoarthritis. DONALD RESNICK,M . D . Chief. Department of Radiology Veterans Administration Hospital 3350 La Jolla Village Drive San Diego, California 92161 REFERENCES I . Resnick D, Shaul SR, Robins JM: Diffuse idiopathic skeletal hyperostosis (DISH): Forestier’s disease with extraspinal manifestations. Radiology I I5:5 13-524, 1975 2. Resnick D, Niwayama G, Goergen TG, Utsinger PD, Shapiro RF, Haselwood DM. Wiesner K B Clinical, radiographic and pathologic abnormalities in calcium pyrophosphate dihydrate deposition disease (CPPD): pseudogout. Radiology 122:1-15, 1977 3. Gerster JC, Baud CA, Lagier R, Boussina I, Fallet GH: Tendon calcifications in chondrocalcinosis: a clinical, radiologic, histologic and crystallographic study. Arthritis Rheum 20:717-722, 1977 Radiographic Survey of the Knees Figure 3. Parellar osteophytes. To the Editor: The letter to the editor by Mink et al. ( I ) has much merit in the areas that they mention: abundant information, reducing cost, and reducing radiation. However, for approximately 254, the standing views of both knees are much more useful if done on a 14 X 17 cassette (standard chest size in a vertical position). This will allow the physician to determine more adequately the amount of varus or valgus deformity, and more bone is seen with very little additional radiation. The amount of technician time and developing time is identical and the cost of the film is neglible for the added information. These will allow the orthopedic surgeons to see what type of total knees might be more appropriate, the adequacy of bone stock, and whether an osteotomy (though rarely indicated in rheumatoid arthritis) may be considered.