TO THE EDITOR:
"The Role of Access of Joint Fluid to Bone in Periarticular Osteolysis. A Report of Four Cases" (79-A: 447—452, March 1997), by Schmalzried et al., regarding four cases of osteolysis of the hip, raised two concerns. One was the authors' acceptance and promotion of the term geode to identify the osteoarthrotic cysts, and the other was their pathophysiological interpretation of the genesis or enlargement of these cysts.
In geological terms, a geode is a nodule found mostly in limestone after solution of the mineral, with deposition of a beautiful array of crystals in the cavity. The term should not be applied to osteoarthrotic cysts, despite the popularization of its use, mostly by radiologists, during the last two decades or so. The geological process emphasizes the deposition, not the formation of the cavity, even though part of the cavity may persist after deposition. In contrast, with cysts, the emphasis is on the progressive lysis and not on what fills or lines the cavity. The lining usually is mostly fibrous or chronic inflammatory tissue.
Related to the semantic question, but more important, is the use by the authors of the term joint fluid to mean that which is in the cavity, ignoring the nature of the fluid and its usual meaning of synovial fluid—that is, containing mucin, as a secretion from synovial cells. There is no doubt that when an osteoarthrotic cyst is lined with inflammatory tissue the fluid in the cyst, whether or not it communicates with the joint, contains inflammatory exudate. There is no evidence, such as hypertrophy of synovial cells or an increase in their number, to support the postulation of an overproduction of synovial fluid. Whether it is increased pressure of the fluid, inflammation, or perhaps irritation by wear particles that is mainly responsible for the cyst is arguable.
Those interested in the question may take into consideration the possibility, if not the probability, that, in normal joints, particles of cartilage that are perhaps submicroscopic are produced (and disposed of) and that more particles are produced in osteoarthrotic joints. In joints with eburnation, there are also particles of bone. Demonstration of those particles poses a major problem in laboratory technique as does the question of whether the fluid in the cysts is synovial or inflammatory—a problem that the authors did not discuss. The fact that much of normal synovial fluid is a transudate rather than a secretion complicates the difficulty of any investigation of the genesis of the cysts.
Jonathan Cohen, M.D.: Franciscan Children's Hospital and Rehabilitation Center, 30 Warren Street, Boston, Massachusetts 02135-3680
Dr. Schmalzried, Dr. Akizuki, Dr. Fedenko, and Dr. Mirra reply:
We regret that our article raised concerns. We intended it to be stimulating but more in a thought-provoking manner. Although the use of the term geode to describe these cystic lesions may not be appropriate from a pathological standpoint, the term is nonetheless used extensively in the orthopaedic literature. Most orthopaedic surgeons recognize this term, and this was the primary reason for our using it in our report.
We agree that the fluid in osteoarthrotic joints likely contains particles of cartilage and bone. The lining of osteoarthrotic cysts, however, is distinctly different from that which is seen in osteolysis associated with total joint arthroplasties. The intense foreign-body inflammatory response, which is characteristic of most osteolytic lesions around total joint implants, is distinctly absent in these osteoarthrotic cysts. The absence of this foreign-body response raises questions, in our minds, as to the number of particles of cartilage and bone present and their relative contribution to the cystic bone resorption in osteoarthrosis.
The characteristics of the fluid around the synovial joint are variable and are a function of the relative health or disease of that joint as well as the amount and type of use to which it is subjected. With regard to the most appropriate description of the fluid from around these osteoarthrotic joints and within the adjacent cysts, there is no question that there is an inflammatory component. It is our position that the osteoarthrotic disease process is the origin of the inflammation and that the juxta-articular cystic bone resorption occurs as a secondary phenomenon if the fluid within the joint gains access to subchondral bone.
Thomas P. Schmalzried, M.D.; Alexander N. Fedenko, M.D.; Joseph Mirra, M.D.: Joint Replacement Institute at Orthopaedic Hospital (T. P. S.) and Department of Pathology (A. N. F. and J. M.), Orthopaedic Hospital, 2400 South Flower Street, Los Angeles, California 90007
Kenneth H. Akizuki, M.D.: Harbor/University of California at Los Angeles Medical Center, 1000 West Carson Street, Torrance, California 90509