First posted December 12, 2012 Last updated December 12, 2012
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Silicone synovitis is a type of inflammatory arthritis caused by breakdown of silicone artificial implants. Over time, these silicone implants wear at the surface. Very small particles of the silicone are worn off the implant. The body attacks these microparticles with cells called macrophages (they are also called "foreign body giant cells") and tries to remove them. Unfortunately, silicone is not digestible by these cells and they die, releasing all of their digestive enzymes. More and more of the macrophages join in the effort, but still fail to remove the silicone microparticles. The effect over time is that these cells create a mass of macrophages and leave a pool of digestive enzymes that eat into the surrounding bones.
There was a line of artificial wrist bones that were made of silicone, made in the 1960's.
Here is what was reported in the first major report of this problem, by Smith, Atkinson, and Jupiter (Journal of Hand Surgery, January, 1985):
Foreign body giant cell synovitis and focal bony destruction requiring secondary surgery developed in nine patients after carpal and radiocarpal arthroplasty with silicone rubber implants. Synovitis followed silicone rubber replacement of the lunate in four patients, the carpal scaphoid in two patients, and the trapezium in one patient, trapezial resurfacing hemiarthroplasty in one patient, and total wrist arthroplasty in one patient. All the removed implants were deformed. Some had changed in color from clear white at the time of insertion to yellow-white or deep yellow upon removal. Scanning electron microscopy of a silicone rubber implant of the lunate removed from one patient revealed extensive fibrillation in the capitate fossa. Light microscopy of the synovium revealed hyperplasia and hundreds of fragments of silicone particulate debris throughout the tissue adjacent to the implant. The silicone debris was surrounded by multinuclear foreign body giant cells in the eight patients from whom the synovium was studied. All patients required revision surgery. We believe that in the patients studied, synovitis represented a biologic reaction to the silicone fragments found scattered throughout the synovium for the following reasons: The synovitis found was not present before surgery (except in the patient with rheumatoid arthritis); the synovitis found was not associated with the condition for which replacement arthroplasty was performed (except in the patient with rheumatoid arthritis); synovitis subsided after implants were removed; and synovitis was noted histologically in areas of silicone debris and appeared directly related to silicone seeding. Fibrillation, fragmentation, and local seeding of silicone after carpal or radiocarpal arthroplasty appear related to gradual deformation of the implant, which was the result of repeated compressive loading and shearing. Clinically significant complications of rubber carpal or radiocarpal arthroplasty with silicone rubber implants may develop from silicone synovitis.
This patient had a silicone implant for arthritis at the base of the thumb. On the xray, you can see it as the slightly white, uniformly dense material at the base of the thumb metacarpal (far left of the xray). You can also see that multiple other bones hae black areas in them. These are areas of resorption. The patient had pain in the pisiform bone, so it was removed. At surgery, the yellow lumps of tissue are masses of macrophages. The bottom right image is a light microscopy image from this patient. The green circle is around a silicone micropartical.
(Photographs courtesy of Dr. Charles Eaton)
In general, the implants need to be removed, but there are usually enough silicone particles in the remaining tissues that cannot be removed and the problem is not completely solved.
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