A Case-Control Study of Prosthetic Implants and Selected Chronic Diseases in Medicare Claims Data

Abstract

PURPOSE: In an exploratory case-control study of a private insurance-claims database, Greenland and Finkle observed associations of certain prosthetic nonbreast implants with certain connective-tissue and neurologic conditions. We wished to test these associations using the same design with new data.

METHODS: We examined these associations in a case-control analysis of Medicare claims data. To control for possible confounding effects of surgery, our analysis examined nonimplant surgeries of severity similar to implant surgeries.

RESULTS: We again found associations of silicone and metal implants with connective-tissue and neurologic conditions, but we also found similar associations of carpal-tunnel surgery with those conditions.

CONCLUSIONS: Possible explanations for these findings include confounding by presurgical conditions. Therefore, we recommend further studies be done in which such conditions can be measured and controlled.

Introduction

Controversy regarding alleged effects of silicone-containing breast implants on connective-tissue and neurologic diseases has had considerable impact on American society. Claims involving hundred of thousands of women and billions of dollars have led to the unprecedented formation of a special scientific advisory panel by the Federal courts, and a bankruptcy filing by Dow-Corning Corporation (1). There have been numerous epidemiologic studies of breast implants; see the FDA review of studies published through 1995 (2) and other studies published since then (e.g., 3, 4, 5, 6, 7). All of these studies suffer from methodologic limitations, such as unstable estimates of effects on rare outcomes or vulnerabilities to selection biases, and their interpretation remains highly controversial 1, 2. At most, it might be agreed the studies suggest that no large effects are present 1, 2.

Motivated by the above controversy, a few groups have also examined the relation of other implanted devices to the diseases in question 6, 7, 8. A University of Michigan group 6, 7 conducted population-based case-control studies of silicone-exposures (including those from medical devices) and non-silicone devices, in relation to scleroderma and undifferentiated connective tissue disease (UCTD), defined as ICD9 710.9 (“collagen disease not otherwise specified”). They had too few exposed scleroderma cases to yield clear results; they did however detect associations of both silicone-containing and silicone-free devices with UCTD.

Greenland and Finkle (8) conducted an exploratory case-control study of prosthetic non-breast implants in a private health-insurance claims database. This study examined both metal-and silicone-containing implants, under the assumption that metal implants would serve as a control exposure for silicone implants (both types of implant are associated with similar indications and medications). Both silicone and metal implants exhibited associations with certain connective-tissue and neurologic conditions, raising the possibility that surgery or indications for surgery (rather than the implants) may have been responsible for those associations.

In all the non-breast implants studies, most of the associations were quite unstable due to the limited numbers of implanted patients. Hence, we conducted another case-control study using public-use Medicare records. The served population is quite different from the original, being older on average (most Medicare recipients are over 65, whereas most of the persons in the original study were under 65). Because the incidence of the diseases in question increases with age and the Medicare population is very large, far more cases were available for study. To investigate whether surgery or surgical indications were responsible for the original observations, we included in the second study several non-implant surgical procedures that involved similar degrees of invasiveness, anaesthesia duration, and perisurgical medication as implant operations.