1. Field of the Invention
This invention relates to a method of producing tissue ingrowth surfaces on surgical implants. More particularly, this invention relates to a method for forming attachment surfaces on implants made of composite materials.
2. Description of the Prior Art
Until recently, most surgical implants such as prosthetic hip stems were made of metal and implanted with the aid of bone cement to provide fixation of the implant in its desired location. With such fixation, however, the implant may tend to work loose from the cement, possibly causing failure of the implant or pain and discomfort to the patient. Alternative means of implant fixation have therefore been attempted.
Because metal implants are relatively stiff (having a high modulus of elasticity), the bone into which they are implanted is stressed in a manner different than under natural conditions. This causes the loss of bone tissue in areas which are not stressed, which bone loss can cause loosening. Therefore, lower modulus composite prostheses such as those described in U.S. Pat. Nos. 3,893,196, 4,750,905, 4,892,552 and 4,902,297 have been developed.
Since it is necessary to place the composite stem immediately adjacent the cortical bone surrounding the medullary canal, into which the implant is placed to insure proper stress transfer, bone cement cannot be used.
One alternative to cement fixation is the use of certain textures on selected areas of the implant surface to produce tissue ingrowth into these areas, and therefore stabilization of the implant. Several patterns for such texturized surfaces can be found in existing metal alloy prosthetic devices, or more recently, polymeric devices. However, the methods for forming fixation surfaces on polymeric devices have proved to be somewhat expensive. In addition, these methods tend to be slow and require exposure of the composite prosthesis to high pressure and temperature to form the ingrowth surface on the prosthesis. One such method is disclosed in U.S. Pat. No. 4,778,469, which while less expensive and lower in pressure and temperature than some other methods, has been improved upon in the present invention.
It is, therefore, the primary objective of the present invention to provide a simple and less expensive means for preparing desired texturized surfaces on body implants made from polymeric composites or other material systems.