Method of forming a temporary implant

Details Method of forming a temporary implant Method of forming a temporary implant

2000-11-10

2002-03-26

Davis, Robert (Department: 1722)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

To produce composite, plural part or multilayered article

C264S318000, C264S328100, C264S317000, C264S279100, C623S901000

Reexamination Certificate

active

06361731

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to orthopedic implants for use in orthopedic surgical procedures and, more particularly, to a method of forming temporary orthopedic implants used in orthopedic surgical procedures.
2. Discussion of the Related Art
A natural joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace the natural joint with a joint prosthesis. However, due to any number of reasons, a small portion of patients that undergo such orthopedic surgical procedures suffer from infections at the surgical site and generally around the implanted joint prosthesis. In order to cure such an infection in a two-stage re-implantation, the implanted joint prosthesis is generally removed, the site is thoroughly debrided and washed, antibiotics are applied to the infected site until the infection is eliminated, and a new revision type joint prosthesis is then implanted during a subsequent orthopedic surgical procedure. Systemic antibiotics may also act as an adjunct to local antibiotic delivery. Another technique, more popular in Europe, is the one stage re-implantation in which the prosthesis is removed, the site is debrided and washed and a new permanent implant is cemented in place using antibiotic loaded bone cement.
The currently available techniques for delivering the antibiotic to the infected joint area include mixing appropriate bone cement, such as (PMMA) poly-methyl-methacrylate, with an antibiotic, such as gentamicin, and applying the mixture to the infected joint area. Another technique involves the use of pre-loaded antibiotic cement beads which are retained on a string or wire. The antibiotic loaded bone cement is packed into the voids created by the explanted joint prosthesis while the joint is distended or the string of antibiotic loaded beads are dropped into the respective voids. During this period, the antibiotic leaches out from the bone cement and into the infected area, while the patient is unfortunately left substantially non-ambulatory or bed-ridden with very limited mobility. In addition, soft tissue contraction in the area about the joint may cause a more difficult revision surgery since the remaining bone portion is smaller than the explanted joint prosthesis. Moreover, the above techniques may also suffer from the disadvantage of sometimes being difficult or messy to use during the orthopedic surgical procedure. This disadvantage is primarily exhibited during the use of the antibiotic loaded bone cement in a doughy state and attempting to fill the appropriate region in the distended joint area.
In order to improve upon this technique, other techniques have involved the use of partial molds or casts in which the mixture of bone cement and antibiotic is packed into these partial molds by use of spoons or spatulas and left to harden. Once hardened, the brittle molds may be broken away and the bone cement, now resembling a joint prosthesis, is applied to the appropriate joint area. However, this technique also suffers from several disadvantages in that the partial molds or casts are made from a brittle material such that the molds are prone to fracturing or breaking before their use. Moreover, the molds are only partial molds in that only portions of the implant are formed and the molds generally have large exposed cavities such as two ends of a tube to receive the bone cement. This makes it extremely difficult to pack or load such molds with the antibiotic loaded bone cement. Furthermore, it is often times difficult to break away or remove these molds from the hardened bone cement.
Such disadvantages are also exhibited in U.S. Pat. Nos. 5,123,927 and 5,133,771 to Duncan, et al. in which a knee prosthesis and a hip prosthesis technique are disclosed. Here again, the disadvantages associated with the '927 and '771 patents are that they are somewhat clumsy and messy to work with. In other words, both the '927 and the '771 patents provide partial molds that are substantially open such that a rigid or hard bearing member is separately implanted into each of the molds to provide for an articulating temporary joint. Here again, however, the molds are filled manually by the use of spoons, spatulas, etc. and the molds do not provide a means for readily removing the molds once the antibiotic impregnated bone cement hardens. In addition, it appears that these molds are also reusable which requires the molds to be cleaned and sterilized before each use.
What is needed then is a method to form a temporary implant which does not suffer from the above mentioned disadvantages. This, in turn, will provide a substantially completely sealed mold which may be filled in an automatic or controlled matter, provide a mold which may be readily handled and easily removed from the hardened bone cement, provide a mold that is easily tearable, provide a means to easily remove the mold from the formed temporary implant, reduce the amount of time a patient is bedridden, increase the efficiency of the surgical procedure while reducing the surgical time and cost, eliminating any recleaning or resterilizing, and create a repeatable procedure by providing a substantially fully enclosed and complete mold. It is, therefore, an object of the present invention to provide such a cement mold to form a temporary implant for use during an orthopedic surgical procedure.
SUMMARY OF THE INVENTION
In accordance with teachings of the present invention, a method for forming a temporary orthopedic implant used in an orthopedic surgical procedure is disclosed. This is basically achieved by providing an improved cement mold which is substantially sealed except for an input port and ventilation ports, as well as having a removal mechanism operable to assist in separating the cement mold from the temporary implant.
In one preferred embodiment, a cement mold to form a temporary implant for use in delivering antibiotics to an infected site includes a first mold and a second mold. The first mold defines a first portion of the temporary implant and the second mold defines a second portion of the temporary implant. A coupling mechanism joins the first mold to the second mold such that the cement mold is substantially sealed to define the temporary implant.
In another preferred embodiment, a cement mold to form a temporary implant for use in delivering antibiotics to an infected site includes an outer sidewall and an inner sidewall where the inner sidewall defines the shape of the temporary implant. An input port is defined by the cement mold and is operable to receive a delivery nozzle to supply antibiotic loaded bone cement within the inner sidewall. At least one ventilation port is defined by the cement mold and is operable to vent trapped air upon filling the cement mold with the antibiotic loaded bone cement through the input port.
In yet another preferred embodiment, a cement mold to form a temporary implant for use in delivering antibiotics to an infected site includes an outer sidewall and an inner sidewall where the inner sidewall defines the shape of the temporary implant. A removal mechanism forming a portion of the cement mold is operable to assist in separating the cement mold from the temporary implant.
In another preferred embodiment, a method for forming a temporary implant includes mixing bone cement during a surgical procedure, selecting an appropriately sized cement mold that is translucent, filling the cement mold with the bone cement to form the temporary implant, determining that the cement mold is filled by viewing through the translucent cement mold, and implanting the temporary implant into a patient.
In another preferred embodiment, a method of forming a temporary implant includes mixing bone cement during a surgical procedure, selecting an appropriately sized cement mold having an input port, filling a cement gun having a nozzle with the bone cement, inserting the nozzle of the cement gu

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