Malleable paste for filling bone defects

Abstract

The invention is directed toward a malleable bone putty and a flowable gel composition for application to a bone defect site to promote new bone growth at the site which comprises a new bone growth inducing compound of demineralized lyophilized allograft bone powder. The bone powder has a particle size ranging from about 100 to about 850 microns and is mixed in a high molecular weight hydrogel carrier, the hydrogel component of the carrier ranging from about 0.3 to 3.0% of the composition and having a molecular weight of about at least 10,000 Daltons. The composition contains about 25% to about 40% bone powder and can be additionally provided with BMP's and a sodium phosphate buffer.

Description

[0001]More than one reissue application has been filed for the reissue of U.S. Pat. No. 6,030,635. The first reissue application is application Ser. No. 10 / 084,090 filed Feb. 18, 2002 which reissued used RE38,522 on May 25, 2004.FIELD OF INVENTION[0002]The present invention is generally directed toward a surgical bone product and more specifically is a flowable gel and a malleable putty based on demineralized allograft bone particles mixed in a fluid carrier comprising a high molecular weight viscous excipient derived from the class of biomaterials known as hydrogels.BACKGROUND OF THE INVENTION[0003]Malleable putty is used to correct surgical defects that may be caused by trauma, pathological disease, surgical intervention or other situations where defects need to be managed in osseous surgery. It is important to have the defect filler in the form of a stable, viscous putty to facilitate the placement of the bone growth medium into the surgical site which is usually uneven in shape ...

AI Technical Summary

Benefits of technology

[0021]A bone putty with a useful bulk viscosity has been achieved by using a very high molecular weight class of soluble biomaterial, hydrogel. The use of high molecular weight hydrogels preferably over one million Daltons allows the achievement of a very malleable bone putty with only 1-3% concentration of the hydrogel in the carrier. The balance of the carrier formulation is a sterile saline or pure water which avoids the toxic problems with the high concentrations of the low molecular weight organic solvents of the prior art.

[0023]The selection of high molecular weight hydrogels allows the use of the preferred small particle size granules of demineralized allograft bone. These small particles pack better in the wound defect and absorb more quickly thereby allowing the bone defect to be remodeled into the natural bone of the patient

[0024]It is an object of the invention to utilize demineralized powdered bone in a particle size that is useful to achieve the malleability characteristics that maximizes the amount of bone in the formulation without creating a gritty, less malleable characteristic.

[0027]It is another object of the invention to provide a premixed bone putty / gel in an oxygen protected carrier to keep the putty / gel from drying out or being degraded.

[0028]It is also an object of the invention to create a bone defect material which can be easily handled by the physician and does not degenerate when contacting blood flow at the surgical site.

Problems solved by technology

This works very well to heal the defect but requires significant secondary surgery resulting in lengthening the surgery, extending the time the patient is under anesthesia and increasing the cost.

In addition, a significant increase in patient morbidity is attendant in this technique as the sturgeon must take bone from a non-involved site in the patient to recover sufficient healthy bone, marrow and blood to perform the defect filling surgery.

This leads to significant post-operative pain.

However, stored blood from other patients has the deficiencies that any blood transfusion would have such as blood type compatibility, possibility of transmission of disease and unknown concentration of BMP which are to a great extent dependent upon the age of the donor.

The problems inherent with using the patients blood as a carrier for demineralized bone powder are the difficulties of mixing the same at the operating site, the difficulty in obtaining a bone paste consistency which can be easily applied to the surgical area, the guesswork in mixing a usable composition at the site and the problem of having a bone paste or gel which will promote optimum bone replacement growth, not be carried away by the body fluids at the operation site or simply fall out of the bone defect site.

The bone in this form is usually very coarse and dry and is difficult to manipulate by the surgeon.

Glycerol also experiences a marked reduction in viscosity when its temperature rises from room temperature (typically 22° C. in an operating room) to the temperature of the patient's tissue, typically 37° C. This combination of high water solubility and reduced viscosity causes the allograft bone material to be “runny” and to flow away from the site almost immediately after placement; this prevents the proper retention of the bone within the site as carefully placed by the surgeon.

This improves both the bulk viscosity and the handling characteristics of the mixture but still leaves the problem of the fast rate of dissipation of the carrier and some bone due to the solubility of the glycerol carrier.

The larger particles of demineralized bone may also retard the development of new bone by the patient because the large bony lamellae do not pack as well as the smaller grainy particles of bone.

Another deficiency of using the bony lamellae is that the ends of the bony fragments are uneven and when packed into the surgical defect, leave uneven filaments of bone protruding out from the defect which can compromise the healing rate.

Glycerol and other similar low molecular weight organic solvents are toxic and irritating to the surrounding tissues.

Furthermore glycerol has been reported to be specifically neurotoxic and this problem is compounded when the concentration of glycerol is at the 20-95% level as disclosed in the U.S. Pat No. 5,073,373 patent.

Unfortunately this bone gel is difficult to manufacture and requires a premolded gel form

Bovine collagen carries the risk of an immunogenic reaction by the recipient patient.

Thus, bovine tissue carries a risk of disease transmission and is not a desirable carrier for allograft tissue.

However, collagen absorbs slowly in the human body, particularly in a bony site with usually a low degree of vascularity.

The slow absorption of collagen can delay the growth of new bone and result in the formation of scar tissue at the site.

This could result in a non-bony healing and a result with much less tensile strength.