Magnesium-base Alloy For Use In Bone Surgery

Abstract

A magnesium-base alloy for use in bone surgery which contains the following components, wt.%:

Description

The present invention relates to magnesium-base alloys employed as a joining and fixation material in bone surgery.

One of the main problems in the operative treatment of bone fractures is finding a material for fixation means which is sufficiently strong, is absorbed after the completion of union and stimulates callus formation. The search for such a material has been made predominantly among organic substances although there are isolated reports of the study and use of inorganic materials, particularly metals.

Magnesium was first employed for osteosynthesis by Lambotte in 1907. In fracture of the bones of the lower leg a magnesium plate secured with gold-plate steel nails was used, but in 8 days the plate disintegrated with the formation of a large amount of gas under the skin. In spite of Lambotte's failure, study of the effect of magnesium on the surrounding tissue and the body as a whole continued.

An attempt to use pure magnesium for osteosynthesis was unsuccessful because magnesium pins disintegrated so quickly that they were unsuitable for the fixation of bone fragments; nevertheless, clinical, X-ray and histological investigations demonstrated that pure magnesium introduced into the body in the form of a pin has no harmful effect.

Attempts were made to dust bone transplants with magnesium and calcium in vacuum and then graft them in the patient's body. It was found that magnesium and calcium promoted rapid restoration of the entirety of the bone, this taking place 3 months sooner than when an untreated autotransplant was employed. Said method, however, is laborious and requires drainage for drawing off the gas formed.

Magnesium alloys with other metals have also been tried. Verbrugge used an alloy consisting of 92 percent magnesium and 8 percent aluminum; E. Bride reported the use of an alloy consisting of 95 percent magnesium, 4.7 percent aluminum and 0.3 percent manganese; M.S. Znamensky used an alloy consisting of 97.3 percent magnesium, 2.5 percent aluminum and 0.2 percent beryllium; B.I. Klepatsky tried an alloy consisting of 82.8 percent magnesium, 85 percent aluminum, 8.5 percent zinc and 0.2 percent manganese.

A review of the literature indicates that magnesium alloys employed for making fixation means dissolve completely in the bone and have no detrimental effect either locally or generally. However, the absorption of previously known magnesium alloys proceeds three or four times more rapidly than required from the standpoint of restoration of the entirety of the bone. Moreover, when said known alloys are used, drainage is necessary to remove the gas formed.

It is an object of the present invention to provide a magnesium-base alloy which has a rate of absorption slower than the process of bone consolidation, which does not involve vigorous evolution of gas and which has high mechanical strength.

It is another object of the invention to provide a magnesium-base alloy which meets the following requirements:

1. Ultimate strength .gtoreq. 28 kg/mm.sup.2 and yield point .gtoreq. 18 kg/mm.sup.2, i.e., the alloy's mechanical strength shall exceed that of bone tissue;

2. The rate of absorption of the alloy compared to the rate of consolidation of the bone shall be such that at the moment of complete restoration of the bone's entirety the alloy shall retain sufficient strength, i.e., the process of absorption shall be completed 1.5-2 months after knitting of the bone;

3. The rate of evolution of hydrogen during absorption of the alloy in the body shall be less or equal to the rate of absorption of hydrogen by the body.

4. The alloy shall contain elements which stimulate the growth of bone tissue, such as calcium and cadmium;

5. The alloy shall not contain elements which are harmful for the living organism, such as lead, beryllium, copper, thorium, zinc, nickel, etc.

The foregoing objects have been accomplished by the provision of a magnesium-base alloy which, according to the invention, contains the following elements, wt.%:

Rare earth metal 0.40-4.0 Cadmium 0.05-1.2 Calcium or aluminum 0.05-1.0 Manganese 0.05-1.0 Silver 0-0.8 Zirconium 0-0.8 Silicon 0-0.3 Magnesium remainder

Neodymium and yttrium are predominantly employed as the rare earth metal although other rare earth metals can be used.

The above alloy is produced by the conventional method by preparing a charge consisting of pure metals and master alloys and melting the same.

One of the advantages of the invention is that it provides an alloy having high chemico-physiological, mechanical and engineering properties. The ultimate strength of said alloy .gtoreq. 28 kg/mm.sup.2 and the yield point .gtoreq. 18 kg/mm.sup.2.

Employment of said alloy for joining bone fragments obviates the necessity of a second operation on the patient for the removal of foreign fastening means (pins, nails, etc.) since said alloy is completely absorbed without the accumulation of gas. Moreover, the stimulation of callus formation promotes the pateient's rapid recovery.

The following examples of variations in the composition of the alloy according to the invention are given by way of illustration.

EXAMPLE 1

Illustrates an alloy of the following composition, wt.%:

Neodymium 2.92 Cadmium 0.27 Calcium 0.24 Manganese 0.11 Magnesium remainder

The above alloy has the following properties:

Ultimate strength 32.6 kg/mm.sup.2 Yield point 24.5 kg/mm.sup.2 Elongation 6.3%

Said alloy was tested in a physiological solution containing 0.9 wt.% NaCl, 0.02 wt.% KCl, 0.02 wt.% CaCl.sub.2, 0.002 wt.% Na.sub.2 CO.sub.3, and the remainder, distilled water. Evolution of hydrogen in 48 hours totalled 3.4 cm.sup.3 /cm.sup.2. The result of the test indirectly gives a conception of the process of absorption of the metal in the body.

EXAMPLE 2

Illustrates an alloy of the following composition, wt.%:

Neodymium 2.46 Cadmium 0.12 Aluminum 0.09 Manganese 0.14 Silicon 0.01 Magnesium remainder The above alloy has the following properties: Ultimate strength 31.6 kg/mm.sup.2 Yield point 25.3 kg/mm.sup.2 Elongation 3.7% Hydrogen evolution in physiological solution of Example 1, 48 hrs. 2.1 cm.sup.3 /cm.sup.2

EXAMPLE 3

Illustrates an alloy of the following composition, wt.%

Yttrium 1.6 Cadmium 0.25 Calcium 0.06 Silver 0.3 Manganese 0.08 Magnesium remainder

The above alloy has the following properties: Ultimate strength 28.4 kg/mm.sup.2 Yield point 23.6 kg/mm.sup.2 Elongation 5.5% Hydrogen evolution in physiological solution of Example 1, 48 hrs. 1.6 cm.sup.3 /cm.sup.2

EXAMPLE 4

Illustrates an alloy of the following composition, wt.%:

Neodymium 1.8 Cadmium 0.09 Calcium 0.08 Manganese 0.13 Zirconium 0.49 Magnesium remainder

The above alloy has the following properties: Ultimate strength 32.2 kg/mm.sup.2 Yield point 21.8 kg/mm.sup.2 Elongation 8.9% Hydrogen evolution in physiological solution of Example 1, 48 hrs. 2.0 cm.sup.3 /cm.sup.2

The properties of the above alloy were determined on specimens 0.5 mm in diameter.

Said alloys were prepared by the following method.

Charges for the preparation of alloys consisted of pure metals (magnesium, cadmium, calcium, aluminum or silver) and master alloys (magnesium-rare earth metal, magnesium-manganese, aluminum silicon or magnesium-zirconium. Charges were melted in electric crucible furnaces at a temperature of 740.degree.-780.degree. C. The order in which the components were charged was as follows: magnesium, master alloy, pure metals.

The charge was melted under a flux of the following composition, wt.%:

MgCl.sub.2 34-40 KCl 25-36 NaCl + CaCl.sub.2 8.0 CaF.sub.2 15-20 MgO 7-10

after melting and thoroughly mixing, the alloy was refined with the above flux and let stand for 15-20 minutes, after which it was poured at a temperature of 760.degree.-780.degree. C through a magnesite filter into moulds.

After preheating and hot pressing at 520.degree.-540.degree. C the blanks were cooled in the air after which they were artificially aged at 160.degree..+-.10.degree.C for 16 hours.

The alloys thus produced were ready for use. Employment of the alloys specified in Examples 1, 2, 3 and 4 for joining bones in bone surgery demonstrated that all of said alloys possessed high mechanical and chemico-physiological properties. Clinical tests showed that said alloys were completely absorbed: pins 3 mm in diameter in 5 months and pins 8 mm in diameter in 11 months. Bones knitted in 4 months.

Fluoroscopic examination revealed no gas bubbles in the soft tissues during the entire period of absorption of said alloys.

Operative treatment of fractures by means of the present alloy reduces the time required for union of the bone by 33-50 percent. In this respect the best showing was made by the alloy described in Example 2.

As is apparent from the figures cited, evolution of gas by the alloys described in Examples 1, 2, 3 and 4 is within the body's absorptive capacity, since said capacity is 4.0-4.5 cm.sup.3 of gas from each sq.cm. of surface of the metal being absorbed per 48 hrs.

Claims

We claim:

1. A bone fastening device, for the fixation of bone fragments, constructed of an alloy, consisting essentially of, by wt.%:

2. A device as in claim 1 which has the following composition by wt.%:

3. A device as in claim 1 which has the following composition, by wt.%:

4. A device as in claim 1 which has the following compositions, wt.%:

5. A device as in claim 1 which has the following composition, wt.%: