DE19804065A1 - Jet cutting method useful for cutting biological tissue, e.g. human connective and skeletal tissue - Google Patents

Abstract

In a cutting process using a jet of liquid abrasive, the liquid contains a water-soluble solid in crystal, powder or granular form as abrasive to increase cutting efficiency.

Description

description

The invention relates to separation processes for biological tissues, especially connective and supporting tissues of the human body such as bones, Cartilage, tendons, inner skin of the joint, menisci, tooth structure etc., as well as for biocompatible materials and materials such as bone cement (PMMA), Implant materials and other materials.

In general, it should be as universal as, for example, a saw or a knife to be used. In addition, selective separation is inherent in the principle different materials from each other possible if their mechanical Differentiate properties sufficiently from each other, e.g. B. meniscal tissue and Cartilage, bone and cartilage, bone and bone cement (PMMA) or Bones and implant material.

In the 1960s, water jets became high kinetic energy originally for aerospace applications, especially for cutting of fiber composite materials. The water jet is now in many Areas of industrial manufacturing technology not just an established cutting, but also drilling and cleaning tools:

The advantages compared to traditional separation processes include athermal character of the cutting process, in the possibility of selective Removal of a material if the mechanical properties are different enough in the low mechanical load of the Workpiece and the extensive freedom from wear of the cutting tool itself. The area of application of "classic" water jet cutting is however mainly limited to non-metallic materials, because the Cutting hard materials, very high pump pressures can hardly be realized.

At the beginning of the eighties, water-abrasive jet cutting was developed, the separating effect of the water jet by adding solids as Cutting or abrasive medium for the processing of metal, glass and ceramic materials could be expanded. The water jet serves here in water abrasive jet cutting as a fluid-borne impulse stream Power transfer to the actual cutting medium, the abrasive.

The accelerated to high speeds by the energy source Abrasive particles lead to local material abrasion Load (micro-machining, micro-notching) on the workpiece. As an abrasive is in the industry mainly uses garnet sand, as this substance has so far conflicting requirements for a high cutting capacity on the Workpiece with low wear on the water abrasive nozzle on the best united.  

The problem with the use of liquid abrasive jet cutting in biological applications is the abrasive itself. B. garnet sand or corundum cannot be used because these particles are water-insoluble and could not be completely removed from the adjacent tissue or material after the actual abrasion process, even with the most careful rinsing and suction. An abrasive used here must therefore have the following properties:

• - Water solubility, so that the abrasive after the actual ablation process, dissolved in dilution liquid and diluted, can be suctioned off
• - biological / pharmacological safety
• - High molecular weight to maintain physiological osmolarity

The substances listed in claim 4 meet these conditions in sufficient measure.

This offers the user a cutting process which has the following advantages over the conventional tools listed above:

• 1. High, effective material removal rate
• 2. Selective removal of different tissues or materials within one certain "pressure window" due to the different mechanical Properties (for example: removal of PMMA while largely protecting the Bones [elastic, good tensile and compressive strength and PMMA (brittle, sensitive to tension and notching]).
• 3. Higher tool range also in the gap.
• 4. "Rinsing out" the overburden (for example, bone cement along one Implant contour: The hard metallic prosthesis materials are made by the comparatively low pressures and relative to industrial ones soft biocompatible abrasives are not attacked, d. H. the cutting beam can also be "blasted" tangentially along curved implant surfaces will)
• 5. Cold cutting process
• 6. low reaction forces of the tool on user and workpiece:
  Manual guidance is possible even at pressures above 1000 bar.

The separation of bones or other tissues is through tools like Knife, osteotome, drill, milling machine and saw partially sufficiently loosened, but surgical tasks that reach the limits are becoming increasingly common:

As an example, the special application as a tool for Removal and implantation of artificial joints in particular Hip endoprostheses explained:

Before a prosthesis with a removal tool is driven out, the Surgeon try to make the connection gap with conventional tools like Separate chisels, routers or drills as much as possible to Reduce area.

Difficulties arise from restricted access to the implant Bone cement connecting gap and extremely limited space in the Femur (a few millimeters).

The disadvantages of the conventional tools mentioned in this process are, in principle, the following:

• - limited reach or depth of cut in the gap
• - non-selective removal, d. H. no removal of bone cement only Protection of adjacent bone
• - Risk of bone splitting due to a minimum space requirement in the interface
• - Risk of thermal damage to adjacent bone tissue

After removal of the prosthesis, the bone cement sheath remains largely in the thigh bone. This must be removed before the start of a re-implantation become. Various corkscrew-like devices are used for this, a number Different shaped chisels as well as drilling and milling tools:

This technology also offers in particular due to the limited space in the Femur shaft little opportunities to work gently, so it is too large substance loss on the bone can occur.

The non-cemented prostheses can usually not be cut without sawing the Remove the bone tube from the bone as the bone tissue enters the Coating or the rough surface structure is ingrown and a great one Part of this connection gap only from the outside using the above-mentioned tools can be solved. Accordingly, the bone loss and thus the loss is large Damage to the implant site of the new prosthesis.  

Since 1976, the possibilities of processing PMMA in the bone during reoperations using high-frequency oscillating metal probes (so-called ultrasonic probes) have been examined. This method has the following problems:

• - The amorphous thermoplastic bone cement (PMMA) is affected by the heat is generated by the vibrations of the ultrasound device at the boundary layer melted. The cement must be removed immediately if it softens , otherwise a new hardening, possibly in a different place, the Consequence would be.
• - The toxic monomeric vapors generated when the PMMA is heated only allow working under perfect fume cupboard and ventilation conditions to.
• - The temperatures generated during removal are close to the prosthesis from 50 ° C to 90 ° C, depending on the cooling method. Through these temperatures thermal damage to the bone tissue is caused. In the range of Cancellous bone is also at risk of co-removal healthy trabeculae due to thermal injury.

Attempts to remove bone cement with laser showed that apart from toxic vapors and the risk of thermal damage adjacent Tissue (see above), the efficiency of this process with removal rates of up to 10 g / h precludes intraoperative use per se.

The problems described above are solved by the in claims 1 to 4 mentioned features solved.  

An embodiment of the invention is shown in the drawing 1 and is in described the following in more detail:

Show it

• 1. the actual handpiece in the form of a cylinder with a one-sided internal thread for receiving the mixing chamber focus unit ( 6 )
• 2. the concentric bore of the pressurized water supply in the handpiece
• 3. a conical, self-sealing internal thread for connecting the Pressure water hose
• 4. a conical fit for sealing against the water nozzle ( 5 )
• 5. the water nozzle, which is inserted with the jet calming tube into the mixing chamber ( 6 ) and thus is positively centered, and which is sealed off from the pressurized water bore ( 3 , 4 ) by a conical fit
• 6. the mixing chamber-focus unit with a concentric bore as a mixing chamber, which tapers conically on one side towards the opening of the soldered focus tube ( 8 ), and an external thread with which the unit is screwed into the handpiece
• 7. a conical bore opening into the mixing chamber as an abrasive feed
• 8. The focus pipe for the water abrasive jet that flows into the conical mixing chamber opening is soldered

Explanation of how this device works

The pressurized water is pressed through the water nozzle ( 5 ) and reaches the mixing chamber ( 6 ) as a focused, compact water jet. There, a spray cone forms around the compact core jet, which wets the mixing chamber walls and thus generates a slight negative pressure based on the principle of the water jet pump. The abrasive material is sucked in air with its conveying medium by this negative pressure and injected into the mixing chamber and into the high-pressure water jet via the abrasive material feed ( 7 ) (injector method). The water abrasive jet is mixed and focused again in the downstream focus tube ( 8 ).

As experiments have shown, the pressure-dependent contact time is the water-soluble Abrasive with its conveying and acceleration medium for a complete Dissolution of the abrasive particles is not sufficient. Therefore, the Abrasive particles when hitting the material to be removed Effect material removal.

Claims (4)

1. Liquid abrasive jet separation process, characterized in that a water-soluble solid in crystal, powder or granule form is introduced to increase the cutting performance as an abrasive in the liquid jet. 2. Liquid abrasive jet separation method according to claim 1 characterized in that as an energy source for the impulse to be transmitted to the abrasive particles Solution of one or more different substances such as physiological salts, Sugar, sugar alcohols, amino acids or polymers are used in the pressure jet. 3. Liquid abrasive jet separation method according to claim 1 and 2 characterized in that the abrasives used are soluble. 4. Soluble abrasives according to claim 1 and 2 and 3 characterized in that crystalline organic compounds such as mono-, di-, oligo- or as abrasives Polysaccharides (fructose, glucose, sucrose, lactose and others), polyhydric sugar alcohols (sorbitol, mannitol, xylitol and others), Amino acids and their polymers (alanine, glycine, histidine, proline, serine, Threonine, valine, leucine, isoleucine and others), inorganic crystalline Compounds such as NaCL or lime salts such as hydroxylapatite can be used.