RU2306898C2 - Bone ostheosynthesis device - Google Patents

Abstract

FIELD: medicine; traumatic surgery; orthopedics.

SUBSTANCE: bone ostheosynthesis can be used for treating fractures of long tubular bones. Device has screws and plate provided with openings for screws. Ends of openings for screws, adjoining bone, are made with curvatures of radius R=0,05-0,25 diameter of screw.

EFFECT: improved efficiency.

3 dwg

Description

The invention relates to medicine, namely to traumatology and orthopedics, and can be used in the treatment of fractures of long tubular bones (especially lower limbs).

The diaphyseal plate of the classical type is known and widely used in the practice of treating diaphyseal fractures (see, for example, Tkachenko S.S. Osteosynthesis. - L .: Medicine, 1987, p. 36), which is a flat oblong plate with holes, installed its middle part at the fracture site and attached with screws to the proximal and distal fragments. This plate is taken as the closest analogue.

To avoid the so-called fracture diseases (joint contracture, muscle atrophy, etc.), the earliest possible activation of patients is currently used - one of the main means of drastically reducing adverse treatment outcomes. However, early activation makes high demands on the strength and reliability of implant designs, since studies have shown, for example, that when walking short-term loads on the implant, which carries the main load at the beginning of rehabilitation, can exceed the patient's weight by an order of magnitude (edited by I. Obraztsova Problems of Strength in Biomechanics. - M.: Higher School 1988, p. 100).

Under these conditions, cases of destruction of implants are relatively often observed. Among such cases, cutting of the screw heads at the point of contact of the plate with the bone is noted.

The objective of the invention is to create a plate for bone osteosynthesis, devoid of the disadvantages of the plate, taken as the closest analogue.

The solution is achieved by creating a fillet of a certain radius in the holes of the plate at the place of their exit towards the bone. The transfer of effort from the fragment to the implant is as follows. The bone first transfers force to the screw. Since the elastic modulus of the bone is significantly lower than that of the metal, contact stresses are equalized due to this (the bone transfers from less loaded areas to less loaded ones and there are no voltage peaks). A completely different picture is observed where the screw transfers the perceived efforts to the plate. There is equality of elastic moduli, and they are very high (in surgical steel 2.10 ⁶ Kg / cm ² ). In turn, this leads to the fact that even at very high loads, the contact area with the edge of the hole remains almost point. At this point, a voltage peak occurs. This picture is further enhanced by a very small, but non-zero rotation of the screw in the bone under load (due to the lower modulus of bone elasticity). The screw falls into conditions that arise, for example, when cutting metal with guillotine shears, which can easily cut plates even from 10 mm steel, while the edges of the plate practically do not crumple - the stresses are localized in the area directly to the cut. On the other hand, everyone knows how difficult it is to cut even thin tin with blunt scissors. Here the voltages are distributed over a large area, and there is no peak voltage.

In our case, a fillet (rounding) of a certain radius on the inner (to the bone) edges of the hole can help. This radius should lie within rather narrow limits, since it cannot be substantially increased - the contact point will lie deep in the plate, which will lead to the appearance of an additional load - stresses from bending moment will be added to the shearing force. Therefore, the fillet rounding radius should be minimal, but at the same time sufficient to significantly reduce peak loads. Our calculations show that it depends on the diameter of the screws used and should lie in the range from 0.05 to 0.25 of the diameter of the screw. Plots of stresses occurring in the screws in the first and second (with fillet) cases are shown in figure 1 and figure 2. For the plate, the described efforts are not terrible, since they are distributed over a large area.

In figure 1 and figure 2

1 - the cortical layer of bone adjacent to the plate 2, the screw 3 connects the plate to the brush, on the lower generatrix of which a diagram of 4 shearing forces is constructed, indicated by arrows.

The technical result from the application of the proposed solution to the problem is to increase the reliability of osteosynthesis in an early functional load.

The device contains a plate with holes for screws. The edges of the holes on the side of the plate adjacent to the bone have fillets (rounding) with a radius lying within 0.05 ... 0.25 of the diameter of the screw.

Figure 3 presents the design of the device. The device is a plate 1 attached by screws 2 to a bone 3 (upper cortical layer is shown). The letter R denotes the radius of curvature of the hole.

Apply the plate in the usual way.

Soft tissues are dissected over the fracture area and reposition of fragments is carried out. A plate is placed on the fracture site with the middle part, cortical layers are drilled. All screws are inserted into the holes, then the wound is sutured in layers.

After consolidation of the fracture, the plate and screws are removed.

Thus, the use of fillets allows you to avoid peak loads and prevent the destruction of screws.

Claims (1)

A device for bone osteosynthesis containing a plate with holes for screws and screws, characterized in that the edges of the holes for screws adjacent to the bone are made with roundings of radius R = 0.05-0.25 of the diameter of the screw.

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