RU2308250C1 - Cotyloid cavity endoprosthesis - Google Patents

Abstract

FIELD: medical engineering.

SUBSTANCE: device has screws and spherical cup having through holes for receiving spongious screws. Metrical thread is available on the screws near the head and spongious thread is available on the rest screw surface. The spongious thread pitch is equal to that of metrical one and both threads are of the same rotation direction. The spongious thread diameter is not greater than that of the metrical one. Metrical thread is available in at least three through holes for receiving spongious screws. Holes for receiving spongious screws in the cup member have their axes intersecting in the same point coinciding with the common hemispheres center at an angle of 105±15° with respect to each other. The cup member is manufactured from metal having porous coating on the external surface.

EFFECT: stable fixation conditions; high strength, reliability, long service life.

2 cl, 4 dwg

Description

The invention relates to medical equipment, is used in traumatology and orthopedics, and is intended to replace a deformed or destroyed acetabulum of the pelvis.

To fix the endoprostheses of the acetabulum to the bone tissue, various profiles of annular and screw grooves are used [Sivash K.M. Hip Alloplasty. M .: Medicine, 1967, p. 70-71, fig. 17 (a, b, c, d)], protrusions, racks [ibid, p. 36, fig. 8 (a, b, c, d) ], including with curly elements [RF patent 2021785, 1994], as well as bone screws [Moshkovich I.A., Vilensky V.Ya. Polymers in traumatology and orthopedics. M .: Medicine, 1978, p.139, Fig. 62].

All of these endoprostheses with the aim of increasing the stability of fixation to the bone do not possess this quality to a sufficient degree. Moreover, acetabular endoprostheses that carry annular grooves on their surface, when they are nailed into the bone, destroy the latter, which increases the duration of treatment.

Known endoprosthesis of the acetabulum [RF patent No. 2021786, 1994], which is a metal bowl with an insert made of a polymer material. On the side surface of the bowl there are petals for fixation in the acetabulum of the pelvis, and indentations inside the bowl are designed to hold the insert in it.

However, such a design also cannot provide reliable fixation of the endoprosthesis.

An acetabulum endoprosthesis is also known [RF patent No. 2131712, 1997], the peculiarity of which is that on the equatorial plane of the hemispherical polymer cup, an annular groove is made concentrically and to the periphery from its cavity, from which channels opening on one parallel to the spherical surface originate while the axis of the channels is pairwise converged, and the fastening elements to the bone are made in the form of brackets placed with the possibility of movement and fixation in the channels.

Placing the outlet openings of the channels on one parallel to the spherical surface of the bowl ensures the creation of a rigid corolla formed by the protruding ends of the staples, which increases the stability of fixation of the endoprosthesis to bone tissue.

However, the fastening elements - staples - are placed in channels made without taking into account the actual distribution of loads between the pelvic bones, which can lead to uneven stresses and deformations in the rigid corolla formed by the protruding ends of the staples, and the corresponding uneven wear of the endoprosthesis and bone fasteners.

The closest technical solution - the prototype - of the invention should be considered an acetabular endoprosthesis, created by the Swiss company Mathys Medical Ltd. (see Al. A. Nadeev and others. "Rational hip joint replacement." - M .: BINOM. Laboratory of Knowledge, 2004, p.64). The specified endoprosthesis has a spherical cup shape with concentric waves on the outer surface. The cup is coated with hydroxylapatite or titanium spraying, has two pins and several holes of different diameters for spongy screws. This design of the endoprosthesis is quite simple to use and provides a strong connection with bone tissue. To prevent scrolling and primary instability, these two pins are used.

However, the separation of the functions of attachment strength and orientation stability relative to the underlying bone leads to uneven load distribution on the ilium, pubic and ischial bones, which increases the risk of instability of the acetabular component. In addition, the bulkiness and complexity of the design of the endoprosthesis increases.

The technical result of the proposed technical solution is to increase the stability of fixation of the acetabular component of the endoprosthesis in the bone tissue, improve the uniformity of the distribution of loads from the endoprosthesis on the pelvic bones, increase the strength, reliability and durability of the fastening of the endoprosthesis in the bone tissue.

The essence of the invention lies in the fact that in the endoprosthesis of the acetabulum containing a spherical cup with through holes for the spongy screws, the metric thread is made from the heads of their heads on the said screws, the rest of the length to the ends of the screws is a spongy thread with a step equal to their step metric threads, and the threads have a stroke in one direction, the diameter of the spongy thread of the screws is not more than the diameter of their metric thread in at least three through holes for the spongy screws metric thread is filled with a step equal to the spongy thread pitch of the screws, while the holes for the spongy screws made with a metric thread in the cup are oriented so that their axes intersect at an angle in the range 105 ± 15 ° to each other at one point coinciding with the common center of the hemispheres forming the surface of the cup, the cup is made of metal and with a porous coating on the outer surface.

In addition, the metric thread on the side of the screw heads can be performed on a section of screws with a length of not more than the difference in the radii of the hemispheres that form the outer and inner surfaces of the cup.

The through holes for the spongy screws in the cup with a metric thread with a step equal to the spongy thread of the screws, and on the screws themselves - from the side of their heads metric threads corresponding to the threads of the cup holes, throughout the rest of the screws - spongy threads - maximize the convergence of the averaged elastic moduli of the endoprosthesis design and bone tissue parameters.

Orientation of the holes in the cup so that their axes intersect at an angle from a range of 105 ± 15 ° to each other in the common center of the hemispheres, provides maximum strength, static and kinematic stability of the structure and, together with the features of the thread on the endoprosthesis elements, increase stability fixation of the acetabular component of the endoprosthesis in the bone tissue, improving the uniform distribution of loads from the endoprosthesis on the pelvic bones, increasing the strength, reliability and durability of the fastening of the endoprosthesis in the bone tissue.

Performing a metric thread on the side of the screw heads on a section of screws with a maximum length of no more than the difference in the radii of the hemispheres forming the outer and inner surfaces of the cup provides guaranteed pressing of the outer surface of the endoprosthesis to the bone tissue of the hip joint and, accordingly, additional reliability of the fastening of the endoprosthesis.

The acetabular endoprosthesis is shown in FIGS. 1-4.

Figure 1 shows a general view of the endoprosthesis, figure 2 shows a section of the endoprosthesis cup with the plane of symmetry of one of the holes for the spongy screws, figure 3 shows the fastening element of the endoprosthesis to the bone tissue - the spongy screw with the features of the threaded fastener, figure 4 - endoprosthesis, view from the side of its attachment to the hip joint.

The device comprises a metal cup 1 formed by hemispherical outer 2 and inner 3 surfaces with a common center 4 (an imaginary point of intersection of the radii of the hemispheres forming the cup surface). Holes 5 are made in the cup for spongy screws with a metric thread 6, the step of which is equal to the spongy thread 7 made on the free end of the spongy screws 8. On the screw head side, a metric thread 9 is made on the screw section of a length of no more than the difference of the radii of the hemispheres forming the outer 2 and the inner 3 of the surface of the cup 1. The axis of the holes 5 intersect at one point, coinciding with the common center 4 of the intersection point of the radii of the hemispheres, at an angle α of intersection with each other, selected in the range 105 ± 15 °.

The specified range of spatial orientation of the fasteners covers the optimal region of maximum strength, static and kinematic stability of the endoprosthesis design and is justified by the natural laws of natural strength and stability of solids based on the following considerations.

From the general postulates of crystallography, which distinguishes seven more or less independent crystallographic systems for the formation of crystalline lattices of solids, it follows that one of them - trigonal (rhombohedral) - can be represented as a result of compression or extension of a primitive cubic Bravais lattice along one of the main diagonals of the cube . In this case, the equality of all sides of the lattice (a = b = c — constant lattice values — segments along the corresponding crystallographic axes) and angles (α = β = γ — angles between the crystallographic axes) remains, but the angles cease to be straight. Thus, at high external pressures and, accordingly, a high level of internal mechanical stresses, the crystal lattice in the phase corresponding to these large pressures should be a face-centered cubic lattice with angles between the axes corresponding to the condition α = β = γ <120 °, but not less 90 °.

An example is the crystal structure of diamond (the angle between the crystallographic axes of which corresponds to the specified range and is approximately equal to ≈112 °). The same crystal structure has classical semiconductors of the fourth group of the periodic table germanium and silicon, which also have high strength characteristics. All the above conditions are satisfied by the equality of the length of the spongy screws and the orientation angles between their geometric axes in the design of the endoprosthesis.

The device is used as follows. One of the conventional methods exposes the area of the hip joint, excise the capsule of the joint and scar-modified paraarticular tissue. In case the femoral head is destroyed, it is excised and replaced with a prosthesis. An altered pelvic acetabulum is excised with a grooved chisel, and then treated with a spherical cutter corresponding to the size of the cup 1 of the implantable acetabulum implant. The latter is introduced into the cavity processed by the mill. The next step is the introduction of the spongy screws 8, first along the spongy thread 7 of the orientation of the endoprosthesis in the bone tissue of the hip joint, and then by the metric thread 6 of the fastening of the spongy screws to the metal cup and the latter to the bone, due to which the endoprosthesis acquires and maintains a stable position. After setting the femoral head (or the femoral endoprosthesis head) into the spherical cavity of the inner surface 3, the wound is sutured in layers.

Claims (2)

1. An acetabular endoprosthesis containing screws and a spherical cup with through holes for spongy screws, characterized in that the said screws have a metric thread on the side of their heads, the rest of the length to the ends of the screws is a spongy thread with a step equal to their metric pitch threads, moreover, the threads run in one direction, the diameter of the spongy thread of the screws is not more than the diameter of their metric thread, at least three through holes for the spongy screws have a metric thread with equal to the pitch of the spongy screw thread, while the holes for the spongy screw made with a metric thread in the cup are oriented so that their axes intersect at an angle in the range of 105 ± 15 ° to each other at one point that coincides with the common center of the hemispheres that form the surface of the cup, the cup is made of metal and with a porous coating on the outer surface. 2. The endoprosthesis according to claim 1, characterized in that the metric thread on the side of the screw heads is made on a section of screws with a length not exceeding the difference of the radii of the hemispheres forming the outer and inner surfaces of the cup.

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