Surface reconstruction cup for forming mixed joint of cotyle of hip joint

Abstract

To provide a cotyle component for surgical treatment of reconstruction of a hip joint surface for saving bones.SOLUTION: In a surface reconstruction cup 10 of a cotyle, a femoral bone head 201 is joined in articulation, the femoral bone head being subjected to shaving into a spherical shape, and from the femoral bone head, a bone spur which may restrict a movable range by abutting to a cotyle is removed. An inner surface of the surface reconstruction cup 10 is formed into an aspherical shape, and causes annular contact with the femoral bone head 201. A surface of the cup 10 which is joined in articulation at inside is coated by an amorphous-diamond-like-carbon or pyrolysis carbon, for reducing wear and friction of the femoral bone head. By avoiding use of a surface reconstruction component on a femur 200, a surgical treatment time is reduced significantly, thereby extremely improving a surgical method. The cup is preferably a double shell type for cement-less fixing, however, the cup may be created as a single shell for cement-less or cement fixing.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an acetabular cup for hemiarthroplasty of the hip joint for use in human and veterinary medicine.The present invention further relates to a dual mobility revision total hip replacement with an acetabular resurfacing cup and a femoral head shaver for preparing the femoral head for articulation in said acetabular resurfacing cup. [Background technology]

[0002] Total hip replacement is considered one of the most successful, quality of life improving surgical procedures of the past century. The history of hip joint surgery in more widespread use began in the late 40's with Austin-Moore's hemi-prosthesis for the femoral head and femoral neck. The femoral stem was cementless with fenestration for bone ingrowth.

[0003] The first total hip prostheses, of the metal-on-metal type such as the Thompson hemiprosthesis modified by McKee, were introduced in the 50s. Clinical results were mixed and acceptance was limited.

[0004] The revolution in clinical acceptability and the beginning of modern total hip replacement is attributed to Charnley with the introduction of the cemented stem and cemented polymer cup in the mid-60s. That basic concept is still in widespread clinical use despite all the advances in cementless fixation of both the femoral and acetabular components.

[0005] In the past 20 years, most of the development of total hip arthroplasty has focused on articulation to reduce wear of the components, which are mostly polymer cups. Today's state of the art is a combination of a femoral ceramic head and a cross-linked, vitamin E-supplemented ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. The acetabular cup is either provided with a metal backing for osseointegration or is cemented.

[0006] Another approach for hip arthroplasty, by the so-called resurfacing procedure, appeared in clinical use in two waves, both of which ended in conceptual failure. The first attempts by Wagner and Amstutz in the mid-70s were not followed by success. The more recent resurfacing approach is due to McMinn and his Birmingham model of resurfacing total hip arthroplasty, based on metal-on-metal articulation. However, excessive wear of the metal components caused major clinical complications and put an end to this second wave of bone-sparing hip arthroplasty.

[0007] Hemiarthroplasties are still commonly used, but for various reasons, more common today is the so-called bipolar model, in which a conventional femoral component is combined with a large diameter head that articulates with the intact acetabulum. This model is, for obvious reasons, limited in use to patients with an acceptable level of degeneration of the acetabular cartilage (usually due to a fracture of the femoral neck in elderly patients).

[0008] In summary, all of the previous hip prostheses discussed above consisted of some kind of femoral component paired to an intact acetabulum or acetabular cup.

[0009] In the last decades of hip arthroplasty, the need for its use in young, active patients has increased. Wear of polymer acetabular cups has become the limiting factor in the durability of the prosthesis. Typically after 7-9 years of surgical procedure, accumulation of wear particles in and around the joint leads to bone loss and aseptic loosening of the components. In the average patient aged 70 years at the time of primary replacement, the revision rate at 15 years after surgery is less than 5%, compared to 20-25% in young, active patients. The most direct reason for this difference is the activity level, and in all laboratory experiments, the wear of the polymer is proportional to the number of cycles.

[0010] Although clinical outcomes have improved with newer wear-resistant articulations, such as ceramic heads on cross-linked UHMWPE cup inlays, the problem of aseptic loosening in young active patients remains a significant factor leading to high revision burdens, as high as one in five in some countries. Secondary procedures last even shorter.

[0011] The use of resurfacing total hip replacements was primarily motivated by the preservation of femoral mass so that eventual revision with a stemmed femoral component could be more easily performed. Since the metal-on-metal designs of resurfacing prostheses have failed due to metal wear causing a so-called "tumor-like" tissue response, this option has essentially disappeared and is performed by only a few surgeons worldwide, mainly for very young patients involved in high-demand sports.

[0012] Hemiprostheses are currently only used when the acetabular cartilage is still in good condition. A patent application by the inventor (US2013 / 0060345A1) discloses a potential improvement over current practice by proposing an aspheric pairing of hemiprostheses, where the prosthesis head is covered by an amorphous-diamond-like-carbon (ADLC) coating or pyrolytic carbon. These carbon coatings have been shown to dramatically reduce wear of the opposing bone when compared to metals or ceramics. Aspheric articulation as described in US Patent No. 8,323,346 (Tepic) reduced wear by approximately three times in laboratory experiments. Summary of the Invention [Problem to be solved by the invention]

[0013] The hip joint replacement proposed by the present invention is of a new type in which the only prosthetic component is an acetabular cup. The acetabular cup hemiprosthesis is combined with a natural femoral head, which remains largely intact and may only be shaved to a substantially spherical shape, removing irregularities such as osteophytes around the head to reduce the risk of impingement. [Means for solving the problem]

[0014] The present invention solves the major problem of bone-sparing hip resurfacing surgery by using only an acetabular component into which articulates the natural femoral head, which has only been shaved into a spherical shape and free of osteophytes that may impinge on the acetabulum and limit range of motion. Preferably, the inner surface of the resurfacing cup is aspherical in shape, resulting in annular contact with the femoral head. The inner, articulating cup surface is preferably coated with a carbon-based material, such as ADLC and / or pyrolytic carbon, to reduce friction and wear of the femoral head. By avoiding the use of a femoral resurfacing component, surgical procedure time is significantly reduced and the surgical technique is greatly advanced. The cup is preferably of a double shell type for cementless fixation, but can also be made as a single shell for cementless or cemented fixation. If the need for a revision surgery arises due to wear of the femoral head, the cup can be maintained and combined with a dual mobility femoral component.

[0015] Thus, a first aspect of the invention is an acetabular resurfacing cup for hemiarthroplasty of the hip joint. The acetabular resurfacing cup is adapted to a natural femoral head, i.e. a femoral head having a natural bone surface. The acetabular cup of the invention is particularly adapted to human medicine, but may also be used in veterinary medicine, for example for dogs.

[0016] The inner surface of the acetabular resurfacing cup faces the femoral head. The shape of this inner surface may be aspheric and may include an annular portion that is spherical in shape. The angle subtended by the annular spherical portion is preferably in the range of 5-30 degrees, more preferably in the range of 10-20 degrees. The angle from the axis of symmetry of the acetabular resurfacing cup to the annular spherical portion is preferably in the range of 25-50 degrees, more preferably in the range of 30-45 degrees. The axis of symmetry of the inner shape of the cup may be offset from the main axis of symmetry of the cup by an angle preferably in the range of 5-30 degrees, more preferably in the range of 15-25 degrees.

[0017] The inner surface of the cup may be coated with any suitable material, for example, a carbon-based material such as ADLC and / or pyrolytic carbon.

[0018] The cup of the present invention may be adapted for cementless fixation, for example by a double shell construction or as a single shell, or the cup may be adapted for cement fixation.

[0019] A further aspect of the invention relates to a hip joint prosthesis comprising the acetabular resurfacing cup described above.

[0020] Yet a further aspect of the invention relates to a femoral head shaver for preparing a patient's femoral head for articulation, in particular for articulation in the above-mentioned acetabular resurfacing cup. The femoral head shaver may comprise a shaving cup covering a generally hemispherical shape with an inner surface that exceeds an angle of about 180 degrees, where the inner surface comprises cutting projections, e.g. cutting flutes, for reaming the bone and openings for removing small pieces of bone. The shaving cup is adapted for rotating and pivoting operations, for example by being connected to a rod or similar element.

[0021] Yet a further aspect of the present invention relates to the combination of the femoral head shaver and acetabular resurfacing cup described above.

[0022] Yet a further aspect of the present invention relates to a method for hemiarthroplasty of a hip joint including the step of implanting the acetabular resurfacing cup described above.

[0023] Yet a further aspect of the present invention relates to the combination of the above-mentioned acetabular resurfacing cup with a prosthetic femoral component, such as a femoral head for a dual mobility revision total hip replacement.

[0024] Yet a further aspect of the present invention relates to a method for dual mobility revision total hip replacement with the above-mentioned acetabular resurfacing cup.

[0025] In a preferred embodiment of the invention, the articulation is aspheric and has a carbon-based coating that provides a novel combination of features, where the acetabulum, and only the acetabulum, is resurfaced with a prosthetic component, while the femoral head is maintained in its essentially natural state.

[0026] This combination has several important advantages. First, only a very small amount of bone needs to be removed. If revision becomes necessary, it is only a femoral revision with a dual mobility femoral replacement in which the head of the primary prosthesis is covered by a polymer cup, which articulates against the resurfaced acetabulum. Reaming of the acetabulum is also minimal, since the thickness of the cup can be only about 1 to about 4 mm, preferably about 1.5 to about 3 mm. Reaming of the acetabulum is generally much less risky than reaming of the femoral cavity, which is known to result in some very serious complications such as pulmonary embolism. With press-fit stems, there is also a high risk of bone cracking. In Birmingham-type resurfacing total prostheses, the femoral head is reamed to a specific shape and then covered by a cement cup with a centering pin. Although bone loss is less than with conventional stem femoral components, the bone blood supply of the remaining femoral head is compromised, which can result in large bone necrosis. In contrast, in the present invention, the head is simply shaved to a spherical shape with the major irregularities removed so that it can fit into the resurfaced acetabulum. Preferably, the cavity of the acetabular cup is aspheric and covered with a carbon-based material coating, e.g., an ADLC coating, or with pyrolytic carbon. The time of the surgical procedure is significantly reduced, as is the cost of the prosthesis. The surgical technique is well known and used by many surgeons for Birmingham-type resurfacing. [Brief description of the drawings]

[0027] [Figure 1] 1 shows a state-of-the-art total hip replacement prosthesis. [Diagram 2] 1 shows a state-of-the-art hip replacement hemiprosthesis. [Diagram 3] 1 shows a state of the art resurfacing hip replacement prosthesis. [Figure 4] 1 shows a hemi-hip replacement prosthesis according to the present invention. [Diagram 5] 1 shows a double shell acetabular hip hemi-replacement prosthesis according to the present invention. [Figure 6] 1 shows a single-shell acetabular hemi-replacement prosthesis according to the present invention. [Figure 7] 1 shows a femoral head shaving instrument according to the present invention. [Figure 8] A revision surgical procedure using a dual mobility femoral head component is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] A state-of-the-art total hip replacement prosthesis (FIG. 1) comprises an acetabular cup 1 fixed to the pelvis 100, a femoral stem 2 (with a femoral head 3 attached to the stem 2) fixed to the femur 200. A typical structure today has an inlay of a polymeric cup, most commonly from crosslinked UHMWPE backed by a metal shell with a porous coating facing the bone. The stem for cementless fixation may also be coated with a porous layer or rough-blasted, for example with a thin coating of hydroxyapatite. The head may be metallic or ceramic. As an alternative to cementless fixation, both the cup and the stem can be cemented into the respective bone with so-called bone cement (two-component poly-methyl-methacrylate).

[0029] A state of the art hemi hip replacement prosthesis (FIG. 2) comprises only a femoral component. A femoral stem 4 is fixed to the femur 200. A large diameter femoral head 5 fits over the stem 4 either directly or via a smaller head to form a bipolar hemi-prosthesis.

[0030] The Birmingham-type resurfacing total hip prosthesis (FIG. 3) comprises a femoral component 6 with a large diameter head (usually cemented to cap the femoral head and reamed down to accommodate the head of the prosthesis) and a centering pin 7 with some space to allow for filling with bone cement 8. The acetabular component 9 is usually cementless and is hammered into a reamed acetabulum 100.

[0031] The hip replacement hemiprosthesis according to the invention (shown in FIG. 4) preserves most of the femur 200 and relies only on an acetabular resurfacing cup 10 fixed within the pelvis 100. The size of the cup 10 is selected to fit the natural femoral head 201 (which is reamed into a spherical shape by removing as little cartilage and bone as possible to create a spherical shape and to remove any gross deformities in the form of osteophytes that tend to form at the neck of the femur). The cup is preferably cementless, but can also be cemented into a reamed-out acetabulum.

[0032] The double-shell acetabular cup according to the invention (shown in FIG. 5a) comprises an outer shell 11 and an inner shell 12. A double-shell acetabular cup for total hip replacement is disclosed in U.S. Pat. No. 7,776,097 (Tepic and Malchau). The cup may comprise perforations 13 in the outer shell to allow rapid infiltration by bone. The outer, bone-facing surface of the shell 11 may be coated with a porous material 14, such as titanium and hydroxyapatite, thereby providing additional micro-fixation. Press-fit stability of the cup in the reamed-out acetabulum may be enhanced by small extensions, such as ribs 15, in the outer shell near the cup opening. The inner shell 12 may be snapped into the outer shell 11 at the cup opening (e.g., snap-pressed), leaving a small gap 16 between the two shells. The size of the gap is typically about 0.5 to about 1.5 mm.

[0033] This combination results in a metal structure that is highly compliant for integration into the pelvic bone without the stress shielding observed when thick, rigid metal backings are used for conventional total hip cups. Preferably, the inner shell of the cup is made of a harder and / or stronger material than the outer shell. In certain embodiments, the tensile strength of the metal forming the outer shell is about 300 to about 600 MPa, preferably about 350 MPa to about 550 MPa, and / or the hardness (Hv) of the metal forming the outer shell is about 100 to about 250 Hv, preferably about 120 to about 200 Hv on the Vickers scale. In certain embodiments, the metal forming the inner shell has a tensile strength of about 700 to about 1,000 MPa, preferably about 800 to about 950 MPa, and more preferably about 900 MPa, and / or a hardness (Hv) on the Vickers scale of about 280 to about 450 Hv, preferably about 300 to about 400 Hv, and more preferably about 350 Hv.

[0034] Preferred metals for the shell are titanium and titanium alloys. For example, the outer shell can be produced from commercially pure (cp) titanium, grade 2, or preferably grade 4. Alternatively, titanium-aluminum-niobium alloys can be used, due to their higher strength but also better biocompatibility. Since the inner shell needs to be stronger and harder than is possible with cp grade titanium, alloys such as titanium-aluminum-niobium (Ti6Al7Nb) and / or possibly titanium-aluminum-vanadium (Ti6Al4V) are the preferred choices. The tensile strength of titanium cp grades is in the range of 350-550 MPa; the hardness is in the range of 120-200 on the Vickers scale (Hv). The corresponding values ​​for Ti6Al7Nb and Ti6Al4V alloys are 900 MPa and 350 Hv.

[0035] The inner shell is aspheric in shape, providing the general advantages set forth in U.S. Pat. No. 8,323,346 (Tepic). The inner surface 17 over the annular band covering an angle 18 of 5 to 30 degrees, more preferably 10 to 20 degrees, is spherical in shape. It is offset from the axis 20 by an angle 19 of 25 to 50 degrees, more preferably 30 to 45 degrees. The portion of the cup between the band 17 and the pole is shaped to create a gap 21 relative to the spherical shape of the annulus 17. The shape of the inner shell from portion 17 outwardly of the cup opening also deviates from a sphere, creating a gap 22. The aspheric shape of the inner surface of the cup aids in lubrication, resulting in less friction and wear at the articulation joint.

[0036] To further reduce friction and wear of the femoral head articulating within the replacement cup, the inner surface of the medial shell is coated with a suitable material such as ADLC or pyrolytic carbon.

[0037] For optimal function of the aspheric articulation, the axis of symmetry 23 of the inner surface shape should be offset relative to the axis of symmetry 20 of the entire cup, as shown in Figure 5b. An angle 24 of 5 to 30 degrees, more preferably 15 to 25 degrees, places the axis 23 in the middle of the range of joint forces in gait. When implanted in the pelvis, the offset 24 should be in the superior direction of the pelvis.

[0038] An alternative construction of an acetabular cup for a hip hemi-replacement is shown in FIG. 6. A single shell 25 with the inner shape disclosed for the cup of FIG. 5 is coated on the outside with a porous layer 26 for cementless bone ingrowth or adapted for cementation into a reamed-out acetabulum, in which case the outer surface is usually simply textured or provided by other such means for an improved interface to the bone cement. This type of cup can be produced by conventional machining or additive manufacturing. The preferred metal for cementless fixation is a titanium alloy. For cemented cups, cobalt-chromium alloys can also be used, and the choice here can be extended to some stainless steels suitable for ADLC coating.

[0039] An instrument 27 for shaving the femoral head into a spherical shape is shown in Figure 7. It should be used with care and preferably only by hand. The reamer 27 covers approximately a hemisphere, i.e. the inner surface of the reamer beyond an angle of about 180 degrees is covered by cutting grooves 28. Openings 29 in the reamer allow for the removal of small pieces of bone during and after reaming of the femoral head.

[0040] In the event that a revision surgical procedure becomes necessary, the cup 10 of the present invention as described above can be retained and only the femoral component can be inserted (FIG. 8). The primary head 31, placed on the femoral neck 32 of the stem 30, is snap-fitted with a secondary head 33 made of a polymer such as UHMWPE or poly-ether-ether-ketone (PEEK). This secondary head can then be articulated into the cup 10.

[0041] The cup-less partial hip joint disclosed in patent application US2013 / 0060345A (Tepic) has been used in hundreds of dogs for over 8 years without any indication of the head penetrating the pelvis. In some cases, dogs regain full hip function within a few weeks, although somewhat slower than with total hip replacements. In other cases, recovery is slower and takes several months to reach a steady state. At this time, it is not clear what slows recovery, but it is safe to say that it is related to the process of bone remodeling around the joint. Since reaming of the acetabulum is always performed to its maximum depth without penetrating the inner wall of the acetabulum, the bone exposed at the joint is very different, ranging from dense subchondral bone to soft cancellous bone and possibly some remnants of the area covered by cartilage.

[0042] In the procedure disclosed in this invention, reaming of the femoral head is less invasive and in many cases the bone just below the articulating surface is dense and sclerotic and possibly devoid of any pain receptors, which should reduce recovery time in addition to shortening the surgical procedure time, thus contributing to an increased benefit-to-cost ratio.

Claims

1. A hip prosthesis for hemiarthroplasty of the hip joint, It consists of a resurfacing cup (10), The acetabular surface reconstruction cup (10) is fitted to articulate with a natural femoral head (201) that has been reamed into a spherical shape by removing as much cartilage and bone as possible to form a spherical shape. The size of the aforementioned acetabular surface reconstruction cup (10) is selected to cover the natural femoral head (201). Hip joint prosthesis.

2. A hip joint prosthesis according to Claim 1, The inner surface of the acetabular surface reconstruction cup (10) facing the femoral head (201) is aspherical in shape. Hip joint prosthesis.

3. A hip joint prosthesis according to Claim 2, The inner surface has an annular portion (17) which is spherical in shape. Hip joint prosthesis.

4. A hip joint prosthesis according to claim 3, The angle (18) covered by the spherical annular portion (17) is in the range of 10 to 20 degrees. Hip joint prosthesis.

5. A hip joint prosthesis according to claim 3 or 4, The angle (19) between the axis of symmetry (20) and the spherical annular portion (17) is within the range of 30 to 45 degrees. Hip joint prosthesis.

6. A hip joint prosthesis according to any one of claims 3 to 5, The axis of symmetry (23) of the inner shape of the cup is offset (offset) by an angle (24) within the range of 15 to 25 degrees from the principal axis of symmetry (20) of the cup. Hip joint prosthesis.

7. A hip joint prosthesis according to any one of claims 1 to 6, The inner surface of the cup facing the femoral head is coated with a carbon-based material. Hip joint prosthesis.

8. A hip joint prosthesis according to claim 7, The carbon-based material is ADLC and / or pyrolytic carbon. Hip joint prosthesis.

9. A hip joint prosthesis according to any one of claims 1 to 8, which is suitable for cementless fixation.

10. The hip joint prosthesis according to claim 9, which is suitable for cementless fixation having a double shell structure (11, 12).

11. The hip joint prosthesis according to claim 9, which is suitable for cementless fixation having a single shell structure (25).

12. A hip joint prosthesis according to any one of claims 1 to 8, which is suitable for cement fixation.

13. A femoral head shaver (27) for preparing the femoral head for articular jointing within the acetabular surface reconstruction cup (10) of a hip joint prosthesis according to any one of claims 1 to 12.

14. A femoral head shaver (27) according to claim 13, The aforementioned femoral head shaver is equipped with a shaving cup that covers approximately a hemisphere, The shaving cup has an inner surface with a gripping angle exceeding approximately 180 degrees. The inner surface is provided with cutting grooves (28) and openings (29), Femoral head shaver.

Images