Reverse shoulder arthroplasty and related methods

Abstract

This invention provides an artificial joint assembly for joining the humerus to the scapula. [Solution] The artificial joint assembly comprises a humeral component fitted to engage with the humerus and a concave disc portion, and a scapula component fitted to engage with a convex surface fitted to engage with the concave disc portion, wherein when the components are implanted and engaged in a resting position, the center of rotation of the prosthesis is displaced downward and medially relative to the natural center of rotation, and the humerus is displaced downward relative to the natural center of rotation.

Description

Technical Field

[0001] The present invention generally relates to prosthesis implants, and more particularly to prosthesis implants for use in total shoulder arthroplasty.

Background Art

[0002] Figures 1 and 2 show the characteristics of a normal human shoulder in the resting position and the abducted position. The human shoulder joint is formed at the location where the head (2) of the humerus (4) engages with the glenoid cavity (5) of the scapula (6). When a healthy shoulder is functioning normally, the articular surface of the humeral head (2) fits into the glenoid cavity (5) like a ball and socket, and the humerus (4) can rotate freely relative to the scapula (6) while remaining held within the shoulder joint. This rotational movement occurs about the center of rotation (8) (hereinafter, the "natural center of rotation" or "nCOR") between the humerus (4) and the scapula (6). This center of rotation (8) is typically located at or near the center of the humeral head (2). In a healthy shoulder, the upward movement of the humerus (4) (in the frontal plane) is restricted by a projection of the scapula (6) called the acromion (10), particularly a portion of the scapula called the coracoid process (12). Further, in a healthy shoulder, the humeral head (2) is held within the glenoid cavity (5) by a complex of muscles and tendons, generally called the rotator cuff, which surrounds and stabilizes the shoulder joint (not shown for clarity).

[0003] Due to injury, trauma, degenerative changes, disease (such as arthritis), or other conditions, pain, discomfort, or difficulty may be experienced when moving the shoulder in the range of motion, or it may even become impossible to move the shoulder at all. Depending on the situation, the symptoms of the shoulder joint may be treated by partially replacing the joint. In partial replacement, the head (2) of the humerus (4) is replaced with a prosthesis implant, while the glenoid cavity (5) remains relatively intact. However, in many cases, the degree of alteration or damage to the glenoid cavity (5) is so great that it cannot engage and hold the head (2) of the humerus (4), making partial replacement either not recommended or impossible.

[0004] When partial replacement is not possible, one of the feasible treatment options is a procedure commonly known as total shoulder arthroplasty, in which the head (2) of the humerus (4) and the glenoid cavity (5) are replaced with an artificial shoulder joint. Furthermore, in most cases requiring total shoulder arthroplasty, the rotator cuff is also damaged, making it impossible to stabilize the head (2) of the humerus (4) within the glenoid cavity (5). Therefore, the components of the total shoulder arthroplasty are of a reverse type. In other words, in a reverse total shoulder arthroplasty, the component transplanted to the scapula (corresponding to the glenoid cavity (5)) is convex or ball-shaped, while the component transplanted to the head (2) of the humerus (4) is concave or socket-shaped. This reverse configuration has been shown to enhance stability when a completely healthy rotator cuff is not present.

[0005] While efforts have been made to develop reverse-type total shoulder arthroplasty (RIDS), the desired results have often not been achieved. The shortcomings of currently available RIDS include, for example, a very limited range of motion, a high risk of dislocation, excessive stress on the bone resulting in joint failure, fracture, or both, complications such as infection, and premature wear requiring additional surgery during the patient's lifespan. Furthermore, current methods for implanting such RIDS often result in insufficient joint alignment, leading to inadequate joint function and range of motion.

[0006] Therefore, in this field of technology, there is a need for a reverse shoulder prosthesis and related methods for implanting it that can provide patients with a range of motion and alignment similar to that of a healthy shoulder, be durable, adequately support the remaining humerus and sternum, and avoid some or all of the shortcomings of existing prostheses. [Overview of the project] [Problems that the invention aims to solve]

[0007] The inventors have confirmed that the defects of existing reverse total shoulder arthroplasty are due to (a) the inappropriate position of the center of rotation between the scapular and humeral components of the prosthesis (hereinafter referred to as "prosthesis rotation center" or "pCOR"), and (b) the inappropriate absolute position of the humerus relative to the scapula after the prosthesis has been placed.

[0008] The present invention provides a novel reverse total shoulder prosthesis that, upon implantation, appropriately positions the pCOR and humerus to provide an optimally functioning prosthesis. More specifically, the pCOR is positioned medially and inferiorly to the position of the nCOR. Furthermore, for optimal positioning, the humerus is translated in a direction lower than the position of the nCOR. [Means for solving the problem]

[0009] Referring to Figure 3, an enlarged view of the contact surface between the scapula (6) and the humerus (4), the inventors, through experiments and simulations, confirmed that the translation vector (20) of the natural center of rotation (8) with respect to the optimal pCOR position (22) has a range of ratios between the lower (24) component and the medial (26) component of the vector (20). The range of ratios between the lower (24) component and the medial (26) component of the translation vector (20) of the center of rotation is 0.6 to 1.2 (resulting in an angular range of 30 to 50 degrees below the horizontal), and a preferred ratio is 0.85 to 1.15 (resulting in an angular range of 40 to 49 degrees below the horizontal). In many cases, the optimal solution is when the medial (26) component and the lower (24) component are equal, i.e., the ratio is 1 (resulting in an angle of 45 degrees below the horizontal). Similarly, the optimal magnitude of the translation vector (20) of the center of rotation is also in the range of 60% to 80% of the radius (28) of the patient's humeral head (2). In many cases, the optimal magnitude of the translation vector (20) of the center of rotation is approximately 70% of the radius (28) of the patient's humeral head (2).

[0010] Similarly, the inventors confirmed that the direction angle (32) of the downward translation vector (30) of the humerus relative to nCOR(8) is 75 to 105 degrees downward from the horizontal. In many cases, the optimal solution is obtained when the translation vector (30) of the humerus is 90 degrees downward from the horizontal. Similarly, the optimal magnitude of the translation vector (30) of the humerus also ranges from 80% to 120% of the radius (28) of the patient's humeral head (2). In many cases, the optimal magnitude of the translation vector (30) of the humerus is approximately 100% of the radius (28) of the patient's humeral head (2).

[0011] For this reason, an artificial joint assembly for joining the humerus to the scapula is disclosed. The humerus and scapula have natural centers of rotation relative to each other, the humerus has a diameter of the humeral head, and the humerus can be positioned between a resting position and an abduction position relative to the scapula. The artificial joint assembly comprises a humeral component having two opposite ends, the first end having a humeral stem fitted to engage fixedly with the humerus, and the second end having a concave disc portion; and a scapular component having two opposite sides, the first side having a scapular base portion fitted to engage fixedly with the scapula, and the second side having a convex surface fitted to engage with the concave disc portion. When the concave disc portion and the convex surface engage, the humeral component rotates freely relative to the scapular component about the center of rotation of the prosthesis. When the humeral stem engages with the humerus, the scapular stem engages with the scapula, and the concave and convex portions engage, the center of rotation of the prosthesis is displaced downward and medially relative to the natural center of rotation. When the humeral stem engages with the humerus, the scapular base engages with the scapula, the concave and convex portions engage, and the humerus is in its resting position, the humerus is displaced downward relative to the natural center of rotation. The direction of displacement of the humerus is 75 to 105 degrees downward from the horizontal. The ratio of the downward displacement of the center of rotation of the prosthesis to the medial displacement of the center of rotation is in the range of 0.6 to 1.2 (30 to 50 degrees downward from the horizontal), preferably in the range of 0.85 to 1.15 (40 to 49 degrees downward from the horizontal), and optimally equal to 1 (45 degrees downward from the horizontal). The displacement of the prosthesis's center of rotation relative to the natural center of rotation is 60% to 80% of the radius of the humeral head, and optimally equal to 70%. The displacement of the humerus relative to the natural center of rotation is 80% to 120% of the radius of the humeral head, and optimally equal to 100%.

[0012] Also disclosed is an artificial joint assembly for joining the humerus to the scapula. The humerus and scapula have natural centers of rotation relative to each other, the humerus has a diameter of the humeral head, and the humerus can be positioned between a resting position and an abduction position relative to the scapula. The artificial joint assembly comprises a humeral component having two opposite ends, the first end being fitted to engage fixedly with the humerus and the second end having a concave surface; a scapular base plate having a longitudinal dimension and two opposite lateral parts, the first lateral part being fitted to engage fixedly with the scapula and the second lateral part having a trunnion displaced downward from the center of the longitudinal dimension; and a glenosphere component having two opposite lateral parts, the first lateral part having an opening fitted to engage fixedly with the trunnion and the second lateral part having a convex surface fitted to engage with the concave surface. When the concave and convex surfaces engage, the humeral component rotates freely around the prosthesis rotation center relative to the glenosphere. In this embodiment, the humeral component optionally includes a stem component having a longitudinal axis and two opposite ends, the first end having a humeral stem and the second end having a coupler contact surface; a coupler component having two opposite ends, the first end having a stem contact surface adapted to engage securely with the coupler contact surface of the stem component and the second end having a cup contact surface; and a cup component having two opposite sides, the first side having a coupler contact surface adapted to engage securely with the cup contact surface of the coupler component and the second side having a concave surface.

[0013] A method for joining the humerus to the scapula using a prosthesis is also disclosed. The humerus and scapula have natural centers of rotation relative to each other, the humerus has a diameter of the humeral head, and the humerus can be positioned between a resting position and an abduction position relative to the scapula. The method comprises (1) the step of fixing and engaging a scapular component with the scapula, and (2) the step of fixing and engaging a humeral component with the humerus, wherein the humeral component is fitted to engage with the scapular component so as to be able to freely rotate relative to the scapular component about the center of rotation of the prosthesis. (3) When the humeral component and the scapular component are engaged, the center of rotation of the prosthesis is displaced downward and medially relative to the natural center of rotation. (4) When the humeral component is engaged with the scapular component in the resting position, the humerus is displaced downward relative to the natural center of rotation. (5) The direction of displacement of the humerus is 75 to 105 degrees downward from the horizontal, and optimally 90 degrees downward from the horizontal. (6) The ratio of the downward displacement of the center of rotation of the prosthesis to the medial displacement of the center of rotation of the prosthesis is in the range of 0.6 to 1.2 (30 to 50 degrees downward from the horizontal), preferably in the range of 0.85 to 1.15 (40 to 49 degrees downward from the horizontal), and optimally equal to 1 (45 degrees downward from the horizontal). (7) The distance of the displacement of the center of rotation of the prosthesis relative to the natural center of rotation is 60% to 80% of the radius of the humeral head, and optimally 70%. (8) The distance of the displacement of the humerus relative to the natural center of rotation is 80% to 120% of the radius of the humeral head, and optimally equal to 100%.

[0014] In this specification, the present invention is illustrated and described as an artificial shoulder joint; however, various modifications and structural changes can be made without departing from the spirit of the invention and within the scope of its gist and equivalents of the claims, and are not intended to be limited to the illustrated details. Furthermore, many of the principles and techniques described below are applicable to prostheses used in other joints of the human body.

[0015] The configuration of the present invention, along with its additional objectives and effects, will be best understood from the following description of the specific embodiments disclosed, in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0016] [Figure 1] A diagram showing the human shoulder bone in the static position for reference in explaining the operating principle of the present invention. [Figure 2] A diagram showing the human shoulder bone in the abducted position for reference in explaining the operating principle of the present invention. [Figure 3] An enlarged view showing the contact surface between the human scapula and the humerus, and a diagram showing the repositioning of the center of rotation and the position of the humerus according to the present invention. [Figure 4] An isometric view of the scapular component of the artificial shoulder joint according to the present invention. [Figure 5] An exploded orthographic projection view of the scapular component of the artificial shoulder joint shown in FIG. 4. [Figure 6] A side view of the scapular component of the artificial shoulder joint shown in FIG. 4. [Figure 7] A diagram showing a plurality of modified examples of different sizes of the scapular component of the artificial shoulder joint according to the present invention. [Figure 8] An isometric view of the humeral component of the artificial shoulder joint according to the present invention. [Figure 9] An exploded orthographic projection view of the humeral component of the artificial shoulder joint shown in FIG. 8. [Figure 10] A side view of the humeral component of the artificial shoulder joint shown in FIG. 8. [Figure 11] A diagram showing a plurality of modified examples of different sizes of the humeral component of the artificial shoulder joint according to the present invention. [Figure 12] A diagram showing the state of the artificial shoulder joint according to the present invention transplanted into the human scapula and humerus in the static position. [Figure 13] A diagram showing the artificial shoulder joint of FIG. 12 with the humerus and scapula omitted for clarity. [Figure 14] A diagram showing the state of the artificial shoulder joint according to the present invention transplanted into the human scapula and humerus in the abducted position. [Figure 15] A diagram showing the artificial shoulder joint of FIG. 14 with the humerus and scapula omitted for clarity. [Figure 16]Figure showing any variant of the humeral component according to the invention with a large convex support element. [Figure 17] Figure showing any variant of the humeral component according to the invention with a two-piece concave support element.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The purpose of the prosthesis disclosed in this specification is to optimize the pCOR and the final placement of the humerus, as described in detail above and shown in Figure 3. Figure 3 is an enlarged view of the contact surface between the humerus and the scapula, showing the vector of the parallel movement of the pCOR and the humerus and the final placement. This optimal positioning is achieved by using the scapular component (100) and the humeral component (200), the details of which are described in the following paragraphs.

[0018] Figures 4, 5 and 6 are, respectively, an isometric view, an exploded view and a side view that fully illustrate the structure of the scapular component (100). The scapular component (100) comprises a base portion (102) adapted to engage fixedly with the glenoid cavity (5) of the scapula (6) via one or more screw holes (104, 106, 108, 110). The screw holes are adapted to receive one or more multi-axis locking screws (112) or single-axis locking screws (116) with corresponding lock caps (114) for fixing the base portion (102) to the glenoid cavity (5). The back surface (118) of the base portion (102) optionally has a stem (120) adapted to be implanted in the glenoid cavity (5) to provide additional torsional support to the scapular component (100).

[0019] The front surface (122) of the base portion (102) has a substantially cylindrical trunnion (124). The trunnion (124) optionally has a hole and has an internal thread (148) adapted to receive a single-axis locking screw (not shown) or a multi-axis locking screw (126) and a corresponding locking cap (128). The outer surface of the trunnion (124) is adapted to receive a Grenosphere core (130), and the Grenosphere core (130) is adapted to receive a hollow Grenosphere cover (132). The Grenosphere core (130) has one or more protrusions (134) that closely correspond to the corresponding openings of the Grenosphere cover (132), thereby preventing the Grenosphere cover (132) from rotating relative to the Grenosphere core (130) after assembly. After assembly, the Glenosphere core (130) and Glenosphere cover (132) form a spherical Glenosphere assembly (144) having an outer surface (152) adapted to contact the humeral component (200).

[0020] The Grenosphere core (130) and Grenosphere cover (132) are provided with screw holes (136, 138) aligned with the trunnion (124) and lock cap (128), and are adapted to receive a fixing screw (140) for securing the Grenosphere assembly (144) to the base (102). To achieve this, an internal thread (142) corresponding to the external thread of the fixing screw (140) is provided at the back of the lock cap (128). If the trunnion (124) does not have a hole and does not receive the multi-axis lock screw (126) and lock cap (128), an internally threaded hole can be provided at the tip of the trunnion (124) to engage with the fixing screw (140). Although a two-part Grenosphere assembly (144) is shown in the embodiments described, similar effects can also be achieved using a single-part Grenosphere (not shown).

[0021] Except for the glenosphere cover (132), all components of the scapular structure (100) are preferably made of metal, such as biocompatible surgical alloys like cobalt-chromium-molybdenum (CoCrMo) or titanium alloy, which are suitable for biomedical applications such as joint replacement surgery, but are not limited to these. The glenosphere cover (132) is formed from a durable yet elastic plastic material, such as ultra-high molecular weight polyethylene (UHMWPE). When a single-component glenosphere is used, it may be made of metal or plastic.

[0022] As clearly shown, the trunnion (124) is positioned considerably below the center (150) of the base (102). This ensures that the center (146) of the glenosphere assembly (144), which will be the prosthesis rotation center (22), is positioned sufficiently below. Furthermore, since the center (146) of the glenosphere assembly (144) is located very close to the base (102), it is also positioned sufficiently inward. As previously stated, positioning the prosthesis rotation center (22) below and inward relative to the natural rotation center (8) is one of the main objectives achieved by the arrangement of the components described.

[0023] Next, Figure 7 shows variations of several scapular components (100) of different sizes that can be used depending on the patient's anatomical structure and the magnitude and angle of the translation of pCOR(22) intended by the physician. As can be seen from the figure, some sizes have one mounting screw and a corresponding hole in the base, while other sizes have up to four holes and screws. Furthermore, the shape of the base (102) varies from circular to elliptical. The base (102) may have other shapes without departing from the principles of the disclosed invention. The described modular configuration makes it possible to assemble the optimal scapular component (100) to match the patient's anatomical structure and the desired position of the prosthesis rotation center (22) by using glenosphere assemblies (144) of various sizes and shapes together with bases (102) of various sizes and shapes.

[0024] Figures 8, 9, and 10 are isometric, exploded, and side views, respectively, that fully illustrate the structure of the humeral component (200). The humeral component (200) comprises a stem (202), a coupler (204), a cup (206), and an assembly screw (208). The stem (202) is a substantially elongated member having a bone marrow stem (210) at one end and a conical portion (212) at the other end. The stem (202) is perforated along its longitudinal axis so that the assembly screw (208) can enter from the end on the bone marrow stem (210) side and engage with the coupler (204) at the end on the conical portion (212) side. The bone marrow stem (210) includes a general bone stem adapted to penetrate the bone marrow of the humerus (4) and engage fixedly with the bone. The bone marrow stem (210) can be adapted for cemented or non-cemented applications. The cone portion (212) has a gradually increasing diameter and is terminated by one or more fins (214). The fins (214) are fitted to engage with the trabeculae within the humerus (4) to transmit torsional loads and to prevent rotation of the stem (202) after implantation. The upper part of the cone portion (212) has a stem shaft opening (218) fitted to receive the coupler (204).

[0025] The coupler (204) includes a stem engagement shaft (220) that engages with a stem shaft opening (218) and is adapted to form a secure treadlock or press-fit between the stem (202) and the coupler (204). Furthermore, the bottom surface of the stem engagement shaft (220) has an opening (222) having an internal thread (238). The internal thread (238) receives the threads (224) of the assembly screw (208) inserted through the bottom of the stem (210) side of the stem (202). In one embodiment, the stem engagement shaft (220) and the shaft opening (218) form a Morse taper that provides a secure friction fit. To further ensure the engagement between the stem (202) and the coupler (204) against torsional forces, the stem engagement shaft (220) may be offset from the centerline of the stem (202). The offset placement of the stem engagement shaft (220) from the center, combined with the Morse taper, results in an extremely strong and torsion-resistant mating between the stem (202) and the coupler (204) after the assembly screw (208) is tightened.

[0026] The upper surface (226) of the coupler (204) has an inclined receiving area with an opening for receiving the cup (206). The inclination angle of the upper surface (226) is such that, after the prosthesis is assembled, the humerus (4) is appropriately displaced laterally and downward relative to the pCOR (22). The intermediate coupler portion (227) is configured to position the humerus (4) further downward relative to the pCOR (22) if necessary to position the humerus in an optimal position. The cup shaft opening (228) of the upper surface (226) is adapted to receive the cup shaft (230) and secure the cup (206) to the coupler (204). The cup shaft opening (228) and the cup shaft (230) may have additional Morse tapers to ensure a secure engagement between the coupler (204) and the cup (206). Furthermore, the coupler (204) has one or more internal (232) and external (234) suture attachment points.

[0027] One end of the cup (206) is provided with a concave surface, or dish portion (236), adapted to engage in close correspondence with the outer surface (152) (see Figures 4-6) of the Glenosphere assembly (144). The other end of the cup (206) is provided with a cup shaft (230). The cup shaft (230) engages with the cup shaft opening (228) to fix the cup (206) with the coupler (204) in order to form an interference fit, as described above. Furthermore, it is optionally provided with a Morse taper or other type of shallow angle self-retaining taper.

[0028] All components of the humeral bone structure (200) are preferably metal compositions, such as biocompatible surgical alloys like cobalt-chromium-molybdenum (CoCrMo) or titanium alloy, which are suitable for biomedical applications such as joint replacement surgery, but are not limited to these.

[0029] Next, Figure 11 shows variations of multiple humeral components (200) of different sizes that can be used depending on the patient's anatomical structure and the magnitude and angle of further translation of the humerus (4) as intended by the physician. As can be seen from the figure, the various sizes include stems (202) of different diameters, conical sections (212) of different tapers, intermediate coupler sections (227) of different lengths, and concave or disc sections (236) of various diameters and curvatures to fit the corresponding glenosphere assembly (144). The described modular configuration allows for the use of stems (202) of various sizes together with couplers (204) and cups (206) of various sizes to assemble the optimal humeral component (200) to match the patient's anatomical structure and the optimal displacement of the humerus (4) relative to the prosthesis rotation center (22).

[0030] The disclosed procedure for implanting a prosthesis in a patient includes the following general steps: First, the size and relative position of the patient's anatomical structures are measured: the humerus (4), humeral head (2), scapula (6), glenoid cavity (5), and natural center of rotation (8). Next, based on the measurements, the scapular component (100) and humeral component (200) are assembled using various modular elements, including appropriately sized base (102), glenosphere assembly (144), stem (202), coupler (204), and cup (206). Then, the glenoid cavity (5) is prepared to receive the scapular component (100), which will be implanted in a suitable position to achieve the desired level of descent of the pCOR (22). Next, the humeral head is removed from the humerus (4), and the humeral component (200) is implanted in its place. Finally, the scapular component (100) and the humeral component (200) are joined, and the shoulder joint is moved from a resting position to an abducted position and vice versa for examination. If any collision is detected between the humerus and the scapula, the alignment of the shoulder joint can be optimized by replacing one or more modular elements of the scapular component (100) or the humeral component (200).

[0031] Figures 12 and 13 show the fully assembled and implanted artificial shoulder joint of the present disclosure in its “resting” position. Figure 12 shows the assembled artificial shoulder joint according to the present invention implanted in a human scapula (6) and humerus (4). Figure 13 shows the same assembled prosthesis including the scapular component (100) and humeral component (200), but the bone is not shown for clarity of illustration. As can be seen from the figures, the prosthesis rotation center (22) is significantly displaced medially and inferiorly relative to the natural rotation center (8), and similarly, the humerus (4) is also displaced even more significantly inferiorly relative to the natural rotation center (8). This arrangement places the humerus (4) in an optimal position to fully rotate to the abducted position, minimizing the risk of collision with any part of the scapula (6).

[0032] Next, Figures 14 and 15 show the fully assembled and implanted prosthesis of the present disclosure after it has been rotated to the “abduction” position. Figure 14 shows the assembled prosthesis according to the present invention implanted in a human scapula (6) and humerus (4). Figure 15 shows the same assembled prosthesis including the scapular component (100) and humeral component (200), but the bone is not shown for clarity of illustration. As can be seen from the figures, the prosthesis rotation center (22) remains significantly displaced medially and inferiorly relative to the natural rotation center (8). In the abduction position, the humerus (4) is in approximately the same position as in a healthy shoulder (see Figure 2), and the range of motion of the shoulder is almost completely restored.

[0033] The disclosed prosthesis can be modified in various ways to accommodate specific circumstances that may arise. One example of such a situation is when, after undergoing reverse total shoulder arthroplasty using the disclosed prosthesis, it is determined that the patient is no longer suitable for continued use of the reverse total shoulder arthroplasty. This situation may occur, for example, when the scapula can no longer support the scapular element (100) due to a re-injury or degenerative changes in the patient. In such a situation, the scapular element can be removed, and the humeral element can be modified to place a glenosphere in place of the cup, allowing it to contact the original glenoid cavity. This avoids the need for a complete replacement of the humeral component, which can be difficult and / or potentially traumatic for the patient. Figure 16 shows an arbitrary modification of the humeral component (200') to address such a situation. As shown in the figure, the cup element (206) of the humeral component is removed, and instead, a larger glenosphere (240) is attached to the coupler (204).

[0034] Figure 17 shows an alternative embodiment of the humeral component (200'') in which the concave support surface is formed of a plastic material and the rest is metal. This embodiment is achieved by using a two-part component consisting of a metal tray (242) and a plastic cup insert (244) having a concave surface in cooperation with it, instead of the cup (206).

[0035] While many embodiments of the present invention have been described, these embodiments are illustrative and not limiting, and many modifications will be apparent to those skilled in the art. For example, each element described herein can be configured in any desired size (for example, each element described herein can be configured in any desired custom size, or each element described herein can be configured in a desired size selected from a “group” of sizes such as small, medium, and large). Furthermore, one or more of the components can be formed from (a) any biocompatible material (which is applied to allow or prevent bone formation on the surface, according to the physician’s intent), (b) plastic, (c) fiber, (d) polymer, (e) metal (pure metal and / or alloy), or (f) any combination thereof. Furthermore, any number of prostheses can be used in any prosthesis (for example, for initial fixation by bonding with cement, and / or for auxiliary fixation by bonding with cement). Furthermore, any number of female features can be used in any prosthesis to increase the bonding area. Furthermore, any number of male features that interlock with bone may be used in any prosthesis to improve initial / auxiliary fixation. Furthermore, any number of bone screws (e.g., for initial and / or auxiliary fixation) may be used in any prosthesis. Furthermore, any steps described herein may be performed in any desired order (and any additional steps may be freely added and / or omitted).

[0036] Furthermore, various modifications and additions can be made to the exemplary embodiments described without departing from the scope of the present invention. For example, while the embodiments described above refer to specific features, the scope of the present invention also includes embodiments having different combinations of features, and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to encompass all alternatives, modifications, variations, and equivalents included in the claims.

Claims

1. An artificial joint assembly for joining the humerus to the scapula, wherein the humerus and scapula have natural centers of rotation relative to each other, the humerus has a diameter of the humeral head, the humerus is positionable between a resting position and an abducted position relative to the scapula, and the artificial joint assembly is a. A humeral component having two opposite ends, wherein the first end has a humeral stem fitted to engage fixedly with the humerus, and the second end has a concave disc portion, b. A scapular component having two lateral parts located on opposite sides, wherein the first lateral part has a scapular base portion fitted to engage fixedly with the scapula, and the second lateral part has a convex surface fitted to engage with the concave plate portion, c. When the concave plate portion and the convex surface engage, the humeral component rotates freely relative to the scapular component about the center of rotation of the prosthesis. d. When the humeral stem engages with the humerus, the scapular base engages with the scapula, and the concave plate and the convex surface engage, the center of rotation of the prosthesis is displaced downward and inward with respect to the natural center of rotation. e. When the humeral stem engages with the humerus, the scapular base engages with the scapula, the concave plate and the convex surface engage, and the humerus is in the resting position, the humerus is displaced in a direction downward from the natural center of rotation. f. The direction of displacement of the humerus is 75 to 105 degrees downward from the horizontal. Artificial joint assembly.

2. The ratio of the downward displacement of the prosthesis's center of rotation to the inward displacement of the prosthesis's center of rotation is within the range of 0.6 to 1.

2. The artificial joint assembly according to claim 1.

3. The ratio of the downward displacement of the prosthesis's center of rotation to the inward displacement of the prosthesis's center of rotation is within the range of 0.85 to 1.

15. The artificial joint assembly according to claim 1.

4. The ratio of the downward displacement of the prosthesis rotation center to the inward displacement of the prosthesis rotation center is approximately 1. The artificial joint assembly according to claim 1.

5. The displacement distance of the prosthesis rotation center relative to the natural rotation center is 60% to 80% of the radius of the humeral head. The artificial joint assembly according to claim 1.

6. The distance of the displacement of the humerus relative to the natural center of rotation is 80% to 120% of the radius of the humeral head. The artificial joint assembly according to claim 1.

7. An artificial joint assembly for joining the humerus to the scapula, wherein the humerus and scapula have natural centers of rotation relative to each other, the humerus has a diameter of the humeral head, the humerus is positionable between a resting position and an abducted position relative to the scapula, and the artificial joint assembly is a. A humeral component having two opposite ends, wherein the first end has a humeral stem fitted to engage fixedly with the humerus, and the second end has a concave surface, b. A scapular base having a longitudinal dimension and two lateral portions located on opposite sides, wherein the first lateral portion is fitted to engage fixedly with the scapula and the second lateral portion has a trunnion that is displaced downward from the center of the longitudinal dimension, c. A glenosphere component having two sides located on opposite sides, wherein the first side has an opening adapted to engage securely with the trunnion, and the second side has a convex surface adapted to engage with the concave surface, d. When the concave surface and the convex surface engage, the humeral component rotates freely relative to the glenosphere component with respect to the prosthesis rotation center. Artificial joint assembly.

8. The aforementioned humeral component is a. A stem component having a longitudinal axis and two opposite ends, wherein the first end has the humeral stem and the second end has a coupler contact surface, b. A coupler component having two opposite ends, wherein the first end has a stem contact surface adapted to engage securely with the coupler contact surface of the stem component, and the second end has a cup contact surface, c. A cup component having two sides located on opposite sides, wherein the first side has a coupler contact surface adapted to engage securely with the cup contact surface of the coupler component, and the second side has the concave surface, The artificial joint assembly according to claim 7.

9. When the humeral stem engages with the humerus, the scapular base engages with the scapula, and the concave plate and the convex surface are engaged in the resting position, a. The center of rotation of the prosthesis is displaced downward and inward relative to the natural center of rotation. b. The humerus is displaced in a downward direction relative to the natural center of rotation, c. The direction of displacement of the humerus is 75 to 105 degrees downward from the horizontal. The artificial joint assembly according to claim 7.

10. The ratio of the downward displacement of the prosthesis's center of rotation to the inward displacement of the prosthesis's center of rotation is within the range of 0.6 to 1.

2. The artificial joint assembly according to claim 9.

11. The ratio of the downward displacement of the prosthesis's center of rotation to the inward displacement of the prosthesis's center of rotation is within the range of 0.85 to 1.

15. The artificial joint assembly according to claim 9.

12. The ratio of the downward displacement of the prosthesis rotation center to the inward displacement of the prosthesis rotation center is approximately 1. The artificial joint assembly according to claim 9.

13. The displacement distance of the prosthesis rotation center relative to the natural rotation center is 60% to 80% of the radius of the humeral head. The artificial joint assembly according to claim 9.

14. The distance of the further displacement of the humerus relative to the natural center of rotation is 80% to 120% of the radius of the humeral head. The artificial joint assembly according to claim 9.

15. A method for joining the humerus to the scapula by a prosthesis, wherein the humerus and scapula have a natural center of rotation relative to each other, the humerus has the diameter of the humeral head, and the humerus can be positioned between a resting position and an abducted position relative to the scapula, and the method is a. A step of fixing and engaging the scapular component with the scapula, b. A step of fixing and engaging a humeral component with the humerus, wherein the humeral component is engaged with the scapular component and is adapted to rotate freely with respect to the scapular component about the center of rotation of the prosthesis, c. When the humeral component and the scapular component engage, the center of rotation of the prosthesis is displaced downward and inward relative to the natural center of rotation. d. When the humeral component engages with the scapular component in the resting position, the humerus is displaced downward with respect to the natural center of rotation. e. The direction of displacement of the humerus is 75 to 105 degrees downward from the horizontal. method.

16. The ratio of the downward displacement of the prosthesis's center of rotation to the inward displacement of the prosthesis's center of rotation is within the range of 0.6 to 1.

2. The method according to claim 15.

17. The ratio of the downward displacement of the prosthesis's center of rotation to the inward displacement of the prosthesis's center of rotation is within the range of 0.85 to 1.

15. The method according to claim 15.

18. The ratio of the downward displacement of the prosthesis rotation center to the inward displacement of the prosthesis rotation center is approximately 1. The method according to claim 15.

19. The displacement distance of the prosthesis rotation center relative to the natural rotation center is 40% to 60% of the radius of the humeral head. The method according to claim 15.

20. The distance of the displacement of the humerus relative to the natural center of rotation is 80% to 120% of the radius of the humeral head. The method according to claim 15.

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