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  Femoral and humeral stem geometry and implantation method for orthopedic joint reconstructionUSPTO Application #: 20070225821Title: Femoral and humeral stem geometry and implantation method for orthopedic joint reconstruction Abstract: The present inventions relate to devices and methods that improve the positioning and fit of orthopedic reconstructive joint replacement stem implants relative to existing methods. For example, an embodiment of the device provides a stem component comprising proximal and distal body portions that can be configured to mimic a geometric shape of a central cavity region created in a bone of a joint for improving conformance and fixation of the stem component thereto. Further, another embodiment provides a system of stem implants that each have a unique medial offset for facilitating the matching of an implant to the geometry of a central cavity region of a bone. Additionally, an inclination angle of a resection surface of each of the implants in the system can remain constant or vary as a function of the medial offset. (end of abstract) Agent: Knobbe Martens Olson & Bear LLP - Irvine, CA, US Inventors: Leo M. Reubelt, Peter L. Verrillo USPTO Applicaton #: 20070225821 - Class: 623022410 (USPTO) Related Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Implantable Prosthesis, Bone, Joint Bone, Hip Joint Bone, Total Femoral Bone (i.e., Including Joint Head And Femoral Stem), Set Of Plural Femoral Securement Members The Patent Description & Claims data below is from USPTO Patent Application 20070225821. Brief Patent Description - Full Patent Description - Patent Application Claims
PRIORITY INFORMATION [0001] The present application claims the priority benefit under 35 U.S.C. .sctn. 119(e) to U.S. Provisional Application 60/784,236, filed Mar. 21, 2006, the entire contents of which are expressly incorporated by reference herein. BACKGROUND [0002] 1. Field of the Inventions [0003] The present inventions relates generally to orthopedic implants, and more specifically, to a reconstructive joint replacement implant and a method of positioning and fitting such an implant. [0004] 2. Description of the Related Art [0005] Anatomically, a joint is generally a movable junction between two or more bones. As used herein, the term "joint" is a broad term that is meant to include the different kinds of ligaments, tendons, cartilages, bursae, synovial membranes and bones comprising the mobile skeletal system of a subject in various quantities and configurations. [0006] For example, the hip joint is a ball and socket joint comprising the "ball" at the head of the thigh bone (femur) with a cup-shaped "socket" (acetabulum) in the pelvic bone. The ball normally is held in the socket by powerful ligaments that form a complete sleeve around the joint (i.e., the joint capsule). The joint capsule has a delicate lining (the synovium). Cartilage, which covers the head of the femur and lines the socket, cushions the joint, and allows the bones to move on each other with very little friction. In a normal hip joint, the spherical head of the thighbone (femur) moves inside the acetabulum of the pelvis. Normally, all of these components replace the worn-out hip socket. [0007] The shoulder is the body's most mobile joint, in that it can turn in many directions. The shoulder is a ball-and-socket joint that is made up of three bones: the upper arm bone (humerus), shoulder blade (scapula) and collarbone (clavicle). In the shoulder, two joints facilitate shoulder movement. The acromioiclavicular (AC) joint joins one end of the collarbone with the shoulder blade; it is located between the acromion (the part of the scapula that forms the highest point of the shoulder) and the clavicle. The other end of the collarbone is joined with the breastbone (sternum) by the sternoclavicular joint. The glenohumeral joint, commonly called the shoulder joint, is a ball-and-socket type joint that helps move the shoulder forward and backward and allows the arm to rotate in a circular fashion or hinge out and up away from the body. The ball of glenohurneral joint is the top, rounded portion of the humerus; the socket, or glenoid, is a dish-shaped part of the outer edge of the scapula into which the ball fits. The socket of the glenoid is surrounded by a soft-tissue ring of fibrocartilage (the glenoid labrum) that runs around the cavity of the scapula (glenoid cavity) in which the head of the humerus fits. The labrum deepens the glenoid cavity and effectively increases the surface of the shoulder joint, which helps stabilize the joint. [0008] The bones of the shoulder are held in place by muscles, tendons (tough cords of tissue that attach the shoulder muscles to bone and assist the muscles in moving the shoulder) and ligaments (bands of fibrous tissue that connects bone to bone or cartilage to bone, supporting or strengthening a joint). A smooth, durable surface (the articular cartilage) on the head of the arm bone, and a thin lining (synovium) allows smooth motion of the shoulder joint. The joint capsule, a thin sheet of fibers that encircles the shoulder joint, allows a wide range of motion yet provides stability of the joint. The capsule is lined by a thin, smooth synovial membrane. The front of the joint capsule is anchored by three geneohumeral ligaments. [0009] The rotator cuff, a structure composed of tendons and associated muscles that holds the ball at the top of the humerus in the glenoid socket, covers the shoulder joint and joint capsule. The rotator cuff provides mobility and strength to the shoulder joint. A sac-like membrane (bursa) between the rotator cuff and the shoulder blade cushions and helps lubricate the motion between these two structures. [0010] The shoulder is an unstable joint easily subject to injury because of its range of motion, and because the ball of the humerus is larger than the glenoid that holds it. To remain stable, the shoulder must be anchored by its muscles, tendons and ligaments. Some shoulder problems arise from the disruption of these soft tissues due to injury or overuse, or underuse of the shoulder. Other problems can arise from degenerative processes. [0011] For example, instability of the shoulder joint can refer to situations that occur when one of the shoulder joints moves or is forced out of its normal position. The two basic forms of shoulder instability are subluxations and dislocations. A partial or incomplete dislocation of the shoulder joint (subluxation) means the head of the humerus is partially out of the socket (glenoid). A complete dislocation of the shoulder joint means that the head of the humerus is completely out of the socket. Anterior instability, for example, can refer to a type of shoulder dislocation where the shoulder slips forward, meaning that the humerus moved forward and down out of its joint. Anterior instability may occur when the arm is placed in a throwing position. Both partial and complete dislocation cause pain and unsteadiness in the shoulder joint. Patients with repeat dislocation usually require surgery. [0012] Bursitis or tendonitis can occur with overuse from repetitive activities, which cause rubbing or squeezing (impingment) of the rotator cuff under the acromion and in the acromioclavicular joint. Partial thickness rotator cuff tears, most often the result of heavy lifting or falls, can be associated with chronic inflammation and the development of spurs on the underside of the acromion or the AC joint. Full thickness rotator cuff tears most often are the result of impingement. [0013] Osteoarthritis and rheumatoid arthritis can cause destruction of the shoulder joint and surrounding tissue and degeneration and tearing of the capsule or rotator cuff. In osteoarthritis, the articular surface of the joint wears thin. Rheumatoid arthritis is associated with chronic inflammation of the synovium lining, which can produce substances that eventually destroy the inner lining of the joint, including the articular surface. [0014] Shoulder replacement is recommended for subjects with painful shoulders and limited motion. The treatment options are either replacement of the head of the humerus or replacement of the entire socket. However, currently available treatment options are less than adequate in restoring shoulder joint function. For example, just as muscles get stronger through use, the density and strength of bone varies with respect to the bone's load history. To ensure proper bone loading and good bone health, accurate implant placement, good bone fit, and restoration of a healthy anatomic position is critical. Existing devices have focused on modifying only the most proximal portion of the stem geometry, known as the neck, to adjust for different angles but do not accommodate variation of the proximal body shape. SUMMARY [0015] Currently, most humeral stems are implanted using a fairly common procedure. First the head is resected and the humeral canal is reamed to a best fit diameter. The humerus is then broached or reamed, using the canal as a guide, to accept the proximal body. One aspect of the present inventions is that this method poses several basic problems. First, because the distal stem is meant to be a tight fit with respect to the reamed cavity, it dictates the position of the stem and therefore, the position of the head. Since the size, location, and orientation of the head with respect to the humeral canal vary greatly from person to person, a single stem geometry per size cannot accommodate natural head placement or proximal body shape. Consequently, head placement is typically adjusted by rotating the prosthetic head around an eccentric taper. This typically results in a proximal fit that is poor because rotating an eccentric head adjusts both posterior and medial head location at the same time, virtually excluding the possibility of perfect placement. Similarly, since proximal body position and orientation are governed by the distal canal, the proximal body must be made small enough to fit the smallest possible envelope within the proximal humerus. This excessively small proximal body causes poor proximal fixation and leads to over-reliance on distal fixation. Over time, when too much emphasis is placed on distal fixation, the strength of the proximal bone begins to deteriorate. This, in turn leads to stem loosening and potentially fracture. While some companies have tried to improve upon this model by offering different neck angles, they typically use the same proximal body geometry and simply vary the resection angle. While this may improve head center placement, it offers little to accommodate varying shapes of the proximal body. [0016] Accordingly, an embodiment of the present inventions is an orthopedic device for joint reconstruction that comprises an implantable stem component comprising a proximal section or proximal body portion. The proximal body of the stem component can be inserted into a central cavity region created in a bone of a joint. According to one aspect, the orthopedic device optionally comprises a distal section or distal body portion, wherein the distal section of the implantable stem component is placed at least one distal stem angle with respect to the proximal body component of the implantable stem component of the device. In this regard, a longitudinal axis of the distal body portion can be oriented at a discrete angle with respect to a neck axis of the proximal body portion. [0017] In accordance with another embodiment, the stem component can taper from the proximal body portion toward the distal body portion to define medial and lateral curved surfaces. The medial and lateral curved surfaces can be configured to mimic the geometric shape of the bone for improving conformance and fixation of the stem component to the central cavity region of the bone. In this regard, the proximal body of the stem component can be inserted into a central cavity region created in the bone of a joint. The attachment portion can be tapered. Further, the bone can be a humerus. The humerus can comprise a proximal portion having a shape and a distal portion. The medial and lateral curved surfaces can conforms to the shape of the proximal portion of the implant. Further, the distal section of the stem component can have a cylindrical, elliptical, tapered, or irregular shape. Additionally, the distal body portion of the stem component can further comprise at least one feature selected from the group consisting of: a groove, a slot, a cutout, and a protrusion. [0018] According to another aspect, the joint is a hip joint. According to another aspect, the joint is a shoulder joint. According to another aspect, the bone is a humerus. According to another aspect, the humerus comprises a proximal portion having a shape and a distal portion. According to another embodiment, the proximal body shape of the device conforms to the shape of the proximal portion of the humerus. According to another aspect, the bone is a femur. According to another aspect, the distal section of the stem component of the device has a tapered shape. According to another aspect, the distal section of the stem component of the device has a cylindrical, elliptical, tapered, or irregular shape. According to another aspect, the distal section of the stem component of the device further comprises at least one feature selected from the group consisting of a groove, a slot, a cutout, and a protrusion. According to another aspect, the distal section of the stem component of the device further comprises a ball. [0019] In another embodiment, a system of orthopedic devices for joint reconstruction surgery is provided. The system can comprise a plurality of stem components, wherein each stem component comprising a distal body portion and a proximal body portion. The stem component can be sized and configured to be implanted to within a cavity of a bone. The distal body portion can define a longitudinal axis, and the proximal body portion can define a neck axis and a head center. Further, the proximal body portion can comprise a resection surface. The head center can be spaced from the longitudinal axis at a medial offset, and the resection surface can be oriented at an inclination angle with respect to the longitudinal axis. In such an embodiment, each stem component of the system can be configured with a different medial offset when compared to other of the stem components of the system. The system can thus provide a variety of potential matching geometries for a surgeon when performing the joint reconstruction surgery. The proximal body of a given stem component can be insertable into a central cavity region created in a bone of the joint. [0020] In an embodiment of the system, each stem component of the system can have the same inclination angle. Further, the inclination angle of each stem component can vary as a function of the medial offset of the respective stem component. In some embodiments, the system can be configured such that each of the stem components of the system has a medial offset of between approximately 4 mm and approximately 15 mm. In addition, in other embodiments, the medial offset can be varied while the inclination angle is constant. [0021] The system can include, for example, at least three stem components. Accordingly, a first stem component can have a medial offset of approximately 12 mm, a second stem component can have a medial offset of approximately 8 mm, and a third stem component can have a medial offset of approximately 5 mm. Additionally, the first stem component can have an inclination angle of approximately 44 degrees, the second stem component can have an inclination angle of approximately 49 degrees, and the third stem component can have an inclination angle of approximately 54 degrees. The inclination angle can be between approximately 30 degrees and approximately 55 degrees. Continue reading... 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