Patent Application
20060224243
The invention relates to orthopaedic implants. In particular, this invention relates to elbow joint prostheses.
Elbow arthroplasty has been used to restore function to diseased or injured elbow joints. The elbow joint is the articulation between the humerus or the upper arm and the ulna and radius of the forearm. The basic anatomic position of the human body is standing upright, arms hanging at the sides with palms forward. The elbow is in extension in this position. Elbow flexion occurs as the humerus is held stationary and the palm is moved upwardly pivoting the forearm about the elbow joint. Varus and valgus loading of the elbow occurs as the elbow is torqued in the coronal plane; i.e. the forearm is abducted/adducted while the humerus remains stationary. Rotating the forearm so that the radius rotates over the ulna to turn the palm toward the posterior side of the body is called pronation. Rotating the hand back to the anatomic position is called supination. Positions and directions relative to the elbow joint may be described in terms of proximal being nearer the elbow joint, distal being further from the elbow joint, anterior being nearer the front of the body on the inside of the elbow, posterior being nearer the back of the body on the outside of the elbow, medial being nearer the centerline of the body, and lateral being further from the center line of the body.
In elbow arthroplasty, a portion of the articulating surfaces of the humerus and ulna are cut away and replaced with substitute implants. In a typical case, the implants include a stemmed humeral component and a stemmed ulnar component pinned together to form a hinge joint. The bones are prepared by creating an opening down along the intramedullary canal into each bone proximal to distal. The implants may be placed directly in contact with the prepared bone surfaces for bony fixation of the implant. Alternatively, bone cement may be introduced into the prepared bones so that it hardens around and locks the components in place.
The present invention provides an elbow prosthesis for replacing a portion of an elbow joint between the humerus and ulna bones.
In one aspect of the invention, the elbow prosthesis includes a humeral component having a stem sized to fit within the intramedullary canal of the humerus and a first articulating portion. The elbow prosthesis further includes an ulnar component having a stem sized to fit within the intramedullary canal of the ulna and a second articulating portion. The first and second articulating portions form a ball and socket joint at the elbow.
In another aspect of the invention, an elbow prosthesis includes a humeral stem, a humeral articulating component, an ulnar stem and an ulnar articulating component. The humeral stem has an insertion portion sized to fit within the intramedullary canal of the humerus and a mounting portion. The humeral articulating component includes a mounting portion mountable to the humeral stem mounting portion and a first articulating portion. The ulnar stem has an insertion portion sized to fit within the intramedullary canal of the ulna and a mounting portion. The ulnar articulating component has a mounting portion mountable to the ulnar stem mounting portion and a second articulating portion. The first and second articulating portions are engageable in joint articulating arrangement.
In another aspect of the invention, a method of surgically repairing a portion of an elbow joint between the humerus and ulna bones includes: selecting a humeral stem having an insertion portion sized to fit within the intramedullary canal of the humerus and a mounting portion; selecting a humeral articulating component having a second mounting portion mountable to the humeral stem mounting portion and a first articulating portion; intraoperatively mounting the humeral articulating component to the humeral stem; selecting an ulnar stem having an insertion portion sized to fit within the intramedullary canal of the humerus and a mounting portion; selecting an ulnar articulating component having a mounting portion mountable to the ulnar stem mounting portion and a second articulating portion; intraoperatively mounting the ulnar articulating component to the ulnar stem; and engaging the first and second articulating portions in joint articulating arrangement.
Various examples of the present invention will be discussed with reference to the appended drawings. These drawings depict only illustrative examples of the invention and are not to be considered limiting of its scope.
Examples of the present invention include elbow prostheses for surgical repair of the elbow joint. The prosthesis may include a humeral component having a stem and a first articulating end and an ulnar component having a stem and a second articulating end. The first and second articulating ends may form a ball and socket joint. For example, the humeral component may include a first articulating end in the form of a ball head and the ulnar component may include a second articulating end in the form of a socket for receiving the ball head. Alternatively, the humeral component may include a first articulating end in the form of a socket and the ulnar component may include a second articulating end in the form of a ball head receivable by the socket.
The humeral and/or ulnar component may include separate modular anchorage components and articulation components that may be joined together at the time of surgery. The modular components may be joined outside of the patient's body and subsequently implanted as an assembly. Alternatively the components may be individually implanted and subsequently joined. The components may permit a variety of different articulation and anchorage components to be assembled as needed to fit a particular patients needs. For example, variations in stem lengths, diameters, materials, surface finish, and/or other parameters may be provided. Likewise, variations in ball head and socket sizes, constraint, materials, eccentric stem connection, and/or other parameters may be provided. The components may be sized and shaped to facilitate a minimally invasive surgical technique in which the individual components are inserted through a small incision and subsequently assembled. An articulation component in the form of a socket may include a separate modular socket liner.
The elbow components may be made of biocompatible materials including metals, ceramics, polymers, and/or other suitable biocompatible materials and alloys and combinations thereof. The stems can be smooth or textured and can include coatings including layers of porous materials, fiber pads, beads, plasma sprayed materials, and/or other suitable coatings. The coatings may include metals, ceramics, polymers, and/or other suitable coating materials.
Modular stems and articulating components may be joined by locking tapers, screws, bolts, adhesives, snap rings, and/or other suitable joining mechanisms. Modular components may include an indexing mechanism for aligning the components in a predetermined relative orientation. The indexing features may include projections and corresponding depressions. In particular, the indexing features may include pins, pegs, bosses, rails, undulations, holes, grooves, and/or other suitable features and combinations thereof. For example, one component may include one or more pegs projecting outwardly and another component may include one or more corresponding depressions for receiving the pegs to orient the components in a desired orientation.
The humeral stem 20 includes an elongated body 22 forming an insertion portion having a first end 24, a second end 26, and a longitudinal axis 28 extending therebetween. The first end includes an articular component 40 engaging male taper 30. Preferably, the taper 30 is of a self-locking Morse taper configuration. The second end 26 may be tapered as shown to ease insertion into the intramedullary canal of the humerus. The humeral stem 20 is provided in a variety of lengths and diameters to permit the surgeon to select the stem size that best fits a particular patient's anatomy and a variety of surface finishes and materials to permit the surgeon to select a desired method of stem fixation. The taper 30 is constant across all stem sizes to permit stems to be interchangeably connected to the ball head 42.
The ball head 42 is in the form of a hemispherical solid having a planar surface 44 formed on it. A female taper 46 is formed into the ball head 42 through the planar surface 44. Preferably the female taper 46 is of a self-locking Morse taper configuration corresponding to the male taper 30 of the humeral stem 20. The female taper 46 includes a longitudinal axis 48 and the ball head 42 includes a centerline 50 extending through the geometric head center 52 and parallel to the taper axis 48 (as shown in
The ulnar articular component 60 includes a body 64 defining a hemispherical socket 62 for receiving the ball head 42. The body 64 has a hemispherical back surface 66 for engaging the ulnar stem component 80. An annular groove 68 is formed in the back surface 66 near the opening 69 of the socket 62. A locking ring 70 is disposed in the groove 68 with a portion that projects outwardly from the groove around its perimeter when the ring 70 is unconstrained. The locking ring 70 is split and resilient so that it is collapsible upon engagement with the ulnar stem 80 such that it projects from the groove 68 a lesser amount. Preferably, the locking ring 70 collapses so that it is fully contained within the groove. The body 64 further includes pegs 72 projecting from the back surface 66 engageable with the ulnar stem 80 to orient the body 64 relative to the stem 80 and prevent rotation of the body. 64 relative to the stem 80. The ulnar articular component 60 is provided in a variety of materials to allow a surgeon to select a desired material. The ulnar articular component 60 may also be provided in a variety of socket 62 configurations to provide differing levels of constraint. For example the socket 62 may extend over the ball head 42 less than half the ball head radius so that is loosely connected to the ball head 42 or it may extend over the ball head 42 more than the ball head radius so that it is a snap fit onto the ball head 42.
The ulnar stem 80 includes an elongated body 82 forming an insertion portion having a first end 84, a second end 86, and a longitudinal axis 88 extending therebetween. The first end 84 includes an enlarged ulnar articular component 60 engaging hollow 90. The hollow 90 is hemispherical to engage the back side 66 of the articular component 60 and includes an annular groove 92 corresponding to the groove 68 in the articular component 60. As the articular component 60 is pressed into the hollow 90, the locking ring 70 is collapsed into the groove 68 in the articular component 60. As the groove 68 in the articular component 60 and the groove 92 in the ulnar stem 80 align, the locking ring 70 expands back to its original size with a portion projecting from the articular component 60 groove 92 into the stem 80 groove 92 to lock the articular component 60 in the hollow 90. When the articular component 60 is seated in the hollow 90, the articular component opening 69 forms a socket angle 98 (
The ball and socket configuration of the illustrative example permits three degrees of rotational freedom which facilitates increased varus/valgus and pronation/supination ranges of motion of the elbow compared to prior art hinge-type elbow prostheses which permit only a single degree of freedom. In addition, the relatively large contact area of the articular components 40, 60 of the present invention result in relatively lower contact stresses between the components 40, 60 to improve the longevity of the prosthesis. The modular construction permits different combinations of components to provide for a desired fit to a patient's anatomy, desired materials, and desired level of constraint.
In use, the illustrative elbow prosthesis 10 is implanted by first preparing the humerus 110 and ulna 112 (
Although an illustrative elbow implant and its use has been described and illustrated in detail, it is to be understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. Accordingly, variations in and modifications to the implants and their use will be apparent to those of ordinary skill in the art, and the following claims are intended to cover all such modifications and equivalents.
