1. Technical Field
The present disclosure relates generally to surgical instruments and more specifically to surgical instruments for grasping spherical implants.
2. Background Information
Orthopedic surgeons may treat acute, chronic or traumatic injuries to the musculoskeletal system by replacing or augmenting injured structures with orthopedic prostheses and implants. For example, a surgeon may replace damaged or degenerated joints of the shoulder, hip, knee, elbow, or hand with a joint-replacement prosthesis, to reduce pain and improve mobility of a patient. Such treatment may be particularly appropriate when other treatment options have been exhausted.
Many joint-replacement prosthesis include a spherical implant that, together with a cup-like structure, form a ball and socket joint. As used herein, the term “spherical implant” should be interpreted broadly to encompass structures placed within the body that are shaped substantially as, or include a portion shaped substantial as, a hemisphere, a spherical cap, a sphere, a partial spheroid, a spheroid, or other similar three dimensional convex body. One specific type of a spherical implant is a glenosphere, which is commonly employed in reverse shoulder replacement surgery.
In a healthy shoulder, the humerus of the arm ends in a ball shaped humeral head, which fits into the socket-shaped scapula of the shoulder. In reverse shoulder replacement surgery, the anatomy is reversed. A ball-like structure is attached to the scapula and a socket is attached to the upper end of the humerus. In reference to the example reverse shoulder prosthesis 100 of FIG. 1, a portion of the humerus (not shown) is cut away and a diaphysis 110, a lower humeral stem, is inserted down the center of the humerus. An epiphysis 120, an upper portion humeral stem, is attached to the diaphysis 110 and also fits substantially within the humerus. The diaphysis 110 and epiphysis 120 are typically made of a hardened metal, such as titanium, cobalt chrome, or stainless steal. The epiphysis 120 holds a lateralised cup 130, typically made from polyethylene or another plastic material, which forms the socket of the new joint.
On the scapular side, a metaglene 140, a hardened metal plate, is attached to the scapula (not shown), typically with multiple bone screws 150. Finally, a spherical implant, in this case, a glenosphere 160, is affixed to the metaglene 140, typically by a central screw 170 or other fastener. The substantially hemispherically shaped glenosphere 160 fits inside the lateralised cup 130 to form the new shoulder joint. Both the glenosphere 160 and the lateralised cup 130 typically come in a variety of different sizes tailored to different body types and other factors. In some cases, size is an expression of diameter. Some common glenosphere diameters include 34 mm, 36 mm, 40 mm, and 42 mm.
When a spherical implant, such as a glenosphere 160, is employed, a surgeon must securely grasp the spherical implant to manipulate it into position and affix it in place. However, due to their curvature, spherical implants are typically quite difficult to grasp with many conventional surgical instruments. Some conventional surgical instruments may readily disengage (for example, slip from) a spherical implant. Other conventional surgical instruments, while better retaining a spherical implant, may damage the implant in the process, for example, by placing excessive pressure on a confined area of the implant, or by allowing the implant to rotate or move against portions of the instrument, which may lead to scratching.
The difficulties of grasping a spherical implant are further compounded by the existence of multiple sizes of spherical implants, for example multiple diameters of implants. Conventional instruments that may perform acceptably with a particular size spherical implant often fail completely, or perform quite poorly, with differently sized implants. Thus, if a surgeon desires the flexibility of using differently sized spherical implants, he or she typically must have on hand a range of different size-specific instruments. This both increases expense and creates logistical burdens.
Accordingly, there is a need for an improved surgical instrument that overcomes the shortcomings of prior designs.