Patent Application
20060161259
The present invention relates to an improved knee joint prosthesis and particularly to a prosthetic knee joint to bridge a thighbone and a tibia and to couple with a femur implanted component on the thighbone to enable a patient to resume normal movement and exercise.
The knee joint prosthesis is first developed by Gunston et al in 1968. It mainly aims to substitute an impaired or degenerated knee joint that cannot function normally. It is made of metal to imitate the condyle of the femur and uses ultra high molecular weight polyethylene (UHMWPE) to substitute the function of knee joint and meniscus cartilage. In 1970s, varying prosthetic knee joints have been developed. Development of the knee prosthesis generally follows two directions. One recommends scarifying the posterior cruciate ligament (PCL) during surgical operation. The other one suggests retaining the posterior cruciate ligament during the surgical operation. Above mentioned knee prostheses are designed with different characteristics. Posterior Cruciate Ligament retained knee prosthesis (CR knee prosthesis) could have good clinical results in long term survival analyses but surgeons should pay more attention to make sure whether the PCL has well function during operation.
In terms of the posterior cruciate ligament substituted knee prosthesis (PS knee prosthesis), PCL is scarified to facilitate surgical approaches. Ligament's function is substituted for an artificial mechanism of a tibial post and a femoral cam. It could provide anteriopostrior stability of the knee joint and recover normal knee kinematics after knee joint replacement. Based on above advantages, PS knee prostheses became more reliable and acceptable since 1990. One of the modern techniques is U.S. Pat. No. 4,213,209. It discloses a knee joint prosthesis which includes a tibial baseplate made of metal and implanted in a tibia, a tibial insert made from polyethylene to be coupled on the tibial baseplate and a femur implanted component made of metal and implanted in the thighbone for moving on the concavities of the tibial insert. Knee joint stability is mainly supported through a bracing member integrally formed with the tibial insert that is coupled with the femur implanted component. When the patient moves or walks, the thighbone drives the femur implanted member to move on the concavities of the tibial insert about the bracing member so that the thighbone and the tibia can maintain a flexuous condition to enable the knee joint of the patient to move like before operation. However, clinical diagnoses over the years show that such type of prosthetic knee joint still has drawbacks that affect its life span, notably:
1. As the femur implanted component is made of metal, while the tibial insert is made from polyethylene, when the femur implanted component swivels is coupled with the bracing member and swivels like screw-home mechanism, due to the difference of materials and the fixed bracing member of the tibial insert, the bracing member (namely post structure) on the tibial insert wears off rapidly and even fractures.
2. Besides the impact of the coupling mechanism set forth above, movement of the femur implanted component will cause the tibial insert to slide slightly on the tibial. As the tibial component is made of metal, backside tibial insert wearing also occurs to the lower surface of the tibial insert. These wearing phenomena not only shorten the life span of the prosthetic knee joint but also produce polyethylene debris, induce osteolysis, and lead components loosening.
The primary object of the invention is to solve the aforesaid disadvantages. The invention employs a separate design and has a moving aperture on a tibial insert to hold a bracing member which is coupled with a femur implanted component. A tibial insert is provided that has a retaining member. The bracing member and the retaining member may be swiveled in the moving aperture. The bracing member is made from a wearing-resistant material and can prevent the tibial insert from sliding and wearing off, thus the life span of the prosthetic knee joint increases.
The foregoing, as well as additional objects, features, and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
Please refer to
The tibial insert 10 has two concavities 11 and 12 that allow the femur implanted component 60 to move thereon. The tibial insert 10 further has a moving aperture 13 formed between the two concavities 11 and 12. The moving aperture 13 holds a bracing member 30 which is coupled with the femur implanted component 60. The bracing member 30 has a fastening section 31.
The tibial baseplate 20 has a holding surface 21 to hold the tibial insert 10, a retaining member 40 which has an anchor section 41 mating the fastening section 31, and an implanting strut 24 extended integrally to couple with the tibia 70.
For assembling the first embodiment set forth above, first, place the tibial insert 10 on the holding surface 21 of the tibial baseplate 20; insert the retaining member 40 in the moving aperture 13. The tibial baseplate 20 has a retaining flange 22 extended from the holding surface 21 on one edge. The retaining flange 22 has an inhibiting section 221 corresponding to an anchor wing 14 formed on the tibial insert 10. Hence the tibial insert 10 is prevented from sliding when the femur implanted component 60 is moved on the two concavities 11 and 12. Moreover, in this embodiment, the bracing member 30 is coupled with the retaining member 40 to swivel in the moving aperture 13. The retaining member 40 has a retaining section 42 which is larger than the moving aperture 13. The tibial dock 20 further has an anchor trough 23 for holding the retaining section 42. The fastening section 31 has external screw threads to engage with internal screw threads formed in the anchor section 41, thus the bracing member 30 and the retaining member 40 may be coupled together and the retaining section 42 is confined by the moving aperture 13 and the anchor trough 23 without escaping. Referring to
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While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
