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JP-7855592-B2 - Monocondylar tibial component

JP7855592B2JP 7855592 B2JP7855592 B2JP 7855592B2JP-7855592-B2

Inventors

  • オコナー．ジョン
  • ドッド．クリストファー
  • マレー．デイヴィッド・ウィクリフ

Assignees

  • ツィマー．ゲゼルシャフト．ミット．ベシュレンクテル．ハフトゥング
  • オコナー ジョン
  • ドッド．クリストファー
  • マレー．デイヴィッド・ウィクリフ

Dates

Publication Date
20260508
Application Date
20220107
Priority Date
20210107

Claims (10)

  1. It is a unicondylar tibial component, A plate having a support surface and an opposing surface configured to be fixed to the proximal end of the patient's tibia, wherein the plate further comprises an anterior end, an lateral end, a posterior end, and an lateral end, the width W of the plate in the inward-outward direction defined between the lateral end and the lateral end, and the longitudinal anterior-posterior axis extending from the lateral end between the anterior end and the posterior end by approximately one-third (i.e., 1/3W) of the width of the plate, defining the longitudinal axis length L of the plate, A first elongated peg protrudes from the opposing surface in the front portion and defines the first peg shaft, The first and second pegs are arranged at an angle of 45° to 70° with respect to the longitudinal front-to-back axis, and are substantially parallel to each other such that the first and second pegs protrude rearward and distally from the plate. The front portion of the plate includes a portion defined by 60% or less of the front of the longitudinal axis length L of the plate, while the rear portion of the plate includes a portion defined by 40% or more of the remaining rear of the longitudinal axis length L of the plate, and no pegs or other fastening devices are placed on the rear portion of the opposing surface. The first and second elongated pegs are positioned at a location that is more than half the width W of the plate in the inward-outward direction from the outer edge of the plate. The aforementioned component is a unicondylar tibial component configured for cementless fixation using a compression fit.
  2. The unicondylar tibial component according to claim 1, wherein the first and second peg axes are positioned at an angle of approximately 60° with respect to the longitudinal anterior-posterior axis.
  3. The unicondylar tibial component according to claim 1 or 2, wherein one or more of the elongated pegs preferably have a high aspect ratio, and each peg preferably has a length of 6 to 12 mm and a maximum diameter of 4 to 8 mm.
  4. (i) one or more of the elongated pegs have an elliptical cross-section, or (ii) one or more of the elongated pegs are tapered, according to any one of claims 1 to 3.
  5. The unicondylar tibial component according to any one of claims 1 to 4, wherein one or more of the elongated pegs have a rounded or tapered tip.
  6. The unicondylar tibial component according to any one of claims 1 to 5, wherein the first elongated peg is positioned at one-fifth of the anterior-posterior axis length, and the second elongated peg is positioned at half the anterior-posterior axis length.
  7. The unicondylar tibial component according to any one of claims 1 to 6, wherein one or more of the elongated pegs include one or more barbs.
  8. The unicondylar tibial component according to any one of claims 1 to 7, wherein each of the elongated pegs is provided with a cementless fixing coating, the coating is not present in any region of each peg, and the diameter of each region is narrower than the maximum diameter of the covered peg.
  9. The unicondylar tibial component according to claim 8, wherein the coating is not present within the base region of each peg adjacent to the opposing surface, so that the diameter of each base region is narrower than the maximum diameter of the coated peg.
  10. The unicondylar tibial component according to any one of claims 1 to 9, wherein one or more of the elongated pegs include a region narrower than the maximum diameter of the peg.

Description

This invention relates to a unicondylar tibial component, and a method and apparatus for implanting it. While this invention particularly relates to a unicondylar tibial component for cementless implantation, it does not exclude others. Knee arthroplasty typically involves a surgeon removing the patient's femur and/or tibia and replacing the joint surface by implanting an artificial femoral component and/or artificial tibial component into the removed bone. This surgery may be a total knee arthroplasty, replacing the joint surfaces of the femur and tibia (and sometimes the patella), or a partial knee arthroplasty, such as a unicompartmental knee arthroplasty (also known as unicompartmental unilateral knee arthroplasty), replacing only a portion of the knee joint surface. The transplanted component needs to be fixed to the excised bone by some means. Therefore, tibial components often contain one or more anchors. These anchors may be located at the base or lateral side of the component and are housed within cavities formed in the patient's bone (e.g., obtained by excavation, carving, burring, or sawing), assisting in fixing the component in place. Such anchors may be keels, which are elongated projections extending from the base of the component approximately parallel to its anterior-posterior axis. Bone cement can be used to fix implants (with or without anchors) in place. Bone cement is useful because it can fill the gap between the excised bone and the base of the implant. However, bone cement can deteriorate or crack over time, potentially causing implant loosening or damage and/or fragmentation within the knee compartment. Furthermore, bone resorption can lead to a breakdown of the bond between the cement and the bone. When a component loosens, it tends to collapse. If a loosened tibial component is subjected to uneven, off-center loading, it can detach and collapse. For example, knee flexion is known to cause anterior detachment of implants on the tibial plateau, potentially leading to implant damage and/or fragmentation within the knee compartment. Cementless fixation in unicompartmental knee arthroplasty, particularly medial unicompartmental knee arthroplasty, can sometimes offer better long-term outcomes than cemented fixation. Cementless components are designed to fix to the resected bone without the use of bone cement. Such components typically include a porous or microporous surface that promotes bone grafting into the component over time, which eventually forms a strong bond between the component and the patient's bone. To ensure the implant remains in place when bone grafting occurs, cementless components usually include one or more fixation mechanisms (e.g., keels) that are embedded in the patient's bone to form a press-fit and/or interlock-fit. Cementless tibial fixation carries two major early complications: tibial plateau fracture and insufficiency. These can lead to implant loosening or collapse, potentially causing pain to the patient. While these complications are rare, they represent a significant problem for patients who experience them. Tibial plateau fractures typically occur in the first few weeks after transplantation. This is likely because a crack occurred during surgery and subsequently propagated through the stressed bone. In cementless fixation, fixation mechanisms such as keels are subjected to impact and press-fitting. This impact can cause cracks. Furthermore, the press-fitting process can create stress within the bone, potentially leading to fracture propagation. Additionally, the use of longitudinal keels requires the formation of grooves within the bone, leading to bone weakening. During unicompartmental knee arthroplasty, the superficial subchondral bone is removed. In a normal knee, this bone acts as a tension band, preventing the protruding medial condyle from fracturing. In a replaced knee, this tension band is removed, making it more susceptible to fracture. Tibial component depression can take a long time to become apparent. During typical functional activity, the load on the tibial component is relatively concentrated when the knee is near extension. As a result, the forces at the bone-implant (or bone-cement) interface below the tibial component are primarily compressive, making it ideal for cementless fixation. Additionally, some shear forces are generated at the interface due to the anterior-posterior movement of the femoral component during activity. These shear forces are relatively small (especially in the case of movable bearings, an order of magnitude smaller than the frictional force between the tibial component and bone). However, during high-load, high-flexion activities, the force is applied more posteriorly to the tibial component. This compresses the bone posteriorly, causing the anterior part of the component to lift from the bone and the component to tilt. Lateral radiographic images typically show a radiolucent area beneath the anterior surface of