Methods and tools for femoral resection in primary knee surgery

Details Methods and tools for femoral resection in primary knee surgery Methods and tools for femoral resection in primary knee surgery

2000-12-23

2003-05-06

Smith, Jeffrey A. (Department: 3625)

Surgery

Instruments

Orthopedic instrumentation

C606S096000

Reexamination Certificate

active

06558391

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to methods and tools used in knee arthroplasty. More particularly, the invention relates to methods and tools used in total knee surgery (primary and revision applications) where an artificial femoral component is installed.
2. Brief Description of the Prior Art
Total knee arthroplasty involves the replacement of portions of the patella, femur and tibia with artificial components. In particular, a proximal portion of the tibia and a distal portion of the femur are cut away (resected) and replaced with artificial components. As used herein, when referring to bones or other body parts, the term “proximal” means closest to the heart and the term “distal” means more distant from the heart. When referring to tools and instruments, the term “proximal” means closest to the practitioner and the term “distal” means distant from the practitioner.
There are several types of knee prostheses known in the art. One type is sometimes referred to as a “resurfacing type”. In these prostheses, the articular surface of the distal femur and proximal tibia are “resurfaced” and replaced with respective metal and plastic condylar-type articular bearing components.
The femoral component is a metallic alloy construction (cobalt-chrome alloy or 6A14V titanium alloy) and provides medial and lateral condylar bearing surfaces of multi-radius design of similar shape and geometry as the natural distal femur or femoral-side of the knee joint.
Prior art
FIG. 1
is a sectional view of a state of the art femoral component. The interior of the component has five planar fixation surfaces
1
-
5
and an intramedullary (“IM”) stem
6
. Prior to installation of the component, the distal femur must be prepared so that it has five fixation surfaces which closely match the interior surfaces of the component and in scenarios where additional stability is desired the IM canal is reamed to accept the IM stem of the component.
More particularly, the distal femur must be resected to have a distal cut surface (corresponding to surface
1
in FIG.
1
), a posterior cut surface (corresponding to surface
2
in FIG.
1
), an anterior cut surface (corresponding to surface
3
in FIG.
1
), an anterior chamfer cut surface (corresponding to surface
4
in
FIG. 1
) and a posterior chamfer cut surface (corresponding to surface
5
in FIG.
1
). These cuts are typically made with oscillating saw blades.
A number of different devices can be used to control the positioning of the saw blades. Flat metallic blocks on which the saw blade is rested, obviously rely to some extent on the skill of the surgeon to avoid tilting of the saw blade, as may happen when the saw encounters a localized harder (sclerotic) section of bone, or when the saw blade has a long travel beyond the guide surface. Slots having small clearance relative to the thickness of the saw blade may also be used. In general these offer better control of the saw blade than open style blocks.
Block type cutting guides are shown in U.S. Pat. Nos. 4,474,177, 4,487,203, 4,502,483, 4,524,766 and 4,567,885.
Fulcrum type cutting guides are described in U.S. Pat. No. 4,718,413 and also in U.S. Pat. No. 4,892,093. These consist of an upper and a lower guide surface which are linearly separated along the plane of intended cut by the saw blade. By providing a separation between the two surfaces the saw blade, including its tooth set, may be introduced between the two surfaces and then biased against them to control the cutting plane.
The separation of the guide surfaces normal to the plane of operation of the saw blade is typically matched to the thickness of the saw blade. The choice of orientation of the guide surfaces is chosen so that any deviation by the surgeon in maintenance of the contact between the saw blades and either of the guide surfaces results in conservative removal of bone, which may be subsequently corrected. The guide of U.S. Pat. No. 4,892,093 sits on the already prepared distal femur and provides for the cutting of four additional cuts.
The femoral components may be located with six degrees of freedom relative to the patient's femoral geometry. These can be expressed in a Cartesian manner relative to orthogonal anatomical reference planes as shown in FIG.
2
. Angulation: Varus-Valgus, Flexion-Extension and Internal-External Rotation. Linear Position: Inferior-Superior, Anterior-Posterior and Medial-Lateral. To position the component on the bone, a number of datum features of the patients anatomy and their relative location as controlled by soft tissue structures at the knee may be utilized.
Two major schools of thought exist as to the optimum method to provide consistent functional placement. The first is independent femoral anatomical placement. In this technique the femoral component is positioned on the femur by referencing datum features on the femur itself. The second is referenced to the tibial position. In this technique the position of the femoral component is controlled relative to the proximal cut of the tibia. The ligaments and other soft tissue structures at the knee joint will in this case affect the femoral component's position. The positional referencing, according to different methodologies, is performed surgically prior to placing the femoral component.
A third technique is varus-valgus and flexion-extension. Angulation of the component in planes is usually performed simultaneously. The reference datum is either the femoral shaft or the line joining the center of the knee and the hip joints. Two major techniques for accomplishing this are currently used. First is intramedullary alignment. A rod is introduced through the center of the knee into the intramedullary space and passed up the inside of the femur to the internal isthmus, establishing an instrument axis within the femoral shaft (medullary canal of the femur). This technique has been found to be very reliable. The second is extramedullary alignment. An external guide rod is aligned with the anterior cortex of the femur, or from the center of the knee to the femoral head.
Current techniques generally require the sequential use of alignment and cutting guides. In most current systems multiple cutting guides are needed to fully prepare the distal femur for the implant. Because these sequential operations require the assembly and disassembly of instrument configurations and the use of intermediate data cut onto the bone, there are penalties in terms of time of surgery and accuracy.
U.S. Pat. No. 5,454,816 discloses an orthopedic instrument for guiding a saw blade for shaping the distal end of a human femur to receive an endoprosthetic femoral component. The instrument includes a base component provided with a guide for guiding cutting elements for shaping all of the necessary surfaces to receive the femoral component to be fitted once the base component is fitted to the bone. Also included are alignment elements for aligning the base component on the bone and elements for attaching the base component to the bone after alignment.
All of the prior art cutting guides have certain drawbacks. These include the inability to provide accurate cuts on a variety of different size femurs, inability to accurately align with one or more of the femoral axes, difficulty in fixation of the guide to the femur, inability to make adjustments in positioning after alignment tools are removed, impingement of soft tissue when securing the cutting guide, etc.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide methods and tools for performing femoral resection.
It is also an object of the invention to provide tools for performing femoral resection which maintain proper alignment while multiple resection cuts are made.
It is another object of the invention to provide methods for performing femoral resection in which a minimum number of tools are used.
It is still another object of the invention to provide methods and tools which enhance the accuracy of femoral resection.
It is also an object of the inventi

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