Instruments and methods for flexion gap adjustment

Details Instruments and methods for flexion gap adjustment Instruments and methods for flexion gap adjustment

2002-03-29

2004-07-06

O'Connor, Cary E. (Department: 3732)

Surgery

Instruments

Orthopedic instrumentation

C606S087000, C606S102000

Reexamination Certificate

active

06758850

ABSTRACT:

BACKGROUND OF THE INVENTION
Present invention relates to systems and method for reconstructing a femoral portion of a knee in preparation for a total knee replacement. More particularly, the invention relates to systems and methods for orienting a cutting block used to resect portions of the femur, and more specifically in such as way as to balance medial and lateral collateral ligament tension.
The typical total knee arthroplasty includes three components, as depicted in FIG.
1
. In particular, the knee prosthesis
10
includes a femoral component
12
, a spacer
13
, and a tibial component
14
. The design of the components of the knee prosthesis
10
is complicated by the fact that the natural knee does not operate like a hinge moving about a single axis. The knee exhibits dynamic external rotation of the tibia relative to the femur as the knee moves from its flexed to its fully extended position. This automatic rotation of the tibia occurs in the opposite direction when the knee is flexed from its fully extended position to produce an internal rotation of the tibia relative to the femur.
Thus, the natural knee exhibits a rotary laxity that allows the tibia to rotate through a limited arc of both internal and external motion at every degree of knee flexion. While the configuration of the components
12
-
14
themselves is important to achieve proper knee motion, the specific placement of these components is also critical. Most particularly, the proximal/distal and anterior/posterior positions of the femoral component
12
are critical for duplicating the kinematics of the knee. Much literature and clinical study has been devoted to determining the proper orientation of the prosthesis components, and particularly the femoral component
12
.
As is known in the field of total knee arthroplasty, and as can be discerned from
FIG. 1
, the femoral component
12
exhibits a three-dimensional saddle configuration. The interior of the component is configured to mate with a prepared end of the femur. For the typical femoral component, the orthopaedic surgeon must make five cuts at the proximal end of the femur, as illustrated in FIG.
2
. In a typical procedure, a distal cut
1
is made across the distal end of the femur F. The anterior-to-posterior (A/P) placement of the femoral component is determined by the anterior and posterior cuts
2
and
3
, respectively. Once those cuts are complete, angled chamfer cuts
4
and
5
are typically made to help secure the femoral component
12
solidly in place. In order to effectively and accurately make these resections, orthopaedic surgeons will typically use a cutting block or cutting guide that is temporarily affected to the distal end of the femur F.
One important factor in determining the proper position of the femoral component, and therefore the proper location for the various cuts
1
-
5
, is the tension in the adjacent soft tissues, particularly the collateral ligaments. Proper tension in the collateral ligaments prevents sideways toggle of the leg. In addition, the collateral ligaments help to limit anterior/posterior travel of the femur relative to the tibia. The spacer
13
(
FIG. 1
) is an important component for maintaining the proper tension in the collateral ligament. With respect to a prosthetic knee, such as the prosthesis
10
, the spacer
13
is necessary to account for the gap that occurs between the distal end of the femur F and the proximal end of the tibia, after portions of both bone ends have been resected.
Knee instruments have evolved that provide means for mechanically distracting the knee joint to exert the proper tension on the ligaments during the knee arthroplasty procedure. One such instrument is illustrated in
FIGS. 3-5
. In particular, a distraction device
20
can include a lower member
22
that is adapted to contact the tibia plateau P (
FIG. 4
) of the tibia T. The distraction device also includes an upper member
24
that contacts the distal end of the femur F, preferably after the first distal cut (cut
1
in
FIG. 2
) has been performed. With this type of distraction device, the upper member
24
includes a medial and a distal member
24
a
and
24
b
, respectively, as depicted in
FIG. 5. A
pair of parallel adjusting members
26
adjust the position of the two upper members
24
a, b
relative to the lower member
22
. Preferably, the adjusting members
26
operate independently so that the medial upper member
24
a
can be adjusted differently from the distal member
24
b
. This independent adjustability of the medial and distal members allows the surgeon to properly orient the mechanical axis of the knee joint relative to the leg bones. Each adjusting member
26
can include an indicator
27
which provides an indication of the joint space, and ultimately the amount of tension applied to the ligaments. The distraction device
20
can be of a variety of types. For the purposes of illustrating the preferred embodiment of the present invention, a distraction device such as the device described in U.S. Pat. No. 4,501,266, issued Feb. 26, 1985, can be implemented. The details of this devise set forth in the '266 Patent are incorporated herein by reference.
In a typical knee arthroplasty procedure, the ligament tension is evaluated with the knee joint in its extended position—i.e. with the femur F and tibia T in alignment. In this position, the prepared surfaces of the femur and tibia are distracted apart by an extension gap G. The ligament tension can be corrected by releasing soft tissue attachments if a medial-lateral imbalance exists, thereby producing a symmetric or parallel extension gap. With this approach, the remainder of the arthroplasty procedure is geared toward maintaining this extension gap.
However, this approach does not account for proper tensioning of the knee when it is in flexion—i.e., when the knee joint is bent. It is with this type of movement that the A/P position of the femoral component
12
is most critical. If the component is offset incorrectly in the A/P direction, the flexion gap will not be correct and will not generate the proper amount of tension in the collateral ligaments. Thus, while the “extension gap first” approach generally assures a proper extension gap, this same approach does not translate to insuring a proper flexion gap. If the flexion gap is incorrect, the ligaments may be too loose or too tight, or the range of motion of the knee may be limited. In addition, poor tensioning in flexion can led to improper femoral rotation, condylar lift-off, accelerated wear of the prosthesis components, and even spin-out or dislocation of the femoral-tibial articulation. It is therefore important to derive a proper A/P position for the femoral component
12
.
Some procedures exist which begin with evaluating the flexion gap and then utilizing this flexion gap as the benchmark for the sizing and positioning of the knee prosthesis components. An approach of this type is shown in U.S. Pat. No. 6,056,756, issued May 2, 2000. While the system and method in '756 Patent correlates to the flexion gap, the A/P placement of the femoral component is made with reference to bony land marks on the femur, and not with reference to the flexion gap itself. Moreover, the approach in '756 Patent makes no account for a proper extension gap, except to the extent that sizing of the prosthesis components relative to the flexion gap achieves similar results when the knee is in extension.
Consequently, there is a need for an instrument and technique that more accurately locates the femoral component on the prepared distal end of the femur. This need is particularly acute with respect to the A/P placement of the femoral component, which is ultimately a function of the resection cuts made in the distal end of the femur (see FIG.
2
). Thus, the need extends to providing an instrument and method for accurately orienting and positioning the cuts that need to be made in the femur to achieve a properly sized femoral component.
SUMMARY OF INVENTION
To address these needs, the present i

Affiliated with

Also associated with

Rating

Instruments and methods for flexion gap adjustment does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Instruments and methods for flexion gap adjustment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Instruments and methods for flexion gap adjustment will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3185187