Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2002-01-29
2004-08-31
Philogene, Pedro (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S018110, C623S019110
Reexamination Certificate
active
06783550
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to prosthetic structures and corresponding surgical methods used to relieve pain caused by disorders of the knee joint. More particularly, the invention relates to prostheses and methods for total knee arthroplasty.
2. The Relevant Technology
The knee is the largest and one of the most complicated joints of the human body. The human knee joint serves an essential function to allow individuals to lead a normal life, while performing its function, in many ways, much better than any device heretofore designed by human engineers. For example, the knee should be able to move from 0° in the straight position to more than 90°, while being completely stable in every other direction.
The bones of the knee joint, when functioning properly, move together with very little friction. To function properly, a healthy knee joint requires an intact layer of hyaline cartilage, the material that makes up the articular cartilage on opposing surfaces of the joint. In addition, the bones of the joint must be in proper alignment and the synovial membranes must produce sufficient amounts of lubricating (synovial) fluid. Furthermore, the surrounding ligaments and tendons must prevent the bones from being placed in abnormal positions.
FIG. 1
is an anterior (that is, taken from the front of the body) cross-sectional view of a human knee
10
. The knee
10
consists of three bones; a femur
20
, a tibia
30
, and a patella
40
. Each of these bones is covered with articular cartilage, which has a smooth glistening surface. Located at the distal end of femur
20
are the femoral condyles
22
having a medial condyle
24
and a lateral condyle
26
separated by an intercondylar fossa or notch
28
. Formation of intercondylar notch
28
is such that patella
40
articulates therethrough during extension and flexion of knee
10
.
Tibia
30
supports most of the weight transmitted between femur
20
and the foot (not shown), while a small portion of the weight is carried by a fibula
42
located substantially parallel to tibia
30
. As such, tibia
30
has a tibial plateau
32
with a medial plateau
34
and a lateral plateau
36
substantially aligned to cooperate with medial condyle
24
and lateral condyle
26
of femur
20
. Medial plateau
34
and lateral plateau
36
of tibia
30
are separated by an intercondylar area formed with an elevated portion or an intercondylar eminence
38
. Intercondylar eminence
38
locates within intercondylar notch
28
to maintain structural support between femur
20
and tibia
30
. Additionally, intercondylar notch
28
separates the spaces of a medial compartment
44
and a lateral compartment
46
formed between the respective medial and lateral plateaus
34
,
36
.
Located within each medial and lateral compartment
44
and
46
are the menisci
50
, shown by the dotted line. Menisci
50
consists of two crescentic lamellae formed to distribute surface stresses between femur
20
and tibia
30
. As such, the upper surfaces of the menisci
50
are smooth and concave to accommodate femoral condyles
24
and
26
, while the lower surfaces are smooth and flat to cooperate with tibial plateaus
34
and
36
.
Surrounding and stabilizing the dynamic structure of knee
10
are a number of varyingly sized ligaments. Particularly, four main ligaments maintain the stability and flexibility of knee
10
: a medial collateral ligament
62
, a lateral collateral ligament
64
, an anterior cruciate ligament
66
and a posterior cruciate ligament
68
. Medial collateral ligament
62
and lateral collateral ligament
64
limit side-to-side motion. Medial collateral ligament
62
extends from medial condyle
24
or portions of femur
20
to medial plateau
34
of tibia
30
. Similarly, lateral collateral ligament
64
extends from lateral plateau
36
or portions of femur
20
to fibula
42
. Anterior cruciate ligament
66
and posterior cruciate ligament
68
, so named because they cross in the middle of knee
10
, are rope-like ligaments formed from interwoven and overlapping fibers. Anterior cruciate ligament
66
and posterior cruciate ligament
68
, extend from the anterior to the posterior of knee
10
and prevent femur
20
and tibia
30
from sliding forward and backward while permitting a wide range of rotational movement.
While the knee generally serves its purpose very well, various disorders of the knee cause a great deal of pain and loss of mobility and function to those who are affected with such disorder. Some knee disorders are congenital; that is, they are present at birth. Other disorders of the knee are brought on by bacterial infections that may occur at any age. Yet still other disorders result from normal “wear and tear” of the knee joint, whether such “wear and tear” arises from age or injury. Perhaps the most wide spread disorder of the knee is arthritis. The term “arthritis” is generally used as a common name for the effects of several degenerative knee disorders, such as by way of example traumatic arthritis, infectious arthritis, osteoarthritis, and rheumatoid arthritis.
Of various types of arthritis, osteoarthritis is perhaps the most common. Osteoarthritis is a degenerative “wear and tear” process that affects substantial numbers of people. The final result of unchecked osteoarthritis is damaged articular cartilage, and subchondral bone which in many cases causes extreme pain as the damaged surfaces are rubbed together during joint movement. Osteoarthritis may also be caused by angular deformity or old fractures. Systemic arthritis such as rheumatoid arthritis or gout affects the synovium (the membrane tissue in the knee that normally lubricates the knee), becomes pathologic and one or more surfaces of the joint are destroyed.
Osteoarthritis may also involve the development of abnormal bone subjacent to the joint surface, known as subchrondral lesions. These subchrondral lesions may take the form of a cyst or sclerosis. Due to the decreased stability of the knee through the generation of cysts and sclerosis and decreased joint space, marginal spurs develop in an attempt to stabilize the joint. Unfortunately, the spurs also cause severe pain, stiffness decreased range of motion, loss of stability, and loss of function.
Generally, osteoarthritis affects people past the age of 60 years without providing any easily recognizable single cause. However, osteoarthritis may develop in younger people due to congenital disease. Furthermore, traumatic injury may cause development of an osteoarthritis condition, such as from various sporting activities.
In the prior art, several methods have been used for alleviating the pain and improving the function of a knee joint affected with a degenerative disorder such as osteoarthritis. One of the most common procedures used in treatment of knee disorders is know as “arthroplasty” and entails the implantation of an artificial joint component into the knee. Arthroplasty has been one of the major areas of advancement in knee surgery during the past quarter century. Knee arthroplasty can take the form of unicompartmental arthroplasty or total knee arthroplasty.
Unicompartmental arthroplasty involves replacement of one of the two compartments of the knee joint. For example, this procedure is used where either of the medial or lateral compartments is damaged, while the remaining compartment and intercondylar notch are otherwise normal. In such a case, it is beneficial to replace the damaged areas of the femoral condyle and tibial plateau with an artificial prosthesis that will work in conjunction with the natural portions of the knee.
The most common arthroplasty procedure used to alleviate pain and restore knee function is total knee arthroplasty, also called total knee replacement. While many different styles of total knee replacement prostheses have been implanted in patients, they generally resemble the prosthetic illustrated in FIG.
3
.
Conventional total knee replacement involves a complete resurfacing of both tibial plateaus
34
,
46
Holme Roberts & Owen LLP
Philogene Pedro
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