Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to surgically
implantable prosthetic devices for replacing the posterior
surface of the patella. More particularly, the invention
relates to a patellar implant and a method for surgically
installing the same which is particularly useful where it
is desired to avoid patellectomy.
The replacement of damaged or diseased joints
in the human body has been known for some time. If the
device used to replace the natural joint structures was
to be movable in a manner similar to the natural joint,
it was once necessary to provide a multiple part structure
of rigid clinically inert material. Generally, metals
such as stainless steel alloys were used for this purpose.
Such rigid structures, however, were subject to breakage
and were difficult to implant and hold in place once implanted.
The rigidity of the appliance can cause undue pressure on
the underlying cartilage and bone. Furthermore, while some
metals are considered to be clinically inert, some risk
of deterioration of the device with time continues to exist.
One prior art patellar implant, for example,
utilized a cobalt-chromium alloy (Vitallium, trademark of
Austenal Laboratories Inc.) cap pinned in position oveT the
cartilage covered posterior surface of the patella for
gliding movement upon the femoral condyles. Unfortunately,
however, such devices are difficult to fix to the patella
and eventually will work loose. Since the material is hard,
there is also a certain amount of inherent abraslon against
the adjacent bone surfaces and cartilage eventually causing
the implant to hang up and cease to function properly.
The present in~ention overcomes the difficulties
encountered in the prior art and provides a prosthetic
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implant for replacing the posterior surface of the patella.
The implant is formed as a body of flexible inert material
and replaces the underlying cartilage of the patella. ;
The implant is particularly adapted for use in cases of
chondromalacia when the femoral portion of the patello-
femoral joint is reasonably smooth. One side of the implant
is contoured or shaped to fit into a recess formed in the
resected posterior surface of the patella. The opposite
side, forms a new posterior surface for the patella and
has a compound articular surface for gliding engagement
with the femoral condyles.
The many objects and advantages of the p~esent
invention will become readily apparent to those skilled in
the art ~rom a consideration of the following detailed
description of the preferred embodiment of the implant
and method for installing same when read in conjunction
wîth the accompanying drawings.
FIG. 1 is a vertical cross section of a knee
joint;
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FIG. 2 is a front view of the knee joint with
the patella rotated to expose its posterior surface;
FIG. 3 is a fragmentary view illustrating the
resected posterior surface of the patella, the support ~;
ligaments and the like having been removed for clarity;
FIG. 4 is a cross sectional view taken along
plane IV-IV of the patella shown in FIG. 3;
FIG. 5 is a top plan view of the patellar implant
of the invention.
FIG. 6 is a bottom view of the patellar implant
shown in FIG. 5;
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FIG, 7 is a cross sectional view of the patellar
implant taken along the plane VII-VII of FIG. 5; and
FIG, 8 is a cross sectional view illustrating
the implant of FIG. 7 installed in the resected portion
of the patella of FIG. 4.
Referring to the drawings, a human knee joint
and the patella are illustrated in simplified diagramatic
form while the implant of the invention is illustrated
in detail in FIGS, 5-8. With specific reference to FIGS, 1-4,
a simplified anatomical illustration will be briefly described ,
to aid in a better understanding of the structure and
installation of the patellar implant. Basically, the knee
joint shown in FIGS, 1 and 2 provides a connection between
the upper end of the tîbia bone 10 and the lower end of the
femur bone 12. The lower end of femur bone 12 is formed
with a pair of generally rounded surfaces 14 and 16 known
as the femoral condyles. The inner condyle of the femur
is generally identified by the numeral 14 while the outer
or external condyle is identified by the numeral 16.
The tibia 10 and femur 12 are connected by
various ligaments and like connective tissues known to those
skilled in the art. The patella generally designated by
the numeral 18 is a sesamoid bone somewhat triangular in
shape (FIGS. 2 and 3) and situated in front of the knee
joint. The outermost or anterior surface 20 (FIGS. 1 and 4)
of the patella is slightly convex. The inner or posterior
surface 22 of a normal patella is generally concave and in
great part cartilage covered, forming a compound articular
surface for gliding on the femoral condyles. A slightly
marked vertical ridge 24 divides the posterior surface 22
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into an external articular facet 26 for gliding engagement
with the outer condyle 16 and an inner or internal articular
facet 28 for gliding engagement with the inner condyle 14.
The lower portion of the patella tapers to a blunt point 30
which is embedded in the patellar ligament 32 while the upper
portion is held by the quadriceps tendon 34 associated with
the tissues of the femur bone. The bursa 36 is located
between the anterior surface 20 of the patella and the skin.
Referring additionally to FIGS. 5-7, the patella
~o implant designated by the numeral 40 is generally circular
in configuration and has a top or upper surface 42 which
corresponds generally to the configuration of the posterior
surface 22 of patel3a 18 illustrated in FIG. 2.
Preferably, the patellar implant 40 of the
invention is molded of flexible elastomeric physiologically
inert material. CLEAN ROOM DOW CORNING Silicone Rubber
Compound No. MDX4-4515 available from the Dow Corning
Corporation~ Midland, Michigan, is one material selected
to meet the requirements of the patellar implant. While
the prosthetic implant is described as being made of silicone
rubber type materials, it will be realized that other flexible,
clinically inert materials having sufficient strength may
be used.
The upper surface 42 of implant 40 is molded to
include surface areas generally corresponding to the surfaces
found on a normal patella These surfaces include a vertical
ridge 44 dividing top surface 42 into an outer, larger
curved, surface portion 46 corresponding to the external ;~
articular facet 26 and a smaller inner curved, surface
portion 48 corresponding to the internal articular facet 28.
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These surfaces 46 and 48 are adapted for gliding engagement
with the outer and inner condyles 16 and 14, respectively.
To aid in the installation of the implant as
will be hereinafter described, the base or back of the
implant 40 is covered with a thin layer of fabric 50.
Preferably, the fabric 50 is a synthetic fiber ~elour wherein
the fiber is a condensate of dimethyl terephthalate and
ethylene glycol which is secured to the back surface in any
conventional manner as by suitable adhesive or if desired
may be fixed simultaneously with molding of the implant.
Two sutures 52 are passed through fabric so as
to have their midportions sandwiched between the fabric
and the implant. The extremities of the sutures hang free
for use in the manner to be described. Preferably, a
polyester, clinically inert, suture material is provided.
Referring additionally to FIGS. 3, 4 and 8, the
preparation of the patella 18 and installation of the implant
40 will be described. By means of conventional surgical
techniques, the posterior surface 22 of patella 18 is
exposed by slitting the supporting side tendons and rotating
the patella to expose the posterior surface 22 thereof.
The patella is rotated generally about an axis parallel to
the tibia 10 and ~emur 12. The posterior surface 22 of
patella 18 is resected to remove the damaged areas such that
a generally flat surface area 5~ remains. A circular
relief or depression 56 is formed in the resected posterior
surface of the patella to accept the implant, the damaged
underlying cartilage on the posterior surface being removed
in this process.
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Circular depression 56 includes a bottom wall
surface 58 and a side wall surface 60 upstanding therefrom.
A series of four generally e~ually spaced holes 62 are
drilled from bottom wall surface 58 through patella 18
to the anterior surface 20. Openings 62 are spaced apart
to correspond generally to the location of the sutures
52 èxtending from fabric 50 of implant 40. After formation
of the circular relief 56 and openings 62, the implant 40
is positioned in recess 56 and secured to bottom wall 58.
Implant 40 is secured in the resected patella by first
cementing it in place to provide an immediate bond, and
in addition, by tying the sutures 52 at the anterior surface
as illustrated in FIG, 8. A physical bond between fabric
50 and bottom wall 58 of the recess can be provided by
cement such as methyl methacrylate which fills in the
spaces between the fabric material conforming to any surface
irregularities of bottom wall 84 and eventually grows to
the surrounding tissues. The upstanding side wall surfaces
60 stabilize the implant and prevent shifting of the implant
with respect to the posterior surface of the patella.
Since the implant 40 is generally symmetrical
in line VII-VII (FIG, S), about an axis defined by its
position in the resected portion of the patella can be
reversed, permitting the implant to be used to rebuild the
patella of either the left or right knee. A suitable
template is preferably utilized by the surgeon in forming the
resection and locating the position for the drilling of the
the suture holes.
After implant 40 is installed and secured in the ;~
resected posterior surface of the patella, it is folded -~ -
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back into position with the formed surface of the implant
in engagement with the condyles. Normal surgical procedures
are followed thereafter to complete the operation.
Those skilled in the art will, of course, readily
appreciate the ~any advantages of the present invention. ;~
Those so skilled will also recognize that many modifications
may be made, and it is intended that modifications be covered
unless the following claims by their wording expressly state
otherwise.
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