U.S. patent number 3,863,273 [Application Number 05/398,925] was granted by the patent office on 1975-02-04 for orthopedic prosthetic implant devices.
This patent grant is currently assigned to Meditec, Inc.. Invention is credited to Robert G. Averill.
United States Patent |
3,863,273 |
Averill |
February 4, 1975 |
ORTHOPEDIC PROSTHETIC IMPLANT DEVICES
Abstract
A prosthetic joint for use in replacement of the ball end of
defective biological hip joints, the prosthetic joint including a
head for insertion into and unattached seating in the socket member
of the biological joint, a bearing insert in the head, the bearing
insert having a spherical seat and being engaged in the head by a
plurality of axially extending ridges on said head which engage
with the bearing insert and prevent the bearing insert from
rotating in the head, a ball shaped member seated in the spherical
seat and having a diameter not more than 65 percent of the diameter
of the head, the bearing insert including means for engaging the
ball shaped member and for retaining such ball shaped member in the
bearing insert while permitting pivotal universal movement of the
ball shaped member and the attaching means in the bearing insert
and means for attaching the ball shaped member to the shaft of an
anatomical member of the joint being partially replaced with the
prosthetic joint.
Inventors: |
Averill; Robert G. (Ringwood,
NJ) |
Assignee: |
Meditec, Inc. (Fair Lawn,
NJ)
|
Family
ID: |
26266813 |
Appl.
No.: |
05/398,925 |
Filed: |
September 20, 1973 |
Current U.S.
Class: |
623/22.17 |
Current CPC
Class: |
A61F
2/32 (20130101); A61F 2310/00017 (20130101); A61F
2002/3208 (20130101); A61F 2220/0025 (20130101); A61F
2002/30594 (20130101); A61F 2002/30616 (20130101); A61F
2002/3233 (20130101); A61F 2002/30487 (20130101); A61F
2002/3611 (20130101); A61F 2002/305 (20130101); A61F
2002/3631 (20130101); A61F 2002/30662 (20130101); A61F
2310/00029 (20130101); A61F 2002/30037 (20130101) |
Current International
Class: |
A61F
2/32 (20060101); A61F 2/00 (20060101); A61F
2/30 (20060101); A61F 2/34 (20060101); A61F
2/36 (20060101); A61f 001/24 () |
Field of
Search: |
;3/1 ;128/92C,92CA |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,215,737 |
|
Dec 1970 |
|
GB |
|
1,047,640 |
|
Jul 1953 |
|
FR |
|
720,092 |
|
Dec 1954 |
|
GB |
|
Primary Examiner: Frinks; Ronald L.
Claims
I claim:
1. An implantable prosthetic joint for use in replacement of the
ball end of defective biological joints, said prosthetic joint
including a head for insertion into and unattached seating in the
socket member of the biological joint being partially replaced by
said prosthesis, a bearing insert in said head, said bearing insert
having a spherical seat, a ball shaped member seated in said
spherical seat in said bearing insert, said bearing insert
including means for engaging said ball shaped member and for
retaining said ball shaped member in said bearing insert while
permitting pivotal universal movement of said ball shaped member,
means for engaging and retaining said ball shaped member in said
bearing insert including a one-piece insert having a plurality of
arcuate sections at the open edge of said insert which, when said
head is removed, are flexible outwardly to allow said ball shaped
member to be inserted into said spherical seat and which, when said
ball shaped member is in said spherical seat, and said head is
placed over said bearing insert, are engaged by said head for
retaining said ball shaped member in said bearing insert, attaching
means in said bearing insert and means for attaching said ball
shaped member to the shaft of the second anatomical member of the
joint being partially replaced.
2. A prosthetic joint as recited in claim 1, in which said means
for engaging and retaining said ball shaped member in said bearing
insert includes means for retaining said bearing insert in said
head.
3. A prosthetic joint, as recited in claim 2, in which said means
for retaining said bearing insert in said head includes a tab, said
head having a recess for receiving said tab.
4. A prosthetic joint, as recited in claim 1 in which said means
for attaching said ball shaped member to the shaft includes a neck
portion having a cross-section smaller than the diameter of said
ball shaped member, said neck portion being connected at one of its
ends to said ball shaped member for engagement with said bearing
insert for pivoting said head in said socket member of the
biological joint when said neck portion engages said engagement
means.
5. A prosthetic joint, as recited in claim 4, in which said
engagement means includes a tapered surface on said bearing
insert.
6. A prosthetic joint, as recited in claim 4, in which said head,
said stem, said ball shaped member and said neck portion are of
metal and said bearing insert is of plastic.
7. A prosthetic joint, as recited in claim 6, in which said metal
is cobalt chrome molybdenum and said bearing insert is of an
ultra-high molecular weight plastic.
8. A prosthetic joint, as recited in claim 7, in which said means
for attaching said stem to said second of the two anatomical
members includes a shaft for intramedullary attachment to said
second of the two anatomical members.
9. A prosthetic joint, as recited in claim 1, in which said head
has a plurality of axially extending bearing insert ridges and said
bearing insert is engaged by said ridges for preventing said
bearing insert from rotating in said head.
10. A prosthetic joint, as recited in claim 9, in which said head
and said bearing insert include cooperating cylindrical and
spherical shaped surfaces and said ridges on said head are on the
cylindrical surface of said head and in engagement with the
cylindrical surface on said bearing insert.
11. A prosthetic joint, as recited in claim 1, in which the
diameter of said ball shaped member is not more than 65% of the
diameter of said head.
Description
This invention relates to femoral hip prosthesis and, particularly,
to a femural head and neck prosthesis for interaction with the bone
structure of the pelvic acetabulum.
The human body joint most commonly affected by disease or injury
and where loss of function causes the severest handicap and can
cause severe pain and discomfort is the hip joint. The pelvis in
the human body contains two hip bones, one at each side of the body
and each containing an acetabulum. The acetabulum or hip socket
receives and forms a seat for the femoral head, or ball, of the
femur or thigh bone.
The angle of the opening of the acetabulum in each of the hips is
angularly disposed relative to the axis of the body and the axis of
the shaft of the femur or thigh bone. Because of this angular
disposition, the femur or thigh bone is connected to the femoral
head by a femoral neck angularly disposed relative to the shaft of
the femur. The femur, femoral neck and femoral head are formed, in
the human body, as one integral bone structure.
The weight of the human body, supported by the pelvis, is
transmitted through the hip, acetabulum and femoral head, to the
femur through the angular disposed femoral neck. Such support is
comparable to what is commonly structurally referred to as an
overhang. The femoral neck forms a lever arm in the overhang
between the femoral head and the shaft of the femur. It is in the
area of the femoral head and femoral neck of the biological joint
where damages by injury to or disease in the hip most often occur.
The instant invention is directed to a femural head and neck
prosthesis for surgical correction of such damage to the biological
joint.
Various attempts have, heretofore, been made to develop
replacements for the femoral head and femoral neck where such bone
portions of the body become damaged through disease or through
injury. In some such replacement devices, movement of the hip and
leg after surgical correction and implant substitution for the
diseased or injured bone structure has been limited. In other
instances, even with limited movement, irritation and degeneration
of the natural bone tissue of the acetabulum has occurred after a
period of time. Such bone tissue damage often requires subsequent
replacement of the acetabulum, itself, and a second replacement of
the femoral head and neck structure. In still other devices
heretofore employed, even though disease or injury was limited to
the femoral head and neck bone structure, replacement of the
otherwise healthy and undamaged acetabulum with a metal or plastic
cup has been required. Such replacement of the otherwise healthy
acetabulum, along with the injured or diseased femoral head and
neck, required more extensive surgery.
In the instant invention it has been discovered that the lever
configuration of the femoral head and neck can be replaced by
surgical implant and that normal movement of the hip and leg can be
preserved. Furthermore, with the arrangement of the present
invention, motion between the prosthetic head and natural
acetabulum which usually results in irritation and damage to the
natural bone tissues of the acetabulum, is avoided. If, because of
subsequent disease or injury, damage to the acetabulum should
occur, the acetabulum can be replaced by further surgery and by the
implant of a metal or plastic socket without the complete removal
of the earlier implanted femoral head and neck of the instant
invention. This means, should subsequent surgery be required
because of later occurring disease or injury, such surgery is much
simpler, reducing operating time and patient risk.
The invention will be more fully described and better understood
from the following description and appended drawings of the
preferred embodiment of the invention in which:
FIG. 1 is a view, in full and phantom line and taken from the
front, showing in full line the normal and healthy bone structure
of a human leg, including a portion of the pelvis, the hip,
acetabulum, femoral head, femoral neck, femoral shaft, knee joint,
tibia and fibula with the outline of the leg shown in phantom
line;
FIG. 2 is an enlarged view, partly in section, of the hip,
acetabulum, femoral head, femoral neck and upper end of the femoral
shaft of FIG. 1;
FIG. 3 is a view, partly in section, of the head, bearig insert and
intramedullary stem of the assembly of the instant invention;
FIG. 4 is an end view taken at 4--4 in FIG. 3, showing the bearing
insert of FIG. 3 with stem removed and the head partially shown;
and
FIG. 5 is a sectional view taken at 5--5 in FIG. 4.
Referring to FIGS. 1 and 2, the structures of the hip, generally
designated 2, includes the pelvis 4, containing the acetabulum or
socket 6. The axis of the acetabulum opening or opening of socket 6
is angular to the vertical axis of the leg and of the body when
standing in an upright position. Femoral head 8 of femur 10 is
seated in acetabulum 6 and is smooth and rounded to fit into the
smooth and rounded cup of acetabulum 6. In the normal, healthy
body, femoral head 8 and acetabulum 6 form a ball and socket joint
allowing the leg to be pivoted forwardly, backwardly and sidewise
in a cone relative to the body and leg axis.
Femur shaft 10 is joined to femoral head 8 by femoral neck 12, the
femur shaft 10, femoral neck 12 and femoral head 8 being a single,
continuous bone structure in the normal, healthy human body. The
center of femur shaft 10 is hollow and, in the healthy body,
contains marrow, surrounded by spongy bone tissue, encased in a
solid outer shell of harder, more solid and rigid bone material. At
its lower end, femur shaft 10 is connected by knee joint 14 to
tibia 16 and fibular 18 of lower leg 20.
As can be seen from FIGS. 1 and 2, when considered with the
angularity of the opening of acetabulum 6, the angularity of
femoral neck 12 and the angularity of femur shat 10, all with
respect to the vertical and weight axis of the body, the bone
structure of femoral neck 12 and the area of acetabulum socket 6
vertically above femoral head 8 are subjected to substantial forces
and stresses, as compared to other areas of the bone structure. A
substantial portion of the body weight supported by pelvis 4 is
transmitted to and supported by the leg through the vertically
opposing bone surfaces of acetabulum 6 and femoral head 8. This
weight is transmitted through angularly disposed femoral neck 12 to
femur shaft 10. In a disease which affects the bone in the hip
structure or in an injury in the area of such structure, failure
commonly occurs in the bone in femoral neck 12 and femoral head 8.
It is to disease or injury in this area to which the device of the
instant invention particularly relates.
Referring to FIGS. 3, 4 and 5, showing the preferred embodiment of
the invention, the intramedullary assembly of the instant invention
includes a head, generally designated 22, a bearing insert,
generally designated 24, and an intramedullary stem, generally
designated 26.
Head 22 has a smooth, spherical outer surface 30, a cylindrical
inner surface 32 and a spherical dome 34. At its circumference,
spherical dome 34 merges with the inner end of cylindrical inner
surface 32. At its outer end, cylindrical inner surface 32
terminates at one end of tapered surface 36 which, at its other
end, terminates with the end of spherical outer surface 30.
Adjacent to its outer end and spaced inwardly from tapered surface
36, cylindrical inner surface 32 has an annulus 38 forming a recess
in surface 32 and extending circumferentially around the wall of
inner surface 32. For purposes more apparent hereinafter,
cylindrical inner surface 32 is provided with longitudinally
extending ribs 33.
In the use of the assembly of the instant invention, as will be
described later in more detail, head 22 is inserted into the
existing cavity of the acetabulum and projects slightly outwardly
beyond the opening or mouth of such cavity. To accommodate for
variations in the sizes of acetabulum cavities, from patient to
patient, heads of different sizes, for example, 1.5-inches diameter
to 2.5-inches diameter are provided. The material of head 22 may be
of any material compatible with the bone tissue of the acetabulum
and with the human body and of sufficient strength to accommodate
the forces to be applied. A metal material has been found to be
preferred and cobalt chrome molybdenum alloy ASTM F-75 and
stainless steel ASTM F-139-71 have been found to be especially
suited to this purpose.
Bearing insert 24 is made from a low-friction material of
sufficient strength and rigidity to accommodate the forces to be
applied. Ultra-high molecular weight polyethylene has been found to
be suitable. The outer surface of bearing insert 24 includes a
spherical dome 40 and a cylindrical surface 42. The end of dome 40
merges with one end of cylindrical surface 42 and, as best shown in
FIG. 3, when assembled, the outer spherical dome 40 and cylindrical
surface 42 of bearing insert 24 mate with spherical dome 34 and
cylindrical inner surface 32 of head 22. To allow for the
difference between the coefficients of expansion of the plastic and
the metal and the greater expansion of the plastic when the
assembly is implanted, the diameter of surface 42 is slightly
smaller than the inner diameter of cylindrical inner surface 32.
Ribs 33 on inner surface 32 engage and project into surface 42 as
bearing insert 24 is inserted into head 22. The inner surface of
bearing insert 24 is spherical at 44 to engage and grip the ball
end of intramedullary stem 26, as later described. Inner spherical
surface 44 merges with one end of tapered surface 46 which, at its
other end, joins one end of wall 48 extending across the end of
bearing insert 24.
The open end of bearing insert 24, for purposes more apparent
hereinafter, is slotted at 50, 52, 54, 56, 58, FIG. 4, the outer
cylindrical surface 42, between slots 56, 58, having an outwardly
extending tab 60 which, the unit is assembled, seats in annulus 38
in head 22. Annulus 62 extends circumferentially around outer wall
42 of bearing insert 24.
Intramedullary stem 26, which is made, preferably, of metal, such
as cobalt chrome molybdenum ASTM F-75 or stainless steel ASTM
F-139-71 or other material of suitable strength and compatibility,
has a ball end 70 having a smooth surface and of a size to fit and
mate with spherical surface 44 of bearing insert 24. Ball end 70 is
joined to stem 72 by a reduced neck portion 74 and a tapered base
76. Neck 74 and base 76 are circular in cross section and,
preferably, are of one piece with ball end 70 integral with stem 72
or formed separately and attached to stem 72 so as to be rigidly
interconnected. In order to provide the desired torque arm
differential between the surface of ball end 70 and the outer
surface of head 22, the diameter of ball end 70 is 65percent or
less of the diameter of head 22.
The intramedullary assembly of the instant invention can be
assembled before stem 72 is surgically implanted in the cavity of
femur 10 or after stem 72 has been implanted and attached to femur
10 following accepted surgical procedures. In such assembly,
bearing insert 24 is placed over ball end 70 of intramedullary stem
26 and ball end 70 is snapped into place to mate with smooth
spherical surface 44 of bearing insert 24. The sub-assembly of
bearing insert 24 and intramedullary stem 26 is then inserted into
head 22. After this has been done, head 22 is inserted into the
acetabulum. The placement of the device of the instant invention in
replacement of the damaged femoral head and neck is then complete
and the balance of the surgical procedure required by the surgery
can be carried out.
When bearing insert 24 is placed over ball end 70 and the ball end
is pushed into the insert, tapered surface 46 on bearing insert 24
is engaged by the spherical surface of ball end 70 and the skirt of
insert 24, between slots 50, 52, 54, 56, 58 and between annulus 62
and the open end of bearing insert 24 are flexed outwardly,
allowing the ball end to be pushed into bearing insert 24 until the
smooth surface of ball end 70 engages the smooth spherical surface
44 of the insert. With bearing insert 24 on ball end 70, head 22 is
placed over bearing insert 24 and is pushed over the insert so that
ribs 33 on the inner cylindrical surface 32 of head 22 bite into
the plastic surface of bearing insert 24. As the insert is pushed
into head 22, tab 60 on outer surface 42 of insert 24 between slots
56, 58 is forced inwardly and when head 22 is in place, snaps
outwardly into annulus 38 in head 22, so that, when assembled,
bearing insert 24 and the inner surface 32 of head 22 will be in
intimate contact, without any play between the two members. Inner
surface 32 of head 22 is provided with axially extending ridges
which engage with and project into outer surface 42 of bearing
insert 24 forming, between the two members, a tight fit without any
play or clearance therebetween.
As can be best seen from FIGS. 1, 2 and 3, when in place in
acetabulum 6, the open of head 22 extends outwardly in the
acetabulum beyond hip bone 4. Neck 74 of intramedullary stem 26 is
smaller than ball 70 and allows for considerable pivotal movement
of stem 26 relative to head 22 without contact between stem 26 and
the sub-assembly of head 22 and bearing insert 24. Should excessive
pivoted movement occur by the individual having an implanted hip
joint of the instant invention moving the leg to an extreme
position of normal range, neck 74 will contact tapered surface 46
on bearing insert 24 and bearing 24 and head 22 will be pivoted in
acetabulum 6 to accommodate such movement, all without contact
with, interference by or damage to the rim of the acetabulum.
In the normal activities of an individual in which the
intramedullary device of the instant invention is implanted,
movement of head 22 relative to acetabulum 6 does not occur.
Sufficient movement for normal body activities is provided in the
instant invention by the universal mounting of ball 70 in bearing
insert 24. Thus, unlike some devices utilized heretofore for hip
implant where movement has been limited to a single plane, in the
instant device movement is permitted in the same manner as in
activities with a normal, healthy hip joint.
The universal bearing, in the instant invention, between the
surface of ball end 70 and spherical surface 44 of bearing insert
24 may be located eccentric with respect to surface 30 of head 22.
This eccentric placement of the bearing during normal body
activities generates forces on the head tending to orientate head
22 within pelvis 2 such that the eccentric displacement will be in
alignment with the direction of force across the hip joint.
Ball end 70 of intramedullary stem 26, when femur 10 is moved, such
as in walking, pivots in spherical surface 44 of bearing insert 24.
Because of the low friction characteristics of the material of
bearing insert 24 and the relatively short moment arm of such
surface, as compared to surface 30 of head 22, head 22 in
acetabulum remains stationary. Thus, wear, irritation and damage to
the bone tissue of the acetabulum may be avoided.
Except for damage by subsequent injury or disease, once the device
of the instant invention is surgically implanted, further surgery
should not be necessary. However, should, because of subsequent
injury or disease, replacement of the acetabulum become necessary
in a patient in which the device of the instant invention is
implanted, such replacement can be accomplished without the removal
of intramedullary stem 26 from femur 10. This can be accomplished
by removing head 22 and bearing insert 24 from stem 26 during such
subsequent surgery and by replacing such insert 24 and head 22 with
a bearing insert and head of a size to accommodate the socket
implanted in replacement of the damaged or diseased acetabulum, or
by fitting the ball end of the femoral stem of the instant
invention directly into the replacement acetabulum. This is of
substantial importance because it simplifies subsequent operations
by eliminating the need for removal of the intramedullary stem
implanted in the femur substantially reducing the time for surgery
which substantially reduces patient risk and cost of surgery.
While especially suited for use in implant hip surgery and shown
and described in connection therewith, the intramedullary assembly
of the instant invention may also be used for surgical replacement
and implant in other joints, for example, in the shoulder. For such
use, of course, changes in sizes and shapes, especially in the stem
to be implanted in the bone would be required.
The terms and expressions which have been employed are used as
terms of description and not of limitation, and there is no
intention, in the use of such terms and expressions, of excluding
any equivalents of the features shown and described or portions
thereof, but it is recognized that various modifications are
possible within the scope of the invention claimed.
* * * * *