U.S. patent application number 12/252610 was filed with the patent office on 2009-02-05 for radial head replacement system.
Invention is credited to Scott P. Steinmann.
Application Number | 20090036991 12/252610 |
Document ID | / |
Family ID | 32825360 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090036991 |
Kind Code |
A1 |
Steinmann; Scott P. |
February 5, 2009 |
Radial Head Replacement System
Abstract
A radial head replacement system includes a radial head
replacement, an apparatus for guiding the resection of a radial
head, and a kit including bone plug and bone plug insertion
instrument. The radial head replacement has a separate adjustable
head portion that may be secured on an implanted stem such that the
implanted radial head replacement smoothly interfaces with the
capitellum of the humerus. In another form, the radial head
replacement uses crossed bone screws that serve to more securely
anchor the stem of the radial head replacement in the
intramedullary canal of the radius. The resection guide includes a
movable cutting guide which ensures a precise resection of the
radial head and thereby allows for better positioning of the
implanted radial head replacement. The bone plug limits the travel
of bone cement beyond the area of affixation of the stem portion of
a radial head replacement to the radius.
Inventors: |
Steinmann; Scott P.;
(Rochester, MN) |
Correspondence
Address: |
QUARLES & BRADY LLP
411 E. WISCONSIN AVENUE, SUITE 2040
MILWAUKEE
WI
53202-4497
US
|
Family ID: |
32825360 |
Appl. No.: |
12/252610 |
Filed: |
October 16, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10767642 |
Jan 29, 2004 |
7452381 |
|
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12252610 |
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60443697 |
Jan 30, 2003 |
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Current U.S.
Class: |
623/20.11 ;
623/23.42 |
Current CPC
Class: |
A61B 17/15 20130101;
A61F 2002/4662 20130101; A61F 2/4614 20130101; A61F 2002/3827
20130101; A61F 2/3804 20130101 |
Class at
Publication: |
623/20.11 ;
623/23.42 |
International
Class: |
A61F 2/38 20060101
A61F002/38; A61F 2/30 20060101 A61F002/30 |
Claims
1. A prosthesis for replacing an end portion of a bone, the
prosthesis comprising: a head, a stem extending away from the head,
a first screw, and a second screw, wherein the stem is dimensioned
to be received in the intramedullary canal of the bone, the
prosthesis includes a first channel extending diagonally from a
first side of the head to an opposite second side of the stem, the
prosthesis includes a second channel extending diagonally from a
second side of the head to an opposite first side of the stem, the
first screw is associated with and arranged in the first channel
and the second screw is associated with and arranged in the second
channel such that the prosthesis can be secured to the bone by
driving the first screw arranged in the first channel into the bone
and driving the second screw arranged in the second channel into
the bone.
2. The prosthesis of claim 1 wherein: the first screw has a length
greater than the first channel, and the second screw has a length
greater than the second channel.
3. The prosthesis of claim 1 wherein: the prosthesis replaces a
radial head.
4. The prosthesis of claim 3 wherein: the head of the prosthesis is
elliptical, and the outer wall of the head of the prosthesis
includes a concave surface dimensioned to interface with the
capitellum of the humerus and a periphery surface dimensioned to
interface with the radial notch of the ulna when the prosthesis is
secured to the bone.
5. The prosthesis of claim 4 wherein: the concave surface is
surrounded by a rim.
6. The prosthesis of claim 1 wherein: the head and stem are
integral.
7. The prosthesis of claim 1 wherein: the first channel has
internal threads.
8. The prosthesis of claim 7 wherein: the second channel has
internal threads.
9. The prosthesis of claim 1 wherein: the first channel is not
threaded, and the first screw is self-tapping.
10. The prosthesis of claim 9 wherein: the second channel is not
threaded, and the second screw is self-tapping.
11. A kit for replacing a radial head, the kit comprising: a radial
head replacement including a head and a stem extending away from
the head, the stem being dimensioned to be received in the
intramedullary canal of the radius, the radial head replacement
including a first channel extending diagonally from a first side of
the head to an opposite second side of the stem, the radial head
replacement including a second channel extending diagonally from a
second side of the head to an opposite first side of the stem.
12. The kit of claim 11 further comprising: a first screw
dimensioned to be arranged in the first channel such that the
radial head replacement can be secured to the radius by driving the
first screw arranged in the first channel into the radius, and a
second screw dimensioned to be arranged in the second channel such
that the radial head replacement can be secured to the radius by
driving the second screw arranged in the second channel into the
radius.
13. The kit of claim 12 wherein: the radial head replacement is
provided with the first screw partially inserted in the first
channel and with the second screw partially inserted in the second
channel.
14. The kit of claim 1 wherein: the head of the radial head
replacement is elliptical, and the outer wall of the head of the
radial head replacement includes a concave surface dimensioned to
interface with the capitellum of the humerus and a periphery
surface dimensioned to interface with the radial notch of the ulna
when the radial head replacement is secured to the radius.
15. The kit of claim 14 wherein: the concave surface is surrounded
by a rim.
16. The kit of claim 11 wherein: the head and stem are
integral.
17. The kit of claim 11 wherein: the first channel has internal
threads.
18. The kit of claim 17 wherein: the second channel has internal
threads.
19. The kit of claim 12 wherein: the first channel is not threaded,
and the first screw is self-tapping.
20. The kit of claim 19 wherein: the second channel is not
threaded, and the second screw is self-tapping.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/767,642 filed Jan. 29, 2004 which claims
priority from U.S. Provisional Patent Application No. 60/443,697
filed Jan. 30, 2003.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention relates to an elbow prosthesis, and more
particularly to a replacement for the radial head and to methods
and instruments for use in replacing a radial head.
[0005] 2. Description of the Related Art
[0006] Fractures of the radial head constitute one of the most
common fractures of the elbow. Radial head fractures can be treated
by excision of the head of the radius. However, this can lead to
joint pain and elbow instability. As a result, prosthetic radial
head replacements have been frequently recommended to obviate the
problems associated with excision of the radial head and to improve
stability of the elbow joint. Examples of a radial head prosthesis
are shown in U.S. Patent Application Publication Nos. 2003/0212457
and 2001/0037154, and in U.S. Pat. Nos. 6,656,225, 6,361,563,
6,270,529 and 6,217,616.
[0007] Radial head replacements generally include a stem portion
designed to extend into the intramedullary canal of the radius and
a head portion designed to replace the radial head. When replacing
the radial head with a radial head replacement, the radial head is
surgically removed and the top of the radius and the intramedullary
canal of the radius are prepared for receipt of the stem. A cement
material is typically inserted into the open intramedullary canal
and the stem is driven into the canal. Often, the stem is fixed to
the radius with a curable acrylic polymer cement such as
polymethylmethacrylate. Alternatively, the stem may be fixed to the
radius using an interference fit (i.e., "press fit") without
cement. In another alternative, the radial head replacement may be
fixed to the radius using bone screws.
[0008] While existing radial head replacements provide satisfactory
results for most purposes, they do have drawbacks. For example, it
may be difficult to position known radial head replacements such
that the end surface of the head portion of the implanted radial
head replacement smoothly interfaces with the capitellum of the
humerus. In extreme cases, the implanted radial head replacement
may even dislocate such that intefacial contact with the capitellum
is precluded.
[0009] One source of this positioning problem is the lack of
adjustability of known radial head replacements. Existing radial
head replacements are typically unitary in design and therefore, do
not allow for relative movement between the stem portion and the
head portion. Thus, the position of the head portion cannot be
adjusted in relation to the stem portion after the stem portion is
inserted in the intramedullary canal of the radius.
[0010] Another source of this positioning problem is the inaccuracy
of some osteotomy cuts of the natural radial head. Generally, the
osteotomy cut of the natural radial head must be made so that the
angle of the cut corresponds to the angle between the stem and head
portions of the radial head replacement. Inaccurate resection can
result in an ill-fitting radial head replacement which may lead to
the dislocation risks noted above. Various resection guides have
been proposed in the orthopedic field. See, for example, U.S. Pat.
Nos. 5,779,709, 5,704,941, 5,601,565, 5,108,396, 4,927,422,
4,736,737, 4,718,414, and 4,686,978 and U.S. Patent Application
Publication Nos. 2003/0158558 and 2003/0114859.
[0011] Another problem with radial head replacement procedures may
develop from the employment of a bone cement for fixation of the
stem to the radius. This problem is primarily related to limitation
of the cement to the area of the stem within the intramedullary
canal of the radius. Specifically, the cement may travel beyond the
area of affixation in the radius. Proper fixation of the stem to
the radius may not be achieved without taking steps to limit the
travel of the cement. U.S. Pat. No. 4,302,855 has proposed one
solution to this problem.
[0012] Yet another problem with radial head replacement procedures
may develop from the use of bone screws for fixation of the radial
head replacement to the radius. For example, bone screws may not
provide for optimum fixation of the radial head replacement to the
radius.
[0013] Thus, there is a need for an improved radial head
replacement that provides for better contact with the capitellum of
the humerus. In particular, there is a need for a radial head
replacement that can be adjusted so that the head portion of the
implanted radial head replacement smoothly interfaces with the
capitellum of the humerus. There is also a need for a radial head
replacement that provides for improved fixation of the radial head
replacement to the radius. There is also a particular need for a
radial cutting guide which ensures a precise resection of the
radial head and thereby allows for better positioning of the
implanted radial head replacement. There is also a need for a means
for limiting the travel of bone cement beyond the area of
affixation of the stem portion of a radial head replacement to the
radius.
SUMMARY OF THE INVENTION
[0014] The foregoing needs are met by a radial head replacement
system according to the invention. The radial head replacement
system may include a prosthesis for replacing the radial head, an
apparatus for guiding the resection of the radial head, and a kit
for plugging an open end of the intramedullary canal of the radius
to restrict the flow of a cement used to fix the prosthesis
stem.
[0015] In one aspect, the invention provides a modular prosthesis
for replacing a radial head. The modular prosthesis has a stem
dimensioned to be received in the intramedullary canal of the
radius, and a head having an outer wall defining an interior space
dimensioned such that the head can be placed over an end portion of
the stem. The outer wall of the head is dimensioned such that the
head can be moved: (i) in an axial direction in relation to an axis
of the stem, and/or (ii) in a first transverse direction in
relation to the axis of the stem, and/or (ii) in a second
transverse direction at an angle to the first transverse direction
when the head is placed over the end portion of the stem.
[0016] The modular prosthesis includes at least one opening in the
outer wall of the head and a screw dimensioned to be arranged in
each opening. Each screw is suitable for contacting the end portion
of the stem when arranged in its associated opening to secure the
head to the stem by constraining movement of the head in the axial
direction and/or in the transverse directions.
[0017] The separate head, stem, and screw(s) of the modular
prosthesis provide a radial head replacement system wherein the
head portion of the implanted radial head replacement can be
positioned in any number of spatial relationships relative to the
stem and thereafter secured to the stem such that the head smoothly
interfaces with the capitellum of the humerus and the radial notch
of the ulna. The head may be adjustable in three planes:
lateral-medial (a transverse direction in relation to the axis of
the stem), posterior-anterior (another transverse direction in
relation to the axis of the stem), and proximal-distal (an axial
direction in relation to the axis of the stem) before being secured
to the stem. As a result, the risk that the implanted radial head
replacement may dislocate is minimized. Thus, the modular
prosthesis overcomes the difficulties in getting the radial head
replacement to track over the capitellum of the humerus.
[0018] In another aspect, the invention provides a prosthesis
having a head, a stem extending away from the head, and at least
two screws. The stem is dimensioned to be received in the
intramedullary canal of the radius. The prosthesis includes a first
channel extending diagonally from a first side of the head to an
opposite second side of the stem. The prosthesis also includes a
second channel extending diagonally from a second side of the head
to an opposite first side of the stem. A screw is associated with
and arranged in each channel such that the prosthesis can be
secured to the bone by driving each screw arranged in each channel
into the radius. The crossed bone screws serve to more securely
anchor the stem of the radial head replacement in the
intramedullary canal of the radius without the need for cement.
[0019] In yet another aspect, the invention provides an apparatus
for guiding the resection of the radial head. The apparatus
includes an intramedullary alignment shaft dimensioned to be
received in the intramedullary canal of the radius, and a movable
cuffing guide suitable for placing on the shaft. The cutting guide
has a base for placing on the shaft and a wall extending laterally
away from the base in a direction of the shaft axis. The wall
terminates in an outermost cutting guide edge for guiding the
resection of the end of the bone. The surgeon may move the cutting
guide to a desired location over the radius and then the radius is
resected accurately using a conventional surgical saw guided by the
outermost cutting guide edge. As a result, the osteotomy cut of the
natural radial head is made at an angle that corresponds to the
angle between the stem and head portions of the radial head
replacement. Thus, inaccurate resection and the associated
dislocation risks noted above are avoided. In another form, the end
portion of the alignment shaft includes a cutting guide mounting
section that is transversely offset from the alignment shaft to
allow the alignment shaft to be placed along the outside of the
radius. In either form of the alignment shaft, the alignment shaft
may be connected to a concave bearing surface dimensioned to
conform to the shape of the capitellum. This also improves the
accuracy of the osteotomy cut.
[0020] In still another aspect, the invention provides a kit for
plugging an open end of the intramedullary canal of the radius to
restrict the flow of a cement used to fix the prosthesis stem
inserted into the canal. The kit includes a plug of medical grade
material and an insertion instrument. The plug is dimensioned to
seal the intramedullary canal at a location below an end of the
prosthesis stem and prevent flow of cement beyond the location. The
insertion instrument is used for placing the plug in the
intramedullary canal. The insertion instrument is dimensioned to be
received in the intramedullary canal of the bone, and the insertion
instrument has a lateral crosspiece to facilitate placement of the
plug at a predetermined depth in the intramedullary canal.
[0021] Therefore, it is an advantage of the present invention to
provide a radial head replacement with an adjustable head portion
such that the head portion can be positioned to smoothly interface
with the capitellum of the humerus.
[0022] It is another advantage of the present invention to provide
a radial head replacement that provides for improved fixation of
the radial head replacement to the radius by way of diagonally
aligned bone screws.
[0023] It is still another advantage of the present invention to
provide an apparatus with a cutting guide system that ensures a
precise resection of the radial head and thereby allows for better
positioning of an implanted radial head replacement.
[0024] It is yet another advantage of the present invention to
provide a means for limiting the travel of bone cement beyond the
area of affixation of the stem portion of a radial head replacement
to the radius.
[0025] These and other features, aspects, and advantages of the
present invention will become better understood upon consideration
of the following detailed description, drawings, and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a fragmentary view showing the three bones of the
human elbow.
[0027] FIG. 2 is a view similar to FIG. 1 where the head of the
radius has fractured and been removed.
[0028] FIG. 3 is a perspective view of the radial head replacement
described in U.S. Pat. No. 6,217,616.
[0029] FIG. 4 is a fragmentary view of an elbow, similar to FIG. 2,
showing the excised radius having been replaced with the radial
head replacement shown in FIG. 3, with spacing provided for clarity
of explanation.
[0030] FIG. 5 is a perspective view of the radial head replacement
shown in FIG. 3, taken from a different angle.
[0031] FIG. 6 is a top view of the radial head replacement shown in
FIG. 3.
[0032] FIG. 7 is a left side elevation view of the radial head
replacement shown in FIG. 3.
[0033] FIG. 8 is a side exploded view of an embodiment of a radial
head replacement according to the invention.
[0034] FIG. 9 is a side view of the radial head replacement of FIG.
8 in an assembled condition.
[0035] FIG. 10 is a top view of the radial head replacement of FIG.
9.
[0036] FIG. 11 is a cross-sectional view of the radial head
replacement of FIG. 9 taken along line 11-11 of FIG. 9.
[0037] FIG. 12 is a cross-sectional view of the radial head
replacement of FIG. 10 taken along line 12-12 of FIG. 10.
[0038] FIG. 13 is a side view of another embodiment of a radial
head replacement according to the invention.
[0039] FIG. 14 is a top view of the radial head replacement of FIG.
13.
[0040] FIG. 15 is a cross sectional view of the radial head
replacement of FIG. 14 taken along line 15-15 of FIG. 14.
[0041] FIG. 16 is a cross sectional view of the radial head
replacement of FIGS. 13-15 as implanted in the intramedullary canal
of a radius.
[0042] FIG. 17 is a top view of a human elbow joint showing in
cross section an intramedullary alignment shaft of an apparatus for
guiding the resection of a radial head as implanted in the
intramedullary canal of a radius.
[0043] FIG. 17A is a top view of a human elbow joint showing in
cross section an alignment shaft of another embodiment of an
apparatus for guiding the resection of a radial head as implanted
in the intramedullary canal of a radius.
[0044] FIG. 18 is a top view of an elbow joint showing an apparatus
for guiding the resection of a radial head as assembled before
resection of a radius.
[0045] FIG. 19 is a top view of an elbow joint showing in cross
section yet another embodiment of an intramedullary alignment shaft
of an apparatus for guiding the resection of a radial head as
implanted in the intramedullary canal of a radius.
[0046] FIG. 20 is a top view of an elbow joint showing an apparatus
for guiding the resection of a radial head as assembled before
resection of a radius.
[0047] FIG. 21 is a front view of a cutting guide suitable for use
with the intramedullary alignment shaft shown FIG. 17, FIG. 17A, or
FIG. 19.
[0048] FIG. 22 is a side view of the cutting guide of FIG. 21.
[0049] FIG. 23 is a top view of the cutting guide of FIG. 21.
[0050] FIG. 24 is a view taken along line 24-24 of FIG. 18 with the
radius removed for clarity.
[0051] FIG. 25 is a view taken along line 25-25 of FIG. 20 with the
radius removed for clarity.
[0052] FIG. 26 is an exploded view of a bone plug and bone plug
insertion instrument according to the invention.
[0053] FIG. 27 is a view showing the bone plug of FIG. 26 implanted
in a radius (shown in cross-section) below the stem of a
prosthesis.
[0054] Like reference numerals will be used to refer to like or
similar parts from Figure to Figure in the following
description.
DETAILED DESCRIPTION OF THE INVENTION
[0055] The present invention is directed to a radial head
replacement system that includes a radial head replacement, an
apparatus for guiding the resection of a radial head, and a bone
plug and bone plug insertion instrument.
[0056] In order to provide background for the present invention,
portions of U.S. Pat. No. 6,217,616 are included herein. U.S. Pat.
No. 6,217,616 describes the functioning of the elbow joint and
shows an example prosthesis for replacing the end portion of the
radius. Turning to FIGS. 1-7 of the present application, there is
shown an elbow joint and the prior art prosthesis of U.S. Pat. No.
6,217,616. Illustrated in FIG. 1 is the distal end portion of the
humerus 11 along with the proximal end portions of the radius 13
and the ulna 15. The distal end portion of the humerus includes a
portion referred to as the capitellum 17 against which the radius
13 articulates, and a portion referred to as the trochlea 19
against which the ulna 15 articulates. The radius 13 is located on
the thumb side of the forearm. The ulna 15 forms a hinge joint with
the humerus 11 which allows for flexion and extension of the
forearm. The capitellum 17 is located on the lateral side of the
humerus 11 and has a convex, generally spherical shape. The ulna 15
includes a trochlear notch 21 which extends in a proximal direction
and resides on the posterior of the distal end of the humerus 11. A
head 23 of the radius 13 contacts the capitellum 17 of the humerus
11 and a radial notch 25 which is formed in the medial portion of
the ulna 15.
[0057] When it is necessary to replace the proximal head 23 of the
radius 13 for any reason, a prosthesis 27 such as that illustrated
in FIGS. 3-7 (and described in U.S. Pat. No. 6,217,616) may be used
to replace it. FIG. 2 shows an elbow joint with the head of the
radius 13 excised, and FIG. 4 shows that joint wherein the head of
the radius 13 has been replaced with the prosthesis 27. Looking at
FIGS. 4-7, the example known prosthesis 27 (further described in
U.S. Pat. No. 6,217,616) has a head 29, a collar 31 and a stem 33,
with the stem 33 of the prosthesis being proportioned to be
received with the intramedullary cavity of the radius 13. The head
portion 29 of the prosthesis has a proximal concave surface 35
which is shaped for contact with the capitellum 17. The radius of
curvature of the generally spherical concave surface 35 is matched
so as to approximate the radius of curvature of the capitellum 17.
This concave surface 35 is surrounded by a peripheral rim 37, which
lies at the proximal end of a peripheral surface 39 of the head,
which surface extends completely therearound and varies in height
as a result of the shape of the head. The head 29 has a medial
region 41 and a lateral region 43. The surface of the medial region
41 of the periphery of the head 29 articulates with the depression
in the side of the ulna 15 referred to as the radial notch 25. The
head 29 also has an undersurface 45 that is substantially
planar.
[0058] Turning now to FIGS. 8-12, there is shown an embodiment of a
radial head replacement 50 according to the invention. The modular
radial head replacement 50 includes a head 59, a stem 52 and set
screws 56a, 56b, 56c. The stem 52 has a body section 53 and an end
portion in the form of a circular plateau 54 that extends upwardly
from the top of the body section 53. The body section 53 of the
stem 52 is dimensioned to be received within the intramedullary
canal of the radius 13.
[0059] The head 59 of the radial head replacement 50 has a proximal
concave surface 61 which is shaped for contact with the capitellum
17. The radius of curvature of the concave surface 61 is matched so
as to approximate the radius of curvature of the capitellum 17.
This concave surface 61 is surrounded by a peripheral rim 63, which
lies at the proximal end of a peripheral surface 65 of the head 59.
The head 59 has a medial region 67 and a lateral region 69. The
surface of the medial region 67 of the periphery surface 65 of the
head 59 articulates with the radial notch 25 in the side of the
ulna 15. The head 59 has an outer wall 71 which forms the concave
surface 61, the peripheral rim 63, and the peripheral surface 65 of
the head 59. The outer wall 71 of the head 59 defines an interior
space 73 of the head 59 (see FIG. 12). The outer wall 71 of the
head 59 also includes openings 57a, 57b and 57c that accept the set
screws 56a, 56b, 56c, opening 57a being omitted from FIGS. 8 and 9
for clarity. The elliptical design of the head 59 of the radial
head replacement 50 better models the normal anatomy of the radial
head.
[0060] The head 59, the stem 52, and the set screws 56a, 56b, 56c
of the radial head replacement 50 are typically provided as
separate components for assembly. However, the set screws 56a, 56b,
56c may be provided in a partially inserted state in the head 59.
The head 59, the set screws 56a, 56b, 56c, and the stem 52 of the
radial head replacement 50 may formed from a biocompatible material
such as a titanium alloy (e.g., titanium-6-aluminum-4-vanadium), a
cobalt alloy, a stainless steel alloy, a tantalum alloy, a
nonresorbable ceramic such as aluminum oxide or zirconia, a
nonresorbable polymeric material such as polyethylene, or a
nonresorbable composite material such as a carbon fiber-reinforced
polymer. Forming the head 59 and the stem 52 of the radial head
replacement 50 from a polished cobalt-chromium alloy may be
particularly advantageous.
[0061] The radial head replacement 50 may be implanted in the
radius 13 as follows. First, the head of the radius 13 is resected
and the intramedullary canal of the radius 13 is inspected and
tools (such as a reamer) may be used to clean material out of the
intramedullary canal. Once the intramedullary canal in the radius
13 has been prepared, the surgeon can then "press-fit" the stem 52
(which is tapered for ease of insertion) into the intramedullary
canal of the radius 13. Optionally, the stem 52 can be cemented in
the intramedullary canal, and/or bone screws can be used to further
secure the stem 52 in the intramedullary canal of the radius
13.
[0062] Next, the head 59 of the radial head replacement 50 is
positioned over the stem 52 such that the circular plateau 54 of
the stem 52 is within the interior space 73 of the head 59 (see
FIG. 12). The head 59 of the radial head replacement 50 is then
moved into contact with the ulna 15 and the capitellum 17 such that
the concave surface 61 of the head 59 contacts the capitellum 17 of
the humerus 11 and the surface of the medial region 67 of the
periphery surface 65 of the head 59 contacts the radial notch 25 in
the side of the ulna 15. The head 59 of the radial head replacement
50 is held in this position and set screws 56a, 56b, 56c are
screwed inwardly until the set screws 56a, 56b, 56c contact the
circular plateau 54 of the stem 52 as shown in FIGS. 11 and 12
thereby locking the head 59 to the stem 52. Optionally, each screw
may be a self-tapping screw suitable for tapping into the plateau
54 of the stem 52, and each screw is inserted to a depth below a
surface of the plateau 54 of the stem 52 to secure the head 59 to
the stem 52.
[0063] The separate head 59, stem 52, and set screws 56a, 56b, 56c
of the radial head replacement 50 according to the invention
provide a radial head replacement system wherein the head portion
of the implanted radial head replacement can be positioned in any
number of spatial relationships relative to the stem and thereafter
secured to the stem such that the head 59 smoothly interfaces with
the capitellum 17 of the humerus 11 and the radial notch 25 of the
ulna 15. The head 59 is adjustable in three planes: lateral-medial
(a transverse direction in relation to the axis of the stem 52),
posterior-anterior (another transverse direction in relation to the
axis of the stem 52), and proximal-distal (an axial direction in
relation to the axis of the stem 52) before being secured to the
stem 52. As a result, the risk that the implanted radial head
replacement may dislocate is minimized. Thus, the radial head
replacement 50 overcomes the difficulties in getting the radial
head replacement to track over the capitellum 17 of the humerus 11.
Also, the separate head 59, stem 52, and set screws 56a, 56b, 56c
of the radial head replacement 50 according to the invention may be
provided in a kit of different sizes for use with the patients
having different radius sizes.
[0064] Turning now to FIGS. 13-16, there is shown another
embodiment of a radial head replacement 80 according to the
invention. The radial head replacement 80 includes a head 89, a
stem 82 and threaded bone screws 104, 106. The stem 82 is
dimensioned to be received within the intramedullary canal of the
radius 13. The head 89 of the radial head replacement 80 has a
proximal concave surface 91 which is shaped for contact with the
capitellum 17. The radius of curvature of the concave surface 91 is
matched so as to approximate the radius of curvature of the
capitellum 17. This concave surface 91 is surrounded by a
peripheral rim 93, which lies at the proximal end of a peripheral
surface 95 of the head 89. The head 89 has a medial region 97 and a
lateral region 99. The surface of the medial region 97 of the
periphery surface 95 of the head 89 articulates with the radial
notch 25 in the side of the ulna 15. The head 89 has a channel 84
with internal threads 85 and a channel 86 with internal threads 87
that accept the bone screws 104, 106 respectively. Optionally, the
threads 87 may be omitted, particularly when self-tapping screws
are used. The elliptical design of the head 89 of the radial head
replacement 80 better models the normal anatomy of the radial
head.
[0065] The integral head 59 and stem 52, and the bone screws 104,
106 of the radial head replacement 80 are typically provided as
separate components for assembly. However, the bone screws 104, 106
may be provided in a partially inserted state in the head 89. The
head 89, the bone screws 104, 106, and the stem 82 of the radial
head replacement 80 may formed from a biocompatible material such
as a titanium alloy (e.g., titanium-6-aluminum-4-vanadium), a
cobalt alloy, a stainless steel alloy, a tantalum alloy, a
nonresorbable ceramic such as aluminum oxide or zirconia, a
nonresorbable polymeric material such as polyethylene, or a
nonresorbable composite material such as a carbon fiber-reinforced
polymer.
[0066] The radial head replacement 80 may be implanted in the
radius 13 as follows. First, the head of the radius 13 is resected
and the intramedullary canal 14 of the radius 13 is inspected and
tools (such as a reamer) may be used to clean material out of the
intramedullary canal. Once the intramedullary canal in the radius
13 has been prepared, the surgeon can then insert the stem 82
(which is tapered for ease of insertion) into the intramedullary
canal 14 of the radius 13. The bone screws 104, 106 are then
screwed inwardly until the bone screws 104, 106 exit the channels
84, 86 respectively, and penetrate into the radius 13 as shown in
FIG. 16. The crossed bone screws 104, 106 serve to more securely
anchor the stem 82 of the radial head replacement 80 in the
intramedullary canal 14 of the radius 13 without the need for
cement.
[0067] Referring now to FIGS. 17-18 and 21-24, there is shown an
apparatus 110 in accordance with the invention for guiding the
resection of a radial head. Looking first at FIG. 17, there is a
view of an elbow joint showing in cross section an intramedullary
alignment shaft 112 of the apparatus 110 as implanted in the
intramedullary canal 14 of a radius 13. The intramedullary
alignment shaft 112 is cylindrical and has a concave bearing
surface 114 at one end. The concave bearing surface 114 is shaped
for contact with the capitellum 17. Preferably, the concave bearing
surface 114 is shaped to conform to the proximal concave surface 61
of the head 59 of the radial head replacement 50 or to conform to
the proximal concave surface 91 of the head 89 of the radial head
replacement 80. The intramedullary alignment shaft 112 may be
dimensioned for a snug fit in the intramedullary canal 14 of the
radius 13, or may be dimensioned for clearance between the
intramedullary alignment shaft 112 and the intramedullary canal 14
of the radius 13.
[0068] The apparatus 110 for guiding the resection of a radial head
includes a cutting guide 140 as shown in FIGS. 21-24. The cutting
guide 140 has a base comprising a vertical wall 146, and a top wall
142 that extends laterally from the vertical wall 146. The top wall
142 terminates in an outermost cutting guide edge 143. In the
embodiment shown, the cutting guide edge 143 is parallel to the
vertical wall 146. However, the cutting guide edge 143 may form an
angle in relation to the vertical wall 146 to provide for an angled
cut. The vertical wall 146 has a notch 148 in its lower portion
that forms a pair of spaced apart legs 149a, 149b.
[0069] The apparatus 110 for guiding the resection of a radial head
is used as follows. First, the head of the radius 13 is partially
resected and the intramedullary canal 14 of the radius 13 is
inspected and tools (such as a reamer) may be used to clean
material out of the intramedullary canal. Once the intramedullary
canal 14 in the radius 13 has been prepared, the surgeon can then
insert the intramedullary alignment shaft 112 into the
intramedullary canal 14 of the radius 13 into the position shown in
FIG. 17. The intramedullary alignment shaft 112 is positioned such
that the concave bearing surface 114 is in contact with the
capitellum 17.
[0070] Next, the cutting guide 140 is placed over the
intramedullary alignment shaft 112 such that the notch 148 of the
cutting guide 140 rests on the intramedullary alignment shaft 112
as shown in FIG. 24. In this arrangement, the cutting guide 140 may
be moved in directions "A" as shown in FIG. 18 along the axis of
the shaft 112. The surgeon may move the cutting guide to a desired
location over the radius 13 and then the radius is resected
accurately using a conventional surgical saw guided by the
outermost cutting guide edge 143. As a result, the osteotomy cut of
the natural radial head is made at an angle that corresponds to the
angle between the stem and head portions of the radial head
replacement. Thus, inaccurate resection and the associated
dislocation risks noted above are avoided.
[0071] Referring now to FIG. 17A, there is shown yet another
apparatus in accordance with the invention for guiding the
resection of a radial head. Looking at FIG. 17A, there is a
horizontal top view of an elbow joint showing in cross section an
alignment shaft 112a of the apparatus as positioned adjacent the
outside of a radius 13. The alignment shaft 112a is cylindrical in
cross-section and has a concave bearing surface 114a at one end.
The concave bearing surface 114a is shaped for contact with the
capitellum 17. Preferably, the concave bearing surface 114a is
shaped to conform to the proximal concave surface 61 of the head 59
of the radial head replacement 50 or to conform to the proximal
concave surface 91 of the head 89 of the radial head replacement
80.
[0072] In the alignment shaft 112a of the apparatus of FIG. 17A,
the end portion of the alignment shaft 112a includes a cutting
guide mounting section that is transversely offset from the
alignment shaft 112a to allow the concave bearing surface 114a to
contact the capitellum 17 while the alignment shaft 112a is placed
along the outside of the radius 13. In particular, the apparatus of
FIG. 17A is used as follows. First, the alignment shaft 112a is
positioned such that the concave bearing surface 114a is in contact
with the capitellum 17. The alignment shaft 112a is placed along
the outside of the radius 13. The alignment shaft 112a is
dimensioned to extend from the styloid process of the radius 13 to
the end of the radius being resected, and the alignment shaft 112a
may include a styloid marker at its end. Preferably, the cutting
guide mounting section is dimensioned to be arranged along an axis
of the intramedullary canal of the radius when in use.
[0073] Then, the cutting guide 140 is placed over the cutting guide
mounting section of the alignment shaft 112a such that the notch
148 of the cutting guide 140 rests on the alignment shaft 112a as
shown in FIG. 24. In this arrangement, the cutting guide 140 may be
moved in directions parallel along the axis of the shaft 112a. The
surgeon may move the cutting guide to a desired location over the
radius 13 and then the radius is resected accurately using a
conventional surgical saw guided by the outermost cutting guide
edge 143. As a result, the osteotomy cut of the natural radial head
is made at an angle that corresponds to the angle between the stem
and head portions of the radial head replacement. Thus, inaccurate
resection and the associated dislocation risks noted above are
avoided.
[0074] Alternative arrangements of the end portion of the alignment
shaft 112a are possible. For example, the end portion of the
alignment shaft 112a may be shaped to conform to the radial notch
25 which is formed in the medial portion of the ulna 15. Various
sizes of the end portion of the alignment shaft 112a may also be
provided.
[0075] Referring now to FIGS. 19-23 and 25, there is shown yet
another apparatus 120 in accordance with the invention for guiding
the resection of a radial head. Looking first at FIG. 19, there is
a horizontal top view of an elbow joint showing in cross section an
intramedullary alignment shaft 122 of the apparatus 120 as
implanted in the intramedullary canal 14 of a radius 13. The
intramedullary alignment shaft 122 is cylindrical and has a
circumferential groove 124 spaced from one end. In the embodiment
shown, the groove 124 is perpendicular to the axis of the shaft
122. However, the groove 124 could be angled in relation to the
axis of the shaft 122 to provide an angled cut. The intramedullary
alignment shaft 122 may be dimensioned for a snug fit in the
intramedullary canal 14 of the radius 13, or may be dimensioned for
clearance between the intramedullary alignment shaft 122 and the
intramedullary canal 14 of the radius 13. The apparatus 120 for
guiding the resection of a radial head includes the cutting guide
140 as shown in FIGS. 21-23 and described above.
[0076] The apparatus 120 for guiding the resection of a radial head
is used as follows. First, the head of the radius 13 is partially
resected and the intramedullary canal 14 of the radius 13 is
inspected and tools (such as a reamer) may be used to clean
material out of the intramedullary canal. Once the intramedullary
canal 14 in the radius 13 has been prepared, the surgeon can then
insert the intramedullary alignment shaft 122 into the
intramedullary canal 14 of the radius 13 into the position shown in
FIG. 19. The intramedullary alignment shaft 122 is positioned such
that the circumferential groove 124 is spaced from the resected end
of the radius.
[0077] Next, the cutting guide 140 is placed over the
intramedullary alignment shaft 122 such that the notch 148 and at
least part of the legs 149a, 149b of the cutting guide 140 rest in
the groove 124 of the intramedullary alignment shaft 122 as shown
in FIG. 25. In this arrangement, the cuffing guide 140 is fixed
against movement in directions "A1" as shown in FIG. 20. The radius
is then resected accurately using a conventional surgical saw
guided by the cuffing guide edge 143. As a result, the osteotomy
cut of the natural radial head is made at an angle that corresponds
to the angle between the stem and head portions of the radial head
replacement. Thus, inaccurate resection and the associated
dislocation risks noted above are avoided. It is contemplated that
the intramedullary alignment shaft 122 can also be configured to
accept the head 59 of the radial head replacement 50 described
above. In such a construction, the intramedullary alignment shaft
122 is left in the radius 13 after resection and the head 59 of the
radial head replacement 50 is secured to the intramedullary
alignment shaft 122 using set screws 56a, 56b, 56c in the manner
described above.
[0078] Various sizes of the intramedullary alignment shaft 112, the
alignment shaft 112a, the intramedullary alignment shaft 122, and
the cutting guides 140 may be provided in a kit for use with the
patients having different radius sizes and for use with different
radial head replacements. For example, the length and width of the
top wall 142 and the length and width of the vertical wall 146 of
the cutting guide 140 may be varied. Also, the length and width of
the intramedullary alignment shaft 112, the length and width of the
alignment shaft 112a, and the length and width of the
intramedullary alignment shaft 122 may be varied. In addition, the
concave bearing surface 114 size may be varied.
[0079] Turning now to FIGS. 26-27, there is shown an apparatus for
plugging an open end of an intramedullary canal of the radius to
restrict the flow of a cement used to fix a prosthesis stem
inserted into the open end of the canal. The apparatus 175 includes
a bone plug 190 formed from a medical grade material such as a
nonresorbable polymeric material (e.g., polyethylene). The plug 190
is dimensioned to seal the intramedullary canal 14 at a location
below an end of the prosthesis stem 52 and prevent the flow of
cement beyond the location. The plug 190 has a mounting hole 192 in
its upper surface.
[0080] The apparatus 175 also includes an insertion instrument 180
for placing the plug 190 in the canal 14 of the radius 13. The
lower portion of the insertion instrument 180 is dimensioned to fit
in the canal 14 of the radius 15. The insertion instrument 180 has
a handle 182 for manipulating the instrument 180, and has a lower
end 188 dimensioned to engage the mounting hole 192 when placing
the plug 190 in the canal 14. The insertion instrument 180 also has
a lateral crosspiece 186 to facilitate placement of the plug 190 at
a predetermined depth in the canal 14. The crosspiece 186 is used
to gauge the distance from the plug 190 to the top end of the
radius 13. The lateral crosspiece 186 may be movable on the shaft
184 of the insertion instrument 180. Once plug 190 is pushed into
the intramedullary canal 14, the insertion instrument is removed
from the mounting hole 192 and the canal 14, and acrylic cement is
forced into the open end of the canal 14. The plug 190 provides an
effective seal within the intramedullary canal 14 of the radius 13,
and prevents the cement from traveling beyond the desired point of
fixation.
[0081] Therefore, it can be seen that the invention provides a
total radial head replacement system. The total radial head
replacement system may include either radial head replacement 50 or
radial head replacement 80, apparatus 110 or apparatus 120 for
guiding the resection of a radial head, and the bone plug 160 and
insertion instrument 170.
[0082] While the invention has been described with reference to the
replacement of a radial head, the methods and devices of the
invention may be used to replace the end portion of other bones
such as, for example, the tibia and the femur. Thus, the invention
is not limited to radial head replacement. Therefore, one skilled
in the art will appreciate that the present invention can be
practiced by other than the described embodiments, which have been
presented for purposes of illustration and not of limitation.
Accordingly, the scope of the appended claims should not be limited
to the description of the embodiments contained herein.
* * * * *