Note: Descriptions are shown in the official language in which they were submitted.
210~0~ ~
L~: OF THE INVEN~ION
l~na tomic Wris t
B~cKGr~uND I~ND SU~ Y OF TIIE INV~NTIO~l :
.
'rh,is invention relates to prosthesis r~edical devices,
and more particulaxly it relat2s to an implantable wrist
prosthee,is which ,incorporates an improved assembly of
components for use as a repl~cement for a dysfunctional
wrlst joint.
' , OME PRIOR ~T
Several prosthesis have been con~trained as hinges and
have resulted in loosening.
~ ' European model by Mueli and an ~merican model by
Hamas produced by Zimmer are simple ball and socket joints.
The problem witll these wrist joints was reproducing the
center of rotation of the wrist which is, in fact, at the
capitate. The~e wrists would frequently go into imbalance.
There was an additional problem with a loosening ~n the
bones since the ~lamas was fixed in only a single metacarpal~
The present Beckenbaugh Mayo Clinic wrist and the
present Biomet wrist fix only a third metacarpal and are
therefore subject to loo~enlng. They also do not allow for
adjustment in the length of the prosthesis which is a
definite limitation to the surgeon and the patient.
Finally, they do not capture the instant center of the wrist
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.
i 21~2~
at the capitate but rather give the patlent an elliptical
artlculation whlcll the s~rgeon hoped would approach the
center of the wrist.
~DDITION~L P~T~NT ~RT
1~he fo]lowlng cited paten~ provide some indication of
prosthetic wrist joints which have been conce~ved. Howevert
nelther these joints nor the joint~ known in the prior art
as }lamas ~oints or the Mueli joint presently ln use, provide
the various desirable features which have been ~ncorporated
in ~pplicant's wrist prosthesis.
You~ et al 4,229,841
Weber 4,307,473
Green et al 4,352,212
Beckenbaugh et a~ 4,784,661
U. S. Patent to Weber, No. 4,307,473 and U. 5. Patent
to Green et al, No. ~,352,212 each show a cylindrical head
of the metacarpal component received within a
semi-cylindrical recess of the radial component.
The ~oum et al patent, No. 4,229,841 relate~ to a wrist
prosthesis with a proximal component af ixed to the radiu~
of the forearm. ~ distal component is affixed to the hand.
Both are connected by a joint which prevents axial rotation
between the components rel~tive to the forearm axi~ hey
provide relative movement of the axi~ for radial-ulnar hand
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movement and flexion-extension hand movement. This
prosthesis structure dlffers substantia11y from the
structure of the instant ln~ention which will be descrlbed
subsequently.
'rhe Beckenbaugh et al U. S. Patent No. 4,784,661 is the
only pertinent patent of the prior art known to the
inventor. It relates to an endo-prosthetic wrist
replacement device comprising two components which have
means for Lntramedullary implantation in the radius and a
metacarpal bone, respectively.
The radial component is provided with a distal head in
which there is a distally facing transversely extending
groove trough of generally semi-cylindrical configuration.
The metacarpal component has a proximally located ovoid ball
head of ~enerally oval shape ln cross section which is
recelved within the head of the radlus component.
It is shaped in the proxlmal-distal direction to
conform to the semi-cylindrical groove trough in a
transverse direction allowing flexion and extension and
radial and ulnar deviation as the oval metacarpal component
moves within the radial trough. The ovoid ball does not
duplicate the instant center of the wrist at the capitate
and the single stem of the metacarpal component is prone to
loosen.
In the speciEication of Beckenbaugh, there is an
adequate aescription of prior art joint prosthesis patents
and this description by Beckenbaugh is hereby incorporated
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by reference into this patent application. It also includes
some indlcatlon oE a prosthetic wrlst ~oint which ha~ been
conceived, and is considered to be the most pertinent prior
art. Ilowever, none of the prior art joints provlde the
various desirable features which have been incorporated in
the wrist prosthesis.
These artiEicial wr~st jo~nts use methylmethacrylate,
an acrylic bone cement used to secure the pros~hetic stems
or spurs to tlle bone~. The metal components are fabricated
from a biologically inactlve metal, Vitallium and high
density polyethylene. ~hese materials are utilized to
minimize friction between metal and plas~ic parts and
thereby ~aximize wear life.
B~C~GROUND, CONST~UCTION ~ND SUMM~R~ OF Tll~ INVENTION
In a preferr~d embodiment of this invention, 1exion or
extension simulating the normal motion of the human wrist i~
provided by the like biconvex joint portion which is
received in a biconcave longitudinal spur portioh pro~ided
in the radius.
The unique p~eferred conf~gurations for the components
of the bearing portions of the -joint movement component
provide an accurate reproductlon of the movement required in
the activities Oe daily living. The normal human ~rist
comprises attachments and actuations of three sets of bone~.
The forearm, comprlsing the radlus and ulnar is one set, the
carpal~ as a second set, and the metacarpal bones comprise
. . . . ... . ~ .
the thlrd set. The carpals are the bones most closely
associated with the motion of the wrist.
~ s aforestated, ln the forearm, there are two bones,
the radius and the ulnar. In the wrist there are eight
carpals, which are divided into rows, the proximal and the
distal. The proximal row includes a navicular, a lunate, a
triguetrum and a pisiform. The distal row includes a
trapezium and a trapezoid, a capitate and a hamate. There
are five metacarpals consecutlvely arranged from the thumb
through the last or little finger.
Wrist movement is divided between the radlocarpal and
mid-carpal joints of the wrist, in a relatively complex
ma~ner. The configuratlon o~ each row of bones changes
according to the position o~ the hand. ~lthough both joints
contribute to all hand motions, palmar flexion is
predominately a mid carpal motion. In dorsiflexion, it i5
radiocarpal.
Ulnar deviatlon also occurs at the radlocarpal joint,
while radial deviation takes place at the mid-carpal radial
level. In the anatomic wrist, the motion is simplified
allowing prosthetic 3S degrees dorsiflexion and 35 degrees
palmar flexion at the radiocarpal component junctiorl and 15
degrees radial and 15 degrees ulnar deviation at the
metacarpal capitate - carpal component.
Deterioration or destruction of the carpal bones, or
loss of integrity of thelr ligaments with secondary
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21 0402~
stlffness and pain affects the joint and results in wrist
disability.
The carpal bones are held together ~y ligaments.
Collateral ligaments provide lateral support of the wrist,
while palmar radiocarpal and dorsal radlo~arpal ligaments
maintain support of the carpal area. These ligaments define
a symmetrical pattern due to insextlons into the scaphoid
lunate, triquetrum and capitate bones. It is important that
the integrity of the radiocarpal and ulnar carpal bands of
ligaments as well as the dorsal and volar capsule be
maintained in carpal bone surgery and that these tissues not
be interfered with or impinged on by the implant.
Currently, there are a number of devices available for
either total or partial prosthesis of the wrist joint.
These devices use one or more of the possible types of
mechanical articulations available, which are the hin~e,
ball and socket, or anatomic spacers.
Most devices use intramedullary stems and methyl
methacrylate bone cement to secure the prosthesis t the
bone. Presently available prosthesis have components
constructed from several types o~ biologically inactive
metals and they are de~igned to articulate with other
components constructed from a pla~tic such a~ high density
polyethylene.
Several methods or techniques are used to insure that
the components remain articulated, and these methods include
the use of soft tissue existent at the time of implantation,
: ~
``' 2104~29
,
the use of pins or scre~s to hold the articulate surface
together and the use of band type locks. certain types of
available prosthesi~ are quite simple while other types
comprise complex mechanical systems, wlth both types having
attendant or inhe~ent disadvantages.
The principal disadvantage oE the simple pro~thesis is
that they may not reproduce an adequate, stable range of
motion of the joint and frequently distort lt, while the
prlncipal disadvalltage of the complex prosthesis is the
potential dlfficulty of surgery and increased failure.
Fin~lly, existing prosthesis do not center the anatomic axis
properly as no other includes the dlstal ulnar as part of
the comp~nent.
Severely arthritLc wrists are presently still
preferentially treated by wrist fusion. ~his procedure
leaves the patient unable to place the hand where he needs
to place it for the activities of dally living wherein 70
degrees of flexion and extension are routinely used.
SoM~ PRINCIPAL OBJECTS ~ND ~DV~NTAGES O~ INVENTION
~ his anatomic wrist lnvention relates to a mechanlcal
device for surgical replacement of certain bones and joints,
in a diseased or otherwise damaged human wrist. More
particularly, it relates to a total wrist prosthesis
providing maximum correspondence of the proviaed motion with
that of the human wrist.
~ -. - :- - - .: : ,
i 21~02~
Total wr.i~t arthroplasty lnvolves prosthetlc
replacement of the wrist by an artlficlal joint designed to
simulate normal wrlst motlon. Prosthetic replacement of the
wrist requires careful consideration of both anatomlc and
mechanical facto~s, together wlth appllcatlo~ of the skilled
surgical techn1ques of implant flxation an~ recogn~tion of
soft tisiue balancé acxoss the wrist.
The surgically imp]antable wrist prosthesis of the
present invention incOrpGrateS an lmpxoved assembly of
components wi1lch is particularly well adapted and intended
for use in replacetnent of the dysfunctional wrist joint.
There are three components to this implantable
prosthesis.
The me~acarpal component comprises a capitate
replacement from which two spurs insert into the medullary
canal of the adjacent, stable, second and third metacarpal
bones. ~ radial component lnserts into the adjacent radius.
The carpal component comes in three adjustable
thicknesses to attach to the capitate as a ball and socket
"pop ball" joint where it is allowed to move in a radial
ulnar deviation plane and articulate with the radial
component as a biconvex articulation with the biconcave
xadial component where lt is allowed to Plex and extend.
There is an addltional and optlonal ulnar component
which allows articulation rom the radlal component to the
distal ulna. Thls is comprised of an ulnar cap whlch
captures an ulnax head ball. It then receives an ulnar stem
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21~402~
which is in turn, inserted lnto the patient's distal ulna by
a flex lock peg. ~ree movement of the ulnar ball wlthin the
ulnar cap, and free motion of the ulnar stem within the ball
allows full and stable pronation and supination.
~ he kinematics of the wrist are very complex in the
motions thereof. In the pàst the wrist motlohs could not be
simply reproduced and incorporated in the design of a joint
prosthesis. sa~ed on experience of previous wrist
arthroplastesis and anatomic and ~lnetic principles found in
the llterature, a successful comp~omise i5 achieved in the
present invention.
'rhe studies which have been directed to normal wri.sts
of healthy individuals have led to the flnding that the
center of rotation of the wrist is located within the head
of the capitate. In tlle case o radial-ulnar deviation, the
center of rotation has been found to lie toward the ulnar
side of the axis of the third metacarpal and the axis of the
distal radius.
The center oE flexion-extension motion of the wrist was
known to be offset toward the palm or volar from the axis of
the third metacarpal of the additional radius also located
in the head of the capitate. Pronation and supination are
rotational movements of the arm about the longitudinal axls
of the distal ulna. The wrist does not rotate significantly
in relation to the radlus, hence the wrist has been
describea as a biaxial joint with two degrees of freedom.
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i -' 210~02~
The index fing~r or second metacarpal is s-table in its
attachment with the capitate and lesser multi~angular
(trapeæoid), function with very little motion occurring
between these bones during all natural positions of
flexion-extension motion or radial-ulnar deviation. : :
Also, the head of the capitate contains the rotation of
~oth of the aforementioned motions. The capitate-third
metacarpal fixed unit is likewise stable, therefore the
logical position choice for the metacarpal component of the ;~
wrist prosthesis is fixation between these stable index and
long fingers ~second and third) metacarpals, a single
metacarpal fixation having proven unstable and quick to
loosen.
The anatomic wrist captures the instant center exactly
with the capitate metacarpal component. It allows radial
ulnar deviation at that point and allows flexion and
extension at the radiocarpal joint within the 70 degrees of
motion that patients historically have found necessary for
the activities of daily living.
Previous ball and socket joints which have allowed 100
to 110 degrees of motion have been known to reduce to the 70
degrees of motion over time as that seems to be the motion
that the patient uses in the activities of daily living.
Finally, the incorporation of an ulnar component to this
wrist is a first and allows stability on the ulnar side of
the joint in patients whose distal radial ulnar joint is
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` i 21~0~
destroyed by the same disease that ha~ dest~oyed the
radiocarpal joint.
~T~IER FE~U~ES ~N~ OTIIER OBJEC~S OF T~E INVENTION
It is a feature of the invention to provlde a new and
novel lmplantable wrlst joint prosthe~is design wherein the
design concerns in use, the ablllty of the surgeon to adjust
carpal height. The fixation of the prosthesis device to two
metacarp~ls parts, thereby further obviating loosening of
the fix, and by allowlng lnclusion o~ and fixatios~ to the
dlstal ulna thereby directed to the lnteraction of a
plurality of components in the prosthesis, which afford a
movement and degree of freedom similar to those of the
natural wrists.
Ohe object lles in a carpal component of varying heigllt
which allows adjustab].e tension and length at the time of
surgery.
Still another object resides in the provi~ion of an
improved wrist prosthesis design which overcomes and/or
obviates substantially all of the shortcomings or
disadvantages o~ prior implantable wrist prosthesis devices
and which wrist prosthesis represents the most anatomlc
replacement of the wrist joint to date and is a signiflcant
advance over exi~tlng implantable compottents..
~ nd still inal optimal object of the lnvention resides
in the provision o a laterally extending plurality of
components compr.tsing a ball and socket joint, which is
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` 2~:~402~
confi~ured to provide for a certain degree of and arranyed
for connection with the ulnar to provide deslred wrist
rotation.
One object of the invention resides in the provlsion of
an implantable wrist prosthesis having a unique metacarpal
attachment, anatomic in design allowing stability while
being easily insertable.
Other objects and many of the attendant advantages of
the invention will be clear to those skllled in the art
and/or made apparent when consldered in connection wi~h the
accompanying detailed description and drawings wherein-
~ he inventlon is descxlbed in detail with reference totwo somewhat different embodiments, the choice of whlch in
practlce, is determilled by the surgeon to fit the needs of
patients. ~ccordingly, the preferred embodiment thereo
which as a wrist joint prosthesis is the more complex of the
two embodiments ln that it incorporates the first ulnar
component device.
It is intended that reference to this second embodiment
as an additional smbodiment shall not limit the scope of the
invention relative to a first prosthesis embodlment, i.e.
not providing an ulnar implant device for rotational
movement of the wrist, as some patients require only the
radius bone implant. ~ence the invention is intended to be
limited only by the scope o~ the appended claims.
210~(~29
DESCP~IPTIO~ OF T1113 DR~WINGS
These and other objects and advantages of this
invention will become more obvious and apparent from the
following de-tailed specification and accompanying drawings
in which:
Fig. 1 is an illustration of a posterior-anterior view
of a skeleton of a right wrist and hand;
Fig. 2 is an illustration of a lateral view of the
skeleton of the wrist with a number of bones being omitted
for purposes of clarity;
Fig. 3 is a diagrammatic posterior-anterior view of the
skeleton of the right hand with a prosthesis according to a
first embodiment of the present invention inserted therein;
Fig. 4 is a diagrammatic view of the skeleton of a
wrist, with the illustration being as observed with the
prosthesis of the major assemblies of the present invention
inserted therein which embodiment is similar to Fig. 3
incorporating the prosthesis of Fig. 3, yet additionally
including a stem implant for the ulna, which as illustrated
has an additional ball and socket joint coupler for the
provision of a certain amount of control of wrist movement
and is further characterized in that the spurs disposed
respectively in the radius and the ulnar reside in a common
plane;
Fig. 5 is a left side elevation view of the metacarpal-
capitate component with elements of the prosthesis shown in
their assembled relationship;
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` 210~029
Fig. 6 is a bottom plan vlew o.~ the metacarpal-cap~tate
subassembly of F.ig. S of the prosthesis in carpal component;
Fig. 7 is a r.ight side elevation vlew of a trough
socket and stem port.i.on of the radial prosthesi~ which
receives and mate~ w.tth the subassembly illustrated in Figs.
and 6 with the stem portion thereoE configured for
insertion into the radius bone
Fig. 8 iS ~ frontal obllque perspective view of the
subAssembly of components of Fig. 7;
Fig. 9 is an assembled side elevation view o~ the
preferred embodiment of the prostilesis of Fig. 4:
Fig. 10 is partially sectional elevation view of ~he
subassembly of Fig. 6:
Fig. 11 is a front end elevation view of the portion of
the implant which includes the implantable stem for the
radius bone of the embodiment of Fig. 3;
Fig. 12 is a top plan view of the element o f Fig . 11;
Fig. 13 is a front end elevation view similar to ~ig.
11 but further illustrating the ball and soc~et joint for
the ulnar implant portion of Fig. 4~ -
Fig. 14 is a top plan view of the element of Fig. 13
Fig. 15 is a left side elevatlon view similar to Fig.
7 but additionally illustrating details of a flex lock peg
disposed at the terminal end oP the stem for implantation
and fixation in the ulnar bone and
Fig. 16 is a detail illustration of the ulnar stem
which is received in the bore of the captive ulnar ball.
~ . , , ,~
2 ~ 2 9
DESC~IPTI~N OF TIIE PRE~EIURE~ ~MBOVIM~N~S ~F Tl~ V~N~ION
In order to better promote an understanding of the
principals oE the invention, reference is now made to the
two preferred embodiments illu~trated in the drawings.
Specific and cons.istent language is used throughout the
description to describe the variations t the two embodiments
(as illustrated in the drawings), wherein the same or like
reference characters are used for the same purpose
throughout the var,lous Figs. of the drawings.
Speciic language relating to wrist anatomy is used to
describe the drawings.
. It is to be understood that no limitation of the scope
of th~ inventlon is intended, although alterations and
further modificati.ons of the two illustrated embodiments of
the wrist prosthesis devices may come to mind or be made.
Such further and/or structurally simpll1ed applications of
the principals o~ radius bone embodiment are herewith not
suggested. The more complex preferred radius and ulna
embodiment of the invention are contemplated to the extent
that would normally occur to one skilled in the ar-t to which
the invention relates without resorting to th~ exercise of
invention.
Referring now to Fig. 1, a showing is made ln profile
of a healthy right wrist skeleton. The hand ls supported b~
two bones, the radius lO and the ulnar 11. These bones bear
upon each othex ~t their distal extremities and th0 distal
face of the radius comprises an important artlcular su~face
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'` . `' ~ ' `. ' ' ~
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'
~ 210~029
indic~ted at 12.
~ dditionally, Flg. 1 illllstrates the bo~es in the hand
including the second metacarpal 13 and the third metacarpal
14 which are just behind the index 15 and middle fih~er 16,
respectively. Eigllt carpal bones (carpus) are shown between
the articular surface 12 of the radius and the metacarpals.
The capitate 17 is fixed, relatively, to the third
metacarpal 14. These two bones move as a unit ko define the
plane of the hand in both flexion-extension and
rad.ial-ulnar~deviat.ion.
Disposed at the hase of the ~econd metacarp~l 13 is a
ca~pal known as the trapezoid.
~ he two axls o~ wrist motion are known to pass through
an area known as a head 17~ of the capitate 17. In Fig. 1,
the radial side of the wrist is the side on which the radius
10 is located, while the ulnar side is the side in which the
ulnar 11 is located.
Fig. 2 of the drawings illustrates the dorsal side of
the wrist which is the side corresponding to the back of the
hand. while the volar or palmar side of the wrist ~s at the
side corxesponding to the side of the palm of the hand.
Referring to Figs. 3 and 4 of the drawings, the~e is
illustrated the ba~sic structural assembly of component
elements of the two embodiments of a wrist pro~thesis as
implanted in a reconstructed wrist. One wrist prosthesis
embodiment, Fig. 3, is for the radius bone 10 and an
alternative more elaborate construction, Fig. 4, which
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`` 21~29
further includes a ball and socket joint and ~tem for the
ulnar bone 11.
The illustration is made with portions thereof not
shown for purposes of clarity, which may be constru~d either
as a second embodiment of the invention or as an
intermediate component comprising a po~tion of Flg. 3
prosthetic wrist joint with the ulnar assembly not belng
shown and thereby illustrating a somewhat pictorial side
view of the hand with the prosthesis of either of two
embodiments incorporated therein.
Referring now, more partlcularly to Flgs. 3 and 4,
there is illustrated a pair of wrist prosthesis embodiments
positioned within the human wrist. Baslc procedures
employed in the implantation o either of the wrist
prosthesis configurations or embodiments oE the pre~ent
invention is well known in the art and does not differ
substantially from other procedures applicable with prior
art devices known to those skilled in the art to which this
prosthesis pertains.
Since these procedures are known to practitioners
skilled in the art, and do not form a part of the present
invention, details o the procedure are not considered
necessary to a full understanding of the descrlption o~ the
present invention and are not provided herein. As can be
noted rom Figs. 3 and 4, in locating the prosthesis in
position certain of the carpals are removed from the wrist
and the distal radius 10 and ulnar 11 are resected. This
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`- 2 ~ 2 ~
removal of the carpi and reseetioning of the distal xadius
and ulnar ls simllar to that carried out in other wrist
prosthesis operations.
By reference to Fig. 3 of the drawings, it will be
observed that the wrist prosthesis 20 includes a
metacarpal-capitate component 21 and a radial component 22.
The metacarpal-capltate component 21 has a fixation spur and
s~em combination 23 which is of a dual nature and is located
through the capitate 17 and into the medullary cavity ak 24
of the second and third metacarpals as indicated at 14. The
radlal component 22 also has a fixation spur 26 which is
located in the medullary cavity at 27 o~ the radius 10.
~ 9 shown with respect to the preferred embodiment of
Flg. 4, the metacarpal component 21 has a convex ball shaped
articulating surface 19 which extends from the base portion
of the metacarpal component. It is pivotally received
within a hemispherlcally concave ball shaped socket in the
carpal component wllicll then provides an articulating surface
for the radial component 22 when the device is inserted in
the wrist.
The detail~ of the preferred embodiment of the
metacarpal component 21 of the prosthesis 20 will be more
particularly described with respect to ~igs. 5 and 6. I'he
metacarpal component 21 lncludes dual fixation stems
indicated at 23 attached to a head portion 25 wherein the
head portion 25 deflnes a seml-spherical articulatlng
18
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:
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s~rface at ~B. The c~pitate stem provides a third point of
fixation for the metac~rpal-capitate component thereby
further decreasing the ch~nce of loosening of this
component.
FUNCT N~L SUMMA~Y OF T~l~ VESCRIPTION
The metacarpal-capitate component is seen with a
central stem which inser~s in the stable third metacarpal
and a shorter second stem which inserts in the second
metacarpal. This position, an~ulation arc and length allows
for easy surgic~l insertion into the two metacarpals
simultaneously with maximum stabilization in the second
metac~rpal while allowing minimal difficulty with its
insertion.
T}~e ball portlon of this metacarpal component matches
the size and position of the patient's capltate. In the
event of collapse of the capitate, lt can still ~ubstitute
for the prior position by removal of less bone.
The carpal component duplicates the joint sur~aces of
the scaphoid and~lunate which have been removed. It comes
in three sizes, increasing at 2mm. increments which allows
adjustment of the carpal height or muscle tension across the
artificial wrist jolnt.
The radial component 22 duplicates the scaphold and
lunate fossa in the normal radlus. It allows 70 degrees of
motion in flexion-extension while being totally
unconstrailled. The radial ulnar deviation occurs at the
19
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metacarpal-capitate component 21 allowing 15 degrees of
radial and 15 decJ~ees of ulnar de~iation which is re~uired
for activities of daily living.
The flexion and extension occurs in an unconstrained
manner at the radio-carpal junction. Ilowever, because it is
unconstrained, it relieves any constraint on radial ulnar
deviation in the metacarpal carpal component.
The radial component 22 is fixed to the distal end of
radius 10 by the rac~ial stem 26 which is held with
methylmethacrylate glue. The metacarpal component stems are
likewise, held in the metacarpals with methylmethacrylate
glue.
In the event that an ulnar component is desired, the
ulnar head is replaced with a cap not shown, but located at
29 and ball 3Q which receives the ulnar stem 31. The ~lnar
stem 31 is glued into the ulna 11 and held at proper length
by the flex lock peg. The shank end of stem 31, as
illustrated in Fig. 16, which is a loose or slip fit in ball
to provide for a desirable longitudinal movement in
fitting the ulnar stem relative to the ball, wh~ch receives
the cylindrical shank end thereof. ~s the radial component
22 is inserted, it is rece~ved ln the radial head ball 19
and this allows ~table support of the radial component 22.
It allows full pronation and supination and is yet,
unconstrained ln distraction to protect from loosening.
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- 21~29
The st~m 26 po~tion as shown in Figs. 7, n, 9 and 12
illustrates the portlon implanted in the distal end of
radius 10 as aforementioned. Fig. 13 shows the addition of
a laterally disposed socket 33 which receives a ball 30 as
shown in Fig. 1~ and which is a view looklng toward the
longitudinal groove o ~ig. 11 and the rear portion of the
hal~-socket of Fig. 13.
Fig. 14 is a plain view ~hich shows an assembly of the
socket 33 and ball element 30 o~ the stem 31 for the ulnar
implantation. It shows a Elex-lock peg 32 locking
arranqement al~o shown in Figs. 9, 14 ancl 16 which retains
th~ stem ln the bone struct~re. ~he loclcing end is
co~prised of a plurality of circular disc-like elements
which will deorm as the implant is inserted in the ulna
bone 11, and WhiCIl thereafter resists longitudinal movement
in the opposite direction thereby preventing loosening of
the connection with the bone.
The details of the spur stems and ball and socket joint
are indicated in further detail in Figs. 5, 6 and 7 whereln
the stPm 23 also includes a depending spur 23 whlch is
implanted in the carpal. The plan view in Fiq. 6 shows the
configuration of the surface of the intermediate membex
which as shown incorporates the ~ocket portlon o the ball
and socket connection.
The capitate ball is captured by the carpal component
in Pig. 5 by the flexibility of the hiqh density
polyethylene.
21
21~029
The ulnar head 23 captures the ulnar ball 30 by
reducing the balls size by freezing. The ball 30 once
expanded to room or body temperature, will turn freely but
is not easily dislocated from the ulnar head.
The configuration can possibly be described in a manner
more readily understood by indicating that a portion of this
would be in the shape of the knuckles of two fingers, that
is, they have a round configuration in plan but are somewhat
cylindrical in elevation as shown by Fig. 10.
Fig. 7 shows the curved view in which the vitallium
portions of Fig~ 6 may articulate in the general
configuration of the intermediate portion contained in the
socket as shown in the cross section in Fig. 10. The major
portion of the sub-assembly of Fig. 6 would ride without
mechanical restraint at the right inside portion thereof in
grooves of longitudinal trough like semi-cylindrical cross
sectional configuration with generally spherical ended
portions of the grooves as shown in the view of Fig. 8.
The two units are assembled as shown in Fig. 9 and a
distally extending spur 23 shown in Fig. 7 is implanted in
the metacarpal while the proximally extending spur 26 i5
implanted in the radius. Fig. 11 is a view looking directly
into the dual grooves of the left hand portion of Fig. 7
while Fig. 12 is a plan view incorporating the grooves of
Fig. 11 therein.
-. . . ~ ~ .. . . '
`' . :. - , ': . '
:~ ~ : : . ,
~ 2 ~
tt is considerecl to be apparent from the foregoing
description that the lnvention provides a
metacarpal~capitate component constructed anatomic
divergence o~ the second, third metacarpal ~tems to give
maximum stability, while allowing ready insertion in the
human hand.
~ ttention is directed to the fact that adjustable
components allow adiustment of carpal length at surgery~ It
is invisioned t:llnt carpal components varying in ~ize by
lncrements of approximately 2mm will accommodate this
adj~stment capability at surgery. Also prosthesis sizes may
vary by about 20 percent between the sizes respectively
between ~ale and female patients.
In the case o female patients wtth large hands, the
larger male size may suEflce.
It is also considered to be apparent that the
availability of the ulnar component and its adjustability
resulting from the slip fit of the ulnar stem in its ball
further enhances the utility of the invention's prosthesis
to provide advantages not heretofore known ln the prior art.
Obviously, many modifications and variations of the
present invention are poss~ble in light o the above
teachings. It is, therefore, to be understood that within
the scope o~ the appended claim~, the invention may be
practiced otherwise than as specifically described.
