Note: Descriptions are shown in the official language in which they were submitted.
~V75~5~
This invention relates to a body ~oint endoprosthesis,
an~ more particularly to an endoprosthesis that transmits
forces in a manner more closely approximating normal physio-
lo~ical s~ress aistribution.
Wear phenomena in the ~oints of aged people, the conse-
quenca of inherited disease, rheumatic inflammatory ailments
and in~uries may leaa to chronic pain conditions and pro-
gressive restriction of ~oint mobility (arthrosis), which
often se~erly limits the sphere of activity and imposes acute
physical stress upon the suffererO
By way of showing the state of the art, reference is
made to the paper "Technischer Fortschritt bei kunstlichen
Huftgelenken" in the periodical Technische Rundschau Su-læer,
4/1974, pages 235 to 245. This treatise gives a review o~
the development of artificial hip ~oints and describes typical
constructional forms known since 1939. From the discussion
in the paper o~ these particular structural ~oxms, it is
apparent that all of the constructions have more of less
serious inherent disadvantages. In addition to wear p~enomena
in the tw~ parts of the joint, the ball and the socket, the
known shaft prosthesis are accompanied by the particular
disad~antage that loosenin~ of the sockets and the sbafts
occurs, accompanied in certain cases by the subsequent breakage
of the shaft~ In the known artificial hip joints, this
loosening o~ the shaft can be attributed to several di~erent
causes. Firstly, the shaft is preferably cemented into the
bone. The cement which is used is the sei~-poly~erizing
synthetic plastic material methyl methacrylat~. The heat
of polymerization resulting from the curin~ of this material
results In temperatures o~ 80 to 100C and can cause thermal
S8S3L
damage of the surrolmding tissue, because the coagulatlon
point of albumen amDunts to 56C, In addition to these
thermonecroses, damaging ef~ects are also revived which
resulted from the mechanical preparation of the bone ~rasping
or similar operations~ carried out during the preparation
of the seating to receive the implant, and at khe same time
there is formed between the damaged area and the bone a screen
of connective tissue, which has a negative influence upon
the anchorage in the bone. The screen of connective tissue
permits micro relative displacements to take place between
the implant and the bone seating. For a fuller treatment
of thi~ condition, re~erence is made to the book Biopolymere
und Biomechanik von_Bihdegewebssystemen, Springer-Verlag
1974, pages 417 to 419, in the article "Zur Problematik der
Zementverankerung im Knochen" by H.G. Willert~
A further cause of the loosening phenomenon is the non
physiological nature of the application of force from the
implant to the bone. For the want of any other exposition
on this sub~ect in the known art, an explanation thereo
now be given with reference to Figs 1, 2 and 3 of the accom-
panying drawings~
In Fig. 1 a sha~t 35 o~ a femur head endoprosthesis
37 is secured in a thigh bone 30 by means of cement 32.
The shaft 35 has a collar 39 and a neck 40 extension termin-
ating in a ball 42 having a center point M. The ball 42
rests in a ball socket 45~ which is secure~ in a pelvis bone
48 by cement 46. The resulting force F~ passes throu~h the
center point M o~ the b~ll 42 and in Fig~ 1 is shown in the
direction in which this resultant force has its ~-ximum value~
In that case, the direction o~ the force with respect to
.
~7~
the longitudinal axis o~ the neck 40 encloses an angleo~ .
If this resultant ~orce F is red~tced to a point A o~ the
seating sur~ace 50 o~ ~he thigh bone 30 cooperating with
the collar 39, then there will act in a direction normal
to the seating sur~ace 50 the force F .coso~ and in the
direction of the seating surface 50 the ~orce component
F~.sin ~ . In addition, due to the parallel displacement
of the resultant ~orce FR there is also e~ective the force
couple FR.a in accordance with the parallelogram surface
51 shown hatched in Fig. 1, The distance a repre~ents the
shortest spacing o~ the point A from the line of action of
the resultant ~orce FR
In Fig. 2 there are indicated qualitatively the surface
pressures acting upon the thigh bone 30 and resulting from
these two force components and the ~orce couple~ It is seen
that the surface pressure p acting normal to the seating
surface 50 is practically constant, while in the physiological
case, represented in Fig. 3, the approximately linear aurve
o~ the normal stress ~ acting at the right hand or medial
edge in Fig. 3 shows a maximum compression stress o~ Gr
D max~
In the physiological case according to Fig 3 there will he
a neutral fiber at a position spaced by a distance e from
this position of maximum compression s~ress so that remote
from it at the left hand or lateral edge in Fig~ 3 there
will be a tensile stress ~Z max.
In the physiological case according to Fig. 3 practically
no normal stxess arises at right angles to the direction
of the fibres o~ the cortical tissue 122 indicated in Fig.
1 and 2, but in the othe~ case the ~orce component FR.sin and
the force coupie FR~a will give rise to the surface pressures
1~'7~
q and r, which act at right an~les to the inner surface of
the cortical tissue. The surface load q at the inner medlal
mar~in of the seating surface 5n has a maximum qmax' which,
in the course of the continuous reconstitution of the bone,
results in a progressive yieldLng of the bone.
Along with this yielding o the bone, the bending stress
of the prosthesis and the cement increases until, due to
further loosening of the shaft 35, cracks appear in the cement
cladding 32, and finally a breakage 55 of the shaft 35 causes
the prosthesis to fail and leads to immobility of the patient~
The relative movements between the collar 39 and the seating
surface 50 arising from this loosening process prevent the
desirable pro~ressive ingrowth of the bone ceiis into porasr
cavities or perforations in the surface of ~he known prostheses.
The above mentioned cracks in the cement cladding lead to
intense corrosion phenomena in the metal (crack corrosion)~
Sinking of the shaft prosthesis is also possihle if the
support afforded by the cortical tissue is lost.
The force F~.cos~C indicated in Fig~ 1 as acting at
right angles to the seating sur~ace 50 is transmitted through
collar 39, ana, in respect of one part, over the seating
surface 50 into the thigh bone 30 and, in respect of another
part, is transmitted onto this thigh bone by virtue o~ the
positive connection between the implant and the thigh bone
30. If it is assumed that ~he case under consideration is
a known impiant of steei, then the relationship of the modulus
of elasticity o~ the steei implant to that o~ ~one is about
8al~ Conse~lently, under load the bone deformation is relatively
greater than that o~ the steel, and there is a relative
displacement of the contacting surfaces o~ the implant and
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:~L07S8S~
the bone. These displacements can lead to shearing o~ o~
the osteoblasts building up to form a bridge between the
bone and the implant, which otherwise are desirable for a
lasting anchorage of the implant in the bone, As a resul~,
there is formed in that regioll a resilient screen of connective
tissue, which permlts further relative displacements and
therefore a loosening of the prosthesis.
In the book entitled Gesammelte ~bhan~lungen zur ~unktion~
ellen Anatomie des Bewegungsapparates by Friedrich Pauwels~
Springer-Verlag 1965, in particular at page~ 4 to 6 o~ the
chapter "Mechanische Faktoren bei der Frakturheilung", a
general description is given of tha influence of mechanical
stimuli upon the final structure of newly formed tissue in
the form of connective tissue~ cartilage or bone~ The force
component FR.sin~ defined above in connection with Fig,
1 can result in the setting up o~ a so-called free shearing
force in the sea~ing surface, preventing the desirable growth
of new hone tissue, this force being explained in the abo~e
cited book of Pauwels in the ~hapter "Die freie Scherkraft"
at pagas 21 to 24.
Furthermore, attempts are also known to anchor shaft
prosthesis in thigh bone without the use of cenent. Fox
this purpose the surface of the shaft is provided with per~or-
ations or macroscopic depressions, in which it is intended
that there shall be a n~wly formed growth of ~one tissue
resulting in an intimately contacting anchorage of the shaPt
of the prosthesis in the thigh bone. Nevertheiessr because
the implantation of hip joint endoprostheses is mostly necessary
in elderl~ patients~ great importance must be placed upon
early mobilization of the patient. If the patien~ is laid
:
--5--
~7~8~L
up ~or too lon~ a time until there is a sufficiently firm
in~rowth of the sha~t o~ the prosthesis, thls clelay can,
for example, cause the risk of pneumonia, mNscular atrophy
and damage to the heart and circulation as well as to the
bladder and kidney system, For example, in experiments with
animals, the time taken for the formation of load bearln~
bone tissue has been at least two months, Consequently,
the kno~n types of prostheses whose anchorage in the thi~h
bone relies exclusively upon the principle of the ingrowth
of bone tissue are therefore very disadvantageous on account
of the lack o~ early mohilization o the patient. Moreover,
because of the difference in the moduli of elasticity anfl
locally high sur~ace pressures, loosening phenomena can
appear at the implant,
In known hip ~oint endoprostheses of this type ~German
Auslegeschrift Speci~ication No~ 1,54i,246, and French Specifica-
tion 2,057,418) a metallic shaft ls formed integrally with
a collar shaped suppor~ slement and a bearin~ stud, upon wh~ch
a ball head is rotatably mounted as the ~irst part of the joint.
There is no joint between the support eiement and the shaft.
In consequence this construction does not remove the aho~e
explained disadvantages.
In a further known hip joint endoprosthesis of the above
mentioned type ~French Specification Wo. 2,210,909) a sha~t
is formed integrally with a collar shaped support element,
to which can be screwed a ~irst joint member in the form of
a ball head to form a rigid unit secured by a clampin~ device~
This construction also lacks a joint between the support element
and the s~ft~
In the Swiss Patent Specification 426,096 there is dis-
closed a hip joint endopros~hesis, to whose shaft there is
... .
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~L~7~S3L
integrally connected a ~irst socket. In this socket there
is mounte~l a freely rotatable ball forming the first ~oint
member, which latter is also supported in a socket ln the pelvis
bone ~orming the second ~olnt member. There is thus the lack
of a support element and accordingly also a lack of the joint
according to the present invention. The forces applied to
the first socket are transmitted exclusively through the sha~t
into the thigh bone, so that the abovementioned disadvantages
are even more clearly noticeable.
It is already known (German Offenlegungsschrift Speciflca-
tion 2,432,766~ to construct an artificial knee joint whlch
during the whole of the movement cycle functions as a crossed
quadrangular linkage having the bridge connected to the thigh
bone and the couple connected to the tibia.
; An ob~ect of the present invention is to provide a body
joint endoprosthesis w~erein the transmission of force into
a first bone takes place analogously to the physiological
condition in such a manner that the stress distribution in
; the first bone corresponds, at least to a good approximation,
to the physiological stress distribution. For the purpose
of promoting the growth of new bone in the seating sur~ace,
relative movements between the seating surface and the support
element should as far as possible be avoided, The anchor~ge
in the first bone should take place without the use of cement,
It should be possible to provide for the early mobilization
of the patient~
`; The invention provides a body joint endoprostheses including
an anchoring palrt ha~ing a shaft adapted to be anchored in
a first bone, and a pivot member connected to the anchoring
part by a pivot jointO The pivot member includes a first body
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~75~S~
joint member and a support element adapted to beax against
a seatin~ surface o~ the first bone. The ~irst ~oint member,
and a second joint member adapted to be connected to a second
bone, ~orm the body implant jOillt. The transmission of force
~rom the supporting element into ~he seating sur~ace is analogous
to the physiological condition, while a~fordin~ the stxessing
conditions which are necessary for the maintenance of the bone
tissue, The ingrowth of bone tissue into the openings and
pores of the prosthesis is considerably acilitated and the
time taken for this process is shortened, The joint resolves
disadvantageous stiffness of the prosthesis, and while maintaining
the necessary functional stability affords mobillty within
the prosthesis itself, which removes the above described dis-
advantage s O
~ ccoxding to one practical ~orm o~ the in~ention, thepivot ~oint is in the form of a hinge ~oint. The resulting
ability of the pivot member to pivot only in one plane is
adequa~e in most cases to provide a transmission o~ ~orce into
the first bone approximating to a large extent to the physio-
logical condition. However, if universal pivotability o~ the
pivot member is desired with respect to the seating sur~ace,
the joint may ba a ball ~oint or a Cardan joint.
The ~oint may also be a knife edge type of construction
or an elastic ~oint~ ~n the last mentioned case, the joint
may include at least one xesilient member, preferably a lea~
spring, clamped between the anchoring part and the pivot member,
w1th the resilient member or members being prestressed to ~orce
the suppoxting element onto the seating sur~ace, The prestress
may produce a suxface pressure of, for example, 0.1 to 0.5
Newtons per square millimete~ ~N~mm2) on the seating surface~
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~75~351
This surface pressure rein~orces the tension of the postoperative
weakened muscles and, during the ingrowth period, prevents
lifting of the pivot memker from the bone section surface~
Moreover, this surface pressure exerts an addltional stimulus
upon the bone structure of the spongiose tissue and the cortical
tissue o~ the seating surface and favors ~he growth o~ bone
into suitable reception openings or pores o the supporting
element.
For the purpose of guiding the supporting element in
parallel relation to the seating surface it is possible in
accordance with the invention to arrange two resilient members
in a pivot plane o~ the pivot member and spaced ~rom each other
in the mann~r of a parallelogram.
According to one practical form of the invention applied
to a hip joint endoprosthesis, the first bone is a thigh bone,
the first joint member is a ball and the support element is
a collar rigidly secured to the ball. This produces a robust
and simple construction. The axis of the joint may be situated
at least approximately in a plane containing the seating surface.
This produces a quasi-physiological transmission o~ ~orce ~rom
the collar to the seating surface.
In this form o~ the invention the second bone is a pelvis
bone and the second joint member is a ball socket anchored
in the pelvis bone. The socket is preferably anchored ln ~he
bone by three studs arranged at the corners of a triangle 50
that the maxLmum resultant force upon the body joint passes
at least approximately through the surface center of gravity
of the triangLev
In another practical form of the invention, an elhow joint
endoprosthesis, the ~irst bona is an upper arm bone, the ~irst
!
~7S~
joint member is a hinge pin, and the support el~ment includes
two condylar shells arranged in spaced relation to each other
and connected to the ends of the hinge pin, In this case
also there is afforded a quasi-physiological transmission of
force from the condylar shells to the oppositely situated
seating surface.
According to a further feature of the lnvention the shaft
is provided with an external sawtooth thread, whose compara-
tively steep flanks are directecl towards the plvot member.
The compara~ively steap flanks of the sawtee~h allow a kind
of barhed hook anchorage of the shaft to take place in the
bone, and can be directed at least approximately normal to
the longitudinal axis of the shaft~ This asymmetrical shape
of the sawtooth is signi~icant because the force F~.cos
acts always in one direction, which is in fact the upward
direction, and thus substitutes the physiological tensile
stresses. Upon the ~lanks of the thread directed normal to
the longitudinal axis o~ the shaft there will be no radial
force resulting from the force Fz.cos ~ , which could exert
upon the bone a non-physiological bursting effec~, `!
Another object of this invention is to provide an instrument
for the insertion and removal o~ body joint endopros~heses
described above~ According to the invention, a rotary tool
is adapted to be rigidly connected to the shaft of the anchorlng
part. This facilitates screwing the sha~t into or out of a
tapped hole in a bone without producing any bending movements.
Undesired stresses upon the bone are thus a~oided~
A holder having a guide device ~or a m~lling tool is
preferably ad~ustably secured to this rotary tool. By virtue
of the stiffness o~ the rotary tool and its coupling to the
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::,. "- .
. . .
~C~7~
shaft it is possible to perform the necessary milling operations
upon the bone which is to receive the shaft, and to do this
in perfectly determinate geometric relationship with reference
to the shaft. During this operation, the shaft there~ore
opera~es as a reference body anchored in the bone which is
to be milled in the same way as later, after the removal of
the instrument, it will be used for the remaining operation
of mounting the endoprosthesis upon the shaft. In this manner,
precise cooperation o~ the respective prosthesis with the bone
parts to be mllled is ensured.
Other objects and advantages of this inventlon will be
seen from the following detailed descrlption~
Fig. 1 is a cross-sectional view iliustratlng the resolution
of forces in prior axt hip joint endopros~heses.
Fig. 2 is a sectional view illustrating how the prior
art hip ~oint endoprosthesis illustrated in Fig. 1 transmits
forces to the femur.
Fig~ 3 is a schematic view illustrating stress distribution
in the physiological ~emur.
Fig, 4 is a femNr head endoprosthesis with a hinge joint
in section along the line IV-IV o~ FigO 5,
Fig, 5 is a side elevation in section along the line V-V
of Pig~ 4~
Fig~ 6 is a side elevation from the left of the represent-
ation in Fig. 5 with the thigh bone in section.
Fig. 7 is a schema~ic diagram corresponding to ~hat of
Fig~ 6 with practical operating quantities insertedD
Fig. 8 is substantially a sectioned ele~ation along the
line VI~I-VIII of Fig~ 9 o~ a femur head endoprosthesis with
a ball joint,
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1~758~1
Flg, 9 is the paxtially sectioned elevation accordin~
to line IX-IX in Fig. 8,
Fig, 10 is essentially a sectional elevation along the
line X-X of Fig. 11 of a femur head endoprosthesis with a knife
edge bearing construction.
Fig. 11 is a partly sactioned elevation along the line
XI-XI of Fig. 10.
Fig. 12 is essentially the sectional elevation along the
line XII-XII of Fig, 13 of a femur head endoprosthesis with
an elastic joint.
Fig, 13 is a partially sectioned elevation along the line
XIII-XIII of Fig~ 12~
Fig, 14 is the sectional elevation along the line XIV-XIV
of Fig. 12.
Fig, 15 is essentially the sectional elevation along the
line XV-XV of Fig, 16 showing another femur head endoprosthesis
with an elastic ~oint.
Fig. 16 is the partial sectional ele~ation along the line
XVI-XVI of Fig. 15.
Fig. 17 is the side elevation from the left of the view
shown in Fig. 16 with a longitudinally sectioned thigh bone.
Fig. 18 is essentially the sectional elevation along the
line XVIII-XVIII of Fig, 19 showing a femur head endoprosthesis
with a Cardan joint,
Fig. 19 is the partially sectioned eleYation along the
line XIX-XIX in Fig~ 18~
Fig~ 20 is the partially sect~oned eievation alon~ the
line XX-XX of Fig. 21 showin~ a ball socket.
Fig, 21 is a plan ~iew of the ball socket accor~ing to
Fig~ 20,
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~17585~
Fi~, 22 is a lon~itudinal section through the ball socket
~ccordlng to Fig, 2Q and 22 with the corresponding ball,
~ ig, 23 is a front elevation of a right hanfl elbow ~olnt
endoprosthesls (without bearing shell).
Fig. 24 is a sectioned elevation along the line XXIV-XXIV
of Fig, 23,
Fig. 25 is the sectioned elevation along the lines XXV-XXV
of Fig, 24.
Fig, 26 is the sectioned e:Levation along the line XXVI XXVI
of Fig, 24,
Fig, 27 is the partially sectioned elevation from the riyht
hand side of the view in Fig, 23,
Fig, 28 is a plan vlew of the bearing shell in Figs, 24,
26 and 27,
Fig, 29 is a side elevation from the left hand side o the
bearing sheli according to Fig, 28,
Fig, 30 is the sectional elevation along the line XXX-XXX
in Fig. 31 of an instrument for the insertion and removal o~
a body joint endoprosthesis,
Fig, 31 is the sectional elevation along the line XXXI-XXXI
in Fig. 30.
Fig. 32 is a side elevation of the instrument with a lon-
gitudinally sectioned rotary tool,
Fig. 33 is t~e sectional elevation along the line XXXIII-
XXXIII of Fig, 32,
Fig, 34 ls a longitudinal section through a shat having
a sawtooth thread~
Figs, 4, 5 and 6 illustrate a femur head endoprosthests
70 embodying this inventionO Preferably, at least the external
surfaces of the endoprosthesis consist of metal coated with
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.. ''' ~:
758S~L
enam~el, i.~., with a vitreous or partially devltxifLed inorganic
coatin~ bonded to the metal at a temperature above 800F~
The metal and enamel constitute a compound body, in which the
components o~ the compound, i.ec, the metal and the enamel,
can be selected and adjusted both with respect to each other
and wi~h respect to the particular demands o~ the situation
to give the optimum results, This compound ma~erial is ideally
biocompatible and possess technical, physical and chemical
characteristics which are superior to all known materials used
for prostheses.
A shaft 73 coated with enamel and provided with an external
rounded thread 75 is screwed into the internal thread 77 of
the thigh bone 30. The external rounded thread 75 provides
complete anchorage of the sha~t in the bone without bone cement,
mastic or the like while still achieving an exceptionaLly good
degree o~ positive and/or non-positive connection between the
shaft and the bone.
Prefexably the thread 75 of the shaft is conically formed
in a manner complementary to the oppositely situated internal
wall of ~h~ thigh bone 30. The maximum degree of care o~ the
bone and a relLable anchorage of the shaft therein are achieved
if the internal thread 77 is cut in advance by means of a thread
core boring and tapping drill or milling tool, not shown in
the drawing, before the shaft is screwed into the bone.
The metallic shaft 73 is surmounted by a cone 79 which
is also enameLled and ground to a ~inish and has a threaded
bore 80, whic~ is ~ot enamelledO Upon the cone 7~ there is
releasably mounted an extension member 83 having a conical
socke~ 82 complementary to the cone 79. A screw 87 penetrates
with appropriate clearance a bore 85 in the conical socket
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:~.
~C~75~
82 and has its non-enamelled thread 89 screwed ~nto the tapped
bore 80 for ~ecurin~ the conical socket 82 with respect to
the cone 79. The underside 90 o~ the screw head and the oppos~ng
reception surface 92 of the conical socket 82 are enamelled
and are ground to make a li~uid tight connection. Screw 87
may be locked in place with liquid synthetic plastic adhesive~
This construction permits a continuous rotary adjustment
and fixing of the conical socket 82 with respect to the cone
79 of the shaft. Even when a comparat~vely small axial com-
pression force is exerted by the screw 87, the cone type o~
connection a~fords substantial load bearing frictional forces
which insure a reliable functioning of the prosthesis. Even
when the shaft 73 is completely enamelled, the cone type o~
connection permits satisfactory working o~ the shaft for the
purpose o~ ~itting and fluid tightness, for example by grinding.
The tapped bore 80 and the threads 89 of the screw do not have
to be enamelled, because it is possible by suitable working
of the opposing enamelled surfaces to obtain a per~ect seal
between the screw head and the conical sockek, which prevents
the ingress of body liquids and secretions.
An arm 95 extends upwardiy from the conical socket and,
as mQy be seen in Fig. 5, encloses an angle 98 with the longitud-
inal axis 96 o~ the shaft 73~ The upper end of the arm 95
carries a hinge eye 100 of a hinge ~oint 102. A hinge pin
103 penetrates ~oth the hinge eye 100 and a fork 105, formed
upon the collar 107 of a pivot member 109 that bears upon the
seating sur~ace 50 of the thigh bone 30 ? The collar 107 is
rigidly connected through a neck 110 to a bali 113, From the
underside of the collar 107 extends a bearing pocket 115 for
a spring 117 o~ silicone rubber~ which supports itsel~ at the
-15-
other side upon a support arm 119 o~ the arm 95,
The use of the extension membex 83 releasably connected
to the shaft 73 makes it possible to preassemhle the pivot
member 10, the ~oint 102 and the extension member 83 before
this structural group is implanted. This shortens the operating
time and also allows, for example, a complete enamelling of
the surface to be effected. The complete structural group
can also be sub~ected, before implantation, to any desired
specialized finishing treatment and quality control,
With the exception of the spring 117, which is also bio-
compatible, the entire external surface of the pivot member
109, the hinge joint 102 and the extension member 83 is enamelle~.
Those enamelled surf~ces of the femur head endoprosthesis 70
which are situated opposite to spongy bone (spongiose tissue)
120 or bone scale (cortical t~ssue) 122 can be suitably prepared
by roughening, creation of artificial pores or the like so
as to present an optimum condition for the inward growth of
bone tissue, and thus to achieve a very desirable secondary
anchorage of the prosthesis in the thigh bone 30, The ingrowth
process is reinforced by the fact that the spring 117 urges
the collar 107 against the seating surface 50 and maintains
definite load conditions on seating sur~ace 50 when the load
on the hip joint is relieved, Preferably, the collar 107 is
pressed against the seating surface 50 with a sur~ace pressure
of 0.1 to 0 5 N/mm2.
The pivot joint 102 and the quasi-physiological transmission
of ~orce into the bone that it provides relieve the shaft 73
of a substantial load as compared with the conditions existing
in known shafts, Thus there is achieved, not only primarily
an adequate anchorage of the shaft in the bone, but also sec
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~L0~85~
ondarily a further improvement in the anchorage by growth of
the bone into the shaft, which favors an early mobiliæation
of the patient.
In Fig. 7 the operatin~ quantities are plotted schematically,
Analogously ~o the physiological condition shown in Fig. 3,
the resultant force FR is transmitted as a substantially tri-
angular surface load 125 onto the seating surface 50. As
already explained in the physiological case according to Fig~
3, a tensile stress is ef~ective outwardly or to the left hand
side of the neutral fiber. In a similar way there will result
from the presence of the hinge ~oint 102 a resultant tensile
force Fz, which, taking into consideration the angle ~ , can
~e resolved into its mutually normally directed components
Fz.cos ~ and Pz.sin ~ , The component Fz,cos~ acts as
a tractive force upon the shaft 73 and is transmitted through
the outer r~und threads 75 thereof into the cortical tisæue
122 of the thigh hone 30. In that region khere will arise
the thrust stresses ~ indicated in Fig. 7,
The axis of the hinge joint 102 is laterally removed by
a distance b from the plane in which is situated the longit-
udinal axis 96 of the shaft 73. This results in a force couple
b.Fz.cos ~ , which acts in the sam~ sense as a moment composed
o~ a frictional force ~,FR and a lever arm d, which corxesponds
to the perpendicular spacing distance from the seating surface
50 to a center point P o that portion o~ the shaft 73 which
is provided with the externally rounded thread 75~ In the
opposite sense there will act a moment consist1ng of the force
component Fz sin~ and a lever arm c, the latter corresponding
to the normal spacing distance rom the center polnt P to ~he
line of action of the force component Fz,sin~ . The moment
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~[)7~
resultinq ~rom the above mentione~ ~orce couple and the above
mentioned two moments ~ives rise to the sur~ace pressure s
at the cortical tissue 122 0 If, for structural considerations,
the spacing distance b is made equal to zero, the above mentioned
force couple b.Fz.cos~ vanishes. The surface pressure s results
then from the resulting moment
M = Fz.sin ~ .c - ~ .PR.d
The deformation o~ the thigh bone 30 resulting from the
surface load 125 acting upon the seating surface 50 turns the
pivot member 109 about the axis of the hinge joint 102 and
can in this way, in any occurring shape condition of the thigh
kone 30, transmit the force into the thigh bone 30 in a manner
analogous to the physiological conditions. ~rom the lower
margin of the bearing pocket 115 to the upper termlnation of
the externally rounde~ thread 75 of the shaft 73 thexe wil1
exist no positive connection between the ~emur head endoprosthesis
70 and its bearing in the thigh bone 30. By this means relative
micro movements of the contact surfaces of the prosthesis and
the bone are decisively reduced.
Figs, 8 and 9 show a femur head endoprosthesis 130, wherein
the joint is designed as a ball joint 131. A ball 133 of the
ball joint 131 is formed at the top of the extension member
83, while there is a ball socket 135 at the underside of the
collar 107.
- In the hearin~ pocket 115 is a spring i37~ consi~ting,
for example, of sili~one rubber having a hardness of A 70~
5 Shore, and having an axial aperature. Through this aperature
leads a ciamping screw 139, ~hich is screwed into a pi~ot stud
; 140 mounted in a bore 141 in the extension member 83. The
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i85~
clamping screw 139 permits the surf~ce pressure exerted by
the collar 107 on the seating surface 50 to be ~inely ad~usted.
This screw may he locked in position by means o~ liquid syn-
thetic plastic adhesive.
The screw 139 also leads through holes 143 and 144 in
the bearing pocket 115 and the extension member 83, while
allowing suficient lateral clearance therein to provide for
any swinging movement. ~ikewise adequate latexal clearance
is provided ~or the head of the screw 139 so that the pivot memher
109 can have motion universally about the ball ~oint 131 and
can afford particularly uniorm ~orce transmission into the
thigh bone 30.
Figs, 10 and 11 show a further ~emur head endnprosthesis
150, wherein the extension member 83 has its head formed as
a hook shapPd knife edge bearing 153, whose free end 155 ~orms
the upper abutment for the spring 117~ At r~ght angles to the
knife edge 153 proceeds a counteracting knife edge 157, which
is formed at the base of the collar 107~ Moreover, the top of
the kni~e edge 153 is in sliding engagement with the underside
of the collar 107~ The knife e~ge bearing 153 and the counter-
acting kni~e edge 157 form a knife edge bearing construction
159, which can be fully enamelled, as can also the ball joint
131 in Figs. 8 and 9.
A ~urther femur head endoprosthesis 160 is shown in Figs~
12 and 130 They show a spring bearing 161 at the top of the
extension member 83 and a further spring bearing 163 ormed
upon the collax 107, The spring bearin~ me~bers 161 and 163
are each provided with a slo~ 165 and 166 respectively~ in
which a lea spring 168 is secured, ~or example by adhesion
or pressing in. Spring 168 is slightly prestressed in such
--19--
107S~3S~
a manner that the collar 107 is applied with the desired sur~ace
pressure to ~he seating surface 50 of the thigh bone 30. The
edges o~ the slots 165 and 166 are strongly rounded of~ at
the places where, otherwise, the de~oxmation of the leaf spring
168 would result in undesirable edge pressures of large dimen-
sions, In this construc~ion, an extension 169 is formed at
the base of the collar 107 for positive latexal guidance of
the pivoting member with the bone as well as to increase the
area of contact with respect to the surrounding bone tlssue
and thereby to enhance the conditions for ingrowth.
Fig. 14 shows the spring supports 161 and 163 and the
leaf spring 168 inserted therein as viewed from a direction
other than that shown in Fig. 12. The elastic joint is shown
at 170.
- Figs. 15, 16 and 17 show a further femur head endoprosthesis
member 83 in the following sequence a leaf spring 175, an
intermediate ring 177, a further leaf spring 179 and a covering
ring 180. The components 175 to 180 are penetrated by a clamping
screw 182, which is screwed into the extension member 83 and
; axially compresses these components. The leaf springs 175
and 179 are thus effectively clamped upon the extension msmber
83. A similar clamping arrangement of the leaf springs 175
and 179 is provided upon the pivot member 109, where again
the leaf springs 175 and 179 as well as a covering ring 184
and an intermediate ring 185 are penetrated and axially compressed
by a clamping screw 187 which is screwed into the collar 107.
The clamping screws 182 and 187 can be locked in their threaded
position by means of liquid synthetic plastic material. This
construc~ion comprising the two leaf springs guided in parallelogram~
fashion also represents an elastic joint 189
~7~
The leaf spring 175 and 179, like the leaf spring 168
in Figs. 12 and 13, may consist of alloy spring steel, which
may be coated, ~or example, with silicone rubber, to avoid
the possibility o any metallic contact with parts o~ the body.
All other parts of the femur head endoprosthesis 160 and 173
may again be fully en~melled.
Figs, 18 and 19 show a fe~r head endoprosthesis 190,
wherein at the upper end OI the extension member 83 there is
arrangea a fork trunnion bearinq 192 within which is rotatably
mounted a hinqe pin 194 passing through said ~ork. The pivot
member 109 carries a further fork bearing 195, which is displaced
through 90 with respect to the fork bearing 192 and is rotatably
mounted upon a hinge pin 197, which is itsel penetrated at
right angles by the hinge pin 194. Both of the hinge pins
194 and 197 penetrate a core 198 and form with the core the
cross member of a Cardan joint 199, i.e., a universal joint
consistin~ of a cross like piece, opposite ends o~ which rotate
within the forked end of bearings 192 or 195. The Cardan joint
199, like the ball joint 131 of Fig. 8, permits a universal
movement of the pivoting member 109 with respect to the thigh
bone 30.
Figs. 20 and 21 show a ball socket 250 for a total hip
joint endoprosthesis. ~rhe external surface of the ball socket
250 is provided with concentric channels 252, 253 and 254 and
with channels 256 to 259 located in planes extending through
the axis 265 oi~ the socket, These channels faciliate and
promote the macroscopic ingrowth o~ new bone tissue into the
surface of the ball socket and thereby effect secondary anchorage
in the pelv~s bone 48 ~Fig. 22~ .
For the primary or ten~porary anchorage orC the ball socket
250 in the pelvis bone 48 there are provided three studs 261,
262 and 263 of button shape, which are arranged at the corners
1~7585i
of a triangle in such a manner that the maximum xesultant ~orce
F~ (Fig. 22) is directed at least a~proximatel~ through the
s~face center of gravity or centroid of this trlanglel i.e,,
at least approximately through the point where three lines,
each of which extends from a corner of this triangle to the
mid-point of the opposite side o~ the triangle, intersect.
Stud 261 is positioned near the apex of the socket 250 ana
the other two studs 262 and 263 are positioned at approximately
one-half the heighth of khe socket. The easiest fitting and
most secure anchorage of the ball socket is achieved if the
axis of the three studs 261, 262 and 263 are positioned with
their lon~itudinal axes in planes which are at least approximately
parallel to each other, with the axis of studs 262 and 263
and lines drawn normal to the base surface of the ball socket
defining an~les larger than the angle defined by the axis of
stud 251 and the radial axis 265 of the ball socket. In the
socket illustrated in the fiqures, the axis of the stud 261
forms an angle 267 of 10 with the main axis 265 of the ball
socket 250, and the axes of the studs 262 and 263 each form
an angle 270 of 25 with respect to normals drawn to the base
surface 269 of the ball socket 250. The stud 261 is provided
at its root with a peripheral groove 272, while each o~ the
two other studs 262 and 263 is provided with an undercut 274
outwardiy directed rom the main axis ~65 of the ball socket
~50~ These undercuts provide an improved anchorage in the pelvis
bone,
The ball socket 250 is provided at its lower edge with
a cavity 275 at one side thereo~ proceeding from the base
surface 269, The sickel shaped formation o~ this cavity, as
seen in plan view, is clear from the assumed external contour
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i ....... . .
~l07585~
of the ball socket 250 shown in dotted lines in Fig~ 21. This
cavity 275 is provided for the unimpeded progression o~ the
musculous iliopsoas subse~lent to the implantatlon, and ~s
positionedt ~or the other hip ~oint, in the mirror image position
with respect to the central pla,ne of the ball socket 250 con-
taining the axis o~ the stud 261, As may be seen in Pig. 21,
the cavity 275 begins at least i~pproximately in a plane that
extends through the radlal axis 265 of the socket and through
stud 262, and extends over an annual range o~ at least approx-
imately 120 to that side of the ball socket xemote from stud
263. In the illustrated socket, cavity 275 extends over an
angle 276 o~ about 125 degrees.
Fig. 22 shows the ball socket 250 fitted in its assembled
position in the pelvis bone 48. In order to prepare the pelvis
bone for the implant, the physiological hip ~oint socket is
first of all milled out with a spherical milling tool. In
this spherical milled cavity three bores are made for the studs
261, 262 and 263 by means o~ a drilling templateG In this
operation the bores are concentrated somewhat closer together
than a distance 278 shown in Fig. 20.
Thereafter the ball socket 250 is inserted in such a manner
that the undercuts 274 of the studs 262 and 263 are guided
over the edge o~ the cor~ical tissue 279 o~ the pelvis bone
48. In this operation the adjacent spongy bone is displaced
towards the side~ Thereafter the ball socket 250 is gradually
inserted into the milled out spherical cavity until the stud
261 snaps into its bore~ Durlng this snapping in operation,
the cortical tissue 279 between the studs is elastically de~ormed
and? after springing back, locks the bali socket 250 in the
inserted position according to Fig, 22~
The special position o~ the studs 261, 262 and 263 with
~23-
107~
refer~nce to the resultant ~orce FR has the result that in
the studs additional thrust s~resses do not arise by the elastic
deformation of the bone under the in~luence of the resultant
force F~ when this force assumes its maximum value, Thus,
the possihle thrust stresses remain at a minimum value.
The ball socket 250 can be metallic and can he coated
wi~h enamel over its entire surface,
Figs. 23 ~o 29 show a total elbow joint endoprosthesis
290, As in the case of the foregoing figures, similar parts
are indicated by the same reference characters.
In this case7 the sha~t 73 is screwed into a humerus bone
293, The extension member 83 is provided with a do~nwardly
pointing stop 295, shown in Figs~ ~3, 24, 26 and 27~ for a
bearing shell 297, which does not appear in Fig. 23 and is
shown inserted in an ulna 299 in Figs. 24, 26 and 27, The
bearing sheli 297 is provided with an abu~ment surface 300
(Fig~ 29~ ~or the purpose of making contact with the stop 295,
which precisely defines the extended position o~ ~he humerus
293 and the ulna 299~ The side surfaces 302 and 303 (Fig~
28) of the bearing shell 297 are axially guided by corresponding
opposite faces of condylar shells 305 and 306, each of which
is provided with a support arm or hinge fork 105 that contains
an eye for ~he hinge joint 102.
A hin~e pin 308, which forms the first ~ody ~oint member, is
rotatably mounted in the bearing shell 297, which forms the
second body joint member~ The hinge pin 308 is made integrally
with the condylar shells 305 and 306 by means of only a compara-
tivaly short connecting member 310 and 311 (Figs, 26 and 27~
of substantially semicircular cross sectional area. Each con-
necting membar 310, 311 is situated only in that peripheral
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:~75 !35~
rec~ion o~ the hinge pin 308 which is emhxaced by the appertaining
condylar shell 305, 306, ~his provides an enlarged seating
surface.
Each condylar shell 3n5 and 306 furthermore is providecl
with a hole 313 for a bone screw 315 (Fig. 27) in the section
of the shell which is free of the connecting piece 310, 311.
A~ter the mounting o~ the condylar shells upon the suitably
prepared condyles 317 and 318 lFig. 25), the screws 315 are
screwed into these condyles for the purpose of temporarily
anchoring the prosthesis. The connecting members 310 and 311
are compara~i~ely small so that as much as possible of the
bone substance of the con~yles 317 and 318 can be left standing
during the preparation of the bed of the implant for anchoring
the bone screws 315, Moreover, with this construction the
musculature can be protected at its osseous connections.
For the implantation of the elbow endoprosthesis, first
of all the distal upper arm bone 293 is milled out in order
to make it possible to provide a tapped bore for the external
rounded thread 75 of the shaft 73. Following this the contact
surfaces ~or the condylar shells are millea. Moreover, the
space for the extension member 83 and its stop 295 are milled
out. When these milling operations have been completed, the
conical sleeve 82 is mounted upon the cone 79 and secured by
the screw 87~ said conical sleeve having the pivot member 320
which includes the condylar shells 305 and 306 as well as the
hlnge pin 308, linked to it by the hinge joint 102~ Then ~he
two bone screws 315 are driven into the condyles 317 and 318
of the upper arm bone ~93. In this manner the pi~oting member
320 is ~emporarily secured~ Its final fixing to the upper
æ m bone 293 should again be followed by ingrowth of the bone
-25-
~7~8~
cells into the pores of the inner condyLar shell surface.
In Fig. 24 and 27 a start of muscle 323 is shown in each
case at the ulna 299r
The bearing shell 297 is provided at its rear side with
anchorage projections in the form of a stud 325 and a tongue
327 arran~ed in spaced relation to an~ direcked away ~rom the
stud 325. The stud 325 is provi~ed at its root with a peripheral
channel 329.
For making the i~plantation, first of all the proxlmal
ulna 299 is prepared by milling out the cylindrical hollow
shell of the physiological joint to the external radius of
the bParing shell 297, and by milling off both sides of the
elbow protruberance (olecranon) to the ~idth of the bearing
shell 297 so as to accept a drilling and milllng template,
By the aid of this template there are made a slot for the tongue
327 and a ~ore for the stud 325. The bearing shell 297 is
first o~ all insexted with the tongue in the appertaining slo~,
and then is "snapped" with the stud 325 in the appertaining
bore. This provides a flrm seating of the shell in the ulna.
The connection is completed by the later ingrowth of bone cells
into the porous bearing shell surface at the contact surfa¢es
of the bone sections.
From the upper edge of the condylar shells 305 and 306
to the lower termination of the externally rounded threads
75 of the shaft 73 there will exist no positive connection
made through bone material between the prosthesis and its bone
support, so that micro relative m~vements of t~e contact surfaces
between the implant and the bone are decisivel~ reduced~ In
correspondence with the various hip joints it is also possible
for the total elbow joint endoprosthesis 290 to he nade of
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. . .
~0758~
metal, whose entire surface is enamelled, The bone screws
315 can also he fully enamelled~
For the purpose of the elbow joint implant, a hin~e ~oint
102 has been described as an example with reference to Figs.
23 ~o 29~ However, in place of t:he illustrated hinge joint
102, it is possible to use for the elbow joint implant other
types of pivot ~oints which have been described above in connection
with the hip joint implant, Also~ while a hip ~oint has been
selected as an example of a body ball joint, and an elbow ~oint
has been selected as an example of a body hinge ~oint suitable
~or the fitting of a prosthesis, it should be noted that the
above disclosed principles are also basically appl~cable to
ali other body joints.
Figs 30-33 illustrate an instrument for inserting the
shaft 73 for the hip joint prostheses illustrated above in
a threaded hole in the thigh b~ne previously prepared, for
example, with a self-centering conical boring tOolq The instrument
may also be used to preciseiy mill the femur for insertion
of the pivot me~ber 107 of these prostheses, and to remove
the shaft 73~
Fig, 30 shows a rotary tool 350 having two tubes 353 and
354 rigidly connected together. The tube 353 carries at its
upper end a key surface 356 and a screw plug 357 threaded
into the tu~e 353. At the lower end o~ the tube 354 there
is secured a conical socket 359 complementary to the cone 79
at the top of shaft 73~
As shown in Fig, 32 a threaded screw 360 passes through
the intexior of the tubes 353 and 354, and is threaded into
the tapped bore 80 in the cone 79 of the shaft 73. By means
of the screw 360 and the complementary conical socket 359,
-27-
~t7S8Sl
the rotary tool 350 can be coupled to the shaft 73 to ~orm
a rigid unit. ~hen the sha~t is being screwed into or out o~
the tapped hole in the thigh bone, the longitudinal axis of
this unit coincides with the axis of the tapped hole. Thus,
the shaft can be screwed in or out without any bending moments,
and undesirecl stresses on the bone are avoided~
A head 363 of the screw 360 bears against a shoulder 365
of the tuhe 353. The screw plug 357 is provicled with a central
bore 367 and its lower sur~ace maintains a certain clearance
from the upper surface of the screw head 363, Through the
bore 367 or the screw plug 357, a hexagon socket key can be
inserted into the hexagon socket o the head 363 for the purpose
of rotating the screw 360. When the screw 360 is rotated back
out of the position shown in Fig. 32, the screw 360 moves
axially upwards relative to the tubes 353 and 354 untll the
upper surface o~ the head 363 bears against the lo~er surface
of the screw plug 357 which forms a stop 370. From this instant
the described relative motion ceases and upon continuin~ the
rotation of the screw 360 the conical socket 359 is withdrawn
from the cone 79. To prevent the screw plug 357 w~rking loose,
it is provided with a left hand thread 371.
With the shaft 73 scre~ed into the thi~h bone 30, when
milling operations are to be carried out upon this bone, a
holder 373 is externally mounted upon the tube 353, as shown
in Figs. 30 to 33, and is clamped in the desired angular position
with reference to the tube 353 by means of a clamp 375 and
clamping screws 377.
In two cantile~ers 379 and 380 of the holder 373 there
are secured two guide ~olts 383 and 384 screwed into the cantilever
379. A carrler 386 is mounted on the guide bolts and ls axially
-28-
displaceable alonq the bolts through a length of feed path
387. Between the carrier 386 and the lower cantilever 379
of the holder 373, a tubular spacin~ member 389 is flttecl
upon the guide bolt 383 to determine the ma~nitude of the feed
path 387, Spacing members 389 of different axial length may
therefore be ~itted for varying the length o~ the feed path
387.
In an aperture 390 (Fig. 30) of the carrier 386 a milling
tool 395 is mounted upon combined axial anfl radial bearings
392 and 393. The milling tool 395 is provided with a continuous
shaft 397, which carries at its lower end a key surface 39g
and a quick change clamping chuck 400, and at its upper encl
a threaded section 402. Upon the threaded section 402 there
are mounted two counteracting fluted nuts 404 and 405 which
are tightened up with respect to the key surface 399 so as
to apply to the bearings 392 and 393 the correct axial stress.
Upon the threaded section 402 there is also applied a union
nut 407 of a flexible shaft 408 driven by a motor, not shown
in the drawing~
In the quick change clamping chuck 400 there is clamped
a combination milling tool 410, comprising an end miller 412
and a cylindrical milling cutter 413 projecting from the base
of the end milling cutter 412.
At the beginning of the milling operation the milling
tool 395 is in a starting position, in which the carrier 386
is supported with its lower pro~ecting arm 415 (Fig. 30) bearing
against the lower side of the upper cantilever 380 of the holder
373, The flexible shaft 408 is then driven so that the combin-
ation milling tool 410 rotates at the desired speefl~, The
milling tool 395 is then ~ed by hand downwardly along the two
--29--
:
~07~3~35~
guide bolts 383 and 38~, whereby initially the cylindrical
millin~ tool 413 ~ills out a hole inside the thigh bone 30,
whereafter the end millin~ tool 412 comes more and more into
en~a~ement with the thigh kone 30 until, in the end position
shown in Fig. 30 the seatinq surface 50 containing spongiose
and cortical tis~ue is completed for the endoprosthesis~ The
plane of the seating surface 50 is thus precisely clefined with
reference to the lon~itudinal axis of the shaft 73, so that
during the entire further course of the operation any further
fitting of the remaining part of the prosthesis is unnecessary.
This method shortens the operation time, protects the patient
and affords a precisely defined seating for the endoprosthesis.
The angle between the axis of the rotary tool and the
milling tool can be suited to all kinds of anatomical requiremen~s
by suitable design of the holder 373, As was mentioned above,
this adaptation to anatomical requirements may be affected
~y insertin~ spacing members 389 of varying length between
the carrier 386 and the holder 373. Thus, the depth of the
milling may he reliably limited~ -
Fig, 34 shows a modified form of shaft 73 with a thread
430 of sawtooth shape, which tapers conically downwards towards
its distal end to suit the shape of the inner wall of the cortical
tissue of the receiving bone, instead of the symmetrical external
round threa~ shown in the previous figures. The steep flanks
433 of the sawtooth thread 430 point towards the p~oximal end
of the shaft 73 and are directed normal to the longitudinal
axis of the shaft 73. Since the flanks 433 are normal to the
axis of the shaft~ and to the tractive ~orce Fz~cos~ that
-30-
. .
~17S~S~
acts upwardly along the axis o the sha~t, the sawtooth thread
eliminates radial forces on the bone resulting from this tractive
force, which could exert a non-physiological bursting effect
on the bone.
The crests 435 of the teeth and the valleys A37 of the
teeth are in each case rounded. This ensures that the bone
which is situated opposite to the sawtooth thread 430 after
insertion thereof is carefully treated and facilitates the
application of an enamel coating 440, shown in chain and dotted
lines in Fig. 34, over the entire shaft 75 with the exception
of the threaded bore 80. A bore 443, which is also enamelled,
is made in the bottom of the shaft 73, into which a deposit
is inserted, for example an antibotic, be~ore the fitting of
the shaf~ 73, For promoting the ingrowth of the surrounding
bone tissue into the shaft 73, the enamel coating can be exter-
nally roughened~
This sawtooth thread can also be designed to be sel~-cutting
by locally interrupting the thread in the axial direction and
pro~iding it with cutting edges.
:, ~
.,
-31-
:
