Note: Descriptions are shown in the official language in which they were submitted.
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IMPLANTABLE FABRIC POUC~I FOR MAMMARY PRaIHESIS
lhe present invention relates to mammary protheseS ard in
particu]ar to an implantable fabric pouch for encapsulating such
mammary protheses.
For a n~ber of years surgeons have augmented and changed
the shape of womens breasts by the introduction of mammary
protheses_mt4 the breast area. Typically these mammary prothesés
have comprised a closed silicone sac filled with gel or saline
solution.
Most patients experience satisfactory mammary augmentation
immediately following the implantation procedure wqth the breasts
simulating natural breasts in contour, appearance, feel
and dynamics~ However during a relatively short period
after the implantation procedure, usually about six months,
many patients experience a contracture of the tissue surrounding
the mammary FrothPsis causing it to assume a spherical
shape and other unnatural attributes. In addition to the upper
surface of the breast tending to display unnatural convexity
the breast may also become tight and not freely moveable.
This problem wqth mammary prot~eses has been appreciated
for some years and for example U.S. patent 3934274 seeks to
overcome the problem by use of a double ~IEn prothesis having
an outer and an inner chamber,the outer chamber of which may be
evacuated once tissue contracture is experienced thereby
relie~ing the forces exerted by the tissue and alleviating the
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unnatural tendency of the prothesis to adopt spherical shape.
To date however a satisfactory longterm solution to the
problem of tissue contracture about a mammary implant has not
been found and this may perhaps be due to the lack of
u~derstanding of the reasons for such tissue contracture.
It is an object of the present invention to reduce the
incidence of tissue contracture around a mammary implant.
Accordingly the present invention disclosesan irplantab3e Pl~h to
contain a mammary ~prothesis formed from a net-like material
fabricated from a bio-compatible non-biodegradable yarn; the pouch being
so constructed that the surface intended to form the anterior layer in
use is relatively inextensible alon~ the cephalic-caudal axis as
~ compared with at least one axis non-Parallel thereto.
The present invention additionally discloses a method
of performing a mammary implant operation comprised of the
steps of:
a) Selecting a pouch in accordance with the present invention
having a diameter of between 0 and 40 per cent greater
than the equilibrium diameter of the pro~es-,s which it
is to contain;
b) Placing the F~t'nesis within the pouch;
c) Locating the pouch and pr~t~esis in the breast such that
the antericr layer of the pouch is relatively inexte:-sible
alon~ the cephalic-caudal axis.
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One embodiment of the present invention will now be
described wqth reference to the acco~panying drawqngs in which:
Figure 1 is a side elevation of a breast with a mammary
Fro ~ sis in a pouch in accordance with the present invention
in vertical section;
Figure 2 is a side elevation in vertical section along
the diameter of a mammary FXo ~ sis and pouch in accordance
with the present invention in an equilibrium position;
Figure 3 is a side elevation in vertical section along
the diameter of a mammary Fro~E~s and pouch in accordance
with the present invention in a fiatten~d.non-equilibrium
state;
Fi.gure 4 is an anteriorview of a mammary Fxo ~ sis inside
~ a pouch in accordance with the present invention as ît would
appear with the patient standing;
Figure 5 is a perspect;ve view of a pouch in accordance
: with the present invention which has been lifted to show
part of the posteriorlayer~
Figure 1 depicts a pouch l in accordance with the present
: ~0 inventi~n encapsulating a silicone mammary F~o~E~is 2 filled ~qth
gel 3. Breast tissue 4 is shown around the anteri.orsurface of
~he pouch. It will be noted that the mammary ~rnthP~i.s is a loose
fit inside the pouch in order that the Fro~Y~is may adopt a natural
teardrop shape there being excess space inside the pouch at 5.
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It has been found desirable that the pouch be slightly
greater in diameter than theiFr~th~sis and in the example depicted
at figure 2 the pouch diameter exceeds the diameter of the
Fro~sis in its equilibrium position by approximately 20 per cent.
If the Fro~is of figure 2 where 10 centimetres in diameter
there would consequently ~e a clearance of approximately one
centimetre at areas 6 Hni7.
This excess space inside the pouch allows the silicone prothesis to
spread or expand or balloon to a limited extent when deformed
as depicted in figure 3 until is occupies the entire lumen of
the pouch. This ensures that the breast will not feel overly
tight and will maintain soft and flexible to the touch.
- Figures 4 and 5 de*ict the orientation of the yarns
comprising the pouch with respect to the mammary pro~Y~is.
As may best be viewed from figure 4 the fabric of the
pouch has st~s 8 running along the cephalic-caudal axis and
according to the present invention these strands are
relatively inextensible. The mammary implarlt 2 may be
seen within the pouch, the upper extremity of ~he Fro~sis being the
semi-circle 9. This view indicates the orientation of the
Fnnth~sis with respect to the pouch with the patient in a stahding
position.The pLnt~eSi~s is naturally maintained in the lower part
o the pouch under the influence of gravity.
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'rhe tenm inextensible where used throughout this
specification refers to the extensibility of the fabric of a
pouch along a certain axis but calculated after the pouch has
been implanted in the body for a period of time adequate to
achieve substantial ingrowth of body tissue through the fabric.
It is necessaryto define the extensiblity of the fabric in this
manner for the following reason.
The embo~iments depicted herein with reference to figures 4
and 5 depict inextensible yarn running parallel to the axes
along which the fabric of the pouch is intended to be inextensible.
- Consequently the extensibility of the fabric in this example
corresponds exactly to the extensibility of the yarn from
which the fabric is manufactured. This relationship between
the extensibility of the fabric and the yarn along these axes
is of course the same both before and after the pouch is implanted
in a patient.
Pouches have however been constT~cted from fabrics in
which the yarn does not run parallei to the cephalic-caudal axis
or other axes intended to carry stress but such pouches nevertheless
achieve inextensibility along the said axes once implanted and
invaded by body tissue. For example the fa~ric can be a tulle net
which is supplied pre-stressed in one direction.
This will produce a diamond pattern between the fabric yarns with
the long axis of the diamonds aligned in the direction of stress.
Aft~r implantation in the body and as the diamonds fill with tissue
the fabric will stabilise and will be far less extensible along the
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axis corresponding to the long axes of the diamond pattern in ~he
abric than along the short axes of the diamonds. The fabric is pre-
stressed in the sense that the cross over points for the fabric yarns
are fixed such that diamond like pattern in the fabric is of a
configuration which gives the desired resistance to distensîon
along certain axes.
It has been found that if the pouch is relatively inextensible
on the anterior side along the cephalic-caudal axis that contracture
of the tissue surrounding the implant is reduced hence preventing
the prothesis adopting a spherical unnatural shapeO Ihe following
theory is advanced as the reason why a pouch in accordance with the
present invention prevents such undesirable contracture although it
should be understood that the invention is not restricted to such theory.
~le applicant's investiga~ions indicate that the collagen bundles
fonmingtheEibrous tissue capsules which cause tightening around breast
protheses develop in response to stress within the tissue. In such
casesthe preclominant forces on the tissue adjacent to the anterior
side of the prothesis are along the cephalic-caudal axis and are caused
principally by the influence of gravity on the prothesis with the
patient in the standing position. There may also be oblique stresses
through tissue on the posterior side o the breast prothesis due to thé
influence of gravity on the prothesis plus the additional influence of
the transverse pull of the pectoral muscles. The applicant's
mvestigations furthermore indicate that fibrous tissue is not amorphous
and featureless but has a definable structure~ In the case of a
fibrous tissue capsule surrounding a conventional breast
prothesis the predominarlt feat.ure of the strllcture is
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collagen b~mdles running parallel to the lines of stress. These
collagen bundles tend to act as ligaments taking up slack and
hence causing undesirable contracture about a mamnary implant.
It has previously been thought amongst surgeons that fabrics
which allow fibr~,-cellular ingrowth also cause increased fibrous
tissue formation which would tend to cause undesirable contracture
in the case of a mammary Fnot~esis. Contrary to this belief the
applicant believes that the introduction of a fabric which gives
support by beinginextensible in a direction parallel to the
predominant lines of stress within the tissue will tend to reduce
the forrnation of fibrous bundles in such direction in response
to such stress. Indeed if the fabric is relatively extensible in
a direction transverse to the predominant lines of stress then
the relative lack of support in such dirèction may cause the
body tissue to form fibrous bundles along such transverse direction.
The combined effect of such extensible and relatively ine~tensible feat ~ s
of a fabric forming a pouch in accordance with the present
invention encourage the formation of body tissue more akin to
the natural denmis rather than the uni-directional tendon like
collagen bundles which the applicant believes are responsible
for undesirable capsule contracture about the implant.
Turning now to figure 4 it rnay be seen that in addition to the
cephalic~xl~l axis inextensible yarn cornprising the fabric
there are additionally oblique yarns 10 within the fabric which
may be relatively extensible. It has been found that a tulle of poly-
ester yarn (the yarn having a diameter between .01 and .5
; mîllimetres) is appropriate. The ideal order of magnitude
for the diameter of th openings 11 in the fabric is between
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one and two millimetres s~lch fabric being not unlike mosquito
netting or bridal veil material although it is considered that
openings in ~he order of .001 millimetres to 5 millimetres would
still give advantageous results.
In the embodiment above described polyester yarn of four
strancls has been considered appropriate in order to achieve the
desired fle~ability although if infection occurs after implantation
it may be ~.ore di~ficult to rid such multifilament(as opposed to
monofilament) yarn of the infection. Nylon or '~oly~x~ylene may also
, 10 be useful,even in monofilament form.
; It is envisaged that the yarn should be non-biodegradable
or at least longterm biodegradable and the term "non-biodegradable"
- where used herein should be contemplated to mean non-biodegradable
' 'within'twelve''months.~'At''present'however it'is'consider'ed that'' '~ '~~'' `'
ideally the material utilised should be non-biodegradable for
five years or more.
Figure 5 shows the o~n~inn of the yarn comprising the
pouch material on the posteriorside and it will be noted that
I there are strands of yarn l2 running in an oblique direction.
`' ¦ 20 These are intended to be inextensible yarns aligned parallel
I to the stresses,caused by the pectoral muscles. The strength of
the pectoral muscles may vary from patient to patient and
consequently a surgeon may wish to remove tissue and observe
fibre orientation in order that a pouch with inextensible
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properties in the correct direction may be chosen. In any event
a pouch should always be selected to such that it is relatively in-
extensible parallel to the lines of stress along the tissue
of a particular patient.
Figure 5 further depicts openin~ 13 to facilitate the
insertion of the mammary prothesis.
It may be appreciated therefore that a pouch in accordance
with the present invention, once invaded by tissue will help
to impart support to t~e fib~s tiss~e along ~e maJor anterior cephalic-caudal
stress lines and furthermore provides a template to encourage fcrraticn of
a collagen network rather than collagen arranged in parallel
bundles akin to aponeuroticl~nents which tend to shorten and
- take up slack.
The term"equilibrium diameter"of a maTmary implant as used
herein shall mean the diameter of the implant when placed in
such a position as it would adopt with t'ne patient lying on
her back. In the case of a double lumen mammary prothesis the
diameter is that which the implant is intended to adopt after
rupture ot the outer compartment.
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