Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Intramedullarv Nail. especiallv Tibial Intramedullary Nail
The invention involves an intramedullary nail, especially a tibial
intramedullary nail, with
pierces extending across the nail for the accommodation of locking screws in
the
proximal and distal areas of the intramedullary nail.
Intramedullary nails, and especially tibial nail systems mostly consist of a
tibial nail made
of titanium. Such intramedullary nails are used in particular with transversal
fractures,
oblique, and spiral fractures, segment fractures, comminuted fractures, open
fractures,
and especially fractures with bone loss, or pathological fractures, as well.
Additional uses relate to the correction of leg length differences,
reconstructions after
tumor sections, pseudo-arthrosis, metaphysis, and epihysis fractures. Known
intramedullary nails contain possibilities for accommodating locks in the
proximal and
distal areas, whereby two locking screws each are usually arranged in the
proximal and
distal areas for a complete lock. During an application, the suitable nail
length is first
determined, and a proximal target device is then attached on a nail of proper
length with
the aid of an adapter. A sliding hammer is slid over a driving rod, and
screwed onto the
adapter. Then the nail is inserted into the entry cavity of the proximal
marrow area by
hand, and driven by blows to the hammer. In case of a tibial nail, the distal
positioning
should ideally be 1 to 2 cm above the tibiatalar system.
The adapter is first tightened for the proximal locking, and the proximal
locking screw
position is determined by a double guiding cannula system. Drilling sheaths
are then
placed on the corticalis by a stab incision, and the respective drilling is
performed. When
the rear of the corticalis has been noticeably drilled all the way through,
the correct
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position is checked, and the required screw length is read on the drill scale.
After
removing the inner drilling sheath, an appropriate self screwing corticalis
screw can be
fastened. The respective drilling for distal locks is usually performed free-
handedly. For a
complete lock in the proximal area it is particularly beneficial if the
drilling holes in the
nail for the accommodation of the locking screw are arranged at intersecting
axles.
The known nails, and in particular the known tibial nails, are not suitable
for all
situations, especially not relating to indications of a metaphysic and
epiphysis fracture.
Bone fragments can only be positioned correctly with the locking screws
arranged at the
distal end, which are also located in this area so that especially small bone
fragments at
the bone end, the fissure of which only extends across a small axial length of
the bone,
cannot be seized by such devices. The invention aims to expand the universal
usability of
an intramedullary nail, and especially of a tibial intramedullary nail to
other cases in
which a successful stabilization of bone fractures may not necessary be
possible after
shearing fractures of the peripheral tibia, and which are unable to improve
the healing
success with regard to epiphysis fractures in particular.
As a solution to this task, the inventive intramedullary nail essentially
consists of the axle
of a pierce at its distal area that extends at an angle to the sheath axle in
the distal area.
Due to the fact that a pierce at its distal area extends to the sheath axle at
the distal area, it
is possible to arrange a locking screw, or possibly a clamping screw in this
area in such a
way that even smaller bone fragments in the epiphysis area are positioned
safely, and can
be maintained in their correct positions. The angle of this pierce at the
distal area to the
respective sheath screw enables screws to be positioned with an angle pointed
back and
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down, and to seize even small fragments in this way. Known tibial nail designs
have
several sections with axles different from each other, and angled towards each
other.
Designs are known in particular, in which the axles of the proximal and the
distal sections
of the intramedullary nail, which contain the pierces for the locking screws,
are bent, or
arranged at an angle, respectively, in the same direction to the axle of the
center section.
Here it is also important that the axle of at least one pierce extends at an
angle in the
distal area to the sheath axle in the distal area. The pierces in the distal
area in
conventional tibial nails are usually arranged in such a way that they are
still oriented
orthogonally to the axle in the center area despite of their angle to the axle
of the nail in
the distal area relative to the axle of the nail.
A benefit of the inventive design is that the angle of the axle of the pierce
is between 65
and 80°, preferably approximately 75°, towards the rear, which
ensures that even small
bone fragments in the epiphysis area can be seized. The ability to seize such
small
fragments is further improved by the arrangement of the pierce with an angled
axle in
close vicinity of the distal end of the intramedullary nail.
An additional improvement of the inventive intramedullary nail is achieved by
the fact
that at the proximal end in addition to at least two pierces with intersecting
axles, at least
one additional distally arranged pierce is intended as an elongated hole with
a longer axle
of the pierce extending in the direction of the axle of the intramedullary
nail. Such an
additional pierce designed as an elongated hole serves to stabilize the
dynamics in order
to avoid possible pseudo-arthrosis. In addition to the rotational stability
achieved by the
two other drill holes for the insertion of the locking screws, this also
enables axial
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movement, and micro movements are allowed by this stabilization of the
dynamics,
which encourage bone growth.
The rotational stability can be achieved by this in a known method, in that at
least two of
the proximal pierces with intersecting axles are locked together by locking
screws,
whereby the proximal end of the tibial nail can be designed at an angle for
the protection
and decrease of irritations of the partellar tendon.
The pierce arranged at the distal end, and angled toward the rear, also
enables fixation of
these bone fragments with shearing fractures of the peripheral tibia, in
particular. A
particularly beneficial simplification in the handling can be achieved by
designing the
inside width of all pierces for locking screws with the same diameter. In
conventional
tibial intramedullary nail systems, screws with a lesser diameter in the
distal area than in
the proximal area are used.
In order to ensure that such locking screws guarantee the required forces, and
especially
the required rotational stability and the distal lock at the lowest outer
diameter, the design
is beneficial such that the locking screws in their center area are designed
as a thread-less
bolt section with a diameter corresponding to the inside width of the pierces.
Such
locking screws designed as thread-less bolt sections in their center area
possess a higher
bending strength, and an increased force absorption of forces applied in the
direction
across the axle of the screw, than screws with continuous threads, whereby the
lock is
successful when the diameter of the thread-less bolt section essentially
corresponds to the
inside width of the pierces.
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In order to also clamp small bone fragments in shearing fractures of the
peripheral tibia
into the desired position, the design is beneficial in such way that the screw
for the pierce
angled toward the axle of the distal section is designed as a clamping screw,
whereby
such a clamping screw is characterized by two thread sections with different
thread
angles.
The invention is described in more detail in the example schematically
illustrated in the
drawing below. Figure 1 shows a side view of the inventive tibial nail, figure
2 shows a
section through the distal end area of the tibial nail according to figure l,
figure 3 shows a
view of a locking or clamping screw, and figure 4 shows the view in direction
of the
arrow IV of the locking or clamping screw in figure 3.
In figure 1 a tibial intramedullary nail 1 is illustrated, the axle of which
is identified as 2
in a semicolon line. The axle of the tibial intramedullary nail 1 is designed
as a multiple
dropped axle, and is angled in the direction of the proximal end 3, as well as
in the
direction of the distal end 4 equally as to axle 2 in the center area of the
tibial
intramedullary nail.
The proximal end has intersecting drill holes 5 and 6 for the rotational lock.
An elongated
hole 7 is additionally intended at the proximal end area, over which an
additional locking
screw can be inserted, whereby an axial movement of the tibial nail 1, and
therefore a
dynamic movement is enabled due to the design of the pierce as an elongated
hole 7.
The distal end 4, also has two drill holes 8 and 9 with a drill axle
essentially extending
orthogonally to the axle 2 for the accommodation of the locking screws. Item
10 in
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figure 1 insinuates a drill hole at the distal end area which is angled to the
rear, and which
is clearly visible in the sectional view in figure 2.
In figure 2 this drill hole 10 is arranged at an angle of approximately
70° towards the axle
11 of the distal area 4 of the tibial nail so that there is a total angle to
the axle 2 at the
center area of the tibial nail of approximately 65°. With the aid of
these drill holes, or
pierces 5, 6, 7, 8, 9, and 10, respectively, conventional locking screws or
clamping
screws can now be inserted, in order to ensure the secure anchoring of the
tibial nail, and
possibly also to firmly affix fragments in this way. A clamping, or locking
screw suitable
for the use of such a tibial nail according to figures 1 and 2 is illustrated
in figures 3 and
4.
Figure 3 shows a locking screw 12, which has a first thread section 14, a
center thread-
less bolt section 15, and a final thread section 16 subsequent to a thread
head 13. A
cutting head 17 is intended at the free end of the locking screw subsequent to
the thread
16, for which, particularly in figure 4, clearance areas 18 are designed for
the transport of
the cut material, in order to ease the insertion of the screw into the bone
fragment, or into
the corticalis.
In this example, the center section 15 of the locking screw is of a thread-
less design, and
has an outer diameter a, which essentially corresponds to the inner cross
section of the
pierce of the tibial intramedullary nail. In order to enable the insertion of
the locking
screws through the pierces, the end thread is designed with an outer diameter
equal to this
diameter a of the thread-less area in the center part at a maximum, whereby
the fixed
attachment is ensured in the bone at the side opposite of the free end by the
respective
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larger diameter thread 14. When the locking screw 12 is to be inserted as a
clamping
screw, the thread 15 must be designed at a lower angle than the thread 16 so
that a
tightening of the bone fragments in the direction of the center, thread-less
area 1 S of the
screw 12 occurs when it is inserted.
