U.S. patent application number 15/652319 was filed with the patent office on 2017-12-28 for surgical screw and method of performing ligament reconstruction using said screw.
This patent application is currently assigned to United States of America as Represented by the Secretary of the Navy. The applicant listed for this patent is Colin Gregersen, Matthew T. Provencher, Daniel J. Solomon. Invention is credited to Colin Gregersen, Matthew T. Provencher, Daniel J. Solomon.
Application Number | 20170367745 15/652319 |
Document ID | / |
Family ID | 43589044 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170367745 |
Kind Code |
A1 |
Solomon; Daniel J. ; et
al. |
December 28, 2017 |
SURGICAL SCREW AND METHOD OF PERFORMING LIGAMENT RECONSTRUCTION
USING SAID SCREW
Abstract
This invention relates to a system and a method for affixing
soft tissue to bones. The system for fixing soft tissue within a
bone tunnel comprising a first fixation member having a proximal
end and a distal end and a bore extending from said proximal end to
said distal end, said first fixation member is adapted for
insertion against a first portion of a soft tissue positioned
within a bone tunnel, a second portion of said soft tissue emerging
from said bone tunnel; a second fixation member adapted to engage
said bore of said first fixation member, having means for
restraining disengagement therewith and a proximal end; and a third
fixation member adapted to engage said second portion of said soft
tissue, having means for coupling onto said proximal end of said
second fixation member and restraining disengagement therewith.
Inventors: |
Solomon; Daniel J.;
(Tiburon, CA) ; Provencher; Matthew T.; (Coronado,
CA) ; Gregersen; Colin; (Salt Lake City, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Solomon; Daniel J.
Provencher; Matthew T.
Gregersen; Colin |
Tiburon
Coronado
Salt Lake City |
CA
CA
UT |
US
US
US |
|
|
Assignee: |
United States of America as
Represented by the Secretary of the Navy
Silver Spring
MD
|
Family ID: |
43589044 |
Appl. No.: |
15/652319 |
Filed: |
July 18, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12855071 |
Aug 12, 2010 |
9737350 |
|
|
15652319 |
|
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61233303 |
Aug 12, 2009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 17/8605 20130101;
A61F 2002/0858 20130101; A61B 17/864 20130101; A61F 2002/0835
20130101; A61B 17/8695 20130101; A61B 17/8685 20130101; A61F
2002/0888 20130101; A61F 2/0811 20130101 |
International
Class: |
A61B 17/86 20060101
A61B017/86; A61F 2/08 20060101 A61F002/08 |
Claims
1) A method for affixing a piece of soft tissue within a bone
tunnel comprising the steps of: a. positioning a piece of soft
tissue inside the bone tunnel such that a portion thereof resides
within the bone tunnel and a second portion of said soft tissue
reside outside the bone tunnel; b. positioning a first fixation
member upon the piece of soft tissue within the bone tunnel; c.
coupling a third fixation member onto distal post portion of a
second fixation member, wherein a proximal head portion of said
second fixation ember prevents disengagement of the third fixation
member from second fixation member; d. pressing a third fixation
member onto said second portion of said soft tissue against bone
surface outside said bone tunnel; and e. restraining disengagement
between the first and the third fixation members by engaging a
second fixation member with the first fixation member.
2) A system for fixing soft tissue within a bone tunnel comprising:
a. a screw-type first fixation member having a proximal end and a
distal end and a bore extending from said proximal end to said
distal end, said first fixation member is adapted to compress a
first portion of a soft tissue positioned within a bone tunnel
against the inside surface of said bone tunnel, a second portion of
said soft tissue emerging from said bone tunnel; and b. a
screw-type second fixation member with a solid distal post adapted
to advance inside said bore of said first fixation member from the
proximal end to distal end, having i. means for restraining
disengagement therewith; and ii. a proximal end with a screw driver
socket; wherein the distal post of said second fixation member is
adapted to uniformly compress said second portion of said soft
tissue against said bone when fully engaged with said first
fixation member.
Description
CROSS-REFERENCE OF RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 12/855,071, filed Aug. 12, 2010, which claims
priority to provisional application 61/233,303 filed Aug. 12,
2009.
TECHNICAL FIELD
[0002] This invention relates to a surgical screw and a method for
anchoring a tendon or ligament implant to bones. More specifically,
this invention relates to the fixation of a ligament using said
surgical screw in reconstruction surgery.
BACKGROUND
[0003] When a ligament becomes detached from a bone, surgery
usually is required to reconstruct the ligament. Often, a
substitute ligament or graft is secured into bone tunnels to
facilitate the incorporation of the ligament and permanent
attachment.
[0004] An example of this type of surgery is the reconstruction of
torn knee ligaments, particularly the anterior cruciate ligament
(ACL) and the posterior cruciate ligament (PCL). Surgical
reconstruction is the standard of care after cruciate ligament
injuries. Tears of knee ligaments can render the knee unstable
leading to recurrent episodes of giving way. Reconstruction of
these ligaments by using tendon grafts can result in restoration of
knee stability and function. To perform a ligament reconstruction,
remnants of the torn ligament are removed. Next, bone tunnels are
drilled in the femur and tibia bones at the attachment site for the
ligament to be reconstructed. A tissue graft is then spanned
between the tunnels with the graft ends buried in the bone tunnels.
Finally, the graft is tensioned and attached securely to the bone
tunnels. The graft then undergoes a slow process of healing, which
creates a firm attachment of the graft to bone, and establishes a
new blood supply for the graft. Over a period of 6-18 months, the
graft remodels to become living tissue, which can resist abnormal
motions of the knee that would result in giving way.
[0005] The fixation of the graft to the bones is of paramount
importance in this type of surgeries as any loosening of the graft
can result in failure to restore knee stability. Furthermore, early
knee motion and exercises which help the patient to recover quickly
from surgery can place significant stress on the graft fixation.
Adequate stability of graft fixation must be achieved to allow the
patient to safely benefit from the effects of early
rehabilitation.
[0006] Several types of tissue grafts are available for use in knee
ligament reconstruction. Each type of graft has certain advantages
and disadvantages. The use of autologous hamstring tendons in knee
ligament reconstruction has grown in popularity because this graft
causes very minimal morbidity to harvest, does not disrupt the
extensor mechanism, creates a very strong soft tissue graft and
does not expose a patient to the risks of using cadaver tissue.
However, fixation of hamstring grafts to the proximal tibial bone
tunnel remains a weak link in successful use of the hamstring
tendons. The proximal tibia often contains soft bone providing a
weak substrate for implant fixation. A second problem is that the
tibia is only covered by a thin layer of soft tissue and a
prominent implant can often be palpated beneath the skin causing
pain. Other types of soft tissue grafts, both of autologous and
cadaver tissue, including achilles tendon, quadriceps tendon,
fascia lata and palmaris longus tendon are used in certain
situations to reconstruct the ligaments. Again the weak link of
fixation to the bone tunnel remains a problem.
[0007] A number of devices are known in the prior art for fixation
of soft tissue grafts to bones. However, as it will become evident,
each of these devices possesses problems that limit their
successful use.
[0008] The first class of devices for soft tissue to bone fixation
is suture anchor, such as the anchor illustrated by U.S. Pat. No.
5,472,452. In his description, Trott discloses a bone anchor which
can be placed in a small bone hole, and then serves as the
attachment site for soft tissues which are sutured to the bone.
Similar type devices are further disclosed by Lee and Sander in
U.S. Pat. No. 5,480,403 and by Hayhurst in U.S. Pat. No. 5,601,557.
A variation on this device is disclosed by Ross, Snyder, Marchand
in U.S. Pat. No. 5,246,441 where a tack is used to secure soft
tissues against the bone as it is driven into a small bone hole.
These devices do not provide sufficient holding strength suitable
for fixation of knee ligament grafts.
[0009] A second class of fixation devices is illustrated by U.S.
Pat. Nos. 4,454,875 and 4,570,623 where metal staples with spikes
on the underside are seen securing ligament tissue to bone. These
devices are undesirable in that they have less than ideal fixation
strength. The devices are often difficult to use and reposition may
cause damage to the bone. They may also be palpable beneath the
skin causing pain and necessitating a second operation for their
removal.
[0010] A third class of fixation device is the interference screw.
An example of this type of implant is the RCI.RTM. screw marketed
by Smith-Nephew Endoscopy Corp (Boston, Mass.). The RCI.RTM. screw
has blunt threads to avoid damage to a soft tissue graft. This
screw is threaded into a bone tunnel alongside of the strands of a
soft tissue graft. The screw holds the graft in place by
compressing the soft tissue graft against the sides of the bone
tunnel. Unfortunately, interference screws have poor fixation
strength against soft tissue grafts.
[0011] A forth class of fixation device uses a screw-washer
combination design. This device consists of a standard bone screw
and a washer, which is placed distal to the bone tunnel. The screw
may be tightened down over a soft tissue graft capturing it against
the tibia or can act as an anchor around which to tie sutures. U.S.
Pat. No. 6,123,711 by Winters et al. discloses such a fixation
system with the screw-washer design. However, the screw-washer
assembly is often prominent, causing pain and requiring a second
operation for implant removal. The tack described by Winters et al.
is only inserted into the top portion of the outside screw,
resulting in weak graft fixation leaving concerns of graft
slippage. In addition, the tack is retained onto the screw by the
barb head of the tack, surgeons are not able to adjust the
tightness of compression exerted by the washer.
[0012] A fifth class of fixation device is a button over which
sutures may be tied. Fixation strength of this type of device is
limited by the strength of the sutures. In some cases the button
may be too prominent and requires post-surgery removal.
[0013] Other implants such as the Endobutton.RTM. of Smith-Nephew
Endoscopy Corp. (Boston, Mass.) and various types of threaded pins
over which the graft is wrapped are only applicable to fixation of
the tendon graft on the femoral side of an ACL reconstruction and
thus do not provide a solution to the weak link on the tibial
side.
[0014] The disadvantages of the available methods of soft tissue
fixation can be summarized as: [0015] A. poor fixation strength
allowing slippage of the graft during early rehabilitation; [0016]
B. limited bone to tendon interface for healing; [0017] C.
prominence of the implant which may cause pain; [0018] D. difficult
to adjust fixation; [0019] E. requirement of second surgery for
implant removal; [0020] F. damage to bone by implant; [0021] G.
implants not amenable to tibia sided graft fixation.
SUMMARY OF INVENTION
[0022] The present invention provides a system and method for
affixing soft tissue to bones. It further provides a system that
has an element for securing the soft tissue piece within a bone
tunnel and another element for securing a second portion of the
soft tissue against the outside of the bone tunnel.
[0023] An embodiment of the system is for fixing soft tissue within
a bone tunnel, which comprising a first fixation member having a
proximal end and a distal end and a bore. The first fixation member
is adapted for insertion upon a first portion of soft tissue
positioned within a bone tunnel. A second portion of the soft
tissue is positioned to emerge from the bone tunnel. The proximal
end of the bore may be pre-threaded for mating with a second
fixation member. The second fixation member may include a distal
post portion threaded for mating with the proximal portion of the
first fixation member. The second fixation member may be further
adapted to be self-tapping, which creates threads inside the bore
of the first fixation member as it is rationally driving into the
first fixation member. A third fixation member may be adapted to
engage said second portion of said soft tissue, and having means
for coupling onto said proximal end of said second fixation member,
and thus restraining it from disengagement from the first fixation
member.
[0024] In a subembodiment, the first fixation member is a screw
type device, having blunt thread adapted to be inserted into the
bone tunnel, pressing the graft inside against the surface of the
tunnel. The second fixation member is a self-tapping screw which
advances when turned, while creating its own threads inside the
bore of the first fixation member. As the second fixation member
advances inside the bore of the first fixation member, uniform
expansion is created along the length of the first fixation member,
further compressed the graft inside the bone tunnel against the
internal wall of the tunnel. The third fixation member may be a
washer, which may contain barbs underneath, and fully engage the
portion of soft tissue that is hanging outside the bone tunnel to
the bone surface.
[0025] In another subembodiment, the first fixation member may
contain a recess to allow the washer to seat flush with the top of
the outer screw. The washer is also indented to allow the inert
screw to seat flush inside the washer. Thus, reducing the size of
the fixation member extending outside the bone tunnel, and reducing
patient discomfort.
DETAINED DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1a shows a side view of an embodiment of the first
fixation member.
[0027] FIG. 1b shows a cross-sectional view of an embodiment of the
first fixation member.
[0028] FIG. 1c shows a top view of the proximal end of an
embodiment of the first fixation member.
[0029] FIG. 2a shows a side view of an embodiment of the second
fixation member.
[0030] FIG. 2b shows a cross-sectional view of an embodiment of the
second fixation member.
[0031] FIG. 2c shows a top view of the proximal end of an
embodiment of the second fixation member.
[0032] FIG. 3a shows an embodiment of the third fixation
member.
[0033] FIG. 3b shows an embodiment of the third fixation
member.
[0034] FIG. 3c shows an embodiment of the third fixation
member.
[0035] FIG. 4 shows a cross-sectional view of an embodiment of an
assembled fixation device.
[0036] FIG. 5 shows the cross-sectional view of the assembled
fixation device stabilizing a soft tissue graft within a bone
tunnel.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The embodiments of the invention, both as to the device and
method of operation, will be better understood from the following
description used in conjunction with the accompanying drawing. It
is to be expressly understood that the drawing is for the purpose
of illustration and description, and is not intended as a
definition that limits the invention.
[0038] An embodiment of the present invention is a system for
fixing soft tissue within a bone tunnel, comprising: a first
fixation member having a bore extending from its proximal end to
about its distal end and adapted for insertion against a portion of
a soft tissue positioned within a bone tunnel, a second fixation
member adapted to engage the bore of the first fixation member, and
having means for restraining disengagement therewith, and a third
fixation member coupled onto the second fixation member and adapted
to engage a portion of the same soft tissue, which emerging from
said bone tunnel. The fixation members may be made of biocompatible
metal or metal alloys such as titanium. Alternatively, one or all
three fixation member may be made of a biodegradable material to
eliminate the need of future removal, such as the materials
described in U.S. Pat. No. 4,356,572, U.S. Pat. No. 5,522,895, U.S.
Pat. No. 4,655,777 and U.S. Pat. No. 5,085,861.
[0039] Biodegradable. The term "biodegradable" is intended for the
purposes of the present invention, to include bioresorbable,
bioabsorbable, biodegradable, and bioerodible materials that are
well known to those of ordinary skill in the art and are described
in Biomaterials Science--An Introduction to Materials in Medicine,
edited by Ratner, B. D. et al., Academic Press, (1996), and include
for example, the following materials: chitosan; isomorphic
ploy(hexamethylene co-trans-1,4-cyclohexane dimethylene oxalates);
poly(glycolic acid); copolymers of poly(glycolic acid) and
poly(lactic acid); polydioxanone; poly(latic acid); PLLA with
Tricalcium phosphate, or PEEK, or polymers having a back-bone
structure selected from the group consisting of: polyanhydrides,
polyphophazenes, polyphosphonates, polyamides, and
polyiminocarbonates; polyhydroxybutyrate; polyhydroxyvalerate;
copolymers of polyhydroxybutyrate and polyhydroxylerate;
polycaprolactone; polydioxanone; poly(.gamma.-ethyl glutamate);
poly(DTH iminocarbonate); poly(Bisphenol A iminocarbonate);
poly(DETOSU-1,6 HD-t-CDM ortho ester); poly(Sebacic
acid-hexadecandioic acid anhydride); poly(ortho esters); poly(amino
acids); and PLOA. Such polymers may optionally include one or more
pharmaceutically active agents for controlled release applications,
such agents including for example: osteoinductive factors including
for example bone morphogenic protein, antiobiotics, and
anti-inflammatory agents.
[0040] Biocompatible. By the term "biocompatible" is intended for
the purposes of the present invention, any material which when
implanted in a patient does not provoke an adverse response in the
patient. A suitable biocompatible material when introduced into a
patient is not toxic or injurious to that patient, or does not
cause immunological rejection.
[0041] FIGS. 1A, 1B and 1C illustrate an embodiment of a first
fixation member (15). In this embodiment, the first fixation member
may be a screw-type device (15) ("outer screw") comprising a blunt
distal end (10) and helical protrusions with a rounded edge (5)
along its body, extending from the distal end (10) to the proximal
end (30). The blunt distal end (10) and rounded edge (5) minimize
damage to the graft tissue. An embodiment of the outer screw (15)
may be generally cylindrical in shape, 20-35 mm in length and 7-12
mm in diameter. The outer screw (15) may gradually decrease in
diameter near its distal end to enable easy insertion into the bone
tunnel. The center of the outer screw may be cannulated creating a
bore (20) extending from its proximal end (30) to its distal end
(10), allowing passage of a guiding wire during surgery. The bore
(20) of the outer screw (15) may be pre-threaded (25) at least
partially from the proximal end. These threads have pitches
matching the threads of a second fixation member (100) ("inner
screw"). They may help to center the second fixation member inside
the outer screw during assembly as it advances inside the bore. The
proximal end (30) of the outer screw (15) may be cut at an angle
(45) of 55 to 60 degrees to the vertical axis, allowing a good
conformation to the tibial cortex surface after insertion into the
bone tunnel. The proximal end (30) of the outer screw (15) may
contain a recess (35) dimensioned to receive a portion of the third
fixation member (200) ("washer") or a portion of the inner screw
(100), allowing them to seat flush within the proximal end of the
outer screw (15) when assembled. Tighter assembly reduces the size
of fixation system extending outside the bone tunnel and thus
minimizes patient discomfort. The proximal end of the outer screw
may also contain a socket (40) for a screw driver, which allows the
outer screw to be driven into the bone tunnel against graft
strands.
[0042] FIGS. 2A, 2B and 2C show an embodiment of the second
fixation member, which may be a screw type device ("inner screw").
The inner screw (100) may be made of a harder material than the
outer screw allowing it to cut into the bore of the outer screw
creating threads as it advances through the bore, such as a
self-tapping screw. An embodiment of the inner screw may be 15-30
mm in length and has a sharp distal end (110), a generally
cylindrical post body (105) and a proximal head. The post body is
at least 3.5 mm in diameter and have helical protrusions (125)
extending along its length. The proximal head of the inner screw
(120) has a diameter larger than the post and may contain a screw
driver socket (130) allowing the inner screw to be driven inside
the outside screw using a screw driver (FIG. 2b).
[0043] FIG. 3a-3c illustrate various embodiments of a third
fixation member (200), a "washer". The washer may be flat (FIG. 3a)
or arched (FIG. 3b) and has a center bore (225) dimensioned to
allow the insertion of the post of inner screw but not proximal
head of the inner screw. The washer may also contain a recess (205)
dimensioned to receive the proximal head (120) of the inner screw
and allowing it to seat flush within the washer. This embodiment
reduces patient discomfort by minimizing the portion of fixation
device protruding from the bone tunnel. The washer (200) may have
multiple barbs (210) protruding from its distal surface (FIG. 3a
and FIG. 3b) designed to compress the soft tissue residing outside
the bone tunnel against the bone surface. The barbs may have a
rounded tip to reduce damages to the soft tissue. The washer may
also has a smooth distal surface (215) and a circular collar (220)
around the bore, which is designed to secure suture between the
washer and the outer screw when assembled (FIG. 3c). The washer may
be of any shape, such as round (FIG. 3d) or football (FIG. 3e)
shaped, and is generally 14 to 18 mm in diameter.
[0044] FIG. 4 shows a cross-sectional view of an embodiment of an
assembled fixation device. The self-tapping inner screw (100) is
driven inside the outer screw (15) causing the outer screw to
uniformly expand along its length and is refrained from
disengagement from the outer screw by their mating thread pitches.
The washer (200) is coupled onto the proximal end of the inner
screw (100) and is refrained from disengagement by the proximal
head (120) of the inner screw. The inner screw (100) may seat flush
inside the recess (205) of the washer (200). It may engage the
inner screw (100) with 20 to 30 degree of freedom of operation. If
the washer of FIG. 3c is used, the proximal end of the outside
screw will also contains a recess to receive the collar of the
washer allowing it to sit flush inside the outside screw.
[0045] In an embodiment, the third fixation member may be
eliminated. Barbs were added under the proximal head of the second
fixation member around the post body, which compresses the soft
tissue residing outside the bone tunnel against the bone surface
when assembled.
[0046] Another embodiment of the present invention is a method for
affixing soft tissue within a bone tunnel comprising: [0047] a.
positioning a piece of soft tissue in a bone tunnel such that a
portion thereof resides within the bone tunnel and a second portion
of said soft tissue reside outside the bone tunnel; [0048] b.
positioning a first fixation member upon the piece of soft tissue
within the bone tunnel; [0049] c. coupling a third fixation member
onto a second fixation member; [0050] d. restraining disengagement
between the first and the third fixation members by advancing a
distal portion of said second fixation member within the bore of
the first fixation member through the proximal end of the first
fixation member; and [0051] e. pressing said second portion of said
soft tissue against bone surface outside said bone tunnel via the
third fixation member.
[0052] The inventive fixation system and method may be used in most
surgical procedures requiring affixation of soft tissue to bone,
such as in anterior cruciate ligament (ACL) and the posterior
cruciate ligament (PCL) reconstruction surgeries.
[0053] For example, in an ACL reconstruction surgery, a new ACL
graft must be affixed to the tibia and femur to replace the damaged
ACL. The replacement ACL may be a tendon with a small portion of
bone on either end such as a patellar tendon autograft or a strong
new ACL formed by looped small tendons such as
semitendinosus-gracilis (hamstring) tendons, or donated achilles
tendon.
[0054] First, small tunnels (300) are drilled into the tibia and
femur as shown in FIG. 5. A replacement ACL is placed into the bone
tunnel following routine surgical procedure, leaving a portion of
the graft outside the tunnel (305). Once the replacement ACL graft
is inserted into the bone tunnel, the outer screw is inserted into
the bone tunnel using a screw driver or guide wire, pressing the
ACL graft against the wall of the bone tunnel (325). The outer
screw (15) may be positioned so its angled proximal end levels with
the bone surface (315) around the bone tunnel (300), making it less
palpable beneath the skin and reduce patient discomfort. A washer
(200) is coupled onto the inner screw and is refrained from
disengagement by the larger proximal head (120) of the inner screw.
The sharp distal end of the inner screw is inserted into the outer
screw and advancing through the bore in a rotational movement
driven by a screw driver. The pre-threaded portion of the outer
screw can serve as guide trail, which ensures that the inner screw
moves in the center of the bore. As the inner screw advance inside
the bore, addition threads are cut into the outer screw and causing
it to slightly expand. The radial uniform expansions along the
outer screw further compresses the soft tissue inside bone tunnel
(330) against the tunnel wall (325), which prevents tissue
slippage. When fully assembled, the washer will press soft tissue
outside bone tunnel (305) against the bone surface surrounding the
tunnel (315) and further prevents graft slippage.
[0055] Another embodiment of the method for affixing soft tissue
using only a first fixation member and second fixation member
comprising:
[0056] a. positioning a piece of soft tissue inside a bone tunnel
such that a portion thereof resides within the bone tunnel and a
second portion of said soft tissue reside outside the bone
tunnel;
[0057] b. positioning a first fixation member upon the piece of
soft tissue within the bone tunnel;
[0058] c. advancing a distal portion of said second fixation member
within the first fixation member through a proximal end of the
first fixation member; and
[0059] d. pressing said second portion of said soft tissue against
bone surface outside said bone tunnel.
Example 1: Biomechanical Testing of a Prototype Fixation System
[0060] Methods:
[0061] A total of 26 porcine tibiae with bone mineral density
obtained by quantitative CT were randomized to human tibialis
anterior tendon fixation with Delta Screw (8), Intrafix (8), and
Tritis (8) devices. Due to a limited number of prototypes, only two
additional specimens were tested using the prototype fixation
devices. The slippage for each specimen was evaluated during
cyclical loading (10 to 250 N at 1 Hz for 500 cycles) followed by
stiffness and ultimate strength determination in a load to failure
test.
[0062] Results:
[0063] The mean slippage displacement measured after 500 cycles was
similar for Delta Screw (1.42 mm.+-.0.43); Intrafix (1.16
mm.+-.0.32); and the prototype (1.61 mm.+-.0.01). The Tritis
implant demonstrated a statistically larger displacement (5.95
mm.+-.3.86, p<0.001). More specifically, cyclical loading
displacements were similar after 100 and 250 cycles, with the
Tritis device exhibiting the largest slippage during the first 250
cycles (4.53 mm.+-.2.74, p<0.00000), versus Delta (1.19
mm.+-.0.41); Intrafix (0.94 mm.+-.0.28); and prototype (0.80
mm.+-.0.01).
[0064] The mean ultimate strength for the devices was Delta (727.5
N.+-.140.9), Intrafix (712.8 N.+-.235.0), and Tritis (467.6
N.+-.98.5, p<0.000). Prototype demonstrated the highest ultimate
strength (797.7N.+-.32.6).
TABLE-US-00001 TABLE 1 BIOMECHNICAL TESTING OF FIXATION DEVICES
Mean Slippage Cyclical Loading Displacement Displacement Mean (500
cycles) (250 cycles) Ultimate Strength Delta 1.42 mm .+-. 0.43 1.19
mm .+-. 0.41 727.5N .+-. 140.9 Intrafix 1.16 mm .+-. 0.32 0.94 mm
.+-. 0.28 712.8N .+-. 235.0 Tritis 5.95 mm .+-. 3.86 4.53 mm .+-.
2.74 467.6N .+-. 98.5 Prototype 1.61 mm .+-. 0.01 0.80 mm .+-. 0.01
797.7N .+-. 32.6
CONCLUSIONS
[0065] In the porcine model with human tibialis tendon graft, the
Delta Screw, Intrafix, and prototype devices displayed superior
cyclical loading, and ultimate failure versus the Tritis device.
The present invention offered the best ultimate strength compared
to the three other commonly used implants.
* * * * *