Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates generally to orthopaedic
implants applied surgically and speci'fically to a new ~flute~
hip nail primarily intended for use 'in the repair of fractures
, of the hip or,for use in the stabilization of surgically
created fractures in the reconstruction of congenital deform-
ities of the hip principally in children. A single piece
fluted hip nail is described including an integral solid
nail-plate junction as wel'l as instrumentation for use 'in the
insertion and later removal of the implant.
The principal aim in treatment of patients having
intertrochanteric hip fractures,,and especially the elderly, is ''
the rapid return to full prefracture activities. Local problems
that must be dealt with include proximal femoral instability '''
and deformity, as well as pain. Rapid mobilization serves to
pre~ent local skin ulceration, urinary-stasis, pneumonia,
,' thromboembolic disease, and other complications arising from
long bed confinement.
Accordingly, the treatment of intertrochanteric
, fractures has conventionally been accomplishe'd by reduction and
internal fixation. Most of the prior ar,t fixat-ion techniques
serve to alleviate pain and permit the patient to be ambulatory, ,
, although they are not generally weight bearing. In some cases
the implants are partially weight bearing during assisted ~'
ambulation. The elderly patient in most cases does not have
; sufficient strength-or coordination to protect the hip from
excessiye stress while walking with the assistance of crutches
or the like.
The prior art has atte,mpted to provide fixation of
,the fracture that is so stable'that the patient's full weight
may bear on the fractured hip. Typical strong nails for this '
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purpose have been developed by E. P. Holt, ~r. (Journal of
sone and Joint Surgery, 45-~: 687-705, June 1963) and
A. Sarmiento (Journal of Bone and Joint Surgery, 45-A: 706-722
June 1963). Others have suggested altering the positions of
the fracture fragments to improve 'the mechanical resistance of
the bone to the''disruptive'forces during weigh~ bearing.
(Dimon et al, Journal of Bone and Joint Surgery, 49-A: 440-
450, April 1967; and Massey, Journal of Bone and Joint Surgery,
46-A: 658-690, April, 1964).
The three most common implants presently being used
for such fracture reduction and fixation are the Jewett nail,
a telescoping screw device, and the Holt nail. Tests on these
devices are to be found in the'literature; note Journal of Bone
and Joint Surgery; 56-A, 899-907, July 1974; Acta chir.
Scandinav. 117: 427-432, 1959, During these tests the Jewett
nail showed bending at the fracture ~ite and continued varus
angulation at relatively low load levels. Anatomical reduction
using a telescoping screw device maintained the desired neck
shaft angle until the screw had completely telescoped.
Continued loading then produced bending at the screw plate
angle. When a femur-fixed with a Holt-nail was tested, the --
load rose rapidly and then dropped off as a result of fracture
of the trabeculae in contact with the nail. Further loading
resulted in bending of the nail.
The forces acting on the head of an adult femur are
quite surprising at first glance. When standing on one leg the
force would bé two a~d one-half times body weight; for walking,
five to six times body weight. Hence, for a 60 kg man it will
be appreciated that the femoral head would be exposed to forces
in the range of 150 to 300 or more kg. With regard to the
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proximal end of the femur, studies show a capacity before `
fracture of 500 kg for the elderly and 1000 kg for the young.
Any implant designed for use in intertrochanteric fracture
treatment must therefore approach these levels. Most of the
internal fixation devices which have been tested have a failure
strength of only 100 to 200 kg.
Hip nails actually undergo two types of bending under ~
the application of force; one is elastic and the other is a ~-
permanent type of deformation. When forces act on a nail below
its elastic limit, the nail will bend and then when pressure ~-
is removed, it will resume its original configuration with no
measurable permanent deformation. If the elastic limit is
surpassed, however, a permanent deformation will result.
For a more detailed discussion of implant systems
with regard to stress parameters, reference may be made to
"Biomechanical Principles of Intramedullary Fixation" Clinical
j Orthopaedics, No. 60, 1968, 13-20.
The unitary one-piece fluted hip nail which is the
subject of this invention provides significantly improved
bending strength in the fixation of fractures as well as in the
stabilization of surgically created fractures in hip reconstruct-
ive surgery on children. Additionally, the new nail, by virtue
of its fluted design, provides improved torsional stability.
A review of the prior art indicates that present
implant devices of this type either severely compromise their
fatigue and ultimate strength by the provision of central driving
recesses and/or central cannulation to facilitate insertion, or
sacrifice stability in order to eLiminate the need for driving
surfaces.
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All known trochanteric implants provid-
ed with fins or vanes to provide rotational stability,
such as United States Patent 2,627,855, issued to
James W. Price on February 10th, 1953 employ a cen-
tral bore for driving which seriously weakens the
device with regard to both fatigue life and the ulti-
mate load carrying capacity.
The prior art de~ices which are devoid of
such a central bore for driving and extraction fore- ~-
go the rotationally stabilizing flutes or fins in
- order to facilitate insertion because such projec-
tions require forcible insertion into the bone.
~herefore, most of the devices now in use employ
a central bore which unfortunately is at the cen-
tral or high stress portion of the nail and support
plate.
It should be further noted that most
known implants have a small or sharp frontal area
for ease in insertion into the bone, and the few
that are blunt lack rotational stability. -
With regard to instrumentation, the
existing implants such as Collison, United States
Patent 2,612,159 have smooth surfaces in the areas
between the screw holes of plate portions which
fit against the upper end of the femur which
makes it extremely difficult to clamp this por-
tion to the bone without slipping of the clamping
; instrumentation which would create surface damage
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to the plate or which could re~uire the instrumenta- ,~
tion to obstruct one or more of the screw holes. ~.
Bearing in mind the above problems in- ~-
herent in the prior art, it is an object of this ;.
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invention to provide an impact/extractor tool which ~
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obviates or mitigates the above disadvantages.
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According to the present invention, there :;
is provided an impactor/extractor tool for attach- -:
ment to a surgical hip nail implant to assist in .: ~
insertion and extraction of the implant in a bone, -~ --
the tool comprising a pair of spaced elongated arms,
block means joining one end of each arm to the
other and adapted to receive impact hammer blows,
: inwardly directed stub means adjacent the free
ends of the arms adapted to engage in buttresses
provided on an implant, and means intermediate
the ends of the arms for moving the same toward
each other to engage the stub means in the
' buttresses.
In order that the invention may be
more fully understood, a preferred em~odiment in
accordance therewith will now be described by way : .
of example with reference to the accompanying draw-
~ ings, in which:-
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; 30,
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FIGURE 1 is a vertical sectional view of the new
implant secured in position in a fractured neck of a femur
which is shown in dotted lines;
FIGURE 2 is a side elevation of the implant;
FIGURE 3 is a front .elevation of the implant; :-
FIGURE 4 is a rear el'evation of the implant;
FIGURE 5 is an enlarged horizontal section through '
the bone plate.portion of the'implant taken on line 5-5 of
Figure 3;
FIGURE 6 is an enlarged section similar to. Figure 5, ::'
but taken on line 6-6 of Figure 3;
FIGURE 7 is a top plan view of the impactor/extractor
instrumentation employed with the implant;
FIGURE 8 is a sectional view of the impactor/extractor " "
tool taken on line 8-8 of Figure.7; ,~
; FIGURE 9 is a side elevation of the fluted nail implant
with the impactor/extractor tool attached théreto;
, FIGURE 10 is a perspective view of the implant in
. place in a femur neck showing the. application of our new bone
', 20 plate clamping to.ol prior to-dri-lling-of the femur;
FIGURE 11 is a plan view of the bone plate'clamping
. instrumentation; and
FIGURE 12 is a graph depicting results of bending
tests of prior art hip nails and the nail of the present
invention.
Referring to the drawings wherein like reference
characters represent like parts, the hip nail of the present
invention is shown g~nerally at 10 and includes a hip nail
portion 11 and a bone plate portion 12 angularly related to each
other and meeting at a junction 13. The entire ,implant may be
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cast, forged and machined from a single block of metal which is ~ ~'
compatible with thb human body. 'Whi'le titanium or various types
of stainless steel are acceptable, we have found that Titanium
type 6 A14U Eli; ASTM F-136 is ideal for this purpose.
The angle 6 included between nail portion 11 and ~-
` plate portion 12 may vary dependent on use. We have found that ~-~
an angle of about 135 is suitable for most fracture use
although with pediatric hip nails, angles of 145 and 115
are preferable for valgus and varus osteotomies, respectively.
With respect to the hip nail portion 11, the length
thereof may be from 2.5 to about 15.2 cm. The major length of
hip nail portion 11 is provided with a plurality of longitudi-
nally extending flutes or vanes 14 commencing with a smooth
transition from junction 13 and terminating in relatively
sharp points 15 defined by a sharply angled face. These points
' 15 serve to cut into the bone during insertion by impaction
into a predrilled bore, and provide a means for gripping the
bone both proximal and distal to the fixation site. This
mechanical locking provides significant torsional stability.
To increase the resistance of the nail portion to
penetration of the femoral head, the end thereof is provided
with a short blunt head 16 of slightly reduced cross-section,
sufficient however to prevent further bone penetration once
insertion is completed.
The bone plate 12 is tapered slightly from junction
13 to its tip and is rounded on its innex and outer faces 17
and 18 in order to properly conform to the femur surface. It
will be noted from an examination of Figures 3 and 4 that the
width of the bone pla~e adjacent the''junction 13 is greater than
the width of the fluted hip nail portion.
106857:~
In order to secure the bone plate to the femur, a - '
plurality of screw holes l9 are'drilled therein and countersunk
as at 20. As best seen in Figures 3 an~ lO,,the holes 19 are
staggered and any number may be provided,,although four, five
or six-hole plates are preferable for an adult implant, and two
~' or three holes for pediatric use. When more than three holes
are employed,,only the top three are staggered or offset.
After the' bone plate has been securely clamped into close
contact with the femur, as later described herein, conventional
bone screws of a compatible metal 21 are inserted into the
holes 19 and brought up tight with a surgical screw driver. ;,
To assist in clamping the'bone plate to the femur ~ '
' without marring the surface of the'implant,,one or more hemi-
, spherical depres'sions 22 are formed on the outer face 18 of
the plate which are engaged by the new clamp instrumentation
also later described herein.
The junction 13 of our new implant has been specially
designed for use of our new impactor/extractor instrumentation.
,' Since this is a critical area of the implant with regard to
stress application, it is the most massive section of the entire
appliance. The material provides a buttress so that there are
two semicircular surfaces provided on each side of the junction
from the outer face 18 as shown at 23. These buttresses are
made parallel to the longitudinal axis of the nail portion 11.
, A generally similar pair of extractor buttresses 24 are formed
on the inner side of junction 13 also parallel to the nail
portion longitudinal axis. These buttresses accommodate
matching stubs or protuberances on the'impactor/extractor
instrumentation later described so that insertion and retraction
forces may be applied to the implant in its areas of maximum
strength.
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Our new impactor/extractor instrumentation for use
in facilitating insertion and retraction of the implant is
shown generally at 30 in Figures 7-9 and includes a pair of
spring arms 31 and 32 connected at their rear ends to a solid
spacer block 33. Screws 34 are preferably used to fasten the
arms to the block. An integral post 35 of cylindrical shape
extends upwardly from the top of the block. Both the rear
face of block 33 and the outer surface of post 35 may be struck
with a surgical mallet in insertion or removal of the implant.
On the inner faces of arms 31 and 32, a pair of opposed
impactor stubs 36 are formed which are coaxial and project
inwardly toward each other. These stubs are adapted to be
received within and engage in the impactor butt~esses 23 and
to this end are cylindrical so as to abut the semicircular
front configuration of these buttresses. A second pair of
opposed stubs 38 of semicylindrical configuration are formed
at the angled ends of arms 31 and 32 and are adapted to be
received within and to engage in the extractor buttresses 24
of the implant. It will be understood that the rear curved ~`
surfaces of the stubs 37 abut against the curved faces of the
buttresses 24.
The arms 31 and 32 are sufficiently spaced apart at
their free ends as shown in Figure 7 so that they may be placed
about the implant 10 with ease and a screw arrangement is
provided to force or tension the arms together so that the stubs
36 and 37 are securely fastened within the buttresses 23 and
24 as shown in Figure 9. An inwardly threaded boss 39 is
formed on the inner face of arm 32 spaced rearwardly of stubs
36. An elongated clearance slot 41 is formed through the arm
31 to receive screw shaft 40. A knurled thumb knob 42 is
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secured on the screw shaft along with a washer 43, the free end
of screw 40 being threadedly received within boss 39. Turning
of the thumb knob 42 will therefore force' arms 31 and 32
together as noted above. ~-~
After the'impactor/extractor instrumentation is
attached to the 'implant, the nail portion 11 may be forced into
a predrilled bore in the femur. A series of sharp blows with
a mallet on the rear face of block 33'or post 35 will transmit
the force through the instrumentation to the strongest areas
of the implant junction -13. Impaction is continued until the
nail plate portion is immediately adjacent the femur. ~t this
time the impactor/extractor instrumentation may be removed and
the bone plate clamp instrumentation applled.
It will be apparent that if for any reason it is
desired at this time or later in the operative procedure to
' remove the implant, the impactor/extractor instrumentation may
again be applied. Percussive'force may then be placed against
the inner face of post 35 to remove the'implant 10.
'~ When it is desired to secure the bone plate to the
shaft of the femur, the bone plate clamp instrumentation 50
is utilized. This device comprises a pair of crossed lever arms
51 and 52 having adjustable fulcrum or pivot means at their area
of crossing to enable use with femurs regardless of size. To
this end arm 51 is formed with a widened projection shown in
Figure 11 which is provided with a plurality of adjustment holes
53 to receive a pivot pin 54 carried by arm 52. The holes are
- circular on the top face but elliptical adjacent the bottom face
thereof. Pin 54 is generally cylindrical however its top
- surface is elliptical so that upon proper alignment it may be
received in either' of the hole-s 53. Thereaftex, slight move-
ment of the arms 51 and 52 wi'th respect to each other will cause
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the elliptical opening to go out of alignment wi.th the .~
elliptical head of pin 54 permitting rotation but obviating
- separation of the arms. .-~
At its. free end, arm 51 has a ball member 55 mounted ~.
thereon adapted to be received wi*hin one of the hemispherical
depressions 22 on the outer face 18 of bone plate 12. Arm 52
at its free end receives an arcuate bone clamp 56 pivoted -. .-
thereto at 57. Arm 52 may be recessed in this area as shown .
in Figure 11 to permit clamp 56 to swing to a limited degree.
Serrations 58 are formed on the inner face of clamp 56 to
ensure a firm purchase on the femur.
Adjustable locking means of the conventional hemostat ~ `
type are provided at tne other ends of the arms 51 and 52 so
that selective compression of the clamp instrumentation about
the bone may be maintained during drilling of the screw holes
19 and application of screws 21. Ratchet bar 59 having a
series of toothed steps 60 is pivotally fastened to arm 51 as
: at 60. A leaf spring 62 secured to arm.51 by a screw 63 serves
to maintain the bar 59 in proper position, all as well known in ~..
the art of medical instrumentation. The free end of arm 52
is formed with a pawl 65 configured to-cooperate and -lock within
the toothed steps 60. Adjacent to pawl 65 is a depending curved
finger guard 64.
The manner of applying the bone plate clamp will be
: apparent from a study of Figure 10. Clamp 56 is placed about
the rear face of the femur with the ball member 55 placed in
one of the depressions 22 of the bone plate. Squeezing of .:
arms 51 and 52 is commenced until the bone plate is drawn up
snugly against the femur and this position will be maintained
by the locking of pawl 65 within the toothed steps 60 until
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the bone plate has been secured in place by screws 21. There-
after slight squeezing pressure is applied on arms 51 and 52
and bar 5g is then released by pivoting the same outwardly
releasing the locking action and allowing removal of the bone
plate clamping instrumentation. It will be observed that the
bone plate clamp permits unobstructed screw fixation without
damage to the plate surface.
Comparative bending tests of our new implant and
selected commonly-used hip nail implants have been conducted
in order to show the improved strength qualities of the new
nail and the same are graphically illustrated in Figure 12.
These tests obtained the relative static strength character-
istics, stiffness and mode of plastic deformation of the
implant test specimens. Our new implant was tested against
a Holt nail made from Vitallium (an alloy of cobalt, chromium
and molybdenum), a Sarmiento "I" Beam Nail plate combination
and old design Jewett Nail and plate and a new design Jewett
Nail and plate. All specimens included a 3 1/2 inch (8.9 cm)
nail and a four hole bone plate. The test specimens were
chosen from commercial sources and the tests were performed
in accordance with the proposed standard test procedure of the
F-4 Committee on Surgical Implants of the American Society
for Testing and Material. The graph depicts the plot of nail
tip displacement in centimeters against the bending moment
of the nail plate junction in Newton-meters and the apparent
merits of our new implant will be apparent.
In order to utilize the strength and rigidity of
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this implant in osteosynthesis it is necessary that loads be
transmitted to the nail from the bone under both torsional
and bending loading. In bending the nail is readily loaded
wherever it comes into contact with cortical bone. Rigidity
at the fracture site will depend on the properties of the
nail and its fit in the canal. However, in the case of tor-
sional loading it is necessary for the nail to have intimate
contact with the cortical bone so that the shear stresses may
be built up between the nail and bone and torque transmitted ;~
from one fragment to another. This contact is achieved herein
by the application of flutes on the nail portion.
The strength of the implant is of course a measure
of the maximum loading that can be applied to the structure
before failure occurs and there are three major causes or
types of such failure: namely, plastic failure, brittle type
fractures and fatigue fractures. Plastic failure is dependent
to a great degree on the type of material chosen for the -
implant and can be predetermined by investigation of-the-stress-
strain curves for various metals. Brittle type fractures
occur in regions of stress concentrations such as notches and
other discontinuities and are avoided here by careful design
especially in the critical nail-bone plate junction area.
Since this junction or transition section must also incorpo-
rate means for both driving and extracting the implant,
external surfaces to cooperate with instrumentation were
incorporated therein. These surfaces or buttresses are
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located at the neutral hending axis so as to prevent damage
to any high stress region of the junction during insertion
or removal. Fatigue fractures occur when an implant is
loaded repetitively and may occur i delayed union is present.
These fatigue fractures are also ostered by scratches,
notches and the like. The specific design of our implant and
its associated instrumentation minimizes the possibility of
such fractures.
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