ENGINEERING
CONSIDERATIONS
OF
M.
St
Traditionally,
adjunct
to
Basom
1944
Mary’s
and
of
others)
of a plaster,
If total
reliance
and
stiffness
of the
hand
An
loads,
by
Previous
work-The
device
(Breek
1951,
KUntscher
contained
published
work
reference
work
has
but
which
various
designs
forces
were
different
in
to pull
different
Lyon,
that
described
tests,
in
These
was
light
often
tibiae,
bending
the
stiffness
of
different
Peterson
is the
are
strength
imposed
to meet
been
purely
stiffness.
of
the
these
1966)
of their
with
particular
(1959),
which
further
may
lead
to
orthopaedic
strength
for
have
and
stiffness.
fixation
of shaft
of Lindahl
(1962,
1964, 1967).
He loaded
axes) and in torsion,
and measured
out
of bone.
(1941),
strength
Measurements
but
at the
related
present
of British
calculations
drilled,
were
the
to
are
broken
last
of screw
Ansell
and
4 millimetre
Scales
screws
presented
which
to fixation
Secondly,
devices
during
experiments
by
strengths
of the
a design
time.
Standard
that might
be applied
restricted
weight-bearing.
for
and
laboratory
of metallic
of devices
fixation
Venable
the
Laing
stiffness
Smith
and
of
problem,
and
Taussig
of
1950,
clinical
Much
Ferguson
different
of comparison
designs
Reeder
bending
of fixation
or
lead
by
devices.
to
torsion
Thirdly,
loads,
nails
possibility
ofearly
results
presented.
were
and
designed
to
of onlay
plates
with
relying
on
mobilisation,
provide
a
better
their
internal
understanding
of
TIlE
JOURNAL
the
screws.
fixation
alone,
is discussed
* The
substance
of part of this paper was communicated
to a meeting
of the Section
of Orthopaedics
Royal Society
of Medicine
on February
1 , 1966, and was reported
in summary
form in the Proceedings
Society
(Laurence,
Freeman
and Swanson
1966).
754
on
function?
safely
and
question
on it.
and
intact
and
maintain
in torsion,
on various
onlay plates and intramedullary
nails are described.
measurements
of the tensile
loads
acting
on screws
while
the device
of intramedullary
of the
both
and
and
in Britain
loads
during
an
are employed.
: what
full
compatibility
of screw
holding
torsional
and
by
and
those
and
used
ofthe
a standard
bending
and
tests,
including
Finally,
designs
to
loads
to the
(about
Cochran
is most
bending
and
mobilisation
provide
transmitting
the
are
the effects
of various
factors
paper-Firstly,
measurements
in which
to
functioning
in
which
measurements
Bechtol,
strength
in bending
also
of this
order
plate
by
the
other
of
Hochman
relevant
on
the
aspects
by
reported
required
estimates
of the
non-weight-bearing
are
been
reported
and
Scope
so far
of onlay
published
in bone,
tests
arise
what
usually
or
or biological
marginally
as
(Breek
upon
stiffness
and
1948,
have
1966,
questions
descriptions
metallurgical
Jones
and
only
argued
relied
tibia,
on
Eggers
summary
been
shaft
advantages.
strength
strength
resistance
is only
have
from
(1968)
and
comprehensive
fractures
the
the
corrosion
which
only
many
of
tibial
acceptable.
descriptions
with
Since
the
in
The
such
(Greene
and
1944,
measurements
dealt
appeared
implants,
kind
but
corrosion.
improvements
the
1958),
of
two
ENGLAND
London
the
has
be
strength
for the
sufficient
Wenger
it
obvious
implant,
provide
contains
1944,
of
can
of sufficient
the
College,
fractures
confer
available
LONDON,
Imperial
alone
to be surgically
Basom
has
to
must
enough
reports
for
mobilisation
literature
and
no
on
at present
implant
SWANSON,
and
fixation
would
non-weight-bearing
yet be small
used
if implants
is to be placed
V.
FIXATION
SHAFT*
in plaster-of-Paris.
if allowable,
implants
acceptable
and
limb
site
S. A.
Hospital
been
internal
at the fracture
absence
one
the
that
TIBIAL
London
has
INTERNAL
THE
THE
and
The
fixation
immobilisation
The
the
Hospital,
internal
immobilisation
OF
M. A. R. FREEMAN
LAURENCE,
From
IN
FRACTURES
OF
BONE
AND
JOINT
of the
of that
SURGERY
ENGINEERING
CONSIDERATIONS
ESTIMATES
Basis
OF
IN
BENDING
of estimates-The
life,
but
upper
measurements
and
or
forces
inserted
action
applied
the
not
body
weakest
the
applies
a
the
tendons
or torsion
but
moment
can
if the
tibia
and
to
TIBIA
by
IN
LIFE
measured
loading.
absence
755
SHAFT
be directly
of
except
THE
in
Appropriate
of violence
is assumed,
the
originating
to longitudinal
contraction,
of
view,
it is obvious
; longitudinal
may
muscles
compression
bending
do
so if, by being
to the
that
compression
or
from
twisting
the
moments
any
at the
offset
from
normal
fracture
the
fixation
site
centre
does
of the
device
not
is
constitute
fixation
device,
it
implant.
TABLE
GREATEST
cannot
modes
and
of the
be subjected
muscular
point
in itself,
shaft
TO
TIBIAL
or ligaments.
engineering
bending
below.
the
tibia
various
walking
to
APPLIED
human
the
outlined
shaft
and
for
OF TIlE
FRACTURES
MOMENTS
to quiet
applied
weight
in bending
a hazard
be
Thus
by muscles,
From
are
OF
by the
inferred
is restricted
thereon.
of
sustained
calculations
will
FIXATION
TORSIONAL
be
can
If weight-bearing
sideways
AND
loads
limits
1NTERNAL
RESISTIBLE
BENDING
I
MOMENT
of subjects
tested
Number
AT
Bending
PROXIMAL
END
moment
in Newton
(Poundsforce
OF
TIBIA
metres
feet)
Musclegroup
Men
Hamstrings
Women
Range
11
17
26-54
35
(19-40)
(26)
Quadriceps
6
(31-44)
(38)
Hip
6
(2880)
(46)
24-48
(17-35)
(29)
(44i93)
(60)
32-40
(24-30)
36
(27)
abductors
3
Hipadductors
6
3
Bending
Mean
39
moments
Limitation
imposed
be applied
to the
through
which
cadaver
knees
by the strength
tibia
oftissues-In
by adjacent
the
necessary
were
tested
parts
forces
in
life,
ofthe
were
body
the
transmitted.
three-point
greatest
would
bending,
bending
be limited
To
using
obtain
moment
which
by rupturing
a value
apparatus
could
ofthe
for
this
similar
to
tissues
limit,
that
three
described
below.
They broke
at bending
moments
(by avulsion
of one end of the collateral
ligament
which
was in tension)
of 139, 170 and 168 Newton
metres
(i.e., 103, 1 25 and 123 poundsforce
feet).
Limitation
by pain
moments
were
imposed
that
obtained
posteriorly,
medially
as
using
possible,
From
subjects
VOL.
at the
were
51 B,
NO.
and
muscle
of the
proximal
young
4,
laterally
power-Normally,
in turn)
respectively
measurements
moment
and
the
force
end
adults.
NOVEMBER
1969
at the
hamstrings,
and
the
moment
tibia
were
would
muscles
without
pain.
forces in four directions
ankle,
and
asking
quadriceps,
of the
limits
lower
could
be transmitted
by the relevant
experimentally
by applying
horizontal
arm,
calculated
hip
values
and
the
subject
abductors
of the
are
greatest
shown
be
Values
(acting
set
to resist
and
hip
the
as hard
adductors.
resistible
in Table
by
for these
anteriorly,
bending
I.
All
the
756
M.
Moments
caused
the
times
the
body
from
the
line
the
of action
resulting
poundsforce
feet).
pounds)
(40
Moments
and
at the
top
conditions
to raise
of
flexed
and
which
ordinary
the
foot
The
l37
to
(l66
use
the
leg medially
were
recorded.
twisting
Newton
foot
and
work-The
saw
were
cuts
axial
the
thinnest
100
per
was
The
OF
of the
of 670 Newtons
54 Newton
(1 889) figures
bending
moment
(150
metres
for the
required
Fischer’s
the
to be about
10 Newton
metres
(7 poundsforce
feet).
could
be applied
to the
under
which
three
men
by
(wearing
the
long
could
axis
significant
THE
TIBIA
leg.
the
subject
with
in
The
way
with
subject
his
to
then
the
rotated
between
moments
tibia
of 226
left
hip
a device
twisting
a mean
difference
tibia
supported
appropriate
in this
feet),
the
shoe)
of the
and
be applied
no
seating
a normal
as possible
normal
Frankel
for
the
AND
cadaver
Burstein
ranged
from
Newton
and
metres
right
legs
or
and
using
strength
widest
DRILLED
tibia
(1965),
in torsional
cent
INTACT
human
and
reduction
70 per
studies
and
This
on
storage
subject
mechanical
cadaver
properties
stored
material
(in this study,
will be reviewed
appear
and thawing.
Materials-Forty-three
and
four
by 2 centimetres
because
cut,
taking
the
effect
of longitudinal
a combination
of the
the
of torsion
cut
strength
was
58 per
of the
intact
and
cent
for
tibia
as
cent.
Before
death
tibia.
be offset
rotation.
by
and
might
of toe-off
to be about
and
to 21 poundsforce
There
strength
cut
is likely
shows
in
that
(l01
measured
compression.
Braune
about
STRENGTH
Previous
at the moment
tibia
calculation
foot
as forcefully
lateral
that,
in the
a fracture
moment
the
moments
feet).
medial
V. SWANSON
show
fixing
measured
with
moment
metres
poundsforce
between
leg and
was
laterally
greatest
284
foot,
twisting
and
twisting
and
plate
leg and
the
extended,
S. A.
force
leg raising-Using
the
greatest
knee
recorded
the
at
tibia
AND
force.
With a body weight
in the region
moment
on the plate
would
be about
by straight
moments-The
FREEMAN
compressive
onlay
of this
bending
of
R.
compression-Calculations
A single
dimensions
ofthe
Twisting
A.
longitudinal
weight.
imposed
weights
M.
by longitudinal
walking,
normal
in
LAURENCE,
to
human
at
18
-
can
be
applied
to
deep freezing)
do not
elsewhere
(Swanson,
be
very
tibiae,
degrees
little
altered
of which
Celsius.
by
eighteen
Before
living
bone
it must
affect the mechanical
in press) : here it may
death
or
were
testing,
subsequent
paired,
the
be
bone
shown
properties
be stated
that
of the
that the
deep
freezing
were
taken
after
death
was
thawed
to
room
temperature.
Apparatus
eighteen
and
methods-The
tibiae
one
paired
holes
had been
made
drill.
Bending
apparatus-Bending
10 SZ BDA 52, of 15 tons
over the upper
four-fifths
tibial
shaft was
bone
was loaded
through
five
both
tests
bending
rig
which
would
three-point
bending
rig,
similar
to
applied
through
were
of
loaded
increase
Torsion
was
machine
to
the
cause
drill
to
The
type
end
a universal
outer
6609
holes
ends
CGG,
in about
of a tibia
of the
in
two
an
universal
tests
local
seconds
cast
with
to
lessen
joints
testing
and
were
stress
Load
the
were
was
applied
start
of
mounted
THE
type
tested
central
Drilled
was
tibiae
rate
AND
which
bending
torsion
(0-1,500
OF BONE
box
unwanted
in an Avery
JOURNAL
in
load
at a uniform
a metal
of
metres
load
in the
loading.
into
transmission
Newton
therefore
concentrations.
plaster-of-Paris
the
machine
1 . The
In
to
diameter
per cent ofthe
indicated
too short
to be tested
in Figure
from
on its 0-170
(i-inch)
hydraulic
+05
were
of bending.
thirty
was
Amsler
shown
and in torsion.
loaded
after
up
3-millimetre
preferred,
rig
to lessen
plane
in bending
fellow
was
a c.
to within
The tibiae
been
intended
for these
with
four-point
in order
joint
used
have
the
in the
a fracture
apparatus-Each
connected
moments.
block
a wooden
with
done
and accurate
load range.
four-point
to failure
whilst
its
cortices
were
capacity,
of any
loaded
intact
testing
poundsforce
JOINT
SURGERY
a
ENGINEERING
CONSIDERATIONS
Figure
I-The
proximal
cell for
clarity).
measuring
Figure
IN
inches)
arrangement
Results-Breaking
These
tables
40
cent
per
force
on
proximal
was
a stated
the same
strengths
show,
screw
(the
two-thirds
having
for
In bending
and
those measured
twice
the
tibiae,
the universal
in bending
in
preparation),
type”
were
the
tests
same
the
paired
bones,
12 per
cent
All
which
the
Celsius
and
in connection
Four-point
moment
rig-A
the
central
points
and
loading
links.
swinging
each
side
inch),
of
Torsioti
testing
in the
tests
protractor
the
VOL.
the
on
intact
and
the
NO.
4,
FIXATION
plate,
and
load
raised
for
machine.
of’ the
indicated
shown
in Tables
load.
This
in Figure
2.
II and Ill respectively.
strength
because
of drilling
of
to break
undrilled
muscle
power.
tibiae
were
about
DEVICES
screwed
in
various
plate,
the
3531
betiding
intact
to bone,
lengths
were
(both
tested
singly
I I-centimetre
screws,
in bending
and
Down’s
4 millimetres
and
as a two-plate
“heavy
duty
Swiss-
The
used
per
plates
in all
inch,
always
all
measured
testing
tibiae.
used
1969
for
with
tibiae
measuring
rig
the
a dial
piece,
gauge
angulations
cast
with
rotation
to
same
human
tibiae
degrees
18
-
described
obtain
above
design
of
to points
reading
to
bending
1.
roller
The
outer
bearings
on
equidistant
0025
calculated
plaster-of-Paris
of
a uniform
in Figure
relative
from
millimetre
from
these
into
metal
in the same
in
Figure
2,
an
intramedullary
which
(00001
dellections.
joints,
universal
is shown
the
machine,
is shown
were
through
arrangement
testing
in order
the
test
were
machine
A typical
used
incorporate
1 . Total
of
torsion
was
of the
of implants
were
a few days)
at
used.
preparation;
two
in Figure
Amsler
was
system
of the
properties
(usually
time
loads-The
tibiae,
deflection
was
NOVEMBER
cent
x 20 threads
inner
tibia.
51 B,
gauge
Standard
on
central
pointer
dial
rig has been
torsion
testing
Stamm
plate.
T6).
The screws
apparatus-Ends
Avery
757
rotation.
in mean
moments
needed
set by pain and
plate
four-point
as shown
bending
in the
Hicks
plate
and the 14-centimetre
steel (En 58 J) or of titanium
(IMI
span
centre,
supported
loaded
the
The
SHAFT
plate.
tests
bending
over
two
the
per
a reduction
of onlay
before
use.
machinejor
with
TIB1AL
2
rig with
bending
for measuring
05
for testing
the mechanical
for varying
lengths
of
stored
thawed
Testing
Apparatus.
the
used
been
THE
in torsion.
Campbell
British
as
OF
of the four-point
a KUntscher
nail
devices
of
ON
Venable
13-centimetre
bones
had
types
the
15-centimetre
of stainless
material
and
accuracy
in torsion
the mean
in life at the limit
self-tapping
were
in the
in a four-point
upper
portion
of a tibia
with
and
were:
plate,
the
made
either
FRACTURES
as that at one end of the preparation
in bending
and torsion
are set out
standard
These
torsion.
plated,
joint
TESTS
Materials-Five
OF
FIG.
of two
showing
and
range,
FIXATION
I
FIG.
two-thirds
the
2-The
INTERNAL
boxes
shows
nail
and
way
as
also
relative
for
a
to
758
M. LAURENCE,
M.
A.
R. FREEMAN
AND
TABLE
BREAKING
STRENGTH
OF TWENTY-TWO
Age in years
HUMAN
Whether
drilled
or not
Sex
I
30
Female
52
Female
V.
SWANSON
II
(a) All bones
Source
S. A.
CADAVER
TIBIAE
IN BENDING
tested
Bending
Newton
moment
metres
at fracture
Poundsforce
feet
No
217
Yes
103
160
75.9
Yes
No
I
156
108
115
79’6
No
I
198
144
146
106
I
68
Male
81
Male
No
Yes
60
Female
No
64
Male
No
196
145
66
Male
No
293
216
67
Female
No
73
Female
No
I I9
74
Male
No
230
74
Female
No
75
Male
No
I
Yes
73#{149}5
324
#{149}
542
238
187
138
8l’3
60’O
87’6
170
95l
701
174
128
76
Female
No
78
Male
No
79
Female
No
81
Male
No
178
132
84
Female
No
152
112
85
Female
No
114
839
(b) Comparison
of paired
579
bones
only,
(Newton
metres)
at fracture
and drilled
Undrilled
Mean
Minimum
at fracture
Mean
Maximum
Drilled
73.5
I
Maximum
Bending
moment
(poundsforce
feet)
650
undrilled
Minimum
moment
985
88’2
_________
Bending
427
133
324
161
970
217
I
144
54’2
238
1 19
716
160
THE
106
JOURNAL
OF
BONE
AND
JOINT
SURGERY
ENGINEERING
CONSIDERATIONS
IN INTERNAL
FIXATION
TABLE
BREAKING
STRENGTH
OF TWENTY-ONE
OF
Age in years
Whether
drilled
or not
Sex
I
34
OF
53
HUMAN
CADAVER
TIBIAE
53
tested
Rotation
at
ankle
Twisting
Newton
moment
metres
External
853
62’9
Yes
External
71’6
528
No
External
451
33.3
Yes
External
490
361
No
External
7l6
528
Yes
External
618
456
No
External
75.5
55’6
Yes
External
588
43.4
No
External
53.9
398
Yes
External
5l9
38’3
Female
I8
Male
Yes
Internal
676
49.9
65
Female
Yes
External
235
174
69
Male
Yes
External
774
571
81
Female
Yes
Internal
314
231
50
Male
No
Internal
89’2
658
51
Male
No
Internal
706
521
60
Female
No
External
402
296
60
Female
No
External
343
25’3
65
Female
No
External
274
202
73
Female
No
Internal
529
390
76
Female
No
External
362
268
of paired
bones
(b) Comparison
only,
undrilled
and drilled
Undrilled
Minimum
Twisting
(Newton
Twisting
moment
metres)
moment
(poundsforce
4,
Poundsforce
No
Male
59
NO.
at fracture
Female
58
NOVEMBER
at fracture
feet)
1969
Drilled
451
49’O
666
588
Maximum
853
71’6
Minimum
33#{149}3
361
Mean
49’!
43.4
Maximum
629
528
Mean
I
at fracture
SHAFT
IN TORSION
Female
p
51 B,
TIBIAL
Female
I
VOL.
THE
III
(a) All bones
Source
FRACTURES
feet
759
760
M.
Screw
load
plated
preparation
body
cell-In
of the
LAURENCE,
order
to
under
load
M.
measure
load,
cell carries
A.
R.
FREEMAN
the
the
load
tensile
cell
a protrusion
force
which
two
thin
strain
V. SWANSON
acting
on
in Figure
fits into
forming
designed
countersink
underside
members
on these
a screw
3 was
the
to the
steel
gauges
S. A.
forces
shown
is transmitted
by
N5
AND
on the
ofthe
head
in tension;
members
plate,
a
The
and
long
wire
connected
of
made.
ofa
electric
were
part
and
the
screw
resistance
to a standard
TENSILE
Tinsley
strain
gauge
Wheatstone
bridge.
MEMBER
Screw
tensile
rig-A
rig was
of bone as a cantilever,
BODY
support
PLATE
test
a length
at
the
free
preferred
SCREW
FIG.
Cross-section
the
Methods
On/a;’
two
for bending
tubes,
plates
the
in
tibia
bending
Technique
held
by
Methods
in
end
nails-The
itself
and
2) the
tibia when
be clinically
the former
“jammed”
tibia
as
held
nail was
inserted
no
was
described
measurable
Figures
the
twisting
shows
during
bending
The
mean
engaged
the
tests
replacement
the
the load
were
needed
minute.
for
bending
force
supported
centre
of the
p/ates-Plates
so
that
were
the
bone
preparation
at
both
cortices
a screw
on bone
when
site.
Thus
later.
bone
into
for
(h-inch)
drill
screws
were
The
in a pair
loaded
span.
screwed
to
the
was
a rectangular
box
above.
strength
and stiffness
of 1)
bond
between
a nail and the
any
kind
in a handdriven
in
WI
ft.
of steel
human
fracture
site
tubes
cadaver
could
not
with
tibiae
interlock
Nm
t3mm
KUNTSCHEIY
(EN
TWO
NAIL
ssi)
7cm
VENABLES
AT
( ENSBJ)
PLATES
driven
into the bone so as to
were measured,
using
half a
whilst
the
to
bending
protruding
in Figure
could
the
2. Nails
transmit
bone.
tests
are
oftorsion
tests
tensile
loads
exerted
plated
required
per
for
tensile
to pull
the fracture
inserted
per
to
steel
through
highest
checked
is discussed
were
or
with
passing
as to open
point
saw-cut
used
a valid
that
a c. 3-millimetre
revolutions
and
on
20-threads
in
of
loaded
screws
shown
in
in Figure
8.
on
screws
10
S
millimetre
was
When
BA
tubes
a way
into
described
moment
of
4 to 7 inclusive,
IV
a region
machine.
were
half
steel
this
with
at the
plated
above,
results
Table
of
rig
a transverse
below)
than
screws
were
tubes
gripped
in a chuck,
as shown
to a normal
surgical
tightness
Results-The
workers
tightness.
nails
of
Intramedullary
nail
3,000
clinical
Onlay
4
with
in such
cortices
saw-cut
with plaster-of-Paris
in the apparatus
the
out
diameter.
tubes
(see
more
attitude;
both
the
tests.
then cast
and tested
never
applied
at about
a transverse
Each
torsion.
was
other
This
testing
with
Steel
obtained
of screws-When
through
between
torsion
by
by
pulled
Amsler
countersunk-head
was
always
to a typical
gap
for
be
arrangement
used
stresses.
in outer
showed
results
nai/s-Kiintscher
“fractured”
to
“fractured”
by nuts.
in its weakest
running
screwdriver
Intramedullary
a 25-millimetre
the
This
been
bending
(1 inch)
of
plate
The
was
made
drill
of
measurements
introduction
were
electric
hand
space
tibiae
retained
by any
tested
to
means
and
bone.
moment
the
holes
by
tubes
screw
was
for
of test,
either
because
to any
preparation
cantilever.
have
screw
of
tensile
the
the
is free
25 millimetres
attached
in the
the weakest
necessary.
The
affixed
about
bending
applied
ofeven
the
tube
were
holes
load
were
ofsteel
clearance
which
the
in
of
which
tests
plates-Plates
lengths
out
cell for
on a screw.
force
end
those
it enables
bone
of a load
measuring
to
because
3
designed
and made
to
with the screw under
withdrawal
inch
preparations.
to pull
TOTAL
out
Sherman-type
of a tibia
was
a single
bone
2,590
screw
Newtons
ANGIJLATION
4-
FIG.
Bending
tests : variation
with
total
angulation
under
THE
load)
for
JOURNAL
OF
15
DEGREES
4
of bending
moment
(that
is, angulation
various
BONE
fixation
AND
JOINT
devices.
SURGERY
ENGINEERING
CONSIDERATIONS
IN
AT 128
INTERNAL
Nm
(s
4
Ibf
TOTAL
OF
EMPTY
CENTRAL
[±---h
HOLE
BENDING
OF
OF
TIlE
TIBIAL
ANGULATION
DEGREES
478
(108)
6
436
(es)
10
(
.4. 408
H-
+
+
EFFECT
0
OF
+
SCREW
19
+1
3
761
SHAFT
MOMENT
Nbf)
168
FRACTURES
RESIDUAL
ON SCREW
DEGREES
W±+I
tt)
TENSION
ANGULATION
EFFECT
FIXATION
T++
+
L-f-+
++
6)
+++±j
POSITIONS
159(35
-
8)
141
++
+1
L++
+1
L±
L
194
(‘
20#{149}4
+
1+
1+
-1-1
+
+1
J
)±
-I-
171
0
SCREW
screws.
Figure
WITH
LOAD
figure
Ibf
-358(81
7.5
J
1+++++++]
7
)
528
(119
15 9
500
(112)
#{247}
49(11)
7
++++++I
B
558(125)
141.
0
CELL
tests:
75
The
that
0
SCREW
LOAD
and forces
tensile
moment
bending
the total
forces
force
on
the
(the
screw
in bending,
four
was applied
moment
on that
on screws
screws
as affected
in
so as to open
screws
was reduced
Nm
having
when
one
half
been
the bending
an
a negative
moment
was applied.
z
20
0
z
0
z
z
2
0
5
0
20
10
TOTAL
ANGULATION
FIG.
FIGS.
Figure
size
(the
7-Bending
on the bending
number
against
7
tests:
stiffness
each
30
,lC
DEGREES
7
AND
8
the
effect
of countersink
of a plated
preparation
curve
represents
the dia-
in millimetres
of
the top of the countersink,
measured
along the axis of a Venables
type plate).
Figure
s-Torsion
tests: variation
of twisting
moment
with total rotation
for various
fixation
devices.
meter
VOL.
51 B,
NO.
4,
NOVEMBER
1969
5
TOTAL
ROTATION:
10
15
DEGREES
FIG.
of
plate
shown
30
a3
eight-hole
tightened);
lOT
0
CELL:
; the forces
bf
f t.
ft.
WITH
LOAD
N (IbI)
by the disposition
of
the fracture
previously
IN
6
FIG.
bending
the
SCREW
HOLE
5
tests:
accompanying
means
EMPTY
angulations
6-Bending
to bending.
changes
(119-132)
141
FIG.
5-Bending
the
B
+
SCREW
Figure
subjected
530-590
+++1
8
are
762
M.
LAURENCE,
M.
A.
R.
FREEMAN
AND
TABLE
LOADS
EXERTED
ON
SCREWS
DURING
S. A.
V.
SWANSON
IV
BENDING
TESTS
ON
PLATED
PREPARATIONS
Tensile
Plate
Total
angulation
5 degrees
.
.
II-centimetre”Swisstype”T6
13-centimetre
Campbell
T6
Venable
EN58J
9-centimetre
(irrespective
Two
(583
force
of screw
Venable
poundsforce),
per unit
with
thickness
with
a range
EN58J
of
.
353
79
503
113
‘
.
.
431
97
716
161
.
.
‘
216
48
470
106
.
.
.
255
480
108
98
Newtons
per
to
bending
loads
acting
of the plate and
reduced
and no
tension)
can
are
screws.
resorption
or
badly
applied
in
intrinsically
the
so as
millimetre
more
to
reduced,
a plane
to
in clinical
in the
“most
Effect
of material
that
the
unfavourable”
of load).
Failing
must
with
tests,
known
vary
being,
as
the
of
another
strength
two
of stainless
on the
made,
or thickness
the
parameter
materials
steel
actual
plates
differed
by
compared
5 to
modulus.
material,
geometrical
Of the
from
of a plate
in
the
The
shape
used
bending
of
in these
37 per
but
is
If bending
the
mechanics
are
In life,
described
site; this
above.
mode
is the
ofthe
Young’s
the
up
the
purpose
not
geometrical
in
the
of area
stresses,
JOURNAL
to a
these
above,
the
the
shape
of
parameter
on
early
plastic
of the
be
up
of
far
depends
the
Young’s
range
and
cross-section.
of titanium
which
by moderate
as the square,
THE
tolerated
the
from measurements
These
apparent
steel can easily
be compensated
(the section
modulus
increases
be
the
or
would
recoverable
to
material,
modulus
yield
ideal
for
to,
plate
curve
preparation,
therefore
of the
and
moment
the
(and
have
stress
of
the
and
(in
do so.
taken,
bending
yield
stiffness
second
plate
fracture
practicable.
rigidity
the
been
range,
as the
tests,
screws,
not
may
has
plastic
stress-strain
cent,
stiffness.
is hardly
be elastic
For
the
involved
but can be inferred
about
the same
proportion.
with stainless
of the plate
should
on the
early
the
the
of an implant-Probably
10 degrees.
known
by about
enhances
it would
deformations
depends
nor
those
is accurately
reproduced.
tests
factors,
purely
if this
and
of the modes
the fracture
usually
fracture
permanent
curve
section
the
easily
and stiffness
clinical
inch).
is subjected
are
however,
the
a situation
represent
any
so as to open
in these
fixed
mean
per
per
fracture
stiffness
strength
containing
such
most
used
that,
stress-strain
as
modulus
that
and
If,
neither
that
compression
many
in bending,
the
and
internally
limit
elastic
limit,
the material’s
might
tested
upon the strength
on removal
which
fracture
were
mode
ofan
to
a plated
strength
preparation.
contributes
to examine
axial
poundsforce
tend to close the fracture,
the bone (in compression)
the
and
plate
the
loads
both
of
bone
reached
poundsforce).
The
(2,640
poundsforce
(2,300-2,970
fracture-If
fracture,
perpendicular
practice
all deformations
the
strength
the
complicated,
unfavourable
While
open
the
loads
applied
to a plated
All the plated
preparations
most
that
to
(362-910
millimetre
not
OF RESULTS
of a plated
When
the bending
has taken
place,
contribute
comminuted
loads
upon the bending
,
221
a range
of 1,610-4,040
Newtons
of cortex
was 461 Newtons
per
anatomy
Poundsforce
.
DISCUSSION
Effect of fracture
10 degrees
.
at 90 degrees
402-520
angulation
Newtons
spacing)
9-centimetre
inch),
.
Total
Poundsforce
Newtons
15-centimetreHicksT6
load on screw
is lower
cannot
of hardness
inferiorities
than
be measured
which
were
oft titanium
increases
in the width
and the second
moment
OF BONE
AND
JOINT
SURGERY
ENGINEERING
of
area
true
CONSIDERATIONS
as
the
cube,
the
ofcobalt-chromium
equal
to
that
The
but
plates
not
are
by
other
of plate,
than
that
Experimentally
this
elastic
followed
supported
by
for
shown
From
and
testing
being
two
the
highest
If the
plate
loads
a given
to
be
stronger
than
any
an
engineering
point
1944,
one
preparation
of onlay
plates
the
must
1944,
antero-medial
the
be
different
mentioned.
the
individual
Venable
and similar
(and therefore
a similar
different
cross-sections
be applied
for
to a size
were
of
The
that
M
1945,
would
designs
were
nails
be
tensile
loads.
the
more
of two
four
calculable,
‘
without
on
the
sizes
sides
of the
than
a single
been described
any
mechanical
consisting
of
antero-lateral
is clearly
aspect
shown.
9 shows
screws,
rigid,
opposite
stronger
has
a preparation
other
expected
and
on
1958)
from
and
be
completely
would
plates
plates-Figure
plate
L
free
and
2)
on
each
the
loads
and
it is obvious
for
body
diagrams
the
plate
alone.
of the
four
screws
inner
screws
that
the
fi
(b)
(d)F4t
11
______________________
.
kFIG.
transfer
showed
Stamm
cross-sections
be much
combinations
Marshall
FLajF
tests:
devices
and
KUntscher
two
obtained
in onlay
each
Hicks
their
plates.
nails-Viewed
All
the
plates,
aspect
straight
highest
(c)
and intramedullary
because
other
which
a
1’
onlay
results
of screwholes
movement
(a)(F
the
Key
on
stiffness
to the
Bending
that
lower
self-explanatory.
it is obvious
4 includes
bone
4 are
opposite
as possible,
would
and the clinical
use of such
including
(e )
therefore
be
modulus
plate.
Figure
increased
bending
cannot
of the
single
Wenger
reported.
be subjected
have
test
angulation
of view,
as nearly
dimensions,
plates,
a given
would
at
those
and
being
or
cross-section
of any
would
of titanium.
2) whereas
Stamm
same
the
results
raise
; and
same
that
763
SHAFT
a Young’s
difference
and
Of
than
The
shown
Figure
deformation.
size and number
a
in
purpose
tibia.
1 ) for
for
plastic
Basom
than
would
the
and
the only
following
TIBIAL
have
Hicks
stiffnesses
curves
this
Venable
Location,
results
bending
the
or, failing
that,
of any tolerable
(Breek
the
lower
the
having
the
THE
implants,
materials
order
OF
tested.
background,
the
effective
and
observed
against
a little
of
all
as
for
loading,
of
the
plates
used
stress
hardness
lengths
such
FRACTURES
cross-section),
form
to torsional
change
in several
lengths
bone
plate
to
in bending),
different
a yield
in the
enough
available
behaviour
are
on
variations
OF
a rectangular
in the
involved.
the
interpretation
are
restrictions
curves,
and
apply
parameters
Two
plate
steel
FIXATION
of
which,
considerations
1 ) Inter-batch
INTERNAL
thickness
alloys
of stainless
same
geometrical
of
of
IN
of load
from
24cm
9
a plate
to
a bone
by screws;
between
the
for
discussion
see text.
To
predict
four-hole
plate
would
to
VOL.
effect
of varying
loads
on
be expected
reduced
bone
the
the
forces
that,
(because
and transmitted
this expectation,
51 B,
NO.
4,
the
NOVEMBER
the
the
outer
as depicted
separation
screws
in Figure
the
product
F.a
through
the
plate).
force
1969
on
may
the
inner
be
9 (c) and
must
The
screw
equal
results
was
ignored
(d),
the
increased
bending
given
little
two
screws
without
error.
separation
moment
in Figure
affected
in each
serious
would
M applied
5 show
by
the
that,
separation
half
of a
Then
it
lead
to
to
the
contrary
of
the
764
M.
screws.
This
deforms
as
takes
bone
acted
at
may
in
closer
The
the
finding
shown
place
rigid.
LAURENCE,
the
inner
measurements
and
the
an
effective
Figure
9 (f).
tested
in this
A screw
R.
FREEMAN
screw
though
the
than
of
it would
study.
hole obviously
24
weakens
V.
SWANSON
plate
contact
is not
ifthe
plate
and
that
the
some
small
the cross-section
completely
between
5 show
millimetres
only to the
applies
A.
The
do
over
about
of course,
S.
effective
in Figure
distributed
distance
result,
AND
as follows.
summarised
plate,
This
A.
be explained
9 (e), so that
Figure
to
NI.
and
the
bone
were
and
from
the
particular
length
as the
plate
completely
force
between
of the
inner
screw,
cross-section
such
and
the
each
compressive
unknown
of a plate
rigid,
bone
plate,
as shown
in
of the plates
Venable
(but
not
the Hicks).
The section
containing
a screw
hole is therefore
the weakest
in such a plate,
and
hence most of the angulation
would
be expected
to occur at one or both of the innermost
screw
holes.
This expectation
is borne
out in practice:
for instance
there was a total angulation
of
6 degrees
a similar
in a plate
whose
with
preparation
centre
span contained
an unoccupied
central
is slightly
offset
by the
These
considerations
would
increased
separation
of the inner
presence
of a screw
lead one to expect
screws
in a four-hole
weakness
increase
in the
preparation
total
The
above
any
in the
significant
is consistent
forces
acting
on
Clearly
a deep
at a total
Strength
of screws
on a screw measured
pull
can
for the ends
a screw
out
of even
weak
but
Loads
it was
on screws
during
observed
(as in the
plates
(applied
the
as
and
component
bending,
in
the
plane,
However,
since
at
bending
the
of screws
one
plates
be expected
6 shows
four-hole
that
screw
in an eight-hole
in each
of a bending
as shown
in Figure
the
the
torsional
the nail
carries
moment.
9 (e)
and
to weaken
a plate
of countersink
sizes
more
than
the
tested,
This
(f),
for
a shallow
bending
with
plate
itself,
torsion
bending
to which they are subjected-The
was considerably
lower
than
the
thin
cortices.
never
tests
tests)
had
distorted
single
plates
were
Thus
bond
the
bending
the
to a clinically
unacceptable
to be weaker
than
bone.
the
were not
of the bone
bond
needed
preparations
extent.
the
load
force
and
screw
on single-plate
preparations
that screws
were pulled
out
found
tensile
tensile
in all singly-plated
between
one.
moments
highest
the
measured,
only when
Thus,
in torsion
between
in inclined
screw
the
measured
not
total
the
is
tensile
to
axes
subjected
loads
angulation
needed
greatly
observed
holes-If
head
produce
of
to
on
the
instead
of
shear
and
in the
and
the
screws
(Table
IV)
this
angulation
affect the loading
torsional
stiffnesses
inclined,
a combination
were
screws
are
the
screws
Hicks
in approximately
in the
of the screws.
of onlay plates
two
9-centimetre
the
plates,
two-plate
at twisting
torsional
strength
and
preparations
moments
stiffnesses
tested
similar
of the
ofintramedullary
the bone
is possible,
in torsion
failed,
to those
needed
various
plates
are
same
it can
nails
from
loose
Venable
ratio
as the
that
nails-Figure
8
As in bending,
It is of interest
bone
through
screw
to break
drilled
tibiae
(Table
III).
The
in the same order
as in bending,
but the
is unsatisfactory.
contact
of the
lying
forces.
be inferred
and intramedullary
by fracture
of all
tensile
shows
the same
kind of behaviour
in torsion
as Figure
4 shows
in bending.
the two-plate
preparation
was appreciably
stronger
than
any single
plate.
holes,
relative
half
,
singly)
each
same
moments
this fact did
Experimentally
that
whole
plate.
of the
halfofa
were in a ratio of about
1 .5 to I and that at higher
a shallow
and a deep countersink
could
be serious.
a bone
the
stiffness
5, that
a small
bone.
Loading
in
was
the
innermost
application
above,
of the range
in relation
to the loads
in the bending
tests
the
Figure
the
the
that
in each
in Figure
gives only
plates.
angulation
of 5 degrees
the difference
between
moments
on
given
four-hole
only
countersink.
displayed
plate
and
screws
plate.
tests,
consequent
countersink
that,
two
to a four-hole
explanation
in
head in the
the findings,
Venable-type
moment,
ofthe
in all these
load
in
the
screws
7 shows
Figure
used
with
bending
separation
apply
mode
increase
result
to
at a given
ofthe
considerations
loaded
plate,
angulation
is independent
no screw hole compared
with 10 degrees
in
hole, at the same
bending
moment.
This
ifthe
Clinically,
nail
is smaller
THE
JOURNAL
every
than
OF
BONE
kind
offit
between
the intramedullary
AND
JOINT
SURGERY
ENGINEERING
CONSIDERATIONS
IN
INTERNAL
FIXATION
OF
FRACTURES
OF
THE
TIBIAL
765
SHAFT
canal (in which event the bone-nail
junction
will have negligible
torsional
strength
and stiffness),
to the state of affairs
in which
the nail is irremovably
jammed.
To obtain
an upper
limit,
preparation
in the latter
state
was tested,
and the result is shown
in Figure
8. Failure
occurred
by fracture
of the bone.
The strength
of the
insertion
can
of cancellous
area
through
the
bone.
with
actually
are
borne
of such
proximal
nail
were
loaded
and
is therefore
(Fig.
which
these
the
not
not
of
a larger
: the
keel
cut
8).
with
those
the
loads
include
in pure
possible.
site
with
compare
do
and
hardly
at
examined
strength
results
1967),
tibia
engages
therefore
as cantilevers,
results
of the
which
torsional
published
1964,
end
of a keel
slight
only
(1962,
present
the
a keel
only
work-The
were
the
and
in the
produced
of Lindahl
with
comparison
nail
use
properties
and
published
those
the
by the
by screws.
preparations
Bending-Lindahl’s
direct
The
bone
other
above
between
a little
cancellous
Comparison
presented
bond
be improved
a
bending,
His
and
bending
results
were certainly
similar
to the present
ones, and plates
of the same general
types (not necessarily
having
the same names)
gave stiffness
similar
to those found
in the present
work ; but Lindahl’s
plates
did not include
any designs
similar
to the Stamm
or the Hicks,
which
in these tests were
the
strongest.
right
Lindahl
angles,
more
which
massive
which
than
Venable
the
Torsion-As
in
series,
stiffness
was
by
This
be
only
OF
All
moment
range
drilled
containing
two
single-plate
strong
than
than
of plate
our
two-plate
plates).
instance,
good
and
plates
the
was
(of
represented
of the
fact
by a more
were
preparation
performance
by
at
(which
Swiss-type)
torsional
is illustrated
preparations
Sherman
preparations
his Sherman
(for
The
design)
imposed
on
Indeed,
by
TIBIA
tibiae
for
that
massive
the
weakest
but
raising,
its
Hicks
torsional
Haggland
tibia
by the
greatest
suggest
that
plate
preparation
(a
in Table
tibia.
plates
provided
of the
diameter
loads
imposed
the
thigh
come
KUntscher
bending,
strengths
withstanding
might
13-millimetre
In
(h-inch)
the
of
contraction
a contraction
V.
intact
of withstanding
capable
THE
IN LIFE
a c. 3-millimetre
with
active
WITH
BONE
torsion
Venable
appears
such
for
THE
of the
two
capable
preparation
figures
the
or
IMPLANTS
TO
strength
made
appear
no
and
the
holes
TESTED
APPLIED
bending
nail
having
OF
LOADS
KUntscher
by
our
STIFFNESS
THE
both
in a two-plate
muscles
close
nail
and
to
all
by
bending
resisted
fracturing
other
plates
deflection).
comparisons
are
internally
fixed
of an
AND
approached
excessive
above
AND
in bending
save
leg
deformations
the
only,
based
on the
fracture.
moments
If the
permissible
needed
more
moments
severe
would
to produce
criterion
be
5 degrees
were
reduced
by
used
up
to
of
total
of allowing
20
per
cent
Fig. 4).
Torsion-In
torsion
no
fixation
Two
can
even
no useful
with
NO.
a keel,
stiffness
4,
the
twisting
remained
that,
difference
NOVEMBER
between
exhibited
plates,
sustain
gave
51 B,
the
device
Venable
deformations
VOL.
its
is summarised
covered
tibia
fail
The
which
type
from
I 3-millimetre
straight
foot.
angulation
and
a
preparations
unresisted
(see
less
observed.
STRENGTH
THE
implant
the
would
were
by two-plate
THE
OF
either
within
drill.
but
cross-sections
the same
expected
exceeded
a preparation
as his strongest
plates)
larger
where
comparison
however,
elastic
had
a femur)
Lindahl.
Bending-No
the
strongest
stiffnesses
STRENGTH
the
our
would
COMPARISON
at
(on
as strong
plates
similar
(which
tested
tested
about
in bending,
both
plate
was
Hicks
moments
elastic
a
up
13-millimetre
in torsion.
1969
drilled
a strength
to
and
as high
and
the
of
the
Down’s
or
beyond
tibiae
of the
Swiss-type
magnitude
nail
was
plates
as
than
drilled
are the only
by
of total
inserted
less
weakest
imposed
5 degrees
K#{252}ntscher
intact
as that
active
in bending,
tibia.
preparations
resisted
rotation;
rotation.
lt is noteworthy
a clinical
fit
into
the
tibia
766
M.
LAURENCE,
M. A.
GENERAL
Thus
it appears
Swiss-type
active
stiffest
plate
that
are
only
R.
FREEMAN
ADEQUACY
two
Venable
stiff
to
sufficiently
OF
AND
S. A.
FIXATION
plates,
V.
DEVICES
a Hicks
the
withstand
SWANSON
plate
moments
or
a Down’s
which
might
heavy
be
duty
imposed
by
movement
of the fractured
leg.
Of these,
the two-plate
preparation
is notably
the
both in bending
and in torsion,
and such a preparation
reaches
the theoretical
maximum
strength
attainable
by a plate
fastened
to the
bone
by screws,
TABLE
THE
STRENGTH
OF TIBIAE
AND
IMPLANTS
namely
the
strength
of the
drilled
V
COMPARED
PROBABLE
WITH
APPLIED
LOADS
(a) Bending
Bending
moment
metres
Poundsforce
Preparation
Newton
Intact
tibia
Drilled
at fracture
tibia
at fracture
Imposed
by quiet
Imposed
by unresisted
Withstood
walking
by implants
KUntscher
Two
plates
Venable
I 1-millimetre
single
single
22-109
(mean 72)
.
.
.
.
.
.
.
.
.
.
80
58
.
.
10
7
leg raising
.
(mean
29-147
(mean
total angulation:
.
.
.
.
50
36
.
.
.
.
.
40
29
nail
.
.
.
.
25
18
.
24
17
(14-centimetre
(Venable)
plate
98)
.
nail
.
plate
43-166
(mean
101)
.
5 degrees
Kflntscher
Strongest
Weakest
at
137)
.
straight
I 3-millimetre
59-226
feet
Stamm)
.
.
.
7
.
5
(b) Torsion
Twisting
moment
metres
Poundsforce
Preparation
Newton
Intact
tibia
Drilled
at fracture
Imposed
by resisted
Withstood
Two
at fracture
tibia
Venable
Strongest
Weakest
plates
single
single
tibia
itself.
excessive
the
plates.
This
forces
very
In addition,
fixation
device
stiffness
comparable
of the
.
.
.
.
.
.
.
.
.
20-29
.
.
22
16
.
.
17
12
.
.
8
5#{149}8
.
.
2
I5
nail
.
keel
a danger
would
that
plate-and-screws
a two
Hicks)
with
limb
it is clear
to
.
.
reveals
the
Venable
(mean
49)
(mean
30-78
(mean 49)
(mean
36)
14-58
36)
14-21
total rotation:
.
(Venable)
fact
on
.
(15-centimetre
Kflntscher
acting
.
.
plate
plate
13-millimetre
.
at 5 degrees
.
22-72
.
rotation
by implants
29-98
feet
no
in
the
be expected
useful
type.
plate
purpose
The
bulk
preparation
clinical
use
of
to fracture
could
be served
of a single
would
THE
such
the
plate
be
JOURNAL
preparations,
tibia
by seeking
having
surgically
OF
before
BONE
since
they
bend
a stronger
a strength
and
unacceptable.
AND
JOINT
SURGERY
ENGINEERING
Type
and
screws
in
CONSIDERATIONS
number
fragments.
of screws-These
of the plate
half
each
ifthe
Even
in the bone,
is a sufficiently
screws
would
threads
insurance
against
weakening
are
screw
holes
one
a stronger
subsequent
corrosion
fatigue
every
should
only
to give
weakening
If at all possible,
OF FRACTURES
cortex,
their
be sufficient.
On this
The use of more screws,
design.
intended
FIXATION
the
strength,
with
implantation.
screws
in a plate
and
the
bone,
ofthe
threads
bone
screw
or of screws
may
having
be justified
possible
bone.
of the
be occupied
two
comminuted
grip
screws,
resorption
should
implantation,
Standard
obvious
767
SHAFT
to hold
British
the
Two
TIBIAL
of
and
basis,
the
of stronger
connection
to
of
hole
OF THE
results
show
that, at the moment
adequate,
unless
more
are needed
are
engaged
apparently
strong
different
IN INTERNAL
by a firmly
held
as an
causes
of such
screw
; empty
be avoided.
SUMMARY
1.
The
probable
during
greatest
restricted
poundsforce
The
feet).
poundsforce
feet).
2.
Twenty-two
human
torsion
when
maximum
tibiae
twisting
were
at
feet)
twisting
when
or nailed
up
to 216
moments
of
236
79
bending
and
275
to
Newton
892
moments
not
previously
a c. 3-millimetre
feet).
Tibiae
Newton
metres
had
(l73
metres
to 571
(58
metres
at bending
if they
tibia
metres
29 Newton
broke
feet)
of the
Newton
to be about
poundsforce
from
to 77’S
fracture
to about
is estimated
in three-point
(427
drilled,
not
(i-inch)
loaded
(202
to
658
poundsforce
feet)
drilled.
3. When
bent so as to open
the
all the single plates tested (reaching
(13
poundsforce
feet)),
feet)
while
and
the
5 degrees
reached
79
at
poundsforce
feet)).
metres
poundsforce
metres
(58
Newton
limit
(31.1
(36 poundsforce
15-centimetre
Hicks
feet)
and
was
49
Newton
metres
Newton
poundsforce
at 226
angulation
(elastic
at 49 Newton
(20.2
total
Stamm
was the strongest
of
moment
of 176 Newton
metres
the weakest
at 422
the
fracture
site, the 14-centimetre
its elastic
limit at a bending
5 degrees
was
limit
In torsion
metres
and
Venable
its elastic
angulation
4.
in men,
moment
loaded
metres
to a plated
to be,
which
had holes made through
both cortices
with
324 to 144 Newton
metres
(238
to 106 poundsforce
broke
poundsforce
applied
is estimated
Newton
drilled;
tibiae
broke
at from
been
drill
in
57#{149}9
to 294
from
moment
weight-bearing
(22
of
bending
metres
Newton
metres
(l66
(36
A 13-millimetre
feet)
poundsforce
poundsforce
feet)
Ktintscher
and
nail
5 degrees
total
feet).
the strongest
5 degrees
rotation
no
dependable
ofthe
plates
167
at
Newton
(elastic
limit
27’S Newton
metres
(l2’3
poundsforce
feet)).
5.
6.
KUntscher
In
both
anterior
nails
in bones
bending
surfaces
and
was
provided
torsion,
stronger
a preparation
than
any
strength
of one
single
plate,
and
in torsion.
Venable
was
plate
on
as strong
each
as the
of
the
weaker
two
drilled
tibiae.
7. The three currently
have
static
mechanical
other
8.
available
metallic
properties
The
highest
may
10.
be
load
1 1.
12.
necessary
Countersinks
shallow
applied
to a screw
as an
in plates
are
during
steel,
choice
bending
tibia.
are mechanically
insurance
against
a source
tests
redundant
subsequent
of significant
An unoccupied
screw hole in the centre
of a plate
Only
the strongest
implants
tested
were
strong
moments
is
to
be
expected
by the
introduced
drilled tibia.
VOL.
the
cobalt-chrome
between
and
them
can
titanium)
be
made
on
was
about
half
at the moment
deterioration
weakness,
that
needed
to
of implantation
in strength.
and
should
preferably
be as
as possible.
twisting
danger
(stainless
that
grounds.
pull a screw out of even a thin-walled
9.
Screws
beyond
four for one plate
but
materials
so similar
51 B,
NO.
4,
NOVEMBER
1969
fact
in
that
restricted
these
is a source
enough
to
weight-bearing.
moments
are
of serious
withstand
In
similar
two-plate
to those
weakness.
the bending
preparations
required
to Ireak
or
a
a
768
M.
LAURENCE,
M. A.
R.
FREEMAN
AND
S. A.
V. SWANSON
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P. G. (1959): Metals
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M. A. R., and SWANSON,
S. A. V. (1966):
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Actual
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D. V. (1958):
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D. (1951): An Impacting
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