D. I. CLARK,. C. E. CROFTS,. M. SALEH. From the University. ofSheffield and Royal. Hallamshfre. Hospital,. Sheffield. The rigidity of a sliding compression screw.
FEMORAL
NECK
COMPARISON
OF
D.
The rigidity
of a sliding
A SLIDING
I. CLARK,
the University
From
FRACTURE
compression
SCREW
C.
ofSheffield
E.
and
screw
FIXATION WITH
CROFTS,
M.
Royal
and three
LAG
SCREWS
Hospital,
Sheffield
SALEH
Hallamshfre
cannulated
lag screws
in the treatment
of subcapital
fractures was compared in five pairs of female cadaver femora. There were no significant differences between the compressive sfrength, bone density, cortical thickness or Singh index of the bones in each pair. A subcapital fracture was standardised using a perpendicular saw cut across the femoral neck. A urnaxial ‘load
test system’
with force
at a frequency fixation
afforded factor
important
and length
of 0.5 Hz
from
by the sliding in the stabifity
measurement
facifities
0 to 3 times
body-weight.
compression of the bone
screw implant
and
F#{248}nstelien 1987). However, compared fixation devices subjects (Van Audekercke
most in vitro using femora et a! 1979;
two
into
account.
et
a!
1980;
et
The
by using paired a static loading
Engesaeter
et
a!
1984).
reports
which
femora system This
an
offemoral
D. I. Clark, Department Newcastle
in vitro neck
study
fractures
MB, ChB, BMed Sci, of Anatomy, University upon Tyne NE2 4HH,
C. E. Crofts,
Department of Sheffield, 2JF, England.
method
which
is
using
investigated (1) paired
BSc, PhD, University Lecturer of Medical Physics and Clinical Engineering, Royal Hallamshire Hospital, Glossop Road,
© 1990
British 030l-620X/90/S1SS
J Bone Joint
VOL.
should be sent
to Dr
D. I. Clark.
Editorial Society ofBone and $2.00 Surg [Br] 1990; 72-B :797-800.
72-B, No. 5, SEPTEMBER
1990
Joint
Surgery
the femora!
Anatomy Demonstrator of Newcastle, Framlington England.
M. Saleh, MSc(Bio Eng), FRCS, FRCS Ed, SeniorLecturer, ofSheffield, Honorary Consultant, Sheffield Health Authority Department of Orthopaedics, Northern General Hospital, Road, Sheffield 55 7AU, England.
Correspondence
Bone
the
same
to simulate
stressing applied in vivo difference between the was
quality
the single
most
Place,
University Sheffield 510 University Barnsley
patient
and
(2) a dynamic
AND
as a previous arthroplasty, were excluded from the stored
properties
at
of the
loading
walking.
METHODS
Fourteen pairs of femora were obtained over the age of 60. Those with known hip
-
a femoral fracture or a tumour study. The specimens were
20#{176}C. Prior
right
from females pathology such
and
to testing,
left
femora
the mechanical were
investigated
by measuring bone density (Dal#{233}n, Hellstr#{246}m and Jacobson 1976), cortical thickness (Griffiths, Swanson and and
Freeman 1971), the Singh using a static compression
The frozen
walking. We report
fixation
screws.
from
initially
from the (Mizrahi
unsatisfactory since in life the fixation device must be able to withstand the cyclical loading pattern associated with
to mimic cyclical was no significant
MATERIALS
is
taken
lag
heads
a! 1987). The the Yariation in the different individuals
not
three
regime
MacKechnie-Jarvis 1983 ; Elmerson limitation of this technique is that mechanical properties of bone from overcame this problem same patient employed
There
unit.
The importance of bone quality in the fixation of femora! neck fractures has been emphasised by in vitro studies (Franke! 1960; Van Audekercke et a! 1979; Husby, H#{248}iseth and studies have from different
was used
Singh three
index was independent
index test.
(Khairi
et a! 1976)
bones were radiographed in pairs. The assessed for each proximal femur by observers and the femora! shaft
cortical thickness measured 120 mm below the greater trochanter using vernier calipers. After the bones had been radiographed they were returned to their storage environment. Using a ND 2100 bone density scanner, readings were taken from the proximal two-thirds of each femur, and from the femoral shaft sections. As soon as the measurements had been made a!! the bones were again returned to storage. Before mechanical testing, the bones were defrosted for six hours at room temperature, carefully cleaned of muscle and soft tissue, and rehydrated with warm saline. The mechanical tests were performed on a Mayes material testing machine (Fig. 1). Static compression tests
were
carried
out
on
six
pairs
of
femoral
shaft
797
D. I. CLARK,
798
sections. diameter
After the bones of each specimen
each sample was length to diameter
adjusted ratio
had defrosted, were measured.
pairs of randomly selected and fitted with two different
at a rate were
to give a 4 to 1 The
for
.
of 3 mm/mm.
performed
on
femora artificially fixation devices.
M. SALEH
Failure of the system was defined as the point at which a deflection of 125% of the value recorded at 30 cycles was observed (a figure set for the proposed British Standard
the length and The length of
using a band-saw of approximately
specimen was loaded to failure The maximum load was recorded. Cyclical compression tests
C. E. CROFTS,
femora!
specimens graphed
head
prostheses
were refrozen to determine the
BSI
after pattern
DD91
:1986).
testing and of failure.
The
later
radio-
five
fractured After the
RESULTS
bones had defrosted, one specimen from each pair was selected at random for fixation with a sliding compression screw, whilst the other was fixed with three self-tapping
Bone quality. In order difference in the bone pretest investigations
)
c r
-jet
that there was no paired femora, four : static compres-
LLR
a
a
-
a
a
.
to be certain quality of the were performed
-
fl,
-
JJJ.JJ#{149}#{149}. .
rOr
1E i.:. i.
.
..
0
:iu iJ:i;i
d#{149}#{149}O
i:i’’ I Fig.
Figure grips.
1
-
cannulated reduction,
The
Mayes
material
testing
lag screws. In order both devices were
unfractured femur. artificially produced neck. Purpose-built anatomical angle the test machine
were The
Hz until recorded deflections
Fig.
in our
experiments.
to achieve an anatomical initially inserted into the
of 20#{176} from the vertical (Fig. 2). The specimen
fracture
1
as used
They were removed and a fracture using a saw cut perpendicular to the grips to hold the bone at an
the lower grip. Each bone was during testing. Each specimen from 0 to 3 times body-weight 0.5
machine
occurred.
were fitted was placed
to in
covered with damp paper was loaded sinusoidally (2. 1 kN) at a frequency of
The load and displacement
graphically and from a digital after 1 and 30 cycles were
display. recorded.
Figure
2
-
The
proximal
femur
held
between
2
the
purpose-built
sion tests, bone density measurements, the Singh index and cortical thickness as measured radiographically. Statistical analysis revealed no significant difference between the right and left femora (Table I). Rigidity. The deflections recorded during the fatigue testing Table
of the five pairs of proximal femora II. There was no significant difference
deflections bones fixed there
was
recorded after the with compression no significant
three
first or 30th cycles for the or lag screws. In addition,
difference
of cycles required to produce with a sliding compression
are given in between the
between
the
number
failure in the femora screw and those fixed
fixed with
lag screws. THE
JOURNAL
OF BONE
AND
JOINT
SURGERY
FEMORAL
The
results
quality
in Table
(Singh
index
pair
of fixed
of each
deflection years) and
(number had the
and
III
compare
bone
density)
bones.
The
the
age
with
bone density of the five pairs. By deflection occurred in bones from (65 years) with the best bone quality
6) and
a high
bend in any the trabecular
Table from
bone
mode.
The
strength(kN)
Bone
(g/cm2)
density
sliding
of the
compression
bone
quality
thickness
largest
screws
in the
to collapse and head.
of At
and
left
femora
Left
14.24±2.79
12.53
0.97 ± 0.06
12
(mm)
right
not
0.96±
0.05
14
5.2±0.26
5.2±0.30
14
7.21 ±0.27
6.97 ± 0.36
site
impacted with the screw sliding down head then began to shear across the
due
to the
screw
barrel
cutting
through
the
femora! neck trabecu!ar bone (Fig. 3a). During loading the three cannulated lag screws were forced back down the drilling of
holes.
the
femora!
sheared
across
converged deformation
A crush neck the
fracture
then
of the
occurred.
fracture
line
inferior
surface
Finally
and
and rotated downwards of any implant was
the
(Fig. observed.
the
screw 3b).
head
threads No
plastic
DISCUSSION The rigidity lag screws
ofthe used
Richards currently
neck
fractures
have
the
population
at
females exclude
±2.4
799
the fracture barrel. The
first
fracture
(84 the
did
Right
6
Singhindex Cortical
the
FIXATION
the
density.
Pairs tested Compressive
bone
contrast, the the youngest (Singh index
of the tests. Failure was due bone in the femora! neck
I. Comparison the same patients
FRACTURE
deflection
4) were from the oldest subject weakest bone (Singh index 3) and
lowest smallest subject Failure
and
against
pair
NECK
from
over bone the
made
been
compared.
risk,
femora
In order were
to reflect
obtained
from
the age of 60 (Lewinnek et a! 1980). To quality as a source of error, paired femora
same
pair were pretesting
compression screw and three in the treatment of femoral
subject
were
shown to be investigations.
to reduce
tested.
The
bones
from
matched mechanically by In addition an attempt
experimental
variables
each four was
to a minimum
by
using a standardised fracture (Klenerman and Marcuson 1970) and ensuring an anatomical reduction. A saw cut perpendicular to the neck was chosen in accordance with Klenerman’s observations that subcapita! a similar angle. During walking, the angle load on the femora! head has been shown
fractures have ofthe resultant to be 10#{176} to 15#{176}
from the midline (Inman 1947; Elson and Charn!ey 1968). The offset angle of the femora! shaft is 7#{176} to 10#{176} (Williams et a! 1989). The optimum loading angle for the femora! vertical; than
head in vitro is therefore 17#{176} to 25#{176} from the 20#{176} was chosen in this study. A cyclical rather a static
simulate weight Fig. Mode screws.
of failure.
3a Figure
Fig. 3a
of the
-
sliding
screw.
reasons. theoretical
3b
Figure
3b
-
of the
lag
1967; cond!y,
Table II. femora
Deflections
recorded
during
fatigue
testing
ofthe
proximal
Table each
loading
regime
was
applied
walking. A loading regime (2. 1 kN acting sinusoidally) First, three times body-weight load acting on the hipjoint Crowninshield, the
British
Brand
and
Standards
III. Age, bony quality pair of fixed femora
is within (Rydell Johnston
Institute and
deflection
Deflection
Deflection
used
1 cycle
30 cydes
Pair
1
71
Compression Lag
7.20 2.88
12.93 11.18
2
65
Compression Lag
1.65 1.74
4.71 3.45
Compression Lag
3.44
3
65
after (mm)
after (mm)
order
the peak 1966 ; Paul 1978).
testing
Bone Pair
Age (yr)
66 67
1
71
55 65
2
65
4.71 3.45
6 6
0.96
65
6.45 5.71
6 6
0.75 0.69
of cycles to failure
1.94
6.45 5.71
65 38
3
Deflection
after
Singh
density
3Ocycles(mm)
index
(g/cm2)
12.93 11.18
5 6
0.95 0.98
1.00
4
84
Compression Lag
18.50 11.40
24.97 22.21
S 3
4
84
24.97 22.21
3 3
0.53 0.56
5
81
Compression Lag
2.75 2.94
4.30
75 150
5
81
4.30
4 4
0.89 0.79
VOL.
72-B,
No. 5, SEPTEMBER
1990
5.46
5.46
to
Se-
recommends under
Number
Screw
Age (yr)
in
of 0 to 3 times bodywas chosen for two
a of
800
D. I. CLARK,
2. 1 kN femoral
sinusoidal
loading
heads. The choice
biomechanical et a! 1981). orientation optimum
of the
pattern three
investigations Mizrahi found
when
lag
screws
inferior showed
tance ofpara!le! screw placement. Both found no improvement in fixation if screws were used. The compression sliding barrel for controlled impaction (Clawson 1964). Its blunt nose preventsjoint Biomechanical
testing better 1961).
provide improved demonstrated by
has
was
based
shown
on
to be the the impor-
authors, however, more than three hip screw has a at the fracture site penetration.
that
a large
threaded
internal fixation than a triflanged The advantage of the side plate
fixation Haboush
to
the
(1952).
femora! In both
shaft devices
to was the
initial event in failure was impaction ofthe This underlines the importance of parallel
femoral neck. placement of
the lag screws sliding action
the
allowing permitted
backing out, and by the compression
hip
controlled screw.
Franke! (1960) showed that in saw cut femoral neck fractures fixed in vitro, the bone absorbed 75% of the load applied to the femoral head and the device the remaining findings
25%. The results in Table III confirm and suggest bone quality to be the most
M. SALEH
shown that in influencing
testing
(Mizrahi et a! 1980 ; Rubin a triangular three-screw
of two superior and one configuration, whilst Rubin
screw provides nail (Brodetti
fatigue
C. E. CROFTS,
Frankel’s important
factor
in the rigidity ofthe bone implant unit. Using an unphysiological static load and femora! heads from different subjects, other workers have shown that both the sliding compression screw and three lag
No benefits commercial article.
in any party
the same a sliding
results three larger fying
paired
femora!
subject compared two Von Bahr compression screw (Engesaeter
static loading difference was
confirm
to use
regime found
of our study, Engesaeter’s
heads
from
lag screws with et a! 1984). A
was used and no significant between the two devices. The using static
a dynamic test results
loading regime and show that
parallel screws provide as rigid a fixation as the sliding compression screw. In addition, by quantithe mechanical strength of the femora, we have
factor
received or will be received or indirectly to the subject
from a of this
screws Scand
BSJ.
Draft for development. Method for determination of endurance properties of stemmed femoral components of hip joint prostheses 1986. BSI(DD91 :1986).
Oawn
DK. Trochanteric fractures treated fixation method. J Trauma 1964; 4:753-6.
Crowninshield RD, Brand RA, Johnston velocity and age on hip kinematics 132:140-4.
and
Dal#{233}nN, Hellstr#{246}m L-C, Jacobson mechanical strength of the femoral 47:503-8.
by the
sliding
RC. The kinetics.
screw
Elson
RA, Charnley J. The prosthetic replacement 6:19-27.
B. Bone mineral neck. Acta Orthop
direction of the hip
plate
effects of walking C/in Orthop 1978; content Scand
ElmersonS, Andersson CB, Pope MH, Zetterberg C. Stability in femoral neck fractures : comparison of four fixation vivo and in cadavers. Acta Orthop Scand 1987 :8:109-12. of the resultant joint. Med and
and 1976;
of fixation devices in
force in total Biol Eng 1968;
Engesaeter LB, Asserson 0, Molster A, et al. Stability of femoral osteotomies fixed by Von Bahr screws or by compression hip EurSurgRes 1984; l6suppl2:37-40.
VH.
Frankel neck.
Mechanical Acta Orthop
factors for internal Scand 1960; 29 :21-42.
fixation
of the
Criffiths WEC, Swanson SAy, Freeman MAR. Experimental fracture of the human cadaveric femoral neck. J Bone [Br] 1971 ; 53-B:136-43.
Husby
T, Hoiseth A, F#{248}nstelien E. Strength fixation : comparison of six techniques Scand 1987; 58 :634-7.
VT. Functional
aspects
BoneJointSurg Khaki
of the
of femoral in cadavers.
abductor
Joint
L, Marcuson
RW.
Intrascapular 1970;
J Bone Joint Surg [Br]
52-B
AC. Femoral compared.
fractures :514-7.
neck fracture Med 1983
J R Soc
Mizrahi
J, Hurlin RS, Taylor transfer and optimum pin Muller screws, of fractured 1980; 18:319-25.
Paul
JP. Forces Mech Engrs
Rubin
R, Trent P, Arnold W, Burstein experimental femoral neck fractures Trauma 1981 ; 21 :1036-9.
of the
hip.
;
of the
J
fixation 76:643-8.
: rigidity
in the
human
body.
A. Knowles : a biomechanical
NW. Forces acting on the femoral head-prosthesis strain gauge supplied prostheses in living persons. Scand 1966; 37 (Suppl 88):l-132.
Van
Audekercke R, Martens study on internal fixation 1979; 141 :203-12.
M, Muller of femoral
R, Dyson Churchill
Edinburgh,
THE
of the and a C/in of five
JK, Solomon L. Investigation of load configuration in the internal fixation, by femoral necks. Med Bio/ Eng Comput
transmitted by joints 1967; 18l(3J):8-13.
PL, Warwick
neck
The significance of hip fractures.
Rydell
ed.
Orthop
Robb JA, et al. Femoral trabecular-pattern content measurement by photon absorption JBone Joint Surg [Am] 1976; 58-A :221-6.
Lewinnek CE, Kelsey J, White AA, Kreiger NJ. comparative analysis of the epidemiology Orthop 1980; 152:35-43.
Williams 37th
fracture
Acta
1947; 29:607-19.
MRA, Cronin JH, index and bone mineral in senile osteoporosis.
MacKechnie-Jarvis techniques
fatigue Surg
fractures
neck
muscles
neck screw. femoral
Haboush EJ. Photoelastic stress and strain analysis in cervical ofthe femur. Bu//Hosp Joint Dis 1952; 13:252-8.
Klenerman femur.
it does not allow of the different
important
study on the use of nails and bolt of the femoral neck. Ada Orthop
in the fixation of fractures 1961 ; 31 :247-71.
found both devices equally effective. Husby et a! (1987) showed that the sliding compression screw was superior to three lag screws, whilst Elmerson et a! (1987) found the reverse, three lag screws providing better fixation
the results since in bone quality
form have been related directly
A. An experimental
Inman
significantly influenced for possible variations femora under test. The only report
was the most of fixation.
REFERENCES
Brodetti
screws have a superior holding power to the Smith Peterson nail (Brodetti 1961 ; Van Audekercke et a! 1979). However, when comparing parallel lag screws to the sliding compression screw there is disagreement. Van Audekercke et a! (1979) and MacKechnie-Jarvis (1983)
than the Richards sliding compression screw. A!! these studies used unmatched femoral heads from a range of male and female subjects. This factor could have
bone quality the outcome
JOURNAL
Proc
Inst
pinning study.
OF BONE
LH. 1989
AND
J
: a study on Ada Orthop
JC, Stuyck J. Experimental neck fractures. C/in Orthop
M, Bannister Livingstone,
of
Gray’s
Anatomy.
:435.
JOINT
SURGERY
