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Number 339, pp 82-91
0 1997 Lippincolt-Raven Publishers
Modified Transverse Locking Nail
Fixation of Proximal Femoral Fractures
B.H. Ziran, MD; N.A. Sharkey, PhD; T.S. Smith, MS; G. Wang;
and M. W. Chapman, MD
tween implant constructs. All anatomic specimens failed, with fractures of the proximal
fragment involving medial and lateral cortices.
Synthetic specimens did not fracture but
showed failure with implant deformation at
the level of the skeletal defect. The use of high
seated transverse locking nails for complex
proximal femoral fractures is a viable option
and has comparable in vitro mechanical performance with reconstruction nails. Although
not shown to be a problem in the present study,
clinical evaluation of screws through the medial femoral neck cortex is required.
It was hypothesized that transverse locking
screws of intramedullary nails, seated above
the lesser trochanter, provide equal strength to
that of reconstruction nails, and that screws
placed through the medial cortex of the
femoral neck do not have adverse biomechanical effects during physiologic loading. Synthetic femurs (n = 10) and paired anatomic
specimen femurs (n = 14) were tested intact
and with an intramedullary device in place. Intact specimens were loaded nondestructively,
then a segmental subtrochanteric defect was
created and either a high seated transverse
locking nail or a reconstruction nail was inserted and statistically locked. Axial and torsional stiffness were determined followed by
axial failure testing. Mechanical parameters
evaluated were stiffness, displacement, and energy. The implanted specimens did not show
any statistically significant difference between
transverse or reconstruction screw constructs
with any of the measured parameters (stiffness, displacement, and energy). Failure tests
in implanted specimens also did not show any
statistically significant difference in yield load,
yield displacement, or energy to failure be-
Fixation of unstable fractures of the proximal femur particularly is challenging because of the large axial forces and bending
moments occurring in this regi0n.6JlJ5~14~26
Although standard intramedullary nails offer
distinct advantages to plates, in cases where
the posteromedial buttress is not intact, nails
where the proximal interlocking mechanism
uses screws directed up the femoral neck
into the femoral head (hereby referred to as
reconstruction nails) or plates must be
used.24.7. 16,18325 One of the commercially
available transverse locking nails (Alta
femoral nail, Howmedica, Rutherford, NJ)
potentially is useful for such fractures because of the design of the proximal fixation.
The proximal holes for crosslocking screws
in this nail are closer to the top of the nail
than other nail designs, and therefore can be
From the Department of Orthopedic Surgery, University of California, Davis, Sacramento. CA.
Implants were provided by Howmedica Inc, Rutherford, NJ.
Reprint requests to B.H. Ziran, MD, Department of Orthopedic Surgery, University of Pittsburgh, 1010 Kaufman Building, 3471 Fifth Avenue, Pittsburgh, PA
Number 339
June, 1997
placed above the lesser trochanter, achieving
fixation in the femoral neck or the femoral
head. The purpose of this study was to measure
the acute strength of a fixation construct in a
simulated unstable proximal femoral fracture,
comparing intramedullary nails locked with
transverse screws to those locked with reconstruction screws.
Experimental Design
In the first experiment, synthetic femurs (Sawbones, Pacific Labs, Seattle WA) were tested nondestructively in torsion and axial loading. The
specimens were first tested intact, and then after
fixation of a simulated unstable proximal femoral
fracture. The independent variable of interest was
fixation device (nails using transverse screws or
reconstruction screws for proximal fixation); the
dependent variables measured were stiffness, deformation, energy to peak load, and energy loss in
cyclic loading.
In the second experiment, the synthetic femurs
from the first experiment, and as paired human
anatomic specimen femurs with simulated unstable
proximal fracture, stabilized with either transverse or
reconstruction screw fixation, were loaded to failure
in axial compression. The independent variables of
interest were specimen type (synthetic, fresh, or embalmed bone) and fixation method (transverse screws
or reconstruction screws), and the dependent variables were stiffness, yield displacement, yield load,
yield energy, and mode of failure.
Modified Transverse Locking Nail Fixation
The human anatomic specimen bones used in
the second part of the study included two pairs of
fresh femurs and five pairs of embalmed femurs.
Age of the donors was unknown. All human specimens were radiographed before testing to rule
out any obvious pathology. In addition, the specimens underwent computed tomography (CT)
scanning at various levels to measure density and
describe morphology. Density was recorded from
two levels (cephalad and central) in the femoral
head, from two intracortical loci on the lateral
cortex of the femoral neck, and from one intracortical locus on the medial cortex of the femoral
neck. Morphologic measurements included
femoral neck diameter at the subcapital level, inner and outer cortical diameters at the subtrochanteric level, offset of the femoral head from
the medullary canal, and total cross sectional area
at the head, neck, and subtrochanteric levels.
Specimen Preparation
Distally, femurs were potted in polymethylmethacrylate to the level of the epicondyles, with
several embedded screws to prevent rotation.
Proximally, the caudad 1/2 of the femoral head
was similarly embedded in polymethylmethacrylate in a fashion that allowed loading through the
femoral head (Fig 1). The anatomic specimen femurs were stripped of all soft tissues and the distal femoral condyles were removed parallel to the
transverse plane. At this point, mounting in polymethylmethacrylate was done identically to the
synthetic femurs.
After mechanical testing of the intact bones
(synthetic and anatomic specimen), an unstable
proximal femoral fracture was simulated by reSpecimens
moving a 3-cm segment of bone. Transverse saw
cuts were made at 1 and 4 cm below the lesser
The synthetic bones (n = 14) tested were second
trochanter, and the intercalary segment was regeneration composite bones, 42 cm in length,
moved. The lesser trochanter also was removed,
consisting of a resin covered fiberglass cortex
but the lateral cortex at this level was left intact to
and a plastic foam filled medullary canal. The
allow lateral cortical purchase for both types of
stiffness of these bones is close to that of fresh
screws (Fig 1).
human femurs, and the specimen to specimen
In the synthetic specimens, canals were
variation is much less (coefficient of variation
reamed to 14-mm diameter for implantation of
<7.3%). However, the composite bones are cona 13-mm x 380-mm nail. In the human
siderably more elastic than fresh human bones,
anatomic specimens, canals were reamed 1
with only approximately 1/5 the energy loss per
loading cycle in axial compressive loading2L.22 mm larger than the size at which the reamer
began cutting the inner endosteal cortex (chat(nonpublished data, Ziran BH, Sharkey NA,
ter). With this technique, anatomic specimens
Smith TS, Wang G , Chapman M W Comparisons
all received 13-mm nails whose lengths were
between synthetic and cadaveric bone specimens
variable depending on the length of the specimen.
in biomechanical testing 1995).
Clinical Orthopaedics
arid Related Research
Ziran et al
by the same trauma surgeon (BHZ) who had clinical experience using both fixation systems.
Mechanical Testing
Fig 1. Osteotomized femur in loading apparatus for axial testing. Note transverse screws
placed cephalad to lesser trochanteric level.
In specimens fixed with reconstruction screws,
the upper fragment was reamed to 17 mm diameter to accommodate the larger proximal segment
of the nail.
Transverse locking screws were placed so that
the most proximal screw exited the medial femoral cortex in the subcapital area and the more
distal of the proximal screws exited above the
lesser trochanter (Fig 1). The reconstruction
screws were placed into the femoral neck and head
without penetration of the femoral head. Distally,
all nails were statically locked with two screws.
Reaming and nailing were done in the laboratory
Axial testing was done using an Instron 1122
testing machine (Instron Corp, Canton, MA)
equipped with a 5-kN axial load cell. The testing
device was interfaced to a personal computer using Asyst scientific software (Asyst Software
Technologies, Inc, Rochester, NY) and an analog
to digital measurement and control system (Series
500, Keithley Instruments, Inc, Cleveland, OH).
Specimens were mounted on a turnstile and
loaded along the mechanical axis, with the
femoral head centered over the condyles. Simulation of muscle loading was not done.13 For nondestructive testing, specimens were loaded
cyclically in compression at 10 mm per minute
top peak loads of 1000 N, and loads were
recorded at 0.05-mm increments of displacement.
Each femur was subjected to five conditioning
loads followed by five loading cycles from which
data were collected and averaged. Destructive axial testing was done with a ramp load to failure
after several low conditioning cycles to 500 N.
During testing in torsional loading (synthetic
specimens only), the femoral head was mounted
by means of an adjustable fixture to a 250-Nm
torsional load cell. The base of the femur was
mounted to an xy sliding table. The fixture was
adjusted so that the axis of rotation was collinear
to the axis of the femoral nail (Fig 2). A torsional
stepper motor (Model S83-93, Compumotor,
Rohnert Park, CA) in series with the load cell was
mounted to the Instron crosshead. The specimens
were loaded cyclically at a rate of 0.05 rad per
second up to 10 Nm of torque. Loading was alternately clockwise and anticlockwise from the neutral position. After five conditioning cycles, data
were collected and averaged from five loading
cycles (Fig 2).
Analysis of Findings
The structural stiffness in the nondestructive tests
was calculated as the slope of the last six digitized data points before achieving peak load and
using elastic portion of the load displacement
curve for destructive tests. Energy to peak load
was calculated as the area under the load versus
displacement curve. Energy loss per cycle was
the percentage difference in area under the loading and unloading load versus displacement
Number 339
June, 1997
ModifiedTransverse Locking Nail Fixation
lyzed using a paired t test. The effects of bone density and morphologic variable measured from the
CT scans in relation to mechanical properties were
evaluated using a stepwise linear regression.
Fig 2. Osteotomized specimen mounted for
torsional testing. Base mounted on an x y table
to allow centering and to reduce extraneous
curves. The 95% secant method was used to determine yield load in destructive tests (the intersection of the load versus displacement curve
with a line whose slope is 95% of the elastic portion of the load versus displacement curve).
A nonpaired test was used for the nondestructive tests using the synthetic femurs. For the destructive axial tests, a two-way analysis of
variance (ANOVA) comparing specimen type synthetic, fresh anatomic specimen, embalmed
anatomic specimen) and fixation method (transverse screws or reconstruction screws) was done,
using a Tukey followup test. Side to side differences in the anatomic specimen groups were ana-
In the nondestructive axial loading tests, there
were no significant differences in stiffness,
displacement, energy to peak load, or energy
loss between constructs stabilized with transverse screw or reconstruction screw methods.
However, both of these constructs were considerably less stiff and less elastic (greater energy loss) than the intact synthetic femurs (Fig
3). Similarly, in torsional testing the two constructs had very similar mechanical values, but
both were 30% to 40% as stiff and less elastic
than the intact femurs (Table 1, Fig 4).
In the axial tests to failure, ANOVA indicated that there was a significant effect of specimen type (synthetic bone versus anatomic
specimen bone) for yield displacement (p <
0.02) and stiffness (p < 0.01). There were no
statistically significant differences in any parameter between fixation devices (transverse
screw or reconstruction screw) in the anatomic
bone specimens or the synthetic bone specimens (Table 2, Figs. 5 6 ) .
Gross examination of the failed specimens revealed several differences in failure
mechanism between specimen types and fixation devices. In the synthetic specimens, transverse screw specimen constructs failed by
bending of the nail at the more distal of the two
proximal screw holes (Fig 7); frequently the
screw in this hole bent as well. In synthetic
specimens with reconstruction screw fixation,
failure occurred by bending of the nail at the
level where it increases diameter proximally
(Fig 8). The most proximal screw often bent,
but did not cut out. There were no femoral neck
fractures in the synthetic specimens.
In human anatomic specimen bone, failure
occurred by a combination of bone failure and
bending of the fixation device. Typically, bone
failure would initiate at a screw hole and
progress to a basicervical fracture of the
femoral neck. In transverse screws constructs,
Clinical Orthopaedics
and Related Research
Ziran et al
TABLE 1. Axial and Torsional NondestructiveTesting Data
Axial (n = 14)
Stiffness (N/mm)
Energy to peak load (N-m)
Axial displacement (rnm)
Energy loss (%)
Torsional (n = 14)
Stiffness (N/rnm)
Energy to peak load (N-rn)
Displacement (")
Energy loss (%)
Screws (n = 7)
Screws (n = 7)
1369 * 100
0.38 .03
0.8 0.1
533 +. 70
1.04 0.15
2.3 0.4
532 ~t39
1.05 0.12
2.4 i 0.4
108 + 10
0.50 & .02
5.4 * 2.0
126 i 23
0.46 .05
4.4 1.9
* 22
* .01
* .01
There were no statistically significant differences between implant types
vide geometric and densitometric inputs for
a stepwise linear regression analysis. No associations were found between the geometric
or densitometric data and the mechanical behavior of the construct under axial load. Side
to side variances and subject to subject variances were not statistically significant.
the fracture started in the medial cortex of the
femoral neck at the site of the more caudad
proximal interlocking screws (Fig 9). In reconstruction screw constructs, the fracture
started on the lateral side at the site of the more
caudad locking screw, but ultimate failure involved the medial cortex of the neck (Fig 10).
In all cases, progression to failure occurred
with bending of the implant and fracture of the
femoral neck. No differences were observed
between fresh and embalmed specimens and
no side to side differences in failure were seen.
Computed tomographic data of the intact
anatomic specimen bones were used to pro-
Anatomic specimen bones (n = 14)
Stiffness (N/mm)*
Yield load (N)
Yield displacement (mm)**
Yield energy (N-m)
Synthetic bones (n = 14)
Stiffness (N/mm)*
Yield load (N)
Yield displacement (mm)**
Yield energy (N-rn)
< 0.02
The authors found no differences in the mechanical properties of unstable proximal
femoral fractures fixed with either transverse
or reconstruction locked intramedullary nails.
Axial Test to Failure
*p < 0 01
Screws (n = 7) Screws (n = 7)
163 * 44
2705 813
32 5 21
149 + 57
2763 f 558
23 + 10
36 20
533 * 70
3165 f 930
13 * 4
22 * 11
532 39
2672 796
17 + 10
Number 339
June, 1997
ModifiedTransverse Locking Nail Fixation
Fig 3. Axial nondestructive test. No
statistically significant differences
between implant types. NS = not
Fig 4. Torsional nondestructive
tests. No statistically significant differences between implant types. NS
= not significant.
Fig 5. Synthetic axial test to failure.
No differences between implant
types. NS = not significant.
Clinical Orthopaedics
and Related Research
Ziran et al
YirM Load
(N x i 0 2 )
(Nlorm I 10)
Esrrgy l o Yidd
Fig 6. Anatomic specimen axial
test to failure. No differences implant types. NS = not significant.
To some extent this reflects the fact that in
this segmental defect model, much of what
is being measured is the mechanical properties of a 13-mm diameter ‘Ti rod, which
was the same in all specimen types. The
findings further show that the proximal
transverse crosslocking screws provide torsional and axial stability similar to that
provided by the cephalomedullary locking
screws of a reconstruction nail. Although
the reconstruction and transverse locked
femoral nails were mechanically equivalent
in the simulation of an acute, unstable
proximal femoral fracture, it is important
to note that these constructs provided only
40% of the axial stiffness and 30% of the
torsional stiffness of the intact bone.558JOJ3
Therefore, in the actual clinical setting, patients with subtrochanteric fractures stabilized with either of these methods may still require significant weightbearing precautions
postoperatively until the fracture has healed
Fig 7. Failed transverse locking nail (left) versus intact reconstruction nail (right).
Fig 8. Failed reconstruction nail (left) versus intact reconstruction nail (right).
Number 339
June, 1997
ModifiedTransverse Locking Nail Fixation
Fig 9. Failed anatomic specimen with transverse locked nail. Note basicervical fracture at
screw hole (arrow).
sufficiently to share the physiologic loads and
avoid fatigue failure.
The two devices and specimen types also
differed in the mechanism of failure. Synthetic
specimens (designed as a fiberglass mesh encased in the cortical material) did not show the
catastrophicfailure and fracture seen in human
bone; failure in synthetic specimens occurred
exclusively in the implants. Both implants
consistently bent at a predictable site of stress
concentration, either at a change of diameter
(reconstruction screws) or a screw hole (transverse screws), with occasional bends in the
fixation screws.Although anatomic specimens
ultimately fractured, there was a variable region of plastic deformation in the load deformation curve. Anatomic specimens fractured
at sites of stress concentration in the bone
(screw holes) and bent at stress concentrations
in the implants (screw holes and diameter
changes). Both implant constructs in human
anatomic specimen bone ultimately failed
through bone in the region of the femoral
neck. In transverse locked specimens, the fracture seemed to be related to the medial screw
holes, whereas in reconstruction locked specimens, fractures seemed to initiate laterally, al-
Fig 10. Failed anatomic specimen with
cephalomedullary locked nail. Note fracture of
medial cortex and crack at lateral cortex.
lowing the medial bone cortex to be forced
against the medial wall of the nail (varus deformity) before failure of the femoral neck.
Implants in anatomic specimens were not as
bent as those in synthetic specimens, indicating a greater (and probably more realistic)
contribution to energy absorbed in failure by
the human anatomic specimen bone. Few
studies have addressed the differences in proximal fixation of intramedullary femoral nails.
Kinast et al9JO found that shorter screws in
transverse locking systems outperformed
(stiffer and stronger) the longer screws in
oblique locking systems. The authors did not
assess reconstruction systems. Johnson et al*
described a loss of mechanical performance
with increasing obliquity of proximal screw
fixation in standard intmmedullary nail systems. The present study did not have such effects between reconstruction and transverse
locking systems, possibly because the effects
the reconstruction screws’ more oblique orientation were offset by their increased diameter.
Ziran et al
The placement of transverse crosslocking
screws used in this study requires drilling a
hole through the medial cortex of the
femoral neck, and there is concern that this
defect may constitute a stress riser that increases the risk of femoral neck fracture.
Edgarton et a15 found that if the diameter of
cortical defects was smaller than 15% of the
outer bone diameter, the strength of the bone
was not compromised, thus suggesting that
such defects may not be clinically important.
Even though failure of anatomic specimen
bones progressed through these screw holes,
it was observed that failure loads of the femurs fixed with the transverse screws were
similar to the failure loads of the femurs
fixed with the reconstruction screws, which
do not penetrate the medial cortex of the
femoral neck. Femoral neck diameters measured from CT data were 4 to 4.5 cm, and the
transverse screw holes were 4.2 mm, less
than the 15% threshold in the study done by
Edgarton et al. Furthermore, in the authors’
clinical experience using transverse crosslocked intramedullary nails to fix unstable
proximal femoral fractures, femoral neck
fractures have not been encountered as a
Swiontkowski et a120 found torsional,
bending, and side to side density differences
of 16.5%, 28.9%, and 12.3%, respectively, in
paired anatomic specimen femurs, suggesting
that using paired femurs to decrease variance
in biologic samples may be only marginally
useful.20Minimalside to side and subject to subject differences in mechanical properties of intact femurs were seen in the current study. The
attempt to correlate morphologic properties of
the proximal femur (geometry and density) with
mechanical performance by regression analysis
did not show any significant relationships and
corroborates findings of previous studies.12.19
One interpretation of this finding would be that
subtle differences in surgical technique may be
of sufficient mechanical importance to overwhelm morphologic differences. For example,
the authors speculate that slight imprecision in
placement of the screw holes could result in
Clinical Orthopaedics
and Related Research
preloads in the construct that would affect its
mechanical behavior when extrinsic loads are
applied. This also may be germane to the observation that the variance in mechanical properties of synthetic bones was much greater when
they had been osteotomized and fixed than
when they were intact.
Analysis of variance indicated that the
type of bone (anatomic specimen versus synthetic) was a significant factor in failure mechanics but that the type of implant was not.
This observation concurs with other studies
that show some of the advantages and limitations of the synthetic bones and the anatomic
specimen bones21.22.24 (nonpublished data,
Ziran BH, Sharkey NA, Smith TS, Wang G,
Chapman MW: Comparisons between synthetic and cadaveric bone specimens in biomechanical testing. J Orthop Trauma [submitted]). Because the synthetic bones are
more readily available, more uniform, and
less expensive than anatomic specimen
bone, their use in this type of comparative
testing seems supported. However, differences in stiffness, displacement, and mode of
failure between constructs using anatomic
specimen versus synthetic bone indicates
that the absolute value of measurements
made using synthetic bone may not be directly applicable to biologic bone. Moreover,
if fatigue testing is contemplated, which
clinically would be the most relevant mode
of failure testing, the synthetic bones would
be inappropriate because their elasticity is
greater than that of true bone, and their
mechanism of failure is different.
Clinically, the transverse locked intramedullary nails offer several advantages that
the reconstruction systems do not offer. Use
of the reconstruction nail requires imaging of
the hip joint, which can be difficult in certain
patients and in certain operative positions.
Because the indication for using a reconstruction nail occurs relatively infrequently,
many surgeons may be less familiar with
their use, thus increasing the likelihood of
intraoperative difficulty. Moreover, the reconstruction nail is usually twice the cost of
Number 339
June, 1997
a standard intramedullary nail. The standard
transverse locking femoral nail thus provides
a familiar, reliable, and cost effective alternative to the reconstruction nail. The authors
have shown that in an in vitro setting, a high
seated transverse locking nail shows satisfactory mechanical performance as compared with a reconstruction nail. Furthermore, synthetic bone seems to provide an
excellent material for comparative testing.
The results of the present study should be interpreted with caution before the completion
of clinical studies with long term followup.
The authors thank Michael Madison, PhD, for his
editorial assistance.
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