anatomical reduction is not necessary in treating non-porotic ...

ANATOMICAL REDUCTION IS NOT NECESSARY
IN TREATING NON-POROTIC UNSTABLE
INTERTROCHANTERIC FRACTURE – A
BIOMECHANICAL STUDY OF PORCINE MODEL
ABSTRACT
Shi-Wei Lin, Jaw-Lin Wang
Institute of Biomedical Engineering
National Taiwan University
Taipei, Taiwan, ROC
Proceedings of IMECE’03
2003 ASME International Mechanical Engineering Congress & Exposition
Washington, D.C., November 16-21, 2003
IMECE2003-42910
fragment was prepared using surgical saw (Figure 1). The fracture
was reconstructed by a compression hip screw, and the anatomical
reduction was achieved with a cerclage wiring (Figure 2A), and
without cerclage wiring (Figure 2B). A static force-controlled load
was gradually applied to the femoral head up to 700 N to simulate
post-operative weight bearing condition for both surgical techniques.
The displacement, strain at tube plate and femur were recorded for
analysis. The stiffness of femur complex, strain at tube plate per load,
and strain at medial side of femur per load were calculated for analysis.
Two-way analysis of variance (ANOVA) was used for the above three
parameters to determine the differences of different cerclage wiring
techniques.
Intertrochanteric fracture occurred more than 200,000 cases each year
in the United States, with mortality rate up to 20 percents. Evans
classified the intertrochanteric fracture pattern to stable and unstable
group. Most of the complications occurred in the unstable group. It is
speculated that in the unstable intertrochanteric fracture, the lag screw
migrates easily into the porotic femur head and than causing fixation
failure. So the treatment of porotic unstable femoral intertrochanteric
fracture depends on the bone quality, severity of comminution,
anatomical reduction and methods of fixation. An abundant of studies
had been focused on how to reinforce the porotic unstable
intertrochanteric fracture including osteotomies, cement augmentation,
anatomical reduction, and different implant applications. Among the
many techniques, the anatomical reduction using cerclage wiring was
widely used to enhance the stability of osteoporotic fractured femur.
However, in the young adult, the application of cerclage wiring is
controversial. The current study compares the mechanical properties
of two anatomical reduction techniques of unstable intertrochanteric
fracture reconstructed by a compression hip screw. Four porcine
femurs of 10 months-old were used to simulate the non-porotic human
bone. The specimens were stripped of all soft tissues. Each femur
was prepared with four holes for dynamic hip screws following the
standard surgical procedure. The anatomical reduction was achieved
by a cerclage wiring and without cerclage wiring. The results reveal
that in the non-porotic porcine model, there is no statistically
difference in stiffness, plate strain and medial bone strain per load. No
matter the unstable intertrochanteric fracture is reduced with cerclage
wire or not. The non-porotic unstable intertrochanteric fracture
anatomical reduction is not necessary if protective weight bearing is
obeyed. However, whether the cerclage wiring is necessary or not for
the osteoporotic unstable femur fracture needs further study.
Fracture Line
Strain Gage
Fracture Line
Strain Gage
Figure 1. An artificial Evans Type-3 intertrochanteric
fracture with a posterior medial bony fragment.
MATERIAL AND METHODS
Four porcine femurs of 10 months-old were used to simulate the nonporotic
human bone. The specimens were stripped of all soft tissues.
Each femur was prepared with four holes for dynamic hip screws
following the standard surgical procedure. The position of lag screw
tip was in the center of femoral head with 5 mm distance to the
subcondral bone in both AP and lateral view. All positions of
insertion were confirmed with radiography. The femur was potted with
epoxy and aligned at 25 degree adduction in the coronal plane and
neutral in the sagittal plane to simulate the leg stance. One strain gauge
was applied on the lateral side of tube plate close to the first screw
hole. The second strain gauge was applied on the medial side of the
femur 2 cm beneath the lesser trochanter (Figure 1). An artificial
Evans Type-3 intertrochanteric fracture with a posterior medial bony
(A)
Figure 2. The unstable intertrochanteric fracture was
reconstructed by a compression hip screw, and the
anatomical reduction was achieved with (A) cerclage wiring,
and (B) without cerclage wiring.
(B)
1
Copyright ©2003 by ASME

RESULTS
The results listed in Table 1 revealed that in the non-porotic porcine
model, there is no statistically difference in stiffness, plate strain and
medial bone strain per load. No matter the unstable intertrochanteric
fracture is reduced with cerclage wire or not.
Table 1: The comparison of mechanical properties of
unstable intertrochanteric fracture constructed by a
compression hip screw with and without the cerclage
wiring
Stiffness
(N/mm)
Lateral Plate Strain
per Force
(micro strain/N)
Medial Bone Strain
per Force
(micro strain/N)
With Wiring 238 (90) 0.024 (0.507) 0.352 (0.506)
Without Wiring 269 (113) 0.047 (0.564) 0.392 (0.405)
p-value 0.685 0.953 0.905
DISCUSSION
Despite the massive effort in solving the high complication rate in the
osteoporotic unstable intertrochanteric fracture surgery, the
complications are still observed such as head varus deformity, lag
screw migration in the head and even the lag screw cut out of the
femur head. Instead of traditional failure testing which is not
reasonable in clinical condition, the current study limited the
maximum loading to 700 N to mimic the post-operative protective
weight bearing. In our non-porotic bone-implant testing, we cannot
see if there is any statistically significant difference for stiffness and
strain at plate and bone between two different cerclage wiring
techniques. The reason may be due to the good quality of bone
strength that makes the purchasing strength of lag screw strong enough
to support the loading in the range of protected weight bearing. Hence
the further anatomical reduction is not necessary. In conclusion, the
non-porotic unstable intertrochanteric fracture anatomical reduction is
not necessary if protective weight bearing is obeyed. However,
whether the cerclage wiring is necessary or not for the osteoporotic
unstable femur fracture needs further study.
ACKNOWLEDGEMENTS
This study was supported by National Science Council, ROC (NSC
90-2314-B002-365)
2
Copyright ©2003 by ASME