The influence of stiffness of the fixator on
maturation of callus after segmental
transport
L. Claes, J. Laule, K. Wenger, G. Suger,
U. Liener, L. Kinzl
From the University of Ulm, Germany
he treatment of large bony defects by callus
distraction is well accepted, but the duration of
treatment is long and the rate of complications
increases accordingly. We have examined the effect of
the stiffness of the axial fixator on reducing the time
for maturation of callus.
We created a mid-diaphyseal defect of 15 mm in the
metatarsal bone in sheep and stabilised it with a ring
fixator. After four days a bony segment was
transported for 16 days at 1 mm per day. After 64
days the animals were divided into four groups, three
with axial interfragmentary movement (IFM) of 0.5,
1.2 and 3.0 mm, respectively, and a control group.
The 3.0 mm IFM group had the smallest bone
density (p = 0.001) and area of callus and the largest
IFM after 12 weeks; it also had typical clinical signs
of hypertrophic nonunion. The most rapid stiffening
of the callus was in the 0.5 mm group which had the
smallest IFM (p = 0.04) after 12 weeks and
radiological signs of bridging of the defect. These
results indicate that suitable dynamic axial stimulation
can enhance maturation of distraction callus when the
initial amplitude is small, but that a large IFM can
lead to delayed union.
T
J Bone Joint Surg [Br] 2000;82-B:142-8.
Received 21 July 1998; Accepted after revision 5 March 1999
Callus distraction is widely used for the treatment of
1,2
defects of tubular long bones.
At the end of the distraction the young callus has low mechanical stiffness and
L. Claes, PhD, Professor and Director
J. Laule, DVSc, PhD, Research Fellow
K. Wenger, PhD, Research Fellow
Department of Orthopaedic Research and Biomechanics
G. Suger, MD, Orthopaedic Surgeon
U. Liener, FRCS, Orthopaedic Surgeon
L. Kinzl, MD, Professor
Department of Surgery
University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.
Correspondence should be sent to Professor L. Claes.
©2000 British Editorial Society of Bone and Joint Surgery
0301-620X/00/19332 $2.00
142
strength; adequate time must then be allowed for maturation before the fixator can be removed. At least two-thirds
of this time is dedicated to passive maturation and most
complications such as loosening or infection of the pins
3,4
occur during this phase if external fixation is used.
Loosening of the pins results in reduced mechanical stability and increased movement in young regenerate bone.
In experimental studies on callus distraction, both deleterious and advantageous effects have been demonstrated
on movement, depending on the amount. A small degree
5
will induce regeneration and maturation of callus, but if it
exceeds a certain limit in the regenerate bone, maturation
decreases and osseous bridging of the defect is inhibited,
6
resulting in hypertrophic nonunion. The specific range of
movement which effectively stimulates young distraction
callus is unknown. The movement which occurs normally
in this tissue during the maturation phase can be estimated
from in vitro measurements of fixators used in distraction
osteogenesis. In a tibial Ilizarov fixator consisting of four
rings, axial movement is in the range of 3 to 6 mm when
axially loaded to 300 N, depending on the amount of
7,8
pretension in the wires.
When pretension is reduced or the wires loosened the
9
axial movements are correspondingly higher. It is not
possible to ensure that patients do not exceed the proposed
load limits. More information, generated from the more
finely-incremented interfragmentary movements (IFM), is
still needed to estimate the degree of axial movement may
be optimal or critical for the maturation of callus.
Studies have shown that in sheep, when pulsed distraction of an amplitude of 0.08 mm was applied for 250
cycles, the ultimate torsional strength of the regenerate
10
improved, but this was not significant. Similar results
were obtained when axial dynamisation was applied two
11
weeks after the end of distraction, indicating a diminished
sensitivity of distraction callus for axial movement during
advanced maturation.
To investigate the effect of axial IFM in young regenerate bone and to determine how much may be optimal, we
developed an animal model which approximated to the
healing conditions in the human tibia. It had the following
criteria: 1) stable, rigid fixation allowing distraction of
callus over at least 15 mm; 2) purely axial-guided movement in the regenerate bone; and 3) adjustable and wellTHE JOURNAL OF BONE AND JOINT SURGERY
THE INFLUENCE OF STIFFNESS OF THE FIXATOR ON MATURATION OF CALLUS AFTER SEGMENTAL TRANSPORT
143
Fig. 1
Diagram of the operative procedure: left, creation of the mid-diaphyseal defect; middle, adjustment of the length of
the defect to 15 mm; and right, daily segmental bone transport of 1 mm in two steps.
controlled amplitude, with monitoring of the movement and
stiffness during maturation of the callus. We used this
model to study our hypothesis that dynamisation of the
fixation device with sufficient axial IFM enhances the
maturation of newly-formed callus, whereas large axial
movements inhibit it.
Material and Methods
We used 32 skeletally-mature female sheep, aged three
years or older, with a mean weight of 80 ± 10 kg. Approval
for the experiment was granted by a German governmental
scientific review board (Regierungsprasidium, Tübingen,
No. 485). Using general halothane anaesthesia, we performed a standardised operation. To prevent plantar flexion
11
of the foot, which can occur during lengthening, we used
a segmental bone-transport model. The fixator was first
applied to the intact metatarsal. We drilled holes for four
Steinmann pins, 4.5 mm in diameter, using a 4 mm drill bit.
The drill and stabilising pins were inserted over a guide 75°
apart. Schanz screws 5 mm in diameter were inserted distally in a medioplantar and proximally in a mediodorsal
direction after predrilling with a 3.5 mm bit (Fig. 1).
Two Steinmann pins, 3 mm in diameter, were inserted
8 mm apart in the transportable bony segment in a mediolateral direction after predrilling with a 2 mm bit through a
drill guide. With the fixator applied to the metatarsal, a
defect 10 mm in length was created in the distal diaphysis
by two osteotomies using an oscillating saw and a guide
(Fig. 1). A bony segment 25 mm in length was resected
from the proximal diaphysis by a third osteotomy, using a
Gigli saw trained along a guide. Before the osteotomies
VOL. 82-B, NO. 1, JANUARY 2000
were performed, the periosteum was resected for 2 mm
around the planned site of the osteotomy. All drilling and
sawing were performed under cooling irrigation with 0.9%
NaCl solution. When all the osteotomies were completed,
sawdust and bone chips were carefully removed to prevent
undesired osseoinduction. The bony segment was then
transported proximally to close the saw gap, and the defect
was adjusted to 15 mm using a distance gauge.
After four days distraction of the callus was begun at
1 mm per day in two increments, morning and evening, and
continued over 16 days, resulting in compression of 1 mm
at the docking site. In a pilot study in vitro with a washershaped loading cell at the docking site (Typ 9031; Kistler,
Winterthur, Switzerland) a compressive force of 170N was
produced. Before docking the axial telescoping system was
locked and the two rings further stabilised by two connecting rods in the sagittal plane.
In one group the IFM was restrained by an axially stiff
fixator (control group) and in the three dynamised groups
the fixators were equipped with a telescopic system allowing axial IFMs of 0.5, 1.2 or 3.0 mm after completion of the
distraction 21 days after operation. The decrease in axial
IFM was measured in vivo by displacement transducers
mounted to the external fixator. During load-bearing the
young regenerate bone was compressed initially by the
designed displacement amplitude, then during unloading
the original defect of 15 mm was recovered by the recoil of
the springs. After 12 weeks the sheep were killed and the
metatarsals removed and investigated morphologically.
External fixator. The fixator consisted of two circular
aluminium frames, one of which was fixed distally on the
metatarsal by two Steinmann pins and one Schanz screw
144
L. CLAES, J. LAULE, K. WENGER, G. SUGER, U. LIENER, L. KINZL
(Stratec, Waldenburg, Switzerland) and the other proximally. The free clamp length of the transfixing pins was
80 mm. The two frames, nominally 60 mm apart, were
fitted to each other by two pairs of mating titanium cylinders (Fig. 1), each pair consisting of an inner and an outer
tube. The inner tube contained a steel spring. The two
symmetrial springs were preloaded to 60 N each so that
loading forces higher than 120 N would initiate an IFM.
Any loads lower than 120 N would not move the ends of
the osteotomy together. The axial movement allowed during loading could be adjusted between 0 and 4 mm. At
unloading the original gap size was recovered by the
release of the springs. Additionally, the cylinders were
equipped to transfix a bony segment with two Steinmann
pins and to transport it over 15 mm by advancing a nut
(Fig. 1). Immediately after the operation and during the
period of distraction, two additional rods connected the
rings in both the stabilised and stimulated groups to
increase further the stiffness of the fixator. The full weight
of the experimental ring fixator was about 2.1 kg.
The isolated biomechanical characteristics of the external
fixator system were determined by testing it mounted to a
Pertinax plastic tube similar in dimensions to the metatarsal
bone. The length of the defect was adjusted to 15 mm and
the complete system tested in free bending, compression
and torsion in the configurations corresponding to before
and at docking of the bony segment. Bending and compression tests were performed on a materials testing machine
(Zwick 1454, Einsingen, Germany). For compression testing, ball mounts were used at both the distal and proximal
ends of the tube to ensure that there was a purely axial
force. The fixator-Pertinax system was loaded to a maximum of 300 N and movement in the area of the defect was
12
measured by an electronic goniometer system. All displacements in the defect, the deflection angles in the frontal
and sagittal planes and the torsional angles around the long
axis of the bone were determined.
The bending stiffness was measured in a combined free
bending and axial compression test with a length of lever
arm of 50 mm and an applied force of 300 N resulting in a
bending movement of 15 Nm. It was calculated as the ratio
of the bending moment to the degree of flexion.
Torsional stiffness was measured in a customised torsional testing machine with the Pertinax tube mounted
proximally and distally. A torsional moment of 5 Nm was
applied and the rotation angle recorded. The torsional
stiffness was defined as the ratio of the applied torsional
moment to the measured rotation angle of the ends of the
osteotomy in the defect.
In vivo measurement of the interfragmentary movement. The decrease in the IFM over the healing period as a
result of the progressive bridging and calcification of the
distraction callus was monitored once a week using an
inductive LVDT (Type SS 102; Collins, Long Beach, California) placed between the distal and proximal frames of
the fixators; the electrical signals of the device were trans-
mitted telemetrically (Biotel 33; Glonner, Planegg, Germany) to a personal computer. As the sheep walked,
displacement curves were generated. The IFM was defined
as the maximum displacement recorded after at least five
steps. Movements smaller than 0.05 mm were not considered to be valid since the accuracy of the LVDT device
and telemetry is in the range of 0.03 mm. Since this had
been previously noted for a stable fixed metatarsal, weekly
IFM was not monitored in this group (control).
Just before dynamisation of the fixator on day 21 after
operation, the inherent displacement of the system was
evaluated by monitoring the deflection of the complete,
locked fixation device as the animal walked. The fixator
was then unlocked and the initial axial movement in the
distraction callus determined from the difference in movement between the locked and unlocked states. Weekly
measurements were then made until the animals were killed
on days 81 to 84, using always the inherent displacement at
day 21 as null. The adjusted values were then normalised to
the maximum measured for the given animal during the
study.
CT studies. After all the sheep had been killed at about 84
days after operation the metatarsals were excised, and the
fixator removed. The healing area was scanned by computed tomography (pQ-CT 960; Stratec, Pforzheim, Germany)
with a voxel size of 0.590 0.590 mm and slice thickness
of 1.0 mm. Fourteen slices were taken along the axis of the
regenerate bone area with a slice distance of 1.5 mm,
including two in the proximal and distal cortices and ten in
the area of regenerate bone. Tissue with a threshold above
3
0.45 l/cm or density greater than 218 mg/cm was considered as bone. Bone density and bone area were calculated with software provided by the manufacturer. The
precision of the bone density measurements is better than
3%.
Statistical analysis The variable of interest is the proportion of sheep with an IFM below 0.3 mm (bony healing) on
the twelfth week. The groups were compared using Fisher’s
exact test. First, an overall test for all three groups was
performed and the variables of density and area were
analysed by analysis of variance. Post-hoc tests within an
analysis of variance were adjusted for multiple comparisons appropriately with Tukey’s HSD test.
Results
In the first three weeks after operation, load-bearing on the
limb was tentative as assessed by daily observation, but
then appeared to become normal after docking.
Stiffness of the external fixator. From the in vitro testing
of the rigidity of the fixator, the maximal axial deformation of the tube and fixator in the stable, locked position
was 0.3 mm under an axial load of 300 N. The displacement of the ends of the osteotomy at the defect in the
sagittal and frontal plane was always less than 0.18 mm if
loaded axially as measured by the goniometer system.
THE JOURNAL OF BONE AND JOINT SURGERY
THE INFLUENCE OF STIFFNESS OF THE FIXATOR ON MATURATION OF CALLUS AFTER SEGMENTAL TRANSPORT
Axial stiffness was 989 N/mm. Under dynamised fixation
the load-displacement curve showed three distinct slopes.
From 0 to 120 N the axial stiffness of the fixator system
was 915 N/mm. From 120 N to approximately 130 N it
equalled that of the springs, 7.69 N/mm, which allowed
full axial movement within a small load range. At 130 N
the bolts prohibited further axial displacement of the rings
and the stiffness returned to 989 N/mm. The axial stiffness
of the fixator used in the control group with two additional
connecting rods in the sagittal plane and 1 mm of compression at the docking site was 1065 N/mm. In free
bending, the angular stiffness of the locked fixator at
docking was 112 Nm/° in the sagittal plane and 50 Nm/° in
the frontal plane. Torsional stiffness measured at the
osteotomy gap in a fixator with locked, stable fixation was
12.3 Nm/°.
Interfragmentary movement. The mean postoperative
IFM under stable fixation was 0.17 mm (0.06 to 0.29),
reflecting the inherent displacement due to elastic deformation of the external fixator and pin-bone contact (Table I).
Thus, measurements below 0.3 mm may occur after bony
bridging. The IFM decreased in all dynamised groups
during the healing period (Table I). The slowest reduction
of the IFM, normalised to individual initial values corrected
for the inherent displacement of the fixator frame, was
found in the 3.0 mm group (Fig. 2). The value in the 0.5
and 1.2 mm groups was 9% and 24%, respectively, of the
initial IFM value after 12 weeks, but in the 3.0 mm group it
145
was 42%. Only the 0.5 mm group reached an IFM as low as
the inherent displacement of the fixator (0.2 mm) at week
12 of monitoring. Radiologically, these specimens were
bridged and were stable. This bridging appears to have
started in the tenth week and was mainly in the 0.5 mm
group. Only one sheep in the 0.5 mm group had an IFM of
0.3 mm or larger after ten weeks compared with five in the
1.2 mm group and seven in the 3 mm group. At the end of
the study at 12 weeks, all of the 0.5 mm group had an IFM
smaller than 0.3 mm whereas in four of the 1.2 mm group
and seven of the 3 mm group it was larger than 0.3 mm.
The number of sheep with an IFM below 0.3 mm was
significantly larger in the 0.5 mm group than in the 1.2 mm
(p = 0.04) and 3 mm groups (Fisher’s exact test, p = 0.001).
This indicates that maturation of callus was most rapid in
the group with 0.5 mm of initial axial movement. In the
3 mm group the mean movement after ten weeks was
1.5 mm and after 12 weeks it was 1.4 mm which indicates
no significant improvement in stiffening and signs of
nonunion.
CT findings. In the 0.5 mm group the distribution of callus
was nearly circular whereas in the 3 mm group it was
irregular (Figs 3 to 5). All animals showed the highest
density of callus next to the proximal and distal cortices.
Toward the middle zone the density decreased in every
group to its lowest value (Fig. 6a) which was significantly
lowest in the 3 mm group (p = 0.001, Fig. 6a, Table II) and
highest in the 0.5 mm group. The mean density of the
3
corresponding intact metatarsal bone was 1199 mg/cm .
There were no statistical significant differences in the area
of callus among the groups in the centre of the defect
(p = 0.86). The area of callus in the 3.0 mm group was
lowest in the middle of the defect and increased towards the
cortices to values significantly larger than the cross2
sectional area of the adjacent diaphysis (160 mm ; Fig. 6b,
Table III). Such a distribution of callus indicates hypertrophic pseudarthrosis as has been described by
13,14
others.
Discussion
Fig. 2
Correlation of interfragmentary movement (IFM) in the distraction callus
with healing time. For comparison of the groups, the IFM is normalised
to the maximum values at the start of the measurements corrected for the
inherent displacement of the fixator frame.
The worst maturation of distraction callus occurred when
3 mm of IFM were allowed when there was a significantly
smaller density and area of callus than for the other groups
at 12 weeks after operation. There were no significant
differences in the density and area of the callus in the
groups with 0, 0.5 and 1.2 mm of axial movement. The
larger IFM stimulated more callus near the zones of the
Table I. The inherent displacement of the fixator and the mean (SD) IFM (mm) over the healing time for the dynamised groups
Inherent
Group (mm) displacement Day 21
0.5
1.2
3
Weeks after operation
4
5
6
7
8
9
10
11
12
0.155 (0.069) 0.559 (0.204) 0.507 (0.242) 0.452 (0.204) 0.437 (0.204) 0.357 (0.109) 0.262 (0.079) 0.271 (0.116) 0.206 (0.104) 0.245 (0.128) 0.202 (0.074)
0.190 (0.100) 1.379 (0.198) 1.104 (0.352) 0.891 (0.365) 0.772 (0.365) 0.646 (0.335) 0.644 (0.454) 0.567 (0.372) 0.577 (0.428) 0.501 (0.373) 0.476 (0.379)
0.156 (0.053) 2.829 (0.471) 2.565 (0.593) 2.193 (0.741) 2.118 (0.741) 2.061 (0.758) 1.880 (0.915) 1.771 (0.857) 1.525 (0.946) 1.559 (0.939) 1.433 (0.996)
VOL. 82-B, NO. 1, JANUARY 2000
146
L. CLAES, J. LAULE, K. WENGER, G. SUGER, U. LIENER, L. KINZL
Fig. 3
CT scans from the middle of the defect (left) and the corresponding scout
view (top, 0.5 mm group; bottom, 3.0 mm group).
cortical defect but not in the middle of the area of callus
distraction. The fastest stiffening was seen in the 0.5 mm
group after ten weeks which had still not been achieved in
the other groups at 12 weeks. In this model, the more IFM
allowed initially, the higher it was at the end of the study
and the lower the resulting callus density (D) in the middle
of the defect (D = 630-50*IFM; r = 0.59). The early bony
bridging of the fibrous interzone in the 0.5 mm group
indicated early maturation of the newly formed callus in the
middle of the defect. In the 3 mm group the IFM was too
large to allow bridging and stabilisation of the defect. One
reason was a movement-induced inhibition of cell and
15
vessel proliferation into the defect.
The new external fixator for segmental bone transport
provides standardised and controlled distraction and maturation of callus, with accurate settings of the telescopic
7,8,16-18
the
axial movement. In contrast to other systems
new ring fixator has a very high bending, torsional and
axial stiffness in all planes, minimising uncontrolled IFM.
The initial, designed axial telescopic movement can be
monitored telemetrically and thus used to determine the
rate of maturation over any selected period of study.
The lengthening index, the ratio of the total fixation time
to the length of new bone obtained, was 56 days/cm in our
study which corresponded to segmental bone transport in the
19
tibia of adult men. The lengthening indices of an absolute
lengthening in the femur or tibia of young sheep are between
11,20-22
25 and 43 days/cm.
This is generally lower than
values for patients which are between 33 and 63 days/
19,23,24
The muscle and other soft-tissue cover of the
cm.
sheep metatarsal is notably less than that of the sheep tibia
and femur which decreases its influence on bone healing.
There are two notable limitations to our study. First, the
measurement of the IFM was complicated by loosening of
pins in the late maturation period which must affect the
accuracy of the IFM data. Measurements of loosening of
pins on removed bones at the end of the study showed an
effect of up to 0.1 mm of axial movement for the 0, 0.5 mm
and 1.2 mm groups and up to 0.3 mm for the 3 mm group.
These movements, however, did not significantly influence
the mean values of interfragmentary movements measured
at this time. Secondly, there was notable variability in the
amount of weight-bearing tolerated by each sheep at the
observation period which must affect the constancy of the
test conditions. These two factors together probably explain
the relatively high scatter in the IFM data.
Figure 4 – High resolution radiograph of an animal
in the 3 mm group taken after killing. Figure 5 –
High resolution radiograph of an animal in the
0.5 mm group taken after killing.
Fig. 4
Fig. 5
THE JOURNAL OF BONE AND JOINT SURGERY
THE INFLUENCE OF STIFFNESS OF THE FIXATOR ON MATURATION OF CALLUS AFTER SEGMENTAL TRANSPORT
Fig. 6a
147
Fig. 6b
Density of callus (a) and area of distraction callus (b) at various locations according to axial movement.
3
Table II. Mean (SD) callus density (mg/cm ) for various locations. Two slices were taken in the proximal and distal cortices
Group
(mm)
0
0.5
1.2
3.0
Slice
Proximal cortex
1
2
3
4
Middle of defect
7
8
9
10
Distal cortex
1111.6
(99.2)
1168.6
(77.9)
1068.3
(75.9)
984.4
(69.3)
839.0
(77.4)
864.9
(94.3)
848.2
(86.1)
785.9
(64.5)
768.6
(58.3)
779.4
(54.0)
743.5
(35.4)
700.5
(44.1)
744.8
(43.2)
760.3
(54.9)
717.7
(36.6)
659.3
(35.8)
726.2
(41.0)
729.7
(41.8)
694.4
(33.4)
638.3
(38.0)
699.4
(38.1)
704.1
(32.2)
675.3
(36.8)
620.1
(39.8)
722.9
(32.9)
758.3
(56.7)
708.9
(26.7)
636.1
(35.0)
755.3
(28.1)
771.0
(58.2)
721.8
(24.3)
663.5
(19.2)
774.1
(39.2)
792.8
(70.0)
746.8
(50.2)
687.0
(32.2)
817.6
(98.1)
893.3
(151.7)
841.2
(119.9)
767.7
(107.8)
950.2
(132.6)
1075.1
(164.8)
980.9
(106.0)
844.1
(158.4)
1033.9
(117.3)
1082.6
(99.3)
988.2
(104.4)
899.8
(63.2)
692.1
(37.5)
726.6
(53.5)
685.8
(37.7)
619.1
(41.2)
1146.0
(67.5)
1188.1
(83.5)
1074.3
(70.3)
913.8
(146.3)
2
Table III. Mean (SD) callus area (mm ) for various locations. Two slices were taken in the proximal and distal cortices
Group
(mm)
0
0.5
1.2
3.0
Slice
Proximal cortex
1
2
3
4
Middle of defect
7
8
9
10
Distal cortex
231.5
(56.2)
226.8
(48.3)
256.8
(55.6)
338.1
(94.8)
250.5
(75.9)
249.3
(68.5)
303.1
(87.2)
389.1
(148.5)
243.7
(106.3)
250.3
(76.6)
290.4
(116.0)
352.3
(161.6)
249.8
(117.5)
260.4
(82.2)
281.0
(141.2)
295.3
(165.5)
253.5
(130.0)
255.8
(99.0)
265.1
(142.9)
238.4
(94.8)
235.6
(123.0)
224.4
(120.7)
244.6
(139.2)
192.3
(184.7)
239.4
(115.0)
264.1
(88.5)
288.6
(139.1)
237.4
(142.4)
233.39
(0.8)
248.5
(71.4)
294.6
(131.9)
280.7
(160.0)
210.3
(69.5)
220.3
(56.0)
289.1
(11.50)
312.4
(155.3)
196.3
(55.4)
219.7
(50.9)
274.6
(84.5)
342.1
(140.4)
200.0
(40.3)
214.4
(43.5)
278.4
(70.9)
360.4
(129.5)
244.5
(57.1)
248.0
(59.4)
283.2
(70.5)
385.5
(112.8)
Our findings have shown that dynamisation of a distraction callus during maturation with 0.5 mm of initial axial
amplitude in the sheep metatarsal bone stimulates maturation
as compared with either no or large IFMs. By contrast, large
IFMs of 3 mm led to large formation of callus at the cortical
defect zone but delayed maturation, showing typical signs of
6
hypertrophic nonunion. Such large deformations of approximately 20% of the length of the defect can often be seen
under clinical conditions. Taking the axial stiffness of stand8
ard ring fixators and a partial loading bearing of 300 to
500 N into consideration, defects up to 60 mm will often
VOL. 82-B, NO. 1, JANUARY 2000
225.9
(129.0)
249.5
(100.0)
255.7
(139.7)
193.3
(166.3)
199.3
(30.5)
198.8
(32.0)
247.1
(61.0)
366.5
(121.0)
produce corresponding axial movements. Additional loosen9
ing of wires can lead to a decreased axial stability.
Fixators with low axial stiffness and loosening of wires
may result in delayed nonunion. Callus distraction may
therefore benefit from the use of stiffer fixators and half
9
pins in addition to or instead of wires.
Although none of the authors have received or will receive benefits for
personal or professional use from a commercial party related directly or
indirectly to the subject of this article, benefits have been or will be
received but are directed solely to a research fund, foundation, eduational
institution, or other non-profit institution with which one or more of the
authors is associated.
148
L. CLAES, J. LAULE, K. WENGER, G. SUGER, U. LIENER, L. KINZL
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