Keywords
biomechanical phenomena - epiphyses/injuries - fracture fixation - humeral fractures
Introduction
Supracondylar fracture is more common in the 4- to 7-year-old age group,[1] corresponding to two-thirds of children hospitalized for elbow trauma and to 30%
of the fractures in this population.[2] Due to the particular anatomy of the elbow and to the ossification order in the
growth nuclei, the supracondylar fracture virtually always behaves in extension patterns,
with posterior medial, posterior lateral and flexion displacements. The displacement
degree is defined by the direction of the deforming force, by the position of the
limb during the trauma, and by the magnitude of this force.[3]
[4]
Gartland classified this fracture in three types according to the displacement degree;
it is agreed that grade 1 fractures require conservative treatment.[5] Some papers describe conservative techniques, that is, reduction and immobilization,
in grade 2 and 3 fractures.[6] However, many authors describe reduction and percutaneous fixation as the gold standard
for displaced fractures.[7]
[8] As such, there is no consensus as to the best positioning of Kirschner wires in
the stabilization of this fracture.[9] Fixation with a cross-wired configuration provides better stability, but there is
a risk of iatrogenic injury of the ulnar nerve. The configuration with two lateral
wires showed lower stability of the crossed wires and lower incidence of ulnar nerve
lesions; in addition, it is technically more challenging, since the space for wire
placement both in divergent and parallel directions is small. However, both configurations
have similar clinical results.[10]
[11]
[12]
[13]
In 1991, Bertol et al[14] published the technique of supracondylar fractures fixation with posterior medial
deviation using an intramedullary Kirschner wire inserted just lateral to the olecranon
and another one lateral at the epicondyle entry, in a presumably easier technique,
since it optimizes the lateral spine space.
Numerous biomechanical studies compare different positional configurations of Kirchner
wires in the stabilization of supracondylar humerus fracture,[13]
[15]
[16] but there are no reports analyzing the configuration with an intramedullary and
a lateral wire. The present study aims to compare fixation techniques using an intramedullary
wire or two parallel lateral wires.
Materials and Methods
The test specimens of the present study were 72 synthetic humeri (model 3022B – left
humerus with medullary canal and spongy material) (Nacional Ossos, Jaú, SP, Brazil),
which were equally cross-sectioned, parallel to the articular surface in the coronal
plane, with a distal guided saw; the section passed into the olecranon fossa at 3
centimeters from the distal humeral edge, simulating a supracondylar fracture ([Fig. 1]). The cross-section was selected because 80% of the supracondylar fractures have
a transverse pattern in lateral radiographs[17]; moreover, the fracture obliquity causes instability.[18]
Fig. 1 Test specimens: cross-section of a synthetic humerus at its distal portion, through
the olecranon fossa at 3 centimeters from the distal edge of the bone, simulating
a supracondylar fracture.
The sectioned synthetic humeri were divided into two groups according to fixation:
a group fixed with two lateral wires (FL) and a group with fixed with an intramedullary
wire and a lateral wire (Fi). All of the models were submitted to the anatomical reduction
and fixation with 2.0 mm Kirschner wires. Each group had a standard fixation model
to assure that the fixations were identical. In the FL group, the fixation was performed
with 2 2.0 mm Kirschner wires entering laterally at the epicondyle, with the most
distal wire at the lower edge of the lateral epicondyle and the proximal wire 1 cm
above the former, parallel to the axis of the humeral shaft, fixed on the opposite
cortical layer, 3 cm above the fracture line.
In the Fi group, the fixation was also performed with 2 2.0 mm Kirschner wires, with
the 1st wire entering 2 mm lateral to the lateral border of the trochlea, at the trochlear
groove, thus becoming intramedullary and introduced up to the transition between the
middle third and the distal third of the humerus, 11 cm from the distal humeral end,
and the 2nd wire inserted in the center of the lateral epicondyle at a 30° angle to the humeral
axis, crossing the 1st wire at 2 cm from the fracture line and fixed in the opposite cortical layer at 3
cm from the fracture line.
Fixations were aided by a perforator and fluoroscopy. All of the specimens were compared
to their respective standardized models by fluoroscopy, complying with the previously
mentioned fixation criteria, and assuring the similarity between them ([Fig. 2]).
Fig. 2 Test specimens compared with their respective standardized models at fluoroscopy,
complying with the fixation criteria and ensuring the similarity between them.
Specimens that did not comply with the fixation criteria were excluded. After the
fixation, the humeri from both groups were sent to the Engineering Laboratory, where,
together with a collaborating engineer, each group was divided into subgroups according
to the performed load tests: subgroup 1, varus load; subgroup 2, valgus load; subgroup
3, load in extension; subgroup 4, load in flexion; subgroup 5, load in internal rotation;
and subgroup 6, load in external rotation.
Load tests were performed on a universal tensile testing machine, model UPM 200 (3022B,
left humerus with medullary canal and spongy material, Nacional Ossos, Jaú, SP, Brazil),
and an HBM U9B (3022B, left humerus with medullary canal and spongy material, Nacional
Ossos, Jaú, SP, Brazil) load cell (20KN = 1mV/V). The test measures the load generated
in Newtons (N) during the continuous displacement promoted by the traction test machine
at a speed of 1 mm/s, with a maximum established displacement of 10 cm, which promotes
an angulation of up to 45° in the specimen with rotation fulcrum at the fracture line
([Fig. 3]).
Fig. 3 Universal tensile testing machine model UPM 200 and an HBM U9B load cell (20 KN = 1
mV/V)
A support for the anatomical coupling of the distal humerus was developed, allowing
the application and measurement of loads in bone models at a point 10 cm proximal
to the fracture line up to a 45° of angulation and/or material failure ([Fig. 4]). A mechanism to create rotational forces from the load established by the tensile
testing machine was also developed ([Fig. 5]). Rotational loads were applied until the breakage of the bone models.
Fig. 4 Applied and measured loads on the specimens, at a point 10 cm proximal to the fracture
line, until reaching a 45° angle and/or material failure.
Fig. 5 Mechanism for the application of rotational loads.
The data generated by the load cell in each bone model show that, during displacement,
the force in N initially increases until it reaches a plateau (which is related to
the higher recorded forces); next, the applied force decreases, which is related to
the bone model breakage and/or to a 45° displacement. In this way, the force in N
when reaching this plateau was defined as the variable to be analyzed, that is, the
maximum force recorded during the displacement, at the end of the linear region of
the graph.
The sample size was calculated in the PEPI (Programs for Epidemiologists) software,
version 4.0, and based on the study by Bloom et al.
[19] For a significance level of 5%, 90% power, and an estimated standard deviation [SD]
of 3.5 with a mean difference of 8N, a minimum total of 6 parts per subgroup was obtained,
totaling 36 per group.
The data analysis was performed with Microsoft Office Excel 2010 software (Microsoft
Corporation, Redmond, WA, USA), comparing FL subgroups to their respective Fi subgroups
through two-tailed t tests. The present study does not have conflicts of interests.
Results
Loading tests results to compare the stability of the two wire configurations are
represented in N in [Table 1]. The two-tailed t test showed that there was no significant statistical difference
in 4 of the 6 loads applied (p < 0.05) ([Table 1]).
Table 1
|
Group (FL)
|
Group (Fi)
|
Two-tailed t test
|
|
Varus (N)
|
28.7 ± 3.5
|
30.7 ± 4.9
|
p = 0.230
|
|
Valgus (N)
|
20.6 ± 5.2
|
22.9 ± 3.4
|
p = 0.240
|
|
Extension (N)
|
19.0 ± 3.4
|
28.7 ± 4.0
|
p = 0.004
|
|
Flexion (N)
|
17.1 ± 1.2
|
22.9 ± 4.0
|
p = 0.015
|
|
Internal Rotation (N)
|
12.55 ± 1.2
|
11.7 ± 2.6
|
p = 0.256
|
|
External Rotation (N)
|
11.2 ± 1.8
|
11.6 ± 1.0
|
p = 0.292
|
In the bone models submitted to the varus load, the mean of the highest recorded forces
during displacement in FL group was of 28.7 N, with a SD of 3.5 N. In the Fi group,
the mean force was 30.7 N, with a SD of 4.9 N. Thus, the two-tailed t test did not
reveal a statistically significant difference between these groups (p = 0.23) ([Fig. 6]).
Fig. 6 Graphic representation of test results of loads in varus, valgus, extension and flexion
and internal and external rotation.
In the models submitted to valgus load, the mean of the highest recorded forces in
the FL group was of 20.6 N, with a SD of 5.2 N. In the Fi group, the mean value was
of 22.9 N, with a SD of 3.4 N. As with the varus load, the two-tailed t test did not
reveal a statistically significant difference between the groups (p = 0.24) ([Fig. 6]).
In addition, there was no statistically significant difference between the groups
at the load tests in internal and external rotation (p = 0.25 and p = 0.24, respectively) ([Fig. 6]).
There was a statistically significant difference between the 2 groups in the extension
load tests (p = 0.004), with a mean of the highest recorded forces in the FL group of 19.0 N and a SD of
3.4 N, whereas the Fi group presented a value of 28.7 Newtons and a SD of 4.0 N ([Fig. 6]). Thus, during the constant displacement established by the test machine, a greater
force was generated and recorded by the load cell in the Fi group compared with the
FL group. As such, we can also suggest that the configuration with an intramedullary
wire and a lateral wire provides greater stability in extension loads when compared
with the configuration with two parallel lateral wires.
Models submitted to the flexion load also showed a significant statistical difference
between the groups (p = 0.01), with the mean of the highest recorded forces in the FL group of 17.1 N and a SD
of 1.2 N, and a mean value of 22.9 N and a SD of 4 N in the Fi group ([Fig. 6]).
Discussion
The main goals of the treatment of displaced supracondylar fractures are anatomic
reduction and a secure fixation with no angular deformities. This is usually achieved
with closed reduction and percutaneous fixation.[20]
[21]
[22] Fixation requires full attention to the clinical and radiological examination of
the contralateral elbow, in addition to true orthogonal projections at fluoroscopy
and the consideration of well-described radiographic parameters for total correction
of the deformity.[23] Defective consolidations are also related to inadequate fixations and technical
errors during the procedure.[19]
Several biomechanical studies have demonstrated that the cross-wire fixation has a
greater rotational stability than the lateral wiring fixations,[15] but with a higher risk of iatrogenic injury of the ulnar nerve.[12] Bloom et al[16] reported that three lateral divergent pins provides the same resistance as two crossed
wires, which are more resistant than two lateral wires, but, in most cases, there
is not enough space for lateral pinning.[19] In a prospective randomized clinical trial comparing lateral and crossed fixation
techniques for the treatment of type III humeral supracondylar fractures, Kocher et
al[11] did not find a significant difference between both groups regarding radiographic
and clinical outcome. In another prospective randomized study, Blanco et al[24] found no significant radiological differences between crossed and lateral wiring
fixation.
Our study shows that the technique with intramedullary wire presents a greater resistance
under flexion and extension loads than the technique with lateral wires; at other
loads, the results are similar. In the former technique, the first step after achieving
a suitable reduction is the introduction of the intramedullary wire,[14] which blocks the forces in axial direction, mainly flexion and extension, safely
allowing the correction of the remaining rotational deformities, that is, this technique
tolerates a rotational adjustment after the precise reduction in the axial direction,
which is not possible with lateral wiring. As such, the intramedullary wire fixation
facilitates anatomical reduction, which maximizes the stability of all fixation configurations.[19] In addition, intramedullary wire fixation maintains a greater lateral space for
wire placement.
Since the clinical results of the two crossed wires technique are similar to those
obtained with two lateral wires,[1]
[24]
[25]
[26] we can assume that, according to the present mechanical study, the clinical results
of the fixation with an intramedullary wire are equivalent to those provided by these
techniques; however, a randomized clinical trial is required to confirm this assumption.
Some limitations of the present study should be recognized. Although the use of synthetic
models for mechanical analysis of fracture reduction techniques is common in the literature,
these investigations do not consider the variability in fracture patterns nor the
anatomy with the surrounding periosteum that may contribute to fragment stability.[15]
[27] Furthermore, the physiological loads acting on the elbow are certainly more complex
than the single axis of the load test directions used in the present study. In addition,
the pins were placed in an ideal situation, without considering the difficulty of
intraoperative insertion, which cannot be simulated. The design of the present study
does not allow direct comparisons of the applied loads in models with organic bones,
allowing only the comparison between the fixation techniques for these fractures.
Conclusion
In the present study, the intramedullary wire fixation provides a greater stability
under flexion and extension loads when compared with the lateral wiring fixation,
with similar results under other applied loads, suggesting acceptable clinical results,
as already proven by Bertol et al.[14] As such, it is an excellent option for the configuration of Kirschner wires when
treating these fractures.
