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Biomechanical Evaluation of Fixation of
Intra-Articular Fractures of the Distal Part of the
Radius in Cadavera: Kirschner Wires Compared
with Calcium-Phosphate Bone Cement*
BY DURAN N. YETKINLER, M.D., PH.D.†, AMY L. LADD, M.D.‡, ROBERT D. POSER, D.V.M.†,
BRENT R. CONSTANTZ, PH.D.§, AND DENNIS CARTER, PH.D.§, CUPERTINO, CALIFORNIA
Investigation performed at the Biomechanics Laboratory, Norian Corporation, Cupertino
Abstract
Background: The purpose of this study was to compare the biomechanical efficacy of an injectable calciumphosphate bone cement (Skeletal Repair System [SRS])
with that of Kirschner wires for the fixation of intraarticular fractures of the distal part of the radius.
Methods: Colles fractures (AO pattern, C2.1) were
produced in ten pairs of fresh-frozen human cadaveric
radii. One radius from each pair was randomly chosen
for stabilization with SRS bone cement. These ten radii
were treated with open incision, impaction of loose
cancellous bone with use of a Freer elevator, and placement of the SRS bone cement by injection. In the ten
control specimens, the fracture was stabilized with use
of two horizontal and two oblique Kirschner wires. The
specimens were cyclically loaded to a peak load of 200
newtons for 2000 cycles to evaluate the amount of
settling, or radial shortening, under conditions simulating postoperative loading with the limb in a cast. Each
specimen then was loaded to failure to determine its
ultimate strength.
Results: The amount of radial shortening was highly
variable among the specimens, but it was consistently
higher in the Kirschner-wire constructs than in the bone
fixed with SRS bone cement within each pair of radii.
The range of shortening for all twenty specimens was
0.18 to 4.51 millimeters. The average amount of shortening in the SRS constructs was 50 percent of that in the
Kirschner-wire constructs (0.51 ± 0.34 compared with
1.01 ± 1.23 millimeters; p = 0.015). With the numbers
available, no significant difference in ultimate strength
was detected between the two fixation groups.
*One or more of the authors has received or will receive benefits for personal or professional use from a commercial party related
directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study
presented in this article. The funding source was the Norian Corporation, Cupertino, California.
†Norian Corporation, 10260 Bubb Road, Cupertino, California
95014-4166. E-mail address: duran_yetkinler@norian.com.
‡900 Welch Road, Suite 15, Palo Alto, California 94304.
§Division of Biomechanical Engineering, Terman Building,
Rooms 550 (B. R. C.) and 561 (D. C.), Stanford University, Stanford,
California 94305.
Copyright 1999 by The Journal of Bone and Joint Surgery, Incorporated
VOL. 81-A, NO. 3, MARCH 1999
Conclusions: This study showed that fixation of
an intra-articular fracture of the distal part of a cadaveric radius with biocompatible calcium-phosphate
bone cement produced results that were biomechanically comparable with those produced by fixation with
Kirschner wires. However, the constructs that were
fixed with calcium-phosphate bone cement demonstrated less shortening under simulated cyclic loadbearing.
Clinical Relevance: A calcium-phosphate bone cement with high compressive strength may provide adequate stability of the fracture and therefore serve as
an alternative to Kirschner wires with their associated
complications.
Distal radial fractures, often referred to as Colles
fractures, frequently occur in women who are more than
forty-five years old and who have fallen on an outstretched hand. The fall creates a compressive load that
fractures the dorsal cortex, typically with comminution.
The fracture may also include a tensile failure of the
volar cortex5. Even though most Colles fractures are
considered to be low-energy extra-articular injuries that
occur in osteopenic bone, intra-articular fractures often
are also classified as Colles fractures. The radiographic
findings include dorsal angulation and displacement, radial shortening, impaction, and comminution; there also
may be a fracture of the ulnar styloid process, carpal
instability, and soft-tissue injury22.
The objectives of treatment of a Colles fracture are
to restore and maintain the anatomy of the wrist in
order to obtain early, painless function28. The current
methods of treatment often do not fulfill these goals.
The traditional method of closed reduction and use of
a cast is indicated for fractures that have little or no displacement or comminution4,5,8,18. If a cast alone is used to
treat an unstable distal radial fracture characterized by
comminution, marked displacement of the fragments,
and interposition of soft tissue, the fracture has a tendency to redisplace within about two weeks8,18,29. Percutaneous pins, external fixation, and operative reduction
and internal fixation therefore are often used to stabilize an unstable fracture1. However, these treatment
methods have their own inherent problems.
391
392
D. N. YETKINLER ET AL.
Rayhack, in a study of displaced distal radial fractures that had been treated with use of percutaneous
pins, reported complications that included loss of reduction, pin-track infection, broken pins, migration of
pins, tendon irritation and irritation of the radial sensory nerve, rupture of the extensor tendon, and Sudeck
atrophy23. Although external fixation may provide more
predictable restoration of radial length, the rate of complications has been as high as 70 percent (thirty-one of
forty-four patients in one series10), mainly because of the
extended period of immobilization. These complications
have included pin-track infection; fracture through pin
sites; radial sensory neuritis; reflex sympathetic dystrophy; and, most importantly, disuse atrophy and stiffness of the joint5,10,11,25. Sommerkamp et al. attempted to
decrease morbidity related to immobilization by using
dynamic external fixators, but they encountered insufficient stability at the fracture site, with more settling
and other complications27. Despite the increasing popularity of more invasive techniques (open reduction and
internal fixation) for the treatment of distal radial fractures, serious complications can occur; these include loss
of fixation, neuritis of the median nerve, reflex sympathetic dystrophy, wound infection, and late posttraumatic arthritis11.
Intra-articular fractures in particular present several
problems. Incomplete reduction usually results in a poor
outcome15. Joint stiffness, articular incongruity, and posttraumatic arthritis also can occur5. Invasive treatment
such as bone-grafting and internal fixation may often be
needed because of the complex nature of these fractures.
Fernandez and Jupiter suggested the use of Kirschner wires as an effective method for fixation of simple
intra-articular compression-type fractures of the distal
part of the radius, which usually do not need bonegrafting5. An alternative method of fixation of these
fractures was biomechanically evaluated in the current in vitro study. We compared the use of SRS (Skeletal Repair System) injectable calcium-phosphate bone
cement (Norian, Cupertino, California) with that of
Kirschner wires.
The cementitious paste was formed by mixing calcium source powder
consisting of calcium carbonate (CaCO3) and α-tricalcium phosphate
(Ca3[PO4]2) and phosphate source powder containing monocalcium
phosphate monohydrate (Ca[H2PO4]2•H2O) with phosphate-buffered
solution. After the material has been implanted, it equilibrates to body
temperature, accelerating the formation of carbonated apatite. It hardens ten minutes after implantation and achieves 50 percent of its
ultimate compressive strength by one hour. Full compressive strength
of fifty-five megapascals is attained by approximately twelve hours
after implantation3.
Selection and Preparation of the Specimens
Ten pairs of fresh-frozen forearms from human adult cadavera
were prescreened with use of plain posteroanterior radiographs to
detect gross anatomical abnormalities. Bone-mineral-density measurements of the ultradistal, mid-distal, and one-third distal regions
were obtained with use of dual-energy x-ray absorptiometry (Hologic
QDR-4500A; Hologic, Waltham, Massachusetts). The average difference between the bone-mineral-density values of the SRS constructs
(0.639 ± 0.183 gram per square centimeter) and the Kirschner-wire
constructs (0.648 ± 0.199 gram per square centimeter) was 0.009 gram
per square centimeter; with the numbers available, this difference was
not found to be significant (p = 0.717).
The radii were removed from the forearms by careful dissection
of the soft tissue around the bone. All radii were wrapped in towels
that had been soaked in saline solution and were stored in tightly
sealed plastic bags at –20 degrees Celsius or less. All specimens were
thawed at room temperature for at least seven hours before the fractures were created.
Each radius was cleaned of all soft tissue and cut to a standard
length of fifteen centimeters from the distal end. The shaft (diaphyseal) end was potted in an aluminum tube with use of dental acrylic
polymer (PERM Reline and Repair Resin; Hygenic, Akron, Ohio). In
addition, an acrylic mold was made of each articular surface of each
radius. Biplanar contact radiographs of the radius and acrylic imprints
of the proximal region of the radius were made to provide a template
to ensure accurate reduction during fixation of the fracture.
Creation of the Fractures
The specimens were placed vertically with 75 degrees of dorsiflexion and 10 degrees of ulnar deviation on an MTS table to simulate
the position of the radius during a fall7,20. Stress-risers were created
with a combination of drilling (1.6-millimeter-diameter drill-holes
spaced two millimeters apart) and scoring of the cortical bone around
the desired three-part intra-articular fracture line19. The fractures were
created by impaction of the specimens, in the same orientation as just
described, against the load-cell in an MTS minibionix servohydraulic
materials testing machine at twenty-five millimeters per second, and
Materials and Methods
Ten pairs of radii from human cadavera were cleaned of soft
tissue. A fracture then was created in each radius with use of a servohydraulic materials testing machine (MTS, Minneapolis, Minnesota).
One radius, randomly chosen from each pair, was stabilized with SRS
bone cement, and the contralateral radius was stabilized with Kirschner wires. Settling of the scaphoid and lunate fossae and of the entire
articular surface was recorded while the fracture constructs were cyclically loaded under conditions simulating intermittent postoperative
loading that would occur in a patient. The specimens then were loaded
to failure to determine the ultimate strength of the constructs.
Material
SRS bone cement is percutaneously injectable and fast-setting;
it cures in vivo to form a carbonated apatite with a low crystalline
order and a small grain size similar to the mineral phase of bone3. This
cement has been reported to be replaced by host bone through an
osteoclast-mediated process similar to normal bone-remodeling3,6.
FIG. 1
Drawing showing the articular surface (A) and an anteroposterior
view (B) of the desired Colles fracture (AO pattern, C2.1).
THE JOURNAL OF BONE AND JOINT SURGERY
BIOMECHANICAL EVALUATION OF FIXATION OF INTRA-ARTICULAR FRACTURES
393
tures had been appropriately reduced, involved insertion of two horizontal and two oblique Kirschner wires.
An orthopaedic surgeon specializing in hand surgery reduced and
fixed all of the specimens. Both specimens of each pair were wrapped
in a plastic bag and were incubated in 100 percent humidity at 37
degrees Celsius in order to simulate physiological body conditions and
to allow curing of the SRS bone cement. The specimens were incubated for twelve to twenty-four hours before testing. No specimens
were refrozen after fixation and before testing.
Calculations of Force on the
Distal Part of the Radius
FIG. 2
Drawing showing Kirschner-wire fixation of a three-part intraarticular distal radial fracture. Two Kirschner wires were placed horizontally across the sagittal fracture line, and an additional two wires
were placed in an oblique pattern across the horizontal fracture line.
were compressed until a fifteen-millimeter displacement of the actuator was achieved20. If the desired intra-articular fracture line (Fig. 1)
was not created, then an osteotome was used to complete the fracture.
The reproducible three-part intra-articular fractures that were made
with this method were consistent with the fracture types treated with
Kirschner wires as described by Fernandez and Jupiter5.
Fixation of the Fractures
One radius from each pair was randomly chosen for fixation with
1.6-millimeter Kirschner wires (Figs. 2 and 3-A)5. The contralateral
radius was stabilized with SRS bone cement (Fig. 3-B).
Before fixation with the SRS bone cement, the loose cancellousbone fragments were compressed with a Freer elevator onto the periphery of the fracture void in order to create a firm cancellous bed
as recommended by the manufacturer. Although impaction of the
fragments increased the size of the void and normally would increase
the instability of the fracture, subsequent injection with SRS bone
cement filled the space that had been created, which was thought to
be beneficial for achieving stability. The SRS bone cement was prepared for use according to the manufacturer’s directions and was
injected through a 12-gauge needle. A paraffin film was wrapped
around the radius to simulate soft tissue.
The operative technique for the control specimens, after the frac-
FIG. 3-A
The current study involved simulation of immediate postoperative weight-bearing on the distal part of the radius. When a patient’s
arm is in a cast, compressive forces may occur on the wrist joint and
at the fracture site because of flexion of the digits. Two major muscletendon units cross over the wrist joint in order to flex the digits; these
are the flexor digitorum profundus and the flexor digitorum superficialis2. In vivo measurements of the tendon forces on these muscles
have been reported while the digits were in flexion2. These forces
ranged from thirty-nine to 196 newtons and from twelve to 147 newtons for the flexor digitorum profundus and the flexor digitorum
superficialis, respectively2. (The force values were converted from the
original mass equivalent.) If the minimum tendon forces are thirtynine and twelve newtons, then the total force is fifty-one newtons. It
has been demonstrated that only 80 percent of the load is transferred
by the distal part of the radius at the wrist joint30; thus, 80 percent of
fifty-one newtons (40.8 newtons) is the force that will be applied to
the distal part of the radius by flexion of each digit. In the current
study, a zero to 200-newton cyclic load (the approximate load due to
flexion of five digits) was used to simulate the immediate postoperative load borne by the distal part of the radius.
Biomechanical Testing of
the Fracture Constructs
After the SRS bone cement had cured, the specimens were placed
vertically on the MTS minibionix servohydraulic materials testing
machine (Fig. 4). The molded acrylic template that was formed from
the individual articular surface of each radius was used to maximize
the load-bearing contact area across the radiocarpal joint after fixation. Six linear variable differential transducers were placed around
the potting tube and were used to measure the axial displacement of
the two distal fracture fragments at six different anatomical sites
(Fig. 4). Data with regard to time, displacement (of the linear variable differential transducers and the MTS crosshead), and load were
collected with Teststar (Minneapolis, Minnesota) on an Excel-5.0
FIG. 3-B
Fig. 3-A: Radiograph showing fixation of a fracture with Kirschner wires.
Fig. 3-B: Radiograph showing fixation of a fracture with SRS bone cement.
VOL. 81-A, NO. 3, MARCH 1999
394
D. N. YETKINLER ET AL.
FIG. 4
Drawing showing top and side views of the placement of the linear variable differential transducers (LVDT) around the distal fragments of
the distal radial fracture for measurement of movement of the fragments in the axial direction. The data that were obtained were used to
calculate settling of the lunate and scaphoid fossae as well as dorsal and volar step-off. (Only linear variable differential transducer 5 is shown
in the side view for the purpose of simplification.)
spreadsheet (Microsoft, Redmond, Washington) with use of an HP
Vectra N2 4/33si computer (Hewlett-Packard, Palo Alto, California).
The specimens first were loaded sinusoidally for 2000 cycles at
one hertz. It was assumed that a patient would use the digits fifty times
a day while the arm was immobilized in the cast. The cast is worn for
approximately six weeks; therefore, the digits would be flexed approximately 2000 times during this immediate postoperative load-bearing
period. The data points at minimum and maximum load levels were
recorded for each cycle. The values for settling (displacement of the
linear variable differential transducers and the MTS crosshead) were
calculated as the difference between the value at the resting position
before the first cycle and that after 2000 cycles.
Posteroanterior and lateral radiographs were made after cycling.
The linear variable differential transducers then were removed, and
the specimen was loaded to failure at twenty-five millimeters per
second with a maximum displacement of fifteen millimeters. The values for force and crosshead displacement were sampled and recorded
at 100 hertz during the load-to-failure part of the experiment. Final
posteroanterior and lateral radiographs were made.
Analysis of the Data
Outcome Parameters
Settling due to the simulated immediate postoperative loadbearing of the distal part of the radius was measured by displacement
of the MTS crosshead. Settling of the lunate and scaphoid fossae was
calculated by averaging the measurements of the displacement of the
three linear variable differential transducers around each anatomical
fossa (Fig. 4). Linear variable differential transducers 1, 2, and 3 were
used for calculations for the scaphoid fossa, and linear variable differential transducers 4, 5, and 6 were used for calculations for the lunate
fossa. The step-off at the volar and dorsal sides of the distal part of
the radius was calculated according to the absolute value of the difference between the displacement measurements from two adjacent
linear variable differential transducers across the intra-articular fracture line (Fig. 4). Linear variable differential transducers 1 and 6
determined the volar step-off, and linear variable differential transducers 3 and 4 determined the dorsal step-off. Finally, after cyclic
loading, the ultimate load to failure was determined according to the
applied peak force during static loading.
Statistical Analysis
A nonparametric analysis, the Wilcoxon signed-rank test, was
used to determine differences between the two types of fixation. Our
null hypothesis was that there was no significant difference (p > 0.05)
between the outcome parameters measured in the specimens that
had been stabilized with Kirschner wires and those measured in the
specimens that had been stabilized with calcium-phosphate bone cement (SRS).
Results
Overall, there was significantly more displacement
(settling) in the Kirschner-wire constructs than in the
SRS constructs (range, 0.18 to 4.51 millimeters comTHE JOURNAL OF BONE AND JOINT SURGERY
BIOMECHANICAL EVALUATION OF FIXATION OF INTRA-ARTICULAR FRACTURES
395
FIG. 5
Graph showing settling of the entire articular surface of the Kirschner-wire (K-wire) constructs compared with that of the SRS constructs.
Each data point represents one pair of specimens.
pared with 0.19 to 1.29 millimeters; p = 0.015) (Table I
and Fig. 5). With the numbers available, no significant
difference in ultimate strength was detected between
the SRS constructs and the Kirschner-wire constructs
(average [and standard deviation], 1996 ± 1413 newtons
compared with 1842 ± 796 newtons; p = 0.721) (Table I).
Measurements of displacement of the individual linear variable differential transducers showed generally
more settling in the Kirschner-wire constructs than in
the SRS constructs (Table II). When the displacement
FIG. 6
Graph showing settling of the scaphoid and lunate fossae in the Kirschner-wire (K-wire) constructs compared with that in the SRS
constructs. Each data point represents one pair of specimens.
VOL. 81-A, NO. 3, MARCH 1999
396
D. N. YETKINLER ET AL.
data for the scaphoid and lunate fossae were examined
separately, it was found that there was significantly more
settling of the scaphoid fossa of the Kirschner-wire constructs than there was of the scaphoid fossa of the SRS
constructs (average, 1.07 ± 1.29 millimeters compared
with 0.27 ± 0.37 millimeters; p = 0.017) (Fig. 6). With
the number of specimens used in our experiment, we
were not able to detect a significant difference in terms
of settling of the lunate fossa between the Kirschnerwire constructs and the SRS constructs (p = 0.139). In
both test groups, the scaphoid fossa settled slightly more
than did the lunate fossa (p = 0.452) (Table II). The
settling of the scaphoid fossa of the Kirschner-wire constructs was correlated linearly with that of the SRS constructs (r2 = 0.802) (Fig. 6). No linear correlation was
observed in a similar analysis of settling of the lunate
fossa (r2 = 0.007).
The step-off data revealed no significant difference,
with the numbers available, between the Kirschner-wire
constructs and the SRS constructs with regard to articular incongruity at the dorsal cortex (0.49 ± 0.48
millimeter compared with 0.30 ± 0.41 millimeter; p =
0.333); however, there was a significant difference between the two constructs with regard to the incongruity
at the volar cortex (0.93 ± 0.89 millimeter compared
with 0.68 ± 0.92 millimeter; p = 0.037) (Table III and
Fig. 7). With the number of specimens used in this experiment, we could not demonstrate that articular incongruity was more prominent on the volar side than it
was on the dorsal side regardless of the type of treatment (p = 0.071). The amount of step-off on the volar
side of the Kirschner-wire constructs was linearly corre-
DATA
TABLE I
OVERALL DISPLACEMENT (SETTLING)
AND ULTIMATE LOAD TO FAILURE
ON
Specimen
Pair
Type of
Construct*
Overall
Displacement
(mm)
Ultimate Load
to Failure
(N)
1
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
–0.61
–0.38
–1.35
–0.49
–0.37
–0.19
–0.60
–0.46
–4.51
–1.29
–1.28
–1.01
–0.55
–0.43
–0.18
–0.24
–0.33
–0.33
–0.28
–0.26
–1.01 ± 1.23
–0.51 ± 0.34
–1745
–860
–2150
–2410
–2790
–5660
–1930
–1890
–694
–953
–1110
–1220
–3130
–2030
–1300
–1060
–2440
–2420
–1130
–1460
–1842 ± 796
–1996 ± 1413
2
3
4
5
6
7
8
9
10
Average and
standard
deviation
*SRS = Skeletal Repair System bone cement (Norian, Cupertino,
California).
lated with that on the volar side of the SRS constructs
(r2 = 0.901) (Fig. 7). No linear correlation was observed
in a similar analysis of dorsal step-off (r2 = 0.033). All
FIG. 7
Graph showing volar and dorsal step-off in the Kirschner-wire (K-wire) constructs compared with that in the SRS constructs. Each data
point represents one pair of specimens.
THE JOURNAL OF BONE AND JOINT SURGERY
397
BIOMECHANICAL EVALUATION OF FIXATION OF INTRA-ARTICULAR FRACTURES
TABLE II
OF THE INDIVIDUAL LINEAR VARIABLE DIFFERENTIAL TRANSDUCERS
AND SETTLING OF THE SCAPHOID AND LUNATE FOSSAE*
DISPLACEMENT
Specimen
Pair
Type of
Construct†
1: Volar
Scaphoid
1
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
Kirschner-wire
SRS
–0.24
–0.46
–0.65
0.00
–0.61
–0.14
–0.66
–0.10
–3.59
–2.80
–1.57
0.00
–0.14
0.06
–0.11
0.38
–0.06
–0.51
0.07
0.01
–0.76 ± 1.10
–0.36 ± 0.90
2
3
4
5
6
7
8
9
10
Average and
standard
deviation
Displacement of Linear Variable Differential Transducer
2: Lateral
3: Dorsal
4: Dorsal
5: Medial
Scaphoid
Scaphoid
Lunate
Lunate
–1.89
–0.06
–1.11
–0.08
–1.90
–0.02
–0.85
–0.32
–5.26
–0.83
–2.05
0.18
–0.25
–0.33
0.18
–0.02
–0.10
–0.31
–0.50
–0.26
–1.37 ± 1.58
–0.21 ± 0.28
–1.54
0.05
–1.65
0.00
–0.18
–0.29
–0.42
0.06
–4.68
–0.26
–0.28
–0.70
–0.41
–0.29
–0.27
–0.72
–0.31
–0.05
–0.96
–0.29
–1.07 ± 1.38
–0.25 ± 0.28
–0.70
0.29
–1.49
0.16
–0.35
0.03
–0.43
0.20
–6.29
–0.58
0.28
0.69
0.11
0.03
–0.64
–0.69
–0.30
–0.06
–0.29
–0.27
–1.01 ± 1.92
–0.02 ± 0.41
6: Volar
Lunate
–0.87
–1.02
0.14
–0.04
–1.14
0.00
–0.03
–0.08
–0.19
–0.01
0.09
–0.02
0.26
0.40
–0.79
–0.62
0.38
–6.79
–0.23
0.10
0.03
0.00
–1.34
–1.69
–0.07
–0.62
0.11
–0.46
–0.64
0.21
–0.16
0.32
–0.18
0.20
–0.14
0.02
–1.26
0.43
–0.32
0.00
–0.37 ± 0.58 –0.72 ± 2.18
–0.27 ± 0.47 –0.25 ± 0.57
Settling of
Scaphoid
Fossa
Settling
of Lunate
Fossa
–1.22
–0.16
–1.14
–0.02
–0.90
–0.15
–0.64
–0.12
–4.51
–1.30
–1.30
–0.18
–0.27
–0.19
–0.07
–0.12
–0.16
–0.29
–0.47
–0.18
–1.07 ± 1.29
–0.27 ± 0.37
–0.86
0.13
–0.88
0.02
–0.18
0.03
0.08
–0.40
–4.23
–0.24
0.10
–0.78
–0.20
–0.11
–0.36
–0.18
–0.09
0.03
–0.37
–0.20
–0.70 ± 1.29
–0.17 ± 0.27
*The values are given in millimeters.
†SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).
of the SRS constructs remained intact throughout the
cyclic-loading experiment.
Discussion
The findings in this study demonstrated that the
fracture fragments of the SRS constructs settled significantly less than did those of the Kirschner-wire constructs. From a practical point of view, these data indicate
that SRS bone cement can provide initial stability that
is comparable with or better than that achieved with
use of Kirschner-wire fixation.
Clinically, when the radius settles, the ulna carries
more load, thereby altering the normal biomechanics
of the wrist. This phenomenon is known as ulnar impaction syndrome and is diagnosed on the basis of radiographic changes, associated pain, decreased grip
strength, and limited rotation of the forearm26,31. In a
clinical study of distal radial fractures, Hutchinson et
al. found that treatment with pins and plaster caused
an average of 2.5 millimeters of shortening of the radius
at four months10. In the current study of cadavera, the
amount of settling in the Kirschner-wire constructs
ranged from 0.18 to 4.51 millimeters. In both study
groups, the scaphoid fossa settled slightly more than did
the lunate fossa, suggesting that the scaphoid fossa
may be more important in terms of load transfer under the loading conditions that were imposed. This finding is supported by those of previous reports indicating
VOL. 81-A, NO. 3, MARCH 1999
that most of the force (50 percent more than that in
the lunate fossa) is transmitted through the scaphoid
fossa30.
There was more volar articular incongruity in the
Kirschner-wire constructs than in the SRS constructs.
The volar cortex was more prone to have articular stepoff than was the dorsal cortex in both test groups. This
finding confirms that a major portion of the load is
transferred by the volar cortex30. Failure to achieve an
anatomical reduction (an articular step-off of less than
one to two millimeters) of intra-articular fragments has
been associated with radiographic evidence of arthritis
in most if not all patients15. In a study of young adults,
twenty-two (92 percent) of twenty-four patients who
had articular step-off were symptomatic15. With an adequate and properly maintained reduction, the rate of
radiocarpal arthritis may be reduced to 5 to 10 percent
(one of thirteen patients in one study12 and three [10
percent] of thirty-one in another study9), even in patients who have a severely comminuted fracture.
Unstable distal radial fractures involving osteopenic bone may not be amenable to open treatment with
metal fixation devices because of the low bone strength.
However, the problem of attaining stability without an
extended period of immobilization remains. Insertion of
a structural material that can transfer load without causing a loss of stability at the fracture site is an attractive
alternative for the treatment of these comminuted frac-
398
D. N. YETKINLER ET AL.
DATA
Specimen
Pair
1
2
3
4
5
6
7
8
9
10
Average and
standard
deviation
Difference†
ON
TABLE III
VOLAR AND DORSAL STEP-OFF
Type of
Construct*
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Difference
Kirschner-wire
SRS
Volar
Step-off
(mm)
Dorsal
Step-off
(mm)
0.78
0.42
–0.36
0.65
0.08
–0.57
0.60
0.11
–0.49
1.07
0.52
–0.55
3.20
2.91
–0.29
1.56
1.68
0.12
0.48
0.52
0.04
0.32
0.06
–0.26
0.26
0.53
0.27
0.36
0.01
–0.35
0.93 ± 0.89
0.68 ± 0.92
0.84
0.24
–0.60
0.16
0.16
0.00
0.17
0.32
0.15
0.01
0.14
0.13
1.61
0.32
–1.29
0.56
1.39
0.83
0.52
0.32
–0.20
0.37
0.03
–0.34
0.01
0.01
0.00
0.67
0.02
–0.65
0.49 ± 0.48
0.30 ± 0.41
–0.24 ± 0.29
–0.20 ± 0.57
*SRS = Skeletal Repair System bone cement (Norian, Cupertino,
California).
†The average of the differences between the two groups.
tures. An intramedullary core of acrylic bone cement
has been used in this manner for primary fixation of
distal radial fractures involving osteopenic bone14,21,24.
The patients have been able to use the hand immediately postoperatively without the need for additional
fixation. Periosteal bone formation has occurred and
osseous union has been established within six to seven
weeks after this procedure16. The incompatible nature of
acrylic bone cements as well as late loosening as a result
of the progression of osteoporosis make the use of poly-
meric materials unattractive for the treatment of distal
radial fractures. The same immediate postoperative stability may be achieved with SRS bone cement without
compromising fracture-healing or long-term structural
integrity.
Jupiter et al. reported that SRS bone cement can
be administered percutaneously and can support the
reduction of the fracture by countering compressive
forces that occur in the comminuted metaphyseal region
of the fractured distal part of the radius13. Those authors
concluded that the material is biocompatible and that it
did not cause any serious complications. Kopylov et al.,
in another clinical study, found that distal radial fractures that were treated with SRS bone cement needed
a shorter period of immobilization because of the stability that was attained by the filling of the metaphyseal
bone defects17.
A related issue that was not addressed in the current
study is the substantial effect that even short-term exposure to the aqueous biological milieu has on the degradation of the bone cement, resulting in the immediate
loss of stabilization within the bone. The effectiveness
with which the cement can be implanted in the laboratory setting is not likely to be duplicated in a clinical
situation. There is a question as to whether the experimental methodology that we used to determine settling
had the necessary precision to reveal small differences
in the amounts of settling between the two treatment
groups.
Operative treatment with use of SRS bone cement
necessitates an open incision and impaction of loose
cancellous-bone fragments, and this might increase the
operative time and the rate of complications compared
with those associated with Kirschner-wire fixation. In
addition, the specimens in the current study required
twelve to twenty-four hours of incubation in 100 percent
humidity at 37 degrees Celsius, and this might have had
a negative impact on both treatment groups, especially
the Kirschner-wire specimens.
In conclusion, the findings in the current study suggest that use of a minimum operative exposure to prepare the fracture void properly as well as filling of
regions of cancellous-bone voids with a biocompatible
calcium-phosphate (SRS) bone cement provides adequate fixation to maintain reduction of intra-articular
distal radial fractures. Patients may start to use the affected limb soon after the operation in order to restore
the function of the hand to the prefracture level.
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