the study design was approved by the ethics committee at our
institution. Twenty consecutive women with osteoporosis who had
a wrist fracture were selected. Upon admission, the medical history of
each patient was recorded by hospital staff, and physical and radiographic
examinations were performed. The inclusion criteria included female
gender, an age of sixty-five years or more, a type-A2 or A3 fracture
of the distal part of the radius according to the AO classification
system16, a fracture resulting
from minor trauma, an ability to communicate with regard to one’s
physical condition, and a bone-mineral-density T score of less than —2.5
in the contralateral radius. Bone-mineral density was measured with
a dual-energy x-ray absorptiometric scanner (Norland XR-36; Norland, Fort
Atkinson, Wisconsin) in an area extending 1.5 cm proximal to the
distal radioulnar joint. The exclusion criteria included an open
fracture, a fracture secondary to a malignant tumor, a bone or soft-tissue
infection at the fracture site, treatment with chemotherapy, multiple
fractures, and severe systemic disease.
After the patients were admitted to the study, the objectives
and the randomization were explained and an informed-consent form
was signed. The patients were randomized, with use of a computer-generated
list, to receive external fixation with either tapered 3.3-3-mm-thread-diameter
standard pins or tapered 3.3-3-mm-thread diameter hydroxyapatite-coated
pins (Orthofix, Bussolengo, Italy).
A total of forty pins were used in each group. The ten patients
who received standard pins had a mean age (and standard deviation)
of 75 6 years, and the ten patients who received hydroxyapatite-coated
pins had a mean age of 74 7 years. The mean bone-mineral density
at the distal part of the contralateral radius was 0.297 g/cm2 in
the group managed with standard pins and 0.301 g/cm2 in
the group managed with hydroxyapatite-coated pins. All of the patients
were right-handed, and none of them were smokers.
Surgical Technique
All of the patients were managed with antibiotic prophylaxis
with cephalosporin (one gram every eight hours for forty-eight hours)
and application of a Pennig-II unilateral fixator (Orthofix). Through small
incisions, two pins were implanted into the radial shaft and two
were inserted into the second metacarpal. Pin location in the radius
and metacarpal was determined by fluoroscopy. The pins were numbered
1 to 4, from proximal to distal, with pin 1 implanted in the most
proximal radial location. Pins 1 and 2 were implanted in the diaphyseal
bone of the radius; pin 3, in the cancellous bone of the proximal
part of the metaphysis of the second metacarpal; and pin 4, in the
diaphyseal bone of the second metacarpal. Standard or hydroxyapatite-coated
pins were implanted after predrilling with a 2.6-mm-diameter drill,
as recommended by the manufacturer. Biplane fluoroscopy was used
during surgery to check pin implantation. All of the pins engaged both
cortices. After each pin was inserted to the desired depth (indicated
by two pin threads extruding from the opposite cortex), a custom-made torque
wrench was connected to the pin and torque was applied to tighten
the pin. After the final insertion torque was measured for each
pin, the fixator was mounted. The pins were not prestressed in any way
at the time of placement of the fixator. The ball joint of the fixator
was locked for the entire period of treatment. Postoperatively,
the pin sites were cleaned daily with saline solution. All fixators
were removed six weeks after surgery. At the time of removal, pin-extraction
torque was measured and radiographs were made.
Clinical Analysis of the Pin Tracks
The classification system of Checketts and Otterburn17 was used to evaluate the pin tracks
when the fixator was removed. According to this system, a grade-1 pin-track
infection is characterized by slight discharge and redness around
the pins that requires only local treatment. A grade-2 infection
is indicated by redness of the surrounding skin, tenderness in the
soft tissues, and, sometimes, discharge of pus. Infections of this
type resolve with local care and oral antibiotics. A grade-3 infection
is similar to a grade-2 infection but fails to improve with intensive
local treatment and antibiotics. The infection resolves when the
involved pin or pins are repositioned, after which it is possible
to continue use of the fixator. Grades 4, 5, and 6 are indicative of
major infection. A grade-4 infection is characterized by severe
soft-tissue involvement that affects more than one pin site and
fails to respond to local treatment and oral antibiotics. It is
necessary to remove the affected pins and to abandon use of the external
fixation device. The clinical appearance of a grade-5 infection
is the same as that of a grade-4 infection, but there is radiographic
evidence of osteomyelitis. It is necessary to remove the affected pins
and to abandon use of the external fixation device. A grade-6 infection
is characterized by the formation of a sequestrum within the bone
and the development of a persistent sinus. Additional surgery is
required to eradicate the problem.
Clinical Analysis of Pain During Pin Removal
All fixators were removed, without the use of general or local
anesthesia, in an outpatient facility. Patients were requested to
rate the pain that they had had during pin removal on a 10-point
visual analogue scale, with 0 indicating no pain and 10, the maximum
expected pain.
Morphological Analysis
After extraction, four hydroxyapatite-coated pins were selected
for morphological analysis. They were embedded in methylmethacrylate
and processed for undecalcified sectioning. Samples were cut perpendicular
to the longitudinal pin axis with an Exact system diamond saw (boron-nitride-blade saw;
Kulzer System, Norderstedt, Germany). After the sections were ground
to a 30-m thickness, they were stained with acid fuchsin and light
green.
Statistical Analysis
The number of patients in this study was selected on the basis
of the comparison between the extraction torques in the two groups,
with a level of significance of 95% and a power of 80%.
Statistical analysis was performed with use of the Statistical Package
for the Social Sciences (SPSS) software (version 7.5 for Windows;
SPSS, Chicago, Illinois). All continuous data are expressed as the
mean and the standard deviation. One-way analysis of variance with
the Scheffé post hoc test and repeated-measures
one-way analysis of variance with the Bonferroni post hoc test
were performed to test hypotheses regarding the means for different
groups or for different measurements in the same patient. When the
Levene test for homogeneity of variances was significant (p < 0.05),
the Mann-Whitney test (two independent groups), the Kruskal-Wallis
test (three or more independent groups), or the Friedman test (three
or more measurements in the same patient) was used to check the
results of analysis of variance. The regression analysis and correlation-coefficient
tests were performed to investigate relationships between two quantitative
measurements. For all tests, p < 0.05 was considered significant.
Biomechanical Results
The mean pin-insertion torque was 461 ± 254
Nmm in the group treated with standard pins and 332 ± 176 Nmm in the group treated with hydroxyapatite-coated
pins (p = 0.01). The mean pin-extraction torque was 191 ± 155 Nmm in the group treated with standard pins and
600 ± 214 Nmm in the group treated with hydroxyapatite-coated
pins (p < 0.0001, power 95%).
Insertion torque differed according to pin position in both groups
(p < 0.0001). The lowest mean insertion torque was found
in position 3 in both the group with standard pins (p < 0.01)
and the group with hydroxyapatite-coated pins (p < 0.009)
(Table I).
Extraction torque differed according to pin position in the group
with standard pins (p < 0.0001), with the lowest mean extraction
torque found in position 3 (p < 0.003). No association
between extraction torque and pin position was observed in the group with
hydroxyapatite-coated pins (Table I).
In the group with standard pins, the extraction torque at each
pin position was lower than the corresponding insertion torque (p < 0.05)
(Table I). In
the group with hydroxyapatite-coated pins, the extraction torque
at each pin position was higher than the corresponding insertion
torque (p = 0.001) (Table I).
In the group with standard pins, a correlation was found between
extraction and insertion torque. Specifically, the pins with the
highest extraction torque were the ones with the highest insertion
torque (r = 0.69, p < 0.0001). No correlation
between extraction and insertion torque was detected in the group with
the hydroxyapatite-coated pins (Fig. 1).
Clinical Results
All of the fractures healed. Neither a cast nor an orthosis was
used after fixator removal. Two patients in the group with standard
pins had a grade-1 pin-track infection. The mean pain rating during
pin removal was grade 2 ± 1 for both groups.
One patient in each group had reflex sympathetic dystrophy.
Morphological Results
After pin extraction, the hydroxyapatite coating appeared to
be intact macroscopically and the metallic surface was not visible.
Histological findings confirmed the absence of exposure of the metallic
substrate.
The increasing number of patients with osteoporosis and the problems
associated with the fixation of fractures in mechanically weak bone
have stimulated the development of new fixation methods. To our
knowledge, this is the first clinical study to show that hydroxyapatite-coated
pins provide better fixation in osteoporotic bone than do similar uncoated
pins (p < 0.0001, power 95%). Insertion torque
was related to pin position along the external fixator in both the
group with standard pins (p < 0.01) and the group with
hydroxyapatite-coated pins (p < 0.009). In both groups,
the lowest insertion torque was associated with the pin that was implanted
in the cancellous bone of the proximal part of the metaphysis of
the second metacarpal.
Theoretically, the insertion torque associated with the hydroxyapatite-coated
pins should have been higher because of the slight increase in their
diameter and surface roughness, but our results did not confirm
this. Insertion torque was lower for the hydroxyapatite-coated pins
than for the standard pins (p = 0.01). This finding could
be due to the greater ability of the hydroxyapatite-coated pins
to cut a thread in the bone during implantation. The lower insertion
torque in the hydroxyapatite-coated pins also could be attributed
to the tapered shape of the pins. In a previous study on bicylindrical
pins, no differences were found between hydroxyapatite-coated and
standard pins with respect to insertion torque9.
It has been reported that a low insertion torque is not desirable
because it can lead to pin-loosening6.
However, in the group treated with hydroxyapatite-coated pins, the
lower insertion torque corresponded to a higher extraction torque
(p = 0.001). In the group treated with standard pins, extraction torque
was correlated with insertion torque (r = 0.69, p < 0.0001).
These findings suggest that, when hydroxyapatite-coated pins are
implanted, a high fixation strength is achieved independent of the
amount of insertion torque.
When standard pins were used, there was severe deterioration
of bone-pin interface strength over time, with the extraction torque
being lower than the insertion torque at each pin position (p < 0.05)
(Table I). In
contrast, when hydroxyapatite-coated pins were used, there was an
improvement in bone-pin interface strength at each pin position
(p = 0.001). In previous studies on normal bone, the higher
fixation strength associated with hydroxyapatite-coated tapered
pins has been shown to correspond to greater bone-pin contact without
fibrous-tissue interposition9,11.
Given the biomechanical results of the present study, we believe
that these pins may maintain their ability to achieve osseointegration
when implanted in osteoporotic bone.
In previous studies, it was reported that the removal of well-fixed
hydroxyapatite-coated pins was more painful than that of loose standard
pins; however, pain was not quantified7,8,10.
In the present study, pain during pin removal was quantified and
no differences were observed between the two groups. However, the
pins in this study were implanted in osteoporotic bone and they were
smaller than those used in previous studies.
Although pin-loosening and infection are less frequently associated
with fixation of a wrist fracture than with long-term fixation of
a fracture involving a weight-bearing limb, we recommend the use
of hydroxyapatite-coated pins for the external fixation of distal
radial fractures, particularly in osteoporotic patients. In the
present study, these pins provided improved fixation and none of
the patients who were treated with such pins had a pin-track infection.
Previous studies on the use of hydroxyapatite-coated pins in normal
bone have shown a correlation between results obtained in loaded
and unloaded conditions and at short and long-term intervals2,8,9,18. Consequently, we believe
that better fixation in osteoporotic bone can also be achieved under
long-term loaded conditions. In conclusion, ours is the first clinical
study, as far as we know, to show that hydroxyapatite-coated pins
provide better fixation in osteoporotic bone than do similar uncoated
pins. Osteoporosis may no longer be considered a contraindication
for external fixation. Furthermore, hydroxyapatite-coated implants
could improve other fixation techniques in osteoporotic bone.