Fluoride Vol. 32 No. 1 7-13 1999
Research Report
7
FLUORIDE CONCENTRATION IN BONE INFLUENCES
PERIPROSTHETIC BONE MINERAL LOSS AFTER
UNCEMENTED TOTAL HIP ARTHROPLASTY
A Bohatyrewicz,a A Gusta,a P Bialecki,a T Ogoński,b
E Dabkowska,b A Spoza and Z Machoyb
Sczecin, Poland
SUMMARY: Factors influencing bone remodelling after cementless total hip
arthroplasty (THA) with Parhofer prosthesis were evaluated in a longitudinal
study of 18 hips in 18 patients who had undergone uncemented THA due to
osteoarthritis. Bone mineral density (BMD) in the femoral neck was determined by dual-energy X-ray absorptiometry (DXA) measurement performed
preoperatively, in periprosthetic femoral regions and prospectively 2 weeks,
3, 6, 12 and 24 months after operative treatment. The concentrations of calcium, magnesium, zinc, and fluoride were measured in cortical and trabecular bone samples taken from the resected femoral head and neck. After the
operation, the regional BMD decreased, but after 12 months it appeared to
be stabilised. Preoperative femoral neck BMD and the fluoride content in
trabecular bone indicated that osteopenia and lower fluoride concentrations
correlated with bone density reduction after THA. No other factors (age,
weight, sex, calcium, magnesium, and zinc concentrations in bone and fluoride concentration in cortical bone) showed significant associations.
Key words: Bone fluoride concentration, Bone mineral density, Perioprosthetic bone
density, Total hip arthroplasty.
INTRODUCTION
Adaptive changes in periprosthetic bone occur following total hip arthroplasties (THA), and bone resorption and remodelling are known to be important factors in the long-term stability of a femoral prosthesis. 1 There is no
evidence that severe resorptive changes cause clinical symptoms or prosthesis
loosening. However, there is a concern that continuous femoral bone resorption may reduce the stability of the prosthesis stem. Consequently, evaluation
and prevention of periprosthetic resorptive changes may be important for the
longevity of the arthroplasty.2
The purpose of the present study was to determine the changes in bone
mineral content around the prosthesis resulting from bone remodelling and to
assess the importance of the following variables on the remodelling process:
patient age, patient weight, duration of implantation, bone mineral density in
contralateral femur, and fluoride, calcium, magnesium, and zinc concentrations in cortical and trabecular bone.
MATERIALS AND METHODS
In September 1993, a longitudinal study of periprosthetic bone mineral
density was undertaken for patients who had undergone cementless total hip
arthroplasty with PM Plasmapore Hip Endoprosthesis System (Aesculap, Tuttlingen, Germany) because of coxarthrosis. Earlier studies with this system
aDept.
of Orthopaedics and Traumatology, Pomeranian Medical Academy, Sokolowskiego 11, 70-891 Szczecin, Poland. bDept. of Biochemistry and Chemistry, Pomeranian
Medical Academy, Al. Powstańców Wlkp. 72, 70-111 Szczecin, Poland.
8
Bohatyrewicz, Gusta, Bialecki, et al.
showed satisfactory experimental and clinical results. 3 The operations were
performed through the anterolateral approach. Partial weightbearing was started 3 weeks after surgery, followed by full weightbearing at 3 months postoperatively.
During the follow-up period, each patient underwent clinical and radiographic examinations coupled with dual energy x-ray absorptiometry (DXA)
measurement of the periprosthetic bone mineral density at 2 weeks, and 3, 6,
12 and 24 months after operative
treatment.
Patients, supine on the table, were
scanned using the software that was
designed to measure the periprosthetic bone mineral content and density (DPX-L, Lunar, Madison, Wisconsin, USA). Seven periprosthetic
regions, resembling the zones described by Gruen4 were defined according to the length of the inserted
stem, thus permitting an accurate
comparison of identical regions of
interest during the longitudinal
study. Medial and lateral sides of the
femur from the level of medial neck
resection to the stem tip were divided into three equal regions: Zones 1
to 3 for lateral side, and Zones 5 to 7
for medial side, and Zone 4 with
equal height to each of the medial
and lateral zones just distal to the
stem tip (Figure 1). Scan resolution
(size per pixel) was 0.6 x 1.2 mm,
Figure 1. The seven regions of
average scan dose was 4.8 mRem,
interest defined according to
and average scan time 5 minutes.
the length of the inserted stem.
To evaluate the precision of DXA
measurements, 8 patients received
three consecutive scans after dismounting and remounting the table during
each scan, and the coefficient of variation was calculated at each zone. The
average precision at each zone was as follows: Zone 1, 5.4%; Zone 2, 3.4%;
Zone 3, 2.3%; Zone 4, 1.8%; Zone 5, 3.7%; Zone 6, 4.1%; Zone 7, 6.3%.
The mineral density values from the different time periods and each subregion were calculated and referenced to the values 2 weeks after surgery. The
percentage change in density in the operated hip was calculated as follows:
BMD 2 weeks after operation - BMD in the same subregion at time x
——————–—–————————————————————————————————————
BMD 2 weeks after operation
Fluoride 32 (1) 1999
x 100
Fluoride and periprosthetic bone mineral loss
9
All values were expressed as the mean percentage BMD change  the
standard error. The DXA measurement of the contralateral femoral neck was
performed during the hospitalization before operative treatment. The precision
error was 2.3%.
Linear regression analysis of the data was done to determine whether a correlation existed between the BMD change and clinical factors, including patient age, patient weight, duration of implantation, and BMD in contralateral
femoral neck before arthroplasty.
Small samples of cortical bone from femoral neck and trabecular bone
from femoral head were taken from the resected bone intraoperatively and
stored frozen. The fluoride concentration was measured with an Orion fluoride ion-selective electrode after dissolving the defatted bone pieces in perchloric acid; calcium, magnesium, and zinc concentrations were measured by
mass absorption spectrometry. 5 The coefficient of variation was 2.7% for fluoride, 3.7% for calcium, 4.1% for magnesium, and 3.9% for zinc. Linear regression analysis was done to determine a correlation between BMD change
and biochemical factors, including fluoride, calcium, magnesium, and zinc
concentrations in cortical and trabecular bone.
By April 1995, 18 hip patients had been enrolled in this study. There were
4 men and 14 women with an average age of 63 years (range, 42-76 years).
RESULTS
Analysis of the BMD changes occurring in all patients at all time intervals
revealed significant decreases in all subregions (Table 1).
Table 1. Bone loss after hip replacement (%)
Time
Zone 1
Zone 2
Zone 3
Zone 4
Zone 5
Zone 6
Zone 7
3
months
9.4
 2.9
9.1
 3.7
7.7
 3.1
7.8
 2.6
8.3
 2.6
10.1
 3.3
12.4
 2.9
6
months
13.1
4.0
12.2
 3.7
9.9
 3.6
9.3
 3.0
10.2
 3.6
13.4
 4.0
17.5
 3.2
12
months
16.8
 3.9
14.3
 4.0
13.2
 3.3
12.7
 3.1
14.5
 4.1
16.1
 4.3
21.2
 3.7
24
months
17.3
 4.2
14.4
 5.1
13.9
 4.2
12.6
 4.1
14.7
 4.3
16.9
 4.1
20.8
 4.8
At 12 and 24 months after the operation, the regional BMD in all seven
zones showed a maximal decrease ranging from 7.3 to 38.8% of that density
present at two weeks postoperatively, but after 12 months the bone density
appeared to be stabilized. The most significant postoperative bone loss ranging from 12.1 to 38.8% was found in the zone 7 calcar area. The cortical zone
4 below the prosthesis showed the lowest, but still substantial decreases, ranging from 7.3 to 18.1%. The percent decrease in all Gruen zones at 24 months
was compared with patient age and weight, and with fluoride, calcium, and
Fluoride 32 (1) 1999
10
Bohatyrewicz, Gusta, Bialecki, et al.
magnesium concentrations in cortical and trabecular bone. The linear regression showed only two variables predictive of the bone loss: BMD in contralateral femoral neck for Gruen zones 1, 2, and 7, and fluoride content in trabecular bone for zone 1 and 2 (Figures 2 and 3).
1.4
1.2
1
0.8
0.6
2
R = 0.3619
0.4
0.2
0
0
5
10
15
20
25
30
25
30
BMD femoral neck
(g/cm2)
BMD femoral neck (g/cm2)
B MD los s in Gruen 1 z one (% )
1.4
1.2
1
0.8
0.6
2
R = 0.4156
0.4
0.2
0
0
5
10
15
20
B MD los s in Gruen 2 z one (% )
1.4
1.2
1
0.8
0.6
2
R = 0.4089
0.4
0.2
0
0
10
20
30
40
B MD los s in Gruen 7 z one (% )
Figure 2. Correlation between percent changes of bone mineral
density in Gruen 1, 2 and 7 zone at 24 months after arthroplasty
and bone mineral density in contralateral femoral neck.
Fluoride 32 (1) 1999
Fluoride and periprosthetic bone mineral loss
11
Other clinical and biochemical variables displayed no relationship to bone
loss. Correlation of patient age with bone fluoride, calcium, magnesium, and
zinc concentration did not show any statistical significance.
90
Fluoride content in trabecular bone (mmol/kg)
75
60
45
30
2
R = 0.4681
15
0
0
5
10
15
20
25
30
25
30
B MD lo s s in G ru e n 1 z o n e (% )
90
75
60
45
30
2
R = 0.3822
15
0
0
5
10
15
20
B MD lo s s in G ru e n 2 z o n e (% )
Figure 3. Correlation between percent changes of bone
mineral density in Gruen 1 and 2 zone at 24 months after
arthroplasty and fluoride content in trabecular bone.
DISCUSSION
It is acknowledged that there are several deficiencies in this study. First,
the bone samples taken from degenerated femoral neck head were not the
same as the bone surrounding the implanted prosthesis. 6 Second, using the
contralateral femur as an indicator of bone mineral content does not account
for this inequality in the same patient. 7 Finally, the sampling method including
only patients with unilateral hip disease and PM Plasmapore hip prosthesis
reduced the number of cases to only 18 and therefore did not necessarily produce a random sample of patients.
The decrease in periprosthetic BMD in the proximal Gruen zones 1 and 7
reflects altered stress distribution and typical increase in bone remodelling
Fluoride 32 (1) 1999
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Bohatyrewicz, Gusta, Bialecki, et al.
after prosthesis implantation, which may also be demonstrated by scintigraphic examination.8
Three factors adversely affect maintenance of bone mass after THA: adaptive bone remodelling and stress shielding secondary to size, material properties, and surface characteristics of contemporary prostheses; bone loss secondary to particulate debris; and bone loss as a consequence of natural aging. 9
Engh et al.10 demonstrated that stem size and extent of porous coating influences femoral bone resorption after primary cementless hip arthroplasty.
Bobyn et al.11 suggested the optimal bending stiffness ratio between bone and
implant should be between approximately 2:1 and 3:1, thereby leading to the
lowest periprosthetic bone loss. The inverse relationship between bone mineral density in contralateral femur and periprosthetic bone loss might be explained by the decreasing of all mechanical properties in surrounding osteoporotic bone.12,13
Grynpas14 suggested that bones with higher fluoride content show more resistance to acid dissolution and reduced rate of bone resorption. Whether the
incorporation of fluoride into bone will reduce the BMD loss after THA remains to be determined.
CONCLUSIONS
 Total hip arthroplasty leads to significant decrease of bone mineral density
measured around the prosthesis stem.
 Periprosthetic bone loss is greater in patients with low bone mineral content and low fluoride concentration in trabecular bone.
 Weight, age, calcium, magnesium and zinc concentrations in bone and fluoride concentration in cortical bone do not correlate with bone loss.
This paper was presented and discussed at the XXIInd Conference of the
International Society for Fluoride Research in Bellingham, Washington USA
(24-27 August, 1998).
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Published by the International Society for Fluoride Research
Editorial Office: 17 Pioneer Crescent, Dunedin 9001, New Zealand
Fluoride 32 (1) 1999