Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Drug for Treating Fractures
Field of the Invention
The present invention relates to new indications for a certain class of
drugs. More specifically. the present invention relates to the use of
bisphosphonates for the promotion of bone growth and in the treatment of
bone fractures. Of the bisphosphonates. Zoledronate and Pamidronate have
been found to be particularly effective when used for such a purpose.
Background Art
Bisphosphonates are characterised by a P-C-P bond. which has a strong
1o affinity for bone mineral. They are analogues of pyrophosphate, containing
a
carbon instead of an oxygen atom. This makes them totally resistant to
enzymatic breakdown in vivo.
Bisphosphonates differ in their actions and potency depending on the
configuration of a side chain. Bisphosphonates inhibit bone resorption
through a direct effect on osteoclast function, and also inhibit osteoblastic
recruitment of osteoclasts. Due to these factors. calcium is retained in the
skeleton and there is a subsequent increase in parathyroid hormone (PTH)
and 1.25-(OH)z vitamin D, leading to increased intestinal calcium absorption.
In growing rats this has resulted in an increase in bone mass (Licata.
"Bisphosphonate Therapy'Am JMed Sci 1997 Jan: 313(1):17-22). In very
high doses. bisphosphonates may actually inhibit bone formation and
osteoblast function. In fact one of the previously well-documented
indications for bisphosphonates is in the prevention of heterotopic
ossification after spinal cord injury or hip arthroplasty. (Stover et al
''Disodium etidronate in the prevention of postoperative recurrence of
heterotopic ossification in spinal-cord injury patients" JBone Joint SurgAm
1976:58(5):683-8 and Finerman and Stover ''Heterotopic ossification
following hip replacement or spinal cord injury. Two clinical studies with
EHDP.'' Metab Bone Dis Relat Res 1981:3:337-42 and Banovac and Gonzalez
''Evaluation and management of heterotopic ossification in patients with
spinal cord injury". Spinal Cord 1997:35:158-62.)
The bisphosphonate etidronate, was first trialed for the treatment of
primary osteoporosis many years ago. Results showed some success in
increasing bone density and possibly controlling fracture rates (Licata,
supra).
Since their. the use of bisphosphonates in the treatment and
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prevention of osteoporosis has become well known. They are particularly
valuable in the management of postmenopausal osteoporosis but indications
for the use of these drugs in the treatment of other disorders affecting bones
has also become well known.
Because bisphosphonates are capable of inhibiting bone resorption
they are used as effective therapeutic agents in several conditions
characterised by increased bone turnover. including Paget's disease.
hypercalcaemia of malignancy and metastatic bone disease (Lombardi.
"Clinical trials with bisphosphonates" Aml Ital Med Int 1992 Jul-Sep; 7(3
Suppl):158S-165S). They have also been indicated in the treatment of
multiple myeloma. breast cancer metastases and osteogenesis imperfecta.
Bone fractures are often par for the course in many of these disorders.
Even where fractures are avoided, however, their risk of occurrence is
dramatically increased by the presence of such disorders. Consequently,
much of the ongoing research into the use of bisphosphonates in treating
these disorders has centred around the safety of COI1t111Ll1Ilg sLlCh
treatment
following a revealed fracture. Many of these studies have found that
bisphosphonates have no adverse effects on the restoration of the mechanical
integrity of a long bone after fracture or on fracture healing (see, for
example.
Goodship et al "Use of a bisphosphonate (pamidronate) to modulate fracture
repair in ovine bone" Allll Oncol 1994: 5 Suppl 7:S53-5: see also Li et al
"Effect of Bisphosphonate (Incadronate) on Fracture Healing of Long Bones in
Rats" J Bone Miner Res 1999 June: 14(6):969-79).
Although the use of bisphosphonates in the above mentioned and
other disorders is well documented. "their mode of action is still being
unravelled. As a result, their full therapeutic potential is gradually being
realised" (see abstract. Russell et al. "Bisphosphonates: from the laboratory
to
the clinic and back again" Bone 1999 Jul: 25(1):97-106).
The present invention provides a considerable number of novel and
important indications for the administration of bisphosphonates.
Description of the Invention
In a first aspect, the present invention consists in a drug selected from
a group consisting of at least one bisphosphonate when used for prOiIlOtlIlg
bone growth.
Preferably, bone growth is promoted at a fracture site. Furthermore, it
is envisaged that bone growth is promoted between a bone and a prosthesis.
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bone fixation device or any other bone or dental implant.
In a second aspect, the present invention consists in a drug selected
from a group consisting of at least one bisphosphonate when used for treating
a fracture.
In a preferred embodiment, the drug of either the first or the second
aspect is the bisphosphonate Zoledronate.
In a further preferred embodiment, the drug of either the first or the
second aspect is the bisphosphonate Pamidronate.
In another embodiment, the drug may be another drug from the group
consisting of bisphosphonates or a combination of two or more
bisphosphonates.
In a third aspect, the present 1I1V8I1t1011 COIISIStS 111 the use of a drug
selected from a group consisting of at least one bisphosphonate for the
manufacture of a medicament for promoting bone growth.
In one embodiment of the third aspect, the drug promotes bone growth
at a fracture site.
In a further embodiment, the drug promotes bone growth between a
bone and a prosthesis.
In a fourth aspect. the present invention consists in the use of a drug
selected from a group consisting of at least one bisphosphonate for the
manufacture of a medicament for treating a fractured bone.
In a fifth aspect. the present invention consists in a method for treating
a fractured bone, the method including administering to a subject with a
fractured bone a therapeutically effective amount of a drug selected from the
group consisting of at least one bisphosphonate.
Preferably, the drug is administered to the subject as a single dose. It
is further preferred that the single dose of drug is administered at an early
stage of treatment of the fractured bone.
In a sixth aspect. the present invention consists in a method for
treating a fractured bone, the method including the steps of:
(a) administering to a subject with a fractured bone a therapeutically
effective amount of a drug selected from a group consisting of at least one
bisphosphonate; and
(b) providing a vibratory stimulus to the fractured bone.
Preferred embodiments disclose that the use of a drug from the class of
bisphosphonates in prOI110t1I1g bOlle growth or treating a fracture may be
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applicable to all clinical alternatives for managing a fractured bone: many
fractures are most appropriately managed by simply applying a plaster cast to
the site at which the fracture has occurred and allowing the bone to heal
whilst splinted in that way: some fractures simply require the patient to
rest:
some fractures may require the application of a range of surgical
interventions: and other fractures are appropriately managed with a
combination of the latter two alternatives. Furthermore, as an alternative or
an addition. as disclosed above, the step of providing of a vibratory
St1II1111t1S
to the fractured bone may also be desirable in certain circumstances. Which
1o ever of these. or other, clinical alternatives is/are chosen for managing a
fractured bone. the present invention discloses the administration of at least
one drug from the class of bisphosphonates to the patient.
There may be several advantages to using at least one drug from the
class of bisphosphonates in the treatment of bone fractures. Nlany of these
are disclosed in considerable detail below. Nevertheless, for reasons which
will now become clear, it is worthwhile noting some of the more general
advantages from the outset. They include, but are not limited to. the
following: bisphosphonates can stimulate osteoblast proliferation and
increase callus formation: they are also potent inhibitors of osteoclastic
bone
2o resorption: they aid in the prevention of osteoporosis. and therefore
decrease
disuse osteoporosis associated with the injury: and they may also
significantly decrease the length of time which is taken for a fracture to
heal.
According to this invention, the circumstances in which
bisphosphonates are applicable to the management of fractures are far
reaching. Indeed. preferred eIIlbOdlIIleIItS disclose that the situations in
which bisphosphonates may be indicated in fracture care include at least:
(i) Increasing new bone formation in distraction osteogenesis:
(a) Bone lengthening
(b) Bone transport
(ii) Increasing new bone formation in fractures treated by open
reduction
(iii) Increasing new bone formation in fractures treated by
intramedullary fixation
(iv) Increasing new bone formation in fractures treated by
external fixation
(v) Delayed union
PCT/AU00/00982
CA 02381302 2002-02-06 Received 30 April 2001
(vi) Improving the ability of bone to support internal fixation
devices in osteoporotic individuals or in locally osteoporotic
bone segments
(vii) Treating fractures in which there are potential impediments to
uncomplicated healing, for example:
(a) Fractures in the elderly including: neck of femur;
supracondylar femur; tibia; ankle; humerus; and the
distal radius (note that this list merely provides
examples, and the use of bisphosphonates according to
this invention is not by any means limited to treating
these fractures only, or any other fractures, for that
matter, in people of all ages)
(b) Pubic rami fatigue fracture
(c) Pathological fracture
(d) Scaphoid fracture
(e) Open fracture
(f) Fracture with periosteal disruption
(viii) Treating fractures that require prolonged immobilisation when
treated non-operatively, for example: femoral fractures, tibial
fractures; and fractures of the foot and ankle.
Further preferred embodiments also disclose a number of additional
indications for using bisphosphonates in orthopaedic procedures. These
include administering bisphosphonates to increase ingrowth of bone into
joint replacement prostheses; and coating joint prosthesis with
bisphosphonates to enhance the latter mentioned ingrowth at a more local
level. Such therapy should also reduce the effects of periprosthetic stress
shielding. Prosthetic implants may be so coated as an alternative, or in
addition to coating with hydroxyapatite or some other osteoinductive
coating.
One preferred embodiment discloses that the drug chosen from the
class of bisphosphonates for carrying out this invention is Pamidronate.
Another preferred embodiment discloses that the drug chosen from the
group is Zoledronate. However, in further preferred embodiments, other
bisphosphonates may be used in addition (where no adverse interaction
results), or as an alternative, to Pamidronate or Zoledronate. Examples of
further bisphosphonates include, but are not limited to, Alendronate,
Tiludronate, Risedronate, Ibandronate and Incadronate.
In further preferred embodiments, the drug is administered to a
AMENDED SHEE
IPEA/AU
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g Received 30 April 2001
patient as a single dose. In this embodiment, it is preferred that the
administration of the drug occurs early during the course of treating the
fractured bone as administration of a bisphosphonate at such an early stage
has a positive effect on the stimulation and proliferation of osteoblasts.
In a further embodiment, subsequent additional doses may be
administered to the patient. In this embodiment, it is envisaged that a
response to the first dose would be assessed before administering additional
doses.
In still further preferred embodiments, the mode of administration
may be as a perioperative intravenous infusion, orally, transdermally or by
some other route. Alternatively a course of an oral bisphosphonate may be
prescribed. All preferred and alternative embodiments of the invention
envisage current and future available modes of administration for the drug.
Such modes of administration must, of course be plausible, convenient and
provide the patient with a therapeutically effective dose for treating and/or
promoting healing of the fractured bone.
The present invention also discloses that in some embodiments, it is
preferable to additionally apply a vibratory stimulus to the fractured bone.
The vibratory stimulus may be provided by ultrasound stimulation and
vibration stimulation, or any other mechanism and/or device capable of
providing vibratory stimulation. In some embodiments, the vibratory
stimulus may be applied at any frequency which is considered to be
effective in the treatment of a fractured bone. In preferred embodiments,
however, the step of providing a vibratory stimulus includes periodically
providing a vibratory stimulus at the resonant frequency of the bone, said
resonant frequency being calculated as a function of the bone's vibratory
response to
'~R'~E"~'UE~ SHEET
~~E~L~U
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the vibratory stimulus. In order to have this achieved, this step may be
broken down into the following components:
(a) providing a vibratory stimulus to the fractured bone:
(b) detecting the vibratory response of the bone to the vibratory
stimulus:
(c) generating a signal representative of the vibratory response:
(d) processing the signal to identify at least one resonant frequency of
the bone: and
(e) providing a signal to adjust the vibratory stimulus to the bone such
1o that it is at, or approximate, the bone's at least one resonant frequency.
Whether or not the step of providing a vibratory St1I11111L1S to the
fractured bone is utilised. preferred embodiments disclose that at least one
bisphosphonate should be administered to the patient early in the course of
treatment. In this regard. different bones and different types of fracture
heal
at varying rates. Accordingly. the early phase of the course depends upon
such variables.
The administration of a bisphosphonate at such an early stage has a
positive effect on the stimulation and proliferation of osteoblasts. In cases
where the provision of a vibratory stimulus is utilised, it is preferable that
such stimulus be provided later in the course of treatment, since mechanical
stimulation will assist in the maturation of the healing fracture. In yet
another preferred embodiment, however, both the administration of a
bisphosphonate and the provision of a vibratory stimulus may occur early in
the course of treatment. In alternative embodiments. they may be used at
opposite times, they may be alternated. or they may both be delivered in the
later stages of treatment as is considered to be most appropriate.
Brief Description of the Drawing-s
By way of example. preferred embodiments of the invention are
described with reference to the accompanying drawings in which:
Fig. 1 shows the generic formula for bisphosphonates.
Fig. 2 is a graph from example 1 illustrating the differences in Bone
Mineral Density (BMD) at the regenerate and at locations both proximal and
distal the regenerate in the control group with lengthened legs and the
control group with non-lengthened legs (there is, of course, no value given
for the BMD at the regenerate for the group with non-lengthened legs):
Fig. 3 is a graph from example 1 illustrating the differences in BMD at
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the regenerate and at locations both proximal and distal the regenerate in the
pamidronate treated group with lengthened legs and the pamidronate treated
group with non-lengthened legs (there is, of course. no value given for the
BIvID at the regenerate for the group with non-lengthened legs):
Fig. 4 is a graph from example 1 illustrating the differences in BMD at
the regenerate and at locations both proximal and distal the regenerate in the
control group with lengthened legs and the pamidronate treated group with
lengthened legs:
Fig. 5 illustrates the histopathological differences between a specimen
from the control group and one from the pamidronate treated group of
example 1:
Fig. 6 is a graph from example 2 illustrating the differences in peak
load for the non-operated and operated pamidronate treated group and for the
non-operated and operated control group: and
Fig. 7 is a graph from example 2 illustrating the difference in findings
with respect to Young's Modulus (1% strain) for the non-operated and
operated pamidronate treated group and for the non-operated and operated
control group.
Figures 8A. 8B and 8C are graphs from example 3 illustrating the bone
mineral content in the proximal. regenerate and distal segments of an
operated tibia at 2. 4 and 6 weeks post operation respectively.
Figure 9 is a graph from example 3 illustrating Bone Mineral Content
(BMC) accrual in the regenerate.
Figure 10 is a graph from example 3 illustrating final BMC at six weeks
as measured by QCT.
Figures 11A. 11B and 11C are graphs from example 3 illustrating BMD
in the proximal, regenerate and distal segments of an operated tibia at 2. 4
and 6 weeks post operation respectively.
Figure 12 is a graph from example 3 illustrating final BMD at six weeks
as measured by QCT.
Figure 13 is a graph from example 3 illustrating final cross-sectional
area at six weeks as measured by QCT.
Figure 14 depicts QCT scans from example 3 of regenerate in rabbit
operated tibiae that were the median for cross sectional area in each group.
Figure 15 is a graph from example 3 illustrating final moment of inertia
at six weeks as measured by QCT.
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Figure 16 is a simplified view of a device for the application of a
vibratory stimulus to a fractured bone.
Preferred Mode of Carrying Out the Invention
In preferred embodiments. zoledronate or pamidronate and/or another
drug from the class of bisphosphonates is used for the manufacture of a
medicament for promoting bone growth or treating a fractured bone.
A therapeutically effective dose of the medicament, or zoledronate or
pamidronate and/or another bisphosphonate alone, is then appropriately
prepared and administered to a patient via an intravenous route.
Preferred embodiments further disclose that such administration of the
drug is to occur early during the course of treating the fractured bone. The
administration of a bisphosphonate at such an early stage has a positive
effect on the stimulation and proliferation of osteoblasts. No further
administration of the bisphosphonate may be required, but can be
administered if desirable after gauging the response of the patient to the
first
dose.
Furthermore, a course of an oral bisphosphonate may be prescribed to
a patient wherein the oral bisphosphonate is taken in the initial three months
of fracture healing. In another embodiment, a course of oral bisphosphonates
2o may be given later in the course of fracture healing to augment callus
formation in a bone healing slowly.
The present invention also discloses that in some embodirients. it is
preferable to additionally apply a vibratory St1111L11L1S to the fractured
bone as
set Ollt in International Application No PCT/AU99/00974 and herein
incorporated by reference. The vibratory stimulus may be provided by
ultrasound stimulation and vibration stimulation, or any other mechanism
and/or device capable of providing vibratory stimulation. In such preferred
embodiments, the step of providing a vibratory St1111L11L1S 1I1C1L1deS
periodically providing a vibratory stimulus at the resonant frequency of the
bone, said resonant frequency being calculated as a function of the bone's
vibratory response to the vibratory stimulus.
With reference to Figure 16. the vibratory stimulation device 10 is
adapted to determine the specific resonant frequency of a bone 11, and to
then subject the bone 11 to stimulation at the specific resonant frequency of
the bone 11. and maintain stimulation at that frequency for a period of time.
This ensures optimal stimulation and thus optimal promotion of bone mass.
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whilst at the same time, avoids the risk of over-stimulation or overloading,
and thus, fracture of the bone.
The device 10 includes a vibration stimulator 12 which. when
activated. stimulates the bone 11 over a range of frequencies, causing
5 vibration of the bone 11. The stimulator 12 is driven by a signal generator
housed in the computer 14. The signal generator, when initially activated.
can cause the stimulator 12 to vibrate over a range of frequencies. The signal
generator can. for example, sweep through this range of frequencies.
Examples of suitable stimulators 12 include a rotating eccentric mass,
10 an electromagnetic shaker, and a variable frequency pulsed ultrasonic
transducer. The stimulator 12 can incorporate a stimulus sensor, such as a
force transducer. to monitor the stimulus provided to the bone by the
stimulator 12.
The vibrations are detected by a detector 13. The detector 13 can
comprise an accelerometer or a plurality of accelerometers. The detector 13
transmits the signals to a computer 14 wherein the signals are converted from
analogue to digital form and then processed to determine the frequency
domain characteristics of the vibratory response. The computer 14 can
incorporate an automatic analysing means that determines the peak
acceleration/velocity/displacement of the bone and so determines the
resonant frequency of the bone. In another embodiment. the computer can
display either numerically and/or graphically the measured characteristics of
the vibratory response to allow manual determination of the resonant
frequency by a user of the device, or a treating physician. The device 10 can
include a manual frequency control 15 for stimulation. Preferably, from the
signals received, the computer 14 identifies one of the resonant frequencies
of the bone 11 and transmits a signal to the stimulator 12 to stimulate the
bone 11 at. or approximate, the one resonant frequency.
The device can incorporate a timer that allows the time of operation of
the stimulator 12 to be pre-set prior to activation. Such a time might be set
by making an appropriate entry into a software programme running on the
computer 14. Preferably, adjustment to the amplitude of the vibratory
stimulus can be made by suitable entries into the software running on the
computer 14.
Whilst Figure 16 depicts a simple representation of the device whereby
the vibration stimulator 12 and the detector 13 are applied to the bone via an
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external frame 16, it is envisaged that they would be applied either to the
skin of the affected limb, wherein the stimulation of the bone could be
imparted transcutaneously, or via a frame. or other like device surrounding
the limb. and in particular, a plaster cast.
It is further envisaged that this method of treatment be used in the
treatment of several bone disorders to promote bone tissue growth and also to
maintain bone mass. Examples include the healing of a fracture site wherein
the vibration caused to the bone results in micro-movement, bending or
torsion at the site of fracture which in tllrll leads to promotion of bone
healing. The stimulation also causes micro-movement. bending or torsion of
the intact portions of the bone. Whlch lIl turn. leads to promotion of bone
formation and prevention of osteoporosis in the intact bone. As the
stimulation imparted by device 10 is regulated to be at the same, or
approximately the same. frequency as the resonant frequency of the bone. the
promotion of bone tissue growth is optimised and occurs at a faster rate than
if the bone is simply stimulated at a frequency unrelated to the resonant
frequency of the bone.
Similarly, it is readily envisaged that the device 10 could be applied
transcutaneously to a bone with a fixation means such as an intramedullary
2o nail holding the bone pieces together. In this manner. the formation of
bone
between the pieces of bone may be increased by the stimulation of the bone
and the fixation means at. or approximate. the bone's resonant frequency.
It can also be envisaged that the device 10 can be transported readily
and therefore used in a patient's home. In this way. the device 10 would be
pre-programmed such that all the patient need do to use the device would be
to attach the vibration stimulator 12 and the vibration detector 13 to the
affected limb. or other body part, and activate the device 10.
In cases where the provision of a vibratory stimulus is utilised. it is
preferable that such stimulus be provided later in the course of treatment.
since mechanical stimulation assisting in the maturation of the healing
fracture. In yet another preferred embodiment, however. both the
administration of a bisphosphonate and the provision of a vibratory stimulus
may occur early in the course of treatment. As disclosed above, however.
these two modes of treatment may be used at opposite times, they may be
alternated. or they may both be delivered in the later stages of treatment as
is
considered to be host appropriate.
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The foregoing disclosure will now provide a more detailed analysis of
the effects which the administration of a drug according to a preferred
embodiment of the invention has on the healing process, and therefore.
treatment of a fractured bone.
Each of the following examples relates to the administration of a
bisphosphonate in distraction osteogenesis. One of the aims of distraction
osteogenesis is to lengthen the limb upon which the procedure is performed.
The performance of a distraction osteogenesis necessitates fracturing of the
bone. Following placement of an external frame on the limb. the bone is cut.
1o During healing. the new bone forms as the frame is slowly distracted.
It is because the bone is fractured during the procedure. that the
results of a study involving distraction osteogenesis are appropriate for
illustrating the effects which the administration of pamidronate has on bone.
Example 1: Pamidronate in Distraction Osteo~enesis (dose 3mg/~
Methods:
Experimental design
Twenty eight-week-old male NZW rabbits underwent tibial
lengthening. Similar rabbit models have been reported. After premedication
with IM Ketamine 15 mg/kg and Xylazine 4mg/kg, anaesthesia was
administered with Halothane 2%, and Oxygen 1 1/min. An open mid-tibial
drill hole osteotomy was performed on each rabbit and an Orthofix M-100
fixator was applied using four Orthofix 3 mm half pins (Orthofix. Bussolengo.
Italy). After a latency of 24 hours the tibia was lengthened 0.375mm every 12
hours for 15 days, producing an 11.25 I111T1 distraction. The fixator was then
left in situ for 27 days to allow the regenerate to consolidate. Pamidronate
3.0 mg/kg diluted to 30mg/100m1 was administered as a single intraoperative
infusion over two hours to 10 of the rabbits: 10 control animals were given
saline infusions. Buprenorphine 0.05 mg/kg was administered at the end of
surgery and again 12 hours post operatively. The animals were supplied with
rabbit pellet and water ad libitum. At 42 days the rabbits were sacrificed
with IV Lethobarb 150mg/kg.
Radiographic and Bone Mineral Density Analysis
Both hind limbs were disarticulated through the knee and the soft
tissues left intact. The limbs were oriented in standard AP and lateral
projections and plain radiographs taken with a Siemens Multix H/UPH
configuration using digital luminescent cassettes with a 50 kV and 4 mA
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exposure with a tube to film distance of 1.1 meters. The distance between
pin sites was measured from each dissected specimen so that each
radiograph could be re-scaled appropriately for measurements of regenerate
length.
Bone mineral density (BMD) measurements were made using a total
body dual energy x-ray densitometer (LUNAR DPX. Radiation Corps.
Madison. Wisconsin). DXA has been used in this context in previous reports.
BIVID scans were performed with the tibia oriented in the antero-posterior
(AP) and lateral projections. using software specifically designed for
measuring small animals (LUNAR DPX. Small Animal Software. 1.0c
LUNAR. Radiation Corps. Madison. Wisconsin). The "HiRes <0.5kg Slow"
scan mode was used ("Fine" collimation, sample size of 0.6 x 1.2 mm. and
sample interval of 1/16 seconds). To calculate CV's of the machine, thirty
scans were performed on a rabbit forelimb over the duration of the study
period. CV's of the BMD, measured by positioning three boxes on each scan.
were 3.6%. 4.5% and 5.7% respectively (from proximal to distal).
Regional BMD measurements were obtained by placing ''regions of
interest" (ROI's) 9.6 mm high on the scan images. For each lengthened tibia.
one ROI was positioned in the regenerate. one proximal to it and one distal to
2o it. In the non-operated tibia. two ROI's were placed so that they matched
the
distal and proximal ROI of the lengthened tibia (ie the same distance from
the bone ends). A total of three measurements were thLlS generated for each
lengthened tibia and two measurements for each non-operated tibia, for each
projection. BMD values were expressed as g/cm~ and group data reported as
mean and standard deviation. Lengthened and non-operated tibia samples
were compared using paired t-tests: non-paired tests were used to compare
between groups.
Histological Analysis
The histological analysis was performed in a blinded fashion by two
pathologists who were observers. Five pairs of tibiae from the Pamidronate
group and five controls were excised sub-periosteally and fixed in 10%
buffered formalin. Each bone was transversely sectioned into proximal.
regenerate and distal bone segments prior to decalcification in standard
EDTA solution over 48 hours. Each segment was then longitudinally sliced
and half embedded in paraffin blocks yielding six blocks per rabbit. Sections
for microscopy were cut at 5 microns and stained with haematoxylin and
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eosin. Both pathologists examined all the sections and made a consensus
assessment of the amount of new bone formation. cortical thickness, extent
of remodelling. and bone formation around the pin sites. As cortical
thickness would be expected to alter depending on the plane of sectioning, it
was not measured precisely. The osteoclast activity in the regenerate was
expressed as number per high-powered field (Olympus. BH2. 40x objective)
The degree of osteoblastic rimming was also assessed.
R esul ts:
Excl usions
There were 3 postoperative complications necessitating exclusion from
DXA analysis: one tibial fracture noted on day 1 near the distal pin sites
(pamidronate group): one femoral fracture on day 23 requiring euthanasia
(pamidronate group): and one common peroneal nerve palsy (control).
Control Rabbit Model
Reliable bone formation occurred in the distraction gap. All tibiae
were clinically and radiographically united at day 42. Bl~ID values from the
AP scan for the lengthened and non-operated limbs are shown in figure 2.
There was a significant reduction in BMD in both the proximal and distal
segments surrounding the lengthening compared with the matched sites in
the non-operated limb (p<0.02). Similar significant differences were present
on the lateral scans.
Pamidronate Group
The reduction in BMD in the proximal and distal segments was not
found in the pamidronate group. with no significant difference in BMD
between the bone of the operated and non-operated limbs at six weeks
(p=0.332 proximal. p=0.256 distal) (Figure 3). The same effect was seen on
the lateral scans.
Figure 4 compares the Bl~tI7 from AP scans of the operated limbs for
rabbits given pamidronate versus controls. The BMD of the proximal and
distal bone surrounding the regenerate has increased by a mean of 40% and
39% respectively (p<0.01). The BMD in the regenerate ~~as increased by a
mean of 43% over the control rabbit tibiae (p=0.017). Lateral scans also
confirmed the above significant differences.
The BI~ff7 for the non-operated limbs of control and pamidronate
groups was not significantly different. These results are compared in Table
1. There was an increase in the mean regenerate area of 22% in the
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pamidronate group (p<0.05).
Histology
Of the ten specimens collected, nine were examined histologically.
The rabbit culled on day 23 was not included in the analysis. The tibiae
5 from the pamidronate group took 24-48 hours longer to decalcify than the
control specimens. The pamidronate group demonstrated increased
regenerate formation with prominent osteoblastic rimming and decreased
numbers of osteoclasts (2.4 / HPF v 3.4 / HPF in controls) with less evidence
of bone remodelling (Fig 5). There was also increased endosteal bone
10 formation in the bone cortex adjacent to the regenerate, producing an
increase in cortical thickness (Fig. 5). There was a marked increase in bone
formation around the pin sites in the pamidronate group. There was a degree
of variability in these factors within the pamidronate group, as with the
variability seen in BMD values.
15 Discussion:
In this experiment, a single dose of 3 mg/kg of pamidronate was given
to the rabbits at the beginning of the lengthening to minimise negative
effects
on bone remodelling. This strategy abolished the osteoporosis seen in
controls and had a markedly positive effect on osteoblast activity and bone
mineral accretion in the regenerate. Osteoclast number and activity
remained reduced at day 42. As the pamidronate was given at the time of
surgery, the marked increase in regenerate formation and mineralisation is
most interesting. Either pamidronate from the surrounding bone leeched out
into the regenerate bone to exert a local effect, or the increase in
regenerate
was due to an anabolic effect secondary to changes in PTH and 1.25-(OH)2
vitamin D. Further research is required to evaluate these hypotheses.
It was hypothesised that a pulsatile pre-dosage regimen would be
desirable when coincident with surgical intervention. As pamidronate has a
strong affinity for bone mineral. it is possible to load the skeleton with a
pulsatile dose that will exert a positive effect for three to six months
(Gloriemc et al. "Cyclic administration of pamidronate in children with severe
osteogenesis imperfecta" N. Engl. J Med 1998: 339: 947-52). Li et al (supra)
set out to determine if patients receiving continuing bisphosphonate therapy
should have this treatment withdrawn in the event of a fracture. They
showed increased callus formation in rat femoral fractures pre-treated with
incadronate. COI1t1I1L1at10I1 Of therapy for sixteen weeks after fracture
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increased callus formation even further, but the new bone did not remodel to
form a cortical shell as in the pre-treated group. They concluded that the
therapy should be ceased to allow remodelling. but that more study was
needed.
Apart from negative effects on remodelling, continuous dosing with
bisphosphonates may not be desirable in distraction osteogenesis because of
a detrimental effect on longitudinal growth. In a study using daily
subcutaneous alendronate. normal growing mice showed diminution in leg
length, as well as decreased ductility after treatment (Raggio et al.
"Alendronate reduces fractures without increasing bone strength in a growing
mouse model of osteogenesis imperfecta" Proceedings of Paediatric
Orthopaedic Society of North America. May. 1999). In the experiment, no
significant change in leg length was noted, although there was a suggestion
of growth inhibition - the non-operated limbs in the control group were
longer than those of the pamidronate group by l.4mm. There were no limb
measurements taken at the time of operation, so this difference could not be
attributed to growth inhibition with absolute certainty. However, growth
inhibition may well have been minimised by the one dose regimen. The
study of Li et al (supra) did not COIIlIIleIlt on longitudinal growth. but the
comparison radiographs indicate that the continually treated rat femora were
shorter than those of the pre-treated and control groups.
The histologic findings in this study suggest an increase in bone
formation, as well as a decrease in bone resorption following the
administration of pamidronate. This was found particularly in the endosteal
region of the bone surrounding the lengthening as well as in the regenerate.
and was more obvious in the operated leg. Other studies have recently
suggested that bisphosphonates influence cells of osteoblastic lineage in a
fashion distinct frOIIl their inhibitory effects on osteoclasts (Giuliani et
al.
"Bisphosphonates stimulate formation of osteoblast precursors and
mineralized nodules in murine and human bone marrow cultures in vitro and
promote early osteoblastogenesis in young and aged mice in vivo" Bone 1998.
May: 22(5):455-61).
As pamidronate increased the bone forming capacity of the regenerate.
it is possible that it's use may increase the risk of premature consolidation.
The length of the regenerate was decreased by a mean of 0.8 mm (8%) in the
rabbits given pamidronate. While this small amount is not alarming, the
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difference did reach statistical significance, such that careful observation
for
this possibility would be required if pamidronate were used clinically.
One rabbit given pamidronate sustained a femoral fracture in their
operated limb on day 23. This may have been a random event, however it is
possible that the bone was made brittle by the pamidronate.
The toxicological effects of bisphosphonates in children are yet to have
been fully evaluated. The dose of 3 mg/kg for this experiment was chosen
because that is the dose commonly given to children with osteogenesis
imperfecta (Glorieux et al. supra).
The large increase in BMD throughout the lengthened limb that were
obtained following a single dose of pamidronate may have a positive
therapeutic effect in children undergoing limb lengthening. The fact that
pamidronate increased the amount of regenerate that formed provides a
promising prospect worth continuing evaluation. Further investigations into
the mechanical properties of the bone after pamidronate treatment.
refinement of the dosage regimen and examination of possible toxicological
effects are required prior to a clinical trial.
Table I
Comparison of
Mean Data between
Pamidronate
and Control
Groups Standard
Deviation, a
er and lower
95% Confidence
Limits in Parentheses
Variable PamidronateControl Di ~erence95% CI ~ valve
Lenglh of lengthened106.0 107.6 -1.57 (-5.76. 0.44
(3.4) (4.5) 2.63)
limb (mm)
Length of non-operated97.4 (2.0)98.8 (2.2)-1.45 (-3.59. 0.18
0.7-1)
limb (mm)
Weight of lengthened10.9 (0.6)8.7 (0.9)2.2 (1.37, <0.001
3.03)
tibia ( )
Weight of non-operated9.3 (0.5)8.1 (0.4)1.19 (0.71. <0.001
1.67)
tibia ( )
Re euerale len 9.6 (0.6)10.4 (0.7)-0.75 (-1.45.-0.0-1)0.04
t1 (mm)
Re enerate area 0.83 (0.09)0.68 (0.13)0.15 (0.03. 0.017
(cm-) 0.27)
AP BMD proximal 0.51 (0.07)0.36 (0.09)0.14 (0.06. 0.004
to 0.23)
re enerate (
cm~)
AP BIVID in regenerate0.47 (0.11)0.33 (0.11)0.14 (0.03. 0.017
0.25)
( cm')
AP BNID distal 0.48 (0.10)0.34 (0.08)0.14 (0.04. 0.007
to 0.23)
re enerate (
cm')
AP BIND in proximal0.48 (0.05)0.44 (0.03)0.04 (0.00. 0.053
0.09)
non-operated
limb
( cm~)
AP BMD in distal0.44 (0.0-1)0.42 (0.02)0.02 (-0.02. 0.31
non- 0.05)
operated limb
( cm~)
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Summary of Findings:
The effect of a single 3 mg / kg dose of pamidronate (Novartis) on Bone
Mineral Density (BMD) was examined in a distraction osteogenesis model in
immature rabbits.
Seventeen rabbits (9 control. 8 given pamidronate) were examined by
Dual X-ray Absorbtiometry (DXA). There was a significant increase in BIND
in the pamidronate group over controls. The mean areal BMD (g/cmz) in the
bone proximal and distal to the regenerate bone was increased by 40% and
39% respectively compared to controls (p<0.05). The BIVID of the regenerate
bone was increased by a mean of 43% over controls (p<0.05). There was also
a 22% increase in mean area of regenerate formed in the pamidronate group
(p<0.05).
Histological analysis of nine rabbits (5 control, 4 pamidronate)
revealed an increase in osteoblastic rimming and mineralisation of the
regenerate in the pamidronate rabbit tibiae. There was also increased bone
formation around the pin sites and an increase in the cortical width of the
bone adjacent to the regenerate in the rabbits given pamidronate.
Pamidronate had a markedly positive effect in this limb-lengthening
model. Not only did it reduce the disuse osteoporosis normally associated
with lengthening using an external fixator, it also increased the amount and
density of the regenerate bone. Further study to examine the mechanical
properties of the regenerate after administration of pamidronate is required.
Example 2: Pamidronate in Distraction Osteogenesis (dose 1mg/kg)
Methods:
Experimental design
Twenty eight-week-old male NZW rabbits underwent tibial
lengthening. After premedication with IM Ketamine 15 mg/kg and Xylazine
4mg/kg. anaesthesia was administered with Halothane 2%, and Oxygen 1
1/min. An open mid-tibial drill hole osteotomy was performed on each rabbit
and an Orthofix NI-100 fixator was applied using four Orthofix 3 mm half
pins (Orthofix. Bussolengo. Italy). After a latency of 24 hOLIrS the tibia was
lengthened 0.375mn every 12 hours for 15 days. producing an 11.25 111111
distraction. The fixator was then left in situ for 27 days to allow the
regenerate to consolidate. Pamidronate 1.0 mg/kg diluted to 30mg/100 ml
was administered as a single intraoperative infusion over two hours to 10 of
the rabbits: 10 control animals were given saline infusions. Buprenorphine
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0.05 mg/kg was administered at the end of surgery and again 12 hours post
operatively. The animals were supplied with rabbit pellet and water ad
libitum. At 42 days the rabbits were sacrificed with IV Lethobarb 150mg/kg.
Radiographic and Bone Mineral Density Analysis
Both hind limbs were disarticulated through the knee and the soft
tissues left intact. The limbs were oriented in standard AP and lateral
projections and plain radiographs taken with a Siemens Multix H/UPH
configuration using digital luminescent cassettes with a 50 kV and 4 mA
exposure with a tube to film distance of 1.1 meters. The distance between
1o pin sites was measured from each dissected specimen so that each
radiograph could be re-scaled appropriately for measurements of regenerate
length.
The disarticulated bones were stripped of all soft tissue and analysed
using a Stratec XCT-960A pQCT scanner and analysis software (Stratec
Medizintechnik Gmbh. Pforzheim. Germany). Two millimetre slices were
obtained. 15 slices in the right (lengthened) tibiae and 10 in the non-
operated
tibiae. Five slices were thus obtained in the regenerate, proximal and distal
bone, and corresponding areas to the proximal and distal bone in the non-
operated limb. Quantitative CT is the noninvasive method with the strongest
predictive power for the mechanical strength of newly formed bone (Harp et
al.. 1994). The software allowed analysis and generation of data on bone
mineral density as mg/cm3. bone mineral content (mg) and cross sectional
area (IIlIllz). Data was also generated for mechanical analysis, namely
moment of inertia (mm~), and maximum y co-ordinate (vertical distance frOIIl
the neutral bending plane in mm).
Strain was calculated for each specimen by formula 1:
Strain = I2Dy
L-
D= deflection
y= vertical distance from centre of mass
3o L= span length
Stress was calculated at 2 mm intervals along the central section of specimen
frOIIl formula 2:
Stress= Mj
I
M= moment at x
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- load Y - load ~~ _ ~)
2 2
y= vertical distance from centre of mass
I= second moment of inertia
x = distance along bone from left roller
5 The Young's modulus of elasticity was calculated as the slope of the
linear portion of the stress/strain curve for each "slice" or 2 mm interval.
The mean Young's modulus values for the control and treated groups
at both the central ''slice'' and for averaged data over the central 1 cm of
regenerate section. were compared using an unpaired two tailed t-test.
10 The area under the stress strain curves for the central "slice'' was
calculated for the distracted tibiae in both control and pamidronate groups.
These were again compared with an unpaired two-tailed t test.
Results:
Reliable bone formation occurred in the distraction gap. All tibiae
15 were clinically and radiographically united at day 42. There was a
significant increase in bone mineral density proximal and distal to the
regenerate in the pamidronate group (Table II). There were also significant
increases in bone mineral content. There was a 13% increase in bone area.
although this was not statistically significant (p=0.2).
20 The lengthened tibiae in the pamidronate group were 32% stronger for
peak load (p=0.004) (Fig 6). The peak load in the lengthened tibiae in the
pamidronate group was the same as that for the non-operated control tibiae.
Young's modulus was not significantly different between operated groups.
and was reduced to only about 30% of the value of the in tact tibiae (Fig 7).
Discussion:
In this experiment. a single dose of 1.0 mg/kg given to the rabbits at the
beginning of the lengthening produced significant improvement in peak load
at six weeks measured by four point bending. As in our previous experiment.
osteoporosis surrounding the lengthening was reduced. Although not
3o statistically significant, there was an increase in callus area. but not as
marked as had occurred in specimens from the group in the previous
experiment treated with 3.0 mg/kg of pamidronate.
The increase in peak load is likely to be due to both increased
regenerate volume and increased mineral content at six weeks. The fact that
modulus of elasticity remained unchanged with pamidronate indicates that
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21
the bone may be no more mature than in controls. Combining
bisphosphonate treatment and mechanical stimulation may prove to be
beneficial: the hypothesis being that the bisphosphonate will increase early
osteoblastic proliferation and increase bone mineral content. while the
mechanical stimulation would accelerate callus maturation.
TART.R II
Com arison
of Data between
Control_and
Pamidronate
Grou s
Control Pamidronate
Mean SD Mean SD % increaseP value
TOT BMC Prox 27.98 6.68 34.52 6.27 23% 0.03
TOT BMC Re 26.13 10.7030.47 6.67 17% NS
en
TOT BMC Dist 28.04 4.65 34.47 4.34 23% 0.004
Total BMD 585.53 69.61650.73 47.06 11% 0.03
Prox
Total BMD 530.06 77.61575.03 62.12 8% NS
Re en
Total BMD 650.40 79.40739.37 56.48 14% 0.01
Dist
Area Prox 52.97 7.94 48.26 7.41 10% NS
Area Re en 53.13 9.71 46.90 11.91 13% NS
Area Dist 46.85 5.73 43.37 6.54 8% NS
Example 3: Zoledronate in Distraction Osteogenesis (dose 0.1m~/kg)
Methods
1o Experimental Design
Twenty-four eight-week-old male NZW rabbits underwent tibial
lengthening. Similar rabbit models have been reported. After premedication
with IM Ketamine 15 mg/kg and Xylazine 4mg/kg. anaesthesia was
administered with Halothane 2%. and Oxygen 1 1/min. After preparation of
the right lower extremity we performed an open mid-tibial drill hole
osteotomy and applied an Orthofix M-100 fixator L1SIIIg fotlr Orthofix 3 mm
half pins (Orthofix. Bussolengo. Italy). The left lower extremity was left in
tact. After a latency of 24 hours the tibia was lengthened 0.375n lm every 12
hours for 14 days, producing a total of 10.5 II11I1 Of dlStraCt1011. The
fixator
was then left in situ for 28 days to allow the regenerate to consolidate.
The animals were randomised such that eight animals were operated
on and given saline-only infusions (controls). eight animals were given 0.1
mg/kg zoledronate over 20 minutes at the time of surgery (single dose
zoledronate), and a further eight animals were given a second dose of
zoledronate 0.1 mg/kg on day 14 (re-dosed zoledronate).
Buprenorphine 0.05 n lg/kg was administered at the end of surgery and
again 12 hours post operatively to all animals. The animals were supplied
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22
with rabbit pellet and water ad libitum. At 42 days the rabbits were
sacrificed
with IV Lethobarb 150mg/kg.
Radiographic and Bone Mineral Density Analysis
Bone mineral content (BMC) and density (BMD) measurements were
made at two, four and six weeks using a total body dual energy x-ray
densitometer (LUNAR DPX. Radiation Corps. Madison. Wisconsin). DXA
scans were performed with the tibia oriented in a jig in the antero-posterior
(AP) projection, using software specifically designed for measuring small
animals (LUNAR DPX. Small Animal Software. !.0c LUNAR. Radiation
1o Corps. Madison. Wisconsin). The ''HiRes <0.5kg Slow" scan mode was used
("Fine'' collimation, sample size of 0.6 x 1.2 nnn, and sample interval of
1/16
seconds).
Regional BMC and BMD measurements were obtained by placing
"regions of interest" (ROI's) 9.6 llllll high on the scan images. For each
lengthened tibia. one ROI was positioned in the regenerate, one proximal to
it and one distal to it. In the non-operated tibia, two ROI's were placed so
that they matched the distal and proximal ROI of the lengthened tibia (ie the
same distance from the bone ends). A total of three measurements are thus
generated for each lengthened tibia and two measurements for each non-
operated tibia. BMC values were expressed in grams (g) and B1W7 values
expressed as g/cmz and group data reported as mean, standard deviation and
95% confidence intervals.
After culling, both hind limbs were disarticulated through the knee
and the soft tissues left intact. The limbs were oriented in standard AP and
lateral projections and plain radiographs taken with a Siemens Multix H/UPH
configuration using digital luminescent cassettes with a 50 kV and 4 mA
exposure with a tube to film distance of 1.1 meters. A calibrated marker on
the film allowed the image to be re-scaled appropriately for measurements of
length in millimetres (mm).
To expand the analysis at six weeks the disarticulated bones were then
stripped of all soft tissues and analysed using a Stratec XCT-960A pQCT
scanner and analysis software (Stratec Medizintechnik Gmbh, Pforzheim.
Germany). Two millimetre slices were obtained. 15 slices in the right
(lengthened) tibiae and 10 in the non-operated tibiae. Five slices were thus
obtained in the regenerate. proximal and distal bone. and corresponding
areas to the proximal and distal bone in the non-operated limb. The software
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allowed analysis and generation of data on bone mineral density as g/cm3.
bone mineral content (g) and cross sectional area (mmz). Data was also
generated for mechanical analysis, namely moment of inertia (llllll~). and
maximum y co-ordinate (vertical distance from the neutral bending plane in
mm) .
Resinis
Exclusions
One rabbit in the single dose zoledronate group died suddenly of a
gastrointestinal illness 9 days after surgery. One rabbit in the re-dosed
group
had failure of distraction and premature consolidation and was excluded.
This left 8 rabbits in the control group and seven rabbits in each of the
zoledronate groups.
Bone Mineral Content (BMC)
The BMC as measured by DXA was similar at two weeks in all groups
i5 (Fig. 8). There was a rapid increase in mineralisation of all three regions
of
the operated limb between week two and week four in the zoledronate
treated animals. This was significantly different for treated groups over
controls in all regions except for single dose animals in the distal segment
(t
test p<0.01). There was a fall off in BMC between weeks four and six in all
regions. This was most marked lIl COIltr01 animals, much reduced in the
single dose group and minimal in the double dose group. such that both
treated groups had significantly increased BMC at six weeks over controls.
The difference between single dose and redosed animals for BMC was
significant at six weeks in the proximal and distal segments, but not in the
regenerate (p<0.01).
The velocity of bone mineral accrual in the regenerate was
significantly higher between weeks 2 and 4 in the treated animals (Fig. 9.
p<0.01). Between weeks 4 and 6. when all groups shed some bone mineral.
this was least so in the redosed zoledronate group (p<0.05 v control. NS v
3o single dose).
At six weeks the BMC as measured by QCT was increased significantly
in all regions in the zoledronate treated animals (p<0.01. ANOVA) (Fig. 10).
The effect was enhanced in the double dose group in a dose-related fashion.
Post-hoc t-tests revealed that the differences between single dose versus
control and double dose versus single dose were both significant (p<0.05).
There was no significant change in the BMC in the non-operated tibiae.
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Bone Mineral Density
The control group Bl~m in the regenerate as measured by DXA
increased between weeks 2 and 4 but dropped off again to the 2-week value
(Fig. 11). The BMD dropped off progressively in the proximal and distal
regions. the expected effect of stress shielding (Fig. 11). In
contradistinction.
the BMD of the regenerate in the zoledronate treated animals increased more
rapidly, and was largely maintained. The zoledronate served to protect the
proximal and distal regions from the effects of stress shielding such that the
BMD was maintained above two-week levels at six weeks. Both zoledronate
treated groups had areal BMD values significantly different from controls at
both 4 and 6 weeks by DXA, but the single dosed and redosed groups were
never significantly different from each other for areal BMD.
At six weeks the volumetric BMD as measured by QCT was increased
significantly in all regions in the zoledronate treated animals (p<0.01.
ANOVA) (Fig. 12). Post-hoc t-tests revealed that the differences between
single dose versus control (p<0.01), but no difference between re-dosed
versus single dose (p>0.05). There was no significant change in the BMC in
the non-operated tibiae. The zoledronate treated animals maintained a BMD
in all regions similar to that of the non-operated control tibiae whereas the
control distracted tibiae showed a significant amount of osteoporosis in all
regions.
Length Measurements at six weeks
There was a dose related difference in the lengths of the non-operated
tibiae of the rabbits, such that the mean tibial length of the single
zoledronate group was reduced by 3% over controls and the re-dosed group
reduced by 7% (ANOVA p<0.01 Table III). The re-dosed zoledronate group
had significantly shorter operated right tibiae as well. but the regenerate
lengths were not different between the groups. These data suggest a small but
definite dose-related negative effect of zoledronate in longitudinal growth at
the physis.
Cross-sectional Area Measurements at six weeks
There was a significant dose-dependant increase in cross sectional area
in all regions in zoledronate treated animals as measured by QCT (p<0.01.
ANOVA). There was no effect at all on the cross sectional area of the non-
operated tibiae (Fig. 13). The most marked effect was seen in the regenerate.
with increases of 56% in the single dose group and 105% in the double dose
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group. but considerable increases in cross sectional area of the adjacent
regions was also seen, ranging from 29% to 72%. The median QCT scan for
each group in terms of cross sectional area is shown in Figure 14
There were even larger increases in moment of inertia, as this is
5 proportional to r~ (Fig.l4). The moment of inertia for the regenerate was
thus
increased by 111% in the single dose group and by 213% in the double dose
group (p=0.02 ANOVA). The difference between single dose zoledronate and
controls was significant by post-hoc unpaired t test (p=0.02). The further
rise in moment in the repeat dose group did not reach significance. as the
10 variability was high (p=0.3). Increases in moment of Illertla lIl
SLIrrOLlIldlllg
regions ranged from 57% to 180%.
Further study to examine the mechanical properties of the regenerate
after administration of Zoledronate is required.
Discussion
15 Although given as a simple IV infusion. the significantly beneficial
effects of zoledronate administration documented in this study were target
organ specific (Figs 10, 12. 13. 14). A massive increase in both the amount of
bone formed and its mineralisation, not only in the regenerate but also in
adjacent regions was produced. Meanwhile there was little or no effect on
20 the non-operated tibia. Several possible hypotheses may explain this.
Although the pathway or even the cell line most directly involved have yet to
be defined. zoledronate seems to produce an inability of the bone to sense its
mechanical environment. Unlike control tibiae. in which the BMD
progressively dropped. bone mineral was not shed in the bone surrounding
25 the osteotomy and distraction. Meanwhile new bone formed in a more
vigorous fashion than in controls. even though the bone was rigidly held in
the fixator.
Another possibility is that osteoclastic inhibition delays remodelling
until more than the usual amount of callus is formed. There is also the
possibility that the bisphosphonates are acting directly on osteoblasts.
perhaps through basic fibroblast growth factor (bFGF). Further study to try
and elucidate exactly which growth factors have been stimulated or inhibited
by bisphosphonate administration is required.
Of importance is the observation that the BMD was returned to the
value of the control non-operated limb and the increases in BNIC were largely
due to increased amount of new bone of normal density. If the density to
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supra-normal levels had simply been increased with no increased amount of
bone formed. then the bone would be osteopetrotic, i.e. brittle and with no
improvement in strength.
A single IV dose at time the time of surgery lends itself well to the
clinical situation when managing skeletal trauma. Zoledronate has a well-
documented safety profile in patients with cancer receiving multiple doses
(Major P. Lortholary. Hon J et al. "Zolendroic acid is superior to pamidronate
in the treatment of tumour-induced hypercalcaemia: a pooled analysis." Proc
ASCO New Orleans, May 2000 19:209 (Abstract 814).. A single perioperative
dose in a well-hydrated trauma patient should be well tolerated. if there is
concern about hydration the treatment could be deferred until it was
adequate. This would reduce the theoretical possibility of nephrotoxicity or
nephrocalcinosis.
In elective situations the administration of IV zoledronate as a 5-20
minute infusion perioperatively should be easily and safely achieved.
Further study is required.
If the treating physician considers the response to a single
perioperative dose sub-optimal. or the treatment course is unusually
prolonged, this study strongly suggests that a further dose will confer
additional benefit. However as a single dose provides over 50% increase in
new bone f01'Illat10I1 lIl this model, a further dose may not be routinely
necessary. Likewise in the paediatric population. appropriate consideration
must be given to the negative effects on longitudinal growth related to
bisphosphonate administration. This study showed a dose related negative
effect on longitudinal growth. although this was only 3% in single dose and
7% in re-dosed animals. it suggests that prolonged administration of
zoledronate in growing children may be ill-advised.
The increase in cross sectional area is an extremely significant benefit.
Regenerate failure has been documented to be largely in bending and fracture
failure in long bones occurs in either bending or torsion. In both bending
and torsion the moment of inertia is proportional to r~, or the square of the
cross sectional area. The 56% increase in cross sectional area of regenerate
thus translates to 111% increase in moment of inertia. The 105% increase in
the re-dosed group equates to a 213% increase in moment of inertia. The
regenerate strength index was increased also in proportion to the cross
sectional area (Table IV).
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The effects seen in this experiment are consistent with the above
findings relating to pamidronate administration.
As the present model follows the animals for only six weeks, no
conclusion regarding remodelling of the new bone formed can be reached. It
is intuitive that the cross sectional area will reduce as the bone remodels.
Producing such a large amount of callus may allow removal of the fixator
before remodelling has occurred. This strategy would allow remodelling to
occur in an environment exposed to physiological loading as the effects of
the bisphosphonate v~~ore off over time, rather that remodelling in the stress
shielded environment of the fixator. Further studies to look at the behaviour
of the bone after fixator removal are required.
TABLE III
Tibial and Regenerate Lengths for Control, Zoledronate and Re-dosed
Zoledronate Grouu
Control Zoledronate
1 Zoledronate
2
Number 8 7 7
Left Tibia Mean 98.00 95.14* 91.14*
SD 1.41 2.48 2.79
Right Tibia Mean 107.75 107.43 101.57*
SD 2.12 4.08 3.21
Regenerate Mean 10.38 11.29 10.57
SD 1.30 1.50 1.90
* Denotes significantly different by ANOVA and post-hoc unpaired t-test
TABLE IV
Regenerate Strength Index for Control, Zoledronate and Re-dosed
Zoledronate Grouu
Control Zoledronate 1 Zoledronate 2
RSI 2.09 3.26 4.49
above control 56% 114%
It will be appreciated by persons skilled in the art that numerous
variations and/or modifications may be made to the invention as shown in
the specific embodiments without departing from the spirit or scope of the
invention as broadly described. The present embodiments are. therefore, to
be considered in all respects as illustrative and not restrictive.
