External bone growth stimulators for spine fusion
Devices used for bone growth after spine fusion
External bone growth
stimulation devices are worn outside the skin and
do not require surgical implantation or
extraction. Typically, the device is worn after spine fusion either as:
-
Small, thin skin pads/electrodes that are placed
directly over the fusion site and deliver a type
of
electrical stimulation called Capacitive Coupling
(CC), or;
-
One or two treatment coil(s) placed into
a brace
or directly onto the skin that deliver a type
of electromagnetic
field called a Pulsed ElectroMagnetic Field (PEMF),
or a Combined Magnetic Field (CMF).
Unlike an internal
(implanted) bone growth stimulator, an external
bone growth stimulator may also be prescribed
for the patient to use several weeks or months after
the fusion surgery if the bone is not fusing as desired.
Depending
on the device and the patient’s situation,
an external bone growth stimulator will be prescribed
to be worn for a specific number of hours each day
(typically
within the range of 2 hours to 9 hours per day). Sometimes
the patient may be allowed to break it up into several
one- or two-hour sessions each day, or to vary the
times that the device is worn each day, to better
suit the
patient’s schedule. Typically, the external bone
growth stimulator will be worn for a period of 3 to
9 months following the surgery.
An external electrical
stimulator is usually lightweight and powered by a
battery, so it is very portable (see
Figure 2). Patients may move about and complete
their daily activities as they normally would with
the
device. However, the surgeon may restrict the patient’s
activities due to the fusion surgery, and there are
some activities that the patient should remove the
device
for (e.g. swimming, bathing).
As with the internal stimulators,
the external device is not painful and the patient
cannot feel any electrical
shocks or vibrations while wearing it.
While external
electrical stimulation devices are considered very
safe, it is important to note that the electromagnetic
effects of this type of treatment are unknown for
pregnant women and for some types of pacemakers and
defibrillators.
Other considerations for bone growth stimulator and spine fusion
A theoretical disadvantage of an external stimulator
versus the internal stimulator is that there may
be
less patient compliance with wearing the external
stimulator the required number of hours. Obviously,
if the patient
does not wear the device, the benefits from the treatment
will not be realized.
A potential advantage of
external stimulators versus internal stimulators
is that the external device is
usually a less expensive treatment option and does
not require the potential second surgery to remove
the battery
pack.
Another major advantage is that an external
bone stimulator can be added after the fusion has
been done if there
is concern that the bone graft is not healing and
a nonunion is developing.
By:
John Sherman, MD
September 24, 2002
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