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Static, Low-Frequency, and Pulsed Magnetic Fields
with an SMF improves bone healing in the first two weeks radiologically and that the
configuration difference in magnetic poles has an effect on bone quality. However, the
SMF was found to have no significant effects on bone mineral density (BMD) values. Xu
et al. (2011) investigated the effects of a gradient SMF (B max of 180 mT for 6 weeks) on
osteoporosis of the lumbar vertebrae in ovariectomized rats. A small disc magnet was
implanted to the right side of spinous process of the third lumbar vertebra. The results
suggested that the SMF increased the BMD values of osteoporotic lumbar vertebrae in
ovariectomized rats.
It has been reported that PEMF stimulation may be clinically beneficial during
fracture healing and for a wide range of bone disorders. Shen and Zhao (2010) examined the effects of a PEMF (15 Hz, 0.8 mT) on disuse osteoporosis (DOP) rats. Eighty
4-month-old female Sprague Dawley rats were randomly divided into intact (INT)
group, DOP group, calcitonin-treated (CT) group, and PEMF-stimulated group. The
right hind limbs of all the rats were immobilized by tibia-tail fixation except for those
rats in the INT group. Rats in the CT group were injected with calcitonin (2 IU/kg
i.p., once a day), and rats in the PEMF group were irradiated with PEMF immediately following operation. The BMD, serum transforming growth factor-β1 (TGF-β1)
concentration, and interleukin-6 (IL-6) concentration of the proximal femur were
measured 1, 2, 4, and 8 weeks after treatment. Compared with the CT and DOP
groups, the BMD and serum TGF-β1 concentration in the PEMF group significantly
increased after 8 weeks. The IL-6 concentration in the DOP group was elevated significantly after operation. The PEMF group showed significantly lower IL-6 levels
than the DOP group. The results demonstrated that PEMF stimulation can efficiently
suppress bone mass loss. Therefore, the authors concluded that PEMF exposure may
affect bone remodeling process by promoting TGF-β1 secretion and inhibiting IL-6
expression.
Benazzo et al. (2008) evaluated PEMF (75 Hz, 1.5 mT, 0.07 mV/cm, 6 h/day for
6 months) effects on the integration of osteochondral autografts in sheep. At one
month, the osteogenic activity at the transplant–host subchondral bone interface was
found to be increased in PEMF-treated animals compared with the controls. Articular
cartilage was healthy in both controls and stimulated animals. At 6 months, complete
resorption was observed in four control grafts only. Cystlike resorption areas were
more frequent within the grafts of sham-treated animals versus those of PEMF-treated
ones. The average volume of the cysts was not significantly different between the two
groups; nevertheless, analysis of the variance of volumes demonstrated a significant
difference. The histological score showed no significant differences between controls
and stimulated animals, but the percentage of surface covered by fibrous tissue was
found to be higher in the control group than in the stimulated one. The IL-1 and
TNF-α concentrations in the synovial fluid were significantly lower and TGF-β1 concentration was significantly higher in PEMF-treated animals compared with the controls. One month after osteochondral graft implantation the authors observed larger
bone formation in PEMF-treated grafts, which favors early graft stabilization. In the
long term, PEMF exposure limited bone resorption in subchondral bone; furthermore,
the cytokine profile in the synovial fluid was indicative of a more favorable articular
environment for the graft.