Use of a permanent magnetic field to inhibit the development of canine osteoarthritis.

This study was designed to determine the potential of a permanent magnetic field to inhibit the progression of osteoarthritis (OA) in a canine model. The magnetic field was created by 72 domino-sized ceramic magnets with surface field strength of 1100 G (0.11 T). The magnetic field strength at the surface of the mattress was 450-500 G (45-50 mT) and was equally distributed over the mattress surface. Eighteen animals had closed resection of their right stifle anterior cruciate ligament. Their kennel floors were covered in one of three ways: no floor mattress (OA) (N = 6); a floor mattress with domino-sized ceramic pieces placed between two layers of foam (sham control OA-MAT) (N = 6); or a floor mattress with domino-sized ceramic permanent magnets placed between two layers of foam (OA-MAT-MAG) (N = 6). Animals were kept in their cages except for 4 h of exercise each day. The left stifle of six animals served as the normal control. The stifle joints were examined at 12 weeks for synovial effusion, gross anatomic appearance, microscopic anatomic appearance (Mankin score), and metalloproteinase (MMP)-1 and -3. Macroscopically, the OA-MAT-MAG group appeared to have less synovitis, less synovial effusion, less disruption of the cartilage surface, and less cartilage ulceration than did the OA group or the control mattress group. The mean Mankin score for the OA-MAT-MAG group was less than that for the OA group (4.2 +/- 0.8 vs. 6.7 +/- 0.3; P <.05) and the control mattress group (4.2 +/- 0.8 vs. 5.2 +/- 0.8; P >.05), but greater than that for the normal left group (4.2 +/- 0.8 vs. 1.0 +/- 0.4; P <.05). These scores show a trend of improvement for OA-MAT-MAG group but the difference with the sham control OA-MAT group was not statistically significant. In immunohistochemical studies, the OA-MAT-MAG group cartilage was stained less heavily for MMP-1 and MMP-3 than were the OA group cartilage and the control mattress group cartilage, but did not differ significantly in MMP-1 and MMP-3 from the normal left group cartilage. The OA-MAT-MAG group did not differ from the normal left group in MMP-3 as determined by Western blot analysis. The study suggests that OA of the medial femoral condyle developed in a canine model exposed to a magnetic field may be inhibited beyond the benefit provided by mattress. Further studies are needed to delineate more precisely the effect of the magnetic field in reducing the severity of OA. Copyright 2004 Wiley-Liss, Inc.