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A clinical study was initiated at the University of Pennsylvania in 1970 to evaluate the use of constant direct current in treating acquired non-union. In 1977 the study was expanded to include twelve participating investigators throughout the United States. The results indicate that, given proper electrical parameters and proper cast immobilization, a rate of bone union comparable to that seen with bone-graft surgery was achieved. Experience dictated that four cathodes, each delivering twenty microamperes of constant direct current for twelve weeks, were required to heal a non-union of a long bone. Of 178 non-union in 175 patients treated with adequate electricity in the University of Pennsylvania series, 149 (83.7 per cent) achieved solid bone union. Patients with a history of osteomyelitis had a healing rate of 74.4 per cent. The presence of previously inserted metallic fixation devices did not affect the end-result healing rate. Of eighty non-unions in seventy-nine patients treated with electricity in the participating investigators' series, fifty-eight (72.5 per cent) achieved solid bone union. Review of the non-unions treated unsuccessfully with constant direct current suggested that inadequate electricity, the presence of synovial pseudarthrosis or infection, and dislodgment of the electrodes are causes for failure with the procedure. Complications of the electrical treatment were minor and there was no deep infection resulting from this procedure in patients without previous osteomyelitis. We concluded that the practicing orthopaedic surgeon utilizing constant direct current to treat non-union should, by adhering to proper fracture management and by following the biophysical principles described herein, be able to achieve a rate of union comparable to that of bone-graft surgery, with a lower associated risk.