A physical therapist prepares to administer iontophoresis for myositis ossificans in the right mid-quadriceps. Which treatment description would be MOST appropriate?

• A. Driving dexamethasone with a high volt pulsed current unit using the negative pole
• B. Driving dexamethasone with a high volt pulsed current unit using the positive pole
• C. Driving acetic acid with a direct current unit using the negative pole
• D. Driving acetic acid with a direct current unit using the positive pole

Answer: (C)

Iontophoresis uses direct current to move charged drug ions through the skin, and the electrode polarity you choose must match the drug’s ion type. Acetic acid provides acetate ions, which are negatively charged. To drive these negative ions into the tissue, you place the solution under the negative electrode (the cathode) and apply direct current. The negative pole repels the negatively charged acetate ions into the underlying tissue, where they can interact with calcium deposits to form soluble calcium acetate and promote dissolution of heterotopic ossification.

Choosing a drug like dexamethasone isn’t addressing the calcified deposits at issue, and using a positive pole with acetic acid would attract (not effectively push) the negatively charged acetate ions, making delivery less efficient.