Background  Medium frequency therapy combined with ultrasound and drugs can effectively prevent and treat hypertrophic scar and soften scar, but there is a lack of systematic and objective research on the treatment of hypertrophic scar by medium frequency therapy.

  Objective  To observe the clinical effect of medium frequency electrotherapy on hypertrophic scar after burn.

  Methods  Thirty patients with hypertrophic scar treated in the Department of Plastic and Burn Surgery of the Affiliated Hospital of Southwest Medical University from June 2017 to June 2019 were randomly divided into control group and observation group, with 15 cases in each group. The patients in the control group were treated with conventional anti scar therapy, rubbed with silicone medicine and scar patch, while the patients in the observation group were treated with conventional anti scar therapy and medium frequency electric therapy. The 20 MHz high-frequency ultrasound was used to collect the skin ultrasonogram of the volunteers' scars and detect the full-thickness of the skin. The hardness of the scars was measured by shore hardness tester. The Vancouver Scar Scale (VSS) was used to evaluate the scar condition, and the scar itching was observed by visual analogue scale (VAS). All the above tests were performed at 1, 3 and 6 months after treatment.

  Results  At 1 month after treatment, the scar thickness of the two groups were thin, with smooth epidermis, and there was a low echo zone between the lower epidermis and the upper dermis; while the scars were significantly thickened at 3 and 6 months after treatment (P＜0.025), with uneven and uplifted epidermis, and there was a hypoechoic area or anechoic area of the whole dermis. At the same time, the scar hardness, VSS score and pruritus VAS score of the both groups at 3 and 6 months were significantly higher than those at 1 month after treatment (P＜0.025), and there was no significant difference in scar hardness between the observation group and the control group at all time points (P＞0.05), but the VSS score of the observation group was significantly lower than that of the control group at 3 months after treatment (P＜0.05), VAS score of the observation group at all time points was lower than that of the control group (P＜0.05).

  Conclusion  Although medium frequency electric therapy cannot effectively inhibit scar hyperplasia, it can soften hypertrophic scar, significantly relieve scar itching and improve scar condition in patients.