Effect of Different Carrier Frequencies of Interferential Current on Upper Trapezius Myofascial Trigger Points: A Randomized Controlled Trial

Interferential current (IFC) is a medium frequency current derived from the interference of two symmetrical, but asynchronous alternating currents ranged from 1 to 10 KHz. The two main currents resulting in a single interference current with properties uniquely different from the two original currents.The lesser current of the two original currents is termed the carrier frequency and the interference current is called the beat frequency. A specific beat frequency can be obtained from several possible interference currents as long as the difference between the original currents is the same. For electro pain modulation, IFC is commonly used form of electrotherapy. It has the advantage of reducing the skin impedance, deeper penetration into tissues and is perceived as more comfortable.

Myofascial pain syndrome (MPS) is a common form of chronic musculoskeletal pain that widely spread and contributing to a significant financial burden and job- related disability. It represents the most common disorder in patients with nonspecific chronic neck pain.The main characteristics of MPS include the presence of myofascial trigger points (MTrPs) which are defined as hyperirritable nodule in a taut band of skeletal muscle fibers which is palpable and tender during physical examination. Trigger points (TrPs) are usually seen in the upper fiber of trapezius. TrPs can be clinically classified as either active or latent. Active TrPs was defined as: MTrPs that refer pain during activity and during rest without any pressure. They prevent full muscle lengthening and induce their weakness. Latent TrPs was defined as: MTrPs that is painful only when palpated. Evidence on the effect of IFC on pain modulation is not confirmed up till now. This might be attributed to multiple factors such as limited number of studies, inappropriate use of the parameters or using single carrier frequency (4 KHz) in majority of studies and the physiological effects of all our modalities are dose dependent. Dose depends on details of parameters including frequency. For IFC, the carrier frequency of the current has been suggested as an important parameter to achieve the most effective hypoalgesic response. However, there remains no evidence to support the selection of one carrier frequency over another. Few studies were conducted to examine the effect of different carrier frequencies by comparing their individual effects. Further researches are needed to prove which carrier frequency is more effective in treatment. Therefore, this study will be conducted to compare the effect of different carrier frequencies of the IFC in the management of upper trapezius chronic TrPs.