Physical Therapy: TENS, Ultrasound, Heat and Cryotherapy
Modalities should always be considered an adjunct to an active treatment program in the management of acute low back pain. They should never be used as the sole method of treatment. The prescribing physician should first be aware of all indications and contraindications for a prescribed modality and have a clear understanding of each modality and its level of tissue penetration.
The goals of treatment should be clear to the patient and the treating therapist from the onset of treatment. Patients are done an injustice when a therapeutic physical therapy program is modality-intensive as opposed to exercise-based. A poor functional outcome has been demonstrated in patients treated with a passive, modality-intensive program compared to those in an exercise-based program.
If at all possible, patients should be instructed in the use of simple modalities at home prior to their physical therapy sessions and in conjunction with their home exercise program.
Transcutaneous Electrical Nerve Stimulation (TENS)
Transcutaneous electrical nerve stimulation (TENS) has been used to treat a variety of pain conditions. Success rates range greatly due to many factors including electrode placement, chronicity of the problem, and previous treatments. It is generally used in chronic pain conditions and not indicated in the initial management of acute low back pain. Documentation of greater than 50% reduction in pain with a treatment trial may help substantiate its true beneficial effects as opposed to a placebo response.
High voltage pulsed galvanic stimulation has been used in acute low back pain to reduce muscle spasm and soft tissue edema (swelling). It is commonly used despite the lack of hard scientific evidence for its efficacy. Its effect on muscle spasm and pain is felt to occur by its counter-irritant effect, effect on nerve conduction, and a reduction in muscle contractility. Use of electrical stimulation should be limited to the initial stages of treatment, such as the first week after injury so that patients may quickly progress to more active treatment, which includes a restoration of range of motion and strengthening. It may often be combined with ice or heat to enhance its analgesic effects.
Ultrasound is a deep heating modality that is most effective in heating tissues of deep joints. It has been found to be helpful in improving the distensibility of connective tissue, which facilitates stretching. It is not indicated in acute inflammatory conditions where it may serve to exacerbate the inflammatory response and typically provides only short-term benefit when used in isolation. It is perhaps best used to improve limitations in segmental spinal range of motion following recurrent or chronic low back pain as an adjunct in facilitating soft tissue mobilization and prolonged stretching by a skilled manual therapist.
The use of ultrasound is contraindicated over a previous laminectomy or peripheral nerve secondary to alterations in membrane stability. It should be discontinued as segmental motion is improved with the patient then moved into an active strengthening program and eventual transference to an independent home exercise program.
Superficial heat can produce heating effects at a depth limited to 1-2cm. Deeper tissues are generally not heated due to the thermal insulation of subcutaneous fat and the increased cutaneous blood flow which dissipates heat. It has been found to be helpful in diminishing pain and decreasing local muscle spasm. Superficial heat, such as the hydrocolater pack, should be used as an adjunct to facilitate an active exercise program. It is most often used during the acute phases of treatment when the reduction of pain and inflammation are the primary goals. If beneficial, it can be incorporated into the education program and utilized on a home basis prior to the therapy program.
Ice packs or cryotherapy are generally more effective in terms of depth of penetration than other superficial thermal modalities. Intramuscular temperatures can actually be reduced by 3-7 degrees C. This is helpful in reducing local metabolism, inflammation, and pain. The analgesic effects of ice result from a decreased nerve conduction velocity along pain fibers and a reduction of the muscle spindle activity responsible for mediating local muscle tone. It is usually most effective in the acute phase of treatment, though the patient can use it after physical therapy or the home exercise program to reduce pain and the inflammatory response. It is applied over an area for 15-20 minutes, 3-4 times per day initially and then on an as needed basis. Peripheral nerve injury and local frostbite secondary to prolonged cryotherapy has been previously described, emphasizing the need for monitoring of cryotherapy use.