The muscles of the back often develop myofascial pain following repeated microtrauma from overuse including improper lifting and bending or from chronic deconditioning of the agonist and antagonist muscle unit. The sine qua non of myofascial pain syndrome on physical examination is the identification of myofascial trigger points. The end result of repetitive microtrauma to a muscle or group of muscles is the trigger point, which is a localized point of exquisite tenderness in the affected muscle or muscle groups. The trigger point is identified by mechanical stimulation of the painful area by palpation (Fig. 113.1). The result of trigger point stimulation is localized pain, referred pain, and an involuntary withdrawal of the stimulated muscle that is known as a “jump sign.” The referred pain associated with myofascial pain syndrome is often misdiagnosed or attributed to other organ systems, leading to extensive evaluations and ineffective treatment. Patients with myofascial pain syndrome involving the muscles of the low back often have referred pain into the hips, sacroiliac joint, and buttocks (Fig. 113.2).

In addition to muscle trauma, a variety of other factors seem to predispose the patient to develop myofascial pain syndrome. The weekend athlete who subjects his or her body to unaccustomed physical activity often develops myofascial pain syndrome. Poor posture while sitting at a computer keyboard or while watching television also has been implicated as a predisposing factor to the development of myofascial pain syndrome. Previous injuries may result in abnormal muscle function and predispose to the subsequent development of myofascial pain syndrome. All of these predisposing factors may be intensified if the patient also suffers from poor nutritional status or coexisting psychological or behavioral abnormalities, including chronic stress and depression. The muscles of the low back seem to be particularly susceptible to stress-induced myofascial pain syndrome.

Stiffness and fatigue often coexist with the pain of myofascial pain syndrome, increasing the functional disability
associated with this disease and complicating its treatment. Myofascial pain syndrome may occur as a primary disease state or in conjunction with other painful conditions, including radiculopathy and chronic regional pain syndromes. Sleep disturbance is common. Psychological or behavioral abnormalities, including depression, frequently coexist with the muscle abnormalities associated with myofascial pain syndrome. Treatment of these psychological and behavioral abnormalities must be an integral part of any successful treatment plan for myofascial pain syndrome.

The muscles of the back work together as a functional unit to stabilize and allow coordinated movement of the low back and allow one to maintain an upright position. Trauma to an individual muscle can result in dysfunction of the entire functional unit. The rhomboids, latissimus dorsi, iliocostalis lumborum, multifidus, psoas, and quadratus lumborum muscles are frequent sites of myofascial pain syndrome (Figs. 113.3 and 113.4). The points of origin and attachments of these muscles as well as the muscles themselves are particularly susceptible to trauma and the subsequent development of myofascial trigger points (Fig. 113.5). Injection of these trigger points serves as both a diagnostic and a therapeutic maneuver.

Ultrasound-guided injection for lumbar myofascial pain syndrome can be carried out by placing the patient in the lateral decubitus position (Fig. 113.6). A syringe containing 10 mL of 0.25% preservative-free bupivacaine and 40 mg of methylprednisolone is attached to a 25-gauge needle of a length adequate to reach the trigger point. For the deeper muscles of posture in the low back, a 3½-inch needle is required. A volume of 0.5 to 1.0 mL of solution is then injected into each trigger point. A series of two to five treatment sessions may be required to completely abolish the trigger point; the patient should be informed of this. The midline of the lumbar spine is identified by palpation as is the iliac crest, and a line is drawn from each of these anatomic landmarks (see Fig. 113.7).

After preparation of the skin with antiseptic solution, a curvilinear low-frequency ultrasound transducer is placed in the transverse plane ˜3 cm laterally from the midline along the line drawn from the iliac crest, and an ultrasound survey is taken (Figs. 113.8 and 113.9). This should place the
transducer at the L2-L3 level. Note that the transverse process blocks ultrasound visualization of the lumbar plexus (see Fig. 113.8). Once the transverse process is identified, the ultrasound transducer is slowly moved in a cephalad direction to identify the acoustic window between two adjacent transverse processes (Fig. 113.10). Once the acoustic window between the adjacent transverse processes is identified, the lateral aspect of the ultrasound transducer is rocked anteriorly to identify the lateral margin of the vertebral body and the erector spinae, psoas, and quadratus lumborum muscles (Fig. 113.11), which is just lateral to the vertebral body (Figs. 113.12 and 113.13). A color Doppler image is then obtained to identify adjacent vasculature to avoid inadvertent intravascular injection (Fig. 113.14).