The scanning electrodes for these paraspinal muscles are placed so that they run parallel to the spine, approx- imately 2 to 3 cm out from the vertebral ridge over the belly of the paraspinal muscle. These muscles may be visually seen in some individuals but may need to be palpated in others. The vertical placement for each site is as follows:
• C-6 placement: For the cervical region, it is probably best to start at the bottom and move upward. The electrode placements go from easy to more difficult. The C-6 electrodes are placed so that the lowest scanning electrode is directly across from the C7/T-1 prominence.
• C-2 placement: This is a very important, yet very difficult site to scan. The potential problems lie with the hairline. The most accurate method for vertical placement is to count up five vertebrae from the C-7 prominence and place the middle of the scanning electrode opposite this spinous process. Alternatively, place the lower electrode for the C-2 scan at the spot where the upper scanning electrode was for the C-4 scan. The residue left behind should help guide this placement, but the practitioner should avoid problems with bridging of the electrode paste.
° Placing electrodes at the hairline can be problematic. Make certain that the abrade for the site is rough and adequate, particularly around the hairline. If the patient’s hairline is too low, so that the upper scanning electrode clearly reaches into a thick patch of hair, it will push scanning technology to its limits. If the scanning electrode that reaches into the ture (all other muscles should remain quiet while the
person hangs on the ligaments). The practitioner should expect to see SEMG activity when the patient is standing.
Tibialis Anterior Placement
To assess the tibialis anterior, the electrodes are placed about a third of the distance from the knee to the ankle, lateral to the tibia on the anterior surface of the lower leg. The electrodes are oriented in a vertical plane rela- tive to the ground, so that they follow the muscle fibers.
Interpretation
The primary action of this muscle is the dorsiflexion of the ankle and inversion of the foot. This muscle lifts the foot during swing through as part of normal gait.
Paralysis may cause “foot drop.” Patients with poor foot control (i.e., excessive pronation) use this muscle exces- sively in an attempt to control the foot or ankle, which may contribute to the development of shin splints.
Digastric/Suprahyoid Placement
To assess the digastric/suprahyoid, the scanning elec- trodes are placed under the chin, so that they run in an anterior/posterior direction, approximately 1/2inch to the left or right of the middle of the chin, following the mus- cle fibers of the digastric muscle. The patient must not raise the head to help the practitioner with this place- ment. The practitioner should ask the patient to sit com- fortably and should provide no specific instructions regarding the position of the mandible. Men with beards cannot be scanned at this site.
Interpretation
This muscle is part of a group of muscles called the suprahyoids. Their primary function is to elevate the hyoid bone during swallowing when the mandible is stable, or to open the jaw when the hyoid is stable. It is an important muscle to assess in patients with tem- poromandibular joint problems.
Posterior Temporalis Placement
To assess the posterior temporalis, the scanning elec- trodes are placed slightly above the ear, toward its pos-
hairline does not make a good, clean contact with the skin (scalp), the poor contact will artificially drive up the SEMG readings as a result of interference with the differential amplifier. When this situation occurs, the practitioner must decide if a high reading is real SEMG or just instrument noise.
° As an alternative means of monitoring the area, the practitioner can place the electrodes at an oblique angle, just below the mastoid process, rather than up into the hairline. This arrangement might better reflect the activity of the group of muscles that cross the atlas/axis joint. Practitioners who use this concept should give it a different label to differentiate it from the C-2 configuration.
• T-4 placement: To locate this site, simply count down four vertebrae from the C-7/T-1 prominence and place the space between the active electrodes directly across from the vertebral prominence.
• T-8 placement: It is typically very easy to count down from the C-7/T-1 prominence, placing the space between the active electrodes directly across from the vertebral prominence. The location of this site is approximately where a woman’s bra strap would run.
• L-1 placement: To locate this site, count down 13 vertebrae from the C-7/T-1 prominence. Another method is to use the iliac crest to determine the L-3 vertebra (see the L-3 placement in the original scan site descriptions), and count up two vertebrae from that point.
• L-5 placement: To locate this site, count down 17 vertebrae from the C-7/T-1 prominence or two vertebrae down from the L-3 vertebra determined using the iliac crest method described previously.
This site is typically below the belt line.
Interpretation
When monitoring from the paraspinal muscles, there are many layers of muscles to consider: The longissimus, spinalis, semispinalis, and multifidus may all contribute to the signal. All of these muscles play a substantial role in
stabilization of the spine. In addition, when both the right and left aspects are activated, extension of the spine occurs. Unilateral contractions of one side lead to ei- ther rotation or lateral bending of the spine.
Some chiropractors believe that an asymmetry in SEMG at one level indicates a rotated or subluxated ver- tebra at that level. This may or may not be true. An un- published pilot study on 25 chiropractic patient records for SEMG (neutral posture) and radiographic findings (using the Gonsted method) indicated that the relation- ship between asymmetry in SEMG and vertebra rota- tion/subluxation varied from level to level. The strongest relationships were found at sites of the greatest spinal instability: the axis and L-5 levels. At the axis, 21 of 25 pa- tients showed abnormal radiographic findings. Of the 23 patients who were scanned at this site, 9 (39%) showed significant SEMG asymmetries. Of those with SEMG asymmetries, 6 (67%) had concomitant radi- ographic evidence. At L-5, 18 of the 25 patients showed radiographic evidence. Of the 22 patients who were scanned at this site, only 6 (27%) had clinically significant asymmetries. Of those with asymmetries, 5 (83%) had concomitant X-ray findings. At the T-1 paraspinals, only 4 abnormal X-ray findings were identified for the 25 pa- tients. Of the 14 patients scanned at that site, only 4 (29%) had clinically significant SEMG asymmetries. Of those 4, only 1 (25%) had a concomitant X-ray finding.
At a similar site, T-7, 4 patients had abnormal X rays; of the 14 patients receiving an SEMG scan at this site, only 2 (14%) were asymmetrical. Both of these patients (100%) had abnormal radiographic findings.
From this brief study, it may be concluded that it is too simplistic to say that an SEMG asymmetry at a given level indicates a rotated or subluxated vertebral body. X- ray evidence of rotation is not always associated with asymmetrical SEMG activity. In addition, when clinically significant asymmetries of SEMG activity are noted, they are not always associated with radiographic evi- dence of rotation. In conjunction with rotation, practi- tioners should consider other diagnostic concepts such as scoliosis, pain displays of splinting/guarding, functional problems, hypermobile and hypomobile segments, and emotional displays.
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CHAPTER QUESTIONS
1. The muscle scanning procedure requires:
a. a scanning head b. abrading the site c. electrode paste
d. holding the electrodes motionless e. all of the above
2. Typically, one must stay on the site for how long before it becomes stable?
a. 2 seconds b. 10 to 20 seconds c. 2 minutes d. 5 minutes
3. Which of the following is notone of the pitfalls of muscle scanning?
a. bridging of electrode paste (values too low) b. excessive resistance (values too high) c. excessive variability (too long at the site) d. excessive movement during range of motion 4. Which of the following is notone of the general clinical
concepts associated with muscle scanning?
a. site of activation/inhibition b. level of symmetry c. impact of posture
d. degree of reciprocal inhibition
5. During muscle scanning, which approach should be used in positioning the patient’s posture?
a. Place the patient in the ideal posture.
b. Allow the patient to assume his or her natural posture.
c. Ask the patient to sit or stand up straight.
d. Always study the end range of motion of a posture.
6. The muscle scanning assessment of the static component of the neuromuscular system provides information about which of the following?
a. hyperactive muscles b. antalgic postures c. trigger points d. both a and b
7. During a muscle scan, an antalgic posture (protective guarding) is noted when:
a. the activation is greater during standing than during sitting
b. the activation is on the ipsilateral side of the pain c. the activation is on the contralateral side of the pain d. both a and c
8. During a muscle scan, muscle splinting is noted when:
a. the activation is greater during sitting than during standing
b. the activation is on the ipsilateral side of the pain c. the activation is on the contralateral side of the pain d. the activation is greater during standing than during
sitting e. both a and b
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