Dystonia

INDEX

 

A sagittal shift backwards is a combination of anterocaput and retrocollis1.

This may develop into a  “Double-chin” posture:
Normally, when looking straight ahead (see Figure 2), the head is aligned almost horizontally on the C-spine. There is a lordosis of the C-spine and hence a flexion of the C-spine on the T-spine. The longus colli and the posterior cervical muscles form a sleeve, which encloses and stabilizes the cervical spine in all positions of the head.  The stabilization of the head and neck is also assisted by both the left and right levator scapulae muscles, which act like a pair of reins to hold the head upright and horizontally on the cervical spine. Thus, normally, the head pivots on the cervical spine, which we can be imagined as a ‘‘see saw’’ in a balanced position.  In the dystonic double-chin posture, this balance is tipped by activation of the suprahyoid group and the longus colli muscles, resulting in a posterior sagittal shift of the head on the C-spine.

Patients with a double-chin posture may have dysphagia before botulinum toxin injection, likely due to involvement of the suprahyoid muscles in swallowing.

Patient Image

From: Reichel G. Dystonias of the Neck: Clinico-Radiologic Correlations [Internet]. In: Dystonia - The Many Facets. InTech; 2012. Available from: http://www.intechopen.com/books/dystonia-the-many-facets/dystonias-of-the-neck-clinico-radiologic-correlations

 

Figure 1. A patient with a "double-chin" posture.

 

a) Anterocaput (flexion at atlantooccipital joint)
b) Retrocollis 
c) Combined effect of anterocaput and retrocollis lead to double chin formation


From: Pandey S, Singh AS. The double-chin posture: Posterior sagittal shift in cervical dystonia.Neurol India 2016;64:556-558

 

Figure 2. Muscles involved in the double-chin posture.

 

Figure shows double chin posture with active longus collis (LC) and suprahyoid muscles (SH) resulting in downward flexion of the neck2.

In addition, there is loss of the normal lordosis of cervical spine (green and yellow lines)

From: Flowers JM, Hicklin LA, Marion MH. Anterior and posterior sagittal shift in cervical dystonia: A clinical and electromyographic study, including a new EMG approach of the longus colli muscle. Mov Disord 2011; 26: 2409–14.

 

Treatment

Posterior sagittal shift involves the longus colli and the supra-hyoid muscles.

                 
               WARNING: risk of dysphagia with injections                         

 

Longus colli contraction causes a loss of the normal cervical lordosis with flexion of the head on the C-spine. The primary action is flexion of cervical spine or neck3.

Longus colli consists of two deep prevertebral muscles which run along the anterior surface of the vertebral column. The muscle takes its origin from the lower cervical anterior vertebral bodies and transverse processes, and inserts into the anterior vertebral bodies and transverse processes several segments above, flexing the head. Typically the muscle does not move much with rotation of the neck.  The prevertebral fascia surrounds the muscle, and separates longus colli from the more anterior oesophagus in the midline and the carotid sheath structures laterally.

Origin
​Upper, central and lower fibres: arise from the anterior tubercles of the transverse processes of C3-C5, anterior surface of vertebral bodies of C5-T3 vertebrae and of the T1-T3 vertebrae respectively.

Insertion

Longus capitis

Longus colli lies posterior and medial to longus capitis4.
The four slips of the longus capitis muscle originate on the anterior tubercles of the C3–C6 transverse processes and run superiorly and medially to insert on the basilar portion of the occipital bone. When contracting bilaterally, the longus capitis acts to flex the head and the proximal portion of the cervical spine. Acting unilaterally, the longus capitis contributes to ipsilateral head rotation3.

Longus capitis and longus colli overlap from C1–C6 and therefore both act on this portion of the cervical spine.

 

Figure 3. Muscles involved in the double-chin posture: longus capitis and longus colli.

 

 

When giving botulinum toxin injections into the longus capitis and longus colli muscles, avoiding superficial structures in the path of the needle to the target muscles creates technical challenges:

1. Longus colli injections using ultrasound: lateral approach
This technique is performed at the level of the cricothyroid cartilage using the anterior scalene muscle and carotid artery as anatomic landmarks. 
Typically, a lateral approach as described, although this may be limited by an anatomic variation where the carotid artery is in a more lateral position, blocking access to the muscles of interest. (Utilizing a medial approach requires that the needle be inserted into and then through the ipsilateral thyroid lobe on its way to the longus colli).

Figure 4. Important structures related to injection of longus colli
(Note: figure shows displacement of cricoid and trachea according to a fluoroscopic approach5; this does not correspond to the lateral approach under ultrasound)

From: Glass GA, Ku S, Ostrem JL, Heath S, Larson PS. Fluoroscopic, EMG-guided injection of botulinum toxin into the longus colli for the treatment of anterocollis. Park Relat Disord 2009; 15: 610–3.

The following is the method described by Farrell et al3.  This is a lateral approach which avoids traversing the thyroid gland and also maximizes the anatomical distance between the needle and the carotid sheath.

The patient is positioned seated on an adjustable examination chair, with the back of the chair sloped approximately 45 degrees backward and with the head resting on a headrest.
Scanning is performed with the neck in neutral rotation followed by maximal contralateral rotation, ie, with the head turned away from the side to be injected. This is to determine if one position or the other provides the safest path to the target. The C6 anterior tubercle to carotid distance is typically longest with full contralateral neck rotation4.

The cervical vertebral transverse processes are determined from the appearance of their respective anterior and posterior tubercles: the tubercles of C5 are of similar size and the neural foramina opening is relatively narrow. C6, in contrast, has a larger anterior tubercle compared to the posterior tubercle and a relative deep neural foramina opening, whereas C7 has a posterior but no anterior tubercle, thus having the appearance of a chair. Anatomically, C6 is approximately 2 cm below the level of the thyroid cartilage.

Longus capitis and longus colli lie anterior to the anterior tubercles of the cervical vertebra (Figure 5).
The longus capitis lies anterior and slightly lateral to the longus colli muscle at the C6 level.  The two muscles are separated by a hyperechoic fascia which is easily identified. With this view, it can be seen that the carotid and jugular vessels are more anterior and safely away from the planned trajectory of the needle to the muscles. It can also be noted that the vertebral artery is posterior to the anterior tubercle, which helps to protect it from accidental puncture

At C6 level, there is overlap of longus capitis and longus colli and both muscles may be injected with a single puncture, with the needle entering longus capitis first, and is then advanced to longus colli3.
 

Figure 5. Lateral approach: ultrasound guided injection of longus colli. 
Needle trajectory: needle track shown in yellow. Note schematic on anterior and posterior tubercles of C6 shown immediately below the ultrasound image

From: P. Boezaart, A. (Ed.). (2016). The anatomical foundations of regional anesthesia and acute pain medicine macroanatomy microanatomy sonoanatomy functional anatomy. BENTHAM SCIENCE PUBLISHERS.

 

Video 1. Ultrasound of important structures at lower cervical level3
Note the jugular vein is typically antero-laterally placed to the carotid artery.


(vv)Vid2US.mp4(tt)

 

Video 2. Demonstration of out of plane injection of longus colli3

(vv)Vid3OOPUS.mp4(tt)



2. Longus colli injections using cricoid cartilage as a landmark (without use of ultrasound).
In order to inject this muscle in the neck without involving the constrictors of the pharynx, the cricoid cartilage may be used as a landmark.
 

Anatomy of the cricoid bone

The patient is positioned on a couch in the supine position, preferably with no pillow.

From the left side:
In a right-handed operator, the injection is done from below. The larynx and trachea are retracted with the left hand, and the needle is inserted approximately 1.5 cm below the cricoid in a cephalic direction directly until the muscle is identified by a burst of activity on the EMG. Retraction of the larynx and trachea allows a medial approach, keeping well away from the vertebral arteries, which, at this level, are situated in the bony canal of the transverse processes. The needle is advanced so that the tip is approximately at the level of the cricoid (C5/6).

The position in the longus colli is confirmed by asking the patient to flex the head forward.
To ensure the injection will be low enough not to compromise swallowing, the patient is asked to sip water through a straw; if no significant muscle activation is noted, the injection goes ahead. If there is activation, the needle is repositioned in and further down and the process is repeated. A second puncture is made 2 or 3 cm below the cricoid, depending on the length of the neck, and again the trachea is retracted and the needle advanced in a cephalic direction for approximately 1.5 cm where the muscle should be encountered. The position is checked by asking the patient to flex the neck forward; however, it is not necessary to recheck the swallow, as this level is below the pharyngeal constrictors. Although the needle is now lower down (C6/7 approximately), the vertebral artery is not at risk because of the medial and relatively superficial nature of the injection. Even though the vertebral artery may not be in the bony canal below C6, it comes in from a lateral direction well away from the injection site2.

From the right-hand side:
For a right-handed operator, the injection is done from above. The larynx/trachea is retracted and the needle is inserted into the skin 1.5 cm above the cricoid. The needle is directed caudally to approximately the level of the cricoid, staying as near to the midline as possible. The position in the muscle is checked as before, as is the involvement of the inferior constrictor. A second puncture is made at the level of the cricoid and extends approximately 1.5 cm below it. By dividing the dose into four, this lessens the likelihood of swallowing complications2.

 

 

 

 

 

 

 

 

 

 

 

 

References

1            Reichel G. Cervical dystonia: A new phenomenological classification for botulinum toxin therapy. Basal Ganglia 2011; 1: 5–12.

2            Flowers JM, Hicklin LA, Marion MH. Anterior and posterior sagittal shift in cervical dystonia: A clinical and electromyographic study, including a new EMG approach of the longus colli muscle. Mov Disord 2011; 26: 2409–14.

3            Farrell M, Karp BI, Kassavetis P, et al. Management of Anterocapitis and Anterocollis: A Novel Ultrasound Guided Approach Combined with Electromyography for Botulinum Toxin Injection of Longus Colli and Longus Capitis. Toxins (Basel) 2020; 12. DOI:10.3390/toxins12100626.

4            Park DY, Kang S, Kang HJ, Choi JK, Do Kim J, Yoon JS. Impact of Neck Position on the Probability of Common Carotid Artery Puncture During Ultrasound-Guided Stellate Ganglion Block. PM R 2019; 11: 463–9.

5            Glass GA, Ku S, Ostrem JL, Heath S, Larson PS. Fluoroscopic, EMG-guided injection of botulinum toxin into the longus colli for the treatment of anterocollis. Park Relat Disord 2009; 15: 610–3.