SP17 Accuracy of Needle Placement by Electrical Stimulation Guidance in Botulinum Toxin Injections in the Lower Limbs of Children with Hypertonia

Mauricio R. Delgado1,3, Yassine Kanaan2; David Wilkes2; Deborah A. Baldwin1, Nancy J. Clegg1

Departments of 1Neurology and 2Radiology, Texas Scottish Rite Hospital for Children Department of 3Neurology and Neurotherapeutics, UT Southwestern Medical Center, Dallas, Texas

To investigate the accuracy of intramuscular needle placement by electrical stimulation guidance for botulinum toxin injections.

Figure 2

Figure 3a: Needle tip within the muscle.

Figure 3b: Needle tip touching the fascia.

Figure 3c: Needle tip outside the muscle.

The intramuscular injection of botulinum toxin (BoNT) in targeted muscles has emerged as a treatment of choice for the management of spasticity as well as for numerous other conditions. BoNT is a neurotoxin complex derived from the bacteria clostridium botulinum. It prevents the release of acetylcholine at neuromuscular junctions, which in turn results in weakness of the injected muscle. One important factor influencing the treatment outcome is the accuracy in delivering the toxin to the target muscle. The needle must be positioned within the targeted muscle in or near motor end plate zones or motor points.

Although accurate injection of the toxin into the desired muscle is crucial for obtaining the best possible clinical result, standardization of the localization technique is lacking. The European Consensus 2009 on the use of botulinum toxin for children with cerebral palsy emphasized the need of accurate localization techniques. They recommended neurophysiological localization (EMG, electrical stimulation) amended by sonography to allow precise identification of any target muscle (Heinen et al. 2010).

The most common BoNT injection guidance techniques in patients with hypertonia include: (1) muscle injection by anatomical knowledge only (AKO) (2) motor end plate localization by electrical stimulation (ES) guidance, and (3) visualization of target muscles by ultrasound guidance (US). Although injection guidance by AKO is the most common technique, its accuracy has been questioned, especially for deep and small muscles (Chin et al, 2005; Yang, et al 2009).

ES guidance increases the accuracy of placement compared to AKO placement by using muscle activation. The potential advantage of ES is that not only does it ensure that the injecting needle is in the target muscle, but that the needle is in close proximity to motor endplates and/or motor points (Childers 2010). Electrical stimulation is easy to perform, does not require formal training, and does not prolong the procedure significantly. However, it does require experience/practice in electrophysiological techniques as well as familiarity with the relevant anatomical landmarks. One major disadvantage is that it does require the patient to have sedation or mask anesthesia, since electrical stimulation requires the patient to be relaxed so muscle twitch can be observed.

Ultrasound helps to identify muscles by showing boundaries of individual muscles, each with characteristic landmarks, and by concurrent oscillations of the intramuscular echo produced by passive movement or tendon stretch. Ultrasound visualizes bones, blood vessels, and nerves and differentiates between the target muscle and neighboring structures (Fietzek et al. 2010). Ultrasound guidance is non-invasive, precise, and real-time. It demands very little time, is painless, and does not expose subjects to radiation. It allows visually guided injection into the center of every targeted muscle belly. Ultrasound guidance is recommended in multiple botulinum toxin studies (Berweck et al. 2002; Berweck & Heinen 2004; Fietzek et al. 2010; Westhoff et al. 2003) and all report that target sites are easily identified. However, ultrasound requires extensive training of personnel and the cost of the equipment is often prohibitive. Although small laptop devices are available for mobile use, most sonography devices in the hospital setting are large and cumbersome. Patient factors can also present challenges with sonography. The injection of deep-seated muscles in larger extremities, especially those in obese patients, cannot be performed with the same visual acuity as in superficially seated muscles. Misaligned extremities demand the use of alternative strategies and expert spatial and anatomical knowledge. Chronic spasticity is associated with substantial atrophy of muscle bulk and significant increases of muscle echogenicity, thus rendering the detection of contour lines far more difficult (Fietzek et al 2010). Finally, ultrasound cannot reliably localize endplate zones (Schroeder et al 2006). Despite these challenges, US is preferred by many clinicians and is often far more accurate.

Currently at our facility, ES is the current standard of care for BoNT injection guidance. Ultrasound guidance for toxin injections is only used for difficult/critical injection site locations, most often for non-intramuscular injections (i.e. salivary gland injections).

This was a convenience sample of 56 children (20 females) with hypertonia of different etiologies, mean age of 7 ± 4.27 years. Subjects were recruited from the PI’s patients scheduled for intramuscular BoNT injections under anesthesia in day surgery at a tertiary care facility. This study was approved by the UT Southwestern IRB and consent was obtained from each subject’s legally authorized representative and assent when appropriate for subjects ten years or older.

Real-time US was performed using the SonoSite S-nerve Portable US machine with a linear transducer (scanning frequency, 13-6 MHz) (see figure 1). Electric stimulation guidance was used with the Digistim II Neuro Technology machine (see figure 2). A low current one per second repetitive electrical stimulation pulse was delivered using a 1.5 inch (37mm) 27 gauge disposable insulated hypodermic needle electrode with Luer Lock Hub.

After declaring needle tip placement in the target muscle by using ES guidance, US imaging was performed by an independent US trained radiologist to verify needle placement accuracy. The injector was informed if the needle tip was (1) within the target muscle (2) touching the muscle fascia or (3) completely outside of the muscle (see figure 3a-c). A research coordinator recorded the needle tip location. If the needle tip was not within the muscle, it was repositioned before the BoNT was injected. The results were analyzed using frequency statistics to report the name of the muscle injected, the number of injection sites and the accuracy of needle tip placement.

A total of 490 BoNT injections were given. Twelve different lower limb muscles were included in the study with an overall accuracy rate of 98% (478/490). The accuracy rate in the most frequently injected muscles was: 98% (112/114) in the soleus muscle, 97% (66/68) medial head of gastrocnemius, 91% (50/55) in the lateral head of the gastrocnemius, 97% (132/135) in the medial hamstrings, 100% (70/70) in the hip adductors, and 100% (19/19) in posterior tibialis. The accuracy rate for the six least frequently injected muscles, iliacus (n=2), lateral hamstrings (n=7), flexor digitorum longus (n=4), flexor digitorum brevis (n=3), peroneus brevis (n=5) and peroneus longus (n=8), was 100% (29/29).

• ES guidance for BoNT injections in the lower extremities in children with hypertonia had an excellent overall accuracy rate of 98%.

• The least accurate rate was 91% for the lateral head of the gastrocnemius.• ES is easy to perform as long as the patient is relaxed.• ES accuracy requires the use of a low stimulation current (1-3mA).• ES is easy to use, does not require formal training and does not prolong the procedure significantly.

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CORRESPONDING AUTHOR:Mauricio R. Delgado, MD, FRCPC, FAANProfessor of Neurology and NeurotherapeuticsUniversity of Texas Southwestern Medical Center at Dallas

Director of Pediatric NeurologyTexas Scottish Rite Hospital for Children2222 Welborn StreetDallas, Texas 75219

Office: 214-559-7831Fax: 214-559-8383Mauricio.Delgado@tsrh.org

Disclosure of Relevant Financial Relationships:We have the following financial relationships to disclose: Grant/Research support from IPSEN.

Disclosure of Off-Label and/or investigative uses: We will not discuss off label use and/or investigational use in our presentation.

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Figure 1

0%  10%  20%  30%  40%  50%  60%  70%  80%  90%  

100%  

Percentage  Outside  the  Muscle  

Percentage  Touching  Fascia  

Percentage  in  Muscle  

0%  10%  20%  30%  40%  50%  60%  70%  80%  90%  

100%  

Percentage  Outside  the  Muscle  

Percentage  Touching  Fascia  

Percentage  in  Muscle  

Figure 4