Ultrasound and EMG Guidance for Botulinum Toxin Injections in Spasticity: How Is the Target Muscle Found?

Why accurate muscle targeting matters

Botulinum toxin reduces the release of a chemical signal at the neuromuscular junction. When used for focal spasticity, it is injected into selected muscles whose overactivity is interfering with a meaningful goal. The aim is not to “turn off” every tight muscle. It is to reduce unwanted activity enough to improve comfort, movement, hygiene, positioning, brace tolerance or another agreed outcome while preserving useful strength.

That balance can be delicate. The forearm, hand, lower leg and shoulder contain muscles that sit close together and may perform different or opposing actions. A needle that enters a neighbouring muscle may produce less benefit in the intended pattern or weaken a movement the person relies on. Small and deep targets may be hard to distinguish through the skin, and anatomy can vary between people. Previous surgery, muscle wasting, contracture, swelling and changes after a neurological injury may make textbook landmarks less dependable.

Accuracy also means more than putting the needle inside a named muscle. The clinician must decide which muscles are contributing to the problem, how much of the resistance comes from neural overactivity, and whether fixed shortening, weakness, poor motor control, pain or joint disease is also present. For example, a flexed wrist may involve several wrist and finger flexors, but injecting all of them could reduce grip that remains useful. In an equinovarus foot, calf activity may coexist with weakness of ankle lifting or fixed shortening. The target list therefore follows a clinical analysis, not a scan alone.

If you are considering treatment, the broader overview of botulinum toxin injections for spasticity explains expected timing, possible benefits and limitations. A separate guide to setting spasticity treatment goals can help turn a general wish such as “less tightness” into an outcome that can be reviewed.

The assessment comes before the guidance method

Ultrasound, EMG and stimulation help locate or confirm a target; they do not decide the treatment goal. A careful assessment usually starts with what the person notices and what matters in daily life. The clinician may observe walking, reaching, opening the hand, dressing, transfers, seating, sleep or care routines. They examine the limb slowly and quickly, test voluntary movement and strength, and look for pain, swelling, skin problems and joint restriction.

Resistance that increases with faster movement supports a velocity-dependent component of spasticity, but a single tone score cannot describe the whole pattern. Measures such as the Modified Ashworth Scale or Tardieu Scale may be combined with range of motion, gait observation and a task that relates to the person’s goal. Our guide to how spasticity is measured explains why functional change matters alongside impairment scores.

Clinicians may also ask whether the posture appears at rest, during an effortful task, only at particular speeds or in response to pain and other triggers. A muscle may feel firm because it is actively contracting, because the tissues have shortened, or both. Botulinum toxin addresses neural activation of muscle; it does not lengthen a fixed contracture or repair a damaged joint. When uncertainty remains, a diagnostic local anaesthetic block, motion analysis or another specialist assessment may sometimes be considered.

Ultrasound guidance: seeing the anatomy in real time

Musculoskeletal ultrasound uses high-frequency sound waves to produce a moving grayscale image. Gel is placed on the skin and a handheld probe is moved over the limb. Muscle layers, fascia, bone surfaces, tendons, blood vessels and many nerves have different appearances. The clinician identifies the target in cross-section or along its length and can often watch the needle approach the muscle in real time.

What ultrasound can add

• Direct anatomical confirmation: the clinician can see whether the needle tip is in the intended muscle rather than a neighbour.
• Depth and individual anatomy: the image shows how deep the muscle is in that person and whether muscle bulk or position differs from an expected landmark.
• Awareness of nearby structures: vessels, nerves, bone and pleura in relevant regions can be identified and avoided.
• Small or deep targets: muscles that are difficult to palpate may be easier to access precisely.
• Distribution within a muscle: the clinician can choose a suitable region or more than one injection point when clinically appropriate.

Ultrasound is particularly attractive where several muscles are packed into a small area, such as the forearm, or where the target lies below another muscle. It can also help in altered anatomy. The image, however, does not automatically reveal which muscle is causing the unwanted movement. A structure can be seen clearly even if it is not the main functional problem. Image quality and interpretation depend on equipment, positioning and training, and very small needle tips can be difficult to see at an unfavourable angle.

The procedure is usually performed with the limb supported. The probe may be covered and the skin cleaned according to local practice. Ultrasound gel and gentle probe pressure are normally the main sensations before the needle is inserted. The scan itself does not expose the person to ionising radiation.

EMG guidance: listening for electrical activity

Electromyographic guidance uses a needle electrode connected to an EMG unit. Electrical signals produced by muscle fibres are converted into waveforms and sound. The clinician advances the electrode through the skin while interpreting the signal and the clinical context. Activity may be heard when a person attempts a movement or when a muscle is active involuntarily.

This is a focused localisation technique during treatment. It is not necessarily the same as a full diagnostic EMG and nerve-conduction examination used to investigate neuropathy or another neuromuscular condition. In an injection session, the aim is usually to support identification of the intended active muscle and then deliver the medicine through the injection needle or an appropriate combined needle system.

Where EMG can help

EMG supplies functional information that a static anatomical image cannot. It may help distinguish activity in a suspected target from surrounding tissues, particularly when the person can activate the movement on request or when there is persistent involuntary activity. The audible feedback can also help the clinician refine needle placement within a broad muscle.

Its limitations are equally important. Electrical activity does not show the boundaries of a neighbouring muscle, blood vessel or nerve. A strong signal confirms active muscle tissue near the electrode but must still be interpreted correctly. Voluntary activation may be difficult for someone with severe weakness, impaired understanding or poor selective control. Needle EMG can also feel uncomfortable, and background activity after an upper motor neurone lesion can complicate interpretation. For these reasons, EMG may be paired with anatomical knowledge, ultrasound or stimulation rather than used in isolation.

Electrical stimulation guidance: producing a visible response

Electrical stimulation for injection guidance is different from functional electrical stimulation used during movement. During localisation, a small current is delivered through or near the injection needle. The clinician watches or feels for the expected contraction—for example, flexion at a particular finger joint or movement of the ankle. The current can be adjusted as the needle position is refined.

A clear, selective movement at a relatively low current supports proximity to the motor point or motor nerve branch being targeted. Stimulation may be useful when the person cannot voluntarily activate the muscle, and it adds functional confirmation that surface anatomy alone cannot provide.

The sensation is often described as brief tapping, tingling or twitching. Some people find it unpleasant, and repeated testing can take time. The visible response may be harder to interpret when joints are very stiff, the muscle is markedly wasted, a nerve is injured or several muscles move together. Stimulation confirms an evoked response but does not provide the same view of vessels and neighbouring anatomy as ultrasound.

Ultrasound, EMG and stimulation: how do they compare?

Research comparing techniques is not perfectly uniform: studies include different diagnoses, muscles, doses, goals and outcome measures. Taken together, systematic reviews support instrumented guidance—ultrasound, stimulation or EMG—over manual landmark placement for many limb injections. Direct comparisons often find ultrasound and electrical stimulation similarly effective, while some analyses rank ultrasound highly for accuracy or outcome. The evidence does not justify a simple rule that one method is always superior.

The practical choice may depend on whether the key uncertainty is anatomical, functional or both. A large superficial muscle with clear landmarks may be approached differently from a deep forearm muscle next to a nerve. The clinician’s genuine competence with a method matters. A sophisticated device cannot correct a poorly chosen target, and a technically accurate injection cannot guarantee a meaningful functional improvement.

Combined guidance is increasingly used in selected situations. Ultrasound may establish the safe needle path and confirm the muscle, while EMG or stimulation confirms activity or the expected movement. This can be especially helpful when anatomy is complex, previous results were inconsistent or the clinical pattern involves several possible contributors.

What happens before, during and after the appointment?

Before the injection

Bring an up-to-date medication list and tell the team about anticoagulants or antiplatelet medicines, bleeding disorders, infection or broken skin near a proposed site, previous reactions to botulinum toxin, swallowing or breathing problems, neuromuscular disease, pregnancy or breastfeeding, and any recent antibiotics or procedures. Do not stop prescribed medication on your own; the treating clinician should advise whether anything needs to change.

It helps to describe what happened after previous injection cycles: which task changed, when benefit began, how long it lasted and whether there was unwanted weakness. Clothing that allows access to the target region can make positioning easier. For a child or a person with needle anxiety, ask in advance about comfort measures, topical anaesthetic, distraction or the need for another pain-management plan.

During the injection

The clinician confirms identity, goals, muscles and dose plan, positions the limb and cleans the skin. With ultrasound, you may see the screen as the probe moves. With EMG, you may hear crackling sounds that change with muscle activity. With stimulation, the limb may twitch briefly. More than one point may be used in a muscle, and more than one guidance method may be used in the same session.

Speak up if you have significant pain, feel faint or need a pause. Brief needle discomfort, pressure and small twitches can occur. A technically guided procedure should still involve communication and consent throughout.

After the injection

Mild soreness, a small bruise or temporary local discomfort can occur. Follow the clinic’s instructions about activity, dressings and when to restart or change any medicine. The effect is not immediate; it usually develops over days and is reviewed in relation to the agreed goal. Rehabilitation may include practising a task, stretching when appropriate, strengthening, splint review, positioning or caregiver training. The best follow-up asks not only whether tone changed, but whether life or care became easier.

People treated for hand and arm spasticity may track hygiene, nail care, dressing, reach or pain. After spasticity following stroke, walking and upper-limb patterns may require coordinated therapy rather than injections alone.

Safety, warning signs and informed questions

Botulinum toxin products carry recognised risks, and safety depends on the product, dose, muscles, health history and other medicines. Seek urgent medical advice if swallowing, speech or breathing becomes difficult, if there is marked generalised weakness, or if another severe or rapidly worsening symptom develops after treatment. Contact the treating team about increasing redness, heat, swelling, discharge, fever, severe pain or weakness that interferes with an important function.

Guidance may reduce uncertainty about needle location, but it cannot remove every risk. Infection prevention, dosing, knowledge of anatomy, recognition of adverse effects and appropriate follow-up remain essential. If a nerve-level treatment is being considered instead, our explanation of phenol neurolysis for spasticity describes a different targeted option and why its localisation also requires specialist skill.

Questions you may want to ask

• Which muscles do you think are contributing to my problem, and what findings support that choice?
• What specific activity, comfort or care goal are we trying to change?
• Will you use ultrasound, EMG, electrical stimulation or a combination, and why is that method suitable here?
• How will you protect useful strength and nearby structures?
• What should I expect to feel during the localisation and injection?
• What rehabilitation or home practice should follow the injection?
• When and how will we decide whether the treatment achieved its goal?

Common misunderstandings

“If ultrasound shows the muscle, the treatment will definitely work.” Ultrasound can improve anatomical confidence, but outcome still depends on diagnosis, target selection, dose, rehabilitation and the goal chosen.

“EMG guidance means I am having a complete nerve test.” A focused EMG localisation during an injection may be much shorter and has a different purpose from a diagnostic EMG study.

“More muscles injected means a better result.” Treatment is selective. Injecting muscles that provide useful stability or grip may worsen function, so the smallest effective, goal-aligned plan is often preferable.

“A lower tone score is the only measure of success.” A score may help describe impairment, but comfort, sleep, walking, care and participation can be more meaningful outcomes.