13.3 Spasticity, Rigidity, and Neuromuscular Tone Assessment
Key Takeaways
Upper motor neuron syndrome can include enhanced stretch reflexes and clonus alongside weakness and loss of selective control.
A catch with faster stretch supports spasticity. Parkinsonian rigidity can be felt during slow movement in both directions and is interpreted with other signs.
The Modified Ashworth Scale grades passive resistance. The Modified Tardieu Scale compares slow range and a fast response using a consistent angle reference.
Select positioning, exercise and adjuncts according to passive range, skin, safety and functional response. Reassess after casting or other interventions.
BoNT-A temporarily reduces acetylcholine release. Coordinate focal and systemic tone treatment with the interdisciplinary team and reassess the patient’s functional goal.
Spasticity, Rigidity, and Neuromuscular Tone Assessment
Evaluate resistance to passive motion alongside voluntary motor control, range, pain and the task the patient wants to perform. Spasticity, stiffness, weakness and impaired selective control can coexist. The treatment goal may be easier care, less pain, improved positioning or better active function.
Features of the Upper Motor Neuron Syndrome
Positive features Negative features
Enhanced stretch reflexes Paresis
Hyperreflexia and clonus Loss of selective motor control
Spasms and extensor plantar response Reduced dexterity
In the classic Lance definition, spasticity is enhanced stretch reflex activity that depends on the speed of stretch. Altered descending modulation and changes in spinal excitability contribute. The response also varies with muscle length and joint position. Observe involuntary and voluntary movement separately. An active flexor synergy can limit reach even when passive stretch elicits little reflex activity.
Joint resistance can also come from muscle and connective tissue stiffness, restricted joint range, pain or guarding. Assess slow passive excursion and compare with the response at faster speeds, then test active movement and the functional task. A change in passive resistance may have a different effect on dressing, standing or walking.
Comparing Spasticity and Parkinsonian Rigidity
| Finding | Spasticity | Parkinsonian rigidity |
|---|---|---|
| Passive movement | A catch or clonus can emerge with faster stretch of the involved muscle. | Sustained resistance can be felt through flexion and extension during a slow clinical examination. |
| Additional observations | Hyperreflexia, clonus and loss of selective movement can accompany an upper motor neuron lesion. | Smooth resistance is called lead-pipe rigidity. Ratchety resistance is called cogwheeling. Look for bradykinesia and other parkinsonian findings. |
The classic distinction is useful at bedside. Instrumented studies show that parkinsonian resistance can also vary with movement amplitude and speed. Interpret the complete neurological pattern.
Clinical Tone Assessment Scales
Modified Ashworth Scale (MAS)
Apply the chosen standardized position and passive movement protocol consistently. The original elbow flexor study moved the elbow from flexion to extension over approximately one second. Document the muscle group and conditions when comparing scores.
| Grade | Passive resistance finding |
|---|---|
| 0 | No increase in resistance. |
| 1 | A catch and release or minimal resistance at the end of the movement. |
| 1+ | A catch followed by minimal resistance through the remaining portion, which is less than half of the range. |
| 2 | More marked resistance through most of the range, with easy passive movement. |
| 3 | Considerable resistance that makes passive movement difficult. |
| 4 | The part is rigid in flexion or extension. |
The MAS is ordinal. It reflects resistance arising from neural and mechanical contributions. Use active examination and other passive measures to investigate the cause.
Modified Tardieu Scale
Compare the response at specified speeds. V1 is as slow as possible, V2 is the speed of the segment falling under gravity, and V3 is as fast as possible under the test protocol. Record slow passive end range (R2) and, when present, the angle of the fast catch or clonus (R1). Also record the quality of the reaction. The commonly used 0–5 scheme describes no resistance (0), slight resistance without a clear catch (1), catch and release (2), fatigable clonus (3), sustained clonus (4) and an immovable joint (5).
Ankle example (dorsiflexion positive, plantarflexion negative)
Fast catch at 15° plantarflexion (R1 = −15°)
Slow end range at 5° dorsiflexion (R2 = +5°)
Difference: +5° − (−15°) = 20°
Use a consistent angle reference and patient position. A clear fast catch well before the slow limit supports a velocity-sensitive component. When both measurements are restricted and close together, examine for limited passive extensibility. Consider pain, positioning and measurement variability. Interpret the result alongside active control, function and the treatment goal.
Physical Therapy Interventions
Supported standing, tilt-table positioning and weight shifts can help practice weight acceptance. Choose alignment, duration and support from the goal and response. Sensory input and Ib force feedback vary with the task. Recheck passive resistance and functional performance directly.
Positioning and stretching can help maintain available motion or permit care. Select stretch and orthosis use around comfort, skin, passive range and an agreed task. The 2026 AHA/ASA guideline supports stretching programmes in poststroke spasticity, based on nonrandomized evidence. Monitor individual range and function because treatment effects vary.
A small controlled cryotherapy study found an immediate change in plantar-flexor resistance after stroke. Select cold only after checking relevant skin, sensation and circulation precautions. Reassess before active practice. Consider NMES as an adjunct for selected patients. Select the target and settings by the response needed, such as an assisted movement for a functional task.
Serial Casting
Define a passive range or care goal → check skin, sensation and circulation
↓
Apply and monitor a cast → reassess range and safety → adapt the next step
Consider serial casting when limited passive range interferes with positioning, hygiene or another agreed goal. A small trial after severe acquired brain injury found improved ankle dorsiflexion after a programme combining casting, botulinum toxin, splinting and motor training. The team selects cast position, review interval and progression based on tissue tolerance and measured response. Arrange an explicit follow-up and aftercare plan.
Warning
New escalating pain, numbness, swelling, color change or cool digits under a cast require urgent clinical assessment for pressure or neurovascular compromise.
Medical and Surgical Interventions
- Oral medication. A prescriber may consider oral agents for generalized spasticity. Baclofen acts at GABA-B receptors and can cause sedation and weakness. Tizanidine is an alpha-2 adrenergic agonist with risks including hypotension, sedation and liver injury. Dantrolene reduces muscle calcium release and can cause weakness and serious liver injury. Review effects on function and follow the prescriber's monitoring and withdrawal plan.
- Focal botulinum toxin type A. A specialist may use it when focal spasticity interferes with function or care. It cleaves SNAP-25 and temporarily reduces acetylcholine release at the neuromuscular junction. Select rehabilitation, orthoses or casting by the goal, measured response and treatment plan. The Saudi Food and Drug Authority advises immediate medical assessment for new difficulty swallowing or breathing after injection.
- Intrathecal baclofen. A specialist team can consider it for severe disabling spasticity that responds inadequately to other interventions. A pump delivers baclofen into cerebrospinal fluid. Interruption can cause life-threatening withdrawal. Sudden rebound spasticity, fever or altered mental status after suspected pump interruption requires emergency assessment and contact with the pump team.
- Selective dorsal rhizotomy. This irreversible procedure sections selected sensory rootlets to reduce stretch reflex activity. A specialist indication is improving walking in selected children with spastic cerebral palsy. Pediatric selection and postoperative rehabilitation are covered in the cerebral palsy section.
Worked case. Eight months after traumatic brain injury, a patient walks with an equinovarus position and difficulty achieving foot flat. Passive resistance scores 3 on the MAS. In a separate speed-controlled test, fast dorsiflexion produces a catch at 15 degrees of plantarflexion and slow testing reaches neutral. Using dorsiflexion as positive, the difference is 0 − (−15) = 15 degrees. This suggests a speed-sensitive component. Check passive restriction, inversion, active control and orthosis fit. Agree on a goal such as safer stance. Discuss focal treatment with the team if examination shows that overactivity contributes, then reassess gait and care needs alongside the passive measures.
During a neurological examination, which bedside finding more strongly supports spasticity than parkinsonian rigidity?
A smooth resistance through both directions of slow movement
Cogwheel resistance with bradykinesia
A reproducible catch with faster stretch of one muscle group, accompanied by brisk tendon reflexes
Resistance only near the end of a painful passive movement
At the ankle, fast dorsiflexion produces a catch at 15° of plantarflexion and slow dorsiflexion reaches 5° past neutral. With dorsiflexion positive, what does the Modified Tardieu comparison suggest?
A 10° gap that diagnoses a fixed bony block
A 5° gap that demonstrates isolated dorsiflexor weakness
A 0° gap that demonstrates identical end points
A 20° gap supporting a speed-sensitive component, to interpret alongside the rest of the examination
Using the Modified Ashworth Scale for the elbow flexors, the examiner detects a catch followed by minimal resistance through the remaining portion, which is less than half of the range. Which grade applies?
Grade 1+
Grade 1
Grade 2
Grade 3
A stroke survivor received focal botulinum toxin type A for spastic wrist and elbow flexors. Which mechanism and rehabilitation approach are appropriate?
Direct activation of spinal GABA-B receptors, followed by training at a fixed time
Cleavage of SNAP-25 with reduced acetylcholine release, followed by goal-based practice guided by the measured response
Permanent blockade of postsynaptic acetylcholine receptors, followed by long-term immobilization
Destruction of muscle fibers, followed by routine rest until the next injection
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