Whilst both spasticity and rigidity describe conditions in which one finds difficulty performing muscular motions, the difference between them arises in how such difficulty is brought about. Both describe forms of hypertonic states affecting an individual’s muscles, joints, and limbs, but a differentiation between the two must be acquired to best achieve a proper diagnosis.
Spasticity vs. Rigidity
Spasticity is often uni-directional, meaning that resistance to movement is only felt when one’s joint or muscle moves in one specific direction. Spasticity is velocity-dependent, meaning that the faster one moves or straightens a joint, the more resistant, tight, or spastic the muscle feels. This can be mild, and only apparent during bouts of strenuous physical activity, or it can be chronic or persistent, causing serious hindrance to one’s movements in moderate to severe cases.
Rigidity is different from spasticity in that resistance to movement in joints is felt regardless of the speed or direction the joint is moving. Rigidity is bi-directional, meaning that one may experience resistance to movements regardless of which direction the joint and muscles are moving in. Muscles that have rigidity feel heavy and like “a lead pipe” when they are moved passively.
The video below will help you to ascertain a clearer understanding between the two.
Characteristics & Causes of Spasticity
Characteristic Features
- Clasp-knife phenomenon: The limb experiencing spasticity suddenly gives way after an initial resistance to movement. Much like how a clasp-knife slightly resists before folding in. This can be caused by over-stretching the joint or muscles (during initial movement), the inverse stretch reflex (during sustained movements), and eventually contractures (a condition wherein muscles shorten/harden).
- Stroking effect: One may experience relief from episodes of spasticity by stroking the affected muscle’s surface, although this will likely not provide relief from contracture.
- Distribution: The sensation of spasticity is distributed differentially, often affecting antigravity muscles (muscles which are the extensors of the back, hips, and knees, which help to maintain proper posture by resisting the pull of gravity).
Causes
Knowing the causes of these medical terms can be very helpful when comparing spasticity vs. rigidity. Spasticity is generally caused by damage or trauma to the portion of the spinal cord or brain which controls voluntary movement, namely the corticospinal tract. This can lead to an imbalance and ‘disconnection’ between the muscles and the nervous system. This can be caused by the following instances:
- Adrenoleukodystrophy
- Amyotrophic lateral sclerosis
- Brain damage resulting from insufficient oxygen
- Encephalitis
- Meningitis
- Phenylketonuria
- Spinal cord injury
- Stroke
- Traumatic brain injury
Characteristics & Causes of Rigidity
Characteristic Features
- Independent from velocity: The amount of resistance does not vary depending on the velocity of movement.
- Associated with extrapyramidal conditions.
- 2 subtypes: Lead pipe rigidity, which is descriptive of an unvarying increase in tone, and cogwheel rigidity, which often results from a tremor pertaining to the central nervous system.
Causes
There are a vast amount of instances and conditions that can cause rigidity. For this reason, many medical professionals carry out tests and studies to try and determine what causes muscle and joint rigidity. There are estimated to be around 60 conditions that can lead to this occurrence, some common ones are listed below:
- Parkinson’s disease
- Multiple sclerosis
- Wilson’s disease
- Multiple system atrophy
- Dystonia musculorum deformans
- Neuroleptic-malignant syndrome
- Catatonia
- Creutzfeldt-Jakob disease
- Steele-Richardson-Olszewski syndrome
- Acute cerebral infraction
- Shy-drager syndrome
- Basal ganglia infection
- Gegenhalten
Knowing the difference when comparing spasticity vs. rigidity will help you to best determine the cause of your condition.