There are many ways to test sensation. These are outlined below with pros and cons of each method.
Ten Testing: compares sensation in injured/non-injured areas in response to light-moving touch where 10/10 is normal and 0/10 is no sensation.
- Pros: quick and easy to use in almost all patients including young children.
- Cons: not as well-accepted or widely-used.
- How:
- Light moving touch (examiner’s finger) is applied to the area to be tested as well as to an area of normal sensation (such as the contralateral uninjured finger)
- The patient is asked to rate the best level of sensation they feel in the test area.
- Ten is normal sensation, diminished sensation is rated on a scale of 0-10*, with 0 being no sensation, 5 being half of normal, etc.
- *Note that Strauch’s original report described using a scale of 1-10, but we find the concept of 0 or no sensation easier for patients to understand.
Two Point Discrimination: provides information on the shortest distance between two points that the patient can perceive as being touched with two versus one point.
- Pros: widely-used and well-accepted; objective data.
- Cons: some patients have a difficult time with this test, time-consuming, highly variable results; can provide misleading information when trying to make treatment decisions. Also, a patient may have normal two point range even with a nerve function abnormality. For example, in early nerve compression moving and static two point discrimination may remain normal.
- How:
- A gauge or 2-point Disk-criminator is used to determine the shortest distance, in millimeters, that the patient can feel the two, not one, points.
- Static and moving two point discrimination can be tested.
- Strictly speaking, the patient should be blinded and the hand immobilized, the same pressure should be placed each time and 10 sets of the test performed per finger with 7 of the 10 trials being correct.
- We do 2 out of 3 consistent answers. We start by introducing the test to the patient with their eyes open watching the test on their good hand so they understand the test. We test moving the point at the pulp from distal to proximal. For static point, we place the prongs transversely at the pulp. When you reach the patient’s limit, you will see them start to move their finger tips a bit as they “search” for more information as they reach the limit of their sensory threshold.
- Normal values for the fingers include < 6mm for static two point and 2-3 mm for moving two point.
Semmes-Weinstein Monofilament Testing (this is a cutaneous threshold pressure test):
- Pros: test provides information on protective sensation, rigorous system can detect relatively minor differences in sensory function, and changes will occur early in nerve compression.
- Cons: extremely time-consuming, high variability, easy to do incorrectly.
- How (briefly):
- Standardized plastic filaments are applied perpendicular to the skin surface.
- The filament should be applied slowly and precisely to the skin in the same fashion for the same amount of time for each test. It should be pressed to produce a slight bend (in all but the thickest monofilaments).
- The patient acknowledges when they feel pressure and testing proceeds until the thinnest fiber that the patient can perceive is reached.
- Normal value in the hand is in the range of the green filament (50mg, 2.83 MN).
Tuning Fork
- Pros: provides quick information, easy to use, provides information on early and late compressive neuropathy sensory changes
- Cons: less widely used, less available in most surgery practices, less applicable to traumatic injuries other than those with an element of nerve compression as the pathology.
- How:
- 256 cycles per second tuning fork is applied to area of suspected nerve compression
- Patient will often have heightened sensitivity to the vibratory sensation in the territory of early compressive neuropathy.