Neutral zero method
The neutral-zero method (NNM, zero crossing method ) is a standardized orthopedic evaluation and documentation index for the mobility of joints . It is expressed as a code that represents the amount of motion a joint can move in degrees around a specific axis. In this way the mobility is clearly traceable and can be documented in reports and letters. Using known standard values , a restriction of movement can be assessed and used as a basis for the expert opinion (see also anatomical position and directional descriptions ).
Range of motion
The freedom of movement is specified as the maximum deflection of the joint from the neutral position in degrees, with the neutral position being referred to as 0 °. The starting point is the "neutral position":
The person stands upright, the arms are relaxed hanging down, the thumbs pointing forward and the feet are parallel. This usually means that the elbows and knees are not fully extended, but rather bent very slightly. The adjacent angles are defined as the zero position. This neutral zero position largely corresponds to the anatomical zero position (anatomical normal position), in which the palms of the hands, however, point forward.
To describe the mobility, the directions in which the test is being carried out must be specified in advance. On the part of the German statutory accident insurance, it has become established to indicate the deflection in the distant direction (stretching ( extension ), outward movement ( abduction ) or outward rotation ( external rotation , supination ) etc.) as the first angle . The second angle is normally 0 ° (= neutral position), the third angle describes the deflection in the direction close to the body (bending ( flexion ), inward movement ( adduction ) or inward rotation ( internal rotation , pronation )). However, there is no binding standard, so that the extent of movement can also be specified the other way around, e.g. B. Flexion / stretching instead of stretching / flexion, with correspondingly reversed order of the angular degrees - which does not change anything in the actual statement.
The normal, undisturbed range of motion of the elbow joint is 10 ° -0 ° -150 ° in extension / flexion. The degree symbol is usually not given.
That means that the arm
- can stretch 10 degrees from the zero position (extension),
- can go into the physiological zero position,
- and bend up to an angle of 150 degrees (flexion).
- Extension / Flexion: 10-0-120
- Spreading / Leading: 45-0-30
- External / internal rotation: 50-0-40
Can the neutral position of the joint z. B. not reached due to damage or not passed through during the overall movement, the value 0 no longer appears in the middle, but on the side where the deficit exists.
A typical example is the restriction of movement in the elbow joint after a fracture with joint involvement. If the maximum flexion is limited to 100 °, but extension is only possible up to 30 ° flexion, i.e. with a 30 ° extension deficit, the result is: extension / flexion 0-30-100.
In the case of an equinus foot in which the neutral position (= 0 °) of 90 ° between the lower leg axis and the foot axis is not reached, the finding is, for example, dorsiflexion / plantar flexion 0-15-30 and describes a deficit / an equinus foot of 15 °. The foot is consistently in a flexed position (plantar flexion). Note that the movement of the foot upwards (i.e. towards the head) is defined as extension (dorsiflexion) and the movement downwards (i.e. towards the floor) as flexion (plantar flexion).
In the case of ankylosis with a fixed joint position or after joint stiffening (arthrodesis) z. B. in the 20 ° flexion position, the finding means flexion / extension 20/20/0 - this corresponds to a range of motion of 0 ° and a extension deficit of 20 °.
Standardized measurement sheets for the upper and lower extremities exist in the German statutory accident insurance sector to document the findings . These measuring sheets contain the standard values of the range of motion of all joints and clarify the systematics of the documentation of findings. In Germany, apart from in the area of GUV, they are also used for private accident insurance and other, for example social judicial assessments.
The information in the form of the neutral zero method cannot be used for a statistical evaluation; rather, it must then be transformed in such a way that only two information remain for the two directions of movement, i.e. instead of flexion / extension 150/0/10, only flexion = Process 150 and stretch = 10. If the neutral position cannot be reached, the corresponding variable is negative, i.e. instead of flexion / extension 100/30/0 the variables are flexion = 100 and extension = -30, which corresponds to the extension deficit. From this it is also very easy to calculate the range of motion ROM as the addition of the two variables - corresponding to 160 ° in the first and 70 ° in the second example. This system and v. a. The range of motion ( ROM ) are widely used outside of the German-speaking area, the neutral zero method is largely unknown.
In addition to the measurement of the passive mobility within the framework of expert reports, the measurement of the active and actively-assisted extent of movement are of great importance for the clinical examination, as they determine the extent of movement that can actually be used in everyday life. In the context of spasticity , a distinction can also be made between the extent of movement in passive slow movement and passive fast movement, which corresponds to the extent of the movement restricted by the spasticity, since with fast movement the spastic muscles contract much earlier and thus reduce the extent of movement relevant to everyday life.
- K.-D. Thomann et al. (Ed.): Orthopedic-Accident Surgery Assessment - Practice of Clinical Assessment . Elsevier, Amsterdam 2008, ISBN 978-3-437-24860-3 , pp. 612 .