Muscle function and grading is helpful to keep track of patient progress and figure out what is and is not working. At the same time, there can be significant variability in the way the tests are used, the precision, etc. For practical reasons and surgical planning, a more simplified scale might be useful. For research purposes and for careful follow-up of recovery after injury and/or surgery, a more detailed scale might be useful.
The 0-5 Scale or British Medical Research Council (MRC) grading system is commonly used:
- 0 – No contraction
- 1 – Flicker/trace contraction
- 2 – Active movement with gravity eliminated
- 3 – Active movement against gravity
- 4 – Active movement against resistance
- 5 – Normal/full power
Subdivisions of grade 4 provide further information:
- 4- Slight movement against resistance
- 4 Moderate movement against resistance
- 4+ Strong movement against resistance
Generally for nerve and tendon transfer purposes, only nerves/muscles with grades of 4 or 5 should be used as donors.
However, in some special cases (where options are very limited as in multiple nerve or nerve root level injuries), we will use a weaker nerve that we expect to recover to a 4 or 5 (even if it is not at the time of the transfer) as a donor to reinnervate and regenerate into a more important muscle (with respect to overall function).
For following patient progress more precisely, tracking grade of function through the full range of motion is useful. In this case, the a more detailed systems such as the 10-point scale (Kendalls, et al.) takes into account movement in the horizontal (gravity- eliminated) plane as well as in the antigravity position and requires movement through the complete range of motion to advance levels up the scale.