Hi Matthew,
The motor level is defined as the lowest key muscle function that has a grade of at least 3/5 provided the key muscle functions represented by segments above that level are 5/5. While this patient has 3/5 strength to C8 on the right and C7 on the left, the segments above those levels (C7 on the right and C6 on the left) are not 5/5.
The most distal levels with 5/5 strength are C5 on the right and left. We then look to the next level down to determine if the motor level is C5 or C6. If C6 has strength of at least 3/5, the motor level is C6. If C6 is scored as 0-2/5, then the motor level would be C5. In this case, C6 is scored at least 3/5, so the motor level is C6 on the left and right.
Hope this helps!
Chrissy