Hi! The motor level is defined as the “lowest key muscle function that has a grade of at least 3, providing the key muscle functions represented by segments above that level are judged to be intact (5/5).”
This patient has full strength in his hip flexors (L2) and 3+/5 strength in his knee extensors (L3). Therefore, L3 is the lowest level with a grade of at least 3/5 with proximal musculature having full strength.