At which level are plantar flexors rated 2/5?

At which level are plantar flexors rated 2/5?

• A. S1
• B. L5
• C. L4
• D. L3

Answer: (A)

Plantar flexion is controlled mainly by the S1 nerve root via the tibial portion of the sciatic nerve, with the gastrocnemius and soleus being the key muscles. In a motor exam, a strength grade of 2/5 means the patient can move the limb only if gravity is removed (movement with gravity eliminated) and cannot move it against gravity or resistance. When the plantar flexors show this 2/5 strength, it localizes preserved motor function to the S1 myotome, making S1 the level that best fits the observed weakness. If the lesion were at a higher level like L3, L4, or L5, you’d expect different patterns of weakness (for example, dorsiflexion weakness points toward L4–L5). Since plantar flexion is the key function for S1, a 2/5 grade there points to S1 as the level.

Plantar flexion is controlled mainly by the S1 nerve root via the tibial portion of the sciatic nerve, with the gastrocnemius and soleus being the key muscles. In a motor exam, a strength grade of 2/5 means the patient can move the limb only if gravity is removed (movement with gravity eliminated) and cannot move it against gravity or resistance. When the plantar flexors show this 2/5 strength, it localizes preserved motor function to the S1 myotome, making S1 the level that best fits the observed weakness.

If the lesion were at a higher level like L3, L4, or L5, you’d expect different patterns of weakness (for example, dorsiflexion weakness points toward L4–L5). Since plantar flexion is the key function for S1, a 2/5 grade there points to S1 as the level.