What nerve is biased during SLR testing when performing dorsiflexion and inversion?

During straight leg raise (SLR) testing, when the ankle is positioned in dorsiflexion and inversion, the primary nerve that is biased is the sural nerve. The sural nerve is responsible for sensory innervation to the skin on the posterior aspect of the lower leg and part of the foot. In dorsiflexion and inversion, the positioning of the foot places tension on the nerve as it courses along the lateral side of the leg and into the foot.

The reason this test specifically biases the sural nerve relates to the mechanics of the leg and how nerves are mobilized under tension. When the foot is placed in dorsiflexion, the foot and ankle complex alters the tension along the pathways of the nerves, and inversion adds further tension that specifically affects the sural nerve.

Understanding the anatomical path and the functional implications of foot positioning is crucial for recognizing which nerve is being recruited or tested during a particular range of motion or functional activity. The sural nerve's exposure to tension during this specific ankle position makes it the most affected in this testing scenario.