**Core Concept:** Bennett's movement is a type of joint motion in the ankle joint, specifically the subtalar joint. The subtalar joint is a hinge joint that allows for inversion (ankle turning inward) and eversion (ankle turning outward). The immediate side shift refers to the side-to-side movement within the joint.

**Why the Correct Answer is Right:** In the case of the correct answer, D (Distal), the distal tibia (lower leg bone) moves laterally (sideways) relative to the talus (foot bone) and calcaneus (heel bone). This movement occurs due to the interaction between the tibia, talus, and calcaneus, allowing for the side shift in the subtalar joint.

**Why Each Wrong Option is Incorrect:**

A. The incorrect proximal option refers to a movement involving the talus and calcaneus, but not the distal tibia. This would not result in the immediate side shift in the subtalar joint.

B. The incorrect distal option involves the talus and calcaneus, but not the distal tibia. This would not result in the immediate side shift in the subtalar joint.

C. The incorrect axial option refers to a movement along the long axis of the bones involved, not the lateral or sideways movement required for the immediate side shift in the subtalar joint.

D. The correct distal option describes the movement of the distal tibia relative to the talus and calcaneus, resulting in the immediate side shift in the subtalar joint.

**Clinical Pearl:** Understanding Bennett's movement is crucial for assessing and diagnosing ankle injuries, particularly those involving the subtalar joint. A physical examination, specifically the test for Bennett's movement, can help differentiate between a lateral ankle sprain and a talonavicular coalition. In a lateral ankle sprain, the patient's foot will exhibit increased inversion (ankle turning inward) and decreased eversion (ankle turning outward) during Bennett's movement. In contrast, a talonavicular coalition would show decreased inversion and eversion during the test.

**Correct Answer:** D (Distal)