Neutral Subtalar Positioning: Assessing Foot Alignment

Neutral Subtalar Positioning (STN) is a critical biomechanical assessment technique. It is used to find the neutral position of the subtalar joint, which serves as the standard reference point for diagnosing foot deformities and prescribing orthotics.

1. Purpose

The primary purpose of finding the Neutral Subtalar Position (STN) is to identify the optimal alignment of the foot where the talonavicular joint is congruous (balanced). It is the reference point used to:

• Classify foot deformities (like forefoot varus/valgus).
• Assess rearfoot to forefoot relationships.
• Ideally position the foot for casting custom orthotics.

2. How to Perform

1. The patient is positioned in prone (lying on their stomach) with the foot hanging off the table edge.
2. The examiner grasps the 4th and 5th metatarsal heads with one hand to control the forefoot.
3. With the other hand, the examiner palpates both sides of the talus head (located just anterior to the ankle malleoli) using the thumb and index finger.
4. The examiner passively supinates and pronates the foot.
5. The neutral position is found where the talus head does not bulge to either side and feels symmetrical or equally prominent under the examiner's fingers.

3. Normal & Abnormal Findings

This is a biomechanical assessment, so we look for alignment rather than a "positive" sign.

Normal Alignment:
In STN, the calcaneus should be vertical (or within 2-4 degrees of varus) relative to the lower leg, and the forefoot should be perpendicular (level) to the rearfoot.

Abnormal Findings (Deformities):

• Rearfoot Varus: The calcaneus is inverted (turned in) when in STN.
• Forefoot Varus: The medial (big toe) side of the forefoot is elevated higher than the lateral side when the rearfoot is in neutral.
• Forefoot Valgus: The lateral (pinky toe) side of the forefoot is elevated higher than the medial side when the rearfoot is in neutral.