Measuring Subtalar Joint (STJ) Neutral
The STJ is neutral when it it is neither pronated nor supinated. Because the STJ's axis is oriented obliquely, the joint's motion is triplanar. In an open chain, the calcaneus and forefoot move simultaneously. In closed chain, when body weight stabilizes the foot against the floor, the STJ motion requires motion in proximal segments and joints like the talus, tibia and knee.
1. Palpate medial and lateral aspects of the head of talus.
2. Invert and evert the rearfoot in the frontal plane.
3. The STJ Neutral is where the talar head protrudes equally on medial and lateral sides.
Hard (and more precise) Way
1. Using a skin pencil, draw a line that bisects the posterior calcaneus and lower 1/3 leg.
2. With the patient prone, let the ankle and foot hang over end of table.
3. Place the calcaneus in the frontal plane.
4. Center a goniometer's axis between the malleoli in the frontal plane.
5. Align the goniometer's stationary arm so that it parallels the line on the leg's distal third.
6. Align the moving arm so that it parallels the line on the calcaneus.
7. Lock the forefoot by grasping the fourth and fifth metatarsal heads and moving them dorsally.
8. Maximally supinate the STJ, realign the goniometer's arms and read the degrees of inversion.
9. Maximally pronate the STJ, realign the goniometer and read the degrees of eversion.
10. Measure total STJ range of motion (inversion + eversion).
11. Divide that number by 3, to get X degrees.
12. The STJ Neutral Position is when the rearfoot is inverted by X degrees from maximally everted.
Regardless of the method used to measure STJ Neutral Position, it is universally accepted as the position used for the fabrication of orthotic devices. Atlas Biomechanics