During a right lateral strain of the SBS, what is the motion permitted for the left second and fifth digits?

• A. Superior and anterior
• B. Inferior and posterior
• C. Rotational only
• D. Inferior and anterior

Answer: (B)

In a right lateral strain, the spheno-occipital complex shifts laterally toward the right, so the left side of the SBS becomes relatively depressed and back. The motion permitted on the left side follows this pattern: it moves inferiorly and posteriorly. This reflects the opposite directional components of a lateral strain between the two sides—the right side tends toward the superior/anterior direction while the left side moves toward the inferior/posterior direction. The other possibilities violate this opposite-side distribution (or ignore the translational component), so the left side’s allowable motion is specifically inferior and posterior.