Pelvic drop is a downward tilt of one side of the pelvis in the frontal plane. In walking, running, and single-leg tasks it most often refers to contralateral pelvic drop: while standing on one leg, the pelvis lowers on the opposite, unsupported side.
A small amount of pelvic drop is part of normal gait. The hip abductors on the stance side, especially the gluteus medius, control how far the opposite side lowers. Larger or uneven drop is commonly observed in running assessments and movement screens.
Trendelenburg Sign
The Trendelenburg sign is a clinical observation made during single-leg stance. It is described as positive when the pelvis drops on the side of the lifted leg instead of staying level, and it is traditionally associated with weakness or poor control of the stance-side hip abductors. A gait pattern showing the same drop with each step is often called Trendelenburg gait. Some people compensate by leaning the trunk over the stance leg, which can keep the pelvis more level while shifting the demand elsewhere. Formal interpretation of the sign belongs to a clinical examination; video can document what is seen but does not establish a cause.
Filming and Observing It
- Use a rear view, centered on the pelvis, with the camera level at hip height
- Fitted clothing or small markers over the back of the pelvis make landmarks easier to see
- Draw a line across both sides of the pelvis and compare it with a horizontal reference
- Running is fast, so 120 fps or higher helps identify the stance frame with the greatest drop
- Compare left and right stance phases from the same clip
Common Pitfalls
- A tilted camera, uneven floor, or treadmill belt angle can create apparent drop
- Waistbands and loose shorts often do not follow the pelvis
- Pelvic rotation toward or away from the camera can look like frontal-plane tilt
- Trunk lean can hide pelvic drop if only the pelvis is watched
Pelvic drop is a useful visual marker for side-to-side control. Typical amounts vary between people, speeds, and measurement methods, so comparing an individual with themselves under consistent filming conditions is usually more meaningful than comparing with a single reference value.