The Pelvis: Using Secondary Supports in Positioning

As I perused my e-mailbox one Monday morning, I came across a request for positioning advice.
Attached was a photo of a woman from the neck up and, admittedly, her head position wasn’t pretty. The requesting therapist wanted my opinion on the most appropriate headrest for her client. My response: I need a bigger picture! Particularly, I really wanted to see how her pelvis was positioned. The therapist wanted to know how the position of her pelvis could possibly have anything to do with the position of her head. I’m so glad you asked…

The pelvis does impact the position of the rest of the body, as well as resultant function. Positioning the pelvis is usually the first step of a seating assessment. Pelvic posture is very dependent upon the angle and contour of the primary support surfaces under the pelvis (the seating surface) and behind it (the back). Secondary supports are commonly used to keep the pelvis in as neutral a position as possible within those support surfaces. The most commonly used secondary support for the pelvis is the pelvic positioning belt. No, not a seat belt — those just keep you from falling out of your seat. A pelvic positioning belt should do just that — position the pelvis. Pelvic positioning belts come in various configurations and can be adjusted to meet a specific client’s needs, such as…

Posterior Pelvic Tilt: The bane of seating specialists everywhere. If the pelvic positioning belt is placed too high, a client can slide right under it. I place the positioning belt anterior and inferior to the ASIS (anterior superior iliac spine of the pelvis), usually around 60° to the seating surface. A secondary support will not correct a posterior pelvic tilt, but can maintain it.

For my clients with particularly strong posterior pelvic tilts, I often combine the pelvic positioning belt with an anti-thrust seat to block forward movement of the ITs (ischial tuberosities) or use a medial knee support, as appropriate, to reduce hip adduction (which loves to hang out with extension and pull that pelvis forward). If that doesn’t work, I occasionally use a rigid subASIS bar. Some of my colleagues use knee blocks, but I’m not a big fan of these.

Pelvic Obliquity:
The most difficult pelvic posture to impact in a seating system. Most clients can assume an oblique posture, despite a pelvic positioning belt.
The positioning belt can be placed over the lap (90° angle to the seating surface) to limit upward movement of the pelvis. As one side of the pelvis is elevated, using a 4-point positioning belt may help. A 2-point positioning belt is typically attached to the wheelchair seat rail or another portion of the frame that results in the desired position (i.e., anterior to the ASIS) and angle (i.e., 60°). A 4-point positioning belt adds two other straps that are attached to a different location on the frame. These additional straps keep the pelvic positioning belt in position and particularly prevent the belt from riding up.
I use a 4-point belt to keep the positioning belt down to limit pelvic elevation. In this case, I typically place the primarily positioning belt at about 60° and attach the secondary straps between 45° and 90° to allow good pelvic positioning and also limit pelvic elevation. This won’t work if the seating material is very soft and allows the low side of the pelvis to sink lower.

Anterior Pelvic Tilt: Challenging to control with a pelvic positioning belt. This is another great time to use a 4-point pelvic positioning belt. The primary positioning belt is placed over the ASIS to pull it back and is attached at around 90° to the backrest. The secondary straps are then attached at between 45° and 90° to the seating surface to keep that primary strap in position. If this is inadequate, pressure may be required over the lower rib cage to minimize spinal lordosis. I have used custom “corsets” or padded, wide chest straps mounted over the lower rib cage (never just the soft tissue).

Pelvic Rotation:
Correct the pelvis, not the legs. Many clients look like they have a leg-length discrepancy, but many more have pelvic rotation.
Sometimes the pelvis rotates if the legs are placed in a symmetrical position on the seat. I almost always place the pelvis in neutral rotation and let those legs assume a windswept position (one adducted, on abducted), if that is what is required to keep the pelvis neutral. One of my favorite tricks is to place the pelvic positioning belt so that it pulls down toward the forward side of the pelvis so that when the belt is tightened, the pelvis is de-rotated. If the positioning belt pulls down over the rearward side of the pelvis, tightening can actually pull the pelvis into further rotation.

Movement and Decent Pelvic Position: Will the two ever meet? Admittedly, I’ve gotten fairly good at nailing down someone’s pelvis into a decent neutral position. Of course, they can never move again… If I tried to provide movement within the seating system, the pelvis would shift and stability was compromised. A secondary pelvic support that wraps the pelvis front and back and is mounted at the sides will truly allow the client to tilt the pelvis forward (into an anterior pelvic tilt) and then assist resuming an upright position without allowing the pelvis to rotate, become oblique or slide into the dreaded posterior pelvic tilt.

So, when positioning the pelvis, match the client’s needs to the most appropriate primary support surfaces and angles. Then, choose the best secondary supports, mounting angles, direction of pull and style. Those secondary supports ensure that the primary supports can do their job.

This article originally appeared in the July 2008 issue of Mobility Management.

About the Author

Michelle is an occupational therapist with more than 25 years of experience and former Clinical Director of The Assistive Technology Clinics of The Children’s Hospital of Denver. She is a well-respected lecturer, both nationally and internationally, and has authored 6 book chapters and nearly 200 articles. She is the editor of Fundamentals in Assistive Technology, 4th ed. Michelle is on the teaching faculty of RESNA, is a member of the Clinician Task Force and is a Senior Disability Analyst of the ABDA.

Mobility Management Podcast