Page 10 - Mobility Management, September 2019

ATP Series
Posterior Pelvic Tilt
So this posterior pelvic tilt impacts how the rest of the body is positioned in the wheelchair and how well a wheelchair user functions as a result.
Impact on Other Body Functions
Compare optimal seated posture with what happens in posterior pelvic tilt.
“Ideally, the pelvis is positioned in neutral to a slightly anterior tilted position,” Lucas said. “In this position, the ASIS and PSIS will be level and parallel to the seating surface. The ischial tuber- osities will be oriented vertically, and there should be little to no contact of the sacrum with the seating surface.
“When a person’s pelvis tilts posteriorly, the ‘tips’ of the ischial tuberosities slide anteriorly and point more horizontally. There will also be a significant increase in surface contact of the sacrum to the seat, thus increasing the chance of pressure injury.”
“Prolonged posterior pelvic tilt can result in skin breakdown, pressure ulcers due to increased pressure and shear forces on the ischial tuberosities and sacrum, nerve pain, digestion problems and respiratory problems,” Hannah said. “A wheelchair user sitting with a posterior pelvic tilt will also likely have a kyphotic posture, which will negatively affect respiration and circulation by increasing pressure on the lungs and heart. The seat depth, cushion well position, and leg channels can all be in a poor position, resulting in increased pressure when the user is sitting forward on the cushion.”
The different position of the pelvis, Lucas added, impacts how other systems work in the body.
“Posterior pelvic tilt by itself is not always that noticeable at first glance,” he said. “However, the position of the pelvis has a strong correlation to the position of other body segments. This correlation leads to the person sitting in a very ‘slouched’ type [of] posture. When the pelvis is not in a well-balanced, neutral position, then it leads to compensatory postural deviations of the lower extremities, trunk, head/neck, and upper extremities. Posterior pelvic tilt tends to facilitate external rotation/abduction of the hips, increased thoracic kyphosis of the trunk, flexion
of the lower cervical spine with hyperextension of the upper
cervical spine, rounded shoulders and internal rotation of the arms. This posture can impair a number of body functions — most notably, respiration, chewing/swallowing, digestion, bowel and bladder elimination and even circulation. It can also mini- mize shoulder range of motion, reach and function; increase pain in the neck, trunk and low back; decrease sitting tolerance; and significantly limit a person’s visual field. In addition, prolonged sitting in this position can cause orthopaedic deformities that limit joint range of motion and create non-reducible deformities.”
And as previously mentioned, posterior pelvic tilt can signifi- cantly raise the risk of pressure injury.
“Posterior pelvic tilt also can be extremely detrimental to an individual’s skin integrity,” Lucas confirmed. “First, as a person begins to shift from a neutral to a posterior tilted position, there
are increased shearing forces that occur at the ischial tuberosities, sacrum and coccyx. This shearing over the bony prominences can be more damaging than pressure itself. Once a posterior tilted posi- tion is achieved, there will likely be a higher amount of pressure over the ischial tuberosities and the sacrum. When positioned in a neutral pelvic tilt, there is little to no pressure over the sacrum.
Posterior pelvic tilt affects the center
of gravity of the wheelchair —
Sam Hannah
“In addition to the increased pressure risk on the buttocks caused by a posterior pelvic tilt, the resultant hip external rota- tion/abduction increases the pressure-related injury risk at the bony prominences in the lower extremities. These at-risk areas include greater trochanters, lateral femoral condyles, fibular head and lateral malleoli. The resultant increased thoracic kyphosis also creates more prominent spinous processes, which increases the risk for pressure points at the apex of the curve.”
And as Hannah pointed out, “Posterior pelvic tilt also affects the center of gravity of the wheelchair, which changes the level of effort required to propel the wheelchair.”
Posterior Pelvic Tilt: Going to the Mat
When creating a strategy to address posterior pelvic tilt, Wade Lucas, PT, DPT, ATP/SMS, Clinical Education Manager at Quantum Rehab, said it’s important to gain a good understanding of the situa- tion: “A thorough evaluation including mat assessment is a must!”
The client, Lucas said, “must be transferred out of the current seating system and onto a firm surface so the team can determine what the person’s natural postural tendencies are and to obtain accurate measurements. Accurate range of motion and linear measurements are vital to the proper setup of the seating system.”
This postural assessment “will help determine the flexibility of postural deviations and asymmetries to guide the placement of
secondary support accessories, such as lateral trunk and thigh supports. Proper angle (~60° in relation to the seat frame) and place- ment of a pelvic positioning system just under the ASIS [anterior superior iliac spine] will limit extension at the hips, thus decreasing posterior pelvic tilt. Utilization of an antithrust cushion can also assist in preventing the ischial tuberosities from translating anteriorly.”
Finally, Lucas added, “the proper size and adjustment of the backrest can provide posterior support at the PSIS [posterior superior iliac spine] and prevent the pelvis from rotating rearward. It is key to always address three points of control when providing postural support in the wheelchair seating system.” m
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