Page 14 - Mobility Management, September 2019

ATP Series
Posterior Pelvic Tilt
Why Posterior Pelvic Tilt Occurs
Posterior pelvic tilt can start simply, as the result of the body trying to find a more comfortable position while sitting.
“Prolonged sitting time in the wheelchair reduces hip flexor muscle and back muscle strength,” Hannah said, “which leads to a curvature of the spine. This can lead to a shift in the
pelvis where the user’s weight is more focused on the backrest, requiring less engagement of their abdominals, glutes and hamstrings. The less those muscles are engaged, the more there is increased likelihood of posterior pelvic tilt.”
“Posterior pelvic tilt is a position of stability, so the body tends to seek out this position,” Lucas explained. “First of all, it allows the person’s center of gravity to shift posterior to their base of support, which increases stability and decreases the workload on postural muscles. Secondly, the shift towards a posterior
tilt causes an increase in surface area contact with the seating support surface, thus increasing stability.
“The person’s physical characteristics can play a role in posterior pelvic tilt development,” he added. “These physical characteristics include hypotonicity/impaired core strength, extensor hypertonicity, tight hamstrings, decreased hip flexion range of motion, and non-reducible thoracic kyphosis.”
Unfortunately, seating can also contribute to posterior pelvic
tilt, Lucas said: “Other potential causes include the improperly set-up or insufficient support in the setup of the seating system. For example, if the seat depth is too long, then the pressure on the popliteal fossa [can cause] the person to slide forward and collapse into a posterior pelvic tilt as they seek support from
the back of the chair. Too much seat depth can also prevent the person from getting their hips all the way back to the back of the chair, causing the pelvis to rock posteriorly to meet the backrest. Legrest length setup is key to pelvic positioning, as well. If the legrest length is too long, then the person must shift the lower extremities forward to use them. This causes the lower half of the pelvis to slide forward and the top half of the pelvis to rock posteriorly.
Posterior pelvic tilt is a position of stability, so the body tends to seek out this position — Wade Lucas
“When the legrests are too short, again there is a lack of support/surface contact area on the posterior thigh, and the body will seek out a more stable positioning. Short legrests may also
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14 SEPTEMBER2019|MOBILITYMANAGEMENT
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