Managing and providing proper interventions/solutions for destructive postural tendencies can be an intimidating task. There often are many different asymmetries occurring all at once. We must often step back and focus at the various body segments one at the time. In order to do this, we must start our evaluation and assessment at the pelvis. The pelvis is the “foundation” of our seated position. This is important as the position of the pelvis impacts the position of all other body segments
When we take a closer, more focused look at the pelvis itself, often times the pelvis is positioned in a posterior pelvic tilt (PPT). As we discussed in the previous segment of this series, PPT is the most commonly seen detrimental posture in the seated position. This position needs to be addressed as it can lead to higher risk for pressure/shear injuries on the seating surface and sliding forward in (and potentially out of) the wheelchair. It also contributes to increased thoracic kyphosis, flexed cervical spine with resulted hyperextension of the upper cervical spine, decreased visual field, difficulty swallowing, and compromise respiratory function, to name a few.
There are many causes of posterior pelvic tilt. This includes proximal/core weakness, insufficient proximal support at the pelvic/lower extremities, extension hypertonicity/spasticity, tight hamstrings, restricted hip flexion range of motion, and improper chair/seating system configuration.
So, what do we do to correct or prevent the person’s pelvis from tilting posteriorly? First, it’s important to narrow down the potential causes of the PPT. For example, if the individual has periods of fluctuating extensor tone or hypertonicity, then interventions should be provided to inhibit this tone or spasticity as much as possible. This can be done by using various therapeutic techniques, consulting with the physician about possible medical options, set up of the wheelchair to attain/maintain flexion at key joints (hips, knees and ankles), or providing an outlet for the tone with cautious and judicious use of power recline.
Let’s say that you have determined the individual’s PPT to be caused by insufficient support. If so, we need to look at the setup of the wheelchair seating system. First, is the length of the seat depth correct? Typically, the seat depth is one to two inches less than the measurement from the buttock to the back of the knee. If the seat depth is set too short, there is insufficient support on the seating surface, which could place the person at risk for pressure injury at the ischial tuberosities or cause them to slide into a PPT as they seek stability due to the lack of support down the posterior thighs. If the seat depth is too long, which is often the case, then it can prevent the person from getting their buttocks to the back of the chair, in good contact with the back support. As they sit, the posterior pelvis will naturally rotate rearward to find support from the backrest. This can happen if the measurement of the person is taken with the pelvis tilted posteriorly and not in neutral.
PPT could also be caused by tight hamstrings. The hamstrings are a two-joint muscle, meaning they cross the hip and knee joints in the back of the leg. Like a rubber band, if you stretch one end (the pelvis in the seated position), the other end tries to come back towards the stretched end. If you try to stretch the other end (the knee with feet on the footplates), the pelvis is pulled into a PPT.
Next, it is important to check that the legrests are adjusted to the appropriate length. If the legrests are too short, it causes increased flexion at the hips. This can cause a PPT if the hamstrings are tight or if hip flexion range of motion is limited. If the legrests are too long, then the person must slide forward in the chair in order to support their feet. This brings their pelvis and low back away from the supports and into a PPT.
Once we have the appropriate set up of the seat depth and legrest length, it’s important to ensure proper support is provided at the posterior pelvis and low back. When providing support, whether we are accommodating a non-reducible asymmetry or correcting a reducible asymmetry, it is important to remember the rule of three. This means that we must ensure support at three points of contact in order to support and maintain that desired position. When discussing PPT, the three important points of control include posteriorly at the posterior superior iliac spines (PSIS) with a properly positioned backrest, a properly positioned (under the ASIS) pelvic belt at approximately a 60-degree angle, and anterior support at the ischial tuberosities with a cushion that has an anterior shelf (see figure 1).
In summary, PPT is a common postural position seen in many wheelchair clients. This position can seem difficult to resolve, but if the cause of the position can be determined, and the adjustment capabilities of the seating system are understood, the intervention can be a much more manageable task.
About Wade Lucas: Wade is a physical therapist and the clinical education manager for Quantum Rehab in the western U.S. In his spare time, Wade enjoys watching his kids compete in their activities, as well as playing golf and watching football.