Pelvic obliquity is an important cause of various problems such as scoliosis, unstable sitting, pain, and pressure injuries (For extra background information see: Literature review – pelvic obliquity in the wheelchair using population). The most common way to quantify pelvic obliquity is by determining the height difference between the left and right Anterior Superior Iliac Spine (ASIS).1
The literature review ‘pelvic obliquity in the wheelchair using population’2 shows the importance of dealing with pelvic obliquity in the wheelchair using population. Based on our literature review it was decided to investigate the effect of Vicair cushions on different degrees of pelvic obliquity. To contextualize the obtained data, it is compared with a Jay J3 foam cushion with fluid insert in the posterior half of the cushion.
When investigating pelvic obliquity it’s important to take into account the following two effects, both of which can be positive depending on the user:
- Accommodation: the cushion adapts to the pressure and offers even pressure distribution without forcing the user into a different position.
- Correction: the cushion supports the pelvis to achieve a more horizontal pelvic, resulting in a more neutral posture.
To evaluate the properties of the cushions, pressure
distribution during loading in various angles (4.57 – 9.17° pelvic obliquity, which is 2 – 4cm height difference at the ASIS level). A literature review revealed that pelvic obliquity below 2cm at the ASIS level is difficult to distinguish. Therefore this is chosen as the minimum for this study. The following range of pelvic obliquity will be investigated:
To assess the response of the cushion to different levels of pelvic obliquity the pressure distribution during loading is examined. The standard filling grade of the cushions is used for this study.
First, the pressure under the left IT is compared to the pressure under the right IT. For the Vicair Vector O2, the pressure under the right IT is 134mmHg with a pelvic obliquity of 2cm to the right, while the measured pressure under the left IT is 117mmHg. This represents a pressure difference of 15%. A large pressure difference indicates a higher risk of problems at the lowest lying bony points.
To get an impression of the total pressure distribution between the left and right sides, the average centre of pressure deviation with respect to the centre of the cushions was also examined.