Pressure redistribution is an imperative component of pressure ulcer prevention, and my experience has been that this is better understood and implemented in supine and side-lying positions than with seating, especially with the specialty beds that are available in both acute and long-term care settings.  Wheelchair positioning and fitting is also a necessary component of PU prevention in all settings.  The most vulnerable anatomical areas for PU formation from prolonged sitting are the ischial tuberosities, the thoracic spine (especially if the patient is kyphotic), and the coccyx.  The seated position in any chair requires postural alignment to protect these areas from prolonged direct pressure (as occurs with asymmetry due to pelvic obliquity) and from shear (that occurs with slouching or forward sliding in the chair).

The principles of a properly-fitting chair are ones that will place the patient in the optimum posture to maintain neutral to anterior pelvic tilt, to support the trunk to prevent side-leaning that places more pressure on one ischial tuberosity, and to provide adequate protection for the thoracic spine.  To properly fit a wheelchair to the individual, the following six measurements are needed:

1. Seat width – Allows the patient to sit without direct pressure on the hips (occurs if the chair is too narrow).  A chair that is too wide reduces the patient’s ability to maneuver the chair and reduces the ability to access hand rims for propulsion or arm rests for pressure self-relief.
2. Seat depth – The front edge of the seat is recommended to be about 1 inch proximal to the popliteal fossa.  This positions the patient so that the majority of the body weight is on the posterior thighs where there is more soft tissue “padding” and decreases pressure on the ischial tuberosities.
3. Seat height – The typical wheelchair seat height is 19 inches, and needs to be altered for taller or shorter individuals.  If the patient is a self-propeller, the seat needs to be lower so that reaching the floor does not require a slouching posture.  If the patient uses a special cushion, fitting needs to accommodate the additional height.
4. Footrest length – The footplate should be 1-2 inches off the ground for clearance, and positioned so that the hips and knees are at approximately 90 degree angles.  A greater angle (95 degrees) may be needed for SCI patients, but too much flexion increases the pressure on the ischial tuberosities and less than 90 degrees causes forward sliding.  The footrests on most chairs are adjustable, and for anyone spending more than 2 hours in the chair, adjustable rests are a must.
5. Armrest height – the armrests on most chairs are adjustable and should allow the patient to support the forearms on the rests without elevating the shoulders (too high) or causing the patient to lean forward (too low).
6. Backrest height – most chairs have a 16-inch height that is sufficient to support the spine; however, this can change with seat cushions, patient size, and functional activities performed from the chair.[1]

While these principles were developed with wheelchair seating in mind, the same principles can be applied and aimed for with bedside chairs.  Although they are not adjustable, supports (such as pillows, wedges, foot stools, and rolls) can be used to optimally position the patient so that the spine is supported, the weight is on the posterior thighs, the feet are flat on the floor, and the patient is not slouching into a posterior pelvic tilt that adds shear to the sacrum/coccyx.

Other NPUAP recommendations for patients are to avoid elevating leg rests if the patient has tight hamstrings and to allow the patient to sit for 2 hours or less.  If the patient has an existing sacral/coccyx ulcer, sitting is limited to 3 times per day for 60 minutes or less.[2] 

Patients who are able to perform self-relief measures should be taught to do the following:

• Push-up or lift using the arm rests with the feet solid on the floor or footrests, every 30 minutes for at least 30 seconds (needed for adequate reperfusion of the tissues).
• Forward lean, either full forward or partially with the elbows on the knees.
• Side shifts.[3] 

While forward lean and side shifts do not totally relieve the pressure from the buttocks, they do partially relieve the pressure, and as the saying goes, in this case anything is better than nothing.

[1] Sprigle S.  Measure it: Proper wheelchair fit is key to ensuring function while protecting skin integrity.  Advances in Skin and Wound Care.  2014;27(12):561-572.

[2] National Pressure Ulcer Advisory Panel, European Pressure Ulcer Advisory Panel and Pan Pacific Pressure Injury Alliance. Prevention and Treatment of Pressure Ulcers: Clinical Practice Guideline. Emily Haesler (Ed.). Cambridge Media: Osborne Park, Western Australia; 2014.  Available at www.internationalguideline.com/static/pdfs/NPUAP-EPUAP-PPPIA-CPG-2017.pdf

[3] Garcia AD, Sprigle S. Pressure injuries and ulcers. In Hamm R (Ed), Text and Atlas of Wound Diagnosis and Treatment: 2^nd edition.  New York: McGraw Hill Education.  2019, 171-198.  Available at https://accessphysiotherapy.mhmedical.com/book.aspx?bookid=1334.