Nursing care
Why shear injures deep tissue when a client slides down the bed
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
Shear happens when the skeleton slides one way while the skin stays stuck to the sheet. The layers between are stretched and distorted, kinking the small blood vessels near the bone. Deep tissue over the sacrum loses blood flow and is damaged even when the surface looks intact, which is why bed angle and lifting technique matter.
What happens in the tissue during a slide
Picture a client with the head of the bed raised steeply. Gravity pulls the trunk toward the foot of the bed, but friction holds the skin of the buttocks against the sheet. The bone moves; the skin does not. Everything in between, including fat, muscle and blood vessels, is pulled sideways and deformed.
Current understanding of pressure injury describes sustained tissue deformation as the starting point. Cells can be damaged by deformation within minutes, followed by inflammation, swelling and loss of blood flow. Deeper injuries arise mainly from high pressure combined with surface shear over a bony prominence, which is why the sacrum and coccyx are classic sites.
Why shear differs from friction and pressure
Friction is the surface rubbing between skin and linen; on its own it tends to abrade the top layer. Shear is the parallel force that travels into deeper layers. In practice the two act together, because friction is what anchors the skin while the skeleton slides. Pressure adds a perpendicular load on top.
The deeper layers near the bone take the worst of it because they cannot move as freely as skin. That is why a shear injury can start below the surface and appear later as purple or maroon discolouration or a deep wound. A client whose skin looked intact yesterday is not proof that no deep damage occurred.
Turn the mechanism into positioning and handling
Pressure injury guidance recommends keeping the head of the bed at or below 30 degrees, or as low as the client's condition allows, because higher elevation increases sliding and sacral shear. Some protocols raise the knee section slightly to limit sliding, provided this does not compromise circulation. Some clients need higher elevation for breathing or aspiration risk, so balance the two plans.
Move clients with a lift sheet, slide sheet or mechanical device and enough staff so the body is lifted rather than dragged. Reposition on a schedule that fits risk, use a 30-degree side-lying tilt rather than lying directly on the hip, and keep linen smooth and dry. Assess sacral and heel skin at each turn and report new discolouration.
Who is most vulnerable to shear and what to watch
Clients who cannot reposition themselves, who slide repeatedly, or who sit propped up for long periods face the greatest shear exposure. Moist skin from sweat or incontinence increases friction, which anchors the skin more firmly while the skeleton moves. Thin, fragile skin and poor circulation lower tolerance further.
Expected findings after repositioning include brief redness that fades. Concerning findings are redness that does not blanch, a boggy or firm area over the sacrum, purple or maroon discolouration, or new pain at a pressure site. These suggest deeper damage and should be documented, reported and folded into a revised positioning and support-surface plan.
Work a hypothetical scenario
Imagine a hypothetical older client who keeps sliding toward the foot of the bed with the head raised steeply for comfort while eating. The nurse finds them slumped. Options are to pull them up by the arms, ask one assistant to help drag them up on the bottom sheet, or lower the head, use a slide sheet with two staff and reposition.
The third option best reduces shear because the body is lifted on a low-friction surface instead of being dragged across linen. Pulling by the arms risks shoulder injury and still drags the sacrum. After eating, the head of the bed can be lowered toward 30 degrees if the client's swallowing and breathing plan permits.
Sources and further reading
Our contemporary understanding of the aetiology of pressure ulcers/pressure injuries (PMC). Tissue deformation, shear at the surface over bony prominences, deep versus superficial injury, and repositioning to cut exposure time.
Backrest position in prevention of pressure ulcers and ventilator-associated pneumonia: conflicting recommendations (PMC). Sliding and shear with higher backrest elevation and the guideline limit of 30 degrees or lowest elevation tolerated.
NHS: Pressure ulcers (pressure sores). Pressure and rubbing as causes, risk factors such as reduced mobility, and repositioning and skin checks for prevention.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our basic care and comfort practice questions are the closest set to what this page covers.
One question from the basic care and comfort set
A nurse is preparing to feed a client who had a stroke and has mild dysphagia. Which action best reduces the risk of aspiration?
Rationale
Upright at 90 degrees with a chin tuck narrows the airway entrance and directs the bolus toward the esophagus — it is the single highest-yield positioning intervention for dysphagia. Thin liquids and straws move fastest and aspirate most easily, side-lying removes the gravity you want, and large bites overwhelm a swallow that is already impaired.
Answer: B
Common questions
Why is 30 degrees the usual head-of-bed limit for pressure injury prevention?
Above about 30 degrees the trunk tends to slide toward the foot of the bed, increasing sacral shear. Clients with aspiration or breathing concerns may need more, so follow the individual plan.
Can shear damage be present if the skin looks intact?
Yes. Shear deforms deeper layers near the bone first, so damage may appear later as purple or maroon discolouration or a deep wound. Keep assessing high-risk sites at each turn.
Is pulling a client up in bed by the arms acceptable?
It is unsafe. It drags the sacrum across the linen, increasing shear and friction, and strains the shoulders. Use a slide or lift sheet, enough staff or a mechanical device.