The best knee pillows for side sleepers

A knee pillow stops your top leg sliding forward and down, which would otherwise twist your pelvis and lower back. With nothing between your knees, gravity pulls the top knee toward the mattress. That adducts the top hip, meaning the thigh angles down and across your body^[4]. Your pelvis rolls forward with it. Cleveland Clinic recommends a pillow between the legs for exactly this reason: it keeps the upper leg from pulling forward and twisting the torso^[5].

Mayo Clinic's advice for back pain is to draw your legs up slightly toward your chest and put a pillow between them, which it says helps align the spine, pelvis and hips^[6]. A 2021 Australian study that filmed people sleeping at home classed side lying with the top thigh forward of the bottom one as a “provocative” posture, because it rotates the spine. When a pillow or duvet held up the top thigh, the researchers counted the posture as supportive instead^[7].

The case for knee pillows rests on biomechanics and clinical advice, not on trials of the pillow itself. We found no study that measured the pelvis or lower spine in side lying with and without a knee pillow, and no trial that compared knee pillows with nothing. Sleep posture research in general is thin: a 2019 scoping review screened 4,186 articles on sleep posture and spinal symptoms and could include only four^[8]. Here is what does exist.

• Home video of sleepers. In the 2021 filming study, adults who woke with low back symptoms spent a median of 135 minutes a night in provocative postures, against 84 minutes for people without symptoms. With 20 people per group, that difference wasn't statistically significant, and the authors say the study may have been too small to detect one^[7].
• Cadaver mechanics. In 18 cadavers, the force of the iliotibial (IT) band pressing on the outer hip bone rose as the hip moved into adduction, reaching 106 newtons at 40 degrees. The same pattern showed up in 12 patients measured during hip replacement surgery^[3]. A clinical review reports the figures as 4 newtons in neutral and 36 newtons at just 10 degrees^[4]. That's why hip specialists care about the angle of your top leg.
• Treatment packages. In a trial of 204 people with gluteal tendinopathy (a common cause of outer hip pain), 77% reported success after eight weeks of physiotherapist-led education and exercise, against 58% after a steroid injection and 29% with wait and see. The education focused on avoiding postures and movements that press the tendons against the hip bone^[9], the same idea behind a knee pillow. But a pillow on its own was never tested.
• Under-knee cushions. The one imaging study we found on leg cushions involved lying on the back. In seven people having lumbar MRI, a cushion under the knees made no appreciable difference to the lower back's curve, so the authors said to use one for comfort alone^[10].

Put together: a knee pillow targets a real mechanical problem, clinicians recommend it, and it's cheap and low-risk. Nobody has shown that it reduces pain on its own. Treat it as a two-week experiment and judge it by how you feel at night and on waking.

If the outside of your hip aches at night, a pillow between your knees is one of the first changes clinicians suggest. Pain over the bony point of the outer hip is called greater trochanteric pain syndrome (GTPS). It used to be blamed on an inflamed bursa, but gluteal tendinopathy is now believed to be the main source^[4]. Either way, the pattern is familiar: pain at the point of the hip that is typically worse at night when you lie on the affected side^[11].

It's common. In a US study of 3,026 adults aged 50 to 79, GTPS affected one hip in 15.0% of women and 6.6% of men, and both hips in another 8.5% of women and 1.9% of men. It was also linked with low back pain and with knee osteoarthritis, so many people shopping for a knee pillow have more than one of these at once^[12].

Why side lying can hurt both hips

Side lying loads the tendons on both sides. The bottom hip is pressed into the mattress. The top hip is compressed too, because the dropped leg pulls it into adduction and the IT band tightens over the bone^[4]. That's why switching sides often just moves the pain.

In a clinical commentary based on limited evidence and their own clinical experience, Alison Grimaldi and Angela Fearon suggest pillows between the knees and shins to cut adduction of the top hip, plus a soft egg-crate overlay to ease pressure on the bottom one. Some people do better rolled a quarter turn toward the stomach, so their weight rests on the front and side of the thigh instead of the bony point. Lying on your back takes the compression off both hips^[4].

Daytime habits count too. The same authors advise against standing with your weight hanging on one hip and sitting with your knees crossed, since both hold the hip in adduction^[4]. Cleveland Clinic's self-care list for gluteal tendinopathy includes both sleeping with a pillow between your knees and not crossing your legs^[13]. Use night pain as your gauge: Grimaldi and Fearon note that changes in night pain often show how the tendon is coping with load^[4].

For low back pain, a knee pillow is a sensible part of a side-sleeping setup, but your mattress probably matters more. Mayo Clinic's side-sleeping advice for back pain has two parts: bend your knees slightly toward your chest, and put a pillow between them^[6].

The strongest trial evidence for back pain in bed is about the mattress. In a double-blind trial of 313 adults with chronic low back pain, a medium-firm mattress beat a firm one for pain in bed (odds ratio 2.36) and disability (2.10) after 90 days^[14]. A 2021 review of 39 articles also favored medium-firm^[15]. A knee pillow can stop your pelvis rolling forward. It can't stop your hips sinking into a sagging mattress.

Sciatica

The Royal Orthopaedic Hospital, an NHS specialist hospital in England, gives specific advice: put a small, firm cushion between your knees when you sleep on your side, or several firm pillows under your knees when you lie on your back^[16]. Choose firm, because a soft pillow flattens and lets the top leg drop again. Most sciatica gets better in a few weeks to a few months^[17]. Some symptoms need emergency care, though, which we list below.

Even if your hips and back feel fine, a knee pillow can help simply by keeping your knees apart. Stacked knees press bony point onto bony point. Pressure-care guides treat bony areas as the most vulnerable, and for people at risk of pressure injuries they recommend pillows between the knees and ankles to keep them from touching^[18].

If your knees are tender from osteoarthritis, a softer pillow may feel better than a dense one. The 5 STARS UNITED is our softest pick. Knee arthritis and outer hip pain often travel together: in the study of 3,026 older adults above, knee osteoarthritis was linked with 3.47 times the odds of GTPS on the same side^[12].

After a knee replacement, Hospital for Special Surgery's guide tells patients not to put a pillow or towel roll under the operated knee, and to support the heel instead so the knee rests straight^[19]. So don't use a knee pillow as an under-knee bolster, and ask your team whether one between the knees is fine when you lie on your side.

After a hip replacement, your surgeon's instructions decide how you sleep, not a product page. The American Academy of Orthopaedic Surgeons says precautions for sitting, bending and sleeping usually apply for the first 6 weeks. They vary from patient to patient depending on the surgical approach, and the risk of dislocation is greatest in the first few months while tissues heal^[20].

After a posterior-approach replacement, for example, Hospital for Special Surgery's guide tells patients not to lie on the operated side. On the other side, they must keep at least two firm pillows between the legs so the legs never cross^[21]. If your hospital gave you a wedge-shaped abduction pillow, use that rather than a regular knee pillow.

The evidence behind these rules is uncertain. A 2020 review of seven studies with 6,900 patients found dislocation rates of 2.2% with hip precautions and 2.0% without after posterior-approach surgery. The difference wasn't significant, but most studies were at high risk of bias^[22]. Once your team clears you, a contoured knee pillow is an easy way to keep your knees apart at home.

Pick the shape by what your top leg does at night: an hourglass for most people, a knee-to-ankle pillow if your top foot drops.

• Hourglass or contour (Contour Legacy, ComfiLife, Cushion Lab): cups both knees, so it stays put better than a flat block. It's the most popular shape. It supports only the knees, so your top shin and foot can still sag toward the mattress.
• Flat rectangle: simple, and it works between the knees or calves, but it slips out more easily.
• Leg pillow (knee-to-ankle): supports the whole lower leg, so the top shin stays level too. That matches the knees-and-shins setup suggested for outer hip pain^[4]. It's also a good fit after hip surgery, if your surgeon approves.
• Strapped designs: an elastic strap keeps the pillow on when you turn. None of our picks include one (the strap in some 5 STARS UNITED photos isn't in the box), so add one if yours keeps escaping.
• Heat and cleaning: solid foam holds warmth between your legs. The Contour Legacy has ventilation holes, and the ComfiLife has a washable zip cover. Our cooling guide covers other fixes.

Thick enough that your top knee sits level with your top hip, so your top thigh runs roughly parallel to the mattress. That position keeps the top hip out of adduction^[4]. Most of our picks hold your knees about 5.5 to 6 inches (14 to 15 cm) apart. Wider hips and taller frames need more, which is why the Cushion Lab Large exists for sleepers about 5′8″ and up.

Check it once in the position you actually sleep in. Lie on your side with your knees bent the way they usually are, and ask someone to look from behind or take a photo. If your top knee still angles down toward the bed, the pillow is too thin or has compressed. If the knee sits higher than your hip, it's too thick. A knee pillow only handles the lower half of your alignment: your head pillow still has to fill the gap between your ear and the mattress, and our guide shows how to measure the loft you need.

Start with a knee pillow if your hips or lower back are the only issue. Choose a body pillow if you also want arm support. A knee pillow is smaller, cooler and easier to keep in place. A body pillow also supports the top arm, which helps with shoulder pain, but takes up more of the bed.

In pregnancy, pelvic girdle pain affects up to 1 in 5 women to some degree, and the NHS suggests a pillow between your legs for extra support in bed^[23]. ACOG suggests side sleeping later in pregnancy with a pillow between the knees, another under the belly, or a full body pillow^[24]. A knee pillow covers the first job. Our body pillow guide covers the U and C shapes that do all three.

A knee pillow is for comfort and alignment. It doesn't treat an injury, an infection or a compressed nerve. The NHS advises seeing a GP if hip pain disrupts your sleep or daily activities, keeps getting worse, or hasn't improved after 2 weeks of home treatment. It advises urgent help for a hot, swollen hip or hip pain with a high temperature. It advises emergency care for severe hip pain after a fall or injury, or if you can't walk or put weight on your leg^[25].

With sciatica, get emergency help if you have it in both legs, weakness or numbness in both legs that is severe or getting worse, numbness around your genitals or anus, or new trouble controlling your bladder or bowels^[17]. Don't wait to see whether a pillow helps.