What is the most common cause of hip pain when lying on the side?

Greater trochanteric pain syndrome (GTPS), which includes trochanteric bursitis and gluteal tendinopathy. Body weight presses on the greater trochanter during side sleeping, irritating the bursa and tendons. GTPS affects women about four times more often than men and peaks between ages 40 and 60.

Is it bursitis or arthritis?

Bursitis/GTPS hurts on the outer side of the hip, is tender to press, and worsens when lying on that side. Osteoarthritis hurts deeper — usually in the groin or front of the thigh — and comes with morning stiffness over 30 minutes and pain when starting to walk.

Can a pillow between the knees really help?

Yes. A firm pillow between the knees keeps the pelvis level and prevents the top leg from rolling the pelvis forward, which reduces tension and pressure on the lower hip's trochanter. It is the single most effective positioning change for side-sleeping hip pain.

What Causes Sharp Pain in Hip When Lying on Side?

Seven Reasons Your Hip Hurts When Lying on Your Side, Ranked

Pain on the outer hip when side-lying is usually a soft-tissue problem around the bony prominence, not the hip joint itself. These are the causes in order of likelihood.

Very common

1. Greater Trochanteric Pain Syndrome (GTPS)

GTPS covers bursitis (inflammation of the fluid cushion over the outer hip) and gluteal tendinopathy (irritation of the tendons that attach there). It affects roughly 10–25% of adults, is about twice as common in women, and peaks at ages 40–60. The hallmark: pain and tenderness on the outer hip, worse lying on that side, climbing stairs, or after sitting. The tendons are overloaded by running, stairs, or long sitting, and the bursa flares in response — side-lying pressure then becomes the trigger that makes it unforgettable at night.

Common

2. Iliotibial (IT) Band Tightness

The IT band is a long band of tissue running from the outer hip to the knee. When it is tight, it presses harder onto the greater trochanter, especially when you lie on the side — the band and bone squeeze the bursa between them. IT band tightness is extremely common in runners and cyclists, and releasing it (foam rolling, stretching, and glute strengthening) often resolves the night pain.

Common

3. Hip Osteoarthritis

While hip OA classically causes deep groin pain, it can also refer aching to the outer hip and buttock, and lying on the affected side compresses the joint. Symptomatic hip OA affects about 10% of people over 55. The distinguishing feature is usually the location: joint pain feels deep and is worse first thing in the morning and with weight-bearing, while GTPS pain is on the bony point and worse with direct pressure.

Less common

4. Gluteal Muscle Strain or Weakness

Weak or strained gluteal muscles (especially gluteus medius) struggle to stabilise the hip, and the tendons attaching at the greater trochanter take the load. This is the mechanism behind most GTPS in runners and in people who sit most of the day. Weakness on one side also makes the hip more sensitive to pressure when lying on it.

Less common

5. Bursitis After Overload or Injury

The trochanteric bursa can flare after a fall on the hip, a long hike, or a sudden increase in exercise. The flare makes the outer hip hot, tender, and painful with pressure — exactly what side-lying delivers. Most flares settle with relative rest and gentle loading within a few weeks.

Less common

6. Referred Pain from the Lower Back

Nerve irritation from the lower spine (lumbar spine referral) can produce aching over the outer hip and buttock that is worse at night. This is considered when the hip itself is not tender to press, or when back pain and leg symptoms travel with it. The treatment targets the back, not the hip.

Rare

7. Fracture or Structural Problems

In older adults, a stress fracture of the femoral neck or a fracture after a fall can present as hip pain that is worse lying on the side. Severe pain, inability to bear weight, or pain after a fall warrants urgent assessment. Other rarer causes include bone conditions and, very rarely, infection — fever with hip pain is an emergency.

How Doctors Sort It Out

Examination: pressing the greater trochanter reproduces GTPS pain; hip rotation tests distinguish joint pain.
Strength testing: side-lying leg raises test the gluteal tendons.
Imaging: ultrasound shows bursal fluid and tendon thickening; X-ray or MRI is used when OA, fracture, or other causes are suspected.

Why the Cause Matters

GTPS is treated with physiotherapy and loading management — not rest alone, and not surgery. Hip OA needs a different plan. And a fracture or infection changes everything. The good news: the most common cause, GTPS, is also one of the most treatable, with exercise-based programmes resolving the majority of cases. See when to see a doctor.

Red Flags Within These Causes

Most causes are treatable, but these versions need prompt attention:

After a fall: hip pain with trouble bearing weight, especially over 65, may be a fracture — urgent assessment.
Fever: hip pain with fever, redness, or swelling can mean infection — an emergency.
Deep groin pain: persistent groin pain with weight-bearing suggests the joint itself and deserves imaging.
Progression: night pain that wakes you every night regardless of position, or weakness in the leg, warrants assessment.

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