Why Does My Back Dimple Hurt?

Pain at or near a back dimple almost always comes from the structures underneath the skin, not from the dimple itself. Back dimples, sometimes called Venus dimples, sit directly over the posterior superior iliac spine (PSIS), a bony landmark where the pelvis and sacrum meet at the sacroiliac joint. That joint, along with a web of ligaments, small nerves, and nearby muscles, is the real source of trouble. One study that specifically examined whether having Venus dimples correlates with low back pain found no statistically significant relationship between the two, even though the dimples do mark a spot where several pain-prone structures converge.

What Sits Beneath a Back Dimple

Each back dimple marks the spot where the iliac bone of your pelvis juts closest to the skin surface. Directly beneath it lies the sacroiliac (SI) joint, a large, irregularly shaped joint that transfers load between your spine and your legs every time you walk, sit, or twist. Thick ligaments bind the joint on all sides. Small sensory nerves called the superior and middle cluneal nerves cross over the iliac crest nearby on their way to the skin of the buttock. And muscles like the erector spinae and multifidus attach to the same bony ridge. When any of these structures gets irritated, inflamed, or compressed, you feel it right where that dimple sits.

Interestingly, people with Venus dimples tend to have a steeper pelvic incidence angle and more sagittally oriented facet joints in the lower spine, which can influence how forces travel through the region.¹ That doesn’t mean the dimple causes pain, but it does hint that the bony geometry in someone with pronounced dimples may distribute mechanical stress slightly differently than in someone without them.

Sacroiliac Joint Dysfunction

The single most common reason for pain pinpointed right at a back dimple is SI joint dysfunction. The SI joint doesn’t move much under normal circumstances, but when it develops too much or too little motion, or when the joint surfaces become inflamed, it generates pain that patients consistently localize with one finger to the PSIS. Clinicians have formalized this observation into the Fortin finger test: if you can point to the spot with a single finger and that spot falls within about a centimeter of the PSIS, the SI joint is a likely culprit. In a study validating this test, all 16 patients identified by the finger-pointing sign went on to have positive provocation injections confirming SI joint pathology.²

SI joint pain often worsens with activities that load the joint asymmetrically. Climbing stairs, rolling over in bed, standing on one leg, or transitioning from sitting to standing can all provoke it. Some people also notice groin pain or pain that radiates into the upper buttock, though it rarely travels below the knee the way sciatica does. That pattern helps distinguish it from a disc problem higher up.

Ligament Strain and Soft Tissue Injury

The SI joint is held together by some of the strongest ligaments in the body, and those ligaments can become a pain source in their own right. The interosseous sacroiliac ligament, the sacrotuberous ligament, and the sacrospinous ligament all anchor the sacrum to the pelvis, and strain or micro-tearing in any of them produces pain that overlaps with SI joint dysfunction. A diagnostic scoring system for posterior ligament pain found that tenderness at the PSIS and over the sacrotuberous ligament, combined with pain while sitting and groin discomfort, were among the strongest predictors of ligament-origin pain.³

Ligament injuries here can follow a specific event, like a fall onto the buttock, a heavy deadlift with poor form, or a sudden twist. But they also develop gradually from repetitive loading, especially in runners or people who spend long hours on their feet with uneven footing. The tricky part is that ligament pain and joint pain overlap so thoroughly that separating the two often requires an injection that temporarily blocks pain signals from the joint itself.

Cluneal Nerve Entrapment

A less well-known source of back-dimple pain involves the cluneal nerves. These small sensory nerves originate from the upper lumbar and sacral spine and travel laterally over the iliac crest on their way to supply sensation to the skin of the buttock. Where they cross the bony ridge, they pass through tight tunnels of connective tissue. If those tunnels narrow, or if scar tissue or muscle tension compresses a nerve against the bone, you get a burning, shooting, or tingling pain right at the dimple area that can radiate into the buttock.⁴

Cluneal nerve entrapment is probably underdiagnosed. The pain it produces mimics SI joint dysfunction so closely that many people go through rounds of SI-focused treatments without improvement. A key clue is that the pain is often more superficial in character, and pressing firmly over the iliac crest itself, rather than deeper over the joint, reproduces it. Leaning against a hard chair back or wearing a tight belt can also set it off. When entrapment is confirmed, treatment may involve a nerve block for short-term relief or a surgical decompression for stubborn cases.

Sacral Stress Fractures

If you’re a runner or endurance athlete and the pain came on gradually without an obvious injury, a sacral stress fracture is worth considering. These fractures occur in the sacral ala, the wing-shaped portion of the sacrum that sits just medial to the SI joint, and they produce deep, aching pain in the back-dimple region that worsens with impact activities and eases with rest. Standard X-rays usually miss them. MRI is the gold standard, showing bone marrow edema before a visible fracture line appears.

Sacral stress fractures are frequently misdiagnosed because the symptoms are vague and overlap with SI joint dysfunction. Some studies estimate that in athletes, sacral stress fractures may account for as many as one in five stress injuries, a far higher proportion than most clinicians expect.⁵ Risk factors include high training volume, relative energy deficiency (formerly known as the female athlete triad, though it affects men too), and low bone density. A case report described a male long-distance runner in his late 20s who endured a month of undiagnosed right-sided low back and buttock pain after a marathon before MRI finally revealed the fracture.

Referred Pain from Higher in the Spine

Sometimes the problem is not at the dimple at all, even though that’s where you feel it. A herniated disc in the lower lumbar spine can send pain signals downward into the buttock and PSIS area through a mechanism called referred pain. Unlike sciatica, which typically shoots down the leg in a defined line, referred buttock pain from a disc tends to be more diffuse and dull. Research on patients who underwent disc surgery found that referred buttock pain improved substantially in the first three months after the disc was addressed.⁶

Referred pain from a disc problem usually comes with other clues: stiffness in the lower back, pain that worsens with prolonged sitting or forward bending, and sometimes numbness or tingling in the leg. If your back-dimple pain started around the same time as leg symptoms, or if it gets worse when you cough or strain, a lumbar disc issue deserves attention before the SI joint gets all the blame.

Pregnancy and Pelvic Girdle Pain

Pregnancy is one of the most common contexts in which people first notice pain at the back dimples. The combination of weight gain, a shifting center of gravity, and hormonal changes that loosen ligaments creates a perfect storm for posterior pelvic pain. Many pregnant people feel sharp soreness right at one or both PSIS landmarks, especially when walking, turning in bed, or standing on one leg to dress.

The popular explanation is that the hormone relaxin loosens the SI joint too much, but the evidence for that is less clear than most people assume. A systematic review of high-quality studies found low evidence for an association between pregnancy-related pelvic girdle pain and relaxin levels.⁷ Biomechanical factors, including the increased load on the pelvis and changes in posture as the belly grows, are probably more important drivers of pain than relaxin alone. The good news is that for most people, the pain resolves within a few months postpartum as the pelvis restabilizes.

How Clinicians Figure Out What’s Wrong

Because so many structures overlap at the back-dimple spot, diagnosis usually involves a combination of hands-on tests rather than a single scan. Provocation tests for the SI joint involve applying force in specific directions to stress the joint and see whether it reproduces your pain. These tests have been validated as reliable indicators of SI joint pathology.⁸ Among them, the FABER test (flexion, abduction, and external rotation of the hip) and the thigh thrust test are particularly useful, and combining the two improves diagnostic accuracy beyond what either achieves alone.⁹

If hands-on testing is ambiguous, a diagnostic injection of local anesthetic into the SI joint under imaging guidance can settle the question. If the pain disappears temporarily after the injection, the joint is confirmed as the source. MRI is reserved for cases where a fracture, inflammatory condition, or disc problem is suspected. Plain X-rays are rarely helpful for soft tissue or joint-surface problems in this area, though they can show bony abnormalities or sacral fractures in some cases.

When Prolonged Sitting Makes It Worse

Many people with back-dimple pain notice that it flares during or after long stretches of sitting, whether at a desk, in a car, or on a couch. There’s a biomechanical reason for that. When you sit, the load on the SI joint and its ligaments shifts compared to standing, and the posterior ligaments can be placed under sustained tension, especially if you slouch or sit asymmetrically. Research on adolescents found that both thoracic kyphosis and lumbar lordosis increased with prolonged sitting over just 30 minutes, and those with existing low back pain showed larger postural changes than those without.¹⁰

If sitting is your main trigger, a few adjustments can help. Keeping your feet flat on the floor with your knees roughly level with your hips takes some load off the posterior pelvis. Avoiding crossing your legs removes an asymmetric force on the SI joint. And standing up to move around every 30 to 45 minutes interrupts the cumulative strain before it builds to the point of pain. Some people also benefit from a small cushion or lumbar roll that prevents the pelvis from tucking under while seated.

Leg Length Differences and Pelvic Tilt

A structural asymmetry that often goes unnoticed is a difference in leg length. Even a modest discrepancy tilts the pelvis laterally, which loads one SI joint more than the other. Research measuring the effect of artificially created leg length differences found that lateral pelvic tilt increased in a straight-line relationship with the discrepancy, and the lumbar back muscles on the longer-leg side worked harder to compensate.¹¹ Over months and years, that asymmetric loading can irritate the SI joint, strain the ligaments, and create persistent one-sided back-dimple pain.

Not everyone with a leg length difference develops pain, and the threshold seems to vary. In that study, lumbar muscle activity spiked non-linearly once the discrepancy exceeded about 34 millimeters, suggesting a tipping point beyond which the body can no longer compensate smoothly. If your pain is consistently one-sided, it’s worth having your leg lengths measured. A simple heel lift in one shoe can correct smaller discrepancies, while larger ones may need a full shoe modification.

Treatment Options Beyond Rest

For most causes of back-dimple pain, a combination of activity modification, targeted exercise, and sometimes manual therapy provides relief. Strengthening the gluteal muscles and deep core stabilizers helps support the SI joint and reduces the load on passive structures like ligaments. Physical therapy programs that include motor control exercises, hip strengthening, and gradual return to loading are the first-line approach for SI joint dysfunction, ligament strain, and postpartum pelvic pain alike.

Pelvic belts are another low-tech option. A computational study found that wearing a pelvic belt relieved strain on several SI joint ligaments, particularly the sacrospinous, sacrotuberous, and interosseous ligaments.¹² The actual motion change was small in absolute terms, but many patients report meaningful symptom relief. Pelvic belts are especially popular during pregnancy and in the early postpartum period.

When conservative measures fail, interventional procedures become an option. Radiofrequency ablation targets the small nerves that carry pain signals from the SI joint. A systematic review of randomized controlled trials found that radiofrequency treatment of the relevant lumbar dorsal rami and sacral lateral branches provided significant pain relief and functional improvement.¹³ The nerves eventually regrow, so the relief is not necessarily permanent, but it often lasts months to a year or more and can be repeated.

When Pain Persists and the Nervous System Gets Involved

Some people go through all the usual treatments and still hurt. When back-dimple pain has been present for months, the nervous system itself can become part of the problem. Central sensitization is a process in which the spinal cord and brain amplify pain signals, so that stimuli that shouldn’t hurt, or that used to be tolerable, now register as painful. In people with chronic low back pain, markers of central sensitization correlated strongly with depression, anxiety, and pain catastrophizing, and those psychological factors predicted sensitization levels more powerfully than pain intensity itself did.¹⁴

This doesn’t mean the pain is imaginary. Central sensitization is a measurable neurological change. But it does mean that for chronic cases, addressing only the joint or the ligament may not be enough. Multidisciplinary approaches that combine physical therapy with cognitive behavioral strategies, stress management, graded exposure to movement, and sometimes medication aimed at calming the nervous system tend to produce better outcomes than any single treatment alone. If you’ve had back-dimple pain for more than three months and standard treatments haven’t helped, asking your provider about central sensitization is a reasonable step.

Sacral Dimples Versus Venus Dimples

A quick note on terminology, because the internet sometimes muddles these. Venus dimples (or back dimples) are the paired indentations over the PSIS in the lower back. Sacral dimples are a completely different thing: small pits or depressions found at the very base of the spine near the tailbone, most commonly noticed in newborns. Sacral dimples in infants are usually harmless, with the reported incidence of abnormal underlying pathology ranging from zero to about three percent when the dimple is small, midline, and close to the anus.¹⁵ Larger, deeper, or off-center sacral dimples in babies can sometimes indicate spinal cord abnormalities and warrant imaging. If you’re an adult whose “back dimple” pain is actually at the very tip of the tailbone rather than a few inches higher at the bony prominence on either side, you may be dealing with a coccyx issue rather than an SI joint problem, and that requires a different evaluation.

The Human Pelvis and Why This Spot Is Vulnerable

It’s worth understanding why the back-dimple area is such a pain hotspot in the first place. The human pelvis is an evolutionary compromise. When our ancestors transitioned to upright walking, the pelvis had to narrow and reorganize to support the full weight of the torso directly over two legs instead of distributing it across four. The modern human pelvis is narrower than that of earlier hominins, with a more circular birth canal and less flaring of the iliac wings.¹⁶ That redesign concentrated enormous forces through the SI joint and the PSIS, a region that in a four-legged animal would handle far less compressive load.

The result is a joint that absorbs massive forces during every stride, squat, and twist, bound together by ligaments that are among the thickest in the body, and threaded with small nerves that have very little room to spare. When you add modern habits like sitting for most of the day, running on hard surfaces, or carrying asymmetric loads, you’re applying stresses to a structure that evolution shaped for walking on varied terrain with frequent rest. The back dimple, charming as it looks, is simply the surface marker of a biomechanical pressure point.