Pain localized to the lower back dimple area is a frequent complaint that often leads people to seek information about its cause. The dimples, often known as the Dimples of Venus, are superficial markers of deeper structures. While the dimple itself does not hurt, the structures directly beneath and surrounding it are common sources of discomfort. Understanding the anatomy of this area and the mechanisms of pain can help determine the source of the ache or sharp sensation you are experiencing. The pain is usually musculoskeletal in origin, involving joints, muscles, or nerves, but occasionally, other tissues may be the cause.
Understanding the Anatomy of the Sacral Dimples
The back dimples are shallow indentations on the skin of the lower back, located directly over the posterior superior iliac spine (PSIS). The PSIS is a bony prominence of the pelvis. These dimples are formed by a short ligament connecting the skin to this underlying bony structure.
The pain originates from structures immediately deep to the dimple, most notably the sacroiliac (SI) joint. The SI joint connects the sacrum, the triangular bone at the base of the spine, to the ilium, the large bone of the pelvis. This joint is a major shock absorber and load-transferring structure, making it susceptible to mechanical stress. Surrounding muscles and connective tissues, like the lower lumbar spine and gluteal muscles, also contribute to the area’s stability and can be a source of pain.
Pain Originating from Muscles and Joints
The most frequent source of localized pain in the back dimple region is the sacroiliac joint. Sacroiliac joint dysfunction occurs when this joint moves either too much (hypermobility) or too little (hypomobility), leading to inflammation, a condition known as sacroiliitis. This joint pain is typically felt on one side, just below the L5 vertebra, and may present as a dull ache or a sharp sensation. The discomfort often increases with movements that load the joint, such as standing up from a seated position, climbing stairs, or walking for long periods.
Muscular issues in the surrounding area can also mimic joint pain and cause localized discomfort. Trigger points, or tight knots of muscle fiber, in the gluteus medius muscle are a common culprit. A trigger point just lateral to the PSIS frequently refers pain directly across the belt-line and into the SI joint region.
This referred pain from the gluteus medius can be worsened by activities like walking, prolonged standing, or sleeping on the affected side. Similarly, strain or spasm in the lower back muscles, such as the erector spinae, can cause tension that radiates to the upper buttock area. Heavy lifting, poor posture, or overexertion can lead to these strains, contributing to the persistent ache near the dimple.
Referred Pain and Other Tissue Issues
Pain in the back dimple area can also originate from structures farther away, known as referred pain. Nerve compression, particularly involving the L4, L5, or S1 nerve roots, often presents as sciatica, which is pain that radiates along the path of the sciatic nerve. While true sciatica typically starts in the lower back and travels down the leg, irritation of these nerve roots near the spine can cause a deep, shooting pain initially localized to the dimple area.
A different type of referred pain comes from conditions affecting the kidneys, which are located in the flank area. Kidney stones or infections (pyelonephritis) can cause severe, sharp pain that radiates from the flank towards the lower back and sometimes down to the lower abdomen or groin. Unlike mechanical back pain, this visceral pain is usually constant, intense, and does not change with movement or position.
Localized skin and soft tissue conditions can also cause sharp pain directly at the dimple itself. A pilonidal cyst or abscess forms near the tailbone and can become swollen, painful, and infected. This condition is caused by a hair follicle or debris, resulting in a distinct, localized pain often accompanied by redness, heat, or drainage.
Warning Signs That Require a Doctor Visit
While most pain in the back dimple area is musculoskeletal and manageable, some symptoms suggest a more serious underlying condition that requires immediate medical attention. The sudden onset of severe weakness or numbness in the legs or groin, especially when accompanied by difficulty controlling the bladder or bowels, is a red flag. These symptoms can indicate a compressed spinal cord or a condition like cauda equina syndrome.
Pain that is accompanied by systemic signs of infection, such as fever, chills, or night sweats, requires an urgent medical evaluation. This combination of symptoms may suggest a spinal infection or a severe kidney infection. Additionally, if the pain at the dimple is localized, worsening, and shows signs of a spreading infection, such as pus or significant swelling, a healthcare provider should assess the area for a possible abscess or cyst.
Finally, any pain that is relentlessly severe, is unrelieved by rest or position changes, or worsens significantly at night should be professionally investigated. A medical professional can conduct physical examinations and diagnostic tests to accurately determine the source of the pain and create a tailored treatment plan.