A dent or indentation in your back can come from several different sources, ranging from a completely harmless anatomical variation to muscle changes, fat loss, or a spinal condition worth investigating. The most likely explanation depends on where on your back the dent is, how long it’s been there, and whether it came with any other symptoms.
Small Dimple Near the Tailbone
The most common type of “dent” in the lower back is a small pit or dimple near the tailbone, sometimes called a coccygeal pit. These sit right at the top of the crease between the buttocks, directly over the tip of the coccyx. They’re a normal anatomical variant with no connection to the spinal cord and need no testing or treatment whatsoever. Between 1.8% and 7.2% of newborns have some form of dimple in this area, and many adults carry one without ever noticing until they happen to feel it or see it in a mirror.
A dimple that sits higher up, above the gluteal crease and over the sacrum (the flat bony plate just above the tailbone), is a different story. True sacral dimples can occasionally be associated with underlying spinal cord abnormalities, particularly a condition called tethered cord, where the lower end of the spinal cord is anchored in a way that restricts its movement. If you’ve had a dimple in this area since birth and also experience chronic constipation, urinary problems, or leg weakness, those could be related. Sacral dimples that are larger than about 5 millimeters, that appear alongside unusual patches of hair, birthmarks, or skin tags in the same area, or that seem to drain fluid are the ones most likely to need imaging, typically an MRI.
Muscle Loss on One or Both Sides of the Spine
If the dent sits along one side of your spine rather than at the base, the most likely explanation is a change in the muscles that run parallel to your vertebrae. These paraspinal muscles form the two ridges you can feel on either side of your spine, and when one area loses bulk, it creates a visible groove or hollow. This can happen after a back injury, a period of prolonged inactivity, or as a side effect of nerve damage that prevents the muscle from firing properly.
Research using MRI scans has found a clear link between paraspinal muscle atrophy and disc problems in the lumbar spine. People with herniated discs show higher degrees of fatty infiltration in these muscles compared to people without herniations. The muscle essentially wastes and gets replaced by fat over time, which can make a section of your back look flatter or sunken compared to the surrounding area. If you’ve had chronic back pain, a known disc injury, or surgery on your spine, localized muscle loss is a strong candidate for what you’re seeing.
Fat Loss From Injections or Inflammation
A smooth, round dent that appeared after receiving an injection in the back is almost certainly localized lipoatrophy. This happens when fat cells in the subcutaneous layer shrink and die off in response to medication or injury. Steroid injections are the most well-known trigger, but it’s been documented after other types of intramuscular injections as well. The body’s immune cells infiltrate the fat tissue at the injection site, gradually reducing both the size and number of individual fat cells until a visible depression forms.
These dents are typically painless and clearly defined. They can appear weeks to months after the injection and may or may not fill back in over time. If you recently had a cortisone shot or another injection in or near the area, this is the most straightforward explanation.
Spinal Curvature and Alignment Issues
Scoliosis, a sideways curvature of the spine, can create an uneven surface across the back that looks like a dent on one side and a ridge on the other. The spine’s rotation pulls the ribs and muscles with it, so one side of the upper or mid-back may appear more prominent while the other looks hollow. Common visual signs include uneven shoulders, one shoulder blade that sticks out more than the other, an uneven waistline, or a tendency to lean to one side.
Mild scoliosis is extremely common and often goes unnoticed until someone points it out. More significant curves are usually picked up during adolescence but can also develop or worsen in adulthood, particularly after age 50 when the discs and joints in the spine begin to degenerate unevenly. If the dent seems to follow a diagonal line rather than a single point, or if you notice asymmetry in your shoulders or hips, spinal curvature is worth considering.
Compression Fractures
In older adults, particularly postmenopausal women, a dent or sudden change in the contour of the upper or mid-back can result from a vertebral compression fracture. These fractures happen when a vertebra collapses under normal body weight due to weakened bone from osteoporosis. The hallmark is a forward rounding of the upper back, sometimes called a dowager’s hump, but smaller fractures can also create a localized step-off or depression that you can feel with your fingers. These fractures permanently alter the shape of the spine and can stack up over time, progressively changing posture.
Skin and Connective Tissue Conditions
Less commonly, a dent can originate not in the bone or muscle but in the skin itself. Morphea, a localized form of scleroderma, causes patches of skin to harden and then atrophy, pulling inward and leaving a sunken area. Early on, these patches look reddish or purplish. Over time, the center becomes firm and waxy, and the underlying fat and soft tissue shrink. In deeper variants, the inflammation reaches the fascia and muscle layers, creating more pronounced depressions and scarring. Morphea patches on the back are not rare and can be mistaken for a structural problem when they’re actually a skin condition.
How the Dent Gets Evaluated
The type of imaging your doctor orders depends on what they suspect. Plain X-rays are the standard starting point for evaluating back pain or visible deformity, and they’re good at showing alignment problems, curvature, and compression fractures. CT scans are preferred when a fracture needs to be mapped in detail. MRI is the go-to for anything involving the spinal cord, nerves, discs, or soft tissue, and it’s the required test for sacral dimples that raise concern about tethered cord or other spinal cord abnormalities. For infants, ultrasound can evaluate the spinal cord without sedation or radiation.
If your dent is painless, has been there as long as you can remember, sits right at the top of your gluteal crease, and isn’t accompanied by any hair tufts, skin changes, or neurological symptoms, it’s very likely a normal coccygeal pit. If it appeared recently, keeps changing, sits higher on the back, or comes with leg weakness, numbness in the groin or inner thighs, or changes in bladder or bowel control, those are signs that something structural is going on and imaging can identify the cause.