Why Does My Back Hurt on One Side Only?
Back pain on one side only usually means the muscles, joints or ligaments on that side are under more stress than the other. This often happens because the pelvis is tilted or rotated, one leg is slightly longer, or a single joint such as the SI joint is irritated. A left lower back strain or right-sided ache is rarely about that spot alone. It is usually part of a wider alignment pattern.
Key takeaways
- One-sided back pain is commonly caused by asymmetry in your pelvis, hips or legs, not just a local muscle problem.
- Lying-down scans can miss these alignment issues because gravity and body weight are removed.
- A standing, weight-bearing image of your whole body can show where the imbalance actually starts.
- Most one-sided back pain is not dangerous, but certain symptoms need urgent medical attention.
What does one-sided back pain actually mean?
It means the discomfort sits clearly on the left or right of your spine rather than across the middle. You might describe it as a left lower back strain that tightens after sitting, or a deep ache on the right that flares when you stand up. The pain can feel muscular, sharp, or like a constant dull pull.
Your spine is not a separate structure. It sits on top of your pelvis, which sits on top of your legs. If anything in that chain is uneven, the muscles and joints on one side of your back end up doing more work. Over time, that side protests.
How do you know if your one-sided back pain is alignment-related?
Alignment-related pain tends to follow patterns. It is usually worse on the same side every time, changes with posture or activity, and does not fully go away with rest alone. Here are the common signs.
The ache is consistently left-sided or right-sided, not alternating.
Gravity loads the uneven side more, so symptoms increase upright.
The muscles on that side feel constantly tense, even after stretching.
You notice one hip sits higher, or your belt line is not level.
What causes pain on one side of your lower back?
Several things can load one side of your back more than the other. The most common causes relate to how your skeleton lines up when you are standing and moving.
When one side of the pelvis sits higher, the spine curves to compensate. This is a common and often hidden cause. Learn more about lateral pelvic tilt.
Even a small difference in leg length shifts your weight to one side. Read about leg length discrepancy.
The sacroiliac joint connects pelvis to spine. When it is inflamed on one side, pain focuses there. See our page on SI joint dysfunction.
A twist in the pelvis loads the muscles on one side unevenly. Explore how a rotated pelvis affects your back.
Other possibilities include a mild scoliosis (a sideways curve in the spine), muscle guarding where one side tightens to protect an area, or strain in the quadratus lumborum, a deep muscle that runs from the pelvis to the ribs on each side.
Is one-sided back pain related to the kidneys?
Sometimes. Kidney pain tends to sit higher, under the ribs towards the back, and may come with other symptoms like a change in how you wee, a fever, or feeling generally unwell. If you have any of these alongside your back pain, see your GP. If the pain is lower and changes with movement or posture, it is more likely to be musculoskeletal.
When should you see a doctor urgently for one-sided back pain?
Most one-sided back pain is not dangerous. However, certain signs need prompt medical attention. Contact your GP, call 111, or go to A&E if you have any of these alongside your back pain:
- Numbness or tingling in your legs, groin or buttocks
- Weakness in one or both legs
- Loss of bladder or bowel control
- Sudden, severe pain that woke you from sleep and does not ease
- Unexplained weight loss or a fever
These could point to something that needs urgent investigation. Do not wait for a scan. Seek medical help straight away.
How does a standing scan show what lying-down imaging misses?
Standard X-rays, CT and MRI are usually done lying down. When you lie flat, gravity is removed, your muscles relax, and your skeleton settles into a neutral shape. A tilt, rotation or leg length difference that causes your pain while standing may not appear at all.
Standing EOS imaging captures your entire skeleton from head to feet in a natural, weight-bearing position. It shows exactly how your pelvis, spine and legs line up under real-world conditions, the way you actually stand and move. If one side is taking more load, it shows clearly.
Lying-down scans are excellent at showing individual structures, but they remove the very forces that create your symptoms. A pelvic tilt or subtle leg length difference may flatten out on the table, so the report comes back looking normal even though you are still in pain.
At ScanAlign, full-body standing imaging uses EOS technology, which delivers about 90% less radiation than a standard X-ray, around ten times less. The scan takes just a few seconds and captures a single, joined-up picture of how your whole body lines up.
When MRI is the better choice: EOS shows bones, joints and alignment. If your clinician suspects a disc problem, a trapped nerve, or soft-tissue damage, MRI is usually the better tool. The two are complementary, not competing.
If your back pain keeps coming back on one side and scans have not explained why, a standing alignment assessment may give you the answer.
Book a free video consultationWhat helps with one-sided lower back pain?
The right approach depends entirely on what is causing the asymmetry. Without knowing the underlying pattern, treatments tend to provide only temporary relief. Here is the general picture.
- Accurate diagnosis first. Understanding whether the problem starts at your pelvis, legs or spine changes the direction of treatment completely.
- Targeted physiotherapy. Once the pattern is clear, a physiotherapist can strengthen the weaker side and release the overworked side, rather than treating both sides equally.
- Orthotics or heel raises. If a leg length difference is involved, a simple shoe insert may rebalance the load.
- Activity modification. Avoiding prolonged one-sided postures (always crossing the same leg, carrying a bag on the same shoulder) can reduce flare-ups.
ScanAlign is a diagnostic imaging clinic. We do not provide treatment ourselves, but the detailed alignment report can help your physiotherapist, osteopath or consultant plan the right next step. If you would like to book a full-body standing scan, we start with a free video consultation to make sure it is appropriate for you.
Frequently asked questions about one-sided back pain
Left-sided back pain, sometimes called a left lower back strain, often points to asymmetry in your pelvis or a slight difference in leg length that shifts your weight to that side. The muscles and joints on the left end up working harder.
The mechanism is the same. Whether the pain is on the right or the left depends on which side is overloaded. The key question is why one side carries more stress, and that usually comes down to alignment.
Possibly. Kidney pain tends to sit higher, under the ribs, and may come with fever, nausea or changes in urination. If you have these symptoms, see your GP. If the pain is lower and changes with movement, a musculoskeletal cause is more likely.
Yes. A lateral pelvic tilt raises one side of the pelvis, which forces the spine to compensate sideways. The muscles on the lower side often become overworked and painful.
No. ScanAlign is a private, self-pay clinic. You can refer yourself. We begin with a free video consultation to discuss your symptoms and confirm a scan is appropriate.
EOS uses about 90% less radiation than a standard X-ray, around ten times less. This makes it one of the lowest-dose imaging options available.
A standard X-ray can show bones and joints, but it usually focuses on one area and is often taken lying down. It may miss the broader alignment picture that explains why one side is overloaded.
The scan itself takes just a few seconds. The full appointment, including positioning and explanation, is longer, but the actual imaging is very quick.
It shows the full chain from your feet to your head in one image, under weight-bearing conditions. You can see whether the pelvis is tilted, whether the legs are different lengths, and how the spine compensates, all the things that explain why one side hurts.
We do not list prices on individual pages. You can find current pricing and what is included on our FAQs and cost page.
Still wondering why one side keeps hurting?
A free video consultation lets you talk through your symptoms and find out whether a standing alignment scan could help.
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- NHS. "Back pain." nhs.uk. Accessed 2025.
- Illés T, Somoskeöy S. "The EOS imaging system and its uses in daily orthopaedic practice." International Orthopaedics, 2012;36(7):1405-1411.
- Khamis S, Yizhar Z. "Effect of feet hyperpronation on pelvic alignment in a standing position." Gait & Posture, 2007;25(1):127-134.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.