Lower back pain on one side is usually musculoskeletal: a strained muscle, an irritated facet joint, the sacroiliac (SI) joint where the spine meets the pelvis, or a disc pressing on a nerve root. Because the kidneys sit on either side of the spine, one-sided pain with fever, nausea or blood in the urine needs a doctor rather than a therapist. When those are ruled out, an independent physical therapist near Carmel can test which structure is responsible.
Last reviewed By the Monon Therapy Collective editorial team
- Usual sources
- Muscle, facet joint, SI joint, disc
- Medical warning signs
- Fever, vomiting, blood in urine, rash
- Questionnaire area
- Lower back
Is one-sided lower back pain muscle or something inside?
Most one-sided low back pain changes with movement and position, and that is the strongest sign it is coming from muscles, joints or a disc. Pain that is the same whether you sit, stand, bend or lie down, and that comes with fever, chills, nausea or blood in the urine, points to an internal cause such as a kidney stone or infection, according to MedlinePlus.
MedlinePlus also lists shingles as a cause of one-sided flank pain; a burning band followed days later by a rash is the clue. If your pain fits either of those pictures, see a doctor or urgent care first. Physical therapy is the right route when the pain follows how you move.
Which musculoskeletal causes favor one side of the low back?
Several structures come in pairs, one on each side, so it is common for only one to be irritated. The table lists the usual suspects and how they tend to behave.
| Possible cause | What it tends to feel like | Read more |
|---|---|---|
| SI joint pain | Pain just beside the dimple at the top of the buttock, worse on stairs, rolling in bed or standing on one leg | SI joint pain |
| Facet joint irritation | Ache beside the spine, worse leaning back and twisting toward the sore side | Facet joint pain |
| Disc pressing on a nerve root | Back pain with pain, tingling or numbness down one leg | Sciatica |
| Muscle strain | Sudden grab after a lift or twist, sore to press, eases over days to weeks | Low back pain |
| Deep buttock muscle irritation | Ache in one buttock that can spread down the back of the thigh | Piriformis syndrome |
Why does sleeping on one side or carrying a child make it worse?
Habits that load one side repeatedly are a common reason pain shows up on that side: carrying a toddler on the same hip, a golf swing that always rotates one way, a bag over one shoulder, or a sleeping position with the top leg dropped forward. None of them is wrong, but they concentrate load on one SI joint or one set of facets.
A therapist looks for those patterns and often fixes them with small changes plus strength work for the hips and trunk. The carrying kids without back pain guide and the golf season back pain guide show what that looks like for two common Carmel routines.
What should I note before a one-sided back assessment?
A few observations help the therapist sort the causes faster. Note them over two or three days.
- Point to the sorest spot: beside the spine, on the bony ridge of the pelvis, or in the buttock?
- Does leaning back and toward the painful side reproduce it?
- Is there any pain, tingling or numbness below the knee?
- Do stairs, getting out of the car or standing on that leg to put on pants bother it?
- Any fever, urinary changes or a rash, even mild? Tell a doctor first.
What tests does a therapist use for pain on one side of the spine?
Expect movement testing in every direction, a neurological screen of reflexes, strength and sensation, nerve tension tests such as a straight-leg raise, and a cluster of pelvic provocation tests used for the SI joint. A therapist also checks hip rotation, because a stiff hip often pushes extra twist into one side of the low back.
The plan usually pairs a direction-specific movement strategy with progressive trunk and hip strength. Spinal manipulation needs a physician order or referral in Indiana, so most therapists start with exercise and other manual techniques. Begin with the lower back questionnaire.
One-sided back pain that needs a doctor, not a therapist
- Fever, chills, nausea or vomiting with the pain.
- Blood in the urine or painful, frequent urination.
- A burning band of pain followed by a blistering rash.
- Numbness in the groin or new bladder or bowel trouble: emergency care.
- Constant pain unchanged by any position or movement.
If you think it is an emergency, call 911.
