Groin, buttock or outside: where it hurts tells you which structure it is

TELLING THEM APART / HIP, SI JOINT OR LUMBAR SPINE

Hip joint, sacroiliac joint and lumbar spine all produce pain in overlapping territory, and all three are commonly present at once in the same person. Sorting them out is the difference between a treatment that works and three that do not.

The single most useful question: where exactly?

• Groin — the hip joint, until proven otherwise. Hip pathology refers to the groin and the front of the thigh, and patients often describe it by cupping the side of the hip with the thumb in the groin.
• Buttock — sacroiliac joint or lumbar referral. The SI joint refers below the L5 spinous process, over the joint itself and into the posterior thigh.
• Outside of the hip, tender to lie on — gluteal tendons, not the joint and not the spine. This is the most frequently misdiagnosed of the three.
• Down the leg past the knee, with numbness or tingling — lumbar nerve root.

That map is not infallible, and it resolves more cases than any scan does.

What points to the hip joint

• Groin pain, and loss of internal rotation on examination — the earliest and most reliable sign
• Pain on rising from a chair and putting on shoes and socks
• Deep, aching, sometimes referring to the knee — hip pathology presenting as knee pain is common and catches people out
• No neurological findings

What points to the sacroiliac joint

• Pain centered below the belt line, over the joint, often pointed to with one finger
• Worse with prolonged standing, stair climbing, and rolling over in bed
• Frequently after a lumbar fusion — a fused segment transfers load here, and this is routinely missed because everyone is still watching the fusion
• Multiple provocation tests positive on examination, which is more informative than any one of them

What points to the lumbar spine

• Pain that changes with spinal position — worse in extension suggests facet, worse in flexion and sitting suggests disc
• Radiation past the knee, with dermatomal numbness or myotomal weakness
• Morning stiffness in the back itself
• Reproduced by spinal movement while the hip stays still

Why all three so often coexist

Because they are mechanically linked and they share a terrain.

Mechanically: a stiff hip forces the pelvis and lumbar spine to compensate through range the hip is no longer providing, which loads the SI joint and the facets. Weak abductors let the pelvis drop with each step, and that asymmetry travels upward. Fuse a lumbar segment and the SI joint absorbs what it used to move.

Biologically: hip cartilage, SI joint and facet joints are all synovial tissue answering to the same systemic environment. Adipose-derived inflammatory signaling reaches all of them through the circulation regardless of load — which is why metabolic syndrome tracks with osteoarthritis in joints that never carried unusual weight. Insulin resistance degrades chondrocyte function and stiffens collagen through glycation everywhere at once.

And the social driver: a job that keeps you seated for nine hours deconditions the gluteal complex, shortens the hip flexors and removes the incidental movement that keeps all three structures tolerant. Then the weekend asks them to perform. That is not a discipline failure; it is a workstation and a commute.

Why guessing is expensive

Three structures, three different treatments, and imaging that will find degenerative change in all three in most people past fifty. Treat the one the scan described loudest and you have a one-in-three chance of aiming at the right thing.

This is where symptom-based silos do their damage. The hip goes to one clinician, the spine to another, and nobody is funded to answer the question of which is generating the pain today. The patient absorbs the cost of that gap, usually across several procedures.

How we settle it

• Examination that isolates each structure — hip range with the spine still, spinal movement with the hip still, SI provocation tests as a cluster.
• A neurological screen, which resolves the radicular question quickly.
• Imaging read against the examination, never in place of it.
• A diagnostic block where it remains genuinely ambiguous. Anesthetize one structure; if the pain goes, you have your answer. That is the rule across this site — we do not treat a structure until a block has told us it is the right one.
• A metabolic panel, because three joints failing together is a signal about the terrain rather than three coincidences.

Sorting out which structure it is

My pain is on the outside of my hip. Which is it?

Almost always the gluteal tendons rather than the joint or the spine. Gluteal tendinopathy.

Can hip arthritis cause knee pain?

Yes, and it catches people out regularly. Hip osteoarthritis.

Why did my SI joint start hurting after a fusion?

The fused segment transfers load to it. Extremely common and frequently missed. After spine surgery.

Do I need an MRI first?

Often not. Examination plus a diagnostic block answers more than a scan does here. How we assess.

Related reading

• Hip osteoarthritis
• Gluteal tendinopathy
• Spine and sacroiliac joint
• Shoulder or neck?

A short self-check before you book

It will not replace an examination, but it will tell you which page to read next.

• Point with one finger to the worst spot. Groin says hip. A spot below the belt line beside the tailbone says sacroiliac. The bony point on the outside you cannot lie on says gluteal tendon. Central low back says spine.
• Sit down and cross the painful leg over the other knee. Groin pain on that maneuver points at the hip joint.
• Stand on the painful leg alone for thirty seconds. Reproducing buttock pain points at the sacroiliac joint or the abductors.
• Lean backward. Reproducing central back pain points at the facets. Sit slumped for a minute; if that is worse, it points at the disc.
• Note whether anything goes past the knee, and whether it is numb or tingling as well as painful.

If several of those reproduce it, that is genuinely useful rather than a failed test — it means more than one structure is contributing, which is the common case and changes the order of treatment rather than ruling anything out.

What happens if we get it wrong

We find out at the follow-up, and we say so. A treatment aimed at a structure that was not generating the pain does not fail quietly — it produces no change, which is information. The plan then changes rather than repeats.

Repeating an identical treatment that produced nothing, without revisiting the diagnosis, is the single most common pattern in this population’s history and it is not a plan.