Yes, you can develop sacroiliac (SI) joint pain after a hip replacement, and it is a recognized source of persistent pain in roughly 5% to 15% of people who are dissatisfied after the operation. The two joints are mechanically linked through the pelvis: changing how the hip loads the bone alters the forces crossing the SI joint. Sometimes the SI joint was the hidden pain generator all along.
The Load-Transfer Mechanism
Your pelvis is a closed ring. The hip socket (acetabulum) sits on one side, the SI joint on the other, and the pubic symphysis closes the loop in front. Force traveling up from the leg crosses the hip, then splits through the bone of the ilium toward the SI joint and the spine. Surgeons call this the pelvic load path.
When a hip is replaced, three things change at once. First, leg length usually changes, often by 2 to 10 millimeters. Second, the offset of the femoral component shifts how far the thigh sits from the midline. Third, the orientation of the cup alters which hip positions feel stable. Each change moves the line of force through the pelvis.
The SI joint capsule contains dense ligamentous tissue and a small synovial cleft. It tolerates compressive load well but responds poorly to shear, the sideways sliding force created when one side of the pelvis rotates relative to the other. A leg-length change of even a few millimeters tilts the sacrum and converts some compression into shear. Over months of walking, that shear irritates the joint.
There is also a nerve explanation. The SI joint is innervated by branches from L4 through S3, and the hip capsule shares upper lumbar and sacral supply. Pain signals from an irritated hip can sensitize the same spinal circuits, a process called convergence. After the hip is fixed, the circuit stays primed, and a mildly irritated SI joint now reads as pain. This is why some patients feel pain move rather than disappear.
Plain language: the hip and the SI joint sit on opposite sides of the same bony ring, so fixing one changes the strain on the other.
How Common, and How Often Is the SI Joint the Real Cause
Persistent pain after total hip arthroplasty affects about 7% to 23% of patients in published cohorts, depending on how pain is defined. Of those with unexplained pain, the SI joint is implicated in a meaningful minority. Studies using image-guided SI joint injections report that 10% to 27% of patients with persistent hip-area pain after arthroplasty obtain substantial relief from an SI joint injection, which implicates the joint as at least part of the source.
Incidence of new SI joint pain specifically attributable to the surgery is harder to pin down. Retrospective series vary widely, from single digits to about 20%, because definitions differ and because imaging findings do not correlate tightly with symptoms. Up to a third of asymptomatic adults show some SI joint degeneration on MRI, so a scan finding alone proves nothing.
Rates of hip replacement itself give context. Over 450,000 total hip replacements are performed in the United States each year, and the number is projected to keep climbing as the population ages. Even a low single-digit rate of new SI joint pain translates into thousands of cases annually.
One counterintuitive detail: the SI joint can hurt more after a technically excellent hip replacement than after a mediocre one, because a well-functioning implant lets the patient walk farther and load the pelvis more. Function unmasks the joint.
Timeline: When SI Joint Pain Appears
| Time after surgery | Typical pattern | What it suggests |
|---|---|---|
| 0–2 weeks | Groin or buttock pain, diffuse | Expected postoperative inflammation |
| 2–6 weeks | Pain localizes to buttock, worse with standing | Early load transfer, gait adaptation |
| 6 weeks–3 months | Pain with prolonged standing, stair climbing | SI joint load intolerance emerging |
| 3–6 months | One-sided low back/buttock pain, referral to thigh | Persistent SI joint dysfunction |
| 6–12 months | Pain stable or slowly improving | Gait retraining window |
| Beyond 12 months | New or worsening pain | Reassess; consider other sources |
| Any time | Fever, wound drainage, sudden severe pain | Red flag; urgent evaluation |
The pattern matters. Pain that is worst in the first days and steadily improves is normal. Pain that appears or worsens after three months, or that changes character, deserves a fresh evaluation rather than reassurance.
Edge Cases That Shift the Risk
Leg-length discrepancy is the strongest mechanical factor. A postoperative difference greater than 5 millimeters is associated with higher rates of low back and SI joint pain; differences beyond 10 millimeters are more likely to need intervention. Templating aims for within 5 millimeters, but soft tissue and component seating add variance.
Stiffness of the hip in rotation matters too. If the replaced hip cannot internally rotate beyond about 10 to 15 degrees, the pelvis must rotate instead during walking and turning. That excess pelvic rotation loads the SI joint directly. A hip that is stable but stiff can therefore protect the implant and punish the SI joint.
Patients with pre-existing lumbar fusion, scoliosis, or a prior SI joint injury carry higher risk. When the spine is fused, the SI joint absorbs motion it was not designed to carry. Adding a hip replacement changes the remaining mobile segment, and the SI joint often becomes the pressure-release valve.
Inflammatory arthritis behaves differently. In ankylosing spondylitis and related conditions, the SI joints are often already involved, and surgery on the hip does not treat that process. Pain may persist or flare independent of the implant.
Revision surgery carries higher stakes. Scarring, altered anatomy, and greater leg-length change make the SI joint more vulnerable than in a primary replacement.
Misconceptions Worth Retiring
The first misconception is that pain after hip replacement must come from the implant. Loosening and infection are serious but uncommon; mechanical low back and SI joint pain are far more frequent explanations for buttock pain. A normal X-ray does not rule out an SI joint source, because the SI joint is poorly visualized on plain films and its cartilage is thin.
The second is that the SI joint only hurts in the buttock. Referral patterns include the groin, the anterior thigh, and the lateral hip, which is precisely where patients expect hip pain. Location alone cannot separate the two.
The third is that imaging settles the question. MRI can show edema, but edema appears in asymptomatic joints and can be absent in painful ones. The professional caveat is that the reference standard is a diagnostic injection of local anesthetic into the joint under image guidance, with a temporary but substantial reduction in pain. Even that test has false positives and depends on technique.
The fourth is that a leg-length difference always needs correction. Small differences are common, often well tolerated, and correcting them with a shoe lift or revision carries its own risks. The decision depends on symptoms and function, not the number alone.
Practical Actions and Thresholds
Track the pattern. Log pain location, timing, and what provokes it for two weeks. Pain that is worst with prolonged standing and eases with sitting or lying down points toward the SI joint. Measure the difference. Ask for a standing pelvic X-ray or a clinical block test if you suspect a leg-length discrepancy. A difference over 5 millimeters with symptoms warrants a conversation; over 10 millimeters is more likely to need action. Try a shoe lift first. A 3 to 6 millimeter lift on the shorter side is a low-risk trial for 4 to 6 weeks before considering anything invasive. Retrain the gait. Ten minutes of daily step practice, focused on equal step length and pelvic leveling, plus gluteal and core strengthening three times per week for 6 to 8 weeks, addresses the muscular side of load transfer. Get the right injection. If pain persists beyond 3 months despite these steps, ask about an image-guided SI joint injection. Relief that lasts hours to days confirms the diagnosis; relief lasting weeks suggests the joint is a major contributor. Escalate carefully. Radiofrequency ablation of the SI joint nerves is an option for confirmed cases, but evidence for durable relief is moderate at best.
Red flags that require urgent contact with your surgical team rather than SI joint management:
Fever above 101°F (38.3°C) or chills Wound drainage, redness, or separation Sudden severe pain or inability to bear weight Calf swelling, warmth, or shortness of breath New numbness, weakness, or bowel or bladder changes
Limits of the Evidence
The honest position is that the link between hip replacement and SI joint pain is plausible, mechanistically supported, and clinically observed, but not precisely quantified. Studies are mostly retrospective, definitions of SI joint pain vary, and diagnostic injections are imperfect. No trial has randomly assigned patients to leg-length targets and measured SI joint pain outcomes.
The clinical recommendation is to treat persistent buttock or low back pain after hip replacement as a diagnostic puzzle, not a foregone conclusion. Evaluate the hip, the spine, and the SI joint in that order, using history and examination first and injections when the picture is unclear. Most patients improve with time, gait retraining, and, when needed, targeted injection. A minority need more, and the ones who do are usually identifiable by a clear mechanical driver: a leg-length difference, a stiff hip, or a fused spine above.
References: American Academy of Orthopaedic Surgeons clinical practice guidance on hip arthroplasty; National Institute of Arthritis and Musculoskeletal and Skin Diseases materials on hip replacement; published cohort data on persistent pain after total hip arthroplasty and diagnostic SI joint injection response rates.