Yes. The sacroiliac joint at the back of the pelvis can start to hurt after a hip replacement, and in one exam-based study roughly 3 in 10 people showed signs of trouble there in the first few months. That means buttock or low back pain after surgery doesn’t always point to the new hip itself.1PubMed. Functional impairment of the sacroiliac joint after total hip replacement This kind of pain is often a short-term reaction while the body adjusts, and it usually responds to treatment rather than another operation. It is also easy to mistake for hip or spine pain, so pain that lingers deserves a specific check.
How Common SI Joint Pain Is After Hip Replacement
The sacroiliac (SI) joint links the base of the spine to each side of the pelvis, and you have two of them. They barely move, but they carry the weight of your upper body down into your legs.
When 50 people were examined within 3 months of hip replacement, nearly 30% had a poorly working SI joint on one side.2PubMed. Functional impairment of the sacroiliac joint after total hip replacement Most of these were on the same side as the new hip, with a few on the opposite side.3The Journal of Bone and Joint Surgery. Sacroiliac joint: function, pathology, treatment, and contribution to outcomes in spine and hip surgery This may explain some of the buttock and low back pain people report after the operation.4PubMed. Functional impairment of the sacroiliac joint after total hip replacement Many of those people, though, already had wear in the SI joint before surgery.5The Journal of Bone and Joint Surgery. Sacroiliac joint: function, pathology, treatment, and contribution to outcomes in spine and hip surgery
That earlier wear matters to you. If your SI joint was already worn, surgery may simply reveal pain that the bad hip had been masking, so the pain is not necessarily a sign the operation went wrong. Telling your surgeon about any back or buttock pain you had before surgery helps them judge the cause.
The figure comes from physical examination, so it shows how often the joint shows signs of trouble, not how many people need treatment. The study was also small, so the exact percentage is a rough guide.
SI joint pain usually sits low, over the dimple at the back of the pelvis, often on one side. It can spread into the buttock or the back of the thigh, and rarely below the knee. It tends to flare when you stand up from a chair, climb stairs, or roll over in bed. Hip-joint pain more often shows up in the groin or front of the thigh.
Why a New Hip Can Strain the SI Joint
Pelvic tilt is how far your pelvis rocks forward or backward when you stand. People whose pelvis tipped well forward before surgery often find it settles backward afterward, while people whose pelvis already tipped backward usually see little change.6PubMed. Changes in pelvic tilt following total hip arthroplasty So the bigger the tilt before surgery, the bigger the shift the SI joints must absorb.7PubMed. Changes in pelvic tilt following total hip arthroplasty This is a tendency across groups, not a prediction for one person, so a large tilt does not guarantee pain.
Sitting is another stress. Normally, sitting down makes the hip bend while the pelvis rolls backward and the low back flattens.8PubMed Central. The Impact of Spinopelvic Mobility on Arthroplasty: Implications for Hip and Spine Surgeons People with SI joint pain after hip replacement showed about twice as much movement at the SI joint between standing and sitting as people without pain.9PubMed. Sacroiliac pain after total hip arthroplasty: a combined analysis of clinical data and three-dimensional imaging in standing and sitting positions Everyday moves like getting in and out of chairs may be what aggravates it.
Years of a bad hip leave a mark as well. People who had their hip replaced for osteoarthritis showed more wear in the SI joint than those who had it for loss of blood supply to the hip bone.10PubMed Central. Hip-sacroiliac joint-spine syndrome in total hip arthroplasty patients A stiff, painful hip seems to push extra load onto the SI joint over years.11PubMed Central. Hip-sacroiliac joint-spine syndrome in total hip arthroplasty patients
Surgery itself may add strain. Hammering the new socket into place has been suggested as a cause, but it does not appear to be the main one.12The Journal of Bone and Joint Surgery. Sacroiliac joint: function, pathology, treatment, and contribution to outcomes in spine and hip surgery Stretching tight tissues at the back of the pelvis during surgery may also strain the joint’s ligaments.13The Journal of Bone and Joint Surgery. Sacroiliac joint: function, pathology, treatment, and contribution to outcomes in spine and hip surgery
Fixing the hip doesn’t instantly fix the pelvis. Muscles and ligaments spent years adapting to limping and a stiff hip, and they need weeks to months to adjust to a hip that moves freely again. During that adjustment the SI joint may take uneven loads, which helps explain why much of this pain is temporary.
Does a Leg Length Difference Cause It
Many people notice one leg feels longer after a hip replacement. A leg length difference can twist the pelvis and load the SI joint unevenly, which is why people suspect it.14The Journal of Bone and Joint Surgery. Sacroiliac joint: function, pathology, treatment, and contribution to outcomes in spine and hip surgery
Feeling longer is not the same as being longer. Early on, a leg often feels longer because of muscle tightness and pelvic tilt, not bone length. That sense often fades within a few months as muscles relax. Your surgeon can measure true length on an X-ray, so it’s best not to add a shoe lift on your own before then.
In people followed for about 6.6 years after hip replacement with an average difference of about 1 cm, leg length was not linked to low back pain.15PubMed Central. Anatomic and functional leg-length inequality: A review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance A small difference alone is unlikely to be why your back hurts. That is a finding about groups, so it doesn’t rule out leg length in a particular person, especially when the difference is large. If the difference is small, the more useful question is what else is loading the pelvis, such as tilt, muscle tightness or earlier wear.
Surgeons sometimes lengthen the leg a little on purpose, because that helps keep a new hip stable in its socket. Lengthening up to 35 mm or shortening up to 21 mm did not reduce function, comfort or satisfaction at six months.16PubMed Central. Anatomic and functional leg-length inequality: A review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance Among nearly 7,000 hip replacement patients, only 0.3% needed another operation to even out leg length.17PubMed Central. Anatomic and functional leg-length inequality: A review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance
Telling SI Joint Pain Apart From Hip or Back Pain
SI joint pain is often mistaken for both hip and spine problems, so pain that persists after hip surgery should prompt a focused check.18American Hip Institute & Orthopedic Specialists. Sacroiliac Joint (SIJ) Pain
A doctor reviews your symptoms and history and does a hands-on exam that can point to the SI joint.19American Hip Institute & Orthopedic Specialists. Sacroiliac Joint (SIJ) Pain The doctor presses over the joint to find tenderness, then pushes or twists the pelvis while you lie down to reproduce the pain. Several positive tests together are more convincing than any one. A numbing injection placed into the joint with ultrasound or CT guidance can then confirm it.20American Hip Institute & Orthopedic Specialists. Sacroiliac Joint (SIJ) Pain If the pain eases soon after the injection, the SI joint is likely the source, though a single injection can occasionally mislead.
The exam can be hard to interpret. Pain from the hip, the lower spine and the SI joint can overlap in the buttock and thigh, so location alone cannot settle where it comes from. You can also have more than one source at once, such as a stiff recovering hip and an irritated SI joint. That is why a careful hands-on exam matters more than a single scan.
Imaging often looks normal even when the joint hurts. X-rays, CT and MRI show structure, not whether the joint is moving poorly or causing pain. Wear may also show up in people with no pain, so an abnormal-looking joint doesn’t prove it is the source. Doctors rely on history, exam and sometimes an injection together.
It helps to bring some details to the appointment. Point to the exact spot that hurts, and note which movements trigger it and when it started relative to surgery. Mention any back or buttock pain from before the operation. Also report pain in the groin, fever, or wound changes, which point elsewhere.
Treatments That Help SI Joint Pain
This SI joint trouble after hip replacement is often temporary.21The Journal of Bone and Joint Surgery. Sacroiliac joint: function, pathology, treatment, and contribution to outcomes in spine and hip surgery A combined approach of physical therapy, pain management and possibly injections can help alongside recovery.22Dr. Nathan Cafferky. Dr. Nathan Cafferky
Physical therapy focuses on strengthening the buttock and core muscles to stabilize the pelvis, with gentle stretches for tight hip flexors and hamstrings. It also works on correcting a limp left over from before surgery. Exercises must respect your surgeon’s hip precautions.
At home, short sessions of heat or ice over the joint can ease it. Avoid sitting for long periods, and stand up using both legs evenly. Sleep with a pillow between your knees, and keep walking within your rehab plan rather than resting completely.
The same guided injection used to confirm the diagnosis can include a steroid to calm inflammation. That can keep the joint calm longer, giving therapy a better chance to work. SI joint pain can also make other hip-area pain, such as tender outer hip tendons, respond less to steroid shots.23PubMed Central. What factors influence pain scores following Corticosteroid injection in patients with Greater Trochanteric Pain Syndrome? A systematic review An untreated SI joint may be part of the reason those shots fall short, so treating it can matter for the other problem too. Injections are generally considered when pain persists despite the basic steps, not as a first move.
Pain lasting beyond about three months or getting worse deserves review. Ask about a numbing injection to confirm the source before considering anything bigger.
For severe pain that fails other treatment, a minimally invasive fusion can lock the joint with small implants. In a small group, pain fell from about 8 to about 2 out of 10 five years after this fusion,24The Open Orthopaedics Journal. Five-Year Clinical and Radiographic Outcomes After Minimally Invasive Sacroiliac Joint Fusion Using Triangular Implants and 82% were still satisfied.25The Open Orthopaedics Journal. Five-Year Clinical and Radiographic Outcomes After Minimally Invasive Sacroiliac Joint Fusion Using Triangular Implants
When Low Back Pain Could Be a Stress Fracture
A sacral insufficiency fracture is a stress fracture of the sacrum, the bone at the base of the spine that the SI joints attach to, caused by normal loads on weak bone. Most people with it are women after menopause, and hip replacement is one listed risk factor.26PubMed. Sacral insufficiency fractures. Spectrum of radiological features. Severe low back pain is its most common symptom.27PubMed. Sacral insufficiency fractures. Spectrum of radiological features. In people with these fractures after one-sided hip replacement, the break was more often on the opposite side to the new hip than the same side.28PubMed. Does Total Hip Arthroplasty Influence the Development and Localization of Sacral Insufficiency Fractures?
Hip replacement fits as a risk factor because surgery changes how load passes through the pelvis, and a long period of reduced activity often comes before it. A history of osteoporosis, or of radiation to the pelvis, adds to the risk.
Signs that suggest a fracture rather than SI joint strain include sudden, severe pain without an injury that makes walking very hard, and pain that persists even at rest. The pain feels much like SI joint or lower back pain, so the fracture is easy to overlook without an MRI or CT. If that sounds like you, ask for an MRI or CT, because plain X-rays can miss it.
Report some other signs promptly: fever, redness or drainage at the wound, new groin pain or a feeling the hip is unstable, and numbness, leg weakness or bladder changes.
If You Already Have SI Joint Problems Before Surgery
The two joints are linked. People who had SI joint fusion were about twice as likely to later need a hip replacement as similar people without it.29PubMed Central. Risk of Total Hip Arthroplasty After Sacroiliac Joint Fusion Surgery: A Nationwide Study A fused joint no longer absorbs any motion, so the hip and lower spine take on more of the work. That doesn’t mean the fusion caused the hip problem, since the two conditions can share causes and develop in the same people.
In a stiffer pelvis, the hip socket’s working angle changes as the pelvis tilts.30PubMed Central. Pelvic motion the key to understanding spine–hip interaction The socket is placed at a chosen angle, but a pelvis that cannot tilt much can’t make up for it, so a socket that suits a flexible pelvis might sit awkwardly. Surgeons may therefore plan socket placement around how your pelvis moves.31PubMed Central. Pelvic motion the key to understanding spine–hip interaction
If this applies to you, mention any prior spine or SI fusion clearly. Ask whether your SI pain might improve once the hip is fixed, and whether standing and sitting X-rays are planned to check pelvic motion. Ask, too, what the plan is if back or buttock pain continues afterward.