Routine Imaging of Hip Recommended After Joint Replacement

Imagine you had a total hip replacement six years ago and everything went just fine. Then bam! You develop pain and swelling somewhere around the hip or thigh. What’s happening? With the aid of X-rays, CT scans, and/or MRIs, the surgeon diagnoses a condition known as osteolysis. The images suggest this problem didn’t just happen but was developing over time.

Osteolysis or bone loss after total joint replacement (knee or hip) can be a problem. Tiny flecks of bone and debris from the backside of the implant lead to osteolysis. Over time the implant can come loose or the bone can fracture.

The authors of this instructional course for orthopedic surgeons recommend routine monitoring starting five years after total hip arthroplasty (THA or replacement). Follow-up X-rays are advised every two to three years after that for as long as the patient has the implant.

The authors discuss the role of X-rays, CT scans, and MRIs in diagnosing and following patients with THA. Risk factors for osteolysis are presented along with the idea that anyone at risk should be monitored even more closely.

Not everyone with osteolysis has symptoms (pain, swelling, loss of motion), especially early on. The only way to know for sure if there is any bone loss is to take an X-ray. Osteolytic lesions look like someone took a bite out of the bone. But X-rays are only a two-dimensional view of a three-dimensional object. So although they show there is a problem, X-rays aren’t enough to tell the surgeon the full extent of the defect.

That’s where CT scans and MRIs come in. These more advanced forms of imaging are considered supplemental. They can be modified to reduce the amount of distortion or “artifact” shown on images caused by the metal. This metal artifact reduction protocol gives the radiologist and surgeon a better view of the bone and soft tissues around the implant compared with regular, traditional CTs or MRIs.

Sometimes both types of imaging studies are needed. That’s because they show different structures: CTs scan the bones whereas MRIs are better at showing changes in the surrounding soft tissues. But does everyone need all of these tests? Not really. The timeline (beginning five years after the patient gets the hip) is the first criteria for testing.

The patients at greatest risk of osteolysis are those who are younger and more active. Men tend to fall into this category more often than women. Because this type of osteolysis is linked with wear debris, it takes time to develop. That’s why routine screening isn’t recommended until five years out. And, of course, as more time passes, the risk increases.

Certain types of implants are more likely to shed metal debris with use. The first ultra-high molecular-weight polyethylene (UHMWPE) implant components (parts) used tend to wear out faster than the newer highly cross-linked UHMWPE implants. So anyone with the conventional UHMWPE should be assessed for sure.

What happens if osteolysis is detected? Well, no immediate treatment is needed. The patient is followed more closely (every four to six months) instead of every two or three years. If there are signs that the lesion is getting larger or worse, then the patient may be a candidate for surgery. Serial (repeated) X-rays shows the rate of progression (how fast and how much worse the osteolysis is developing).

Treatment of osteolysis following hip replacement is not the focus of this instructional course. Instead, surgeons interested in reviewing the indications for when and how to use imaging studies to screen for the presence of osteolysis and then monitor the progression of disease will find this information helpful. A dozen photos of X-rays, CT scans, and MRIs are provided to help illustrate what to look for on both sides of the hip implant (acetabular or socket-side and round head at the top of the femur or thigh bone).