The defining characteristic of ankylosing spondylitis (AS) is inflammation affecting the vertebrae of your spine. In most people with the condition, though, these aren’t the only joints affected.
“Hip problems are very common in patients with ankylosing spondylitis,” says Charles Lawrie, MD, an assistant professor of orthopedic surgery at Washington University School of Medicine in St. Louis. “A little over 50 percent will end up having hip involvement.”
In addition, a smaller number of people with AS will see their knees, shoulders, or small joints of their hands or feet affected.
Often, joint problems outside the spine become severe enough to warrant joint replacement surgery, with hip replacement as the most common operation.
According to Dr. Lawrie, most people with AS hip involvement will require joint replacement at a younger age than is typical for other forms of arthritis affecting the hips, such as osteoarthritis — typically between ages 40 and 60, rather than 55 to 75.
Here’s how the decision to have joint replacement surgery typically plays out in people with AS.
Hip Replacement to Restore Function and Reduce Pain
In a typical hip replacement for someone with osteoarthritis, the procedure is performed to reduce pain, according to Lawrie.
But in people with AS, “it may not just be pain that we’re performing the procedure for, but also restoration of function because of the stiffness” in the affected joints, he says.
A common indication for hip replacement in people with AS is flexion contracture, which means that “the hip is stuck up a little bit, and the patient can’t straighten the leg out,” Lawrie says.
Hip replacement has been shown to be a reliable solution for restoring normal joint motion in people with AS, and can even help with a person’s spinal alignment by changing the way they stand and walk, says Lawrie.
In people with less-advanced AS that hasn’t affected their hip mobility to a significant degree, reducing pain can also be a reason for replacement surgery, Lawrie adds.
How Joint Replacement Is Different in AS
In people with mild AS who have joint replacement primarily for pain, the procedure won’t differ much from how it’s typically performed in people with osteoarthritis, says Lawrie. This means your orthopedic surgeon will oversee the process, and you can expect a similar range of outcomes.
But in most people with AS who undergo joint replacement to address mobility, the process is more complex.
“Patients with more severe disease may be on some higher-powered medication,” such as biologics, which requires coordination between your orthopedic surgeon and rheumatology team regarding when you stop and start taking the drug, Lawrie says. That’s because certain drugs for AS can cause problems with wound healing.
More Complex Surgery
When it comes to the actual surgery and recovery, hip replacement tends to be more complex in people with AS because of a number of factors.
“From an anesthesia standpoint, some of these patients can have a very stiff cervical spine,” which can require special techniques for intubation during the procedure, says Lawrie. And spinal anesthesia — which is widely used in general for hip replacement procedures — isn’t an option if a fused spine limits access to your spinal canal.
Longer Recovery Period
During the procedure, bone around the hips usually needs to be removed in people with AS. “That leaves a pretty good surface area of bleeding bone at the end of surgery,” says Lawrie, and results in a longer, potentially more complicated recovery. “It may take months to resolve some of their contractures even once the joint has been replaced,” he says.
After the surgery, people with AS are at greater risk for joint dislocation, wound healing problems, and infection. For all these reasons, he recommends having the procedure done at a specialized surgery center that’s familiar with considerations for AS.
Life After a Joint Replacement for AS
Most people with AS who undergo hip replacement see substantial functional improvements, says Lawrie, a finding that he’s seen personally and that is also backed up by studies, including one presented at the 2015 meeting of the American College of Rheumatology.
While most people with AS continue to experience some inflammation and problems in the area, the majority state that their replaced joint is free of pain one to two years after the surgery, Lawrie notes.
One way that inflammation can continue to affect a replaced joint is when it occurs at the sites where tendons insert into your bone, a condition known as enthesitis. This can cause pain in the joint area, even though your prosthetic joint isn’t directly susceptible to inflammation.
Despite the risks associated with joint replacement, Lawrie emphasizes that it can enhance mobility and reduce pain for many people with AS. It’s “a very reliable, good solution for helping with hip problems, and can even help with posture problems,” he says. But going into it, “you should know that it’s not going to be the same run-of-the-mill hip replacement that your friend without AS may have had.”