A new study by researchers at Hospital for Special Surgery (HSS) in New York City reveals that symptomatic lower back pain resolved in 82% of patients after total hip arthroplasty (THA) and identifies which patients are more likely to have their back pain resolved. This study is available online as part of the AAOS 2020 Virtual Education Experience.

“For patients, it is important to know that hip and spine arthritis often coexist, and the majority of the time, an individual’s back pain is better after hip replacement surgery,” said lead study author Jonathan M. Vigdorchik, MD, a hip and knee surgeon at HSS. “However, there are certain times where you might want to have spine surgery first, and that should be discussed with a physician who can evaluate and understand both hip and spine conditions and the relationship between them.”

A complex interplay exists between the hip and the spine. Some back pain may be caused by abnormal mechanics from hip osteoarthritis. In this new study, the researchers set out to compare patients whose back pain resolved after THA with those whose back pain did not resolve and identify how to predict this using spinopelvic parameters.

“Very frequently, patients come to see us with symptoms of both back pain and hip arthritis,” said Dr. Vigdorchik. “We wanted to know what percentage of the time back pain went away after total hip arthroplasty and whether we can predict patients whose back pain will go away after their hip replacement.”

The researchers evaluated and collected demographic data on a consecutive group of 500 patients who underwent THA for unilateral hip osteoarthritis at HSS. They excluded patients with previous spine surgery or femoral neck fractures. All patients underwent standing and sitting anteroposterior and lateral X-rays of the hip and lumbar spine pre- and postoperatively. Oswestry Disability Index scores and Visual Analog Scale scores were calculated preoperatively at six weeks and postoperatively at one year.

Of the 500 patients, 41% had documented lower back pain prior to their hip surgery. Of that group, 82% had their back pain resolve after hip replacement at a minimum of one year follow-up. The average Oswestry Disability Index in these patients preoperatively was 32+/-5% (moderate disability) and post-operatively was 9+/-3% (minimal disability, p<0.001). When comparing spinopelvic parameters between the groups, all patients whose back pain resolved had a sacral slope change from standing to sitting of more than 10 degrees, while the patients whose back pain did not resolve had a change of less than 10 degrees. Sacral slope change is a parameter that clinicians examine on a lateral X-ray that shows how much the pelvis and spine move in relationship to each other during different activities, such as going from a standing to a sitting position.

“There is definitely a group of patients whose back pain predictably goes away after hip replacement surgery, and those are people who have flexible spines,” said Dr. Vigdorchik. “When we took standing and sitting lateral X-rays, and we saw specific changes in patients with flexible spines, those were the patients whose back pain very reliably went away. Their back pain was exacerbated or even caused by their hip arthritis. Then there were certain patients who had a stiff, degenerative spine whose back pain did not go away, and that is because their spine arthritis had progressed to the point beyond which the hip was causing an effect.”

The findings should help clinicians counsel patients. “If clinicians get these X-rays and they see the certain things we saw, they can counsel their patients that their back pain will reliably go away after their hip replacement, and that it is safe to do the hip replacement first as opposed to going through spine surgery first for the back pain,” said Dr. Vigdorchik.