Issue: August 2017
August 09, 2017
9 min read

Aging spine poses challenges for acetabular cup positioning

Issue: August 2017
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Coordinated movements of the spine in conjunction with the pelvis and hip, known as the hip-spine connection, may adversely affect or limit both areas of the body, particularly when pain is present. Surgeons may be able to identify the cause of pain in the hip or spine that is vague or does not follow a typical pattern by reviewing a patient’s history or through a physical examination. However, it may be more difficult for surgeons to make an accurate diagnosis when more than one problem contributes to pain symptoms.

How the acetabular cup is positioned during total hip arthroplasty (THA), especially in cases of a degenerative or aging spine, can make a difference in whether patients will develop corresponding spine pain or have the resolution of existing pain, according to sources who spoke with Orthopedics Today.

“The back can refer pain to the hip. The hip can refer pain to the back and there have even been studies that have shown back pain may be from differing gait mechanics in the arthritic hip and that, when you restore the normal mechanics with a hip replacement, some people’s back pain actually goes away,” Aaron J. Buckland, MD, assistant professor of orthopedic surgery and director of spine research at NYU Langone Health, told Orthopedics Today.

Douglas A. Dennis, MD
As mobility of a severely degenerated or fused spine often cannot be changed, Douglas A. Dennis, MD, urged orthopedic surgeons to improve their analysis of lumbopelvic mobility in patients prior to total hip arthroplasty.

Image: Fransisca Mascarenaz

Diagnostic injection using fluoroscopy to confirm placement into the hip joint may help determine the main source of a patient’s pain, according to David J. Mayman, MD, an orthopedic surgeon at Hospital for Special Surgery.

“We will do diagnostic injections into the hip joint to try to determine how much of [the patient’s] pain is coming from their spine and how much of their pain is coming from their hip,” he said.

However, if there is no singular source for the pain, meaning it is being caused by both the hip and the spine due to arthritis or degeneration, surgeons must decide which pathology to treat first. In the past, surgeons often performed THA first because it was an easier operation to carry out with more predictable outcomes, according to Mayman.

Buckland noted that in the same situation some surgeons will focus on the patient’s main complaint.

“If you think the patient has a lot of pain due to hip arthritis, do the hip first,” Buckland said. “If most of the patient’s pain is related to the fact they have lumbar stenosis or spondylolisthesis, then address that first.”


Hip dislocation after spine surgery

David J. Mayman, MD
David J. Mayman

Despite the sparse data about the hip-spine connection and some debate about whether it is more beneficial to perform hip or spine surgery first in these cases, Buckland noted results have shown a 7% to 8% risk of hip dislocation after spinal realignment among patients who have already undergone THA.

“We have seen a couple of people over the years who had a hip replacement and were doing fine and then 5 years to 10 years later have a spine fusion, and then end up dislocating their hip. It’s incredibly rare that somebody dislocates their hip 10 years after they have a hip replacement,” Mayman said. “The only variable was that they had a spine fusion before they dislocated their hip,” he said.

Research by George E. Lewinnek, MD, and his colleagues in the 1970s identified a “safe zone” of the hip for cup placement that would decrease the risk of acetabular displacement in patients undergoing THA. However, a study in Clinical Orthopaedic and Related Research in 2016 by Matthew P. Abdel, MD, and his colleagues showed 58% of 9,748 patients who underwent primary THA experienced dislocation despite their socket being within the Lewinnek safe zone.

Regarding possible hip displacement in patients with hip-spine pathology, placement of the acetabular component is one of several factors to consider, Mayman noted.

“There is the spine, the position of the femoral implant, the muscles, the tendons and the ligaments. There are a lot of things that affect stability of the hip joint,” he said.

When the lumbar spine is fused for degeneration or deformity, the pelvic tilt can change, which, in turn, changes the position of the acetabular cup as well as the amount of pelvic tilt change between sitting vs. standing, according to Buckland. He noted these changes may affect the patient’s risk for dislocation.

Hip, spine analysis

Aaron J. Buckland, MD
Regardless of why a patient’s lumbar spine was fused, Aaron J. Buckland, MD, said hip dislocation risk increases due to reduced protective pelvic tilt and acetabular anteversion change from standing to sitting.

Image: Andrew Neary/NYU Langone

Douglas A. Dennis, MD, adjunct professor of bioengineering at the University of Denver and attending surgeon at Colorado Joint Replacement, told Orthopedics Today, “If a fusion involves the lumbar spine, particularly a fusion to the sacrum, that can have a significant effect on lumbopelvic mobility, which then can change the 3-D position of where [a patient’s] pelvis is positioned in daily activity.”


As surgeons — and surgery — are unable to change the mobility of the spine that is severely degenerated or has already undergone a fusion, Dennis urged orthopedic surgeons to analyze lumbopelvic mobility prior to THA. He suggested making appropriate adjustments to the cup position before THA to accommodate any spinal stiffness and other possible changes.

Buckland said one way to do this is to perform a sitting and standing analysis of the patient.

In addition to such an analysis, Mayman noted surgeons should use radiographs to identify any issues with the spine prior to hip surgery.

“Traditionally, people who come in for a hip replacement have a pelvis radiograph so you can see their hips, but you cannot see their spine,” Mayman said. “If I could make one suggestion to [surgeons], it would be that before you do a hip replacement you get some lumbar spine radiographs so you can tell if there is lumbar spine pathology.”

For patients who need a spine fusion after they have already undergone THA, navigation performed prior to any spine surgery may help predict any changes in lumbar pelvic inclination, Wayne G. Paprosky, MD, FACS, professor of orthopedics at Rush University, said.

“If we can do some detailed computer analysis beforehand, we may be able to predict, after we fuse this patient’s spine, [that] this is going to significantly change the lumbar pelvic inclination,” Paprosky said. “Maybe we would rather do that beforehand, be able to predict then which angle this [cup] should be, as opposed to conventionally doing the hip surgery first and then trying to match it afterward,” he said.

Polyethylene wear, edge loading

John M. Redmond, MD
John M. Redmond

Hip dislocation is a chief concern among surgeons who treat patients with dual hip-spine pathology. However, after THA, patients may also experience increased rates of polyethylene wear when an acetabular cup is improperly placed, according to Paprosky.

Paprosky also noted patients may experience additional pain from femoroacetabular impingement or the way in which the patient adapts his or her lumbosacral pelvic motion.

Buckland said, “If you have edge loading of a component, you can have increased wear of the bearing and, in the case of the ceramic [bearings], this edge loading can also give a squeak which gives an audible noise when patients walk.”

Surgeons should be aware that many patients with hip and spine disease have general medical conditions, such as psoriatic arthritis, rheumatoid arthritis and ankylosing spondylitis, according to John M. Redmond, MD, of Southeast Orthopedic Specialists in Jacksonville, Fla.


“The other thing we worry about, which we see every once in a while, is tendonitis around the hip, with the most common one being iliopsoas tendonitis,” Mayman said, noting this occurs when the tendon rubs on the acetabular component at the front of the hip.

Dual mobility components

Use of a dual mobility hip socket, one in which the polyethylene liner moves inside the artificial hip socket, has been shown to reduce the risk of several of these complications, especially hip instability and dislocation. It provides a much bigger, functional femoral head, Mayman said.

“[This] gives you a much more stable hip,” Mayman said. “We are starting to use that in a lot of people who have bad spines because we are worried about their hip joint stability.”

However, the dual mobility hip socket is a relatively new prosthesis in North America. Therefore, because it may be associated with other complications, such as increased wear rates, surgeons are not using it in every patient for primary THA, Mayman said, noting he reserves dual mobility cups for patients with an aging spine.

However, one problem he foresees is that with THA being performed in younger, more active patients, it is impossible to predict who will later have to undergo spine surgery that could change the position of their pelvis.

“What we do not know at this point is how to predict who, in 10 years or 15 years from now, is going to have a bad spine and whether we should do anything different about their hip replacement today because they may have a bad spine in the future,” Mayman said. “At this point, we are not doing anything different unless we see they have a bad spine at the time of the hip replacement.”

Surgeon collaboration

Wayne G. Paprosky, MD, FACS
Wayne G. Paprosky

When patients undergoing THA present with spine issues, it may make sense for specialist hip and spine surgeons to collaborate on a treatment plan, according to Mayman.

Hospital for Special Surgery has a team that includes individuals from the biomechanics laboratory, a spine surgeon, hip surgeons and a radiologist. They research the patient’s hip-spine relationship and determine the best treatment options. This collaborative group has worked together for 3 years, during which time everyone involved has learned something from a different perspective, Mayman said.

“The spine surgeon looks at this from a completely different perspective than the hip surgeon, and the hip surgeons see something completely differently than the spine surgeon,” Mayman said. “Ultimately, at the end of the day, the patient does not care whether it is the hip surgeon or the spine surgeon [who treats them]. They want their back to feel good and they want their hip to feel good. We learn things from each other and I think we are treating patients better because we learn things from each other.”


Paprosky said viewing the patient’s problem from different perspectives may be beneficial and ultimately result in fewer hip dislocations and more predictable outcomes.

“[Hip and spine surgeons are] going to have to work together ... so we can at least give these patients more of a predictable outcome,” he said.

This goes beyond simply determining which of the surgeries should be done first. At the very least, hip and spine surgeons should collaborate to minimize the potential for dislocation, Paprosky said. “If dislocation does not come into play, at least minimize other potential issues [the patient] may have with another joint,” he said.

According to Buckland, collaboration between hip and spine surgeons is especially beneficial for patients with deformity or malalignment, or for complex diagnostic decisions in which it is unclear if the deformity is in the hip, spine or both areas.

“It is important that patients understand they have two problems. Then, by having a spine surgeon and hip surgeon work together, we can try to differentiate the pathology that is most symptomatic,” Redmond said.

Through collaboration, hip and spine surgeons can tailor interventions that meet preoperative expectations, which will lead to greater patient satisfaction, he said.

“Patients are most dissatisfied if their preoperative expectations are not met and so identifying both problems ahead of time is important,” Redmond said.

Next paradigm shift

Dennis, who is an Orthopedics Today Editorial Board Member, believes individualized cup positioning should be the next paradigm shift in THA and it will lead to greater patient satisfaction. This is called for because cup positioning should vary between patients.

“I truly think where we are going to get to is, when we do a total hip, we study the relationship of the spine to the pelvis and rather than having a blanket recommendation or putting all of your cups ‘here,’ it would be individualized cup positioning based on the mobility at the lumbosacral junction,” Dennis said.

However, until an algorithm for acetabular cup placement among patients with an aging spine is developed, surgeons should examine all factors related to this complex problem, including femoral offset, femoral anteversion and leg length, Redmond said.

“My personal preference in these patients is to avoid the posterior approach to their hip,” he said. “Direct anterior and anterolateral approaches seem to be inherently more stable. Then, during templating, surgeons can consider increasing femoral offset to aid in stability and then intraoperatively increase femoral head size by reaming up or have a dual mobility prosthesis available.”


After that, confirm intraoperatively that impingement-free motion occurs and adjust the acetabular component if necessary, Redmond said. – by Casey Tingle

Disclosures: Paprosky reports he is involved in navigation with Intellijoint Surgical. Buckland, Dennis, Mayman and Redmond report no relevant financial disclosures.

Click here to read the POINTCOUNTER, “In patients with concurrent hip and spine pathology, does it matter which condition is corrected first?