Assessing Bone Health for Spinal Fusion: Novel Technique

A new method for evaluating microscopic bone health prior to—and predicting complications after—spinal fusion? An expert on the technique, called high-resolution quantitative computed tomography, weighs in.

Peer Reviewed

A patient’s bone health can mean the difference between regaining mobility and quality of life after spinal fusion and continuing to deal with pain or disability. That means detecting skeletal abnormalities prior to surgery is crucial, but a 2021 study in the journal Bone suggests the most widely used technology for the task may not be ideal. 

Spine surgeon assessing bone health prior to fusion with HR-pQCTWhat's stopping HR-pQCT from more widespread adoption in a clinical setting?

Researchers from the Hospital for Special Surgery (HSS) in New York City looked at 54 men and women scheduled for spinal fusion at HSS between December 2017 and December 2019. Patients underwent conventional scans with dual x-ray absorptiometry (DXA) as well as scans with a technique called high-resolution quantitative computed tomography, usually abbreviated to HR-pQCT or Xtreme CT.

The hypothesis was that a more sensitive measure of bone quality through Xtreme CT might identify skeletal abnormalities that DXA would not pick up, and these readings would correlate with postoperative complications. 

That turned out to be correct. Of the 54 patients, 14 of them experienced problems within six months after surgery, including: 

  • Fractures
  • Loosened bone screws
  •  Broken rods
  • Abnormal bending in the spine

These patients were much more likely to have abnormalities in their initial Xtreme CT scans that weren’t evident with DXA imaging, according to study lead Emily Stein, MD, an HSS endocrinologist and bone specialist.

“The problem here is that a DXA scan may not be giving spinal surgeons all the information they need about potential abnormalities and deficits in their patients’ bones,” she says. “What appears normal on the scan may, in fact, turn out to be weak bone during surgery.”

Need for Strong Fusion Outcomes

Spinal fusion is the one of the most commonly performed orthopedic surgeries in the United States, and the recent study noted that more than 400,000 patients undergo the procedure every year. While many are operations are successful, up to 45 percent of patients can experience complications, and the AAOS notes that these issues range from ongoing pain, infection, nerve damage, poor wound healing, pseudoarthrosis, and blood clots. 

Often in order to identify patients who may have postoperative skeletal issues, including loosening of surgical hardware such as bone screws and rods, surgeons have come to rely on DXA imaging. Available since 1987, DXA is able to provide information on the amount of bone present with very little radiation exposure. 

Yet, because DXA is using a two-dimensional X-ray technology, its results may be compromised by sclerotic or degenerative changes in the bone, says Stein, and even calcium in the blood vessels may skew results. That can make it look like there’s more bone than is actually present.

“Without that level of information, surgeons can’t plan properly,” says Stein. “Surgeons have described doing a fusion on what they thought was strong bone, only to find that it feels soft once they’re in there. That makes it hard to get a good anchor and it can be a big problem.”

For example, anchoring a screw or rod onto softer bone can result in fractures, breaking rods, and loosened screw, she adds. Knowing who’s at risk from the start can go a long way toward reducing complications. 

Because it offers such high resolution and 3D microarchitecture of the bone, Xtreme CT can highlight factors like cortical density and porosity, trabecular thickness and separation, and arterial calcification. Stein says having information like that is exciting, because it better identifies the deficits that might put a patient at higher risk for spinal fusion complications. 

Unfortunately, there’s a hitch: Xtreme CT equipment isn’t available in clinical settings. 

Wider Adoption? Not Yet

Currently, Xtreme CT is only in research labs at academic sites, Stein says. Not only is it expensive, but it yields complex datasets that require additional analysis and interpretation she adds. By contrast, DXA equipment is more affordable and widely available. 

“HR-pQCT is not going to replace DXA as a clinical tool,” says Stein. “However, our results offer stronger evidence that DXA has limitations, and that’s why it’s important for all of us to consider multiple ways that we can optimize bone health in patients presenting for surgery, rather than relying on scans alone.”

For example, she says, clinicians should ensure patients are getting adequate intake of calcium and vitamin D, and evaluate the potential effects of medications that are known to contribute to bone loss. 

“Lowering complications begins with better understanding of who is at risk and why,” says Stein. “We can’t rely fully on DXA scans to give us all the information needed for preventing spinal fusion complications.”

Updated on: 03/22/21
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MRI-Based Tool Assesses Bone Quality Prior to Spine Surgery
Emily Stein, MD
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