Spine specialists at HSS have been using a 30-camera array, called 3dMD, in the lab for several years, but the new study shows that the system produces clinically meaningful information. Because 3dMD does not rely on ionizing radiation, the technology may help adolescents with scoliosis avoid many of the repeated and potentially harmful x-rays that conventional care requires.

“Determining spinal range of motion is a lot more difficult than it sounds,” said Roger Widmann, MD, chief of the Pediatric Orthopedic Surgery Service at HSS and co-principal investigator on the new study. The conventional gold standard has been the use of x-ray imaging; however, x-ray tests are expensive, and long-term exposure to radiation from the scans has been linked to cancers.

The new technology provides a “safe, repeatable, inexpensive measurement of spinal range of motion that can be used in both a research and clinical setting,” Dr. Widmann said.

Information from the 3dMD scans can help spine surgeons determine the optimal approach to operative treatments and allow them to better track the progress of scoliosis patients following surgery. “The technology gives you objective measures of range of motion so you can improve your surgical decision-making,” Dr. Widmann said.

The HSS team presented their findings today at the 2023 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS) in a poster titled “3D Surface Topographic Optical Scans Yield Highly Reliable Spine Range of Motion Measurements in Adolescents.”

The 30-camera array can generate a whole-body image of a standing person in under 2 milliseconds – fast enough to eliminate any blurring from even the slightest movement in any direction.

In previous studies, the HSS team and their colleagues have shown that images generated with the ultrafast cameras match the anatomy beneath the skin. That alignment is critical for 3dMD to be useful in the clinic as a way to guide treatment for scoliosis, which affects between 2% and 3% of youth in the United States, or 6 to 9 million people.

Treatment for scoliosis frequently involves physical therapy or the use of braces to correct the curvature of the spine – a measurement called the “Cobb angle” – but in the most severe cases, surgery may be necessary.

For the new study, Dr. Widmann’s group used 3dMD to image 254 boys and girls with scoliosis and 53 without the spinal deformity as they underwent several exercises designed to work the torso in various directions.

“This is teaching us which parameters are more useful and which are not,” says Howard Hillstrom, PhD, a biomechanical engineer at HSS, senior director of the Leon Root, MD Motion Analysis Laboratory and co-principal investigator on this project.

The new study found two movements that were reliably able to differentiate youth with scoliosis from those with normal spines: bending as far to the left and right as possible while standing, and bending toward the floor as if to touch the toes.

In the first case, patients with scoliosis show significant asymmetry between one side and the other in terms of how far to each side they can bend. Meanwhile, scoliosis patients are not able to bend as far toward the floor – as measured from a point on their collarbone – as those with unaffected spines, Dr. Hillstrom said. “That’s good enough to distinguish healthy kids from those with scoliosis because most kids are so flexible they can get to the floor and those with scoliosis probably can’t.”

Although the assessments make sense both intuitively and clinically, the latest study shows that they are also an objective measure of scoliosis. The entire process, from the start of the scan to the generation of results, takes under 10 minutes, Dr. Hillstrom added.

“And now we have this system that acquires these variables and doesn’t require ionizing radiation to do so,” he said, noting that this is critically important because scoliosis patients have a significantly greater incidence of cancer, breast cancer, and cancer mortality than those without the condition – an increase many experts attribute to the radiation they receive from x-rays and CT scans.

The process of diagnosing scoliosis starts early. “The first time someone notices that a child may have scoliosis is usually when the school nurse sees it during a routine examination,” Dr. Hillstrom said. “The nurse tells the parent to take the child to a doctor, and the first thing a physician will do is order an x-ray.”

The HSS team now has imaging studies of more than 300 adolescent patients with scoliosis in its 3dMD database. “Of those, approximately 50 are a year out from surgery and 30 are two years out, providing the ability to look at the long-term benefits of the technology on range of motion and other parameters [such as angle of trunk rotation, back surface rotation, and asymmetry in lateral bending and twisting”, Dr. Widmann said. 

Authors: Alon Wolf, PhD; Ankush Thakur, MS,BS (HSS); Benjamin N. Groisser, BA, (Technion); Caroline C. Gmelich, BA; Don Li, MD,PhD; Hila Otremski, MD; Howard J. Hillstrom, PhD; Jessica H. Heyer, MD; Kira Page, BA; Kyle Morse, MD; Matthew E. Cunningham, MD, PhD, FAAOS, (HSS); Michael T. Hresko, MD,FAAOS, (Boston Children's Hospital); Roger F. Widmann, MD, FAAOS, (HSS); Ron Kimmel, DPHIL (OXON)

Spinal fusion is among the most commonly performed orthopedic surgeries in the United States, with more than 400,000 patients undergoing the procedure each year. Although most cases are successful, as many as 45 percent of patients experience complications after the operation, often resulting from the bone’s inability to tolerate the hardware surgeons use to support the skeleton. 

The most widely used technology to evaluate patients’ bones before spine fusion surgery is called dual x-ray absorptiometry, or DXA. DXA imaging gives physicians a rough sense of the strength of a person’s bone, but it is not foolproof. In some cases, surgeons find that patients whose DXA scans appear normal have bones that are so weak that the appliances they use during spinal fusion are at risk of failure. 

The HSS researchers hypothesized that a more sensitive measure of bone quality could identify abnormalities in the skeleton that DXA does not detect, and that these defects would be linked to postoperative complications. 

For the new study, the team led by Emily Stein, MD, an endocrinologist and bone specialist, along with spine surgeons Han Jo Kim, MD, Matthew Cunningham MD, PhD, and Frank Schwab, MD, turned to a cutting-edge technique for assessing bone called high-resolution peripheral quantitative computed tomography (HR-pQCT). HR-pQCT can separately measure how much bone is in the outer (cortical) and inner (trabecular) compartments and measure on a microscopic level how the inner trabecular bone network is organized, including the number, thickness and spacing between the parts of that network called trabeculae. These measurements—known broadly as the microarchitecture—may provide a much more robust assessment of skeletal health than DXA, particularly in this population of patients who frequently have changes in the area of the fusion which undermine the utility of DXA. 

“DXA provides a two-dimensional measure of bone density, or the amount of bone present, whereas HR-pQCT provides a true three-dimensional measurement of the bone density,” Dr. Stein said. “This provides additional information about the structural features of bone that can be leading to weakness or fragility.”

The study included 54 men and women scheduled for spinal fusion at HSS between December 2017 and December 2019. Patients underwent conventional DXA scans, as well as HR-pQCT scans of the radius (forearm) and leg bone (tibia).

Of the 54 patients in the study, 14 experienced complications within the first six months of surgery, including broken rods, loosened bone screws, fractures and abnormal bending of the spine. Although the number of people in the study was small, the researchers found that those with abnormalities on HR-pQCT were significantly more likely to experience complications than those without such defects -- abnormalities that were not evident on DXA imaging. These abnormalities involved lower bone mineral density in the trabeculae (the spongy tissue in the center of bones), fewer and thinner trabeculae, as well as thinner cortices.

“We used HR-pQCT to show for the first time that abnormalities in the microscopic structure of bone are directly related to the development of complications after fusion. Our study identified several abnormalities in patients who had complications,” Dr. Stein said.

For the moment, HR-pQCT is a research tool that’s not widely available to surgeons. “I think that it does provide a lot of additional information that we’re not getting from DXA. On DXA, the spine is almost always going to look fine, which can be misleading,” noted Dr. Stein. 

Dr. Stein’s group is expanding their study to include more patients. “Spinal fusion surgeries are so invasive, the potential for complications is high,” she explained. “We want to have the most optimal strategies for lowering complications in our patients, and that begins with understanding who is at risk and why. In our future work with additional patients, we hope to be able to define which features, or group of features of the bone structure is most important in contributing to surgical success. This will help us to devise the most targeted treatment strategies for our patients.”

Dr. Stein's team published their findings in the journal Bone, and made available online first on November 4, 2020.