3D imaging enhances accuracy of musculoskeletal diagnosis, surgery
Evolving 3D imaging technologies have changed the surgical landscape in spine, TJA, oncology
Recent expansion of and advancements in 3D imaging have allowed radiologists and orthopedic surgeons to increasingly work in tandem to better treat patients with a variety of musculoskeletal conditions.
Numerous advancements, primarily in CT and MRI, have allowed for the creation of 3D imaging and 3D-printed models that aid in the planning and execution of knee, hip and spine surgeries.
“Probably the most significant advancement that allowed for the shift from 2D imaging to 3D imaging to occur is the technology being able to achieve thin slice thickness on the CT scanner,” Nancy M. Major, MD, clinical professor of radiology-diagnostics at University of Colorado Anschutz School of Medicine, told Orthopedics Today.
Although CT has been the primary type of orthopedic 3D imaging, MRI has begun to emerge as another important imaging modality within the specialty. According to Hollis G. Potter, MD, chair of the department of radiology and imaging and Coleman Chair in MRI Research at Hospital for Special Surgery in New York, MRI 3D imaging was made especially relevant through the incorporation of parallel imaging, which shortened scan acquisition time.
“We are now working on things like deep learning de-noising algorithms, which use artificial intelligence to take some of the noise away from MR images and further shorten scan time,” Potter told Orthopedics Today.
As 3D imaging technology continues to evolve, radiologists and orthopedists interviewed for this Cover Story discussed the charting of a complex yet intuitive technology-based course for the planning and execution of a variety of surgical procedures related to musculoskeletal conditions and injuries.
Transition from 2D to 3D imaging
Regarding 3D imaging with a CT scanner, Major noted an evolution from what was a lengthy examination that involved a full slab of tissue and featured only cross-sectional imaging in the axial plane to one that is performed with slice thicknesses that are thinner and a table that moves and spirals in a helical fashion.
“That technology changed the way we could perform CT imaging and therefore helps clinicians with reformations in the sagittal and coronal projections, as well as reconstruction in 3D imaging,” Major said.
According to Andrew T. Pennock, MD, pediatric and sports medicine surgeon at Rady Children’s Hospital-San Diego, 3D CT imaging is the primary modality he has seen used in a clinical context, particularly for planning surgeries. However, he said the application of 3D MRI is improving and it will likely soon have additional uses.
“Most of these technologies require some sort of post-acquisition processing, which can be time-consuming and can have some associated costs,” Pennock said. “That’s why we’ve mainly used it for research purposes on the MRI side.”
Using 3D imaging, either CT or MRI, in conjunction with orthopedic surgeries has provided significant advantages over the use of 2D imaging alone, according to Brad L. Penenberg, MD, chief of the division of hip and knee arthroplasty at Cedars-Sinai Medical Center in Los Angeles.
“This new technology has the ability to transform a standard 2D digital X-ray into a 3D model that can then be viewed in a preferred position even if the X-ray is malpositioned. That is a major breakthrough in intraoperative imaging capability,” he said. “It can eliminate the need for something like an O-arm and allows the surgeon, during the course of the operation with the patient under anesthesia, when time is critical, to essentially take a 2D image which then finds its place within a 3D model. That 3D model then becomes freely movable and can be positioned for automatically generating measurements in the desired orientations.”
Reports note that 3D imaging has also allowed for a deeper understanding of the anatomy of the spine.
“It allows you to visualize the entire spine to see what is going on, and it gives surgeons a better visualization of a simultaneous sagittal-coronal, as well as an axial view when you see it in 3D imaging,” Shay Bess, MD, director of surgical quality and resource utilization for spine services at Presbyterian/St. Luke’s Medical Center in Colorado, said.
Aside from CT and MRI, other scanning modalities also incorporate 3D imaging, such as the whole-body surface photographic system made by 3dMD, which Potter said is especially efficacious for patients with scoliosis. The photographic system tracks changes in the spinal curvature without use of an X-ray and provides an option for reducing the burden of ionizing radiation, which is particularly important for pediatric patients, she said.
According to sources, 3D imaging is helpful when used for certain musculoskeletal conditions, such as pediatric and adult spine deformity.
“It’s extraordinarily helpful in the context of spinal deformities, including large deformities or congenital anomalies where the vertebrae are misshapen and/or missing and are congenitally merged and absent with other parts of the spine,” Bess said. “It’s also helpful for patients who have had prior surgery or surgeries where the anatomy is distorted due to prior fusion surgeries.”
However, Bess noted that in a routine non-deformed spine, 3D imaging may be less necessary, although it may still be helpful, especially if image guidance is being used to place implants.
3D-printing technology allows surgeons to generate truly patient-specific implants, according to Bess.
“The 3D imaging can be used both in the interbody space, as well as with screws and other implants that we use for spinal fixation and fusion,” he said. “Patient-specific 3D-generated implants are the way of the future vs. having patient non-specific implants. I believe the field of patient-specific 3D-generated implants is markedly going to expand.”
The use of 3D reconstructions has improved overall preoperative surgical planning from the radiologist’s end, especially with musculoskeletal tumors and for some novel hip imaging techniques that allow surgeons to see how much bone might need to be removed, according to Major.
“For hip replacement, there is no apparent disadvantage to enabling creation of this 3D workable model so we can adjust pelvic or femoral orientation in order to make accurate measurements and avoid repeating X-rays,” Penenberg said.
The downsides with CT imaging, especially among younger patient populations, relate to radiation exposure, according to Pennock.
“I tend not to choose CT as my first-line imaging modality, so the MRI certainly has advantages because we’re typically getting an MRI anyway to confirm the ACL tear, as well as any associated injuries and pathology,” he said. “We can process those MRI images in a 3D format, and it gives a good 3D sense of the anatomy.”
In addition, particularly for complex trochlear morphology, it can be time- and labor-intensive to construct 3D MR images, he said. “It’s not that practical in its current format, and that is why I’ve learned to use the 2D imaging for surgical planning purposes.”
3D imaging for hips, knees, spine
3D imaging has come to play a role in assessing and treating the hip-spine connection, particularly in identifying the correct orientation of the pelvis, according to sources. Patients with advanced degenerative disc disease who have a stiff lumbar spine or those who have had prior spine surgery, will exhibit restricted motion in the lumbar spine alone, or the lumbosacral junction may be immobilized or have significantly reduced mobility, according to Penenberg.
“Historically, we took X-rays of the pelvis at a prescribed orientation with the patient in the supine position, but what we’ve learned in the last few years is that people with spine disease may have a completely different pelvic orientation when they stand or move from a seated to a standing position,” he said. “There may or may not be flexibility between the spine and the pelvis, so this realization led to the understanding that when we measure the cup position, the functional orientation now for most people is considered to be the standing pelvis X-ray as opposed to the traditional supine X-ray.”
Using that image as a reference, orthopedic surgeons can then proceed with the hip replacement using electronic or robotic guidance techniques. According to Penenberg, surgeons can obtain a 2D X-ray and then project it into a pre-formed 3D mesh based on the patients preoperative MRI or CAT scan via an algorithm contained within newly developed software, a process which reorients the 2D X-ray image to match the preoperative reference X-ray.
Use in surgical planning
For presurgical planning of spinal surgeries, 3D imaging offers more granular details of the spine.
“A 3D model provides a detailed framework from which surgeons can then plan out not only where to place implants or pedicle screws, but also determine what areas need an osteotomy or may have had a prior decompression,” Bess said. “Beyond further enhancing the accuracy of surgical planning, it forces surgeons to plan surgeries, which is half the battle. If we take the time to plan, even if the plan is subject to change, the act of surgical planning puts surgeons that much further ahead and prepares the surgeon and the patient for the surgery.”
3D imaging for preoperative planning of total hip replacement surgery is relatively new and has been enabled through new software that can use 3D imaging to plan cup position and offer more precision in component sizing requirements. According to Penenberg, surgeons now have the option to look at a CT or MRI scan through a 3D imaging software program and choose appropriate implants with correct sizing and placement. However, surgeons must also account for other factors, such as limb length adjustments and offset adjustments, based on the amount of hip disease present.
“When we do the templating, we make an evaluation on standard X-rays and we can make measurements regarding limb length inequality, bone loss and movement of the hip center away from the normal position,” Penenberg said. “Then, we can use the 3D preop templating to achieve accuracy in terms of sizing information, and then use that sizing information during the course of the surgery to stay safe and to expedite decision-making during the operation.”
For total knee replacement, intraoperative 3D imaging is used mainly in the context of robotics, which Penenberg noted has evolved significantly faster than robotics for hips. Orthopedic surgeons have generally accepted robotics for knees more readily than for hips on multiple fronts, such as bone preparation and implant placement, which must be considered for knees and the use of 3D imaging, he said.
“The imaging information we get during knee replacement is now tied to the use of robotics and robotic guidance, but hip replacement hasn’t gone down that road extensively thus far,” Penenberg said. “The cost of entry for hip robotics remains substantial.”
3D imaging in orthopedic oncology
In the context of orthopedic oncology surgery, determining the size of the tumor mass can be as important as determining what structures and tissue the mass may encroach upon. As an example, Potter discussed a tumor surgeon who needs to know whether a tumor in the thigh might be right up against the sciatic nerve.
“Going into surgery, the surgeon wants to know exactly what he or she is going to encounter when they open the patient up, so 3D imaging can be helpful in assessing tumor encroachment on vital neurovascular structures or muscle,” she said.
The orthopedic oncologist will often use MRI to assess the soft tissue structures, which is helpful if the lesion exists within the soft tissues, according to Major. If the lesion originated in the bone, however, the MRI helps show the extent of the lesion, and 3D reconstructions for CT may help show the course of a vessel over the lesion.
She said 3D imaging can help oncologists address important questions for surgery.
“What does the bone look like?” Major said. “How much of it is going to be resected? Can we place limb salvage hardware in there? In the setting of orthopedic oncology, it’s useful to have as much of that information as possible before going into the OR, so it is generally a combination of studies that helps to make these decisions.”
Added steps, training considerations
Overall, 3D imaging that aids surgically treating musculoskeletal conditions comes with few additional steps or extra training on the part of radiologists and orthopedic surgeons, according to sources.
“Once you’re analyzing the 3D imaging, most orthopedic surgeons are comfortable with it, whether it’s via MRI or any other modality, because it’s become so commonplace, especially for CT,” Pennock said. “It seems most orthopedic surgeons and musculoskeletal physicians are comfortable with it.”
The training radiologists receive during residency is adequate for interpreting any 3D examination that accompanies a study, which means they “grow up” with the tools to interpret this imaging, according to Major.
However, Potter said radiologists may benefit even more from partaking in an orthopedic imaging fellowship.
In the radiology suite, no additional equipment is required for 3D imaging, with the baseline requirement for its use being a CT scanner that can produce a narrow enough slice thickness, Major said.
However, use of 3D imaging technology may come with some additional costs. That may vary by institution.
“Most of the insurance providers we have run across at our institution have not reimbursed 3D imaging, so that is a cost we either eat or are putting into our research budgets,” Pennock said.
He noted the primary equipment required for 3D imaging used during surgery is an iPad or computer monitor attached to a CPU, as well as the 3D software, which can cost between $80,000 and $90,000. He said that is cheaper than and has similar precision to robotic surgical equipment.
Regarding specific software, Penenberg worked with Radlink Inc. to develop 2D to 3D technology within a proprietary software package.
“It walks the surgeon through the process, making all the required measurements, so at the end of the case, they know exactly what they have and, if there are adjustments that need to be made, they can be made during the course of the operation. We are no longer dependent on a postoperative X-ray to determine the accuracy of our operation when it is likely too late and high risk to make certain corrections,” he said.
Other specific 3D imaging technologies include the EOS X-ray imaging system, which Pennock has used to assess rotational anomalies of the lower extremities. He describes it as a “promising technique.”
Potter Sectra’s 3D post-processing software package, Ortho Tool.
“It’s worked well for us for assessing trauma, such as pelvic or acetabular fractures and complex upper extremity fractures,” she said. “It also allows us to do 3D models of conditions that require highly precise bone resection, such as for ... femoroacetabular impingement.”
Future era for imaging, innovation
Pennock said 3D, real-time ultrasound may usher in a new era of orthopedic surgical innovation.
“At our institution, we’re interested in better understanding the trochlear morphology in newborn children, and the 2D ultrasound doesn’t do justice to the complex anatomy of the knee,” he said. “A 3D ultrasound has no radiation, minimal cost and still allows us to see the articular cartilage. I’m predicting we’re headed in that direction.”
Techniques like preoperative virtual arthroscopy and preoperative operative planning may remove a lot of the guesswork of surgery, according to Potter.
“The concept of using fiducial markers in the operating room, potentially with robotic-assisted surgery, is going to streamline things and decrease anesthesia time, decrease operative time and overall improve operative recovery and the surgical outcome,” Potter said.
Bess emphasized the importance of additional research in shaping and improving applications of 3D imaging.
“I don’t think you can put technology over research,” Bess said. “I think you must have the research supporting the technology. We have this technology, and now we need to apply it to what we are finding in and, hopefully improving, for our patients. Only research will provide these answers.”
- Bess S, et al. Spine. 2016;doi:10.1097/BRS.0000000000001202.
- Line B, et al. Spine. 2020;doi:10.1097/BRS.0000000000003473.
- For more information:
- Shay Bess, MD, can be reached at 1601 E. 19th Ave., Suite 6250, Denver, CO 80218; email: firstname.lastname@example.org.
- Nancy M. Major, MD, can be reached at email: email@example.com.
- Brad L. Penenberg, MD, can be reached at 120 S. Spalding Dr., Beverly Hills, CA 90212; email: firstname.lastname@example.org.
- Andrew T. Pennock, MD, can be reached at Rady Children’s Hospital, 3030 Children’s Way, San Diego, CA 92123; email: email@example.com.
- Hollis G. Potter, MD, can be reached at Hospital For Special Surgery, 535 E 70th St., New York, NY 10021; email: firstname.lastname@example.org.