When to Use 2D Radiography versus 3D CT for Orthopaedic Surgical Planning and Post-Op Evaluation

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Clinical studies identify when to use 3D computed tomography for foot and ankle injuries.

By Anish R Kadakia, MD, Northwestern Memorial Hospital

Although computed tomography for medical imaging has been available for some time, weight-bearing 3D CT is a relatively new modality. For the past year, Northwestern Memorial Hospital has been evaluating when and whether to use 3D CT rather than 2D weight-bearing radiography for preoperative planning and post-op evaluation.

Based on my experience, here are my recommendations for when to use 3D CT for orthopaedic surgical planning and post-op evaluation rather than 2D radiography. For all clinical cases described in this blog, I am referring to weight-bearing images, regardless of modality.

When to Use 2D Radiography versus 3D CT for Foot and Ankle Injuries

In general, I use weight-bearing CT imaging for cases where it is difficult to determine the primary problem; and/or when I want to see the actual structure of a joint. Specifically:

Preoperative surgical planning

• Deformity and extent of arthritis for the midfoot.
• Hindfoot, midfoot, and ankle nonunion/malunion.
• Hindfoot deformity.
• Flat foot deformity, especially for obese patients.
• Nonunion/malunion of a fracture
• Fractures where the 3D anatomy is critical to fixation (trimalleolar ankle fractures, talus/calcaneal fractures, midfoot fracture)
• 1^st MTP/Great toe pain to determine the cause of pain. Many patients presume it is a bunion when in reality, arthritis is the problem. The images make the problem clear to them and help them understand that they need a fusion.

Post-operative evaluation

• Evaluate malunion and/or non-union, and syndesmotic incongruity.
• Following arthrodesis to determine whether any growth and union has occurred. 

The weight-bearing images we have captured with 3D computed tomography have changed my surgical plan two out of three times. And for post-op, I can see the truth, even when the outcome is not as good as I hoped it would be. The modality we use is the CARESTREAM OnSight 3D Extremity  System which includes excellent metal artifact suppression. All the images I reference in this blog were captured on the Carestream system, which is located within our facility.

When Not to Use 3D CT for Orthopaedic Surgical Planning and Post-Op Evaluation

Through my experience this past year, I have also determined when it does not make sense to use the OnSight System.  In the cases below, I order weight-bearing 2D X-rays:

• When a patient is clear that they do not want surgery, regardless of diagnosis.
• Toe fusion – unless I need the image to educate a patient who insists the problem is a bunion.
• Post op at 6 weeks, with some exceptions. 

Clinical Cases for 3D Computed Tomography in Surgical Planning for Foot and Ankle

Malunion and syndesmotic incongruity

This patient was an active skier who had previously received an open reduction and internal fixation of the fibula at another hospital. He was given the green light to be weight bearing as tolerated.  He came to me with his post-op X-rays which showed no issues.

However, our weight-bearing CT image showed the fracture morphology, and allowed me to identify the malunion of the posterior malleolus (untreated) and syndesmotic incongruity. The OnSight System has 3 X-ray sources for an improved field of view, so I could capture nearly the entire foot and ankle in a single view.  In contrast, regular CT can only capture the calcaneus to distal midfoot.

I scheduled the patient for a 360 repair of his ankle fracture. By seeing the real injury early on – and the need to revise it – we likely prevented further damage through weight-bearing activities.

Triple arthrodesis  

In this case, a new patient came to me after having had a triple arthrodesis two years prior. The patient presented with lateral hindfoot pain. The cause was inconclusive on the X-ray. Was it lateral ankle arthritis? Was it nonunion? A malunion? That looked likely; however, it could be just the tilt of the X-ray. Diagnosis was complicated further by the patient’s obesity. The amount of soft tissue in the foot made it difficult to assess how much healing had taken place from previous surgeries.

With a weight-bearing CT, it was obvious that the ankle was not the problem. The cause was the nonunion/malunion of the subfibular impingement, and lateral ankle arthritis. Again, note the importance of a weight-bearing CT. Had I done a non-weight-bearing CT, the foot could kick back into a neutral position during imaging.

“CT images give me more information and definitive answers about alignment and union.” – Dr. Anish Kadakia

The weight-bearing 3D CT image let me plan my osteotomy. The patient underwent a third revision and I was able to rotate the calcaneous back into place. If I didn’t have a weight-bearing CT image, I might have decided to do simple lateral wall exostectomy, and there would be no calcaneus left.

At six months post-op, I did a weight-bearing X-ray, but it was difficult to see if any healing was taking place. However, the weight-bearing CT showed some healing. The patient knows that a TAA is likely in the future. However, the good news for now is that his hind foot is fusing well.

Going forward, all his images will be done on the OnSight because of the amount of soft tissue in his foot. Having CT instead of 2D radiography images post op gives me more information and definitive answers about alignment and union.

Infected ORIF talus

This patient had 17 previous surgeries with complications, and needed to know if she was facing amputation. The 3D CT image showed that she had an infected ORIF talus, and that two flaps were required.

Following the surgery, the weight-bearing CT image let me accurately determine union and alignment. I also was able to see integration of bone, bone growth, and that there was no hardware failure. I don’t know what her long-term prognosis will be, but at least for now, I can see that she is healing.

3-month-old ankle sprain

This patient had been weight-bearing with pain for three months before he saw me. I could not see anything amiss on the X-ray. He was very swollen and diabetic so I casted him and told him to be non-weight-bearing.

After multiple serial exams and casting to reduce the swelling, the foot was deforming more. A weight-bearing CT showed a hindfoot subluxation that had formed over time, likely during the three months he was weight bearing before coming to see me. This injury is nearly impossible to diagnosis on 2D X-ray.  Without the weight-bearing CT, it would have been difficult to formulate a logical surgical plan.

At three months post-op, I ordered a weight-bearing CT so I could see the anatomy detail and give him appropriate information to guide his treatment. I could tell him with confidence that he could now start weight bearing, and the deformity was corrected.

Metal Artifact Reduction Enhances Orthopaedic Image Capture

For several of these cases, my ability to make accurate diagnoses was possible in part because of the metal artifact suppression software in OnSight. In my opinion, Carestream’s metal artifact suppression is the best in the industry.

Advanced scatter and metal artifact reduction algorithms enhance my ability to visualize the joint or fracture of interest, despite the presence of hardware. I can actually see the structure of a joint. I can see where a plate ends without getting all that scatter, and the plates don’t obstruct the view.  

Here is an example of where the suppression helped inform my diagnosis.  I performed an intraoperative correction of deformity through fusion for post-traumatic arthritis secondary to a non-surgical treatment of a trimalleolar ankle fracture.  At eight months out, the patient – who is a laborer – wanted to return to work. He did not have any pain and the X-ray looked good.

However, he has a lot of metal in his foot so I ordered a 3D CT which showed only moderate union – about 20 to 30 percent. Also, the back was not healed. For these reasons, I advised him to restrain from hard labor. I could not have been as definitive in my counsel if the system did not have excellent artifact suppression.

Radiation Dose of OnSight 3D CT Compared to 2D Radiography and Regular CT

Some of my orthopaedic colleagues have asked about the level of radiation dose. The radiation dose of the Carestream OnSight system is 1/3 that of a traditional CT.  If you’d like more information on this topic, read the white paper on CBCT Dose Considerations below.

Also, depending on the patient, one CT image from the Carestream OnSight System might save the patient from receiving multiple non-definitive X-rays. That certainly was the case for my patient with triple arthrodesis. It also saved him money.

3D weight-bearing CT has revolutionized my orthopaedic practice

The clinical cases I shared are just a few examples of how 3D weightbearing CT has changed and improved my surgical plans. However, the Carestream OnSight system has changed my practice for the better in other ways, too.

The system is physically located within our practice. It does not require a shielded room, and it has a very small footprint. Having it on site allows us to image patients and review the results in one office visit. I did not fully understand the benefit of this initially. But after a year, I can say that the ability to do this in office and on the same day has increased patient satisfaction and improved my surgical capture.

I already mentioned one example of increased patient satisfaction: patients who need a fusion rather than bunion removal. With the CT images, they can clearly see the problem and understand the need for fusion.

Here is another example. A female patient came to see me after seeing multiple surgeons. She was 2 year s/p Lapidus; 1 year s/p “synthetic cartilage” replacement and had complications. The X-ray image was hard to interpret.  With the WB CT, I was able to determine that the 1^st metatarsal was fused in a dorsiflexion malunion, leading to transfer metatarsalgia.  Additionally, the metatarsal head had some sufficient bone left dorsally, which was important for surgical planning.

With this information, I was able to create a plan to plantarflex the 1^st TMT fusion through a revision osteotomy and then perform an arthrodesis of the 1^st MTP joint. Without the knowledge of the dorsiflexion malunion of the 1^st metatarsal, isolated fusion of the 1^st MTP would not have restored the mechanical advantage of the 1^st ray and left the patient with a deformity and continued pain.  Although I told her I was not certain about the outcome, she opted to have me do the surgery. She said the CT image gave her the confidence that it was the right step.

For myself and my orthopaedic patients, using 3D CT rather than 2D radiography is letting us see and understand the truth much better than we could before.

Resources:

• Learn More about the Carestream OnSight 3D Extremity System.
• Read the white paper on CBCT Dose Considerations.
• Read the blog by Dr. Bryan D. Den Hartog, M.D., Orthopedic Surgeon Twin Cities Orthopedics, on 3D Extremity Imaging in Orthopaedic Practice.
• Read the blog by Dr. Lew Schon, M.D. FACS, on Extremity Reconstruction’s Game Changer: Weight-Bearing CT Imaging.
• Read the blog on Building Orthopaedic Practice Revenue with the OnSight Extremity System.

Anish R Kadakia, MD is a Professor of Orthopedic Surgery at Northwestern University/Northwestern Memorial Hospital. He received his medical degree from Northwestern University Feinberg School of Medicine (2000). His postgraduate training was Resident: Northwestern University, McGaw Medical Center, Orthopaedic Surgery (2005); and Fellow: Mercy Medical Center, Baltimore, MD, Orthopaedics (2006).

He is board Certified by the Orthopaedic Surgery, American Board of Orthopaedic Surgery. His honors and awards include: James Stack Teaching Award, Orthopedic Surgery (2016); Top 16 Orthopedic Foot and Ankle Surgeon in North America, Orthopedics This Week (2015); and William S. Smith Resident Teaching Award, University of Michigan – Department of Orthopedic Surgery (2011).

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