Anna Fischer November 29, 2018

Precise planning for complex surgery

Soldiers say that no battle plan survives the first contact with the enemy. But when the ‘enemy’ in question is cancer, and the battle is to save a limb or even a life, the plan has to work. No surprises. It’s a familiar and complex challenge that surgeons face day in, day out.

Which is why as well as viewing and analyzing detailed information from MRI or CT scans before a major operation, many surgical teams now also call on 3D visualization and 3D-printed models to make sure planned procedures reflect reality.

 

Pre- Chemo and –Op Images of the left femur with the Ewing sarcoma
Pre- Chemo and –Op Images of the right femur with the Ewing sarcoma

 

“With all the soft tissues and skin in the way, what surgeons experience in surgery can be completely different to what they see on a 2D scan”, explains Mieke Motmans, Clinical Engineer at Materialise. “Using 3D digital and physical models gives an extra level of information and to work out exactly how best to proceed – it’s like the difference between outlining a journey on a paper map, and using a GPS that tells you exactly where you are going and when you will get there.” It was exactly this precision that PD Dr A.H. Krieg and his colleagues at the University Children’s Hospital in Basel, Switzerland – the people tasked with saving Daria’s leg – knew they needed for this procedure.

 

Charting the surgical procedure

The plan was complex and courageous: remove the tumor and reconstruct Daria’s femur using a combination of her own live fibula and an allograft (donor) bone. “Endoprostheses (artificial bones) are the usual limb-salvage treatment if the tumor is close to the knee joint or extends to the epiphysis”, says Dr Krieg, “but this is rarely possible for children as young as Daria – there are high complication rates. Making the reconstruction a success meant using 3D printing to its full potential and working with the right experts.”

Materialise has worked hand-in-hand with surgeons on planning for over 2000 osteotomy cases – corrective surgery where a bone is cut to allow realignment – and has designed and printed more than 700 custom implants or endoprostheses. It’s that experience that Dr Krieg wanted for Daria. “I’d actually worked with Mieke and her team before, so I knew they could help”, recalls Krieg. “The first step was uploading our MRI and CT scans of Daria’s leg to Materialise’s online portal for evaluation.”

Motmans, who specializes in oncology (cancer) cases, and her team’s initial work involved aligning meshes from the CT and MR, checking them in the Mimics medical imaging processing software and verifying the tumor’s position. “Finding the tumor outline is where we start,” she explains. “Sometimes tumors are only visible in MRI, so Mimics helps us transfer its boundaries to the more accurate CT scans. Then we combine the CT scan ‘slices’ to build the 3D bone geometry model that lets surgeons see the overall picture and zoom in to the detail.

“Some surgeons have a very clear idea of what they want to do, while others will simply send us the scans and ask us for a solution. Either way, getting to this stage – seeing the 3D model – is often a critical moment. The model’s accuracy lets us verify the planned approach and sometimes it can be very obvious that the initial plan just isn’t going to work.”

The Basel team collaborated remotely with Materialise to map out the surgical procedure – which side to access the bone from, where there was too much soft tissue – and position the resection planes that would be used to show exactly where saw cuts would be needed around the tumor. It was an intricate process. The team had to retain as much original bone as possible to keep Daria’s knee joint intact and to support the screws for the titanium bridge that would hold the remaining bone, the allograft and fibula as they grew together during osteosynthesis. But as her tumor was so big, and so close to her knee, the margins were tight. Together, the engineers and surgical team repeatedly fine-tuned their plans, poring over CT scans of potential allografts to find the best-fitting donor bone.

 

Charting_the_surgical_procedure_0.jpg

 

“Where to cut the tumor influenced the size of the hole, which in turn governed the required shape of the donor bone,” explains Motmans. “We couldn’t print anything until the whole planning stage – where to resect the tumor and allograft, the plate size, the position of the screws – was complete.”

Flawless planning prevents unpleasant surprises

Though they had to trim their normal safety margins and sacrifice the lower epiphyseal (growth) plate which contains the live growing bone tissue, the surgeons were finally confident enough to set the resection planes. Then it was time to make the plans reality.

Materialise 3D-printed the models and the three cutting guides – two for the femur and one for the allograft. Slots created in these templates would be used to position the surgeon’s saw blade exactly, with carefully positioned holes also directing the drill to ensure correct screw positions and insertion angles. The allograft guide developed also defined the channel where the fibula would be inserted. With models showing pre- and post-operative bone geometry, Motmans was able to check that each cutting guide and plate fitted exactly, before shipping them on the next plane to Basel.

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As with all operations it supports, Materialise also supplied posters with images and step-by-step surgical instructions to pin to the wall of the operating room, plus a report summarizing the operation process and metrics. So would Daria be able to dance again?

“The operation lasted ten hours, involved seven surgeons and was a great success,” reports Dr Krieg who led the team. “Although Daria still has a long way to go in rehabilitation, she now has the chance to make a nearly full recovery and use her leg without major restrictions.”

 

X-ray-6-weeks-and-3-months-after-surgery.jpg
X-ray 6 weeks and 3 months after surgery

 

For Motmans, Daria’s successful procedure is the perfect example of why 3D Printing is such a vital surgical aid. “The skilled teams that perform these operations are amazing”, she concludes.

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“To be able to help them is a privilege. 3D printing means surgeons can plan ahead, allowing them to deal with problems before they even enter the operating room, and so avoid surprises during surgery. That’s an outcome that’s great for everyone.”
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