October 17, 2019
Computer-assisted design technology complements navigation system in pioneering orthopaedic surgery
BY Sarah Zizinia
Combining a 3D virtual cutting guide with a surgical navigation tool allowed MD Anderson surgeons to perform a complicated pelvic reconstruction more efficiently while increasing the anatomic accuracy and likely durability of the repair.
In this first such case, the combined technology allowed a more precise fit for an implant crafted from the patient’s fibula.
“When there is a really good fit, the survivorship of the implant is optimized. Precise cuts, precise implants, good fixation – the implant won’t fail,” says surgeon Justin Bird, M.D., associate professor of Orthopaedic Oncology. “That’s what we’ve been challenged with for years. We have the technology to make implants but current pelvic implants fail at a very high rate due to infection and mechanics.”
Earlier this year, Bird met a 38-year-old patient who had been diagnosed with chondrosarcoma, a type of bone cancer that starts in cartilage cells. The tumor on her ilium, the uppermost part of the hip bone, was believed to be the result of a hereditary condition called Multiple Hereditary Exostoses. MHE causes the patient to develop osteochondromas, which are benign entities with bone and a cartilage cap, in various parts of the body. Patients with this condition are more commonly at risk for developing a malignant sarcoma from the osteochondroma.
The patient also had metastatic lesions on her lungs and spine. Historically, chondrosarcomas do not typically have effective chemotherapy options but this patient responded remarkably well to treatment. Following chemotherapy, surgery was necessary to address the primary tumor on the inner wall of the ilium.
The typical surgical approach to this type of tumor is an internal hemipelvectomy, which is a technically demanding procedure. During surgery, a portion of the pelvis is removed while preserving blood supply and nerve function to the lower limb. Various reconstructive options are available to the surgeon to reconnect the pelvic ring depending on the location of the tumor.
An innovative marriage of technologies
Bird, who partnered with Alexander Mericli, M.D., assistant professor of Plastic Surgery, decided that part of the fibula bone, found in the lower leg, should be used to stabilize the pelvic ring once the tumor and affected bone were resected. The use of the patient’s own living bone (as opposed to hardware) can lead to lower infection rates and better mobility outcomes. Patients will usually have normal gait and mobility in about three years when using bone.
As the pelvis is a complicated space, the surgery required unique cutting angles. The tumor, nerves and joints can be in the way and the patient is positioned differently in surgery than when CT images are initially taken. The surgeons decided to explore the use of a virtual cutting guide to achieve optimal results. Mericli commonly uses 3D cutting guides for mandible reconstruction.
An engineering company provided a 3D reconstruction of the patient’s CT scan showing the tumor on multiple planes so the surgeons were able to decide ahead of time where they wanted to make their cuts. Based on that data, a virtual cutting guide was made and imported into Brain Lab, an intraoperative navigation system.
Once the patient was in the operating room, another CT scan was taken for a real-time image of the patient in position. The navigation system allows the surgeons to use their tools to simultaneously touch the patient and see the cutting guide on the screen.
Because of the precise measurements of the planned resection, Mericli knew the exact size of the fibula that was needed to reconstruct the pelvis.
Benefits and outcomes
According to the surgeons, the main benefits of this kind of technology are more anatomically accurate and durable reconstructions, as well as reduced operative time.
“Without this modeling, we do this work but it’s a lot of craftsmanship and oftentimes, the cut of the bone is not exactly what we had envisioned and the space is much different. We have to do measurements intraoperatively and that makes for a longer surgery time,” explains Bird.
“Usually these surgeries can last until two or three in the morning. With this one, we were done by 6 p.m. and I think in part that was because the operation was made much more efficient by virtue of this upfront planning,” says Mericli.
Bird adds that the success of this surgery could have bigger implications – more precise implants. “We will be able to create 3D implants that have a greater chance of successfully matching the resection space.”