Rush University Medical Center Chicago, Illinois

Limb preservation is now the procedure of choice for the treatment of bone cancer. This operation is performed in 2 complex steps: The first is to remove the cancer with adequate margins, and the second is to reconstruct the bone and, at times, the joint.

With advances in chemotherapy, imaging, and reconstruction, patients can expect excellent oncologic and functional outcomes. Patients are living longer; therefore, the durability of the reconstruction is an important issue. With the potential to improve longterm implant durability, 3-D printing represents an excellent manufacturing technique for these cancer devices. In this process, a laser is applied to metal particles to layer the desired shape and size of the implant horizontally. Surface features, such as pores of critical diameter, can also be designed into the implant to aid tissue ingrowth.

Conventional modular oncology devices are either cast or machined and have limited ability to aid bone and soft tissue ingrowth. With 3-D technology, variable porosity sizes can be engineered into the device in specific locations to promote either bone or soft tissue healing. The healing of soft tissue such as tendons and ligaments is critically important for the function of the prosthesis. For example, reattachment of the hip abductor tendons to the prosthesis will greatly aid in the patient’s gait, strength, and implant stability. Reattachment of the patellar tendon to proximal tibial components will also improve quadriceps function and overall gait.

With 3-D techniques, orthopedic oncology devices can be printed in cobalt chrome or titanium, and alternative porosity sizes can be incorporated into the stems and collars to facilitate bone ingrowth. This application has better long-term fixation over a cemented device because it eliminates the possibility of cement failure, a common mode of failure in older implants.

The printing technology can be extremely useful during an operation on a patient with cancer. Using patient-acquired 3-D digital data from a CT and an MRI, an anatomic model can be printed for the surgical team. This model accurately depicts the extent of the cancer in the bone and soft tissues, allowing the surgeon to remove the cancer with a minimal amount of normal tissue. It also shows the relationship of the malignancy to the nerves and blood vessels so they can be spared during the resection.

Using this technology, a surgeon can sometimes save the joint from resection, allowing for a more normal functional outcome. A cutting guide can be printed to aid the surgeon in removing just the right amount of bone and tissue to ensure an adequate cancer operation but spare normal bone.

Bone allografts are frequently used to restore bone removed after limb salvage surgery. Critically, the donated bone must be the exact size and shape to replace the missing bone. The 3-D—generated cutting guide can be used to accomplish this purpose. The guide can be placed on the allograft to create a precise fit. This graft is then placed in the patient and held in position with metal plates and screws until healing occurs.

The pelvis is a particularly challenging site for performing limb salvage, as it is a very large, complex bone with critical function. It supports the spine and hip joint. Removal of pelvic cancer in the past was a very difficult and dangerous procedure. Vital structures such as the bladder, the bowel, blood vessels, nerves, and arteries lie in close proximity to the pelvis and are in jeopardy during these operations.

Before modern technological advances, surgeons performed pelvic bone cuts freehand, with a significant amount of surgical estimation. However, 3-D—printed cutting guides allow the engineers and surgeon to more precisely plan the resection to ensure complete removal of the cancer. This same technology can be used to manufacture a pelvic replacement implant to restore the hip joint.

Currently, 3-D—printed cancer devices undergo rigorous FDA review, with more checks for safety and effectiveness compared with more conventional machined or cast devices. At Rush University Medical Center, we use 3-D technology in our clinical practice and have found it to be quite useful. Our division is also studying its efficacy from the perspective of oncologic outcomes as well as functional impact. We look forward to seeing what the future holds for this promising technology.

Articles

Limb preservation is now the procedure of choice for the treatment of patients with bone cancer.

Alan T. Blank, MD, MS

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3-D Printing Technology Enhances Limb Preservation in Cancer Operations