Extendable Leg Implant

The Gift of Growth

High-tech Extendible Implant Enables Femur to Grow Despite Limb Salvage Surgery 

By Lindy Keane Carter

Osteosarcoma (bone cancer) in children is rare. Approximately 400 cases are diagnosed in the U.S. every year according to the American Cancer Society. For those children whose cancer involves the growth plate at the end of their arm or leg bone, removal of the growth plate along with the tumor is necessary, leaving them with the possibility of uneven limbs when they stop growing. Rare as well are surgeons who have used the British-made extendible prosthesis that enables the extremity to grow as it would have, a procedure that has been done in the U.S. approximately 100 times since 2002. Lee R. Leddy, M.D., Associate Professor in the Department of Orthopaedics at MUSC Health, is the only orthopaedic oncologist in South Carolina who has experience with the JTS Extendible Bone Implant (Stanmore Implants Worldwide Ltd., Elstree, UK). This implant is designed to be lengthened over time by a magnet to ensure that both legs or arms will be equal in length when a child has finished growing. Leddy has implanted the prosthetic device twice in South Carolina, the most recent recipient being an eight-year-old from Columbia, SC. During the seven-hour surgery, Leddy and the surgical team first removed eight inches of the boy’s femur, including the growth plate, while preserving tendons, nerves, muscles, and blood vessels. Then the team assembled and implanted the customized prosthesis. The final step was to carefully replace the vasculature and tissue around the prosthesis and close the wound.

Leddy says this prosthesis is a dramatic improvement over the ways orthopaedic oncologists have previously met the challenges of limb salvage surgery in the skeletally immature patient. “Prior to this implant, the child would often require a surgery to manually lengthen the prosthesis every three to four months,” he says. “Being able to reliably lengthen the extremity without surgery is a major advantage. However, it is important to realize how critical the team approach is when treating these complex problems.”

The team of specialists who collaborated on this complex case included musculoskeletal radiologists who interpreted radiographs and magnetic resonance imaging reports, pathologists who evaluated biopsy tissues, sarcoma-trained surgical oncologists who helped resect the cancer and reconstruct the extremity, operating room nurses, oncologists who made recommendations regarding chemotherapy, and physical therapists who worked with the patient to help return him to an active life.

During follow-up visits every four to six weeks, the boy will place his leg into a doughnut-shaped magnet that will drive a gearbox to extend the prosthesis nine centimeters over the next eight years, the remainder of the boy’s projected growth. In his case, the magnet is proximal to the knee joint because his tumor was in the distal femur. For proximal femoral replacements, the magnet is near the level of resection. For tibia replacements, it is slightly below the knee joint.

Prior to this technology, options for a child whose growth plate had to be removed due to cancer were amputation; rotationplasty, in which the child’s ankle is substituted for the knee joint; or implants that required repeated surgeries to lengthen the prosthesis. With this device, future operations are not necessary. In August 2014, Zeke J. Walton, M.D., joined the Department of Orthopaedics, making him the second orthopaedic oncologist at MUSC Health who will be performing this and other procedures in treatment of complex bone cancer cases.