Feb. 25, 2017
Osteosarcoma and Ewing's sarcoma are the most common primary bone cancers in children and young adults, with a peak incidence in patients ages 10 to 25. These cancers primarily affect the metaphyseal portions of the bone in the hip and knee and because they are aggressive, amputation was long considered the only way to achieve local control of the tumor. Yet for decades, survival remained dismal — around 10 to 20 percent — even after amputation.
Today, the five-year survival rate for local pediatric bone cancers is 60 to 80 percent — a dramatic improvement since the 1970s, according to Peter S. Rose, M.D., a oncologic orthopedic surgeon at Mayo Clinic's campus in Rochester, Minnesota.
"Several simultaneous developments completely changed the outlook for these patients," he says. "Adjuvant chemotherapy regimens allowed better local and systemic control, improved imaging with CT and MRI allowed surgeons to more accurately assess the extent of the tumor and plan resection, and the development of custom implants opened the possibility of reconstruction instead of amputation, which was traditionally the treatment of choice. At one time, many surgeons believed limb salvage wasn't a viable option, but now limb-salvage techniques are the standard of care for most tumors."
Long-term studies dating back 30 years, including those at Mayo Clinic, have shown that limb-sparing operations performed with wide margins and chemotherapy do not compromise survival and, because techniques for limb salvage have improved significantly in the last few decades, oncological results are now comparable to amputation.
A Mayo Clinic study published in the September 2016 issue of Journal of Surgical Oncology reviewed 204 adult patients who underwent endoprosthesis for a malignancy of the proximal femur. Following the procedure, the mean Harris Hip and Musculoskeletal Tumor Society scores were 75 and 18, respectively. Five-year survival was 54 percent for patients with primary disease.
Surgical management in skeletally immature children
Reconstruction after resection of the proximal femur in children presents a special challenge for surgeons, however. After salvage, the limb should have an acceptable degree of function and cosmetic appearance and should be capable of withstanding the demands of normal daily activity as well as or better than an artificial limb.
But the prostheses typically used to achieve these aims in older teens and adults are unsatisfactory for skeletally immature children undergoing resection of the entire distal or proximal portion of the bone. Removal of the growth plate creates the potential for leg-length inequality in the contralateral limb, which continues to grow normally at a rate of about 1.6 centimeters a year. The younger the child when diagnosed with bone cancer, the greater the potential discrepancy at skeletal maturity.
Limb-length inequalities have profound functional and cosmetic consequences for young patients. Expandable implants that can be lengthened periodically were developed in the 1970s to address these issues.
The first generation of these implants had a worm gear mechanism that allowed a telescoping cylinder to increase the length by turning a screw through a small surgical incision. This had to be done repeatedly to keep pace with growth on the contralateral side and therefore required multiple surgical procedures with associated pain, rehabilitation time and infection risks.
The new generation of expandable prostheses solves these problems by using stored energy inside the implant that is activated noninvasively with a magnet outside the body. This allows controlled expansion without the need for surgery. Studies indicate little difference in cosmesis and function between traditional modular and noninvasive expandable implants. Both, however, have a high complication rate as well as bone loss around the stem of the prosthesis that may limit future revision options.
"With the expandability and flexibility come problems with durability," Dr. Rose says. "An endoprosthesis in a child will eventually need to be converted to an adult implant, and even implants in young adults will wear out in a few years, mainly due to infection and mechanical or fixation failure. All are difficult issues and some may overlap, but a discrete and frequent problem is how to obtain fixation in the bone when revisions are needed. Patients are already missing a large amount of bone due to cancer, so when a prosthesis wears out and further damages the bone, how do we adjust for that?"
One answer is self-adjusting compressive fixation, a relatively new limb-salvage technology that uses compression, via a traction bar, to stimulate osteointegration and provide fixation for short end segments after bone or tumor resection. It differs from traditional stemmed prostheses in that it requires only 4 to 8 centimeters of residual bone for fixation.
A study published in Clinical Orthopaedics and Related Research in February 2016, retrospectively reviewed 27 patients who underwent distal femoral reconstructions with the prosthesis over a 13-year period. The authors reported an 11 percent failure rate at 10 years.
Christopher P. Beauchamp, M.D., an orthopedic surgeon at Mayo Clinic's campus in Arizona, has been one of the pioneers in using compressive fixation and says it is an important option that can be incorporated into pediatric reconstructions. Still, prostheses eventually wear out.
"It's fair to say that over time, there is the expectation that all implants in children will wear out, but we hope to get 10 years of good solid function, and that is a great result," Dr. Rose says. "We have achieved this here at Mayo Clinic by adapting technologies and techniques from hip and knee replacements and revisions and using them in new ways for patients with cancer. This has been possible because of the collaborative work among cancer surgeons and orthopedic surgeons, including those who specialize in complex hip and knee replacement."
For more information
Houdek MT, et al. Functional and oncologic outcome of cemented endoprosthesis for malignant proximal femoral tumors. Journal of Surgical Oncology. 2016;114:501.
Zimel MN, et al. Revision distal femoral arthroplasty with the Compress prosthesis has a low rate of mechanical failure at 10 years. Clinical Orthopaedics and Related Research. 2016;474:528.