Minor leg length discrepancies are common — 23 percent of the general population has a discrepancy of at least 1 centimeter. The prevalence of leg length discrepancies requiring correction is about 1 in 1,000, whereas the most severe problems, such as congenital femoral deficiency, are quite rare. Limb lengthening has long been an accepted treatment for both common and complicated discrepancies and deformities, although the indications have broadened considerably over the last 100 years.
Originally used to correct discrepancies resulting from poliomyelitis, war injuries, and fracture malunion or nonunion, limb lengthening is now used for a wide range of congenital, metabolic, oncologic and post-traumatic orthopedic problems. It is also an accepted treatment for short stature — a common feature of some musculoskeletal syndromes. The goal of the Limb Lengthening and Regeneration Clinic at Mayo Clinic's campus in Rochester, Minnesota, is to improve pain and maximize function for patients with limb deformities and deficiencies while simultaneously managing the underlying disorders.
To accomplish this, the clinic brings together eight subspecialists within orthopedic surgery — including surgeons trained in orthopedic trauma, pediatric orthopedics, orthopedic oncology, foot and ankle surgery, and hand and upper extremity surgery — as well as plastic and reconstructive surgeons, medical geneticists, endocrinologists, and radiologists. Stephen (Andy) A. Sems, M.D., an orthopedic surgeon at Mayo Clinic's campus in Minnesota and a consultant in the limb clinic, says this reflects the traditional Mayo approach.
"In the Mayo model, experts from different specialties and subspecialties collaborate on each case. This has been the standard throughout the institution for decades, and now we are applying it to limb lengthening," he says. "Our long-term goal is to provide patients with the highest quality outcomes they can hope for."
Arguably the greatest recent advance in limb lengthening was the 2011 Food and Drug Administration approval of Precice, an implantable intramedullary rod (nail). The rod, which is indicated for limb length discrepancy and short stature, is surgically implanted in the intramedullary canal of the tibia or femur. It has a magnetic metal spindle connected to a series of gears.
The gears, in turn, are connected to a coupling and threaded drive shaft that is activated by an external, remote-controlled device operated by the patient. The remote control contains two magnets that rotate the spindle. Depending on the direction, the distracting rod either lengthens or shortens at a maximal rate of 1 millimeter a day, thus achieving 50 millimeters of lengthening in about 50 days. The shortening function can be used for soft tissue problems or to stimulate additional bone formation.
Accurate rate control is one of the major advantages of the new device. Earlier implantable rods were plagued by imprecise distraction, leading to nerve injuries, joint contractures and nonunions.
A review published in 2014 in Clinical Orthopaedics and Related Research evaluated the accuracy, precision and associated complications of the Precice rod in 24 patients who underwent tibial or femoral lengthening or both between 2012 and 2013. The most common etiologies were congenital leg length discrepancy, post-traumatic growth arrest and fracture malunion.
The mean total lengthening was 35 millimeters, with an accuracy of 96 percent and precision of 86 percent. All patients achieved the intended distraction goal without a change in bone alignment or knee and ankle range of motion. One patient experienced implant failure caused by a nonfunctioning distraction mechanism; six others had nonimplant-related complications, including delayed bone healing. In Mayo Clinic's experience, the complication rate is less than 5 percent.
"One of the main complications we see is knee joint stiffness with femoral lengthening and ankle joint stiffness with tibial lengthening, so our patients undergo aggressive physical therapy every day during the lengthening and consolidation periods. Maintaining range of motion and preventing contractures during the one- to three-month rehabilitation phase reduces the time to return to normal function," Dr. Sems says.
The device is usually removed 12 to 24 months after implantation, when the bone has fully healed on all four cortices.
Some patients needing limb lengthening who have previous implants, associated deformities, active infection or other confounding factors may need treatment with an external fixator rather than an internal system. The fixator, which consists of two or more rings connected to six telescopic struts that can be lengthened or shortened, allows gradual lengthening and deformity correction by adjusting strut lengths according to a computer-generated treatment plan.
Complications such as pin tract infections and soft tissue tethering as well as the physical and psychological discomfort patients often experience are limitations, but Dr. Sems says experience with external fixators has improved dramatically. "Twenty-five years ago, many patients with limb deficiencies and deformities were told nothing could be done for them," Dr. Sems says. "But there have been tremendous advances in the last five years and our clinic now has options for almost all patients."
For more information
Kirane YM, et al. Precision of the Precice internal bone lengthening nail. Clinical Orthopaedics and Related Research. 2014;472:3869.