By: John E. Herzenberg, M.D., F.R.C.S.C., Shawn C. Standard, M.D., and Stacy C. Specht, M.P.A.
Case: A 15-year-old boy presents with limb length discrepancy that resulted after damage to the growth plate of the femur. The injury occurred during a football game 3 years earlier. Physical exam showed a healthy young man who walked with a limp and had full range of knee motion. The right femur was 3 cm shorter than the right. Surgical and non-surgical options were discussed with the patient and his family.
Discussion: Limb length discrepancy may result from congenital, post-traumatic, and developmental etiologies. Differences greater than 1 to 2 cm can cause a limp, back pain, hip pain, and/or arthritis. External shoe lifts can alleviate these issues but are not typically accepted by young adults. Surgical lengthening of the short limb offers a permanent solution. Classically, the method to lengthen a short leg required using an external fixator for many months. Potential complications include pain, scarring, infection, and fracture after lengthening. Wearing the external fixator for months at a time can be difficult to tolerate both physically and psychologically. Recently, alternative methods for limb lengthening have been developed that use fully implantable telescopic intramedullary rods.
In 2001, the first generation intramedullary telescopic rod was introduced in the USA. This was the Intramedullary Skeletal Kinetic Distractor (ISKD). The ISKD lengthened via a one-way mechanical ratchet mechanism. After the bone cut was performed and the ISKD was implanted, the leg was rotated back and forth. This movement caused the ISKD and the limb to lengthen through the bone cut. Having implanted more than 280 of these devices, we have had generally good results, but the mechanism was difficult to control accurately. As a result, many limbs inadvertently lengthened too quickly or too slowly. Lengthening too quickly may prevent the bone from healing and can cause joint contractures, excessive pain, and even peroneal nerve stretch injuries.
More recently, second generation technology has been released. The Precice rod, approved by the FDA in January 2012, contains a tiny internal magnetic motor, gearbox, and telescopic mechanism. Although similar in external appearance to the ISKD, the Precice rod lengthens only when an external magnetic field generator is placed against the leg. The external magnetic field generator is held next to the leg for a few minutes to power the magnetic motor inside the rod in a precisely controlled fashion.
In this case, the patient opted to have his femur lengthened with the Precice rod. Seven days after the Precice rod was inserted, he started the lengthening process at a rate of 1 mm/day. This rate was increased to 1.5 mm/day when rapid bone healing was seen on follow-up radiographs. Pain was well controlled with oral analgesics. Joint range of motion was maintained throughout the lengthening process during physical therapy sessions five times a week. Radiographs were obtained weekly to ensure that the Precice rod and the external magnetic field generator were working properly. The femur lengthened 3 cm uneventfully over the course of four weeks (Fig. 1A). It was fully healed six weeks after lengthening was complete (Fig. 1B). At this time, the patient was allowed to fully weight bear without assistive devices and has returned to full activity.
Since January 2012, we have implanted 17 Precice rods. Although our experience is still early, the Precice rod appears to be a significant improvement over the first generation ISKD technology, providing a more accurate rate of lengthening and less pain than with the ISKD.
John E. Herzenberg, M.D., F.R.C.S.C., director, Shawn C. Standard, M.D., head of pediatric orthopedics, and Stacy C. Specht, M.P.A., research program manager – all at the International Center for Limb Lengthening, Sinai Hospital of Baltimore. Contact Dr. Herzenberg at firstname.lastname@example.org.