Limb Lengthening: A New Breakthrough for Limb Length Discrepancy (LLD)
In August 2011, a new implantable lengthening device called the Precice was approved by the FDA. It was developed by Ellipse Technologies in conjunction with a team of orthopedic surgeon consultants, including Dr. Dror Paley. Ellipse used an internal lengthening mechanism that they had developed for use in the spine. The major advance of this device is that it has complete rate control and can even go reverse (shortening). Inside the lengthening nail there is magnet, which is connected to a gearbox that is connected to a screw shaft. Rotating the magnet also rotates the screw shaft and lengthens or shortens the telescopic nail. To rotate the internal magnet there is an external actuator that is held by hand and applied to the limb. The actuator has two magnets that are rotated by a motorized system while they are held against the leg at the level of the internal magnet in the nail. It takes hundreds of revolutions of the external magnet to effect a 1 mm change in length of the nail. The actuator lengthens the nail if it is facing one way and shortens it if it is facing the other way. It takes 7 minutes to achieve 1mm. The nail is designed to be able to lengthen against a force of 80kg (176 lbs). The forces that need to be resisted inside the limb have been reported to be up to 50 kg (110 lbs). Therefore, this nail is more than strong enough to lengthen the limb.
Although each nail is for one-time use, the actuator can be used for many patients. At present, the FDA approved the use of the actuator only for the physician’s office. This means that the patient must come in to the office daily to have the lengthening performed, including on weekends and holidays. The Precice can lengthen up to 6.5cms, although this amount may increase in future models. Our orthopedic technologist performs the lengthening for each patient daily. If there is any problem he alerts the clinical team, and the patient is seen by a physician assistant or doctor the same day. Since patients undergo daily physical therapy (PT) sessions at the Paley Institute, we coordinate the lengthening session with the physical therapy schedule. Patients have an x-ray every week to monitor the lengthening. The x-rays are measured to confirm that the amount of lengthening that the actuator did has in fact been achieved. After the x-ray they are seen by one of our doctors or PA’s.
The Precice ushers in a new era for limb lengthening. We now finally have a device that can be implanted with minimal incision surgery and which can perform lengthening by a remotely controlled mechanism without rate control problems. The safety factor with this device is excellent since it can be lengthened at any rate and can even be reversed to shorten the limb. Rate control should eliminate most of the complications we saw with the ISKD. At present, we are the only center in the United States to implant this device but we expect other centers to start using it.
Despite the ease of insertion and use, the limb lengthening process remains the same and the risks associated with limb lengthening remain unchanged. For these reasons it is still essential that a surgeon experienced in limb lengthening and in the treatment of lengthening complications be he one performing the procedure and following the patient. (see complications section below)
Recovery from Implantable Limb Lengthening
The typical recovery from femoral or tibial lengthening is as follows:
1) Surgery and hospitalization: 3-4 days
2) Distraction phase; daily lengthening one mm per day; walking with crutches or walker; 50% weight bearing (WB) allowed on the lengthened leg and full WB on the untreated leg; daily physical therapy (PT); patient allowed to shower, bathe and go in swimming pool; patient allowed to drive 2 weeks after surgery (for patients over age 18)
3) Consolidation phase until full WB permitted = 1 month in most but can be longer. The end of this phase is when the bone on the x-ray appears to bridge the lengthening gap at least on one side. WB is progressed to full WB.
4) Rehabilitation phase: full WB without crutches, regaining of muscle strength and joint range of motion to normal. Usually 1-3 months.
5) Return to sports usually by 4-6 months after surgery.
Removal of Implant
The implantable lengthening device should be removed. Although it is made of inert metal (either titanium or stainless steel), there are also other materials including rare earth magnets, etc. The moving parts also can lead to wear and even corrosion. For these reasons it is preferable to remove the device. The device can usually be removed as early as one year after surgery. There is no urgency in the timing of removal but it should be done. The removal is an outpatient procedure. It can be deferred for more than one year.