Limb Lengthening: How Does It Work?

The limb lengthening process works by gradually growing new bone and soft tissues (skin, muscle, nerves, blood vessels, etc). This new growth is called tissue regeneration. Bone and soft tissue regenerate when they are distracted (pulled apart) at a very slow rate of approximately 1 mm per day. If the rate of distraction is faster than this, bone may fail to form between the two ends of the bone that are being pulled apart and soft tissues, such as muscle, may experience contracture (get too tight) or nerves may become paralyzed. If the rate of distraction is too slow, premature consolidation may occur (the bone may consolidate too soon), preventing the lengthening device from further pulling it apart. There are many different lengthening devices used. The most common are external fixators, which are devices that attach to the bone by means of thin wires or thicker pins that have a screw threading at their attachment to the bone. There are also lengthening devices that are fully implanted inside the bone. These devices do not require external pins. The different devices are described separately.

There are two phases of lengthening until the bone is fully healed: the distraction phase and the consolidation phase. The distraction phase is the lengthening phase. After the desired length is obtained, the newly regenerated bone is still very weak because of lack of calcium within it. The hardening and calcification of this new bone is called the consolidation phase.

Methods of Lengthening

At the The International Center for Limb Lengthening, we use a variety of orthopedic devices to distract the bone and soft tissues. The decision regarding which device to use is individualized for each case, so that the best method to achieve the desired correction can be chosen. There are two general types of devices: external fixators and internal fixators. The external devices attach to the bone from outside the body by means of wires and threaded pins. The internal devices are implanted inside the body and lie on the bone or inside the marrow cavity of the bone. The best known and most versatile techniques are with monolateral (one-sided, or straight bar) external fixators (e.g., Orthofix, Heidelberg, EBI) and circular external fixators (e.g., Ilizarov, spatial frame). External fixators are applicable to almost all cases. To shorten the time in the external fixator, we often combine the external fixator method with an internal nail to perform the lengthening over nail (LON) technique. This method is not applicable to all cases. We have also used a fully implantable self-lengthening nail and a self-lengthening prosthesis that have an internal mechanism that performs the lengthening and thereby eliminates the need for an external fixator. This method is available for certain cases.

External Fixation Alone

When only an external fixator is used, the fixator needs to remain in place for both the distraction and consolidation phases. If the fixator were removed at the end of the distraction phase, the new bone would collapse and reshorten. Therefore, the external fixator needs to remain in place until the regenerated bone appears solid enough on the radiographs (x-rays). At that point, the device can be removed. Often, a cast is applied to temporarily protect the bone from breakage for an additional short time. The total time in the external fixator can be estimated to be approximately 1 month for each centimeter lengthened in children and 1.5 to 2 months or longer per centimeter in adults.

Lengthening over Nail

To decrease the external fixator treatment time, eliminate the need for post-removal casting, and decrease the risk of breakage of the new bone, we developed a method called LON. With LON, we insert a metal rod into the bone together with the external fixator. The rod fits in the marrow cavity of the center of the bone, and the external fixator is applied around the peripheral part of the bone so that the external fixator pins do not come in contact with the metal rod. The bone is lengthened as described above. After lengthening is completed, the patient goes back to the operating room for the insertion of special screws that lock the rod to the bone. With screws at both ends of the rod on opposite sides of the lengthening zone, the external fixator is no longer needed. The external fixator is removed during the same operation. Therefore, the total external fixation treatment time is much shorter and is equal to the distraction phase instead of the distraction plus consolidation phase. This usually reduces external fixator time to less than half.

Fully Implantable Lengthening Nails and Prostheses

The most recent development is that of fully implantable devices that can lengthen the limb from within without the need for an external fixator. This has many advantages, including no risk of pin infection, no muscle tethering by the pins, less pain, and better comfort. Unfortunately, this method is mostly limited to skeletally mature children and adults. Therefore, many patients cannot be treated by this method. Impantable lengthening technology has also been applied to hip and knee joint replacement prostheses. These are mostly used in reconstruction after bone tumor excision and for congenital deficiencies of the femur and tibia.

Puddu Plate	Internal Nail
Heidelberg External Fixator	Taylor Spatial Frame
Orthofix External Fixator Ilizarov	External Fixator
Lengthening over nail technique
Implanted self-lengthening nail and prosthesis

The International Center for Limb Lengthening
Sinai Hospital of Baltimore
2401 West Belvedere Avenue
Baltimore, Maryland 21215, USA
phone: 410-601-8700
toll-free: 800-221-8425
fax: 410-601-9576