Lengthening Over Nail
What is bone lengthening over a nail?
Bone lengthening over a nail is a procedure to lengthen bones that are shorter than normal due to injury, growth disturbance or a birth defect. The goal of regenerating bone length is to give the person equal limb lengths. This will help with cosmetic appearance and function.
How is new bone formed?
When a bone is broken, immature bone is formed at the region of the break. This is a precursor to new bone formation and is not as hard as mature bone, but rather is moldable or pliable. Eventually, this immature bone will be replaced with bone which is hard and can bear full weight. If this immature bone is “stretched out” slowly over time before it is replaced with new bone, the bone can be made longer with new bone filling in the gap. This is how limb lengthening is done.
To lengthen a bone, the bone is cut or divided in a certain place. When the bone is cut, the two segments created can be moved apart.
What is a frame or external fixator and how does it work?
External fixation devices have been developed to control this movement. This is a hardware scaffolding outside of the body, hence “external” fixation. These devices are made of strong metal and will keep the bones stable as they undergo lengthening. The bone to be lengthened may be too small for use of newer magnetic lengthening nails that are placed inside the canal or central aspect of the bone; therefore, external fixation must be used to accomplish this goal. External fixation is built on to the arm or leg like scaffolding along the side of a building. Metal rings or bars are attached to the bones with pins or wires. Special nuts or components will be turned each day on the external fixator to create the movement of the two bone segments. A prescription will be given that tells the patient how many turns need to be made each day. As the segments move away from each other, immature bone and then new bone is formed in between the region of distraction creating length.
What is the nail for?
To shorten the time needing an external fixator, lengthening over a nail was developed. A small diameter metal nail can be placed in the center of the bone. The external fixation device’s pins and wires can be placed through the bone in strategic places around the nail that was placed in the center of the bone in such a way as to not be in contact with the nail. After the desired length of the bone has been gained, the nail is locked with screws to prevent shortening and the external fixator can be removed. The remaining nail in the bone’s canal will continue to give it stability while the newer bone created with the lengthening matures and hardens. The advantage of having the nail is that it allows the external fixator to be removed much earlier than would be the case if only an external fixator was used.
The technique “lengthening over a nail” or LON, was very helpful in the past. However, the development and release of modern, telescopic, magnetically powered lengthening nails (Precice), has made the LON technique much less necessary. It is now mostly used in countries where the Precice is unavailable.
How long does this treatment last?
After the surgery, one should expect a 3 to 4-day hospital stay. During this time in the hospital, patients and their family members will be taught how to care for the pin sites and keep them clean. Also, education will be given on how the external fixation device works and how to perform the bone lengthening by turning the components of the external fixator. The lengthening or distraction process usually starts 6-7 days after the operation.
The time it takes to lengthen the bone depends on the length difference between a person’s legs or arms. More commonly, bones can be lengthened at about 1 millimeter per day. The time it takes for the bone to harden or mature in children after the distraction is usually twice as long as it takes for the lengthening itself. In adults this may take 3 to 4 times longer. Diabetes and tobacco use are known to slow bone healing.
A rule of thumb is that it takes one month for bone to form for every centimeter (0.4 inches) of length gained. For example, if three centimeters (1.2 inches) of length or new bone are to be created, it will take about 30 days for forming the new bone, then an additional 2-3 months for healing and the bone to become hard and stable. This would be approximately four months wearing the external fixation before it could be taken off. However, expect this estimation to be shorter because the nail that is placed will give the bone stability so the external fixator may be taken off sooner, basically as soon as the lengthening has concluded (one month).
What potential problems can arise?
Problems that may occur with this procedure are pain, infection of the surgical sites and the bone, loss of motion in the joints, problems with healing new bone, nerve or blood vessel injury, blood clots, problems with the hardware and need for other procedures to help with healing and correction.
One particular risk of LON is for pin infections, which are common and may spread to involve the implanted intramedullary nail, which would allow infection to spread up and down the bone canal. For more information about pin site infections, please see the External Fixators page of the website.