Limb lengthening with the Fitbone™ intramedullary nail

Intramedullary nails have become a valuable alternative to external fixators in the treatment of limb length discrepancies, achieving limb lengthening with faster rehabilitation time and a lower rate of complications. They do not have components crossing the skin, so there is no risk of pin tract infection, and the absence of a bulky frame means that daily activities are less impacted.

There are several types of intramedullary nails that can be used for limb lengthening, each characterized by different actuation methods: some have magneto-mechanically driven systems, others are mechanically driven, and the Fitbone™ nail has a motorized system.

In the following sections, we will describe how the Fitbone™ intramedullary lengthening nail can be used to correct limb length discrepancies and provide a short overview of the available literature reporting on its use.

Using the Fitbone™ to correct limb length discrepancies

The Fitbone™ intramedullary lengthening nail, developed by Prof. Rainer Baumgart in Germany, has an electrical motor but no battery. Instead, the motorized drive is hermetically encapsulated in an induction coil and does not have contact with the exterior, so the patient’s skin can be fully closed once the surgery ends. The motor is powered by electricity transmitted by a second induction coil placed on the exterior surface of the body, adjacent to the internal coil. This electrical supply can be supplied either intermittently three to four times a day.

The creator of the Fitbone™ also proposed a new method of surgical planning, devised to achieve lengthening without creating deformity. With this approach, called reverse planning method, the planning starts with the intended final result of the projected lengthening, working backward to the preoperative status. The locking position and the nail diameter are taken into consideration to provide a final result in which all geometrical values are achieved, including the mechanical axes, equality of limb length and torsion, as well as correct physiological alignment of joints.

Regarding lower limb lengthening, the Fitbone™ system can be used in both the femur and tibia, either using the antegrade and retrograde approach in the femur and the antegrade approach in the tibia. Briefly, the SAA has a straight construction, with a sliding longitudinal hole in its middle, allowing for lengthening and bone transport, while the TAA is available in both a straight version and one with a Herzog bending for the tibia.

Current literature regarding the use of the Fitbone™ intramedullary nail

Since its introduction in clinical practice, there have been several reports regarding the use of the Fitbone™ intramedullary nail in different populations, across several indications, and sometimes comparing it with external fixators or other intramedullary nails. The intent of this section is not to provide an exhaustive report on the available literature, but to highlight some examples of the use of the Fitbone™ system.

In 2008, Krieg and colleagues used the Fitbone™ on eight adolescents, evaluating if it could reduce hospitalization, rehabilitation time, and complication rates when compared with external fixation. Based on the results, they concluded that some patients could benefit from this system. When compared with external fixation, the use of the Fitbone™ Nail resulted in earlier full weightbearing, faster rehabilitation, and excellent functional results with less complications.

In 2015, Küçükkaya and colleagues reported on the use of the Fitbone™ Nail to perform femoral lengthening and deformity correction in 22 patients. After a follow-up of two and a half years, the mean lengthening obtained was 5.8 cm, and a range of angular correction of 2 to 22 degrees, with complete consolidation being obtained in all cases except two. Secondary loss of length, sometimes referred to as running back or backtracking, was observed in two patients.

Conclusion

The use of the Fitbone™ intramedullary nail enables limb lengthening without the discomfort and complications caused by an external fixator.

Some of the advantages of this motorized lengthening nail include a complete control of the distraction amount, speed, and rate, which can be modified according to bone healing, joint contracture, rehabilitation, and need for pain management.

The reverse planning method can guarantee a correct geometric result, such as the alignment of the mechanical axis and orientation of all joints within the physiological range, and can be used whether or not there is a concomitant deformity that needs to be corrected along with the limb discrepancy.

This flexibility of the Fitbone™ system, which allows for limb lengthening procedures along with deformity correction, makes it a useful surgical option representing a new era of relatively safe and predictable corrections, even in complex situations.

References

• Krieg AH et al. Acta Orthopaedica 2011;82:344–50.
• Krieg AH et al. Clin Orthop Relat Res 2008;466:189–97.
• Küçükkaya M et al. J Orthop Sci 2015;20:149–54.
• Baumgart R. Orthop Traumatol 2009;21:221–33.
• Baumgart R et al. Practice of Intramedullary Locked Nails. Springer-Verlag; 2006, p. 189–98.

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