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In this series the treatment including the rate was tailored to each patient; slowing the rate when there appeared to be deficient regenerate or soft-tissue tightness, and increasing the rate in situations where there was exuberant callus at risk of premature consolidation. Because of the reversibility the Precice permits dynamization by cycles of daily compressiondistraction (1 to 2mm each) to stimulate consolidation. This was used in a few cases that showed slow healing. In 1 case that initially looked like it would require bone grafting the distraction gap united without surgery.

Another well-reported problem with implantable lengthening nails is difficulty with distraction. Kubiak and colleagues attributed this to impingement and friction secondary to a straight nail attempting to lengthen a curved femur, as well as, compressive forces caused by the soft tissues that are substantial enough to limit lengthening. This complication is still the most frequent one with the Albizzia nail. Failure to distract can be related to wear of the teeth of the internal ratchet gear or due to the inability of the patient to turn the limb the full 20 degrees due to pain. Similarly with the ISKD, some patients have too much pain to rotate the femur the 3 to 9 degrees needed. Manipulation by the surgeon in the office to manipulation under epidural or other anesthesia has been used to treat this problem. Botox injection into the quadriceps to reduce muscle spasm is also useful. Incidence of failure to distract with ISKD varies, from 0%36 to 64%32 of whom 6/7 of the patients in that series required a return to the OR.36 Similarly, the Simpson et al27 series had a rate of 24.2% (8/33) of ISKD nails that were difficult to distract, and 75% (6/8) of those needed a return to the OR.

In our series we had 7 cases of failure to distract. One of these occurred due to user error. The nail was introduced retrograde into a femur for lengthening and deformity correction. The ERC device was applied facing distally causing compression instead of distraction. This lead to breakage of the mechanism at the junction of the coupling of the gears to the drive shaft. The nail was exchanged and the lengthening proceeded normally once the ERC device was applied correctly. In 1 bilateral case, the femur failed to continue to lengthen after about 4.5 cm. The lengthening was stopped. When the nails were extracted 1 year later the mechanism was found to have failed. This probably occurred due to excessive resistance from abundant callus. One case of premature consolidation and 2 cases of dense regenerate also had a failed mechanism. It is difficult to know if this failure of the mechanism occurred after repeated lengthening attempts against the force of a prematurely consolidated bone or did the premature consolidation result from failure of the nail mechanism to continue to distract against increasing resistance.

Mechanical failure of other implantable nails can be divided into 2 groups: mechanical failure of the distraction mechanism and breakage of the integrity of the nail itself. In the Baumgart et al21 series of 12 cases, 2 patients required reoperation for the failure of mechanism. There were no nail breakages in this series. In a Fitbone series of 24 nails, 2 patients had to have exchange nails to larger diameter Fitbone nails as the gears were too weak for distraction. Both these patients had congenital deformities.22 Another Fitbone cohort of 8 patients reported 1 mechanism failure and 1 nail breakage; both were also congenital etiologies.23 The ISKD initial series (20 nails) reported 2 hardware failures; both nails broke with patients fully weight-bearing and at the junction of the proximal and distal components. Design changes were made in the nail and authors claimed no further breakages. This further stresses the importance of in vivo analysis of these devices and appropriate engineering adjustments to improve product design. No mention of mechanism failure was noted in this series.37 Another review of 57 ISKD nails revealed no nail breakages, however, 3 failures of the lengthening mechanism. One requiring an exchange nail with an examination of the failed nail showing a jammed ratchet mechanism. The other 2 nails required manipulation another anesthesia, however, 1 nail acutely lengthened 3 cm instead of 3mm despite external monitoring; once again illustrating the unpredictability of these nails.33 In the largest ISKD series of 242 devices, 15 (6.2%) experienced mechanical failure. Ten of these failures were nail fractures, 2 of which were in the same patient undergoing stature lengthening. Most fractures were in the male component, however, other areas of nail were prone to failure as well. The remaining 5 nails failed at the lengthening mechanism; 2 of which failed due to assembly error.36 Ensuring the functionality of the nail during surgery, as in our surgical protocol would circumvent these types of complications. In 41 Albizzia nail insertions, 3 failures were related to the distraction mechanism and 1 nail fracture, all required reoperation (Guichet et al).37