Magnetic Intramedullary Lengthening Nails Can Be Lengthened to Their Maximum Capacity with No Increased Nail Complications: A Study of Pediatric and Adult Populations.

Background: Magnetic intramedullary lengthening nails (MILNs) have become an increasingly popular method for long-bone distraction osteogenesis as a means of overcoming the limitations of bone lengthening with an external fixator. While factors such as nail diameter, alignment, and other mechanical characteristics have been associated with an increased risk of nail breakage, the relationship between the percentage of maximum lengthening utilized and nail breakage remains unexplored. We specifically assessed overall complications, with and without the inclusion of contractures, based on the amount of distraction (25% to 60%, 61% to 90%, and 91% to 100% of maximum).

Methods: We retrospectively reviewed the records for 176 pediatric patients and 109 adult patients who had undergone limb lengthening and had ≥24 months of follow-up. The cohort was further stratified by the amount of distraction: 25% to 60% (n = 75 children and 30 adults), 61% to 90% (n = 72 children and 29 adults), and 91% to 100% (n = 29 children and 50 adults). The mean ages were 14.53, 13.53, and 12.49 years, respectively, in the pediatric cohorts and 27.1, 34.3, and 23.8 years, respectively, in the adult cohorts. The percentages of males and females were 48% vs. 52%, 54.2% vs. 45.8%, and 48.3% vs 51.7%, respectively, in the pediatric cohorts and 56.7% vs. 43.3%, 51.8% vs. 48.2%, and 58% vs. 42% in the adult cohorts. Complications included contractures, loss of length, bone fracture, axial deviation, nail failure, failure to lengthen, nail fracture/failure, and screw failure. Analysis of variance (ANOVA) was conducted to compare mean complications across the 3 distraction categories, and Tukey pairwise t tests were performed to compare mean complications between individual distraction categories.

Results: Without contractures, complication rates were similar between the pediatric cohorts (p = 0.09): 4.0% (25% to 60% distraction), 13.9% (61% to 90% distraction), and 6.9% (91% to 100% distraction). With contractures included, complication rates were greatest in the 61% to 90% pediatric cohort (38.9%), followed by the 91% to 100% cohort (27.6%) and the 25% to 60% cohort (13.3%) (p = 0.002). Similarly, the adult population had a homogeneous rate of complications without the inclusion of contractures (p = 0.13). Likewise, we observed a similarly variable distribution with contractures considered, with the greatest frequency in the 91% to 100% group (36%), followed by the 61% to 90% group (31%) and the 25% to 60% group (10%) (p = 0.04).

Conclusions: This is the first study to explore the relationship between the percentage of nail lengthening and nail complications. The speculation that full extension of the nail could lead to increased nail bending or breakage was not consistent with our findings. This finding was consistent whether contractures were included or not.

Level of evidence: Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.