When is it Safest to Remove Motorized Internal Lengthening Nails after Treatment Completion?

Background: Motorized intramedullary lengthening nails (MILNs) are a convenient option for limb lengthening. One MILN manufacturer states the nails should be removed 1 year following surgery. However, there is no scientific evidence specific to the optimal bone condition for nail removal. This study aimed to identify the optimal conditions for MILN removal for stature-lengthening patients. Methods: A retrospective review was performed of patients who underwent simultaneous bilateral lower extremity stature lengthening with MILN over a 10-year period. We excluded patients whose nails have not yet been removed. Data on the patient’s age, sex, details of the surgery, follow-up time, the timing of nail removal, and complications were collected. Results: Sixty-four patients were included with an average age of 31.6 ± 12.4 years, and an average follow-up time of 1.6 ± 0.8 years. A total of 142 bone segments included 122 femurs (85.9%) and 20 tibias (14.1%). The average lengthening achieved was 67.5 ± 10.8 mm (range 42–80 mm). The median time to nail removal was 387.5 days with an average of 522.1 ± 406.2 days (range 231–3480). MILNs were removed prior to 1 year for 36 (25.3%) and after 2 years for 14 (9.9%) segments. One patient experienced a fracture through regenerated bone following MILN removal. Conclusions: The appearance of four cortices seems fully protective of post-removal fracture, whereas fewer than four cortices may pose a risk for postremoval fracture. Cortical development seems more important than total implant retention time. Prolonged nail retention does not appear to cause adverse events.