Osteotomy Site Venting Enhances Femoral Bone Consolidation With Magnetic Intramedullary Lengthening Nails.

Background: Magnetic intramedullary lengthening nailing has demonstrated benefits over external fixation devices for femoral bone lengthening. These include avoiding uncomfortable external fixation and associated pin site infections, scarring, and inhibition of muscle or joint function. Despite this, little has changed in the field of biologically enhanced bone regeneration. Venting the femoral intramedullary canal at the osteotomy site before reaming creates egress for bone marrow during reaming. The reamings that are extruded from vent holes may function as a prepositioned bone graft at the distraction gap. The relationship between venting and the consolidation of regenerating bone remains unclear.

Questions/purposes: (1) Do bone marrow reamings extruded through venting holes enhance the quality of bone regeneration and improve healing indices and consolidation times? (2) Is venting associated with a higher proportion of complications than nonventing?

Methods: We performed a retrospective study of femoral lengthening performed at one hospital from December 2012 to February 2022 using a magnetic intramedullary lengthening nail with or without venting at the osteotomy site before reaming. This was a generally sequential series, in which the study groups were assembled as follows: Venting was performed between July 2012 and August 2016 and again from November 2021 onward. Nonventing was used between October 2016 and October 2021 because the senior author opted to create drill holes after the reaming procedure to avoid commitment to the osteotomy level before completing the reaming procedure. Outcomes were evaluated based on bone healing time, time to achieve full weightbearing, and complications. Sixty-one femoral lengthening procedures were studied (in 33 male and 28 female patients); two patients were excluded because of implant breakage. The mean age was 17 ± 5 years. The mean amount of lengthening was 55 ± 13 mm in the venting group and 48 ± 16 mm in the nonventing group (mean difference 7 ± 21 [95% CI 2 to 12]; p = 0.07). The healing index was defined as the time (in days) required for three cortices to bridge with new bone formation divided by the length (in cm) lengthened during the clinical protocol. This index signifies the bone formation rate achieved under the specific conditions of the protocol. Full weightbearing was allowed upon bridging the regenerated gap on three sides. Consolidation time was defined as the total number of days from the completion of the lengthening phase until adequate bone union (all three cortices healed) was achieved and full weightbearing was permitted. This time frame represents the entire healing process after the lengthening is complete divided by the amount of lengthening achieved (in cm). Patient follow-up was conducted meticulously at our institution, and we adhered to a precise schedule, occurring every 2 weeks during the distraction phase and every 4 weeks during the consolidation phase. There were no instances of loss to follow-up. Every patient completed the treatment successfully, reaching the specified milestones of weightbearing and achieving three cortexes of bone bridging.

Results: The mean healing index time in the venting group was faster than that in the nonventing group (21 ± 6 days/cm versus 31 ± 22 days/cm, mean difference 10 ± 23 [95% CI 4 to 16]; p = 0.02). The mean consolidation time was faster in the venting group than the nonventing group (10 ± 6 days/cm versus 20 ± 22 days/cm; mean difference 10 ± 23 [95% CI 4 to 15]; p = 0.02). No medical complications such as deep vein thrombosis or fat or pulmonary embolism were seen. Two patients had lengthy delays in regenerate union, both of whom were in the nonventing group (healing indexes were 74 and 62 days/cm; consolidation time was 52 and 40 days/cm).

Conclusion: Femoral lengthening with a magnetic intramedullary lengthening nail healed more quickly with prereaming venting than with nonventing, and it allowed earlier full weightbearing without any major associated complications. Future studies should evaluate whether there is a correlation between the number of venting holes and improvement in the healing index and consolidation time.

Level of evidence: Level III, therapeutic study.