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

Abstract

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.

Introduction

Although there has been progress in the field of fixation devices since the revolutionary work of Gavril Ilizarov [21, 23, 24], who established the principles of distraction osteogenesis, there has been little advancement in biological regeneration. A shift from external devices (such as Ilizarov frames, hexapods, and monolateral frames) to all-internal intramedullary devices [6, 14] (such as the Precice® [Nuvasive Specialized Orthopedics] and Fitbone^™ [Orthofix Medical Inc]) has yielded excellent clinical results, reduced complications, and improved patient tolerance and satisfaction [32, 40]. However, questions remain about the benefits of these new devices regarding treatment time [19, 25, 42], particularly concerning the length of time needed for regenerative consolidation. This time frame can exacerbate the complication rate, create psychosocial burdens, and impair a patient’s quality of life. Additionally, inserting intramedullary lengthening nails into a reamed canal can potentially elevate both intraosseous and intramedullary pressure, increasing the risk of fat embolism syndrome [31] and potentially compromising surgical outcomes. Additionally, inserting intramedullary lengthening nails into a reamed canal can potentially elevate both intraosseous and intramedullary pressure, increasing the risk of fat embolism syndrome [31] and potentially compromising surgical outcomes.

Therefore, one recommended surgical technique [36] is to first vent the femur by drilling multiple holes at the planned osteotomy site to reduce pressure on the bone marrow during reaming and implant insertion. However, to our knowledge, there are no studies proving there is decreased fat embolism in patients undergoing lengthening by venting the canal before reaming. In addition, it has been observed that bone marrow and cortical reamings exit vent holes and are easily seen on postoperative radiographs as dense material around the osteotomy site (Fig. 1). These reamings appear to hasten healing, and it has been postulated, but never proven, that this extruded bone marrow acts as a prepositioned graft around the distraction gap, which may improve regenerative bone healing and reduce the consolidation time. Patients treated with the nonventing technique do not exhibit a radiodense cloud of bone on postoperative radiographs and do not tend to show accelerated healing (Fig. 2). Considering the potential advantages of reducing the likelihood of fat embolism and enhancing bone healing, a comparison between groups of patients who underwent venting and those who did not may help determine whether venting accelerates regenerate bone consolidation and influences complication rates.

Fig. 1.

(A) This radiograph shows an example of venting before reaming; note the radiodense particle of bone reamings around the osteotomy site. (B) This radiograph was taken from the same patient after distraction and shows robust healing and hypertrophic, regenerate bone.

Fig. 2.

(A) This radiograph shows an example of nonventing before reaming; note the absence of radiodense particles of bone reamings around the osteotomy site. (B) This radiograph was taken from the same patient after distraction and shows unimpressive healing and atrophic, regenerate bone.

Therefore, in this study, we asked: (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?

Patients and Methods

Study Design and Setting

This was a retrospective, comparative study performed at Tel Aviv Sourasky Medical Center’s Dana-Dwek Children’s Hospital and conducted by two highly experienced orthopaedic surgeons (RG, ES) specializing in limb deformity correction, who have 10 and 25 years, respectively, of extensive expertise in the field of deformity correction procedures. This was a generally sequential series, in which all patients were subjected to femoral lengthening surgery using the antegrade Precice nail at our medical institution. The study cohorts were retrospectively categorized as follows: patients who underwent venting procedures between July 2012 and August 2016 and again from November 2021 onward and a nonventing group, who underwent procedures from October 2016 to October 2021. This stratification was implemented because the senior author’s (ES) decided to conduct drill hole procedures after the reaming process during this period to avoid committing to the osteotomy level before completing the reaming procedure.

Patients

We reviewed medical records from December 2012 to February 2022 to collect data on femoral lengthening procedures that were done with a Precice magnetic intramedullary lengthening nail, with or without venting holes. In this study, we included children and adults who underwent lower limb–lengthening procedures in our institution from December 2012 to February 2022. These patients successfully completed the prescribed treatment duration, achieving the specified clinical endpoint of three cortices. Importantly, no patients were lost to follow-up or experienced mortality during the observation period.

Patient Groups

The study group included 61 patients (33 male and 28 female patients), two of whom were excluded because of hardware failure (nail breakage) during the consolidation phase [18]. Both patients were in the nonventing group and did not follow our weightbearing instructions. Their exclusion yielded a final study group of 59 patients (31 male and 28 female patients) with a mean age of 17 ± 5 years. There were 25 patients in the venting group and 34 patients in the nonventing group. The two groups were comparable regarding age, sex, and surgical indications (Table 1). 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) (Table 2).

Table 1.

Characteristics of the study groups

Characteristic	Venting group (n = 25)	Nonventing group (n = 34)
Age in years	18 (11-43)	18 (11-32)
Indications
Short stature	2	2
Congenital short femur	4	6
Hemihypertrophy	3	1
Idiopathic	2	6
Multiple enchondromas	2	3
Status postinfectious disease	3	2
Posttraumatic	4	7
Other acquired LLD	5	7

Data presented as mean (range) or number; LLD = limb length discrepancy.

Table 2.

Surgical outcomes according to study group

Surgical outcome	Venting group (n = 25)	Nonventing group (n = 34)	p value
Planned lengthening achieved	100 (25)	100 (34)
Lengthening in mm	55 ± 13	48 ± 16	0.07
Healing index in days/cm	21 (11.6-36.2)	31 (12.5-137)	0.03
Consolidation index in days/cm	10 (0.4-25)	20 (1-125)	0.03

Data presented as % (n), mean ± SD, or median (range).

Surgical Techniques

The two senior authors (RG, ES) performed all surgical procedures. No patients had any associated angular limb deformities. Therefore, there were no acute angular or rotational corrections of deformities. Surgery was performed under fluoroscopic guidance similar to standard intramedullary trauma nailing, with the patient in a lateral decubitus position. The technique involved a percutaneous approach via the gluteal muscles down to either the piriformis fossa or the tip of the greater trochanter, depending on which approach the surgeon selected. There were differences in surgical technique for the nonventing (Fig. 3) and venting (Fig. 4) groups. In the nonventing group, a threaded guide pin was positioned under biplanar image intensifier control (Fig. 3A). An 11-mm entry reamer was passed into the proximal femoral metaphysis to allow passage of the ball-tipped guidewire down to the distal femoral diaphysis (Fig. 3B-C).

Fig. 3.

Surgical steps in the nonventing protocol: (A) Entry of a 3.2-mm guide pin can be either piriformis (depicted) or trochanteric. (B) An 11-mm broaching reamer on power is inserted over the guide pin. (C) A beaded guidewire is inserted for reaming. (D) Flexible reamers are used beginning at 8 mm and increasing by 0.5-mm increments until they are 2 mm greater than the proposed nail diameter. (E) Insert a lengthening nail to just above the level of the osteotomy. (F) At the intended osteotomy site, make multiple passes with a 4.8-mm solid drill bit through a 1-cm skin incision. (G) Osteotomy is completed with a 10-mm osteotome. (H) A nail is advanced and locked proximally and distally. (I) After gradual lengthening, new bone formation is seen filling the gap. With permission. Copyright 2024, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore. A color image accompanies the online version of this article.

Fig. 4.

Surgical steps in the venting protocol: (A) Begin by making venting holes at the proposed osteotomy site, using a 4.8-mm solid drill bit inserted through a 1-cm skin incision. (B) Entry of a 3.2-mm guide pin can be either piriformis (depicted) or trochanteric. (C) An 11-mm broaching reamer with power is inserted over the guide pin. (D) A beaded guidewire is inserted for reaming. (E) Flexible reamers are used beginning at 8 mm and increasing by 0.5-mm increments until they are 2 mm greater than the proposed nail diameter. The reamings can be seen exiting the vent holes. (F) Insert a magnetic lengthening nail to just above the level of the osteotomy. (G) Osteotomy is completed with a 10-mm osteotome. (H) A nail is advanced and interlocked proximally and distally. (I) After gradual lengthening, new bone formation is seen filling the gap. With permission. Copyright 2024, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore.

Between July 2012 and August 2016, and starting from November 2021 onward, we used the following surgical technique: We created drill holes (venting) through a 1-cm incision at the osteotomy level to decrease risk of fat embolism (Fig. 4A) [34]. This was done before reaming. After venting, the guidewire was replaced and sequential reaming approximately 2 mm greater than the nail diameter was undertaken (Fig. 4E). The nail was then inserted just proximal to the corticotomy (Fig. 4F), and the osteotomy was completed with a 10-mm osteotome (Fig. 4G). The nail was passed across the reduced osteotomy in the reamed intramedullary canal and locked with two proximal and two distal locking bolts (Fig. 4H). To help control rotation, a stout Steinman pin was drilled into the distal femur at the level of the lateral epicondyle, immediately before the osteotomy. The Steinman pin was placed parallel to the proximal nail’s jig handle once the nail was inserted into the osteotomy site.

Aftercare and Criteria to Allow Weightbearing

All patients were allowed toe-touch weightbearing with crutches immediately after surgery, and they started physical therapy on the first day postoperatively.

Between October 2016 and October 2021, the senior author (ES) opted to create drill holes after the reaming procedure (Fig. 4) to avoid commitment to the osteotomy level before completing the reaming procedure. This approach allowed us to ensure that the minimum distance between the osteotomy site and the tip of the nail would be sufficient according to the recommendations for the surgical technique (length of nail beyond the osteotomy = 3 cm + desired lengthening + 4 to 5 cm) (Fig. 3).

After 6 days, a lengthening protocol was initiated at a rate of 0.25 mm, three times per day (totaling 0.75 mm per day). If adequate callus formation was observed on serial radiographs, patients were allowed to raise the distraction rate to 1 mm per day (0.25 mm, four times per day). Weightbearing of 10 to 20 kg was recommended, and crutches or a walker were permitted. Patients wore a knee extension brace at night, and they performed knee and hip ROM exercises three times per day. Patients were seen at 2-week intervals for clinical assessment of hip and knee ROM and underwent radiography to observe the progression of lengthening and bone regeneration. Once the anticipated lengthening had been achieved, patients were reviewed monthly until the consolidation of bone regeneration (Fig. 3I, Fig. 4I). Full weightbearing was permitted once three cortices were bridged on AP and lateral views of the femur.

Primary and Secondary Study Outcomes

The principal objective of this study was to evaluate the bone healing time. To accomplish this, we used the bone healing index, defined as the total number of days from insertion of the Precice nail until adequate union was achieved (defined as bone bridging of three of four cortices on AP and lateral views), divided by the amount of lengthening achieved (in cm) [32, 41]. Both the healing index and the consolidation index are related to treatment time in bone lengthening procedures. The healing index is calculated as the time (days) required for three cortices to bridge with new bone formation divided by the length (cm), and the consolidation index encompasses the entire healing process after lengthening is complete; it represents the total time required for full and stable bone union. A single consultant orthopaedic surgeon (YW), who was blinded to the group’s characteristics, assessed the radiographs. The surgeons who performed the procedure did not judge the consolidation. The reviewer was an independent and external doctor from our team who works as a pediatric orthopaedic surgeon in a different hospital.

Our secondary objective was to evaluate reoperations and subsequent complications. To fulfill this objective, we examined any complications related to the implant, as well as issues with bone and soft tissue, by reviewing hospital and clinic records. We specifically sought evidence in medical charts pertaining to fat embolism or pulmonary embolism.

Ethical Approval

Ethical approval for this study was obtained from the Tel Aviv Sourasky Medical Center, Tel Aviv, Israel (TLV-0641-19).

Statistical Analysis

SPSS software (version 18.0, IBM Corp) was used to detect differences between the venting group and the nonventing group. The data were normally distributed, and nonparametric statistical approaches were used. A p value less than 0.05 was considered significant. We did not do a subgroup analysis by gender because the gender groups were too small.

Results

Do Bone Marrow Reamings Extruded Through Venting Holes Enhance the Quality of Bone Regeneration?

Our evaluation of the effect of bone marrow reamings extruded through venting holes on the quality of bone regeneration demonstrated improvements when using venting. 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) (Table 2). Patients in the venting group were allowed progressive weightbearing once lengthening was completed and regenerate bone became visible. Full, unprotected loads were gradually permitted when three of four cortices exhibited cortical bridging. These results underscore the potential enhancement of bone regeneration quality through bone marrow reamings extruded through venting holes.

Is Venting Associated With a Higher Proportion of Complications Than Nonventing?

One patient underwent release of the iliotibial band for a flexion-extension contracture of the knee that did not respond to physiotherapy. No medical complications such as deep vein thrombosis or fat or pulmonary embolism were seen. Two patients had lengthy delays in regenerative union, both of whom were in the nonventing group (healing indexes were 74 and 62 days/cm; consolidation indexes were 52 and 40 days/cm). Two patients had hardware failure (nail breakage) during the consolidation phase, both patients were in the nonventing group and did not follow our weightbearing instructions.

Discussion

Canal venting during limb lengthening was first described in 1997 by Paley et al. [37]. This was done to prevent fat embolism. Interestingly, Paley et al. [37] vented distally, just beyond the proposed position of the distal tip of the intramedullary nail. In subsequent research on Precice nailing, the technique morphed into a protocol to vent at the osteotomy level before reaming [27, 38]. Other authors described venting as a way of preventing fat embolism [35], and the surgical guide provided by the manufacturer [34] elucidates the purported benefits of reamings exiting vent holes to promote more-rapid bone healing, although there is no proof. Given that a direct comparison of patients with venting with those treated without venting has not been done, to our knowledge, we compared the two techniques and the impact of venting and nonventing on the quality of bone regeneration. Our results showed that venting the osteotomy site before reaming the intramedullary femoral canal improved the healing index and consolidation time compared with nonventing. This equates to reduced treatment time (time between nail insertion and achievement of adequate union to allow full weightbearing on the operated-on leg) by almost 10 days per 1 cm lengthened.

Limitations

First, our study relates only to the femur. Extrapolation to the tibia should be considered cautiously and warrants further study. Second, the follow-up duration, although encompassing the treatment target for all participants, may not sufficiently capture long-term outcomes, particularly late complications associated with the lengthening procedure or bone consolidation. Extending the follow-up duration would enhance the study’s ability to comprehensively evaluate the long-term efficacy and potential later complications of the intervention. Third, the study design is retrospective, and it was focused on the analysis of femoral lengthening procedures during a specific period at a single hospital. This design, although informative, may introduce inherent biases associated with retrospective analyses. Fourth, a larger sample for the study groups would offer more robust statistical analysis and potentially yield more comprehensive insights into the effects of venting on bone regeneration. The inclusion of a larger and more diverse participant pool could enhance the generalizability of the study findings. Fifth, the study includes pediatric and adult patients with varying medical conditions, potentially introducing variability in bone healing and consolidation rates owing to physiologic differences, variation in bone density, and distinct healing capacities between these demographic groups. Sixth, the evaluation of bone healing and consolidation primarily relies on radiographic assessments, introducing a potential source of subjectivity and interobserver variability. Incorporating objective, quantifiable measures could bolster the reliability and precision of the results. Finally, there was inadequate control for potential confounding variables that may influence bone healing, including comorbidities, nutritional status, smoking history, or concurrent medication use. Considering and accounting for these variables in the analysis would bolster the study’s capacity to isolate and assess the specific impact of venting on bone regeneration.

Do Bone Marrow Reamings Extruded Through Venting Holes Enhance the Quality of Bone Regeneration?

Our study demonstrated that venting the femoral canal boosts bone regeneration during distraction osteogenesis with the femoral Precice magnetic intramedullary lengthening nail, reducing the consolidation period and enabling earlier full weightbearing. The extensive bone marrow extrusion around the osteotomy site was visible in the cloud of marrow and bone reamings seen on postoperative radiographs taken immediately after surgery (see Fig. 1). Hypothetically, with more venting holes, more bone marrow exits the holes. Further research is warranted to evaluate the correlation between the number and size of venting holes and improvement in the healing index and consolidation time.

Distraction osteogenesis is a complex procedure used for bone lengthening, correction of bone deformity, and management of bone loss. New bone is formed in three stages: the latency period, the distraction phase, and the consolidation phase [5, 21, 23, 24]. Although the technique has been used for more than seven decades, the prolonged consolidation time necessary for satisfactory new bone tissue formation is still a challenge [7, 8]. Upregulation of osteogenic factors, such as bone morphogenetic proteins (BMPs), transforming growth factor beta (TGF-β), fibroblast growth factor (FGF), and insulin growth factor, is essential for bone formation in the distraction gap [4, 10, 16]. In addition, several studies have shown that vascular endothelial growth factors (VEGFs), platelet-derived growth factors (PDGFs), and angiopoietins are important for the formation of new blood vessels and promotion of new bone at the distraction gap [3, 11, 22]. Bone marrow is the most readily available source of mesenchymal stem cells [2, 12]. It is also colonized with different cell types, including osteoblasts, osteoclasts, adipocytes, macrophages, and hematopoietic stem cells [33]. Together with various growth factors, such as transforming growth factor (TGF), FGF, insulin-like growth factor (IGF), VEGF, and PDGF, these cells create a dynamic and diversified microenvironment that is vital for bone regeneration [15, 29, 33, 39]. Theoretically, with more bone marrow extruded from the femoral venting holes, the more bone-regenerating stem cell and growth factors will be present in the distraction area. There are no data to support the idea that more or larger drill holes result in a greater quantity of extruded bone marrow. In 2020, Drela et al. [9] reported that human mesenchymal stem cells isolated from the bone marrow of the femoral shaft have similar biological characteristics to mesenchymal stem cells derived from the iliac crest. Moreover, growth factor expression, such as epidermal growth factor (EGF), FGF, IGF, and PDGF, was much higher in femoral shaft bone marrow aspiration than in iliac crest aspiration [9]. Bone marrow mesenchymal stem cells have been used clinically for more than 20 years [17] for conditions such as osteogenesis imperfecta [20], promotion of bone fusion in spinal fusion surgery [1], direct injection into the defect site of a bone nonunion [26], and treatment of early-stage avascular and steroid-induced femoral head osteonecrosis [13].

Surprisingly, the relative advantages of these technologies for bone lengthening regeneration have not been widely applied clinically. The correlation between the number of mesenchymal stem cells in bone marrow and the effectiveness of the treatment is unclear and may be a fertile area for study. The authors of a 2018 systemic review concluded that approximately 30,000 mesenchymal stem cells would be needed for bone nonunion or osteonecrosis, whereas only 0.001% to 0.01% of mononuclear cells derived from bone marrow are mesenchymal stem cells [28]. This would mean that an enormous amount of bone marrow must be aspirated to achieve an effective concentration and quantity for regenerating bone.

Is Venting Associated With a Higher Proportion of Complications Than Nonventing?

Limb-lengthening procedures have historically employed venting techniques to address concerns about fat embolism syndrome during reaming. Venting involves creating openings in the bone to release pressure and potentially facilitate bone healing through marrow extrusion. However, strong scientific evidence for these benefits has been limited.

This study explores the rationale behind venting practices. Traditionally, venting was performed before reaming, determined by the osteotomy site and nail length (especially with femoral antegrade nails). This approach limited flexibility in nail length and width selection based on individual bone anatomy. To address this limitation, a nonventing period was implemented. During this time, the senior author (ES) reamed first, then determined the optimal osteotomy level and nail length based on the exposed anatomy. This approach was successful with a large number of cases, with no major complications reported. However, concerns arose about potential delays in bone formation with the nonventing method. A preliminary study supported this concern, leading to a return to venting techniques. Our subsequent study compared the two approaches. We found no significant difference in complication rates between venting and nonventing groups. However, the venting group demonstrated statistically faster bone formation.

Conclusion

The findings of this study indicate that femoral canal venting enhances bone regeneration after distraction osteogenesis with the femoral Precice magnetic intramedullary lengthening nail. It decreases the time to achieve consolidation and allows earlier full weightbearing. We did not observe any major complications; however, we were severely underpowered to assess complications, and future, larger (and probably multicenter) studies would be needed to do so. Based on our data, our current practice is to use venting before reaming, and we recommend prereaming venting for intramedullary femoral lengthening.