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Infection rates and risk factors with magnetic intramedullary lengthening nails
⁎Corresponding author: Phillip K. McClure. pmcclure@lifebridgehealth.org
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
Surgical site infection (SSI) related to magnetic intramedullary lengthening nails (MILNs) can lead to delayed consolidation or loss of limb function, resulting in deleterious effects to a patient's quality of life. With the rise of MILNs, we sought to determine the incidence rate and risk factors for infection during limb lengthening with MILNs.
We reviewed a consecutive series of patients who underwent femoral and/or tibial lengthening with an MILN at a single institution between 2012 and 2020 (n = 420). SSI was defined according to CDC-NHSN criteria (including superficial and deep infections) with postoperative surveillance time of 12 months. Demographic, health metrics, comorbidities, limb- and surgery-related factors, were assessed as potential risk mediators of SSI.
Incidence of SSI was 3.3 % (14/420). This was divided into superficial (0.5 %,2/420) and deep (2.9 %, 12/420) infections. Of deep infections, 75 % (9/12) were osteomyelitis. Of the 14 limbs that developed SSI, 57 % (8/14) had a history of prior external fixation in the same limb and 38 % (5/14) had a previous infection of the same limb. A subanalysis of patients with a history of prior external fixation in the same bone was associated with SSI, as compared to those without previous external fixation. None of the surgery-related infection risk factors reached statistical significance.
The total incidence of infection with MILNs was 3.3 % at 24 months follow-up. The risk of deep infection was 2.9 %. Patients with a history of previous external fixation and prior infection show an independent association with increased rate of infection recurrence in the same bone. These patients could be considered a high-risk group for developing deep tissue infection. Potential algorithms include prolonged oral antibiotics after MILN insertion or simultaneous injection of absorbable antibiotic at the time of the nail insertion.
1 Introduction
Surgical site infections (SSI) related to MILNs, the popular method of choice for treating limb length discrepancy, can lead to severe complications, including delayed consolidation, limb function loss, and even amputation.1 Reported incidence of these complications in trauma literature has ranged from.9 to 23 %.2 Retrospective studies suggest that previous use of external fixation may be associated with increased rates of SSI after MILN, although no studies have assessed this relationship in patients histories which utilized exclusively MILNs.1,3
Risk factors for SSI include patient-related variables such as advanced age, cognitive impairment, diabetes, and smoking, as well as surgery-related factors like delay to operation, duration of the operation, and presence of intraoperative complications.4 Trauma literature has reported an association between prior external fixation and the occurrence of SSI, with up to a 2.53 times higher risk.1,5–7 Notably, duration of pin indwelling, which can range from 4 to 12 months, had the greatest association with development of a pin site infection.8 The use of MILNs for limb lengthening has been reported in literature to minimize pin site infection, which is a complication present in nearly 100 % of cases using external fixators.8,9 The management of SSI is complex and clinically diverse, requiring careful consideration when utilizing MILNs for limb deformity correction.
Published studies on limb lengthening with MILNs have primarily focused on technique optimization rather than infection-related outcomes. As such, knowledge surrounding the incidence, risk factors, and infection management outcomes remain scarce. A better understanding of these complications could lead to the development of prevention protocols versus ex post facto treatment strategies. Thus, the objective of this study is to assess the incidence and potential risk factors related to occurrence of infection following femoral or tibial limb lengthening with MILNs.
2 Methods
Our study is a retrospective evaluation of a large-scale, single center experience of limb lengthening with MILNs occurring between 2012 and 2020 (n = 420). Patients with femoral or tibial limb length discrepancy who underwent limb lengthening with an MILN (PRECICE®, NuVasive, Inc.) and had at least 12 months follow-up were included. The exclusion criteria comprised patients whose care was transferred to other institutions following the operation or whose follow-up time period was less than 12 months. The study included 186 females and 191 males with a mean age of 24 years (9-73). The etiology of limb length discrepancy varied, with congenital (congenital femoral deficiency, fibular hemimelia), skeletal dysplasia, and post-traumatic conditions being the predominant etiologies (Table 1). Chart review was utilized to identify clinical management and or/sequelae of mechanical failure complications.
| N (%) | |
| Age (Mean) (SD) | 19.6 (11.8) |
| Gender | |
| Male | 194 (46.2) |
| Female | 226 (53.8) |
| Race | |
| Caucasian | 320 (76.2) |
| Asian | 32 (7.6) |
| African American | 34 (8.1) |
| Declined to answer | 20 (4.8) |
| Native Hawaiian | 1 (0.2) |
| American Indian | 1 (0.2) |
| Hispanic | 2 (0.5) |
| Multiple | 10 (2.4) |
| Etiology | |
| Achondroplasia | 70 (16.7) |
| Congenital | 130 (31.0) |
| Ollier Disease | 15 (3.6) |
| Post-Traumatic | 55 (13.1) |
| Neonatal Sepsis/Septic Growth Arrest | 20 (4.8) |
| Hemihypertrophy | 20 (4.8) |
| Growth Arrest | 15 (3.6) |
| Slipped Capital Femoral Epiphysis | 10 (2.4) |
| Polio | 10 (2.4) |
| Russell-Silver Syndrome | 10 (2.4) |
| Marfans | 10 (2.4) |
| Dysplasia | 20 (4.8) |
| Stature | 15 (3.6) |
| Laterality | |
| Left | 173 (41.2) |
| Right | 247 (58.8) |
| Bone | |
| Femur | 288 (68.6) |
| Tibia | 126 (30.0) |
| Humerus | 6 (1.4) |
| Entry | |
| Trochanteric | 171 (40.7) |
| Piriformis | 98 (23.3) |
| Tibial Rod | 76 (18.1 |
| Retrograde | 36 (8.6 |
| Intercondylar | 14 (3.3) |
| Suprapatellar | 11 (2.6) |
| Antegrade | 9 (2.1) |
| Others | 5 (1.1) |
2.1 SSI classification
SSI was defined according to CDC-NHSN criteria10 (including superficial and deep infections) with postoperative surveillance time of 12 months. SSIs were divided into superficial incisional, deep incisional and organ/space infection (Table 2). Superficial incisional SSI occurred within 30 days and involved skin and subcutaneous tissue of incision. Deep incisional infection occurred within 30–90 days postoperatively with involvement of fascial and muscle layers. Those infections occurring 30–90 days after the surgical procedure and involving structures deeper then fascial/muscle layers were considered organ/space infections. Bone osteomyelitis was classified as an organ/space infections. Additionally, those infections classified as osteomyelitis were subdivided according to the Cierny-Mader stratification.11 This classification is based on the anatomy of the bone infection and the physiology of the host.12 If osteomyelitis developed in one bone and later was detected in a different bone, these were recorded as separate instances.
| SSI | Criteria |
| Superficial incisional | Occurred within 30 days post-operatively and involved skin and subcutaneous tissue of incision |
| Deep incisional | Occurred 30–365 days post-operatively and involved fascial/muscle layers |
| Involving organ/space | Bone osteomyelitis |
2.2 Risk factors included in analysis
Demographics, health metrics, comorbidities, limb- and surgery-related factors were assessed as potential risk factors for SSI. These included the following: age, sex, body mass index (BMI), smoking status, intravenous drug use (IVDU), diabetes mellitus (DM) or other immunosuppressive disease, vascular and neuromuscular disease, prior radiation treatment and cancer, etiology of disease, previous trauma or infection to the limb being lengthened, prior external fixation in the same or different limb, prior surgery on the same bone, perioperative blood loss, blood transfusion, antibiotic type/dose at induction of anesthesia, and duration of surgery.
2.3 Statistical analysis
Study data was anonymized and analyzed using Microsoft Excel 2008 (MicrosoftCorp, Redmound, Washington, United States). The related statistical analysis was performed with the MedCalc® software (Ostend, Belgium). The odds rate of each variable was studied for the occurrence of infection and the respective 95 % confidence intervals were estimated by unadjusted logistic regression. The statistical significance level was set to P ≤ 0.05 or less.
3 Results
3.1 Incidence of SSI in femoral and tibial lengthening with MILN
Incidence of overall SSI was 3.3 % (14/420). These were divided into superficial 0.5 % (2/420) and deep 2.9 % (12/420) infections. Infections involving organ/bone osteomyelitis comprised 2.1 % (9/420) of the cohort. Of the 14 limbs that developed SSI, 57 % (8/14) had a history of prior external fixation in the same limb and 38 % (5/14) had a previous infection of the same limb. A majority of the 14 (79 % 11/14) had a history of previous surgery in the same limb. A subanalysis of patients with a prior surgery to the involved limb was associated with SSI, as compared to those without a background of surgical intervention (Table 3).
| Prior Ex-fix same Bone | Prior Ex-fix different Bone | Prior surgery same Bone | Previous Infection in bone treated | Previous Trauma in bone treated | |
| Total PT out of 420 | 149 | 143 | 258 | 34 | 57 |
| Total infection post MILN | 8 (5.4 %) | 7 (4.9 %) | 11 (4.3 %) | 5 (14.7 %) | 3 (5.3 %) |
| Superficial infection | 0 (0 %) | 0 (0 %) | 2 (18 %) | 1 (20 %) | 1 (33.3 %) |
| Deep infection | 2 (25 %) | 2 (29 %) | 3 (27 %) | 0 (0 %) | 1 (33.%) |
| Osteomyelitis | 6 (75 %) | 5 (71 %) | 6 (55 %) | 4 (80 %) | 1 (33.3 %) |
There were 3 separate cases with stage 3 or worse osteomyelitis, including 1) a 56-year-old female with a previously failed, infected right total knee arthroplasty (TKA) (stage 3 osteomyelitis in a type A host) underwent a femoral MILN insertion for a 5 cm limb length discrepancy correction with subsequent development of osteomyelitis in the right knee, requiring revision arthroplasty and replacement of the MILN, 2)a 60-year-old male with a history of poorly controlled DM and multiple previous post-traumatic right foot and ankle infections following ankle fusion and infection had an MILN inserted to correct his 6 cm right tibial length discrepancy. After 3 months, he developed tight toe osteomyelitis (stage 3 osteomyelitis in a type B host), which was managed with debridement and intravenous antibiotics, and 3) a 51-year-old female who had suffered a traumatic right tibial injury and undergone treatment with external fixation had struggled with chronic osteomyelitis since 2015. An MILN was inserted to correct the ensuing 6 cm limb discrepancy, after which she developed progressive pain and swelling in the right limb requiring operative debridement and resection of infected right tibial bone (stage 4 osteomyelitis in a type A host). All 3 cases of advanced osteomyelitis occurred in adults with a previous history of infection and surgical intervention to the affected limb.
3.2 SSI risk factors relating to MILN in femur and tibia
3.2.1 Patient-related factors
We found one patient-related factor to be strikingly associated with SSI risk in patients undergoing limb lengthening with an MILN—history of uncontrolled DM, where 50 % 2/4) developed SSI. one of the 2, 1 developed deep tissue infection with positive staphylococcus aureus, and 1 had stage 3 osteomyelitis which required eventual digit amputation.
3.2.2 Limb-related factors
Previous history of infection in the same limb (5/14; P = 0.043), previous surgical intervention to the limb (11/14, P = 0.002), and prior use of external fixator (8/14, P = 0.039) showed a significant association with subsequent development of SSI in MILN procedures.
The following factors were not associated with increased rates of developing SSI after MILN in our cohort: sex (P = 1.9), BMI (P = 0.97), and smoking status (P = 0.079), IVDU (P = 0.067). None of the patients with history of irradiation/cancer, neuromuscular, or immunosuppressive or vascular disease, 2/420, 21/420, 2/420 and 7/420 respectively, developed SSI post MILN (Table 4). The etiology of length discrepancy was not an observably impactful variable influencing SSI during or after lengthening with an MILN (P = 0.98). Of the assessed surgery-related factors (perioperative blood loss, blood transfusion, antibiotic type/dose at induction of anesthesia, and duration of surgery) none showed significant association with SSI in our cohort.
| Smoking Status | IVDA | Average BMI | Peripheral Neuropathy | Hx of Cancer | Endocrinopathy | Thyroid Disease | Neuromuscular Disease | Immuno suppressive disease | Diabetes Mellitus | Vasular Disease | At time of SURG Steroid Use | No known comorbidities | |
| Total PT out of 420 | 14 | 1 | 23.2 | 2 | 2 | 3 | 6 | 21 | 2 | 4 | 7 | 25 | 333 |
| Total infection post MILN | 1 | 0 | 25.4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 14 |
| Superficial infection | 1 | 0 | – | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| Deep infection | 0 | 0 | – | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 3 |
| Osteomyelitis | 0 | 0 | – | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 8 |
4 Discussion
Limb lengthening with MILNs constitutes a significant clinical challenge with often unpredictable outcomes. Similarly, SSIs remain a major cause of morbidity and mortality, despite improvements in infection control techniques and surgical practice, imposing substantial demands on healthcare resources.13 Our critical evaluation of 420 segments treated with MILNs for limb deformity identified an overall (deep and superficial) infection rate of 3.3 %. Of those, 2.1 % developed osteomyelitis. A subanalysis of osteomyelitis cases revealed an association with DM, as well as a history of surgical intervention and/or infection in the affected limb. Our study also highlighted prior external fixation as a risk factor to developing SSI with MILNs.
This research is the largest published series to date investigating SSIs as they relate to MILNs. However, it is not without its limitations. Although there are established criteria for diagnosing SSIs, each physician's clinical judgement is still variable and influenced by the level of expertise and diagnosing experience. We chose to use the CDC-NHSN classification to aid in standardizing these criteria. Additionally, retrospective literature has inherent limitations to analyzing potential risk factors. However, we bolstered the statistical power of our conclusions by purposefully utilizing a comparatively larger dataset than similar studies. Factors such as smoking, obesity and DM did not show statistical significance as risk factors for SSI in our cohort overall. This finding could have been due to the relative youth of the study population (mean age 24 years) and may not be generalizable to older patients. Simultaneously, sampling a younger population may be advantageous, as it could mitigate the potentially confounding influence of age as a variable for developing infection.
From our case series of 420 patients who were treated with MILNs for limb length discrepancy, we reported a 3.3 % overall incidence of SSI. This is comparable with rates described in literature for tibial shaft fractures utilizing MILNs (4.3 %).14 In contrast, SSI incidence rates as high as 6.4 % were reported in a recent study by Pantelli et al. for subtrochanteric femoral fractures.15 We did not observe a significant difference in the development of SSI between different limbs. Prior external fixation is reported in trauma literature to be a risk factor for developing SSI infections after subsequent MILN insertion.16 Eight of 15 limbs that developed SSI in our cohort had a prior history of external fixation in the same limb.
We found the rate of deep SSI to be 1.3 % in those limbs previously treated with external fixation versus those naïve to it. These cases were treated with incision and drainage, and long-term antibiotics. Comparably, other studies have reported a 1.7–5.4 % deep infection rate for femoral shaft fractures treated with initial external fixation and subsequent conversion to MILNs.17 Pin tract infections are inevitable when using an external fixator,18 and can be a source of deep infection spreading to the MILN. Kristiansen and Steen reported that in tibial lengthening with a similar technique, deep intramedullary infections occurred in 1/9 patients.19
Bacterial osteomyelitis is the most serious potential complication with MILNs. Three of 14 limbs (21 %) in our SSI cohort developed osteomyelitis reflecting stage 3 or stage 4 disease. We additionally found that only DM and prior infections in the affected limb were associated with an increased incidence of osteomyelitis. Gordon et al. reported 2/9 (22 %) cases of osteomyelitis and Hae-Ryong Song reported on 3/22 (14 %) of patients who developed osteomyelitis, all of whom had a history of prior infection.20,21 We found a a 2.1 % overall rate of osteomyelitis (n = 420). In a recent study by Frommer et al. exploring the potential risks and benefits of MILNs using anterograde approach for femoral lengthening, an osteomyelitis rate of 3 % was described (n = 90). This discrepancy may be due to a much lower cohort number in the referenced study.22
The early identification of risk factors for SSI, in particular for deep infections which can lead to non- or delayed union and/or mortality, is crucial to optimizing treatment with MILNs. This is the first study to establish an incidence rate of SSI and examine risk factors for infection development as they relate to limb lengthening with MILNs. History of prior infection, treatment with an external fixator, and/or previous surgical intervention in the affected limb were strongly associated with the development of SSI. Moreover, DM emerged as a major risk factor for developing osteomyelitis with an MILN. To minimize infection and optimize care when treating patients with MILNs for limb length discrepancy, the attending physician should consider modifiable risk factors such as prompt surgical treatment adequate antibiotic coverage, and appropriate wound management. Patients who are particularly at risk for infection – especially those who had prior infections --should receive a comprehensive workup to exclude persistent infection before undergoing distraction osteogenesis with an MILN.
Funding
None.
Patient consent
No patient consent needed due to retrospective nature and public database.
Ethical approval-
IRB exemption due to retrospective nature and public database Authors’ contribution.
Credit author statements
PM- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
JD- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
JH-Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
JH Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing. MM- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
SB- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
Use of AI tool
No use of AI tool.
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