Abstract
Purpose
There is high burden of long bone fractures in low- and middle-income countries (LMICs). Given a limited availability of fluoroscopy in LMICs, the Surgical Implant Generation Network (SIGN) developed two types of intramedullary nails: the SIGN standard nail and the SIGN Fin Nail. A limited number of studies have analyzed healing outcomes with the SIGN Fin Nail and the current study is the largest one to date. The purpose of this study is to compare outcomes between the SIGN standard nail and SIGN Fin Nails in adult femoral shaft fractures treated with a retrograde approach.
Method
A retrospective cohort study of adults with femoral shaft fractures was performed using the Sign Online Surgical Database (SOSD). The primary outcome was achieving full painless weight bearing and the secondary outcomes assessed were radiographic healing and infection. A propensity-score adjustment was performed for potential confounders and effect modification due to fracture location was tested using a Mantel-Haenszel test for heterogeneity.
Results
Of 19,928 adults with femoral shaft fractures, 2,912 (14.7%) had the required 6-month follow-up to be included. The overall propensity score weighted relative risk between the Fin and Standard Nail for achieving painless weight-bearing was 0.99, 95% CI [0.96–1.03] and for radiographical healing was 0.99, 95%CI [0.97–1.02]. The propensity score weighted relative risk for infection was 1.30, 95% [0.85–1.97]. Use of the Fin nail was also significantly associated with shorter surgery times (p < 0.005, effect size = 24 min). Sub-group analysis based on fracture location and injury cause demonstrated no change in relative risk.
Conclusion
The Fin nail showed no change in relative risk in terms of achieving full painless weightbearing or radiographic healing compared to the standard nail for retrograde nailing of femoral shaft fractures in adults. The heterogeneous nature of the cohort and large sample size allow for generalizability and add to a growing base of literature supporting use of the Fin Nail for retrograde femoral nailing. However, there are limitations as we could not correct for comminution at the fracture site or measure radiographic alignment or shortening.
Keywords: Clinical outcomes, Femur fractures, International, Intramedullary nailing, Long bone fractures, Orthopaedics, Resource-limited setting, SIGN
1. Introduction
The yearly mortality caused by orthopedic trauma is higher than HIV/AIDS, malaria, and tuberculosis combined.1 Road Traffic accidents alone lead to 1.2 million deaths and 50 million injuries annually globally.2 Femoral fractures are the most common and pose a significant risk to quality of life.3,4. The burden of trauma in LMICs are further compounded by a lack of resources for proper treatment.
SIGN fracture Care (Richland WA) was created to address the challenging nature of treating femoral shaft fractures in low-resource settings. The SIGN Standard Intramedullary Nail does not require fluoroscopy for placement using an external device to align the interlocking screws instead. Since 1999, SIGN has treated more than 200,000 fractures in more than 50 countries.5,6 Although often used successfully, the standard nail still carries the risk of missing proper placement of interlocking screws.7
The SIGN fin nail was introduced to further simplify placement as it does not require proximal interlocking screws. The proposed mechanism behind Fin Nail fixation is through an interference fit within the medullary canal using a flute rather than interlocking screws. Although it has the potential to decrease operating time, the Fin Nail may decrease the stability of fixation.8,9, 10
The SIGN Online Standard Database (SOSD) has collected data on >180,000 fractures since 2000 providing an opportunity to study outcomes of the Fin Nail on a large scale.11 Although cumulative usage of the Fin Nail to date remains below 10% for all fractures, there are an increasing number of Fin nails placed, especially in the retrograde approach (>50% of nails placed retrograde in 2020). A limited number of studies have analyzed healing outcomes with the SIGN Fin Nail and the current study is the largest one to date. The purpose of this study is to compare outcomes between the SIGN standard nail and the SIGN Fin Nail in adult femoral shaft fractures treated via a retrograde approach.
2. Methods
2.1. Data collection
Prior to study commencement, appropriate IRB approval was obtained. Data was collected via the SOSD database which collects patient demographics, surgical data and follow-up data on patients using SIGN Nails. Prior to study commencement, appropriate IRB approval was obtained. A data export was performed using Metabase software from the SOSD (Metabase, Mountain View, CA, USA).
Study Participants The study population included patients aged 16 years or older with femoral shaft fractures treated in the retrograde approach with either a SIGN Standard Nail or Fin Nail. Inclusion criteria included having a femoral fracture treated from 2016 to 2020 with a SIGN nail, either standard or fin nail, as well as a minimum of 6 months follow up. Intertrochanteric and Femoral neck fractures were excluded from this study.
2.2. Statistical analysis
Demographic characteristics were summarized by nail type (Fig. 1). The hypothesis tested was that outcomes would not differ based on IM nail used. A propensity score model and inverse probability of treatment weighted (IPTW) analysis were used to assess the relationship between IM nail used and painless weight bearing and radiographical union.
Fig. 1.
Figure showing the balance of confounding variables before vs after adjustment.
Propensity scores are one method to control for confounding in observational studies and are defined as probability of receiving a treatment based on a set of baseline covariates..12,13 IPTW uses the inverse of the propensity score to assign weights to patients and generate a pseudo-population of patients where treatment assignment is independent. Using IPTW weights, an average treatment effect is estimated, defined in our study the effect of Fin Nail usage assuming each patient had the opportunity to be treated with either nail.14
Using determined covariates such as age, gender, nonunion at surgery, days from injury to surgery, injury cause, fracture location, and world bank income class of country, a propensity score model was developed. A directed acyclic graph (Fig. 2) describes the proposed causal relationship between IM nail used and painless weight bearing/radiographic healing including potential confounding from covariates. A balance check using IPT weights was performed to assess if patient characteristics were matched between treatment groups. The groups were adequately balanced if no covariate had a standardized difference greater than 0.10. The model was then used to estimate the overall propensity-adjusted treatment effect of nail type on achieving painless weight bearing and radiographic healing. Painless weightbearing was defined as achieving painless weight bearing as marked on the last follow-up tracked in the database. Radiographic healing was assessed using the question “Is the X-ray healed?” posed to surgeons.
Fig. 2.
Figure showing the distribution of patients identified, excluded, included and those lost to follow-up.
Potential effect modification was tested for injury cause and fracture locations. Risk ratio point estimates and confidence intervals for treatment groups were estimated for each stratum and the Mantel-Haenszel test of heterogeneity was used to assess effect modification. A p value < 0.2 was considered significant for effect modification.
All statistical analysis of de-identified data set was completed with Stata 16.0 (Statacorp, College Station, TX, USA).(see Fig. 3)
Fig. 3.
Figure showing the directed acyclic graph for the relationship between the type of nail received during treatment and achieving full painless weight bearing.
3. Results
The SOSD was queried and 95,944 femoral fractures in patients ≥16 years old were identified. 19,913 fractures met initial inclusion criteria. The study population contained 1932 (67.7%) patients were treated with a Standard Nail and 965 (33.3%) were treated with the Fin Nail.
Regarding the study population, 363 (87.5%) patients achieved full painless weight bearing and 2549 (92.07%) achieved radiographic healing. Crude analysis revealed no difference in relative risk between the Fin Nail and Standard Nail for both painless weight bearing (RR = 1.00, CI [0.98–1.03]) and radiographical healing (RR = 0.99, CI [0.97–1.02]). Stratified analysis based on injury cause and fracture location demonstrated no effect modification for either radiographical healing or painless weight bearing (p > 0.2, Mantel-Haenszel test). Use of the Fin Nail was associated with significantly shorter operating times (effect size 24 min, p < 00.001).
Age, sex, and world bank classification were covariates associated with achieving painless weight bearing (p < 0.05, Table 2). After IPTW-adjustment, patient characteristics across debridement groups were considered balanced and applied to the model. The propensity score-adjusted relative risk of achieving painless weight bearing with treatment with a Fin Nail was 0.99, 95% CI [0.96–1.03] when compared to treatment with a Standard Nail. The propensity score-adjusted relative risk of achieving radiographical healing with treatment with a Fin Nail was 1.00, 95% CI [0.97–1.02].(see Table. 1)
Table 2.
Table showing the distribution of patients who successfully achieved painless weight bearing vs those who did not.
| Didn't achieve Painless Bearing |
Achieved Painless Bearing |
p-value | |
|---|---|---|---|
| N = 363 | N = 2549 | ||
| Age | 39.04 (16.75) | 35.54 (14.84) | <0.001 |
| Sex | 0.001 | ||
| F | 129 (35.5%) | 696 (27.3%) | |
| M | 234 (64.5%) | 1853 (72.7%) | |
| GA class | 0.43 | ||
| Closed | 311 (85.7%) | 2255 (88.5%) | |
| GAI | 11 (3.0%) | 76 (3.0%) | |
| GAII | 20 (5.5%) | 89 (3.5%) | |
| GAIIIa | 14 (3.9%) | 101 (4.0%) | |
| GAIIIb | 6 (1.7%) | 23 (0.9%) | |
| GAIIIc | 1 (0.3%) | 4 (0.2%) | |
| Open | 0 (0.0%) | 1 (0.0%) | |
| Mechanism of Injury | 0.21 | ||
| Road Traffic Accident | 279 (78.2%) | 1994 (78.9%) | |
| Fall | 49 (13.7%) | 309 (12.2%) | |
| Explosive Blast | 0 (0.0%) | 16 (0.6%) | |
| Gun Shot | 9 (2.5%) | 101 (4.0%) | |
| Other | 20 (5.6%) | 108 (4.3%) | |
| World Bank Classification | 0.006 | ||
| LIC | 101 (28.5%) | 933 (37.1%) | |
| LMIC | 246 (69.3%) | 1551 (61.6%) | |
| UMIC | 8 (2.3%) | 30 (1.2%) | |
| HIC | 0 (0.0%) | 3 (0.1%) | |
| Fracture Location | 0.086 | ||
| Distal | 197 (56.0%) | 1292 (51.3%) | |
| Middle | 124 (35.2%) | 1064 (42.3%) | |
| Proximal | 12 (3.4%) | 70 (2.8%) | |
| Segmental | 18 (5.1%) | 84 (3.3%) | |
| Subtrochanteric | 1 (0.3%) | 7 (0.3%) | |
| Days from Injury to Surgery | 69.17 (346.06) | 60.13 (1124.76) | 0.88 |
| Arrived with Non-Union | 0.32 | ||
| No | 300 (83.3%) | 2174 (85.3%) | |
| Yes | 60 (16.7%) | 374 (14.7%) |
Table 1.
Table showing the basic demographic distribution of patients who received treatment with standard nail vs FIN nail.
| Total |
Standard Nail |
Fin Nail |
p-value | |
|---|---|---|---|---|
| N = 2912 | N = 1932 | N = 965 | ||
| Age | 35.98 (15.13) | 37.29 (15.54) | 33.42 (14.01) | <0.001 |
| Sex | 0.53 | |||
| F | 825 (28.3%) | 554 (28.7%) | 266 (27.6%) | |
| M | 2087 (71.7%) | 1378 (71.3%) | 699 (72.4%) | |
| GA class | 0.043 | |||
| Closed | 2566 (88.1%) | 1710 (88.5%) | 843 (87.4%) | |
| GAI | 87 (3.0%) | 51 (2.6%) | 35 (3.6%) | |
| GAII | 109 (3.7%) | 62 (3.2%) | 46 (4.8%) | |
| GAIIIa | 115 (3.9%) | 79 (4.1%) | 36 (3.7%) | |
| GAIIIb | 29 (1.0%) | 24 (1.2%) | 5 (0.5%) | |
| GAIIIc | 5 (0.2%) | 5 (0.3%) | 0 (0.0%) | |
| Open | 1 (0.0%) | 1 (0.1%) | 0 (0.0%) | |
| Mechanism of Injury | 0.021 | |||
| Road Traffic Accident | 2273 (78.8%) | 1477 (77.4%) | 785 (81.6%) | |
| Fall | 358 (12.4%) | 243 (12.7%) | 114 (11.9%) | |
| Explosive Blast | 16 (0.6%) | 11 (0.6%) | 4 (0.4%) | |
| Gun Shot | 110 (3.8%) | 77 (4.0%) | 32 (3.3%) | |
| Other | 128 (4.4%) | 100 (5.2%) | 27 (2.8%) | |
| World Bank Classification | <0.001 | |||
| LIC | 1034 (36.0%) | 726 (38.1%) | 304 (31.9%) | |
| LMIC | 1797 (62.6%) | 1143 (60.0%) | 644 (67.6%) | |
| UMC | 38 (1.3%) | 33 (1.7%) | 4 (0.4%) | |
| HIC | 3 (0.1%) | 3 (0.2%) | 0 (0.0%) | |
| Fracture Location | <0.001 | |||
| Distal | 1489 (51.9%) | 976 (51.3%) | 504 (52.9%) | |
| Middle | 1188 (41.4%) | 753 (39.6%) | 430 (45.2%) | |
| Proximal | 82 (2.9%) | 75 (3.9%) | 6 (0.6%) | |
| Segmental | 102 (3.6%) | 91 (4.8%) | 11 (1.2%) | |
| Subtrochanteric | 8 (0.3%) | 7 (0.4%) | 1 (0.1%) | |
| Days from Injury to Surgery | 61.25 (1059.72) | 66.55 (1298.53) | 51.14 (183.62) | 0.72 |
| Arrived with Non-Union | 0.016 | |||
| No | 2465 (82.6%) | 1621 (84.1%) | 844 (87.5%) | |
| Yes | 428 (17.4%) | 307 (15.9%) | 121 (12.5%) |
4. Discussion
The SIGN Standard Nail has demonstrated successful outcomes in several studies.15, 16, 17, 18, 19, 20 One systematic review of fixation with SIGN nails including studies from 2000 to 2016 analyzed 14 studies with 47,169 cases. The complication rate was 5.2% and rates of achieving painless weight bearing or successful radiographical healing were measured >90%.21 Another study analyzing 175 patients concluded no significant difference between fixation with SIGN Standard nails and commercial cannulated interlock IM nails with regards to achieving full range of motion, painless weight bearing or radiographical union.18
The purpose of the current study was to compare outcomes between patients treated with Fin Nails vs those treated with Standard nails in the retrograde approach for adult femoral shaft fractures. Few studies have been published on outcomes of adult femoral shaft fractures treated with the retrograde approach with the Fin Nail. However, results have been encouraging.22,23 A prospective cohort study at a tertiary referral center conducted on 85 patients treated between 2012 and 2013 reported equivalent outcomes between the Standard Nail and the Fin Nail with regards to quality of life, radiographical healing, pain, infection, and range of motion. Of 74 patients with minimum 1-year follow-up, the reported reoperation rate was 4% for Fin Nails and 5% for Standard Nails with no reported non-unions. A retrospective review of 249 femoral shaft fractures treated with the Fin nail in the retrograde approach reported a 92% union rate and 84% achieving painless weight bearing.23 Another analysis of 28 retrograde fractures treated with the Fin Nail and matched with the Standard nail concluded equivalent outcomes in terms of post-operative coronal and sagittal plane alignment.24
Evidence to date suggests the Fin Nail is viable to use in the retrograde approach with comparable results to the standard nail though no large-scale comparison has been performed. The current study attempts to use the SOSD to assess outcomes comparing the Standard Nail and the Fin Nail using propensity score analysis to control for potential confounders. Propensity score adjusted analysis is a validated approach to address confounding by achieving a balanced distribution of covariates across treatment groups.13 Inverse probability of treatment weighting (IPTW) uses patient weights calculated from the inverse probability of receiving treatment to generate a pseudo population where treatment assignment is independent of covariates.12 An average treatment effect is estimated using this pseudo-population which, in the present study, reflects the effect fixation with a Fin Nail had on achieving painless weight bearing or radiographical healing. Even after adjusting for potential confounding variables, no significant difference was observed in outcomes between treatment with the Standard and Fin Nail.
Though the Standard Nail was designed for low-resource setting without fluoroscopy, the Fin Nail has a key advantage as it does not require proximal interlocking screws in the retrograde approach which significantly shortens operative time (effect size 24 min, p < 0.001). The novel nature of the Fin Nail leads to skepticism as fixation via a proposed interference fit may not achieve adequate fixation and long-term outcomes. The current retrospective review demonstrates equivalence between the already successful standard nail and the novel Fin Nail along with comparable outcomes to previously reported data.
While the size and international nature of the SOSD cohort make the findings from this study unique, there are a few limitations that are worth noting. First, the observational or non-randomized nature of this study may lead to potential confounding. While we attempted to address this issue with our propensity score-weighted modeling and subgroup analyses, we could not adjust for any unmeasured confounding such as fracture comminution. Second, outcome assessment was self-reported and criteria for radiographical healing varies between surgeons. Lastly, the overall follow-up rate of our patient cohort was only around 14%, though we still had 2897 fractures included in the study population.
5. Conclusion
The present study assessed full painless weight bearing and radiographic healing of adult femoral shaft fractures treated in the retrograde approach with a SIGN Fin Nail and SIGN Standard Nail. There was no significant difference in relative risk between nails, thus the Fin Nail is equivalent to the Standard Nail in the Retrograde approach.
6. Ethics
This study's data was generated using the SIGN database, an international, deidentified trauma. All data and analyses were conducted on an encrypted virtual desktop. All data is deidentified and not made directly available to the user of the platform assuring the data is secure.
Funding
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
No Funding sources to disclose.
Permission
This was a retrospective database study that used deidentified patient data. Guardian/patient permission not applicable.
CRediT authorship contribution statement
Aditya Subramanian: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing, Data curation, Formal analysis. Babapelumi Adejuyigbe: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing, Data curation, Formal analysis. Kian Niknam: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing, Data curation, Formal analysis. Francisco Gomez-Alvarado: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing. Saam Morshed: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing, Supervision. David Shearer: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing, Supervision.
Declaration of competing interest
No conflicts of interest to disclose.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
SIGN Fracture Care International.
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