Safety and Ecacy of the META-TAN in Femoral Shaft Fractures: A Retrospective Case Series of 33 Patients

Introduction: Despite advances in femoral shaft fracture xation, the nonunion rate remains relatively high; and there is limited data on the ecacy and failure rate of specic implants. The Smith & Nephew TRIGEN META-TAN provides the ability to treat femur shaft fractures in isolation, with associated ipsilateral femur injuries, and provides various options for proximal and distal xation. The aim of this study is to evaluate the early failure rate of the META-TAN, while comparing the nonunion rate to what is currently presented in the literature. This study is the rst of its kind in evaluation of a specic implant for treatment of femoral shaft fractures and ipsilateral pathology. Material and Methods: Patients over 18 years of age, with traumatic femur shaft fractures, treated with the META-TAN and available for a minimum of 3-month follow-up were included for analysis. Data was collected by retrospective chart review and review of existing radiographs. Demographic data, injury details, AO/OTA fracture classication, and implant details were recorded for each patient. Primary outcome measured was implant failures (screw or nail breakage). Secondary outcomes measured included malunion, nonunion, deep infection, post-operative complications, and need for reoperation. Results: Of the 33 patients included for analysis, 1 patient went on to non-union. There were no cases of implant failure. The single nonunion was a high-energy mechanism, open fracture, and higher level AO/OTA classication. The remaining 32 reached radiographic union at 3 months. Conclusion: The nonunion rate of the META-TAN nail is comparable to what is reported in the literature. The META-TAN is a safe and effective implant to treat femoral shaft fractures with a variety of ipsilateral femoral shaft injuries and reliably leads fracture union. Further studies are needed analyzing implant failure and comparing specic implants.


Introduction
Femoral shaft fractures represent a common orthopaedic problem that may occur as the result of highenergy mechanisms in younger patients or low-energy injuries in elderly patients. Although intramedullary nailing remains the gold standard for femoral shaft fracture xation 1-4 , the question still remains for patients with ipsilateral femoral neck and shaft fractures, femoral bow variations, distal third femoral shaft fractures, number of interlocking screws, and type of proximal xation. While the union rate and functional outcomes remain high with this technique, the nonunion rate remains 1-11% 3,4,6,8,9,11,12 and implant failures are severely underreported.
The Smith and Nephew TRIGEN META-TAN (trochanteric antegrade nail) system is able to treat various femoral pathologies, such as ipsilateral femoral shaft and neck fractures, proximal femur fractures with narrow intramedullary canals, nonunion, malunion, pathologic fractures, and other complex pathology.
The smaller diameter proximal integrated screws combined with smaller diameter proximal nail can provide linear compression and rotation control of the fracture site, while minimizing bone loss compared to other lag screw designs, which is important for hip fractures in young patients. For mid-shaft fractures, the nailing system has an increased femoral mode, which accommodates better xation between the trochanters. The bow of the nail also increases with the length of the nail. For distal femoral fractures, there are three screw options within 40 mm of the distal aspect, with the most proximal screw allowing for 5 mm of dynamization.
Currently, there are no studies on the outcomes or failure rate of speci c implants for treatment of femur shaft fractures. There is literature on treatment of hip fractures in the elderly with speci c implants, but the implant failure rate remains limited. The goal of our study is to further evaluate the safety and e cacy of the Smith and Nephew TRIGEN META-TAN in a variety of femur shaft fractures in orthopaedic trauma. We hypothesize that there are high union rates and favorable clinical outcomes associated with this nailing system.

Material And Methods
A retrospective chart review was performed at an urban university-based level 1 and urban level 3 trauma centers. Study data was collected through retrospective chart review and review of the existing radiographic studies. Patients were identi ed through the coding database of our institution. Institutional Review Board (IRB) approval was obtained from our institution (Protocol #HSC2019328E).
Patients over 18 years of age who underwent intramedullary nail xation of their femur shaft fractures with the Smith and Nephew META-TAN from January 2015 -June 2019 were included in this investigation. We also included acute femur shaft fractures with ipsilateral proximal femur pathology (femoral head, neck, and intertrochanteric region), if they were treated with a single implant. Exclusion criteria included other nailing systems, retrograde nail xation, femoral shaft fractures with an ipsilateral proximal femur fracture treated with two implants, intra-articular distal femur fracture, and pathologic fractures from neoplastic disease.
The surgical technique was according to widely established recommendations as described in the TRIGEN META-TAN surgical guide. 5 The Smith and Nephew META-TAN allows for adaptability with optional intertrochanteric and cephalomedullary xation of the femur as well as three optional distal interlocking screws for proximal, midshaft, and distal third shaft fractures. 1 The implant comes in sizes 9 to 13 mm in diameter, a 14 mm proximal diameter, and interlocking options within 15 mm, 25 mm, and 35 mm of the tip of the implant with up to 15 degrees off of axis xation. The device can also be statically or dynamically locked distally. 1 Locking of the set screw proximally for xed angle xation along with the integrated lag and compression screws makes it suitable for a femoral neck and shaft fracture with an 8 mm diameter proximal lag screw to minimize risk of damage to femoral neck blood supply. 1 Regarding our post-operative protocol, the weight-bearing status of the injured lower extremity was determined by the treating surgeon. Patients were considered as incomplete follow-up if clinical and radiographic outcome data was not available for a minimum of 3 months after surgery. A minimum follow-up of 3 months was chosen since literature has reported a high rate of union at that time point. 3 The following preoperative and perioperative data points were collected from chart review and existing radiographs: age, gender, race, ethnicity, body mass index (BMI), American Society of Anaesthesiologists (ASA) scale, medical co-morbidities, social history (tobacco, ethanol, illicit drug use), baseline ambulatory status (no assistive device, cane, walker, wheelchair), mechanism of injury, open or closed injury, fracture location, fracture type according to the AO/OTA classi cation system, operative time, nail size (as de ned by diameter), number of distal screws, type of proximal xation, primary use of bone graft, estimated blood loss, perioperative complications, and perioperative mortality.
The primary outcome measure was mechanical hardware failure. The following secondary outcome measures were recorded: malunion (de ned as 5 degrees of radiographic varus/valgus malalignment, 10 degrees of radiographic procurvatum/recurvatum malalignment, or more than 10 degrees of clinical rotational deformity), non-union (as de ned by the need of a secondary surgical procedure to improve healing), peri-implant fracture, postoperative surgical complications, such as wound dehiscence, hematoma, super cial infection, deep infection, sepsis, and postoperative medical complications, such as thromboembolic events, pneumonia, urinary tract infection, and myocardial infarction.

Results
Based on the current procedural technology (CPT) 25706, a total of 435 patients were initially screened for participation in this retrospective study. However, 375 patients did not meet our inclusion criteria: 125 patients treated with a retrograde nail, 220 patients xed with a different antegrade implant, 23 individuals under the age of 18, and 7 patients with duplicate medical record numbers. Therefore, a total of 60 patients treated with the Smith and Nephew META-TAN were investigated in this study. However, 27 of the patients did not meet the minimum 3-month follow up, but none of these patients had radiographic evidence of implant breakage or failure at the last visit. The demographic and clinical outcome data of the remaining 33 patients are represented in Table 1 and Table 2.
All 33 patients were treated with the Smith and Nephew META-TAN, shown in Fig. 1, for their femur shaft fractures. All nails had a trochanteric starting point similar to that shown in Fig. 2a and 2b. The fracture patterns included eleven AO/OTA 32-A1 fractures, seven 32-A2 fractures, ve 32-A3 fractures, one 32-B1 fractures, three 32-B2 fractures, two 32-B3 fractures, two 32-C2 fractures, and two 32-C3 fractures. The type of proximal xation was cephalomedullary mode in 18 fractures and femoral mode in 15 fractures, as shown in Fig. 3a and 3b. Of the 18 patients with cephalomedullary xation, one patient had a nondisplaced ipsilateral femoral neck fracture while the remaining 17 patients were performed based on surgeon preference. All 15 of the femoral mode xations were performed by surgeon choice as well. The number of distal interlocking screws was zero in 1 patient, one in 8 patients, two in 22 patients, and three in 2 patients. The number of distal interlocking screws was chosen by surgeon preference. The three distal interlocking options can be seen in Fig. 4. There were no incidences of screw or nail breakage.

Discussion
The current standard treatment for femoral shaft fracture remains the intramedullary nail due to its minimally invasiveness, allowance for early weight bearing, and minimal disruption to soft tissue. [1][2][3][4] However, the incidence of femoral shaft nonunion after intramedullary nailing is still 1-11%. 3,4,6,8,9,11,12 The Smith & Nephew META-TAN is theorized to promote bone healing with its novel antegrade intramedullary design that can treat a variety of femur fracture pathology. In our retrospective cohort, we observed 1 nonunion in 33 patients without any mechanical failures, con rming our hypothesis that this nailing system is a safe and effective The patient with a femur shaft nonunion can be further interpreted by the demographics. The patient is a thirty-four year old male non-smoker, involved in a high speed motor vehicle collision, who sustained an open proximal third AO/OTA 32-B3, shown in Fig. 5, treated with a reamed, statically locked intramedullary nail with reconstruction proximal xation and two distal interlocking screws shown in Fig. 6. Our patient did not have any immediate postoperative complications, but did have risk factors for nonunion: high-energy mechanism, comminuted fracture on the AO/OTA classi cation, and an open fracture. At his six-month follow up visit he was found to have persistent pain at the fracture site, limited mobility, and radiographic evidence of a delayed union shown in Fig. 7. He ultimately went on to nonunion and was treated with a reamed exchange nail augmented with autograft, and supplemental plate xation.
The versatility of the implant can be demonstrated by the case of a 22-year old male passenger involved in a high-speed motor vehicle collision. He sustained a closed comminuted right femoral shaft fracture with a non-displaced right femoral neck fracture shown in Fig. 8. Temporary xation of the neck was obtained rst with threaded k-wires, followed by insertion of a reamed META-TAN with cephalomedullary xation and two distal interlocking screws shown in Fig. 9 There is a scarcity of literature on femoral shaft fractures treated with a speci c intramedullary implant, especially evaluating implant failure, nonunion rates, and functional outcomes. There is also a scarcity of literature on speci c implant failures rates. The versatility of the Smith and Nephew META-TAN nail lies its multiple modes of xation with intertrochanteric and cephalomedullary screws in the proximal femur along with optional distal interlocking screws for distal xation. 1 Also, its proximal reconstruction screws are a smaller diameter than other implants decreasing the risk of blood supply disruption to the femoral head. This antegrade nailing system is inserted through a trochanteric entry point, which is associated with better femoral version, and lower revision rates compared to the piriformis start point. 16 With antegrade nailing, elderly patients can be expected to have more functional de cits compared to their younger counterparts. 17 Functional outcomes also show some hip abductor weakness and a possible transient change in patients' gait. 18,19 Overall, our investigation shows that Smith and Nephew META-TAN nail has a nonunion rate for femoral shaft fractures comparable to the literature but also allows for multiple modes of xation with a single implant. There was no incidence of implant failure, but with lacking data in the literature on this, no comparison can be drawn.
Limitations of our study include its retrospective design. Our study does not allow for conclusions on long-term outcomes and had a relatively small sample size of 33 patients. Also, we have a number of patients lost to follow up prior to three months, but none demonstrated signs of hardware failure at their last follow up. The con guration of nail xation was not standardized and chosen under the discretion of the treating surgeons. A standardized protocol would be di cult given the signi cant variability of fracture patterns. In addition, we did not have a comparison group treated with a different nailing system.

Conclusion
Although xation of femoral shaft fractures has been successful with modern implants, the nonunion rate remains high in a subset of fractures and there is the potential for implant failure in a non-united fracture. Regardless of implant used tobacco use, open fractures, unreamed nails, and high-energy fracture patterns are associated with higher nonunion rates. The Smith and Nephew META-TAN nail shows similar nonunion rates as reported in the literature with a low failure rate; but allows for multiple modes of xation in the same femur. While we showed that it is a safe and reliable implant for xation of femoral shaft fractures, we could not overcome certain patient demographics. Further randomized studies are needed to compare different nailing systems to determine if a particular nail is superior to others.    showing the trochanteric start point on the AP and lateral image of the hip. Figure 3 showing the reconstruction mode and intertrochanteric mode for proximal xation.