The stability of a hip fracture determines the fatigue of an intramedullary nail

A probabilistic approach for assessing the mechanical performance of intertrochanteric fracture stabilized with proximal femoral nail antirotation

Maintaining post-operative mechanical stability is crucial for successfully healing intertrochanteric fractures treated with the Proximal Femoral Nail Antirotation (PFNA) system. This stability is primarily dependent on the bone mineral density (BMD) and strain on the fracture. Current PFNA failure analyses often overlook the uncertainties related to BMD and body weight (BW). Therefore, this study aimed to develop a probabilistic model using finite element modeling and engineering reliability analysis to assess the post-operative performance of PFNA under various physiological loading conditions. The model predictions were validated through a series of experimental test. The results revealed a negative nonlinear relationship between the BMD and compressive strain. Conversely, the BW was positively and linearly correlated with the compressive strain. Importantly, the compressive strain was more sensitive to BW than to BMD when the BMD exceeded 0.6 g/cm3. Potential trabecular bone compression failure is also indicated if BMD is equal to or below 0.15 g/cm3 and BW increases to approximately 2.5 times the normal or higher. This study emphasizes that variations in the BMD significantly affect the probability of failure of a PFNA system. Thus, careful planning of post-operative physical therapy is essential. For patients aged > 50 years restrictions on high-intensity activities are advised, while limiting strenuous movements is recommended for those aged > 65 years.

Implant fracture of the TFNA femoral nail

BACKGROUND

The TFNA (Trochanteric Fixation Nail Advanced) Proximal Femoral Nailing System (DePuy Synthes) is frequently used for intramedullary fixation of proximal femoral fractures. The aim of this study was to evaluate all TFNA implant fractures at a UK trauma unit to ascertain any patient or surgical factors associated with implant failure.

METHODS

A retrospective study was carried out identifying all patients that sustained a TFNA implant fracture over a five-year period. Data was collected on demographic information, ASA, co-morbidities, mechanism of injury, fracture pattern according to the AO/OTA classification, procedure details and time to failure. Radiographs were assessed by two independent reviewers to identify tip-apex distance (TAD), calcar TAD, reduction quality and union status at time of implant failure.

RESULTS

Six cases were identified, all with implant breakage at the aperture for the proximal screw. All femoral fractures were intertrochanteric reverse obliquity type (OA/OTA 31A3). Two were traumatic fragility fractures and the remainder atraumatic. Mean time from index surgery to revision was 441 days (104-963). Mean TAD was 20.5 mm (15-24) and mean calcar TAD 24 mm (18-32). All six cases displayed radiographic non-union at the time of implant fracture.

CONCLUSION

Pathological fractures resulting in reverse obliquity type fracture patterns and subsequent non-union appear to be contributory factors to TFNA breakage at the proximal screw aperture. This may be further exacerbated by alterations to the nail design from previous generations. In these patients, close follow up with clinical and radiographic surveillance should be employed. Further biomechanical and clinical studies are required to compare this finding against other nail designs.

Medial Calcar Comminution and Intramedullary Nail Failure in Unstable Geriatric Trochanteric Hip Fractures

Background and Objectives: An increasing global burden of geriatric hip fractures is anticipated. The appropriate treatment for fractures is of ongoing interest and becoming more relevant with an aging population and finite health resources. Trochanteric fractures constitute approximately half of all hip fractures with the medial calcar critical to fracture stability. In the management of unstable trochanteric fractures, it is assumed that intramedullary nails and longer implants will lead to less failure. However, the lack of power, inclusion of older generation femoral nails, and a variable definition of stability complicate interpretation of the literature. Materials and Methods: Between January 2012 and December 2017, a retrospective analysis of operatively treated geriatric trochanteric hip fracture patients were examined at a Level 1 Trauma Centre. The treatment was with a long and short version of one type of trochanteric nail. Unstable trochanteric fractures with medial calcar comminution were examined (AO31A2.3, 2.3 & 3.3). The length of the medial calcar loss, nail length, demographics, fracture morphology, and relevant technical factors were examined in univariate and multivariate analysis using competing risk regression analysis. The primary outcome was failure of fixation with post-operative death the competing event and powered to previously reported failure rates. Results: Unstable patterns with medial calcar comminution loss constituted 617 (56%) of operatively treated trochanteric fractures. Failure occurred in 16 (2.6%) at a median post-operative time of 111 days (40-413). In univariate and multivariate analysis, only younger age was a significant predictor of failure (years; SHR: 0.91, CI 95%: 0.86-0.96, p < 0.001). Nail length, medial calcar loss, varus reduction, and other technical factors did not influence nail failure. Conclusions: In a cohort of unstable geriatric trochanteric hip fractures with medial calcar insufficiency, only younger patient age was predictive of nail failure. Neither the length of the medial calcar fragment or nail was predictive of failure.

Comparison of Early Fatigue Failure of the TFNa and Gamma 3 Cephalomedullary Nails in the United States From 2015 to 2019

OBJECTIVES

To compare reports of implant fatigue failure submitted to the FDA of 2 commonly used cephalomedullary nails.

METHODS

In total, 2724 medical device reports from the FDA's MAUDE database from Jan 2015 to Oct 2019 were reviewed for the Trochanteric Femoral Nail-Advanced (TFNa) and Gamma 3 implants.

RESULTS

Data from 342 implant failures included in the MAUDE database were analyzed. TFNa and Gamma 3 had 183 and 159 reported fatigue failures, respectively. All failed implants fractured in the same location through the proximal screw aperture. Time from implantation to failure was on average 2 months shorter for TFNa implants that were reported fractured than for Gamma 3 implants reported, a difference that was statistically significant (P < 0.05). In total, 100 implants were reported to have failed within the first 4 months (53 and 47 for TFNa and Gamma 3, respectively). For Gamma 3 implants that failed in the first 4 months, almost all of the available manufacturers' inspection reports revealed implant notches at the point of failure from drilling. For TFNa implants that failed early, only one reported notch was noted in the available inspection reports.

CONCLUSIONS

In contrast to other studies regarding fatigue failure, reported failures in both TFNa and Gamma 3 occurred earlier than can be attributed to delayed or nonunion. The reported failures of the TFNa in the MAUDE database occurred earlier than did those of the Gamma 3. Early failures of the Gamma 3 seemed to be the result of iatrogenic implant notching.

LEVEL OF EVIDENCE

Therapeutic Level III. See instructions for authors for a complete description of levels of evidence.

Comparison of Fragment Removal Versus Internal Fixation for Treatment of Pipkin I Femoral Head Fractures: A Finite Element Analysis

Fragment removal and internal fixation are the principle treatments for Pipkin type I femoral head fractures. The aim of this study was to compare, using a finite-element method, changes in stress on the femoral head after 2 different operation types. A three-dimensional (3D) finite-element model of a Pipkin type I femoral head fracture was generated with MIMICS and ABAQUS software. A 3D numerical screw model was reconstructed based on data from BIOFIX and using SOLIDWORKS software. The screw was implanted in the fragment and femoral head to reconstruct the implantation. Stress changes on the femoral head after removal of the fragment and internal fixation were investigated. Mean stresses along 13 points were 16.94 ± 16.79 MPa in the fragment removal group and 14.17 ± 14.08 MPa in the internal fixation group (P &lt; 0.05). Random tests indicated that the mean stresses along 50 randomly determined points were 25.41 ± 12.12 MPa in the fragment removal group and 19.45 ± 14.62 MPa in the internal fixation group (P &lt; 0.05). Compared with internal fixation, fragment removal led to greater stress that was more concentrated in the femoral head.

A new perspective towards failure of gamma nail systems

Uncommon causes of nail failures and surgical reinterventions were determined. The study included 23 osteoporotic patients, 13 of whom followed a fast recovery program with early walking (FWB group). The other 10 patients were not allowed full weight bearing until 6 weeks (NFWB group). The T-score was determined before surgery for all cases. A case with a nail breakage after a failed DCS implant fixed in another clinic was also analyzed. The nail was revised and the broken implant underwent a metallurgic and microscopic examination. The average T-score was 2.5 for the patients that followed the fast recovery program and 2.7 for the patients from non-full weight bearing. Four patients, 1 from the NFWB group and 3 from FWB group, presented a screw cut-out. It was found that the errors of the guiding instruments may create dents, scratches or micro-fractures on the titanium coating that lead to an early implant failure. Imperfect reduction leads to incorrect implant placement and a high incidence of failure. Damaging the titanium protective coating, in a low force, high cycles scenario can cause structural failure. Delays in fracture healing and material fatigue are the most common causes of nail failure and can lead to catastrophic complications.

Does auxiliary cerclage wiring provide intrinsic stability in cephalomedullary nailing of trochanteric and subtrochanteric fractures?

Purpose

The aim of this study was to assess functional and radiological results following cephalomedullary nailing with and without use of auxiliary cable cerclages in a large series of trochanteric and subtrochanteric femoral fractures.

Methods

In a retrospective study of prospectively collected data between January 2014 and March 2019, a total of 260 consecutive patients (155 women and 105 men) with the diagnosis of AO/OTA A1 to A3 fractures were included. The mean age of patients was 76.4 ± 15.6 years. According to the AO/OTA classification, 72 A1 fractures, 124 A2 fractures, and 64 A3 fractures were found. In 72 patients with auxiliary cerclage wiring three A1 fractures, 27 A2 fractures and 42 A3 fractures were assessed. In the patient group with auxiliary cerclages, fracture healing according to the Radiographic Union Score for Hip (RUSH) within one year after surgery was assessed in 68 out of 72 patients (healing rate 94%). The mean RUSH in the group with cerclages was 28.7 ± 2.2 points and was 28.5 ± 2.2 points in the group without cerclages (p = 0.72). In 91 patients available for a complete follow-up, mean functional outcome according to the Lower Extremity Functional Scale (LEFS) was 65.3 ± 17.2 points in the group with cerclages versus 58.4 ± 21 points in the group without cerclages (p = 0.04).

Conclusion

The additional use of cerclages provides intrinsic stability and enables axial alignment and medial cortical support during anatomical fracture reduction and cephalomedullary nail insertion. In the current study, this technique resulted in significantly better functional long-term outcomes than without cerclages. Therefore, it can be recommended as a useful supportive tool especially in comminuted trochanteric and subtrochanteric fractures. Trial registration number DRKS00020550, 01/30/2020, retrospectively registered.

Risk Factors Associated with Failure of Cephalomedullary Nail Fixation in the Treatment of Trochanteric Hip Fractures

Background

Intramedullary (IM) nailing is widely performed in elderly patients with trochanteric fractures. Thus, it is important to identify causative factors associated with fixation failure. We investigated fixation failures after IM nailing in elderly patients with trochanteric fractures and compared the failure group with nonfailure group to identify risk factors of fixation failure.

Methods

A total of 396 patients aged 65 years or older underwent IM nailing for trochanteric fractures between January 2012 and August 2016 at our institution. Of those, 194 patients who were followed up for more than 12 months were enrolled in this study; 202 patients were excluded due to death during follow-up, bedridden status before injury, and loss to follow-up. All patients underwent plain radiography and preoperative computed tomography (CT).

Results

Fixation failure occurred in 11 patients (5.7%). Seven patients had stable fractures (AO/OTA); eight patients had basicervical fractures (confirmed by CT). Five patients had comminution in the greater trochanter (confirmed by CT). Regarding fracture reduction, eight patients showed discontinuity in the anterior cortex. The position of the lag screw on the lateral view was in the center in six patients and in a posterior area in the other five patients. On the basis of comparison with the 183 patients without fixation failure, risk factors of fixation failure were higher body mass index (BMI; p = 0.003), basicervical type of fracture (p = 0.037), posterior placement of the lag screw on the lateral view (p < 0.001), and inaccurate reduction of the anterior cortex (p = 0.011).

Conclusions

Among the risk factors of fixation failure after IM nailing in elderly patients with trochanteric fractures, discontinuity of the anterior cortex and posterior position of the lag screw are modifiable surgeon factors, whereas higher BMI and basicervical type of fracture are nonmodifiable patient factors. Therefore, care should be taken to avoid fixation failure in IM nailing for patients with a basicervical type of fracture or higher BMI or both.

Parametric Finite Element Analysis of Intramedullary Nail Fixation of Proximal Femur Fractures

Proximal femur fracture fixation with intramedullary nailing relies on stability at the fracture site and integrity of the fixation construct to achieve union. The biomechanics that dictate fracture site stability and implant stress depend on fracture type as well as implant features such as nail length, nail diameter, presence of distal fixation screws, and material composition of the implant. When deciding how to fix a fracture, surgeons have choices in these implant-related design variables. This study models all combinations of a range of implant variables for nine standard AO/OTA proximal femur fractures using finite element analysis. Under simulated maximum load during gait, the maximum stress in the implant and screws as well as interfragmentary motions at the fracture site in the axial and shear directions were computed. The results were separated by fracture type to show the influence of each design variable on measured biomechanical outcomes. Filling the reamed canal with the largest fitting nail diameter reduced axial and shear interfragmentary motion for all fracture types. Nail length was less predictive of shear interfragmentary motion for most simulated fracture types than other construct variables. Furthermore, gapping at the fracture site predisposed the construct to higher implant stresses and larger interfragmentary motions. Clinical significance: Biomechanical outcomes from this computational study can aid in surgical decision-making for optimizing hip fracture fixation with IM nailing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2358-2366, 2019.

Experimentally validated structural finite element method analysis of a tibial intramedullary nail: Optimal choice of the contact settings

This article focuses on the static structural analysis of a tibial intramedullary nail, carried out by the finite element method. The investigated subject is concerned with the issue of frictional contacts that, generating a non-linear problem, play an important role in numerical analyses. Experimental tests were also developed on tibial intramedullary nail specimens. The experimental results, in terms of force-displacement, were used to calibrate and validate the finite element analysis, by tuning the contact parameters available in the software.

Risk factors for intramedullary nail breakage in proximal femoral fractures: a 10-year retrospective review

INTRODUCTION Intramedullary nailing is a common treatment for proximal femoral fractures. Fracture of the nail is a rare but devastating complication that exposes often frail patients to complex revision surgery. We investigated which risk factors predict nail failure. METHODS We reviewed all cases of nail breakage seen over a 10-year period in a single busy trauma unit; 22 nail fractures were seen in 19 patients. Comparison was made with a group of 209 consecutive patients who underwent intramedullary fixation of a proximal femur fracture with no nail breakage over a 2-year period. RESULTS In the fractured nail group, mean age was 70.4 years (range 55-88 years).The mean time to fracture was 10 months (range 2.5-23 months). Logistical regression was used to show that low American Society of Anesthesiologists (ASA) score, subtrochanteric fracture and pathological fracture were independent risk factors for nail fracture. CONCLUSIONS Young patients with a low ASA score are at highest risk of nail breakage. We advise close follow-up of patients with these risk factors until bony union has been achieved. In addition, there may be merit in considering other treatment options, such as proximal femoral replacement, especially for those with pathological fracture with a good prognosis.

Biomechanical rationale for implant choices in femoral neck fracture fixation in the non-elderly

Femoral neck fractures represent a relatively uncommon injury in the non-elderly population often resulting from high-energy trauma. The cornerstone of their management is anatomic reduction and stable internal fixation of the femoral neck in an attempt to salvage the femoral head. Complications including avascular necrosis of the femoral head, non-union and post-traumatic osteoarthritis are not uncommon. The clinical outcomes of these patients can be improved with good pre-operative planning, optimization of surgical procedures and introduction of new improved implants and techniques. In the herein study, we attempt to describe the biomechanical properties of the hip and compare the performance of the most commonly used devices. Experimental evidence suggests that in Pauwels type III fracture patterns a cephalomedullary nail was significantly stronger in axial loading. Moreover, in unstable basicervical patterns cannulated screws (triangular configuration) demonstrated a lower ultimate load to failure, whereas in subcapital or transervical patterns both the cannulated screws (triangular configuration) and the sliding hip screw demonstrated no compromise in fixation strength. The fracture pattern appears to be the major determinant of the ideal type of implant to be selected. For a successful outcome each patient needs to be considered on an individual basis taking into account all patient and implant related factors.

The effect of fracture pattern stability on implant loading in OTA type 31-A2 proximal femur fractures

BACKGROUND

Internal fixation of OTA type 31-A2 proximal femoral fractures can be performed with either a sliding hip screw and side plate (SHS-P) or a sliding hip screw and intramedullary nail (SHS-IMN). Controversy exists as to which is the best implant for these types of fractures. The primary aim of this study was to investigate the stability of 31-A2 fractures as a function of loss of medial cortical buttress. The secondary aim was to assess the influence of fracture stability on the different internal fixation constructs.

METHODS

Simulated simple intertrochanteric fractures were made in 12 cadaver proximal femurs. Six fractures were fixed with an SHS-P and 6 with an SHS-IMN. Both implants were instrumented with a strain gauge at the lag screw-nail/plate interface to allow assessment of implant load bearing (ILB). A primary fracture line, in accordance with the 31-A2 OTA classification, was created after which 3 subsequent horizontal osteotomies in 1-cm increments were made across the medial cortex. Compressive loading up to 1050 N was performed after each osteotomy.

RESULTS

ILB was presented as percentage of maximal ILB. SHS-P constructs increased their load bearing gradually. For SHS-P constructs, ILB was 8.1% ± 1.8% in the intact state, increasing to 49.6% ± 14.0% after the initial intertrochanteric osteotomy (P = 0.0002), 68.7% ± 15.9% after the first medial osteotomy (P = 0.028), and 80.0% ± 15.9% after the second medial osteotomy (P = 0.15). After the first-level medial osteotomy, SHS-IMN constructs reached a plateau in which the implant carried the entire load.

CONCLUSIONS

Type 31-A2 fractures become increasingly unstable with increased medial comminution (or fragment size). SHS-P constructs were more load sharing than SHS-IMN constructs. These findings may help guide the surgeon in choice of implant for a 31-A2 intertrochanteric fracture, leaning toward SHS-IMN for the more unstable fracture patterns.

Auxiliary locking plate improves fracture stability and healing in intertrochanteric fractures fixated by intramedullary nail

BACKGROUND

Intertrochanteric fractures present a significant management challenge due to their low inherent stability. The objective of this study was to determine whether an auxiliary locking plate decreases interfragmentary motions and improves fracture healing in intertrochanteric fractures treated by intramedullary nail.

METHODS

Biomechanical tests and a clinical retrospective study in intertrochanteric to subtrochanteric nonunions were performed. Six synthetic femurs were osteotomized intertrochanterically and fixated with a long gamma nail and an additional locking compression plate. Mechanical tests were conducted that simulated the hip joint force during gait cycle. Following the initial test, the locking compression plate (LCP) was removed from each specimen and the test was repeated. Interfragmentary motions, strains on implants and osteosynthesis stiffness were determined. For the clinical part of the study, 13 intertrochanteric to subtrochanteric nonunions were treated with revisional long gamma nail and additional locking compression plate. Complications and time to union were determined.

FINDINGS

Biomechanically, interfragmentary rotation was 48% smaller (P=0.047) and interfragmentary shear movement was 42% smaller (P=0.007) with locking compression plate. Strains on the nail decreased by 20-27% (P<0.027) and the osteosynthesis stiffness increased by 23% (P=0.005) with locking compression plate. Clinically, fracture healing was achieved in eleven out of 13 patients after 9.0months (range 4 to 22months).

INTERPRETATION

The findings of our study indicate that auxiliary locked plating considerably improves biomechanical performance and results in successful healing of unstable intertrochanteric to subtrochanteric femur fractures.