Biomechanical assessment of composite versus metallic intramedullary nailing system in femoral shaft fractures: A finite element study

Biomechanical Principles of Intramedullary Nails in Veterinary and Human Medicine

Intramedullary nails are specialized metal rods inserted into the medullary cavity of a fractured bone and secured to reduce load on the fracture site, provide stability, and permit healing. The purpose of this review is to highlight the biomechanics of orthopaedic intramedullary nailing, as well as discuss the biomechanical considerations that have shaped implant design and fixation technique in veterinary and human medicine. Relevant studies were included from the PubMed database and Google Scholar for discussion on the basic science and nail design of intramedullary nails. Implant design and implementation continues to progress, with new innovative designs currently under investigation. A lack of consensus remains on the superior implant material. Recent studies, particularly in human populations, have supported the use of reaming based on reoperation rates, nonunion rates, and dynamization. Design modifications, such as the expandable intramedullary nails and angle-stable interlocking designs, have been investigated as methods of improving cortical contact and resisting torsional stress. Intramedullary nailing is a valuable stabilization technique for long bone fractures across a variety of species. The technology continues to undergo design improvements in both veterinary and human medicine.

Biomechanical testing of a computationally optimized far cortical locking plate versus traditional implants for distal femur fracture repair

BACKGROUND

This study experimentally validated a computationally optimized screw number and screw distribution far cortical locking distal femur fracture plate and compared the results to traditional implants.

METHODS

24 artificial femurs were osteotomized with a 10 mm fracture gap 60 mm proximal to the intercondylar notch. Three fixation constructs were used. (i) Standard locking plates secured with three far cortical locking screws inserted according to a previously optimized distribution in the femur shaft (n = 8). (ii) Standard locking plates secured with four standard locking screws inserted in alternating plate holes in the femur shaft (n = 8). (iii) Retrograde intramedullary nail secured proximally with one anterior-posterior screw and distally with two oblique screws (n = 8). Axial hip forces (700 and 2800 N) were applied while measuring axial interfragmentary motion, shear interfragmentary motion, and overall stiffness.

FINDINGS

Experimental far cortical locking plate results compared well to published computational findings. Far cortical locking femurs contained the highest axial motion within the potential ideal range of 0.2-1 mm and a sheer-to-axial motion ratio < 1.6 at toe-touch weight-bearing (700 N). At full weight-bearing (2800 N), Standard locking-plated femurs had the only axial motion within 0.2-1 mm but had an excess shear-to-axial motion ratio. Nail-implanted femurs underperformed at both forces.

INTERPRETATION

For toe-touch weight-bearing, the far cortical locking construct provided optimal biomechanics to allow moderate motion, which has been suggested to encourage early callus formation. Conversely, at full weight-bearing, the standard locking construct offered the biomechanical advantage on fracture motion.

Mechanical effect of changed femoral neck ante-version angles on the stability of an intertrochanteric fracture fixed with PFNA: A finite element analysis

Objective

Change of femoral neck ante-version angle postoperatively due to inadequate reduction could result in unsatisfying treatment outcome of intertrochanteric fracture. However, the influence of increased or decreased femoral neck ante-version on the biomechanical stability of the bone-implant complex has rarely been studied.

Methods

A finite element model of a complete normal human femur with normal femoral neck ante-version as 13° was established accurately by scanning a 64 year old female femur. The models of 31-A1.1 intertrochanteric fractures with different femoral neck ante-version angles of 3°, 5.5°, 8°, 10.5°, 13°, 15.5°, 18°, 20.5°, 23° were created. They were assembled with a proximal femoral nail anti-rotation (PFNA) device. The biomechanical differences with varying femoral neck ante-version angles were compared using finite element analysis method.

Results

As the femoral neck ante-version angle gradually increased from 13° to 23°with a gradient of 2.5°, the peak von Mises stress was gradually increased from 137.82 MPa to 276.02 MPa. Similarly, the peak von Mises stress was gradually increased from 137.82 MPa to 360.12 MPa with the femoral neck ante-version angle decreased from 13° to 3°. When decreased ante-version angle of 7.5° and increased ante-version angle of 10° will exceed the yield strength of femoral (240.32 MPa), the risk of femoral fracture will increase significantly. The maximum displacement of the femur was significantly reduced for increased ante-version models than for decreased ante-version models, whether the changes of ante-version angles were 2.5°, 5°, 7.5° or 10°. The maximum stress of PFNA was found in the intersection of main nail and helical blade, and became greater gradually as the ante-version angle increased or decreased with a gradient of 2.5°. The maximum stress of PFNA was presented in the model 5.5° with the maximum stress of 724.42 MPa (near to the yield strength of titanium alloy of 700-1000 MPa), producing the breakage risk of PFNA. The maximum displacement of the PFNA was significantly reduced for increased ante-version models than for decreased ante-version models, whether the changes of ante-version angles were 2.5°, 5°, 7.5° or 10°.

Conclusion

Based on the results of present study, it was demonstrated that the anatomical reduction of femoral neck ante-version was vital to secure the optimal stability. Abnormal femoral ante-version could increase the potential risk of failure for intertrochanteric fracture after PFNA. The stability of increased femoral ante-version (less than 10°) was superior to the stability of decreased ante-version (less than 5°) for the cases of difficulty to acquire anatomical reduction. The clinical implication of the finding was that increased femoral neck ante-version had an advantage of mechanical stability towards the decreased femoral neck ante-version for the cases of comminuted intertrochanteric fracture and failure of anatomical reduction.

Mechanical evaluation of revision surgery for femoral shaft nonunion initially treated with intramedullary nailing: Exchange nailing versus augmentation plating

INTRODUCTION

Exchange nailing (EN) or augmentation plating (AP) has been employed to treat nonunions after intramedullary nailing for femoral shaft fractures. Although instability is a factor in hypertrophic nonunion, mechanical evaluations have been limited because the contribution of the callus to fracture site stability varies with healing. Our previous study illustrated the potential for evaluation using a finite element analysis (FEA) that incorporates callus material properties. This study aimed to mechanically evaluate revision surgery for nonunions using FEA.

MATERIALS AND METHODS

A quantitative computed tomography-based FEA was performed on virtual revision models of a patient with suspected nonunion after intramedullary nailing. In addition to the initial nailing model (IN) with an 11-mm diameter (D) and 360-mm length (L), four EN models with D12mm (EN1), D13mm (EN2), D12mm-L400mm (EN3), and D13mm-L400mm (EN4) nails and three AP models with 5- (AP1), 6- (AP2), and 7-hole (AP3) plates were created. As with bone, callus was assigned inhomogeneous material properties derived from density based on an empirical formula. The hip joint reaction force and muscle forces at maximum load during the gait cycle were applied. The volume ratio of the callus at the fracture site with a tensile failure risk of ≥1 (tensile failure ratio) and bone fragment movement were evaluated.

RESULTS

The tensile failure ratio was 11.6 % (IN), 10.1 % (EN1), 6.3 % (EN2), 10.9 % (EN3), 6.2 % (EN4), 6.4 % (AP1), 7.2 % (AP2), and 7.7 % (AP3), respectively. The bone fragment movement showed an opening on the lateral side with the initial intramedullary nailing. However, both revision surgeries reduced the opening, leading to compression except in the EN1 model. The proximal bone fragments were internally rotated relative to the distal fragments, and the rotational instability was more suppressed in models with lower tensile failure ratio.

CONCLUSIONS

For EN, the increase in diameter, not length, is important to suppress instability. AP reduces instability, comparable to a 2 mm increase in nail diameter, and screw fixation closer to the fracture site reduces instability. This study suggest that AP is mechanically equivalent to EN and could be an option for revision surgery for femoral shaft nonunions.

Fixators dynamization for delayed union and non-union of femur and tibial fractures: a review of techniques, timing and influence factors

The optimal balance between mechanical environment and biological factors is crucial for successful bone healing, as they synergistically affect bone development. Any imbalance between these factors can lead to impaired bone healing, resulting in delayed union or non-union. To address this bone healing disorder, clinicians have adopted a technique known as "dynamization" which involves modifying the stiffness properties of the fixator. This technique facilitates the establishment of a favorable mechanical and biological environment by changing a rigid fixator to a more flexible one that promotes bone healing. However, the dynamization of fixators is selective for certain types of non-union and can result in complications or failure to heal if applied to inappropriate non-unions. This review aims to summarize the indications for dynamization, as well as introduce a novel dynamic locking plate and various techniques for dynamization of fixators (intramedullary nails, steel plates, external fixators) in femur and tibial fractures. Additionally, Factors associated with the effectiveness of dynamization are explored in response to the variation in dynamization success rates seen in clinical studies.

Biomechanical design optimization of distal femur locked plates: A review

Clinical findings, manufacturer instructions, and surgeon's preferences often dictate the implantation of distal femur locked plates (DFLPs), but healing problems and implant failures still persist. Also, most biomechanical researchers compare a particular DFLP configuration to implants like plates and nails. However, this begs the question: Is this specific DFLP configuration biomechanically optimal to encourage early callus formation, reduce bone and implant failure, and minimize bone "stress shielding"? Consequently, it is crucial to optimize, or characterize, the biomechanical performance (stiffness, strength, fracture micro-motion, bone stress, plate stress) of DFLPs influenced by plate variables (geometry, position, material) and screw variables (distribution, size, number, angle, material). Thus, this article reviews 20 years of biomechanical design optimization studies on DFLPs. As such, Google Scholar and PubMed websites were searched for articles in English published since 2000 using the terms "distal femur plates" or "supracondylar femur plates" plus "biomechanics/biomechanical" and "locked/locking," followed by searching article reference lists. Key numerical outcomes and common trends were identified, such as: (a) plate cross-sectional area moment of inertia can be enlarged to lower plate stress at the fracture; (b) plate material has a larger influence on plate stress than plate thickness, buttress screws, and inserts for empty plate holes; (c) screw distribution has a major influence on fracture micro-motion, etc. Recommendations for future work and clinical implications are then provided, such as: (a) simultaneously optimizing fracture micro-motion for early healing, reducing bone and implant stresses to prevent re-injury, lowering "stress shielding" to avoid bone resorption, and ensuring adequate fatigue life; (b) examining alternate non-metallic materials for plates and screws; (c) assessing the influence of condylar screw number, distribution, and angulation, etc. This information can benefit biomedical engineers in designing or evaluating DFLPs, as well as orthopedic surgeons in choosing the best DFLPs for their patients.

Which of the three different intramedullary nail designs is superior in the treatment of femoral shaft fractures?

Aim: The aim of this study a retrospective comparison was the clinical and radiological results results of patients with femoral shaft fracture made oftreated with three different types of intramedullary nail (IMN). Material and Method: The study included 54 patients operated on in our clinic because of femoral shaft fracture. The records were retrospectively examined of 18 patients applied with locked IMN (LIMN), 17 with blade expandable IMN (BEIMN), and 19 with talon distalfix IMN (TDIMN). The groups were compared statistically in respect of age, gender, BMI, affected side, operating time (mins), radiation exposure (number of shots), time to union (weeks), visual analog scale (VAS) score, soft tissue problems associated with implant irritation, amount of shortening (mm), coronal, sagittal and torsional angulation (degrees). Results: The mean VAS score of the TDIMN group was determined to be statistically significantly higher than that of the LIMN and BEIMN groups (p=0.008, p=0.045). The operating times were similar in the BEIN and TDIMN groups (p=0.768) and significantly shorter than in the LIMN group (p

Effective Treatment of Femur Diaphyseal Fracture with Compression Plate - A Finite Element and In Vivo Study Comparing the Healing Outcomes of Nailing and Plating

BACKGROUND

The rigidity in osteosynthesis causes primary healing, and it takes longer to heal. The flexibility provided to the fixation allows micromotion between fragments which accelerates secondary healing.

METHODS

In this study, the healing outcomes of nailing and plating in different fixation stabilities were investigated and compared by using a finite element tool. The clinical observational study was also performed to verify the results of the finite element analysis. The nonlinear contact analysis was performed on 5 different fixation configurations capturing nail and plate in immediate post-surgery.

RESULTS

The finite element analysis results showed that flexibility instead of rigidity in interlock nail implantation increases the axial and shear micromotion near the fracture site by 47.4% (P < 0.05) and 12.4% (P < 0.05), respectively. For LCDCP implantation, the flexible fixation increases the axial and shear micromotion near fracture site by 75.7% (P < 0.05) and 25.3% (P < 0.05), respectively.

CONCLUSION

Our findings suggest that flexible fixations of interlock nail and LCDCP provide a preferred mechanical environment for healing, and hence, the LCDCP in flexible mode can be an effective alternative to interlock nail for the femur diaphyseal fracture.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43465-022-00795-1.

The influence of composite bone plates in Vancouver femur B1 fracture fixation after post-operative, and healed bone stages: A finite element study

Conventional stainless steel or titanium plates are used for bone fracture fixation to provide support at fracture location. Plates with high elastic modulus reduce the transfer of compressive load at the fracture location (due to stress shielding), causing failure. The objective of the study is to find for composite bone plates with different types of fibers and varied fiber orientations for post-operative (PO) and healed bone (HB) conditions which can reduce the stress shielding. Femur fracture fixation was constructed with 12 holes narrow type with metal and composite bone plates. The fracture gap was constructed with soft bone region for post-operative (PO) condition and harder bone for healed bone (HB). Composite bone plates with different configurations (fiber directions) and types (thickness and width) were analyzed to study the stress distribution and movement in the fracture location. The models were analyzed and the stresses in plate and callus, movement and strain in axial and shear direction in both metal and composite bone plates were studied. The metal and composite plates (carbon fiber/epoxy, fiberglass/epoxy, and flax/epoxy) used for most common Vancouver type B1 fracture to observe the biomechanical behavior of different models in PO and HB condition. The FE simulation on different configurations and types of composite plates provide in-depth idea about choosing the suitable composite bone plate. There are variations in behavior for varying types and configurations, but the performance of most of the plates are either better or similar to that of metal plate, except the plates with higher width.

Metal and composite bone plates for B1 periprosthetic femoral fracture in healthy and osteoporotic condition: A comparative biomechanical study

The major concern after total hip arthroplasty (THA) is the incidence of periprosthetic fracture in the weaker bone, which can lead to subsequent revision surgery. Achieving the suitable fixation without affecting the stability of the well-fixed prosthesis remains controversial. Most of the studies examined the behavior of the Periprosthetic Fracture (PF) fixation (Vancouver “B1” type) through computational and experimentation on healthy bone condition with metal plates. The aim of the present study is to analyze the influences of the metal and composite bone plate PF fixation on the axial and shear movement at the fracture site. The PF fixation constructs were modeled with medical graded stainless-steel plate (construct A), titanium plate (construct B) and carbon/epoxy composite bone plate (construct C) with 12 holes and a 4 mm fracture gap. Analysis was carried out for all the stages (stage 1—Normal bone, stage 2—THA, stage 3—Immediate Post-Operative (IPO), stage 4—Post-Operative (PO) and, stage 5—Healed Bone (HB)) under various loadings for intact and osteoporosis conditions. The results showed higher stress in cortical bone for stage 3, whereas in all the other stages lower stresses were experienced in the cortical and cancelous bone under peak load in construct C for osteoporosis model compared with other constructs. The present study suggested the construct C may be suitable for osteoporosis bone conditions.

Mechanical evaluation of a novel angle-stable interlocking nail in a gap fracture model

OBJECTIVE

To describe the mechanical characteristics of a novel angle-stable interlocking nail (NAS-ILN) and compare them to those of a locking compression plate (LCP) by using a gap-fracture model.

STUDY DESIGN

Experimental study.

SAMPLE POPULATION

Synthetic bone models.

METHODS

Synthetic bone models simulating a 50 mm diaphyseal comminuted canine tibial fracture were treated with either a novel angle-stable interlocking nail (NAS-ILN) or a locking compression plate (LCP). Maximal axial deformation and load to failure in compression and 4-point bending, as well as maximal angular deformation, slack, and torque to failure in torsion, were statistically compared (P < .05).

RESULTS

In compression, the maximal axial deformation was lower for NAS-ILN (0.11 mm ± 0.03) than for LCP (1.10 mm ± 0.22) (P < .0001). The ultimate load to failure was higher for NAS-ILN (803.58 N ± 29.52) than for LCP (328.40 N ± 11.01) (P < .0001). In torsion, the maximal angular deformation did not differ between NAS-ILN (22.79° ± 1.48) and LCP (24.36° ± 1.45) (P = .09). The ultimate torque to failure was higher for NAS-ILN (22.45 Nm ± 0.24) than for LCP (19.10 Nm ± 1.36) (P = .001). No slack was observed with NAS-ILN. In 4-point bending, the maximal axial deformation was lower for NAS-ILN (3.19 mm ± 0.49) than for LCP (4.17 mm ± 0.34) (P = .003). The ultimate bending moment was higher for NAS-ILN (25.73 Nm, IQR [23.54-26.86] Nm) than for LCP (16.29 Nm, IQR [15.66-16.47] Nm) (P = .002).

CONCLUSION

The NAS-ILN showed greater stiffness in compression and 4-point bending, and a greater resistance to failure in compression, torsion, and 4-point bending, than LCP.

CLINICAL IMPACT

Based on these results, NAS-ILNs could be considered as alternative implants for the stabilization of comminuted fractures.

Biomechanical behavior of retrograde intramedullary nails in distal femoral fractures

Fractures of the distal femur affect three different groups of individuals: younger people suffering high-energy trauma, elderly people with fragile bones and people with periprosthetic fractures around previous total knee arthroplasty. Main indications of intramedullary nailing are for supracondylar fractures type A or type C of the AO classification. The main objective of the present work is to analyze, by means of FE simulation, the influence of retrograde nail length, considering different blocking configurations and fracture gaps, on the biomechanical behavior of supracondylar fractures of A type. A three dimensional (3D) finite element model of the femur from 55-year-old male donor was developed, and then a stability analysis was performed for the fixation provided by the retrograde nail at a distal fracture with different fracture gaps: 0.5 mm, 3 mm y 20 mm, respectively. Besides, for each gap, three nail lengths were studied with a general extent (320 mm, 280 mm and 240 mm), considering two transversal screws (M/L) at the distal part and different screw combinations above the fracture. The study was focused on the immediately post-operative stage, without any biological healing process. In view of the obtained results, it has been demonstrated new possibilities of blocking configuration in addition to the usual ones, which allows establishing recommendations for nail design and clinical practice, avoiding excessive stress concentrations both in screws, with the problem of rupture and loss of blocking, and in the contact of nail tip with cortical bone, with the problem of a new stress fracture.

The history of intramedullary nailing

PURPOSE

To summarize the evolution of intramedullary nailing, highlight important milestones, introduce the atmosphere of the era concerning the first uses and development of intramedullary nailing, and present the status of nailing in modern international orthopaedics and traumatology.

METHOD

A thorough literature search was undertaken in PubMed and Google Scholar as well as in physical books in libraries to summarize the literature on the history and evolution of intramedullary nailing.

RESULTS

The first use of an intramedullary device was attested in ancient Egypt; however, the first use of intramedullary nailing was reported in 1524 in Mexico, and the first medical journals reported on intramedullary nailing around the mid-1800s. The evolutions of intramedullary nailing including approach, material, cross-section and shape, and reaming technique occurred in the twentieth century. During the 1960s, intramedullary nailing was abandoned in favour of plate and screws osteosynthesis; however, in the 1970s, 1980s, and 1990s, a surge of novelties including flexible reaming, interlocking, and use of image intensification and titanium nails led to the advent of the second-generation intramedullary nailing. Today, intramedullary nailing has become the standard treatment of long bone fractures with low infection rates, small scars, excellent stabilization of the fractures, and immediate mobilization of the patients.

CONCLUSION

Intramedullary nailing has revolutionized the treatment of long bone fractures. However, with numerous nail designs, a lot of information on their efficacy is lacking. Considerably more work will need to be done to determine the optimal nail specifications.

Biomechanical optimization of the far cortical locking technique for early healing of distal femur fractures

This finite element study optimized far cortical locking (FCL) technology for early callus formation in distal femur fracture fixation with a 9-hole plate using FCL screws proximal to, and standard locking screws distal to, the fracture. Analyses were done for 120 possible FCL screw configurations by varying FCL screw distribution and number. A hip joint force of 700 N (i.e. 100% x body weight) was used, which corresponds to a typical 140 N "toe-touch" foot-to-ground force (i.e. 20% x body weight) suggested to patients immediately after surgery. Increased FCL screw distribution (i.e. shorter plate working length) caused a decrease at the medial side and an increase at the lateral side of the axial interfragmentary motion (AIM), mildly affected shaft and condylar cortex Von Mises max stress (σ_MAX), increased plate σ_MAX, and decreased shaft FCL screw and condylar locking screw σ_MAX. Increased FCL screw number decreased AIM and σ_MAX on the shaft cortex, condylar cortex, plate, and FCL screws, but not condylar screws. The optimal FCL screw configuration had 3 FCL screws in plate holes #1, 5, and 6 (proximal to distal) for optimal AIM of 0.2 - 1 mm and reduce shear fracture motion, thereby encouraging early callus formation.

A biomechanical study on the laminate stacking sequence in composite bone plates for vancouver femur B1 fracture fixation

BACKGROUND AND OBJECTIVES

Composite bone plates are proposed for fracture fixation in periprosthetic femoral fracture. Metallic plates, having high stiffness compared to bone lead to stress shielding, reduce the compression force in the fracture site, affectthe healing process. Reduction of stiffness in the axial direction due to above reason without lowering the stiffness in transverse to avoid much of shear strain and thus avoiding instability at the fracture site leads to selective stress shielding. This can only be achieved through meticulously designed fiber reinforced composite. In the present work varied fiber orientations in the stacked laminates with varied fiber types are employed in a post-operative femur fixation for the in-silico analyses of their effectiveness using finite element analysis.

METHODS

In this study a Total Hip Arthroplasty (THA) model is constructed with composite bone plates. Three-dimensional narrow type metal plate is modeled with 12 holes and length of 194 mm. Three different types of composite bone plates are modeled with 12 holes of different size for the analysis i.e. Type 1 (5.6 mm thickness and 16 mm width), Type 2 (6 mm thickness and 16 mm width) and Type 3(6 mm thickness and 18 mm width). Anatomical 3D FE models of THA with composite bone plates are constructed to find out the interfacial stresses and strains. The finite element software ANSYS is used to perform the analysis.

RESULTS

A three-dimensional FE model of immediately post-operative femur fixation is developed and studied the maximum stress distribution, strain and movement in axial/shear direction in the metal and composite bone plate near to the fracture site. In the present study, the metal and composite plate (carbon/epoxy, glass/epoxy and flax/epoxy) used for most common Vancouver type B1 fracture to observe the biomechanical behavior of different models in IPO condition using FEA.

CONCLUSIONS

Optimizing the fiber orientations of composite bone plates of Total Hip Arthroplasty (THA) model by controlling the biomechanical stresses could be a favorable approach. The finite element analysis approach gives a viable solution to design the composite bone plate and for designing future models that preserves the biomechanical function of THA with composite bone plate.

Improvement in Functional Outcomes After Elective Symptomatic Orthopaedic Implant Removal

INTRODUCTION

The relative indications for removing symptomatic implants after osseous healing are not fully agreed on. The purpose of this study was to (1) determine whether patients showed improvement in functional outcomes after the removal of symptomatic orthopaedic implants, (2) compare the outcomes between upper and lower extremity implant removal, and (3) determine the rate of implant removal complications.

METHODS

A prospective study was conducted between 2013 and 2016. Patients completed a Short Musculoskeletal Function Assessment outcome questionnaire before implant removal and at the 6-month follow-up. Demographic data were stratified and compared between upper and lower extremity groups and between preimplant removal and 6-month postremoval.

RESULTS

Of the 119 patients included in the study, 85 (71.4%) were lower extremity and 34 (28.6%) were upper extremity. Significant improvement after implant removal was seen in the dysfunction index (P ≤ 0.001), bother index (P ≤ 0.001), and daily activities domain (P ≤ 0.001). Depression or anxiety (P = 0.016) were statistically significant predictors for an improved Short Musculoskeletal Function Assessment dysfunction index score at 6 months. The complication rate was 10.1% (n=12) for the cohort.

DISCUSSION

Implant removal in both the upper and lower extremity presented notable improvement in dysfunction. Complications that require surgical intervention are extremely rare.

Multi-Axis Fatigue Experimentation System of Intramedullary Implants for Femur and Tibia

Current designs of leg-lengthening implants have faced serious failures due to inadequacies in the mechanical design. The failure typically is the result of fatigue induced by a combined loading condition with axial and shear components acting in the tubular body of the implant. One of the reasons leading to the failure is improper verification testing for the design of the fatigue limit. The current test standards for pre-clinical design phases of nail implants are relatively straightforward and widely accepted yet cannot produce the three-dimensional stress state representative of the anticipated operation in a patient during the consolidation phase. This work introduces a major improvement toward a method for verifying fatigue life of tubular as well as solid implants under combined torque, axial load, and bending. The report describes a new loading fixture, a calibration method, and compares the qualification results of finite element simulation analyses and experimental measurements during cyclic loading tests. The findings state that the fixture produces controlled multi-axial loadings to study varied osteotomy locations, quasi-static strength and fatigue of intramedullary implants at an intermediate, 2 Hz, cycle rate. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 38:984-995, 2020.

Comparative analysis of the biomechanical behavior of anterograde/retrograde nailing in supracondylar femoral fractures

Supracondylar femoral fractures account for a noticeable percentage of the femoral shaft fractures, affecting two etiological groups: high energy trauma in young men, with good bone quality, and older women with osteoporotic femur. Surgical treatment of those kind of fractures remains controversial, with different surgical options such as plate and sliding barrel locking condylar plate, less invasive stabilization system (LISS) or intramedullary nailing, which has emerged as a new fixation choice in the treatment of that type of fractures. The present work performs a comparative study about the biomechanical behavior of anterograde and retrograde nailing in supracondylar femoral fractures type A, in order to determine the best choice of nailing and locking configuration. A three-dimensional finite element model of the femur was developed, modeling femoral supracondylar fracture and different nailing configurations, both for anterograde and retrograde nails. The study was focused on the immediately post-operative stage, verifying the appropriate stability of the osteosynthesis. The obtained results show a better biomechanical behavior for anterograde nails, providing a better stability from the point of view of global movements, lower stresses in screws, and less stress concentration in cortical bone. So, for the analyzed fractures and osteosyntheses types, anterograde nailing has demonstrated to be a better surgical option, being an excellent indication in supracondylar fractures of femur, with clear benefits compared to retrograde nailing, providing a better stabilization which enables for a more satisfactory fracture healing.

Biomechanical analysis of the stability of anterograde reamed intramedullary nails in femoral spiral fractures

Femoral shaft fractures present high morbidity and important complications and consequences, being spiral fractures the most complicated from a biomechanical point of view, being unstable and without possibility of getting a good contact between nail and femoral endosteum. Femoral diaphyseal fractures are treated, usually, by means of intramedullary nailing. So, it is necessary to know the osteosynthesis stability and which locking screws combination is optimal. This work studies the use of reamed locked intramedullary nails in spiral femoral fractures located along zones 2 and 4 of wiss, depending on the spire length, corresponding to 32-A spiral type in AO/OTA classification, which represent a percentage of 23% within the total of diaphyseal fractures. A three-dimensional finite element model of the femur was developed, modeling a spiral fracture with different spiral lengths and gaps. A femoral nail was used, considering two transversal screws both at the proximal and the distal parts. The study was focused on the immediately post-operative stage, verifying the appropriate stability of the osteosynthesis. Reamed intramedullary blocked nails provide appropriate stability of femoral spiral fractures, considering global mobility of femoral head with respect to femoral condyles, relative displacements between fragments at fracture site, stresses at nail and locking screws, and stresses at cortical bone. The obtained results show that the use of blocked reamed nails in spiral femoral fractures can be considered as an appropriate surgical technique, providing sufficient stability in order to obtain an adequate fracture healing.

A NEWLY DESIGNED ASSEMBLY LOCKING COMPRESSION PLATE TO TREAT COMMINUTED FRACTURES OF THE FEMORAL SHAFT: A BIOMECHANICAL STUDY

The aim of this paper is to compare the biomechanical characteristics of a newly designed assembly locking compression plate (NALCP) and traditional locking compression plate (LCP) for internal fixation of femoral-shaft comminuted fractures. A femoral-shaft wedge fracture model (AO classification 32-C2.1) was created in six pairs of femoral specimens ([Formula: see text]) randomly divided into two equal groups. Biomechanical properties were tested with axial and torsional loading tests. The relative maximum displacement of fracture blocks and strain was recorded. A strain diagram was made; the fatigue test results of NALCP specimens under axial load were recorded. Under axial load, the relative maximum displacement of fracture blocks in the [Formula: see text], [Formula: see text], and [Formula: see text] axes was smaller in NALCP specimens than in LCP specimens ([Formula: see text] and 0.01, respectively). Under torsional load, the relative maximum displacement of fracture blocks in the [Formula: see text] and [Formula: see text] axes in NALCP specimens was less than that in LCP specimens ([Formula: see text]) but no statistically significant difference in the [Formula: see text] axes ([Formula: see text]) was found. In both cases, the main NALCP strain was higher than the LCP strain ([Formula: see text]) but no statistically significant difference in mean strain ([Formula: see text]) was found. Our NALCP provides strong mechanical stability for comminuted femoral fractures and can effectively avoid stress concentration, reduce stress shielding, and facilitate bone healing.

Intramedullary nailing biomechanics: Evolution and challenges

This article aims to review the biomechanical evolution of intramedullary nailing and describe the breakthrough concepts which allowed for nail improvement and its current success. The understanding of this field establishes an adequate background for forthcoming research and allows to infer on the path for future developments on intramedullary nailing. It was not until the 1940s, with the revolutionary Küntscher intramedullary nailing design, that this method was recognized as a widespread medical procedure. Such achievement was established based on the foundations created from intuition-based experiments and the first biomechanical ideologies. The nail evolved from allowing alignment and stability through press-fit fixation with nail-cortical wall friction to the nowadays nail stability achieved through interlocking screws mechanical linkage between nail and bone. Important landmarks during nail evolution comprise the introduction of flexible reaming, the progress from slotted to non-slotted nails design, the introduction of nail ‘dynamization’ and the use of titanium alloys as a new nail material. Current biomechanical improvement efforts aim to enhance the bone–intramedullary nail system stability. We suggested that benefit would be attained from a better understanding of the ideal mechano-biological environment at the fracture site, and future improvements will emerge from combining mechanics and biological tools.

Functional Outcomes of Symptomatic Implant Removal Following Ankle Fracture Open Reduction and Internal Fixation

BACKGROUND

Orthopedic implant removal following open reduction internal fixation of a fracture is a common procedure, especially in the foot and ankle. The purpose of this study was to evaluate functional change after the removal of symptomatic implants following ankle fracture open reduction internal fixation (ORIF) using the Short Musculoskeletal Function Assessment (SMFA) outcome score. We hypothesized that implant removal after ankle fracture would result in improved functional outcomes.

METHODS

Retrospective review of prospectively collected data on patients with a closed ankle fracture between 2013 and 2016 was performed. Inclusion criteria were skeletal maturity, symptomatic ankle implants and completion of the SMFA questionnaire prior to and 6 months after removal. Exclusion criteria were development of a nonunion, prior or current infection, peripheral neuropathy or ongoing litigation surrounding the surgery. The primary outcome was change in SMFA score from baseline to follow-up using Wilcoxon signed-rank test. Additional logistic regression models evaluated the effects of age, sex, body mass index, smoking status, and patient American Society of Anesthesiologists scores.

RESULTS

The study population consisted of 43 patients. There was a statistically significant improvement in function, represented by a decrease in SMFA scores from baseline to the 6-month follow-up period (∆ = -4.1 [95% confidence interval, -7.0, -1.3]; P = .003). Secondary outcome measures of the bother index and daily activities domain also demonstrated significant improvements ( P = .005 and P = .002, respectively). Additional logistical regression models identified no significant effects by assessed covariates for change in SMFA scores.

CONCLUSION

Patients with symptomatic implants following ankle fracture ORIF had a statistically significant improvement in function following implant removal. There appears to be value in removing implants from the ankle in patients who report discomfort during daily activities. Further investigation into the specific indications for implant removal and the impact of injury and fracture pattern on outcomes is warranted.

LEVEL OF EVIDENCE

Level IV, case series.

The influence of nail blocking conditions in cattle femoral fractures

BACKGROUND

To investigate the effect of different fixation strategies of the intramedullary interlocking nail (IIN) on the mechanical behavior of a polymeric implant applied for femoral fracture fixation in calves, and to evaluate the performance of a glass fiber-reinforced polymer applied in a bovine femoral fracture reduction system, five Holstein male animals with a mean weight (±SD) of 62.8 ± 20.4 kg and aged 74 ± 15 were used to generate biomechanical parameters for this study. Twelve models of the fractured bovine femur, simulating a simple oblique fracture, were developed for use during the simulations. The models were divided into three groups, with each group of four models being associated with a different fixation strategy. Models were used to simulate the loading conditions corresponding to a calf in the transition (decubitus position to static position) condition. The maximum stresses found in each set (bone/implant) were compared with the reference stresses of each nail material.

RESULTS

Maximum implant stresses were found in the screws and at the interface between the screw and the nail. The performance of implants was influenced by the material and fixation strategy, which can be confirmed by the stress values found in the set. The analysis indicated that the composite nail is able to withstand the loading demands in all fixation strategies.

CONCLUSIONS

The finite element analysis (FEA) demonstrated that all polymeric materials analyzed provided sufficient resistance to withstand the loading forces imposed to the femur when an adequate blocking strategy was applied.

Analysis of the Impact of Configuration of the Stabilisation System for Femoral Diaphyseal Fractures on the State of Stresses and Displacements

Introduction

The treatment of femoral diaphyseal fractures by intramedullary nailing has become a common procedure in orthopaedic surgery. The purpose of this numerical simulation was to present how the changes in configuration of the stabilisation system can affect the stress and displacement state in the bone tissue and implanted device.

Material and Methods

The numerical comparison of the stabilisation variants for the type 32-A2 femoral diaphyseal fracture (according to the AO classification) performed by using the Charfix2 (ChM®) anatomical nail locked in a number of chosen ways. The displacement and the stress distributions both in the bone and implant were obtained and analysed by computational simulation.

Results

In all models, there was the same characteristic distribution, which shows there were minimal rotational movements of the bone around the anatomical axis. In all cases, stress concentrations were generated in the nail material in the area of the fracture gap.

Conclusions

The obtained results indicate that there is a visible advantage to one-plane distal stabilisation in the reduction of stresses regardless of the type of proximal stabilisation. The results of calculations indicate that the use of proximal stabilisation with a neck screw reduces the possibility of damage to the implant.

A Validated Open-Source Multisolver Fourth-Generation Composite Femur Model

Synthetic biomechanical test specimens are frequently used for preclinical evaluation of implant performance, often in combination with numerical modeling, such as finite-element (FE) analysis. Commercial and freely available FE packages are widely used with three FE packages in particular gaining popularity: abaqus (Dassault Systèmes, Johnston, RI), ansys (ANSYS, Inc., Canonsburg, PA), and febio (University of Utah, Salt Lake City, UT). To the best of our knowledge, no study has yet made a comparison of these three commonly used solvers. Additionally, despite the femur being the most extensively studied bone in the body, no freely available validated model exists. The primary aim of the study was primarily to conduct a comparison of mesh convergence and strain prediction between the three solvers (abaqus, ansys, and febio) and to provide validated open-source models of a fourth-generation composite femur for use with all the three FE packages. Second, we evaluated the geometric variability around the femoral neck region of the composite femurs. Experimental testing was conducted using fourth-generation Sawbones® composite femurs instrumented with strain gauges at four locations. A generic FE model and four specimen-specific FE models were created from CT scans. The study found that the three solvers produced excellent agreement, with strain predictions being within an average of 3.0% for all the solvers (r2 > 0.99) and 1.4% for the two commercial codes. The average of the root mean squared error against the experimental results was 134.5% (r2 = 0.29) for the generic model and 13.8% (r2 = 0.96) for the specimen-specific models. It was found that composite femurs had variations in cortical thickness around the neck of the femur of up to 48.4%. For the first time, an experimentally validated, finite-element model of the femur is presented for use in three solvers. This model is freely available online along with all the supporting validation data.

Influence of gap size, screw configuration, and nail materials in the stability of anterograde reamed intramedullary nail in femoral transverse fractures

Femoral shaft fractures are among the most severe injuries of the skeleton. They are associated with high morbidity and mortality. The most appropriate treatment depending on the type of fracture and location level should be chosen. A finite element model of the femur has been developed, analyzing various types of fractures in the subtrochanteric and diaphyseal supracondylar area, with several gap sizes, being stabilized with a single combination of screws for the intramedullary nail. The mechanical strength of the nail against bending and compression efforts was studied comparing two materials for the nail: stainless steel and titanium alloy. Beside the finite elements (FE) simulations, a clinical follow-up was carried out, considering a sample of 55 patients, 24 males, and 31 females, with mean age of 52.5 years. Localizations of fractures were 22 in the right femur and 33 in the left one, respectively. A good agreement between clinical results and the simulated fractures in terms of gap size was found. Non-comminuted fractures have a mean consolidation time of 4.1 months, which coincides with the appropriate mobility at fracture site obtained in the FE simulations, whereas comminuted fractures have a higher mean consolidation period estimated in 7.1 months, corresponding to the excessive mobility at fracture site obtained by means of FE simulations. The obtained results between both nail materials (stainless steel and titanium alloy) show a higher mobility when using titanium nails, which produce a higher rate of strains at the fracture site, amplitude of micromotions and bigger global movements compared to stainless-steel nails. Steel nails provide stiffer osteosyntheses than the titanium nails. In conclusion, anterograde locked nail is particularly useful in the treatment of a wide range of supracondylar fractures with proximal extension into the femoral diaphysis.

Carbon-Fibre-Reinforced PEEK radiolucent intramedullary nail for humeral shaft fracture fixation: technical features and a pilot clinical study

PURPOSE

This prospective pilot study investigated the safety and efficacy of a novel radiolucent intramedullary nail (IMN) made of Carbon-Fibre-Reinforced Polyaryl-Ether-Ether-Ketone (CFR-PEEK) for humeral shaft fracture fixation.

STUDY DESIGN

A prospective, single-arm, four-centre study.

PATIENTS AND METHODS

A total of 46 patients with 46 humeral fractures classified as 12 A-B were treated with a novel CFR-PEEK IMN and followed for 12 months.

RESULTS

Most of the patients (65%) were female; the mean age was 65 ± 17 years. The average operating time was 66.75 ± 19.84 minutes and X-ray exposure was 104.11 ± 98.01 seconds. All patients postoperatively reported selflimiting shoulder pain and three patients developed iatrogenic transient radial palsy. Two patients required repositioning of the implant. No implant-related complications were observed. Radiological consolidation was achieved in all 43 patients who completed the 12-month follow-up.

CONCLUSIONS

The CFR-PEEK IMN is user-friendly and safe. Its bone-matching elastic modulus seems to contribute to its clinical efficacy. This, together with compatibility with modern imaging techniques, can be considered a further evolution of IMN designed to stabilise humeral shaft fractures.

Influence of screw combination and nail materials in the stability of anterograde reamed intramedullary nail in distal femoral fractures

Intramedullary nailing (IM) is a technique universally accepted to treat femoral diaphyseal fractures. The treatment of fractures located in the distal third remains a controversial issue though. A finite element model of the femur has been developed, analyzing distal fractures with several gap sizes combined with different interlocking combinations of distal screws with one oblique screw proximally to stabilize the intramedullary nail. The mechanical strength of the nail against bending and compression efforts was also studied. Beside the FE simulations, a clinical follow-up of 15 patients, 6 males and 9 females, with mean age of 53.2 years was carried out. Localizations of fractures were 10 in the right femur and 5 in the left femur, respectively. A fairly good correspondence agreement between clinical results and the simulated fractures in terms of gap size was found. Non-comminuted fractures had a mean consolidation time of 20.5 weeks (4.8 months), a tendency corresponding well to the mobility obtained in the FE simulations; Comminuted fractures on the other hand exhibited a higher mean consolidation period of 22.2 weeks (5.2 months) secondary to the excessive mobility at fracture site obtained by means of FE simulations. The best stability at fracture site was found for the system with three distal screws and the system with two distal screws placed medial lateral. The highest leverage of distal screws was obtained maximizing the distance between them and choosing the coronal plane for their orientation. The results obtained with both nail materials (stainless steel and titanium alloy) show a higher mobility when using titanium nails. Steel nails provide stiffer osteosyntheses than the titanium nails. In conclusion, the best screw combination in terms of stability to produce fracture healing and the least difficulties during treatment is the one which had one oblique proximal screw with two distal lateral screw implanted in the coronal plane.

Interlocking intramedullary nail fixation with additional bone grafting from trochanter via a femoral hollow trephine in the treatment of femoral shaft fractures: design and clinical application

PURPOSE

The purpose of this study was to describe and evaluate the clinical application of the technique of interlocking intramedullary (IM) nailing via an entry point at the tip of greater trochanter using a specially designed femoral hollow trephine to stabilize diaphyseal fractures of the femur.

METHODS

From February 2010 to April 2014, 35 consecutive patients with femoral shaft fractures were treated by the therapy of bone grafting from trochanter region with interlocking IM nail. The average age of these 23 male and 12 female patients was 37.5 years (range, 22-67 years). Fractures were classified according to AO classification system (15 type A, 17 type B, 3 type C). Femoral canal reaming and the collection of cancellous bone were simultaneously performed in a single step with the specially designed femoral hollow trephine, followed by regular IM nailing procedure.

RESULTS

Of the 35 cases, the mean volume of spongy bone obtained was 5.63 cm³ (range, 3.0-7.0 cm³). Thirty-five patients with femoral shaft fractures had a mean follow-up period of 16.2 months (range, 12-22 months). All patients achieved bony union, at a mean of 5.4 months (range, 4-6 months). No patient developed a delayed union or a nonunion. There were no complications such as infections, injury of vascular and nerve, or heterotopic ossification in hip.

CONCLUSIONS

These results indicate that the technique of use of IM nailing with the femoral hollow trephine significantly decreases the occurrence of nonunion in femoral shaft fractures.

An Effective Approach for Optimization of a Composite Intramedullary Nail for Treating Femoral Shaft Fractures

The high stiffness of conventional intramedullary (IM) nails may result in stress shielding and subsequent bone loss following healing in long bone fractures. It can also delay union by reducing compressive loads at the fracture site, thereby inhibiting secondary bone healing. This paper introduces a new approach for the optimization of a fiber-reinforced composite nail made of carbon fiber (CF)/epoxy based on a combination of the classical laminate theory, beam theory, finite-element (FE) method, and bone remodeling model using irreversible thermodynamics. The optimization began by altering the composite stacking sequence and thickness to minimize axial stiffness, while maximizing torsional stiffness for a given range of bending stiffnesses. The selected candidates for the seven intervals of bending stiffness were then examined in an experimentally validated FE model to evaluate their mechanical performance in transverse and oblique femoral shaft fractures. It was found that the composite nail having an axial stiffness of 3.70 MN and bending and torsional stiffnesses of 70.3 and 70.9 N⋅m², respectively, showed an overall superiority compared to the other configurations. It increased compression at the fracture site by 344.9 N (31%) on average, while maintaining fracture stability through an average increase of only 0.6 mm (49%) in fracture shear movement in transverse and oblique fractures when compared to a conventional titanium-alloy nail. The long-term results obtained from the bone remodeling model suggest that the proposed composite IM nail reduces bone loss in the femoral shaft from 7.9% to 3.5% when compared to a conventional titanium-alloy nail. This study proposes a number of practical guidelines for the design of composite IM nails.