Comparison of 4 Methods for Dynamization of Locking Plates: Differences in the Amount and Type of Fracture Motion

Does helical plating for proximal humeral shaft fractures benefit bone healing? - an in silico analysis in fracture healing

OBJECTIVES

Helical plating is an established alternative to straight plating for humeral shaft fractures in order to prevent iatrogenic radial nerve damage. However, a previous biomechanical investigation indicated differences in fracture healing for helical plating due to a potential shift of interfragmentary movements compared to straight plating. Therefore, fracture healing simulations were performed to assess any differences in bone healing of helical vs. straight plating.

METHODS

A systematic workflow for fracture healing analytics was created, covering essential steps of bone modelling, implant modelling, finite element modelling, fracture healing simulation and result analysis. Computational humerus models with an AO12C2 fracture and straight and helical osteosynthesis were created. An established fracture healing model was used to simulate callus formation over 112 days under physiological loading. The predicted tissue differentiation and interfragmentary movement (IFM) was tracked over the entire simulated healing course.

RESULTS

Helical plating resulted in larger interfragmentary movements for compression and shear components, and in a greater proportion of near and far cortical movement. Vascularization and tissue formation were deferred, but cortical bridging was achieved.

CONCLUSIONS

Helical plating resulted in slightly deferred bone healing due to larger interfragmentary shear movements. Considering the advantage of helical plating in clinical context, a slightly deferred bone healing is justifiable.

Far cortical locking versus standard locking screw fixation in simulated femoral fractures: A biomechanical meta-analysis

Introduction

Far cortical locking (FCL) is a concept of locking plate fixation with reduced stiffness and symmetric micromotion to improve callus formation. The goal of our study was to review biomechanical data evaluating FCL plate and screw fixation versus standard locking (SL) plate and screw fixation by analyzing studies of cadaveric and synthetic bone models to draw biomechanical conclusions.

Methods

Biomechanical studies that compared FCL and SL plate fixation for simulated femoral fractures were reviewed for construct stiffness, load to failure, axial motion at the near and far cortices, and the difference between near and far cortical axial motion to demonstrate motion symmetry.

Results

FCL decreased stiffness by 1.069 kN/mm compared to SL (95 % CI 0.405 to 1.732, p = 0.002). FCL demonstrated greater axial motion than SL in the near cortex by 0.425 mm (95 % CI 0.359 to 0.491, p < 0.001) and in the far cortex by 0.456 mm (95 % CI 0.378 to 0.534, p < 0.001). FCL resulted in symmetric motion with no significant difference between far and near cortices with the far cortex displacing 0.347 mm more than near (95 % CI -0.038 to 0.731, p = 0.78). SL resulted in asymmetric motion favoring the far cortex by 0.270 mm (0.096-0.443, p = 0.002). Construct strength was not significantly different with FCL load to failure 0.367 kN greater than SL (95 % CI -0.762 to 1.496, p = 0.524).

Conclusion

FCL screw fixation in femoral fractures achieves the goals of reducing construct stiffness and promoting more symmetric axial motion while maintaining construct strength. These results support the overall biomechanical goals of far cortical locking and should encourage investigation into its effects on clinical and radiographic outcomes.

Implant Design and Its Applications in the Fixation of Osteoporotic Bones: Newer Technologies in Nails, Plates and External Fixators

Background

Osteoporosis, characterised by decreased bone mass and degradation of bone tissue, poses a major global health concern, particularly for the ageing population. The traditional fixation techniques often fail in osteoporotic bones due to their diminished density and strength. Technological advancements in orthopaedic implants, specifically nails, plates, and external fixators, have emerged to address these challenges.

Materials and Methods

Improvements in implant design focus on material properties, surface modifications, and geometric advancements. Titanium and its alloys are favoured for their biomechanical properties such as lower elastic modulus and high strength-to-weight ratio. The biodegradable materials like polylactic acid and magnesium alloys offer the advantage of gradual resorption as bone heals. Surface modifications, such as coatings with bioactive materials and drug-eluting surfaces, promote osseointegration and enhance fixation strength.

Results and Discussion

Intramedullary (IM) nails have evolved to enhance stability and minimise complications associated with osteoporotic fractures. Third and fourth-generation nails incorporate surface treatments for better integration and healing. The advances in screw design, locking mechanisms, and flexible axial stimulation have improved fixation and allowed micromotion, which promotes fracture healing. The use of external fixators, particularly for complex fractures in osteoporotic bones, offers less invasive treatment options with adaptable stiffness for improved healing.

Conclusion

Technological innovations in implant materials, design, and surgical techniques have significantly improved the management of osteoporotic fractures. Newer technologies, including 3D printing, virtual and augmented reality, and artificial intelligence, show promise in enhancing implant customization, surgical planning, and postoperative outcomes. However, further clinical validation and research are needed to expand their clinical applications.

Don't mind the gap: reframing the Perren strain rule for fracture healing using insights from virtual mechanical testing

Aims

The "2 to 10% strain rule" for fracture healing has been widely interpreted to mean that interfragmentary strain greater than 10% predisposes a fracture to nonunion. This interpretation focuses on the gap-closing strain (axial micromotion divided by gap size), ignoring the region around the gap where osteogenesis typically initiates. The aim of this study was to measure gap-closing and 3D interfragmentary strains in plated ovine osteotomies and associate local strain conditions with callus mineralization.

Methods

MicroCT scans of eight female sheep with plated mid-shaft tibial osteotomies were used to create image-based finite element models. Virtual mechanical testing was used to compute postoperative gap-closing and 3D continuum strains representing compression (volumetric strain) and shear deformation (distortional strain). Callus mineralization was measured in zones in and around the osteotomy gap.

Results

Gap-closing strains averaged 51% (mean) at the far cortex. Peak compressive volumetric strain averaged 32% and only a small tissue volume (average 0.3 cm3) within the gap experienced compressive strains > 10%. Distortional strains were much higher and more widespread, peaking at a mean of 115%, with a mean of 3.3 cm3 of tissue in and around the osteotomy experiencing distortional strains > 10%. Callus mineralization initiated outside the high-strain gap and was significantly lower within the fracture gap compared to around it at nine weeks.

Conclusion

Ovine osteotomies can heal with high gap strains (> 10%) dominated by shear conditions. High gap strain appears to be a transient local limiter of osteogenesis, not a global inhibitor of secondary fracture repair.

Clinical and Radiographic Results of a Retrograde Nail-Washer Combination Versus Lateral Locked Plating for Distal Femur Fractures

OBJECTIVES

The objective of this study was to report outcomes of the Retrograde Femoral Nail-Advanced with Lateral Attachment Washer (RFNA-LAW) (Synthes, Paoli, PA) compared with laterally locked plates (LLP) when treating AO/OTA type 33 distal femoral fractures.

METHODS

DESIGN

Retrospective chart review.

SETTING

Single, academic, Level-1 Trauma Center.

PATIENT SELECTION CRITERIA

All adult patients who had fixation of an AO/OTA type 33 distal femoral fracture with the RFNA-LAW combination or LLP from 2018 to 2023 with follow-up to union or a minimum of 1 year.

OUTCOME MEASURES AND COMPARISONS

The main outcome measure was union. Secondary outcomes included implant failure, infection, and alignment immediately postoperatively and at final follow-up. Primary and secondary outcome measures were compared between the RFNA-LAW and LLP groups.

RESULTS

Forty-eight patients (19 female) with a mean age of 56 years (range 19-94 years) were in the RFNA-LAW group. Fifty-three patients (29 female) with a mean age of 66 years (24-91 years) were in the LLP group. There were no significant differences when comparing body mass index, diabetes, smoking status, mechanism of injury, or fracture classification between groups ( P > 0.05). There was no difference in immediate, postoperative alignment ( P = 0.49). When comparing anatomic lateral distal femoral angle measurements at final follow-up, there was significantly more malalignment in the LLP group ( P = 0.005). There were 8 implant failures (15%) in the LLP group compared with 1 in the RFNA-LAW group (2%) ( P = 0.02). There were 14 reoperations (26%) in the LLP group compared with 4 (8%) in the RFNA-LAW group ( P = 0.02).

CONCLUSIONS

The Retrograde Nail Advanced-Lateral Attachment Washer combination demonstrated a high union rate when treating complex fractures of the distal femur. When compared with lateral locked plating, this implant combination demonstrated significantly lower rates of nonunion and reoperation.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Biomechanical design of a new proximal humerus fracture plate using alternative materials

Comminuted proximal humerus fractures are often repaired by metal plates, but potentially still experience bone refracture, bone "stress shielding," screw perforation, delayed healing, and so forth. This "proof of principle" investigation is the initial step towards the design of a new plate using alternative materials to address some of these problems. Finite element modeling was used to create design graphs for bone stress, plate stress, screw stress, and interfragmentary motion via three different fixations (no, 1, or 2 "kickstand" [KS] screws across the fracture) using a wide range of plate elastic moduli (EP = 5-200 GPa). Well-known design optimization criteria were used that could minimize bone, plate, and screw failure (i.e., peak stress < ultimate tensile strength), reduce bone "stress shielding" (i.e., bone stress under the new plate ≥ bone stress for an intact humerus, titanium plate, and/or steel plate "control"), and encourage callus growth leading to early healing (i.e., 0.2 mm ≤ axial interfragmentary motion ≤ 1 mm; shear/axial interfragmentary motion ratio <1.6). The findings suggest that a potentially optimal configuration involves the new plate being manufactured from a material with an EP of 5-41.5 GPa with 1 KS screw; but, using no KS screws would cause immediate bone fracture and 2 KS screws would almost certainly lead to delayed healing. A prototype plate might be fabricated using alternative materials suggested for orthopedics and other industries, like fiber-metal laminates, fiber-reinforced polymers, metal foams, pure polymers, shape memory alloys, or 3D-printed porous metals.

Material Properties and Engineering Performance of Bone Fracture Plates Made from Plant Fiber Reinforced Composites: A Review

Bone fracture plates are usually made from titanium alloy or stainless steel, which are much stiffer than bone. However, overly stiff plates can restrict axial interfragmentary motion at the fracture leading to delayed callus formation and healing, as well as causing bone "stress shielding" under the plate leading to bone atrophy, bone resorption, and plate loosening. Consequently, there have been many prior efforts to develop nonmetallic bone fracture plates with customized material properties using synthetic fibers (e.g., aramid, carbon, glass) in polymer resin. Even so, plant fibers (e.g., flax, roselle, sisal) offer additional advantages over synthetic fibers, such as availability, biodegradability, less toxicity during processing, lower financial cost, and recyclability. As such, there is an emerging interest in using plant fibers alone, or combined with synthetic fibers, to reinforce polymers for various applications. Thus, this is the first review article on the material properties and engineering performance of innovative bone fracture plates made from composite materials reinforced by plant fibers alone or supplemented using synthetic fibers. This article presents material-level fiber properties (e.g., elastic modulus, ultimate strength), material-level plate properties (e.g., fatigue strength, impact toughness), and bone-plate engineering performance (e.g., overall stiffness, plate stress), as well as discussing general findings, study quality, and future work. This article may help engineers and surgeons to design, fabricate, analyze, and utilize novel bone fracture plates.

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.

Delayed Union and Nonunion: Current Concepts, Prevention, and Correction: A Review

Surgical management of fractures has advanced with the incorporation of advanced technology, surgical techniques, and regenerative therapies, but delayed bone healing remains a clinical challenge and the prevalence of long bone nonunion ranges from 10 to 15% of surgically managed fractures. Delayed bone healing arises from a combination of mechanical, biological, and systemic factors acting on the site of tissue remodeling, and careful consideration of each case's injury-related, patient-dependent, surgical, and mechanical risk factors is key to successful bone union. In this review, we describe the biology and biomechanics of delayed bone healing, outline the known risk factors for nonunion development, and introduce modern preventative and corrective therapies targeting fracture nonunion.

Advances in Dynamization of Plate Fixation to Promote Natural Bone Healing

The controlled dynamization of fractures can promote natural fracture healing by callus formation, while overly rigid fixation can suppress healing. The advent of locked plating technology enabled new strategies for the controlled dynamization of fractures, such as far cortical locking (FCL) screws or active plates with elastically suspended screw holes. However, these strategies did not allow for the use of non-locking screws, which are typically used to reduce bone fragments to the plate. This study documents the first in vivo study on the healing of ovine tibia osteotomies stabilized with an advanced active plate (AAP). This AAP allowed plate application using any combination of locking and non-locking screws to support a wide range of plate application techniques. At week 9 post-surgery, tibiae were harvested and tested in torsion to failure to assess the healing strength. The five tibiae stabilized with an AAP regained 54% of their native strength and failed by spiral fracture through a screw hole, which did not involve the healed osteotomy. In comparison, tibiae stabilized with a standard locking plate recovered 17% of their strength and sustained failure through the osteotomy. These results further support the stimulatory effect of controlled motion on fracture healing. As such, the controlled dynamization of locked plating constructs may hold the potential to reduce healing complications and may shorten the time to return to function. Integrating controlled dynamization into fracture plates that support a standard fixation technique may facilitate the clinical adoption of dynamic plating.

Distal femur fractures: basic science and international perspectives

Distal femur fractures are challenging injuries to manage, and complication rates remain high. This article summarizes the international and basic science perspectives regarding distal femoral fractures that were presented at the 2022 Orthopaedic Trauma Association Annual Meeting. We review a number of critical concepts that can be considered to optimize the treatment of these difficult fractures. These include biomechanical considerations for distal femur fixation constructs, emerging treatments to prevent post-traumatic arthritis, both systemic and local biologic treatments to optimize nonunion management, the relative advantages and disadvantages of plate versus nail versus dual-implant constructs, and finally important factors which determine outcomes. A robust understanding of these principles can significantly improve success rates and minimize complications in the treatment of these challenging injuries.

Low Young's Modulus TiNbSn Alloy Locking Plates Accelerate Osteosynthesis in Rabbit Tibiae

A new beta TiNbSn alloy with a low Young's modulus of approximately 40 GPa has been developed to resolve the stress shielding by Young's modulus divergence. In this study, the efficacy of TiNbSn alloy locking plates on bone repair is compared to that of commercially pure titanium (CP-Ti). The TiNbSn alloy and CP-Ti, which have Young's moduli of 49.1 GPa and 107 GPa, respectively, were compared. Male Japanese white rabbits were anesthetized, and osteotomy and osteosynthesis with locking plates were performed on the right tibia. The bone repair was assessed using micro-computed tomography (CT), histomorphometry, immunohistochemistry, and mechanical testing. Micro-CT, histomorphometry, immunohistochemistry, and mechanical testing were performed four weeks after osteotomy. Six weeks after surgery, micro-CT and mechanical testing were performed. Micro-CT analysis at four weeks after surgery showed that the intramedullary fracture callus in the TiNbSn alloy group had more bone volume and numerous bridging structures compared to the CP-Ti group (CP-Ti vs. TiNbSn alloy, 34.3 ± 13.1 mm3 vs. 61.3 ± 19.6 mm3, p = 0.02; mean ± standard deviation). At four weeks post-osteotomy, the healed tibia showed significantly higher strength in the TiNbSn alloy group compared with CP-Ti (CP-Ti vs. TiNbSn alloy, 81.3 ± 31.2 N vs. 133.7 ± 46.6 N, p = 0.04). TiNbSn alloy locking plates had a more positive impact on bone formation and bone strength restoration than the CP-Ti locking plates during the early phase of bone healing.

Influence of knee flexion on early femoral fracture healing: A combined analysis of musculoskeletal dynamics and finite elements

BACKGROUND AND OBJECTIVES

Knee flexion causes a certain amount of misalignment and relative movement of the fractured ends of the femur fracture, and if the flexion angle is too large it will affect the stability of the fracture and the healing process, making it challenging to design a safe range of flexion. However, due to a lack of basic understanding of the effect of knee flexion on the mechanical environment at the fracture site, clinicians are often unable to provide an objective and safe range of motion in flexion based on subjective experience. The aim of this study was to evaluate the effect of knee flexion on plate and fracture healing using finite element analysis (FEA).

METHODS

A human musculoskeletal model was constructed based on CT scan data, and the mechanical properties of the fracture site were changed by adjusting the knee flexion angle. The joint forces, muscle forces and moments acting on the femur were obtained by inverse dynamics analysis, and the biomechanical properties of the fracture-plate system were analyzed using finite elements. A finite element model of the fracture-plate system without muscle loading was also constructed. The effect of knee flexion on the safety of plate fixation and fracture healing was evaluated in terms of the biomechanical properties of the plate and the interfragmentary motion of the fracture.

RESULTS

As the knee flexion angle increases, the von Mises stress of the locked compression plate (LCP) first increases, then decreases, then increases again. The deformation from compression bending to tension twisting occurs simultaneously. At 30° of flexion, shear interfragmentary motion (SIM) was dominant and inhibited fracture healing; at more than 45° of flexion, the plate was twisted and deformed to the lateral side of the body, and the fracture site underwent greater misalignment and relative motion, with destructive effects on bone scabs and healing tissues. If muscle loading is not taken into account, the plate will undergo predominantly bending deformation and will overestimate the interfragmentary strain in the far and near cortex.

CONCLUSIONS

Knee flexion causes the plate to deform from compression bending to extension and torsion, which has an important impact on the safety and healing process of the fracture, and this study provides a biomechanical basis to guide the clinician in the post-operative rehabilitation of femoral fractures in the clinical setting.

Stability Analysis of Plate-Screw Fixation for Femoral Midshaft Fractures

An understanding of the biomechanical characteristics and configuration of flexible and locked plating in order to provide balance stability and flexibility of implant fixation will help to construct and promote fast bone healing. The relationship between applied loading and implantation configuration for best bone healing is still under debate. This study aims to investigate the relationship between implant strength, working length, and interfragmentary strain (εIFM) on implant stability for femoral midshaft transverse fractures. The transverse fracture was fixed with a fragment locking compression plate (LCP) system. Finite element analysis was performed and subsequently characterised based on compression loading (600 N up to 900 N) and screw designs (conventional and locking) with different penetration depths (unicortical and bicortical). Strain theory was used to evaluate the stability of the model. The correlation of screw configuration with screw type shows a unicortical depth for both types (p < 0.01) for 700 N and 800 N loads and (p < 0.05) for configurations 134 and 124. Interfragmentary strain affected only the 600 N load (p < 0.01) for the bicortical conventional type (group BC), and the screw configurations that were influenced were 1234 and 123 (p < 0.05). The low steepness of the slope indicates the least εIFM for the corresponding biomechanical characteristic in good-quality stability. A strain value of ≤2% promotes callus formation and is classified as absolute stability, which is the minimum required value for the induction of callus and the maximum value that allows bony bridging. The outcomes have provided the correlation of screw configuration in femoral midshaft transverse fracture implantation which is important to promote essential primary stability.

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.

Outcomes of the First Generation Locking Plate and Minimally Invasive Techniques Used for Fractures About the Knee

Background

Locking plate technology was developed approximately 25-years-ago and has been successfully used since. Newer designs and material properties have been used to modify the original design, but these changes have yet to be correlated to improved patient outcomes. The purpose of this study was to evaluate the outcomes of first-generation locking plate (FGLP) and screw systems at our institution over an 18 year period.

Methods

Between 2001 to 2018, 76 patients with 82 proximal tibia and distal femur fractures (both acute fracture and nonunions) who were treated with a first-generation titanium, uniaxial locking plate with unicortical screws (FGLP), also known as a LISS plate (Synthes Paoli Pa), were identified and compared to 198 patients with 203 similar fracture patterns treated with 2nd and 3rd generation locking plates, or Later Generation Locking Plates (LGLP). Inclusion criteria was a minimum of 1-year follow-up. At latest follow-up, outcomes were assessed using radiographic analysis, Short Musculoskeletal Functional Assessment (SMFA), VAS pain scores, and knee ROM. All descriptive statistics were calculated using IBM SPSS (Armonk, NY).

Results

A total of 76 patients with 82 fractures had a mean 4-year follow-up available for analysis. There were 76 patients with 82 fractures fixed with a First-generation locking plate. The mean age at time of injury for all patients was 59.2 and 61.0% were female. Mean time to union for fractures about the knee fixed with FGLP was by 5.3 months for acute fractures and 6.1 months for nonunions. At final follow-up, the mean standardized SMFA for all patients was 19.9, mean knee range of motion was 1.6°-111.9°, and mean VAS pain score was 2.7. When compared to a group of similar patients with similar fractures and nonunions treated with LGLPs there were no differences in outcomes assessed.

Conclusion

Longer-term outcomes of first-generation locking plates (FGLP) demonstrate that this construct provides for a high rate of union and low incidence of complications, as well as good clinical and functional results. Level of Evidence: III.

Efficacy of Far Cortical Locking Screws in Treating Distal Tibia Fractures in Comparison With That of Standard Locking Screws

There are no clinical studies about treatment of distal tibia fractures using far cortical locking (FCL) screws, even though it has been shown to be superior to standard locking screws in biomechanical studies. We compared the efficacy of FCL screws to that of traditional locking screws. Twenty-five distal tibia fractures were treated with minimally invasive plate osteosynthesis using traditional locking screws, whereas 20 were treated using FCL screws. We retrospectively compared time taken for callus formation and radiographic bone union between 2 groups. The effect of age, sex, diabetes, and smoking history on bone healing was analyzed. Complications were also noted. As a result, there was no significant difference in age (p = .292), sex (p = 1.0), diabetes (p = 1.0), or smoking history (p = .704) between 2 groups. Time to callus formation was 77.5 days in the FCL group, and 96 days in the traditional group (p = .023). Average time to bone union was 134.8 days, and 163.1 days in the FCL group and the traditional group, respectively (p = .017). There was one case of screw loosening in the FCL group, and one case of screw breakage in the traditional group. This study suggests that FCL screws promote quicker healing of distal tibia fractures than traditional locking screws.

Early peri-implant fractures after distal femur fracture locked plating?

PURPOSE

To report the peri-implant fracture rates after locked plating of distal femur fractures and examine risk factors.

METHODS

Over a 7 year period, 89 AO/OTA 33A/C distal femur fractures were identified and reviewed. After excluding treatment with intramedullary nails, age under 50, those with the proximal femur protected, or those without 6 months of follow-up, 42 distal femur fractures in 41 patients, mean age 72.3 were studied. All were treated with lateral locked plating of distal femur fractures. The details of the constructs were recorded. Mean follow-up was 562 days (18.7 months).

RESULTS

3/42 were open injuries, 9/42 were type C, 16/42 were type A, and 17 were periprosthetic above a knee arthroplasty. Two patients were treated with a dynamic plating construct using all far-cortical locking (FCL) screws in the diaphysis. 40 patients were treated with a variety of non-dynamic diaphyseal constructs including locking, non-locking, and four with 1-2 FCL screws distally. There was one asymptomatic nonunion. 2/2 patients in the dynamically plated group experienced a peri-implant fracture versus 1/40 in the non-dynamically plated group (p = 0.001). 3/9 with an all-locked construct versus 0/25 patients with a most proximal non-locking screw experienced a fracture.

CONCLUSIONS

The overall peri-implant fracture risk was 7.1% (3/42), 3/17 patients with a locking screw most proximal experienced a peri-implant fracture, 3/9 with an all-locking construct, and 2/2 patients with a dynamic construct experienced a fracture. These findings merit additional clinical and biomechanical study.

A 20-Year Review of Biomechanical Experimental Studies on Spine Implants Used for Percutaneous Surgical Repair of Vertebral Compression Fractures

A vertebral compression fracture (VCF) is an injury to a vertebra of the spine affecting the cortical walls and/or middle cancellous section. The most common risk factor for a VCF is osteoporosis, thus predisposing the elderly and postmenopausal women to this injury. Clinical consequences include loss of vertebral height, kyphotic deformity, altered stance, back pain, reduced mobility, reduced abdominal space, and reduced thoracic space, as well as early mortality. To restore vertebral mechanical stability, overall spine function, and patient quality of life, the original percutaneous surgical intervention has been vertebroplasty, whereby bone cement is injected into the affected vertebra. Because vertebroplasty cannot fully restore vertebral height, newer surgical techniques have been developed, such as kyphoplasty, stents, jacks, coils, and cubes. But, relatively few studies have experimentally assessed the biomechanical performance of these newer procedures. This article reviews over 20 years of scientific literature that has experimentally evaluated the biomechanics of percutaneous VCF repair methods. Specifically, this article describes the basic operating principles of the repair methods, the study protocols used to experimentally assess their biomechanical performance, and the actual biomechanical data measured, as well as giving a number of recommendations for future research directions.

Rethinking the 10% strain rule in fracture healing: A distal femur fracture case series

Since the 1970s, the 2%-10% rule has been used to describe the range of interfragmentary gap closure strains that are conducive for secondary bone healing. Interpreting the available evidence for the association between strain and bone healing remains challenging because interfragmentary strain is impossible to directly measure in vivo. The question of how much strain occurs within and around the fracture gap is also difficult to resolve using bench tests with osteotomy models because these do not reflect the complexity of injury patterns seen in the clinic. To account for these challenges, we used finite element modeling to assess the three-dimensional interfragmentary strain in a case series of naturally occurring distal femur fractures treated with lateral plating under load conditions representative of the early postoperative period. Preoperative computed tomography scans were used to construct patient-specific finite element models and plate fixation constructs to match the operative management of each patient. The simulations showed that gap strains were within 2%-10% only for the lowest load application level, 20% static body weight (BW). Moderate loading of 60% static BW and above caused gap strains that far exceeded 10%, but in all cases, strains in the periosteal region external to the fracture line remained low. Comparing these findings with postoperative radiographs suggests that in vivo secondary healing of distal femur fractures may be robust to early gap strains much greater than 10% because formation of new bone is initiated outside the gap where strains are lower, followed by later consolidation within the gap.

Scattering and clustering the proximal screw construct in unilateral locking plate osteosynthesis of distal femoral fractures

INTRODUCTION

The importance of fixation construct in locking compression plate (LCP) is not well enlightened until recently. The aim of this study was to investigate radiological and clinical outcomes of scattering and clustering of the proximal screw fixation construct in unilateral LCP treatment of the distal femoral fractures.

MATERIALS AND METHODS

Patients who were treated for distal femoral fractures using unilateral LCP between January 2014 and December 2019 in our institute were included in this retrospective study. They were divided into groups 1 (35 cases, scattered proximal screw fixation) and 2 (35 cases, clustered proximal screw fixation). Mean follow-up period was 23.6 months for group 1 and 21.3 months for group 2. Medical history, patient demographics, injury characteristics, and surgical characteristics were reviewed and analyzed. Radiological findings including time to callus formation, bridging callus formation, union, and symmetry of the union were assessed and compared between the groups. Clinical outcomes included total blood loss during the operation, postoperative range of motion, and number of revision surgery.

RESULTS

The time for callus formation (5.8 weeks in group 1 vs. 4.1 weeks in group 2, p = 0.009) and bridging callus formation (12.5 weeks in group 1 vs. 10.7 weeks in group 2, p = 0.009) was significantly earlier in group 2. Despite similar union rates between groups, the mean time for radiological union was longer in group 2 (10.7 vs 7.4 months, p = 0.001). Though statistically insignificant, more asymmetric union was observed in group 2 (17 vs 11 cases).

CONCLUSIONS

Despite a delay in initial callus and bridging callus formation, scattering the proximal screws was better in achieving earlier and more balanced radiographic union than the clustered fixation. We recommend to avoid bridging more than five holes in the whole plate fixation construct to lessen the asymmetric callus formation and to prevent eventual plate breakage.

Spatial Bridge Locking Fixator versus Traditional Locking Plates in Treating AO/OTA 32-A3.2 Fracture: Finite Element Analysis and Biomechanical Evaluation

Objective

To compare the biomechanical behaviors of the spatial bridge locking fixator (SBLF), single locking plate (SP), and double locking plate (DP) for AO/OTA 32‐A3.2 fractures using finite element analysis and biomechanical tests.

Methods

Axial loading of 700 N was conducted on the AO/OTA 32‐A3.2 model via finite element analysis. The von Mises stress and the interfragmentary movement (IFM) were comparatively analyzed in the three configurations above. On the mechanical tester, axial and torsional loading of 30 synthetic femurs (five specimens of each configuration for each test at random) was performed, and the interfragmentary movement, torsion angle, stiffness, and ultimate load were recorded and analyzed.

Results

The finite element analysis (FEA) results showed that the von Mises stress of the spatial bridge locking fixator (SBLF) was lower than that of the single locking plate (SP) and higher than that of the double locking plate (DP). At 700 N, the axial IFMs were 0.15–0.38 mm (SBLF), 0.03–0.84 mm (SP), and 0.02–0.07 mm (DP). The biomechanical experiment indicated that the axial interfragmentary movements (IFMs) were 0.44 ± 0.23 mm (SBLF), 1.02 ± 0.40 mm (SP), and 0.07 ± 0.07 mm (DP) (p < 0.001). The axial IFM of the SBLF group had the highest probability (79.26%) of falling within the ideal range (0.2–0.8 mm), and the SP and DP groups had probabilities of 27.10% and 3.14%, respectively. The axial stiffness in the SBLF group (1586 ± 130 N/mm) was significantly lower than that in the DP group (10,264 ± 2671 N/mm) (p < 0.001) but greater than that in the SP group (725 ± 178 N/mm) (p = 0.396). The range of axial loads to ultimate failure was 3385–4527 N (SBLF), 3377–4664 N (SP), and 3780–4804 N (DP). The shear motion of the fracture end was 0.35 ± 0.14 mm (SBLF), 0.16 ± 0.10 mm (SP), and 0.08 ± 0.04 mm (DP) (p < 0.001). The torsional stiffness was 1.68 ± 0.14 Nm/degree (SBLF), 2.32 ± 0.29 Nm/degree (SP) (SBLF&SP, p < 0.001), and 3.53 ± 0.73 Nm/degree (DP) (SBLF&DP, p < 0.001).

Conclusions

The SBLF structure may exhibit a better biomechanical performance compared with the SP and DP in providing the best quantity and more symmetrical interfragmentary movement for AO/OTA 32‐A3.2 fractures.

Mechanical Fatigue Performance of Patient-Specific Polymer Plates in Oncologic Mandible Reconstruction

Mandible defects are conventionally reconstructed using titanium plates. However, titanium causes metallic artifacts which impair radiological imaging. This study aims at evaluating mechanical fatigue of radiolucent fiber-reinforced polyetheretherketone (f-PEEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polyphenylsulfone (PPSU) polymer plates for mandible reconstruction. A total of 30 plates (titanium [n = 6], f-PEEK [n = 6], PEEK [n = 6], PEKK [n = 6], PPSU [n = 6]) were implanted in synthetic mandibulectomized polyurethane mandibles. Servo-pneumatic mechanical testing with cyclic application of 30−300 N at 3 Hz was conducted. Bite forces were 70% on the unresected and 30% on the resected side. Total number of cycles was set to 250,000. Testing was aborted in case of plate or screw failure. Axial load to failure was tested with a speed of 1 mm/s. Kruskal−Wallis and Dunn’s post hoc tests were used. Titanium, f-PEEK, and PEEK showed no failure in fatigue testing and PPSU (p < 0.001) failed against titanium, f-PEEK, PEEK, and PEKK. Titanium allowed the highest load to failure compared to f-PEEK (p = 0.049), PEEK (p = 0.008), PEKK (p < 0.001), and PPSU (p = 0.007). f-PEEK, PEEK, and PEKK withstood expected physiological bite force. Although titanium plates provided the highest fatigue strength, f-PEEK and PEEK plates showed no failure over 250,000 chewing cycles indicating sufficient mechanical strength for mandible reconstruction.

Boundary Conditions Matter - Impact of Test Setup On Inferred Construct Mechanics in Plated Distal Femur Osteotomies

The mechanics of distal femur fracture fixation has been widely studied in bench tests that employ a variety of approaches for holding and constraining femurs to apply loads. No standard test methods have been adopted for these tests and the impact of test setup on inferred construct mechanics has not been reported. Accordingly, the purpose of this study was to use finite element models to compare the mechanical performance of a supracondylar osteotomy with lateral plating under conditions that replicate several common bench test methods. A literature review was used to define a parameterized virtual model of a plated distal femur osteotomy in axial compression loading with four boundary condition sets ranging from minimally to highly constrained. Axial stiffness, longitudinal motion, and shear motion at the fracture line were recorded for a range of applied loads and bridge spans. The results showed that construct mechanical performance was highly sensitive to boundary conditions imposed by the mechanical test fixtures. Increasing the degrees of constraint, for example by potting and rigidly clamping one or more ends of the specimen, caused up to a 25x increase in axial stiffness of the construct. Shear motion and longitudinal motion at the fracture line, which is an important driver of interfragmentary strain, was also largely influenced by the constraint test setup. These results suggest that caution should be used when comparing reported results between bench tests that use different fixtures and that standardization of testing methods is needed in this field.

Is retrograde nailing superior to lateral locked plating for complete articular distal femur fractures?

INTRODUCTION

Nonunion rates for distal femur fractures treated with lateral locked plating (LLP) remains as high as 18-22% despite significant advances with implant design and construct modulation. However, whether treatment of distal femur fractures with rIMN has improved outcomes compared to LLP has not been well characterized. The purpose of this study was to compare outcomes of complete articular distal femur fractures (AO/OTA 33-C) treated with either LLP or rIMN.

METHODS

106 distal femur fractures in 106 patients between January 2014 and January 2018 were identified. Medical records were reviewed to collect patient age, gender, body mass index, sagittal and coronal plane alignment on immediate postoperative radiographs, time to union, incidence of nonunion, and incidence of secondary operative procedures for repair of a nonunion.

RESULTS

Of 106 patients, 50 underwent rIMN and 56 underwent LLP. The mean age at the time of injury was 51 years (21 to 86 years) and there were 55 males. Average coronal alignment of 83.7° of anatomic lateral distal femoral angle (aLDFA) and sagittal alignment of <1° of apex anterior angulation in the rIMN group. In the LLP group there was an average of 87.9° of aLDFA and 1.9° of apex anterior angulation (p = .005 and p = .36). Average time to union in the rIMN group was 6 months and 6.6 months in the LLP group (p = .52). Incidence of nonunion in the rIMN group was 11.8% and 27.5% in the LLP group (p = .008). There were 8 secondary procedures for nonunion in the rIMN group and 18 in the LLP group (p = .43).

CONCLUSIONS

Our results demonstrated a higher nonunion rate and coronal plane malalignment with LLP compared to rIMN. While prospective data is required, rIMN does appear to be an appropriate treatment for complete articular distal femur fractures with a potentially decreased rate of nonunion .

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.

Axial Micromotion Locking Plate Construct Can Promote Faster and Stronger Bone Healing in an Ovine Osteotomy Model

Fixing bone fractures with controlled axial interfragmentary micromotion improves bone healing; however, the optimal type of implant construct for this purpose is still lacking. The present study describes a novel axial micromotion locking plate (AMLP) construct that allows axial interfragmentary micromotion of 0.3 or 0.6 mm. We investigated whether the AMLP constructs enhance bone healing compared to an ordinary locking plate (LP) using an ovine osteotomy model. The stiffness of the constructs was tested under axial loading. We created a 3-mm osteotomy in the left hind leg tibia of sheep that was then stabilized with a 0.3- or 0.6-mm AMLP or LP construct (n = 6/group). Bone healing was monitored weekly by X-ray radiography starting from week 3 after surgery. At week 9, the specimens were collected and evaluated by computed tomography and torsional testing. We found that the AMLPs had a lower stiffness than the LP; in particular, the stiffness of the 0.6-mm AMLP construct was 86 and 41% lower than that of the LP construct for axial loads <200 and >200 N, respectively. In the in vivo experiments, tibial osteotomies treated with the 0.6-mm AMLP construct showed the earliest maximum callus formation (week 5) and the highest volume of bone callus (9.395 ± 1.561 cm³ at week 9). Specimens from this group also withstood a 27% greater torque until failure than those from the LP group (P = 0.0386), with 53% more energy required to induce failure (P = 0.0474). These results demonstrate that AMLP constructs promote faster and stronger bone healing than an overly rigid LP construct. Moreover, better bone healing was achieved with an axial micromotion of 0.6 mm as compared to 0.3 mm.

Assessment of the efficacy of the far cortical locking technique in proximal humeral fractures: a comparison with the conventional bi-cortical locking technique

Background

Locking plate fixation is one of the treatment strategies for the management of proximal humeral fractures. However, stiffness after locking plate fixation is a clinical concern. The mechanical stiffness of the standard locking plate system may suppress the interfragmentary motion necessary to promote secondary bone healing by callus formation. The far cortical locking (FCL) technique was developed to address this limitation in 2005. FCL increases construct flexibility and promotes callus formation. Our study aimed to evaluate the clinical and radiological outcomes of the FCL technique when implemented in proximal humeral fracture management. Furthermore, we compared the surgical outcomes of FCL with those of the conventional bicortical locking (BCL) screw fixation technique.

Methods

Forty-five consecutive patients who had undergone locking fixation for proximal humeral fractures were included in this study. A proximal humeral locking plate (PHILOS) system with BCL screw fixation was used in the first 27 cases, and the periarticular proximal humeral locking plate with FCL screw fixation was used in the final 18 consecutive cases. Functional capacity was assessed using the constant score, American Shoulder and Elbow Surgeons (ASES) score, and range of motion. Radiographic outcomes were evaluated using the Paavolainen method of measuring the neck-shaft angle (NSA).

Results

No significant differences in clinical outcomes (ASES score, constant score, and range of motion) were found between the two groups. The union rate at 12 weeks was significantly higher in the FCL group (94.4%) than in the BCL group (66.7%, p = 0.006). No significant differences in NSA were found between the two treatment strategies. The complication rate was not significantly different between the two groups.

Conclusions

When implemented in proximal humeral fractures, the FCL technique showed satisfactory clinical and radiological outcomes as compared with the conventional BCL technique. The bone union rate at 12 weeks after surgery was significantly higher in the FCL group than in the BCL group. However, no significant difference in the final bone union rate was found between the two groups.

Biomechanical design using in-vitro finite element modeling of distal femur fracture plates made from semi-rigid materials versus traditional metals for post-operative toe-touch weight-bearing

This proof-of-concept study designs distal femur fracture plates from semi-rigid materials vs. traditional metals for toe-touch weight-bearing recommended to patients immediately after surgery. The two-fold goal was to (a) reduce stress shielding (SS) by increasing cortical bone stress thereby reducing the risk of bone absorption and plate loosening, and (b) reduce delayed healing (DH) via early callus formation by optimizing axial interfragmentary motion (AIM). Finite element analysis was used to design semi-rigid plates whose elastic moduli E ensured plates permitted AIM of 0.2 - 1 mm for early callus formation. A low hip joint force of 700 N (i.e. 100% x body weight) was applied, which corresponds to a typical 140 N toe-touch foot-to-ground force (i.e. 20% x body weight) recommended to patients after surgery. Analysis was done using 2 screw materials (steel or titanium) and types (locked or non-locked). Steel and titanium plates were also analyzed. Semi-rigid plates (vs. metal plates) had lower overall femur/plate construct stiffnesses of 508 - 1482 N/mm, higher cortical bone stresses under the plate by 2.02x - 3.27x thereby reducing SS, and lower E values of 414 - 2302 MPa to permit AIM of 0.2 - 1 mm thereby reducing DH.

Biomechanical comparison of distal femoral fracture fixation: Analysis of non-locked, locked, and far-cortical locked constructs

To assess whether far-cortical locking (FCL) screws alter the fracture site strain environment and allow shorter bridge plate constructs for supracondylar femoral fractures, we tested the fracture site displacement under force of synthetic left femora with a 5-cm metaphyseal fracture gap, modeling comminution. Five models of nine constructs were tested (three types of diaphyseal screws [nonlocking, locking, and FCL] and two plate lengths [13 holes and 5 holes]). Long plate models using three or four diaphyseal screws (working length 13.5 or 7.5 cm, respectively) were compared with short plates with three diaphyseal screws (working length 7.5 cm). Models were loaded axially and torsionally; 100 cycles in random order. Primary outcome measures were axial and torsional fracture site stiffness. FCL screws decreased rotational stiffness 19% (P < .01) compared with baseline nonlocking screws in the same plate and working length construct, mirroring the effect (20% decrease in stiffness, P < .01) of nearly doubling the nonlocking construct working length (7.5-13.5 cm). Similarly, FCL screws decreased axial stiffness 23% (P < .01) in the same baseline comparison. Fracture site displacement under loading comparable to a long working length nonlocked plate construct was achieved using a shorter FCL plate construct. By closely replicating the biomechanical properties of a long plate construct, a fracture site strain environment considered favorable in promoting fracture healing might still be achievable using a shorter plate length. Clinical Significance: It might be possible to optimize fracture site strain environment and displacement under loading using shorter FCL plate constructs. Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 00:00-00, 2020.

Biomechanical assessment of screw safety between far cortical locking and locked plating constructs

With the emerging concerns for more flexible and less stiff bridge constructs in the interest of stimulating bone healing, the technique of far cortical locking has been designed to reduce the stiffness of locked plating (LP) constructs while retaining construct strength. This study utilized simulation with diaphyseal bridge plating biomechanical models to investigate whether far cortical locking causes larger screw fracture risk than LP during rehabilitation. The fracture risk of the screws in the far cortical locking constructs increases in the non-osteoporotic and osteoporotic diaphysis compared with the screws in the LP constructs.

Biomechanical Stability of Volar Plate Only Versus Addition of Dorsal Ulnar Pin Plate: A Dorsal Ulnar Fragment, C-3-Type, Distal Radius, Cadaver Fracture Model

OBJECTIVE

To determine if the addition of a dorsal ulnar pin plate provides improved stability characteristics in the management of intra-articular distal radius fractures with an associated dorsal ulnar fragment.

METHODS

OTA/AO type C3 fractures, with a dorsal ulnar fragment of one-third or one-half the width of the distal radius, were simulated in 9 matched pairs of fresh-frozen cadaveric arms randomized between fixed-angle volar plate only versus volar plate with addition of a dorsal ulnar pin plate. Prepared specimens were mounted in a custom load frame and loaded in extension with stepwise cyclic load increase. Dorsal plane interfragmentary displacements were compared between the 2 fixation constructs at 50-N and 100-N cyclic load.

RESULTS

The addition of the dorsal ulnar pin plate significantly reduced interfragmentary displacements for the dorsal ulnar fragment at the 50 N load application, resulting in mean interfragmentary displacements of -0.1 ± 0.2 mm in comparison to -0.3 ± 0.2 mm with the volar plate-only construct. No other interfragmentary displacement comparisons were significant. No differences were found comparing the one-third and one-half size fragments.

CONCLUSIONS

The addition of a dorsal ulnar pin plate improved stability characteristics with respect to the dorsal ulnar fragment.

CLINICAL RELEVANCE

The addition of the dorsal ulnar pin plate, although statistically significant, improved displacement by less than 0.3 mm on average and thus may not prove to be important in clinical scenarios.

Biomechanical Response under Stress-Controlled Tension-Tension Fatigue of a Novel Carbon Fiber/Epoxy Intramedullary Nail for Femur Fractures

Metallic intramedullary nails are the "gold standard" implant for repairing femur shaft fractures. However, their rigidity may eliminate axial micromotion at the fracture (causing delayed healing) and they may carry too much load relative to the femur (causing "stress shielding"). Consequently, some researchers have proposed fiber-reinforced composite nails, but only one evaluated cyclic fatigue performance. Therefore, this study assessed the cyclic fatigue response of a carbon fiber/epoxy nail with a novel ply stacking sequence of [0₂/-45/45₂/-45/0/-45/45₂/-45₂/45₂/-45/90₂] previously developed by the present authors. Nails were cyclically loaded in tension-tension at 5 Hz with a stress ratio of R=0.1 from 30% - 85% of the material's ultimate tensile strength (UTS). Thermographic stress analysis, rather than conventional fatigue testing, was used to obtain high cycle fatigue strength (HCFS), below which the nail can be cyclically loaded indefinitely without damage. Also, the mechanical test machine's built-in load cell and an extensometer were used to create stress-strain curves, from which the change in static E^O and dynamic E* moduli were obtained. Results showed that HCFS was 70.3% of UTS (or about 283 MPa), while E^O and E* remained at 42 GPa without any dRegradation during testing. The current nail shows potential for clinical use.

Mechanical Effects of Bone Substitute and Far-Cortical Locking Techniques in 2-Part Proximal Humerus Fracture Reconstruction: A Cadaveric Study

OBJECTIVES

To make direct comparisons of the biomechanical properties of a control (CTL) group and implants that were augmented with far cortical locking (FCL), bone substitute material (BSM), and a combination of both (ALL) to determine which fixation is most effective in reducing implant failure.

METHODS

The constructs were tested with osteopenic cadaveric specimens in a two-part fracture model. Specimens were subjected to a battery of nondestructive torsion and axial compression tests, followed by a cyclic test. Construct stiffness and cycles to failure were documented, pre- and post-test fluoroscopy was performed, and implant and bone kinematics were quantified.

RESULTS

During nondestructive testing, the BSM group exhibited significantly increased torsional and axial stiffness compared with the FCL (P = 0.006, P < 0.001) group and ALL group (P < 0.001, P = 0.006). There were no significant differences in resistance to cyclic loading between groups. Fluoroscopic analysis indicated significant differences in the motions of nonlocked cannulated screws (used in BSM and ALL) versus locked screws (used in CTL and FCL).

CONCLUSIONS

Patients with poor bone quality and proximal humerus fracture may necessitate added compliance or rigidity to achieve fixation. Both have exhibited favorable biomechanical characteristics in this cadaveric 2-part proximal humerus fracture model.

Clinical outcomes in periarticular knee fractures with flexible fixation using far cortical locking screws in locking plate: a prospective study

PURPOSE

Periarticular fractures around the knee joint are treated traditionally by locking plates which provide excellent stability but suppress callus formation. Far cortical locking (FCL) screws allow axial motion and enhance uniform callus formation. Our study aims to evaluate the outcomes of FCL screws in traditional locking plate in periarticular fractures of the knee.

METHODS

Thirty patients with periarticular fractures of the knee joint were operated with locking plate using FCL screws. All patients were evaluated clinically and radiographically using X-rays at 6, 12, 24 weeks, 1 year and with CT scan at 12-weeks follow-up.

RESULTS

The average time for complete union was 20 weeks in tibial fractures and 24 weeks in femur fractures. Average time to full weight bearing ambulation was 4.8 ± 0.93 weeks. One patient had delayed union in which union was complete after 9 months.

CONCLUSION

This study shows that FCL screws in locking plates allow uniform callus formation and fracture union with minimal complication rates.

Clinical effects and risk factors of far cortical locking system in the treatment of lower limb fractures

INTRODUCTION

This study aims to analyze clinical effects between far cortical locking (FCL) system and standard plating techniques in the treatment of lower limb fractures and identify potential preoperative risk factors for complications in patients treated with FCL system.

METHOD

We retrospectively analyzed 76 patients treated with FCL system (the study group) and 68 patients treated with standard plating techniques (the control group) between January 2014 and January 2017. Patients were followed up for a minimum of one year. Surgery-related complications, fixation features, fracture healing rates, the radiographic union scores, and knee functions (Kolment scores) were analyzed between the two groups in the study. Besides, we analyzed eight preoperative characteristics for surgery-related complications, including age, gender, presence of risk factors affecting bone healing, cause of injury, AO/OTA fracture classifications, facture sites, presence of open fractures, and presence of bone losses.

RESULTS

The distributions of baseline date were similar between the two groups (P＞0.05). The average number of FCL screws was 4.5 (range: 3-9) in the study group. The average time to union was 2.8 ± 0.9 months in the study group and 3.6 ± 1.0 months in the control group (P＜0.001), and average time to whole weight bearing was 2.3 ± 0.8 months and 2.8 ± 1.2 months, respectively (P = 0.004). Regarding radiographic union score, the study group scores were significantly higher than the control group scores at 1 and 3 months after surgery (P＜0.001), while it becomes insignificant between the two groups at 6 and 12 months after surgery (P = 0.19 and P = 0.15).The working lengths, fracture healing rates, complication rates, and Kolment scores were similar between the two groups (P＞0.05). In the multivariate analysis, fracture sites (OR = 5.34; 95% CI, 1.11-25.75; P = 0.03) and presence of open fractures (OR = 6.19; 95% CI, 1.05-36.38; P = 0.04) were significant associated with complications, whereas other variables were not included.

DISCUSSION

FCL system can truly accelerating bone healing and allow earlier whole weight bearing. Fracture healing rates and complication rates were similar between patients treated with FCL implants or conventional plating techniques. Patients with shaft fractures and open fractures trended to have higher complication rates.

CONCLUSIONS

FCL system is superior to standard plating technique in terms of early callus formation, but standard plating technique is not inferior to FCL system in terms of final fracture healing, surgery-related complication, and function outcome. Fracture site and presence of open fracture are the independent factors for complications in patients treated with FCL system.

Far Cortical Locking Fixation of Distal Femur Fractures is Dominated by Shear at Clinically Relevant Bridge Spans

OBJECTIVES

Far cortical locking (FCL) constructs have been shown to increase axial interfragmentary displacement while limiting shear and have been specifically recommended in the treatment of distal femur fractures. However, there is no available data regarding their mechanical behavior within the range of bridge spans typically used for comminuted distal femur fractures. This biomechanical study of distal femur locked plate fixation assessed 4 methods of diaphyseal fixation for associated axial and shear displacement at bridge spans typically used in clinical practice.

METHODS

Distal femur locking plates were used to bridge simulated fractures in femur surrogates with 4 different methods of diaphyseal fixation (bicortical locking, bicortical nonlocking, near cortical locking, and FCL). Axial and shear displacement were assessed at 5 different bridge spans for each fixation method.

RESULTS

Diaphyseal fixation type was associated with the amount of shear (P = 0.04), but not the amount of axial displacement (P = 0.39). Specifically, FCL constructs demonstrated greater shear than bicortical locking (median 4.57 vs. 2.94 mm, P = 0.02) and bicortical nonlocking (median 4.57 vs. 3.41 mm, P = 0.02) constructs.

CONCLUSIONS

Unexpectedly, FCL constructs demonstrated greater shear than bicortical locking and nonlocking constructs and similar axial displacement for all fixation methods. Bridge span had a dominant effect on displacement that interacted negatively with more flexible FCL diaphyseal fixation. Potentially interactive construct features are best studied in concert. Given the complexity of these relationships, computational modeling will likely play an integral role in future mechanotransduction research.

Pitfalls and limits of locking plates

The use of locking plates relies on novel mechanical and biological concepts: the bone healing is endochondral because of the elasticity of the constructs. Preoperative planning is required to determine the fracture reduction strategy and select the implants. The type of plate and the type of screws and their position determine the mechanical properties of the construct. Failure of locking plate fixation is a new phenomenon that differs from conventional plate fixation. These are brought on by inadequate planning, which is made worse when minimally invasive surgery is performed. Often, the fracture is not reduced correctly (leading to malunion), the implant length is incorrect, or the screw type, number, location and implantation sequence are inappropriate. Together these can result in an overly rigid construct with poor healing and implant failure or the opposite, an overly flexible construct that can compromise healing. The return to weight bearing after fracture fixation must be adapted to the type of fracture and construct. While locking plates provide better bone purchase, especially in osteoporotic bone, "en bloc" pulling out of the implant is possible. Delayed fractures at the end of the plates are also possible but can be avoided by making the correct biomechanical choices during fixation. For epiphyseal fractures, there are risks of cut-out and impaction of locking screws in cancellous bone related to the fracture pathology. In the long-term, locking plates can be difficult to remove; however, specialized instrumentation can make this easier.

Evolution of fracture treatment with bone plates

Internal fixation of bone fractures by plate osteosynthesis has continuously evolved for more than 100 years. The aim of internal fracture fixation has always been to restore the functional capacity of the broken bone. The principal requirements of operative fracture management, those being anatomical fracture reduction, durable fixation, preservation of biology, promotion of fracture healing and early patient mobilization, have always been crucial but were accomplished to different extents depending on the focus of the specific fracture fixation principle employed. The first successful approach for internal fracture fixation was anatomic open reduction and interfragmentary compression. This secured the fracture fragments, maintained alignment and enabled direct healing of the fracture fragments. However, the highly invasive approach inflicted an immense amount of biologic stress to the area surrounding the fracture site. Modern preferably anatomically pre-contoured locking plates with relative stability of the bone-implant construct enable durable fixation while allowing a less invasive approach that preserves the biology at the fracture site. In contrast to conventional plating, locked plating provides a certain amount of flexibility, which is required to induce the formation of periosteal callus through interfragmentary motion. Most recently the concept of dynamic plating was introduced, which aims to induce more controlled interfragmentary motion and active stimulation of periosteal callus formation. This review article describes the historic development of plating from conventional plating to locked and dynamic plating.