Application of Far Cortical Locking Technology in Periprosthetic Femoral Fracture Fixation: A Biomechanical Study

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.

Optimal design and biomechanical analysis of sandwich composite metal locking screws for far cortical locking constructs

In the interests of more flexible and less stiff bridge constructs to stimulate bone healing, the technique of far cortical locking has been designed to improve locked plating constructs in terms of stress concentration, stress shielding, and inhibition of issues around fracture healing. However, far cortical locking screws currently lack objective designs and anti-fatigue designs. This study investigates an optimization algorithm to form a special locking screw composed of various metals, which can theoretically achieve the maintenance of the excellent mechanical properties of far cortical locking constructs in terms of fracture internal fixation, while maintaining the biomechanical safety and fatigue resistance of the structure. The numerical results of our study indicate that the maximum von Mises stress of the optimized construct is less than the allowable stress of the material under each working condition while still achieving sufficient parallel interfragmentary motion. Numerical analysis of high cycle fatigue indicates that the optimized construct increases the safety factor to five. A high cycle fatigue test and defect analysis indicates that the sandwich locking constructs have better fatigue resistance. We conclude that the sandwich locking construct theoretically maintains its biomechanical safety and fatigue resistance while also maintaining excellent mechanical properties for fracture internal fixation.

The race for the classification of proximal periprosthetic femoral fractures : Vancouver vs Unified Classification System (UCS) - a systematic review

Background

Periprosthetic femoral fractures (PFFs) represent a major cause for surgical revision after hip arthroplasty with detrimental consequences for patients. The Vancouver classification has been traditionally used since its introduction in 1995. The Unified Classification System (UCS) was described in 2014, to widen the spectrum by aiming for a more comprehensive approach. The UCS also aimed to replace the Vancouver classification by expanding the idea of the Vancouver classification to the whole musculoskeletal apparatus. After introduction of the UCS, the question was raised, whether the UCS found its place in the field of analysing PFFs. Therefore, this systematic review was performed to investigate, the use of the UCS compared to the established Vancouver classification.

Methods

Medline was searched for reports published between 1 January 2016 and 31 November 2020, without language restriction. Included were original articles, irrespective of the level of evidence and case reports reporting on a PFF and using either the Vancouver or the UCS to classify the fractures. Excluded were reviews and systematic reviews.

Results

One hundred forty-six studies were included in the analysis. UCS has not been used in a single registry study, giving a pooled cohort size of 3299 patients, compared to 59,178 patients in studies using the Vancouver classification. Since 2016, one study using UCS was published in a top journal, compared to 37 studies using the Vancouver classification (p=0.29). During the study period, the number of yearly publications remained stagnant (p=0.899).

Conclusions

Despite valuable improvement and expansion of the latter UCS, to date, the Vancouver system clearly leads the field of classifying PFFs in the sense of the common use.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05240-w.

Simplified Mechanical Tests Can Simulate Physiological Mechanics of a Fixation Construct for Periprosthetic Femoral Fractures

Plate fractures after fixation of a Vancouver Type B1 periprosthetic femoral fracture (PFF) are difficult to treat and could lead to severe disability. However, due to the lack of direct measurement of in vivo performance of the PFF fixation construct, it is unknown whether current standard mechanical tests or previous experimental and computational studies have appropriately reproduced the in vivo mechanics of the plate. To provide a basis for the evaluation and development of appropriate mechanical tests for assessment of plate fracture risk, this study applied loads of common activities of daily living (ADLs) to implanted femur finite element (FE) models with PFF fixation constructs with an existing or a healed PFF. Based on FE simulated plate mechanics, the standard four-point-bend test adequately matched the stress state and the resultant bending moment in the plate as compared with femur models with an existing PFF. In addition, the newly developed constrained three-point-bend tests were able to reproduce plate stresses in models with a healed PFF. Furthermore, a combined bending and compression cadaveric test was appropriate for risk assessment including both plate fracture and screw loosening after the complete healing of PFF. The result of this study provides the means for combined experimental and computational preclinical evaluation of PFF fixation constructs.

A New System for Periprosthetic Fracture Stabilization-A Biomechanical Comparison

In recent years, an increase in periprosthetic femur fractures has become apparent due to the increased number of hip replacements. In the case of Vancouver type B1 fractures, locking plate systems offer safe procedures. This study compared the distal lateral femur plate (LOQTEQ^®, aap Implantate AG) with a standard L.I.S.S. LCP^® (DePuy Synthes) regarding their biomechanical properties in fixation of periprosthetic femur fractures after hip arthroplasty. We hypothesized that the new LOQTEQ system has superior stability and durability in comparison. Eighteen artificial left femurs were randomized in two groups (Group A: LOQTEQ^®; Group B: L.I.S.S. LCP^®) and tested until failure. Failure was defined as 10° varus deformity and catastrophic implant failure (loosening, breakage, progressive bending). Axial stiffness, loads of failure, cycles of failure, modes of failure were recorded. The axial stiffness in Group A with 73.4 N/mm (SD +/− 3.0) was significantly higher (p = 0.001) than in Group B (40.7 N/mm (SD +/− 2.8)). Group A resists more cycles than Group B until 10° varus deformity. Catastrophic failure mode was plate breakage in Group A and bending in Group B. In conclusion, LOQTEQ^® provides higher primary stability and tends to have higher durability.

The impact of stem fixation method on Vancouver Type B1 periprosthetic femoral fracture management

INTRODUCTION

Our understanding of the impact of the stem fixation method in total hip arthroplasty (THA) on the subsequent management of periprosthetic femoral fractures (PFF) is still limited. This study aimed to investigate and quantify the effect of the stem fixation method, i.e., cemented vs. uncemented THA, on the management of Vancouver Type B1 periprosthetic femoral fractures with the same plate.

METHODS

Eight laboratory models of synthetic femora were divided into two groups and implanted with either a cemented or uncemented hip prosthesis. The overall stiffness and strain distribution were measured under an anatomical one-legged stance. All eight specimens underwent an osteotomy to simulate Vancouver type B1 PFF's. Fractures were then fixed using the same extramedullary plate and screws. The same measurements and fracture movement were taken under the same loading conditions.

RESULTS

Highlighted that the uncemented THA and PFF fixation constructs had a lower overall stiffness. Subsequently, the mechanical strain on the fracture plate for the uncemented construct was higher compared to the cemented constructs.

CONCLUSION

PFF fixation of a Vancouver type B1 fracture using a plate may have a higher risk of failure in uncemented THAs.

Differences between two sequential uncemented stem sizes in total hip arthroplasty: A comparative biomechanical study and potential clinical implications

Background: Early failure of uncemented femoral stems associated with incorrect sizing is a known postoperative complication. Surgeons are often faced with the question of whether an uncemented stem of adequate stability or a larger-sized stem should be implanted, especially when the proximal femoral cancellous bone is adequate. The biomechanical effect of sub-optimal stem sizing in the femur remains unclear. This study investigated the mechanical behaviour of two sequential sized uncemented stems of the same type. Methods: Six laboratory models of synthetic non-osteoporotic femora were randomly divided into two groups and implanted with either a nominal or oversized uncemented hydroxyapatite-coated nonporous titanium collarless stem. Stiffness, uniaxial strain, and pattern of strain distribution were measured under an anatomical one-legged stance. Results: Oversized stems demonstrated a higher overall stiffness compared to nominal; however, this was not statistically significant. The nominal stem showed a higher strain in the neck and the proximal medial diaphyseal region. The oversized stem showed higher strains in the distal region around the implant tip. Conclusion: Opting to use a larger stem may potentially increase primary stability, thus allowing safer early mobility. However, higher stiffness may lead to stress shielding, bone loss, and thigh pain in the long term. In addition, strains in the diaphysis and the tip of the stem may predispose to periprosthetic fractures, especially in osteoporotic bones, making this a relatable aspect for users and biomechanical loading. Given the wide range of complex factors that need to be considered when choosing stem size in uncemented THA surgery, this study’s results should be interpreted cautiously.

Impact of periprosthetic femoral fracture fixation plating constructs on local stiffness, load transfer, and bone strains

Secondary femoral fractures after the successful plate-screw fixation of a primary Vancouver type B1 periprosthetic femoral fracture (PFF) have been associated with the altered state of stress/strain in the femur as the result of plating. The laterally implanted condyle-spanning plate-screw constructs have shown promises clinically in avoiding secondary bone and implant failures as compared with shorter diaphyseal plates. Though the condyle-spanning plating has been hypothesized to avoid stress concentration in the femoral diaphysis through increasing the working length of the plate, biomechanical evidence is lacking on how plate length may impact the stress/strain state of the implanted femur. Through developing and experimentally validating finite element (FE) models of 3 cadaveric femurs, this study investigated the impact of plating on bone strains, load transfer and local stiffness, which were compared between FE models of 2 different plating systems that each had a diaphyseal configuration and a condyle-spanning configuration. Under simulated gait-loading, the condyle-spanning constructs of both plating systems were shown to lower the bone strains around the distal fixation screws (up to 24.8% reduction in maximum principal strain and 26.6% reduction in minimum principal strain) and in the distal metaphyseal shaft of the femur (up to 15.9% and 25.7% reductions in maximum and minimum principal strains, respectively), where secondary bone fractures have been typically reported. In the distal diaphyseal and metaphyseal shaft of femur, FE models of the condyle-spanning constructs were shown to increase the local compressive stiffness (up to 152.9% increases under simulated gait-loading) and decrease the transfer of compressive load (37.1% decreases under simulated gait-loading), which may be indicative of the lowered risks of bone damage.

Morphological Measurement of the Femoral Anterior Bow in Chinese Population Based on Three-Dimensional Computed Tomography

Purpose

The femoral anterior bow is an important factor in matching a femoral implant to a femur. However, its morphology in the Chinese population has rarely been reported. In this study, a three-dimensional measurement approach was adopted to provide accurate data. The aim was to supply a reference for designing a long-stemmed femoral prosthesis that is more suitable for Chinese people.

Methods

Computed tomography data were collected from both lower limbs of 96 normal volunteers and reconstructed into a three-dimensional model using Mimics software. The parameters of the femoral anterior bow were measured using medical image analysis software. Statistical analysis was conducted using independent-samples and paired-samples t-tests with SPSS software.

Results

All the indexes showed significant sexual difference (P < 0.05). The minimum cross-sectional area of the femoral medullary cavity was larger in men (10.77 ± 1.53 mm) than in women (9.79 ± 1.27 mm). The distance from the position of the maximum curvature to the lower edge of the lesser trochanter was also larger in men (60.93 ± 5.81 mm) than in women (56.31 ± 2.80 mm). However, the curvature of the femoral medullary cavity centerline was larger in women (883.57 ± 249.74 mm) than in men (958.79 ± 266.61 mm). The femoral anterior bow morphological indexes of Chinese subjects were different from the published data for other populations. There were no significant differences between left and right femoral anterior bows in either sex (P > 0.05).

Conclusion

The three-dimensional measurement approach adopted in this study is more convenient and accurate than previous conventional methods, with high repeatability. The morphological indexes of the femoral anterior bow in this research suggest that population characteristics should be taken into account. This study will provide references for the design of long-stemmed femoral prostheses in the Chinese population.

A comparative study of 3D printing and heat-compressing methods for manufacturing the thermoplastic composite bone fixation plate: Design, characterization, and in vitro biomechanical experimentation

Metallic bone fixations, due to their high rigidity, can cause long-term complications. To alleviate metallic biomaterials' drawbacks, in this research new Glass Fiber/Polypropylene (GF/PP) composite internal fixations were developed, and an investigation of their mechanical behavior was performed through in vitro biomechanical experiments. Short randomly oriented, long unidirectional prepreg, and long unidirectional fiber yarn were considered as reinforcements, and the effects on their mechanical properties of different manufacturing processes, that is, 3D printing and heat-compressing, were investigated. The constructed fixation plates were tested in the transversely fractured diaphysis of bovine tibia under axial compression loading. The overall stiffness and the Von Mises strain field of the fixation plates were obtained within stable and unstable fracture conditions. The samples were loaded until failure to determine their failure loads, strains, and mechanisms. Based on the results, the GF/PP composite fixation plates can provide adequate interfragmentary movement to amplify bone ossification, so they can provide proper support for bone healing. Moreover, their potential for stress shielding reduction and their load-bearing capacity suggest their merits in replacing traditional metallic plates.

The effect of surgeon-controlled variables on construct stiffness in lateral locked plating of distal femoral fractures

Background

Nonunion following treatment of supracondylar femur fractures with lateral locked plates (LLP) has been reported to be as high as 21 %. Implant related and surgeon-controlled variables have been postulated to contribute to nonunion by modulating fracture-fixation construct stiffness. The purpose of this study is to evaluate the effect of surgeon-controlled factors on stiffness when treating supracondylar femur fractures with LLPs:

Does plate length affect construct stiffness given the same plate material, fracture working length and type of screws?

Does screw type (bicortical locking versus bicortical nonlocking or unicortical locking) and number of screws affect construct stiffness given the same material, fracture working length, and plate length?

Does fracture working length affect construct stiffness given the same plate material, length and type of screws?

Does plate material (titanium versus stainless steel) affect construct stiffness given the same fracture working length, plate length, type and number of screws?

Methods

Mechanical study of simulated supracondylar femur fractures treated with LLPs of varying lengths, screw types, fractureworking lenghts, and plate/screw material. Overall construct stiffness was evaluated using an Instron hydraulic testing apparatus.

Results

Stiffness was 15 % higher comparing 13-hole to the 5-hole plates (995 N/mm849N vs. /mm, p = 0.003). The use of bicortical nonlocking screws decreased overall construct stiffness by 18 % compared to bicortical locking screws (808 N/mm vs. 995 N/mm, p = 0.0001). The type of screw (unicortical locking vs. bicortical locking) and the number of screws in the diaphysis (3 vs. 10) did not appear to significantly influence construct stiffness (p = 0.76, p = 0.24). Similarly, fracture working length (5.4 cm vs. 9.4 cm, p = 0.24), and implant type (titanium vs. stainless steel, p = 0.12) did also not appear to effect stiffness.

Discussion

Using shorter plates and using bicortical nonlocking screws (vs. bicortical locking screws) reduced overall construct stiffness. Using more screws, using unicortical locking screws, increasing fracture working length and varying plate material (titanium vs. stainless steel) does not appear to significantly alter construct stiffness. Surgeons can adjust plate length and screw types to affect overall fracture-fixation construct stiffness; however, the optimal stiffness to promote healing remains unknown.

Biomechanical evaluation of glass fiber/polypropylene composite bone fracture fixation plates: Experimental and numerical analysis

Little is known about the impact behavior of composite fixation plate used in the fracture healing of long bones diaphysis. Hence, this study examined polypropylene composite fixation plates using different glass fibers and measured their biomechanical responses under axial impact loading experimentally and numerically. Short randomly oriented, long unidirectional prepregs and fiber yarn of glass were considered as reinforcements, and fixation plates were fabricated through two different heat-compressing and 3D printing processes. Furthermore, assessing the fixation plate structures impact behavior was carried out using in vitro impact test and finite element analysis (FEA). Impact damping behavior, damage mechanisms, and stress and strain pattern of the composite fixation plate structures were obtained under various bone fractures and impact energies. The impact load-time responses and the failure mechanisms demonstrated that fixation plate structures with more plastic behavior and lower stiffness could act as an initial shock absorber and dampen the transmission of axial impact load by distributing the impact energy over time. Therefore, considering the ability of stress shielding and adequate interfragmentary movement which amplifies bone ossification, the proposed Glass Fiber/PP (GF/PP) composite fixation plates could serve as a proper alternative in orthopedics.

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.

Biomechanics of Osteoporotic Fracture Fixation

PURPOSE OF REVIEW

Fractures of osteoporotic bone in elderly individuals need special attention. This manuscript reviews the current strategies to provide sufficient fracture fixation stability with a particular focus on fractures that frequently occur in elderly individuals with osteoporosis and require full load-bearing capacity, i.e., pelvis, hip, ankle, and peri-implant fractures.

RECENT FINDINGS

Elderly individuals benefit immensely from immediate mobilization after fracture and thus require stable fracture fixation that allows immediate post-operative weight-bearing. However, osteoporotic bone has decreased holding capacity for metallic implants and is thus associated with a considerable fracture fixation failure rate both short term and long term. Modern implant technologies with dedicated modifications provide sufficient mechanical stability to allow immediate weight-bearing for elderly individuals. Depending on fracture location and fracture severity, various options are available to reinforce or augment standard fracture fixation systems. Correct application of the basic principles of fracture fixation and the use of modern implant technologies enables mechanically stable fracture fixation that allows early weight-bearing and results in timely fracture healing even in patients with osteoporosis.

Periprosthetic fracture fixation of the femur following total hip arthroplasty: A review of biomechanical testing - Part II

BACKGROUND

Periprosthetic femoral fracture is a severe complication of total hip arthroplasty. A previous review published in 2011 summarised the biomechanical studies regarding periprosthetic femoral fracture and its fixation techniques. Since then, there have been several commercially available fracture plates designed specifically for the treatment of these fractures. However, several clinical studies still report failure of fixation treatments used for these fractures.

METHODS

The current literature on biomechanical models of periprosthetic femoral fracture fixation since 2010 to present is reviewed. The methodologies involved in the experimental and computational studies of periprosthetic femoral fracture fixation are described and compared with particular focus on the recent developments.

FINDINGS

Several issues raised in the previous review paper have been addressed by current studies; such as validating computational results with experimental data. Current experimental studies are more sophisticated in design. Computational studies have been useful in studying fixation methods or conditions (such as bone healing) that are difficult to study in vivo or in vitro. However, a few issues still remain and are highlighted.

INTERPRETATION

The increased use of computational studies in investigating periprosthetic femoral fracture fixation techniques has proven valuable. Existing protocols for testing periprosthetic femoral fracture fixation need to be standardised in order to make more direct and conclusive comparisons between studies. A consensus on the 'optimum' treatment method for periprosthetic femoral fracture fixation needs to be achieved.

Biomechanical Analysis Using FEA and Experiments of Metal Plate and Bone Strut Repair of a Femur Midshaft Segmental Defect

This investigation assessed the biomechanical performance of the metal plate and bone strut technique for fixing recalcitrant nonunions of femur midshaft segmental defects, which has not been systematically done before. A finite element (FE) model was developed and then validated by experiments with the femur in 15 deg of adduction at a subclinical hip force of 1 kN. Then, FE analysis was done with the femur in 15 deg of adduction at a hip force of 3 kN representing about 4 x body weight for a 75 kg person to examine clinically relevant cases, such as an intact femur plus 8 different combinations of a lateral metal plate of fixed length, a medial bone strut of varying length, and varying numbers and locations of screws to secure the plate and strut around a midshaft defect. Using the traditional “high stiffness” femur-implant construct criterion, the repair technique using both a lateral plate and a medial strut fixed with the maximum possible number of screws would be the most desirable since it had the highest stiffness (1948 N/mm); moreover, this produced a peak femur cortical Von Mises stress (92 MPa) which was below the ultimate tensile strength of cortical bone. Conversely, using the more modern “low stiffness” femur-implant construct criterion, the repair technique using only a lateral plate but no medial strut provided the lowest stiffness (606 N/mm), which could potentially permit more in-line interfragmentary motion (i.e., perpendicular to the fracture gap, but in the direction of the femur shaft long axis) to enhance callus formation for secondary-type fracture healing; however, this also generated a peak femur cortical Von Mises stress (171 MPa) which was above the ultimate tensile strength of cortical bone.