Effects of construct stiffness on healing of fractures stabilized with locking plates

Biomechanical analysis of the tandem spinal external fixation in a multiple-level noncontiguous lumbar fractures model: a finite element analysis

Objective

This study aimed to investigate the biomechanical characteristics of the tandem spinal external fixation (TSEF) for treating multilevel noncontiguous spinal fracture (MNSF) using finite element analysis and provide a theoretical basis for clinical application.

Methods

We constructed two models of L2 and L4 vertebral fractures that were fixed with the TSEF and the long-segment spinal inner fixation (LSIF). The range of motion (ROM), maximum stresses at L2 and L4 vertebrae, the screws and rods, and the intervertebral discs of the two models were recorded under load control. Subsequently, the required torque, the maximum stress at L2 and L4 vertebrae, the screws and rods, and the intervertebral discs were analyzed under displacement control.

Results

Under load control, the TSEF model reserved more ROM than the LSIF model. The maximum stresses of screws in the TSEF model were increased, while the maximum stresses of rods were reduced compared to the LSIF model. Moreover, the maximum stresses of L2 and L4 vertebrae and discs in the TSEF model were increased compared to the LSIF model. Under displacement control, the TSEF model required fewer moments (N·mm) than the LSIF model. Compared to the LSIF model, the maximum stresses of screws and rods in the TSEF model have decreased; the maximum stresses at L2 and L4 in the TSEF model were increased. In the flexion condition, the maximum stresses of discs in the TSEF model were less than the LSIF model, while the maximum stresses of discs in the TSEF model were higher in the extension condition.

Conclusion

Compared to LSIF, the TSEF has a better stress distribution with higher overall mobility. Theoretically, it reduces the stress concentration of the connecting rods and the stress shielding of the fractured vertebral bodies.

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.

Numerical study of pedicle screw construction and locking compression plate fixation in posterior pelvic ring injuries: Analyzed by finite element method

BACKGROUND

The aim of this study was to compare the biomechanical performance of pedicle screw construction and locking compression plate fixation in posterior pelvic ring injuries analyzed by finite element method.

METHODS

A 3-dimensional finite element model of the spine-pelvis-femur complex with ligaments was reconstructed from computed tomography images. An unstable posterior pelvic ring injury was created, which was fixed with a pedicle screw construction or locking compression plate. A follower load of 400 N was applied to the upper surface of the vertebrae to simulate the upper body weight, while the ends of the proximal femurs were fixed. The construct stiffness, the maximum vertical displacement, the maximum posterior displacement, the maximum right displacement, and the overall maximum displacement of the sacrum, and stress distributions of the implants and pelvises were assessed.

RESULTS

The construct stiffness of the pedicle screw model (435.14 N/mm) was 2 times that of the plate model (217.01 N/mm). The maximum vertical displacement, the maximum posterior displacement, the maximum right displacement, and the overall maximum displacement of the sacrum in the pedicle screw model were smaller than those in the plate model (0.919, 1.299, 0.259, and 1.413 mm in the pedicle screw model, and 1.843, 2.300, 1.053, and 2.895 mm in the plate model, respectively). The peak stresses of the implant and pelvis in the pedicle screw model decreased by 80.4% and 25% when compared with the plate model (44.57 and 34.48 MPa in the pedicle screw model, and 227.47 and 45.97 MPa in the plate model, respectively).

CONCLUSION

The study suggested that the pedicle screw construction could provide better fixation stability than the locking compression plate and serves as the recommended fixation method for the treatment of posterior pelvic ring injuries.

Biomechanical effects of muscle loading on early healing of femoral stem fractures: a combined musculoskeletal dynamics and finite element approach

Femoral stem fractures (FST) are often accompanied by muscle injuries, however, what muscle injuries affect fracture healing and to what extent is unknown. The purpose of this study was to analyze the extent to which different muscles affect FST healing through a combined musculoskeletal dynamics and finite element approach. Modeling the lower extremity musculoskeletal system for 12 different muscle comprehensives. Muscle and joint reaction forces on the femur were calculated and these data were used as boundary conditions input to the FSTs model to predict the degree of muscle influence on fracture healing. Finally, we will investigate the extent to which muscle influences FST healing during knee flexion. Muscle and joint forces are highly dependent on joint motion and have a significant biomechanical influence on interfragmentary strain (IFS) healing. The psoas major (PM), gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) muscles play a major role in standing, with GM > PM > GL, whereas the gluteus medius posterior (GMP), vastus intermedius (VI), vastus medialis (VM), vastus lateralis superior (VLS), and adductor magnus distalis (AMD) muscles play a major role in knee flexion, with VLS > VM > VI > AMD > GMP. Mechanical stimulus-controlled healing can be facilitated when the knee joint is flexed less than 20°. Different muscles exert varying degrees of influence on the healing of fractures. Therefore, comprehending the impact of particular muscles on fracture site tissue FST healing can aid orthopedic surgeons in formulating improved surgical and rehabilitation strategies.

A novel model of locking plate and locking spongious screw: a biomechanical in vitro comparison study with classical locking plate

BACKGROUND

Locking plates are commonly used for the fixation of comminuted, periprosthetic and osteoporotic bone fractures. These plates are secured to the bone with screws, creating a stable connection with fixed angle between the plate and the screws. In this biomechanical in vitro study, our aim is to evaluate and compare the novel locking plate-locking spongious screw model with FDA approved classical locking plate.

METHODS

Sawbone PCF-15 osteoporotic bone model was utilized to simulate osteoporotic bone conditions. Two screws were used to attach both the classical locking plate and the novel locking plate-locking spongious screw model to these bone models. The attachment strength of the screws to the bone blocks was measured by pull-out tests.

RESULTS

Novel locking plate-locking spongious screw model exhibited an 84.38% stronger attachment to the osteoporotic bone model compared to the current locking plate model.

CONCLUSIONS

In conclusion, one of the important problems in the locking plates which is the high Pull-out risk of the locking spongious screws can been resolved with our proposed new model and has a chance of having a better purchase especially in osteoporotic bones.

Severity of Complications after Locking Plate Osteosynthesis in Distal Femur Fractures

Background: Locked plating for distal femur fractures is widely recommended and used. We systematically reviewed clinical studies assessing the benefits and harms of fracture fixation with locked plates in AO/OTA Type 32 and 33 femur fractures. Methods: A comprehensive literature search of PubMed, Embase, Cinahl, Web of Science, and the Cochrane Database was performed. The studies included randomized and non-randomized clinical trials, observational studies, and case series involving patients with distal femur fractures. Studies of other fracture patterns, studies conducted on children, pathological fractures, cadaveric studies, animal models, and those with non-clinical study designs were excluded. Results: 53 studies with 1788 patients were found to satisfy the inclusion and exclusion criteria. The most common harms were nonunion (14.8%), malunion (13%), fixation failure (5.3%), infection (3.7%), and symptomatic implant (3.1%). Time to full weight-bearing ranged from 5 to 24 weeks, averaging 12.3 weeks. The average duration of follow-up was 18.18 months, ranging from 0.5 to 108 months. Surgical time ranged between 40 and 540 min, with an average of 141 min. The length of stay in days was 12.7, ranging from 1 to 61. The average plate length was ten holes, ranging from 5 to 20 holes. Conclusion: This review aimed to systematically synthesize the available evidence on the risk associated with locked plating osteosynthesis in distal femur fractures. Nonunion is the most common harm and is the primary cause of reoperation. The overall combined risk of a major and critical complication (i.e., requiring reoperation) is approximately 20%.

Biomechanical analysis of titanium-alloy and biodegradable implants in dual plate osteosynthesis for AO/ASIF type 33-C2 fractures

Background and objective

Treating geriatric osteoporotic distal femur fractures has always presented challenges, but developing biodegradable materials has brought new opportunities for therapeutic intervention. Despite this progress, there currently needs to be more evidence-based biomechanical guidelines for using dual plate fixation and biodegradable materials in treating osteoporotic comminuted distal femoral fractures.In this study, finite element analysis was conducted to evaluate the mechanical effectiveness of different implant materials (titanium alloys, biodegradable materials, and combinations of both) in the fixation of physiological and osteoporotic distal femoral fractures.

Methods

We constructed finite element models of 33-C2 fractures and three types of plates: the Lateral Less Invasive Stabilization System (LISS) plate, the titanium-alloy medial plate (TAP), and the biodegradable plate (BP). To evaluate the biomechanical advantages in both physiological femur (PF) and osteoporotic femur (OF) conditions, three scenarios were developed: LISS + TAP, LISS + BP, and double biodegradable plates (DBPs). Five loading conditions were applied to measure structural stiffness, fracture micromotion, and implant stress: medio-lateral four-point bending, antero-posterior four-point bending, axial loading, torsional loading, and sideways falling. Several parameters were examined, including peak Von Mises Stress (VMS) of the femur and lateral plate, maximum displacement, bending angle, torsional angle of fracture, and risk of fracture.

Results

In four-point bending tests, the lateral plate of the DBPs group exhibited a slightly lower peak VMS compared to the LISS + TAP and LISS + BP groups. When subjected to axial loading, the stiffness values of the LISS + TAP (OF) were 1.42 times and 1.86 times higher than LISS + BP (OF) and DBPs (OF) groups, and the peak VMS of lateral plate of DBPs (OF) construct was approximately 2% and 16% lower than that of the LISS + TAP (OF) and LISS + BP (OF) constructs. Under torsional loading, DBPs (OF) demonstrated rotational stiffness that was respectively 2% and 52% greater than that of LISS + TAP (OF) and LISS + BP (OF). Regarding the peak VMS of femur, the values of DBPs (OF) were almost 8% and 15% lower than those of LISS + TAP (OF) and LISS + BP (OF).

Conclusions

The use of DBPs at 11.33 GPa facilitated early mobilization of load-bearing joints but exhibited limited ability to support full weight-bearing activities. Though LISS + TAP met practical strength requirements, one should consider the potential biological irritation and stress shielding. Thus, employing a combination of biodegradable and metal internal fixation is a valid approach to effectively treat weight-bearing joint fractures in clinical practice.

Effect of lag screw on stability of first metatarsophalangeal joint arthrodesis with medial plate

Background

First metatarsophalangeal joint (MTP-1) arthrodesis is a commonly performed procedure in the treatment of disorders of the great toe. Since the incidence of revision after MTP-1 joint arthrodesis is not insignificant, a medial approach with a medially positioned locking plate has been proposed as a new technique. The aim of the study was to investigate the effect of the application of a lag screw on the stability and strength of first metatarsophalangeal joint arthrodesis with medial plate.

Methods

The bending tests in a testing machine were performed for models of the first metatarsal bone and the proximal phalanx printed on a 3D printer from polylactide material. The bones were joined using the locking titanium plate and six locking screws. The specimens were divided into three groups of seven each: medial plate and no lag screw, medial plate with a lag screw, dorsal plate with a lag screw. The tests were carried out quasi-static until the samples failure.

Results

The addition of the lag screw to the medial plate significantly increased flexural stiffness (41.45 N/mm vs 23.84 N/mm, p = 0.002), which was lower than that of the dorsal plate with a lag screw (81.29 N/mm, p < 0.001). The similar maximum force greater than 700 N (p > 0.50) and the relative bone displacements lower than 0.5 mm for a force of 50 N were obtained for all fixation techniques.

Conclusions

The lag screw significantly increased the shear stiffness in particular and reduced relative transverse displacements to the level that should not delay the healing process for the full load of the MTP-1 joint arthrodesis with the medial plate. It is recommended to use the locking screws with a larger cross-sectional area of the head to minimize rotation of the medial plate relative to the metatarsal bone.

Biomechanical comparison of titanium alloy additively manufactured and conventionally manufactured plate-screw constructs

AIM

To biomechanically compare the bending stiffness, strength, and cyclic fatigue of titanium additively manufactured (AM) and conventionally manufactured (CM) limited contact plates (LCP) of equivalent dimensions using plate-screw constructs.

METHODS

Twenty-four 1.5/2.0-mm plate constructs (CM: n = 12; AM: n = 12) were placed under 4-point bending conditions. Data were collected during quasi-static single cycle to failure and cyclic fatigue testing until implants plastically deformed or failed. Bending stiffness, bending structural stiffness, and bending strength were determined from load-displacement curves. Fatigue life was determined as number of cycles to failure. Median test variables for each method were compared using the Wilcoxon rank sum test within each group. Fatigue data was also analysed by the Kaplan-Meier estimator of survival function.

RESULTS

There was no evidence for a difference in bending stiffness and bending structural stiffness between AM and CM constructs. However, AM constructs exhibited greater bending strength (median 3.07 (min 3.0, max 3.4) Nm) under quasi-static 4-point bending than the CM constructs (median 2.57 (min 2.5, max 2.6) Nm, p = 0.006). Number of cycles to failure under dynamic 4-point bending was higher for the CM constructs (median 164,272 (min 73,557, max 250,000) cycles) than the AM constructs (median 18,704 (min 14,427, max 33,228) cycles; p = 0.02). Survival analysis showed that 50% of AM plates failed by 18,842 cycles, while 50% CM plates failed by 78,543 cycles.

CONCLUSION AND CLINICAL RELEVANCE

Additively manufactured titanium implants, printed to replicate a conventional titanium orthopaedic plate, were more prone to failure in a shorter fatigue period despite being stronger in single cycle to failure. Patient-specific implants made using this process may be brittle and therefore not comparable to CM orthopaedic implants. Careful selection of their use on a case/patient-specific basis is recommended.

What is the stable internal fixation for the unstable and osteoporotic supracondylar femoral fractures: a finite element analysis

BACKGROUND

Osteoporotic supracondylar femoral fractures (OSFF) have historically been managed by the lateral anatomical locking plate with reasonable success. However, for some kinds of unstable and osteoporotic supracondylar femoral fractures (UOSFF), especially with bone defects, unilateral locking plate (ULLP) fixation failed or resulted in implant breakage. This paper is going to explore what is the stable internal fixation for UOSFF by adding the bilateral locking plate (BLLP) fixation.

METHODS

OSFF models were divided into two groups according to the fracture line type, which would be further subdivided according to their angle of fracture line, presence of bone defect, location, and degree of bone defect. Thereafter, kinds of locking plate fixation were constructed. A 2010-N load was applied to the femoral head, and a 1086-N load was applied to the greater trochanter. In this condition, the maximum von Mises stress distribution of models were investigated.

RESULTS

Firstly, it was obviously found that the stress concentration in the BLLP group was more dispersed than that in the ULLP group. Secondly, according to the fracture line analysis, the stress value of fracture line type in "\" model group was higher than that of "/" model group. Moreover, with the increase in fracture line angle, the stress value of the model increased. Thirdly, from the bone defect analysis, the stress value of the medial bone defect (MBD) model group was higher than that of the lateral bone defect (LBD) model group. And as the degree of bone defect increased, the stress value increased gradually in the model group.

CONCLUSION

In the following four cases, lateral unilateral locking plate fixation cannot effectively stabilize the fracture end, and double locking plate internal fixation is a necessary choice. First, when the angle of the fracture line is large (30, 45). Second, when the fracture line type is "/." Third, when the bone defect is large. Fourth, when the bone defect is medial.

The Influence of Sagittal Pin Angulation on the Stiffness and Pull-Out Strength of a Monolateral Fixator Construct

Monolateral pin-to-bar-clamp fixators are commonly used to stabilize acute extremity injuries. Certain rules regarding frame geometry have been established that affect construct stability. The influence of sagittal pin angulation on construct stiffness and strength has not been investigated. The purpose of this biomechanical study was to demonstrate the effect of a pin angulation in the monolateral fixator using a composite cylinder model. Three groups of composite cylinder models with a fracture gap were loaded with different mounting variants of monolateral pin-to-bar-clamp fixators. In the first group, the pins were set parallel to each other and perpendicular to the specimen. In the second group, both pins were set convergent each in an angle of 15° to the specimen. In the third group, the pins were set each 15° divergent. The strength of the constructions was tested using a mechanical testing machine. This was followed by a cyclic loading test to produce pin loosening. A pull-out test was then performed to evaluate the strength of each construct at the pin-bone interface. Initial stiffness analyses showed that the converging configuration was the stiffest, while the diverging configuration was the least stiff. The parallel mounting showed an intermediate stiffness. There was a significantly higher resistance to pull-out force in the diverging pin configuration compared to the converging pin configuration. There was no significant difference in the pull-out strength of the parallel pins compared to the angled pin pairs. Convergent mounting of pin pairs increases the stiffness of a monolateral fixator, whereas a divergent mounting weakens it. Regarding the strength of the pin-bone interface, the divergent pin configuration appears to provide greater resistance to pull-out force than the convergent one. The results of this pilot study should be important for the doctrine of fixator mounting as well as for fixator component design.

Prediction of fracture nonunion leading to secondary surgery in patients with distal femur fractures

Aims

Several previously identified patient-, injury-, and treatment-related factors are associated with the development of nonunion in distal femur fractures. However, the predictive value of these factors is not well defined. We aimed to assess the predictive ability of previously identified risk factors in the development of nonunion leading to secondary surgery in distal femur fractures.

Methods

We conducted a retrospective cohort study of adult patients with traumatic distal femur fracture treated with lateral locking plate between 2009 and 2018. The patients who underwent secondary surgery due to fracture healing problem or plate failure were considered having nonunion. Background knowledge of risk factors of distal femur fracture nonunion based on previous literature was used to form an initial set of variables. A logistic regression model was used with previously identified patient- and injury-related variables (age, sex, BMI, diabetes, smoking, periprosthetic fracture, open fracture, trauma energy, fracture zone length, fracture comminution, medial side comminution) in the first analysis and with treatment-related variables (different surgeon-controlled factors, e.g. plate length, screw placement, and proximal fixation) in the second analysis to predict the nonunion leading to secondary surgery in distal femur fractures.

Results

We were able to include 299 fractures in 291 patients. Altogether, 31/299 fractures (10%) developed nonunion. In the first analysis, pseudo-R2 was 0.27 and area under the receiver operating characteristic curve (AUC) was 0.81. BMI was the most important variable in the prediction. In the second analysis, pseudo-R2 was 0.06 and AUC was 0.67. Plate length was the most important variable in the prediction.

Conclusion

The model including patient- and injury-related factors had moderate fit and predictive ability in the prediction of distal femur fracture nonunion leading to secondary surgery. BMI was the most important variable in prediction of nonunion. Surgeon-controlled factors had a minor role in prediction of nonunion.

Medial augmentation plating of aseptic distal femoral nonunions

BACKGROUND

Distal femur nonunions are well-recognized contributors to persistent functional disability, with limited data regarding their treatment options. In the current study, we asked whether additional medial augmentation plating is a feasible treatment option for patients with aseptic distal femoral nonunion and intact lateral implants.

METHODS

We conducted a single-center, retrospective study including 20 patients treated for aseptic distal femoral nonunion between 2002 and 2017. The treatment procedure included a medial approach to the distal femur, debridement of the nonunion site, bone grafting and medial augmentation plating utilizing a large-fragment titanium plate. Outcome measures were bone-related and functional results, measured by the Hospital for Special Surgery Knee Rating Scale (HSS) and the German Short Musculoskeletal Function Assessment questionnaire (SMFA-D).

RESULTS

Eighteen of 20 nonunions showed osseous healing at 8.16 ± 5.23 (range: 3-21) months after augmentation plating. Regarding functional results, the mean HSS score was 74.17 ± 11.12 (range: 57-87). The mean SMFA-D functional index was 47.38 ± 16.78 (range 25.74-71.32) at the last follow-up. Index procedure-associated complications included two cases of persistent nonunion and one case of infection.

CONCLUSIONS

According to the assessed outcome measures, augmentation plating is a feasible treatment option, with a high proportion of patients achieving bony union and good functional outcomes and a few patients experiencing complications.

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.

Biomechanical study of the stiffness of the femoral locking compression plate of an external fixator for lower tibial fractures

BACKGROUND

A locking compression plate (LCP) of the distal femur is used as an external fixator for lower tibial fractures. However, in clinical practice, the technique lacks a standardized approach and a strong biomechanical basis for its stability.

METHODS

In this paper, internal tibial LCP fixator (Group IT-44), external tibial LCP fixator (Group ET-44), external distal femoral LCP fixator (Group EF-44, group EF-33, group EF-22), and conventional external fixator (Group CEF-22) frames were used to fix unstable fracture models of the lower tibial segment, and anatomical studies were performed to standardize the operation as well as to assess the biomechanical stability and adjustability of the distal femoral LCP external fixator by biomechanical experiments.

RESULTS

It was found that the torsional and flexural stiffnesses of group EF-44 and group EF-33 were higher than those of group IT-44 and group ET-44 (p < 0.05); the flexural stiffness of group EF-22 was similar to that of group IT-44 (p > 0.05); and the compressive stiffness of all three EF groups was higher than that of group ET-44 (p < 0.05). In addition, the flexural and compressive stiffnesses of the three EF groups decreased with the decrease in the number of screws (p < 0.05), while the torsional stiffness of the three groups did not differ significantly between the two adjacent groups (p > 0.05). Group CEF-22 showed the highest stiffnesses, while group ET-44 had the lowest stiffnesses (P < 0.05).

CONCLUSIONS

The study shows that the distal femoral LCP has good biomechanical stability and adjustability and is superior to the tibial LCP as an external fixator for distal tibial fractures, as long as the technique is used in a standardized manner according to the anatomical studies in this article.

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.

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.

Radiographic Outcomes of Talonavicular Joint Arthrodesis With Varying Fixation Techniques in Stage III Adult Acquired Flatfoot Reconstruction

Utilization of the talonavicular joint (TN) arthrodesis as an isolated procedure or in combination with hindfoot arthrodesis has been described in the literature for treatment of numerous hindfoot conditions. When used in isolation or with concomitant hindfoot arthrodesis, the TN joint has demonstrated nonunion rates reported as high as 37% in the literature. Despite previous research, there remains a lack of agreement upon the ideal fixation technique for TN joint arthrodesis with and without concomitant subtalar joint arthrodesis. The purpose of this study was to retrospectively compare the radiographic and clinical results of TN joint arthrodesis as part of double arthrodesis procedure utilizing 4 separate fixation constructs in the treatment of advanced hindfoot malalignment in stage III adult-acquired flatfoot deformity. We retrospectively reviewed 105 patients who underwent TN joint arthrodesis as part of double arthrodesis procedure utilizing 4 separate fixation constructs. Our results demonstrated a nonunion rate of 16.2%, with 17 nonunions identified within our patient population. One (2.4%) nonunion was observed in the 3-screw cohort, 7 (33.3%) nonunions were observed in the 2-screw cohort, 4 (16.0%) nonunions were observed in the 2-screw plus plate cohort, and 5 (29.4%) nonunions were observed in the 1-screw plus plate cohort. The difference in nonunion rate between the 4 cohorts was statistically significant. Based on these results, we conclude that the use of a 3-screw construct for TN joint arthrodesis as part of double arthrodesis procedure demonstrates a statistically significant reduction in nonunion rate and should be considered a superior fixation construct for this procedure.

Comparison of Screw Quantity and Placement of Metacarpal Fracture Fixation: A Biomechanical Study

BACKGROUND

It is recommended to have 6 bicortical screws for plate fixation of long bone fractures; however, many metacarpal fractures do not allow 6 screws due to size limitations and proximity of crucial anatomical structures. The purpose of this biomechanical study was to determine whether the mechanical properties of a 4-screw nonlocking construct are noninferior to those of a 6-screw nonlocking construct.

METHODS

Metacarpal sawbones were used to simulate a midshaft, transverse fracture. Nonlocking bicortical screws were placed in the 6-hole plate, and the metacarpals were randomly assigned to 2 equal study groups: (1) 4 screws, 2 on either side of the fracture (4S); and (2) 6 screws, 3 on either side of the fracture (6S). The metacarpals were tested in a cyclic loading mode and load to failure in a cantilever bending mode.

RESULTS

Maximum deflection was significantly higher for 4S compared with 6S. Cyclic root mean square (RMS) was also significantly greater for 4S at 70 and 100 N. There were no statistically significant differences observed between the 2 constructs for maximum bending load, bending stiffness, and cyclic RMS at 40 N. The maximum bending load in 4S and 6S was 245.6 ± 37.9 N and 230.8 ± 41.9 N, respectively; 4S was noninferior and not superior to 6S. Noninferiority testing was inconclusive for bending stiffness.

CONCLUSIONS

A 4-screw bicortical nonlocking construct is noninferior to a 6-screw bicortical nonlocking construct for fixation of metacarpal fractures, which may be advantageous to minimize disruption of soft tissues while maintaining sufficient construct stability.

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.

Biomechanical Analysis of the External Fixation in a Lumbar Fracture Model: A Finite Element Study

Purpose

This study aimed to investigate the biomechanical characteristics of the external spinal fixation for treating lumbar fracture through finite element analysis (FEA) and provide a theoretical basis for its further application.

Methods

Two different models of L3 fracture fixed with the external spinal fixation and the internal fixation system respectively were constructed. The ROM, maximum stresses at L3, and the screws of the two models were measured under load control. Subsequently, the applied torque, the maximum stressed at L3, L1/2, L2/3, L3/4, L4/5 discs and the screws were analyzed under displacement control.

Results

Under load control, the external fixation model reserved more ROM than the internal fixation model (40.4–48.0% vs 30.5–41.0%). Compared to the internal fixation model, the maximum stresses at L3 and screws in the external fixation model were increased. Under displacement control, the external fixation model required fewer moments (N·mm) than the internal fixation model (flexion: 7500 vs 12,294; extension: 7500 vs 9027). Further, the maximum stresses at L3 and the screws in the external fixation model were greater than those of the internal fixation model, while the maximum stresses at the upper and lower adjacent discs of fixed segments were less than the internal fixation model.

Conclusion

Compared to the internal fixation system, the external fixation has a better stress distribution with the greater overall mobility. It theoretically reduces the stress concentration of the adjacent discs and the stress shielding of the fractured vertebral body.

Influence of the Near-Cortical Over-Drilling Technique on the Mechanical Behaviour of Locking Plate Constructs Applied in Maned Wolf's Femur

OBJECTIVE

 The aim of this study was to evaluate the influence of near-cortical over-drilling holes on the mechanical behaviour of locking plate constructs applied in maned wolf's femur by using mechanical testing and finite element method (FEM).

STUDY DESIGN

 Seven pairs of adult maned wolves (Chrysocyon brachyurus) femur bones were randomly distributed into four groups. In all groups, a 3.5 mm locking compression plate, designed with 12 combi-holes and one locked, was applied to the lateral surface of the femur. G1 (n = 4) received bicortical locking screws placed in holes 1, 3, 5, 8, 10 and 12. In G2 (n = 5), the plate was applied as used in G1, but the application of the locked screws involved the near-cortical over-drilling technique. In G3 (n = 4), the plate was applied as used in G2, but the size of the near-cortical over-drilling was larger. The combi-holes 6 and 7 were maintained over a 10 mm fracture gap without screws. All constructs were tested for failure in the axial load. The axial load was applied eccentrically to the femoral head.

RESULTS

 Statistical differences were observed in the maximum load with G3 > G1 and G3 > G2, and in the deflection with G2 > G1 and G2 > G3. The FEM showed the lowest total displacement of the bone-plate constructs as well as of the plate in G1 compared with G2 and G3.

CONCLUSION

 The near-cortical over-drilling technique used in unstable fractures induced in the maned wolf's femur showed by static axial compression test that maximum load and deflection are dependent on drill hole size induced in the near-cortex. Based on FEM, the lowest total displacement of the bone-plate constructs was observed in Group 1.

Biomechanical analysis of fixation methods in acetabular fractures: a systematic review of test setups

Purpose

Optimal anatomical reduction and stable fixation of acetabular fractures are important in avoiding secondary dislocation and osteoarthritis. Biomechanical studies of treatment options of acetabular fractures aim to evaluate the biomechanical properties of different fixation methods. As the setup of the biomechanical test can influence the experimental results, this review aimed to analyze the characteristics, comparability and clinical implications of studies on biomechanical test setups and finite element analyses in the fixation of acetabular fractures.

Methods

A systematic literature research was conducted according to the PRISMA guidelines, using the PubMed/MEDLINE and Web of Science databases. 44 studies conducting biomechanical analyses of fixation of acetabular fractures were identified, which met the predefined inclusion and exclusion criteria and which were published in English between 2000 and April 16, 2021. The studies were analyzed with respect to distinct parameters, including fracture type, material of pelvis model, investigated fixation construct, loading direction, loading protocol, maximum loading force, outcome parameter and measurement method.

Results

In summary, there was no standardized test setup within the studies on fixation constructs for acetabular fractures. It is therefore difficult to compare the studies directly, as they employ a variety of different test parameters. Furthermore, the clinical implications of the biomechanical studies should be scrutinized, since several test parameters were not based on observations of the human physiology.

Conclusion

The limited comparability and restricted clinical implications should be kept in mind when interpreting the results of biomechanical studies and when designing test setups to evaluate fixation methods for acetabular fractures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00068-022-01936-9.

A Novel Three-Dimensional Computational Method to Assess Rod Contour Deformation and to Map Bony Fusion in a Lumbopelvic Reconstruction After En-Bloc Sacrectomy

Introduction: En-bloc resection of a primary malignant sacral tumor with wide oncological margins impacts the biomechanics of the spinopelvic complex, deteriorating postoperative function. The closed-loop technique (CLT) for spinopelvic fixation (SPF) uses a single U-shaped rod to restore the spinopelvic biomechanical integrity. The CLT method was designed to provide a non-rigid fixation, however this hypothesis has not been previously tested. Here, we establish a computational method to measure the deformation of the implant and characterize the bony fusion process based on the 6-year follow-up (FU) data.

Materials and Methods: Post-operative CT scans were collected of a male patient who underwent total sacrectomy at the age of 42 due to a chordoma. CLT was used to reconstruct the spinopelvic junction. We defined the 3D geometry of the implant construct. Using rigid registration algorithms, a common coordinate system was created for the CLT to measure and visualize the deformation of the construct during the FU. In order to demonstrate the cyclical loading of the construct, the patient underwent gait analysis at the 6th year FU. First, a region of interest (ROI) was selected at the proximal level of the construct, then the deformation was determined during the follow-up period. In order to investigate the fusion process, a single axial slice-based voxel finite element (FE) mesh was created. The Hounsfield values (HU) were determined, then using an empirical linear equation, bone mineral density (BMD) values were assigned for every mesh element, out of 10 color-coded categories (1st category = 0 g/cm³, 10th category 1.12 g/cm³).

Results: Significant correlation was found between the number of days postoperatively and deformation in the sagittal plane, resulting in a forward bending tendency of the construct. Volume distributions were determined and visualized over time for the different BMD categories and it was found that the total volume of the elements in the highest BMD category in the first postoperative CT was 0.04 cm³, at the 2nd year, FU was 0.98 cm³, and after 6 years, it was 2.30 cm³.

Conclusion: The CLT provides a non-rigid fixation. The quantification of implant deformation and bony fusion may help understate the complex lumbopelvic biomechanics after sacrectomy.

Individualized cyclic mechanical loading improves callus properties during the remodelling phase of fracture healing in mice as assessed from time-lapsed in vivo imaging

Fracture healing is regulated by mechanical loading. Understanding the underlying mechanisms during the different healing phases is required for targeted mechanical intervention therapies. Here, the influence of individualized cyclic mechanical loading on the remodelling phase of fracture healing was assessed in a non-critical-sized mouse femur defect model. After bridging of the defect, a loading group (n = 10) received individualized cyclic mechanical loading (8–16 N, 10 Hz, 5 min, 3 × /week) based on computed strain distribution in the mineralized callus using animal-specific real-time micro-finite element analysis with 2D/3D visualizations and strain histograms. Controls (n = 10) received 0 N treatment at the same post-operative time-points. By registration of consecutive scans, structural and dynamic callus morphometric parameters were followed in three callus sub-volumes and the adjacent cortex showing that the remodelling phase of fracture healing is highly responsive to cyclic mechanical loading with changes in dynamic parameters leading to significantly larger formation of mineralized callus and higher degree of mineralization. Loading-mediated maintenance of callus remodelling was associated with distinct effects on Wnt-signalling-associated molecular targets Sclerostin and RANKL in callus sub-regions and the adjacent cortex (n = 1/group). Given these distinct local protein expression patterns induced by cyclic mechanical loading during callus remodelling, the femur defect loading model with individualized load application seems suitable to further understand the local spatio-temporal mechano-molecular regulation of the different fracture healing phases.

Comparison of a standardized four-point bending test to an implant system test of an osteosynthetic system under static and dynamic load condition

Current test standards of osteosynthetic implants examine the bone plate and screw separately leading to unrealistic load scenarios and unknown performance of the system as a whole, which prevents the identification of characteristic failures in clinical use. A standardized static and dynamic four-point bending test (ASTM F382) was performed on a bone plate. Based on that standard, an advanced implant system test (IST) was designed and performed to test a mechanical construct consisting of a bone plate, screws and an artificial bone substitute out of Polyoxymethylene (POM). The test object was an osteosynthetic system to treat fractured ulna bones. Both results of the conventional and advanced test method were analyzed and compared to one another. The static results show a similar yield point (YP) relative to the bending moment with just 9% difference. Dynamic results show a bi-phasic behavior of the displacement vs. cycle data for the IST. The secondary phase can be defined as a constantly increasing plastic deflection or ratcheting effect quantified by its slope in mm per one million cycles, leading to a 10 times higher slope for the IST than the conventional test. The IST has a high impact on the test results and the resultant interpretation of the mechanical behavior of the osteosynthetic system. A constantly increasing plastic deflection might lead to fatigue failures and to a loss of the mechanical durability. The development of new standardizations referring to the whole system within reasonable boundary conditions of individual biomechanical applications is crucial for high quality mechanical analysis.

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.

Strategies to Improve Bone Healing: Innovative Surgical Implants Meet Nano-/Micro-Topography of Bone Scaffolds

Successful fracture healing is dependent on an optimal mechanical and biological environment at the fracture site. Disturbances in fracture healing (non-union) or even critical size bone defects, where void volume is larger than the self-healing capacity of bone tissue, are great challenges for orthopedic surgeons. To address these challenges, new surgical implant concepts have been recently developed to optimize mechanical conditions. First, this review article discusses the mechanical environment on bone and fracture healing. In this context, a new implant concept, variable fixation technology, is introduced. This implant has the unique ability to change its mechanical properties from “rigid” to “dynamic” over the time of fracture healing. This leads to increased callus formation, a more homogeneous callus distribution and thus improved fracture healing. Second, recent advances in the nano- and micro-topography of bone scaffolds for guiding osteoinduction will be reviewed, particularly emphasizing the mimicry of natural bone. We summarize that an optimal scaffold should comprise micropores of 50–150 µm diameter allowing vascularization and migration of stem cells as well as nanotopographical osteoinductive cues, preferably pores of 30 nm diameter. Next to osteoinduction, such nano- and micro-topographical cues may also reduce inflammation and possess an antibacterial activity to further promote bone regeneration.

Improving mandibular reconstruction by using topology optimization, patient specific design and additive manufacturing?-A biomechanical comparison against miniplates on human specimen

In this study, topology optimized, patient specific osteosynthesis plates (TOPOS-implants) are evaluated for the mandibular reconstruction using fibula segments. These shape optimized implants are compared to a standard treatment with miniplates (thickness: 1.0 mm, titanium grade 4) in biomechanical testing using human cadaveric specimen. Mandible and fibula of 21 body donors were used. Geometrical models were created based on automated segmentation of CT-scans of all specimens. All reconstructions, including cutting guides for osteotomy as well as TOPOS-implants, were planned using a custom-made software tool. The TOPOS-implants were produced by electron beam melting (thickness: 1.0 mm, titanium grade 5). The fibula-reconstructed mandibles were tested in static and dynamic testing in a multi-axial test system, which can adapt to the donor anatomy and apply side-specific loads. Static testing was used to confirm mechanical similarity between the reconstruction groups. Force-controlled dynamic testing was performed with a sinusoidal loading between 60 and 240 N (reconstructed side: 30% reduction to consider resected muscles) at 5 Hz for up to 5 · 10⁵ cycles. There was a significant difference between the groups for dynamic testing: All TOPOS-implants stayed intact during all cycles, while miniplate failure occurred after 26.4% of the planned loading (1.32 · 10⁵ ± 1.46 · 10⁵ cycles). Bone fracture occurred in both groups (miniplates: n = 3, TOPOS-implants: n = 2). A correlation between bone failure and cortical bone thickness in mandible angle as well as the number of bicortical screws used was demonstrated. For both groups no screw failure was detected. In conclusion, the topology optimized, patient specific implants showed superior fatigue properties compared to miniplates in mandibular reconstruction. Additionally, the patient specific shape comes with intrinsic guiding properties to support the reconstruction process during surgery. This demonstrates that the combination of additive manufacturing and topology optimization can be beneficial for future maxillofacial surgery.

The influence of the number of holes in the open wedge high tibial osteotomy on knee biomechanics using finite element analysis

BACKGROUND

The most significant differences of high tibial osteotomy (HTO) were found in terms of plate length, and this was related to number of holes distal region of the plate below wedge. The purpose of this study is to evaluate the biomechanical effects of three different designs medial opening wedge plates.

HYPOTHESIS

The design of the HTO plate influenced the outcome of the biomechanics.

METHODS

The HTO model was simulated using finite element (FE) model. This FE investigation included three types of loading conditions corresponding to the loads used in the experimental study for model validation and model predictions for clinically relevant loading scenarios. The average stress and contact stress were evaluated.

RESULTS

The highest average stress was observed in the TomoFix. Conversely, the stress on the bone declined in the order of Puddu, Maxi and TomoFix plates. The micromotion in the wedge displayed a similar trend to the stress on bone. The highest and lowest contact stresses on the medial meniscus were observed in the Puddu and TomoFix plate, respectively. However, an opposite trend was observed in the lateral meniscus. The contact stress on medial and lateral menisci decreased and increased, respectively, in all three different plates when compared to those in the intact model.

DISCUSSION

The TomoFix plate exhibited the highest stability relative to the micromotions of the wedge. However, in terms of the stress on the bone and plates, a stress-shielding effect could exist in the TomoFix plate. Additionally, the contact stress on the articular surface suggested that a complicated relationship could exist with respect to the plate design.

LEVEL OF EVIDENCE

IV.

The role of mechanical stimulation in the enhancement of bone healing

The biomechanical environment plays a dominant role in the process of fracture repair. Mechanical signals control biological activities at the fracture site, regulate the formation and proliferation of different cell types, and are responsible for the formation of connective tissues and the consolidation of the fractured bone. The mechanobiology at the fracture site can be easily manipulated by the design and configuration of the fracture fixation construct and by the loading of the extremity (weight-bearing prescription). Depending on the choice of fracture fixation, the healing response can be directed towards direct healing or towards indirect healing through callus formation. This manuscript summarizes the evidence from experimental studies and clinical observations on the effect of mechanical manipulation on the healing response. Parameters like fracture gap size, interfragmentary movement, interfragmentary strain, and axial and shear deformation will be explored with respect to their respective effects on fracture repair. Also, the role of externally applied movement on the potential enhancement on the fracture repair process will be explored. Factors like fracture gap size, type and amplitude of the mechanical deformation as well as the loading history and its timing will be discussed.

Comparison of three methods of Müller type C2 and C3 distal femoral fracture repair

Background

We compared the outcomes of three fixation techniques for Müller type C2 and C3 distal femoral fractures.

Methods

We retrospectively analyzed patients undergoing internal fixation for Müller type C2 and C3 distal femoral fractures via locking plate (Group A), lateral locking condylar plate and medial contoured reconstruction plate (Group B), and lateral locking condylar plate and anterior reconstruction plate (Group C). Knee joint functional recovery and functional outcomes were evaluated 12 months postoperatively.

Results

Patients included 34 men and 24 women aged 25 to 74 years (mean, 50.3 ± 10.73 years). Operating times were longest in Group B and similar in Groups A and C. Bleeding volume in Group A was smaller than in Group B and similar to that of Group C. Functional outcomes were excellent in 18 (31%) fractures, good in 24 (41%), moderate in 11 (19%), and poor in 5 (9%). Good-to-excellent results were achieved in 56%, 82%, and 83% of patients (Groups A, B, and C, respectively). Groups B and C's outcomes were superior to Group A's outcomes. No significant difference in postoperative complications between the groups existed.

Conclusion

Lateral locking condylar and anterior reconstruction plating was useful for complex type C distal femoral fractures.

Association of Gap Healing With Angle of Correction After Opening-Wedge High Tibial Osteotomy Without Bone Grafting

Background:

Studies have reported that opening wedge high tibial osteotomy (OWHTO) without bone grafting has outcomes that are similar to or even better than those of OWHTO with bone grafting, especially after use of a locking plate. However, a consensus on managing the gap after OWHTO has not been established.

Purpose:

To determine the degree of gap healing achieved without bone grafting, the factors associated with gap healing, and whether additional gap healing would be obtained after plate removal.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

This retrospective study included 73 patients who underwent OWHTO without bone grafting between 2015 and 2018. Patients in the study were divided into 2 groups based on the correction angle: small correction group (<10°; SC group) and large correction group (≥10°; LC group). The locking plate used in OWHTO was removed at a mean of 13.5 months after surgery in 65 patients. Radiographic indexes were measured: gap filling height, gap vacancy ratio (GVR), and osteotomy filling index. The acceptable gap healing was defined as an osteotomy filling index ≥3. The factors related to gap healing around the osteotomy site were selected after multicollinearity analysis.

Results:

Although both groups achieved acceptable gap healing regardless of the correction angle, the SC group showed higher and earlier gap healing than did the LC group (gap healing rate 81.4% in the SC group vs 41.7% in the LC group at 3 months postoperatively). The GVR was 8.6% in the SC group and 15.3% in the LC group at 12 months after surgery (P = .005). Both the amount of time that elapsed after surgery and the correction angle were associated with gap healing (P < .05). Additional gap healing was observed after plate removal, as the GVR decreased 2.7% more in the patients with plate removal than in patients who did not have plate removal (P = .012).

Conclusion:

All patients achieved acceptable gap healing without bone graft. The degree of gap healing was higher in the SC group and increased over time. Gap healing was promoted after plate removal. Considering the results of this study, a bone graft is not necessary in routine OWHTO in terms of gap healing.

Temporal Changes in Reverse Torque of Locking-Head Screws Used in the Locking Plate in Segmental Tibial Defect in Goat Model

The objective of this study was to evaluate changes in peak reverse torque (PRT) of the locking head screws that occur over time. A locking plate construct, consisting of an 8-hole locking plate and 8 locking screws, was used to stabilize a tibia segmental bone defect in a goat model. PRT was measured after periods of 3, 6, 9, and 12 months of ambulation. PRT for each screw was determined during plate removal. Statistical analysis revealed that after 6 months of loading, locking screws placed in position no. 4 had significantly less PRT as compared with screws placed in position no. 5 (p < 0.05). There were no statistically significant differences in PRT between groups as a factor of time (p > 0.05). Intracortical fractures occurred during the placement of 151 out of 664 screws (22.7%) and were significantly more common in the screw positions closest to the osteotomy (positions 4 and 5, p < 0.05). Periosteal and endosteal bone reactions and locking screw backout occurred significantly more often in the proximal bone segments (p < 0.05). Screw backout significantly, negatively influenced the PRT of the screws placed in positions no. 3, 4, and 5 (p < 0.05). The locking plate-screw constructs provided stable fixation of 2.5-cm segmental tibia defects in a goat animal model for up to 12 months.

A custom-made distal humerus plate fabricated by selective laser melting

This study aims to evaluate the mechanical performance of custom 3D-printed titanium plates in the treatment of distal humerus fractures. Rigidity of four plating configurations were investigated by finite element analysis. The results reveal that implementation of custom designs with minimal screw holes, lateral-medial linking screw and lateral brim could significantly improve stiffness and consequently leads to better biomechanical stability as compared to standard osteosynthesis design. Biomechanical testing was also performed to validate practical usability. The results confirm that newly designed custom plates fabricated by selective laser melting is a possible alternative for the treatment of distal humerus fracture.

Risk factors for implant-related fractures after proximal femoral osteotomy in children with developmental dysplasia of the hip: a case-control study

Background and purpose - Proximal femoral osteotomy (PFO) is commonly performed to treat children with developmental dysplasia of the hip (DDH). Implant-related femoral fractures after osteotomy are sometimes reported, but the potential risk factors for these fractures remain unclear. We investigated the association of implant-related fractures with PFO and potential risk factors for these fractures.Patients and methods - We retrospectively reviewed 1,385 children undergoing PFO for DDH in our institution from 2009 to 2016 after obtaining institutional review board (IRB) approval and identified 27 children (28 hips, fracture group) with implant-related femoral fractures after PFO. We selected 137 children (218 hips, control group) without fractures who matched the children in the fracture group by age, weight, surgeon, and surgical period. Relevant clinical data were collected and compared between the 2 groups. Multiple analyses of risk factors for implant-related fractures were conducted by logistic regression with the stepwise regression method.Results - The occurrence rate of implant-related fractures was 1.9% (27/1,385). Compared with the control group, the fracture group more commonly exhibited bilateral involvement (74% vs. 53%, p = 0.04), used a spica orthosis for immobilization after osteotomy (43% vs 21%, p = 0.01) and exhibited mild remodeling at the osteotomy site (46% vs. 19%, p = 0.003), and less commonly required capsulotomy during osteotomy (61% vs. 79%, p = 0.03). According to the multiple regression analysis, the only factor identified as an independent risk factor for implant-related fractures was mild remodeling at the osteotomy site (OR = 3.2, 95% CI 1.4-7.5). Remodeling at the osteotomy site was significantly associated with varus osteotomy (coefficient = 1.4, CI 1.03-1.8). The fracture occurred at a mean of 12 months (2.2-25) after osteotomy or 3.3 months (0-12) after implant removal. In children undergoing implant removal, the fractures mostly occurred at the osteotomy site (n = 13/15), while in those with the implant remaining, the fractures mostly occurred in the screw hole (n = 8/13).Interpretation - The type of PFO performed is not associated with implant-related fractures in children with DDH. Children with mild remodeling at the osteotomy site should be closely followed up, regardless of whether the hardware is removed, and high-intensity activity should not be permitted until moderate or extensive remodeling is confirmed. After PFO, the implants should be removed when solid union is achieved at the osteotomy site.

Metaphyseal callus formation in pilon fractures is associated with loss of alignment: Is stiffer better?

OBJECTIVE

To assess the relationship between metaphyseal callus formation and preservation of distal tibial alignment in pilon fractures treated with internal plate fixation.

DESIGN

Retrospective Review SETTING: Academic Level I Trauma Center PATIENTS: Forty-two patients with AO/OTA type C2 or C3 pilon fractures treated with plate fixation.

INTERVENTION

Internal fixation with anterolateral plating, medial plating, or both. Modified Radiographic Union Score in Tibial fracture (mRUST) scores were determined from six-month radiographs.

MAIN OUTCOME MEASUREMENTS

Change in lateral and anterior distal tibial angles (LDTA and ADTA) at six months post-operatively.

RESULTS

High callus formation (mRUST ≥ 11 at six months) was associated with a greater loss of coronal reduction as measured by LDTA compared to low callus formation (mRUST < 11): 3.8 vs 2.1° (p = .019), with no difference in ADTA change between groups. In a multivariable logistic regression controlling for age, smoking, obesity, and open fracture, higher mRUST scores were a predictor of coronal reduction loss of five or more degrees (OR 1.71, p=.039). Dual column plating did not independently predict maintenance of alignment.

CONCLUSIONS

Recent literature has popularized dual column fixation for pilon fractures, but it remains unknown whether increased metaphyseal stiffness enhances or impairs healing. In this series, decreased metaphyseal callus formation was associated with maintained coronal alignment, suggesting that a stiffer mechanical environment may be preferable to prevent short term reduction loss in these complex injuries.

LEVEL OF EVIDENCE

III.

Cyclic Damage Accumulation in the Femoral Constructs Made With Cephalomedullary Nails

Background: The purpose of this study was to evaluate the risk of peri-prosthetic fracture of constructs made with cephalomedullary (CM) long and short nails. The nails were made with titanium alloy (Ti-6Al-4V) and stainless steel (SS 316L).

Methods: Biomechanical evaluation of CM nail constructs was carried out with regard to post-primary healing to determine the risk of peri-implant/peri-prosthetic fractures. Therefore, this research comprised of, non-fractured, twenty-eight pairs of cadaveric femora that were randomized and implanted with four types of fixation CM nails resulting in four groups. These constructs were cyclically tested in bi-axial mode for up to 30,000 cycles. All the samples were then loaded to failure to measure failure loads. Three frameworks were carried out through this investigation, Michaelis–Menten, phenomenological, and probabilistic Monte Carlo simulation to model and predict damage accumulation.

Findings: Damage accumulation resulting from bi-axial cyclic loading in terms of construct stiffness was represented by Michaelis–Menten equation, and the statistical analysis demonstrated that one model can explain the damage accumulation during cyclic load for all four groups of constructs (P > 0.05). A two-stage stiffness drop was observed. The short stainless steel had a significantly higher average damage (0.94) than the short titanium nails (0.90, P < 0.05). Long titanium nail group did not differ substantially from the short stainless steel nails (P > 0.05). Results showed gender had a significant effect on load to failure in both torsional and bending tests (P < 0.05 and P < 0.001, respectively).

Interpretation: Kaplan–Meier survival analysis supports the use of short titanium CM nail. We recommend that clinical decisions should take age and gender into consideration in the selection of implants.

A mechanobiological approach to find the optimal thickness for the locking compression plate: Finite element investigations

This study aimed at finding the acceptable range, and the optimal value for the locking compression plate (LCP) thickness (THK), through simulating the osteogenic pathway of bone healing, and by checking bone-plate construct's strength and stability. To attain the goals of this research, a multi-objective approach was adopted, which should trade-off between some conflicting objectives. A finite element model of the long bone-plate construct was made first, and validated against an experimental study. The validated model was then employed to determine the initial strength and stability of the bone-plate construct, for the time right after surgery, for various thicknesses of the LCP. Afterward, coupling with a mechano-regulatory algorithm, the iterative process of bone healing was simulated, and follow up was made for each LCP thickness, over the first 16 post-operative weeks. Results of this study regarding the sequence of tissue evolution inside the fracture gap, showed a similar trend with the existing in-vivo data. For the material and structural properties assigned to the bone-plate construct, in this study, an optimal thickness for the LCP was found to be 4.7 mm, which provides an enduring fixation through secondary healing, whereas for an LCP with a smaller or greater thickness, either bone-implant failure, unstable fixation, impaired fracture consolidation, or primary healing may occur. This result is in agreement with a recent study, that has employed a comprehensive optimization approach to find the optimal thickness.

Biphasic plating improves the mechanical performance of locked plating for distal femur fractures

Internal fixation by plate osteosynthesis is the gold standard treatment for distal femur fractures. Despite improvements that preserve the biological conditions for bone healing, there are concerns standard locked plating constructs may be overly stiff. Biphasic plating is a novel concept designed to provide suitable fracture motion and increased implant strength to support early full weight-bearing. This study aims to demonstrate that the Biphasic Plate can be incorporated into a pre-contoured distal femur plate while providing adequate flexibility and increased implant strength. The mechanical performance of the Biphasic Plate (BP) was investigated in comparison to a standard locking plate for the distal femur (LCP-DF). Constructs were formed by mounting the implants on a bone substitute. The construct stiffness and strength under axial loading and the magnitude of interfragmentary movement were determined using finite element analysis. The Biphasic Plate exhibited a bi-linear stiffness response; at low loads, the BP construct was 55% more compliant and at high loads 476% stiffer than the LCP-DF. The Biphasic Plate provided more consistent interfragmentary movement over a wider loading range. At partial weight-bearing loads, the Biphasic Plate produced larger interfragmentary movements (0.18 vs. 0.04 mm). However, at loads equivalent to full weight-bearing, the maximum movements were substantially smaller than the LCP-DF construct (1.5 vs. 3.5 mm). The increased flexibility at low loads was provided without sacrificing implant strength with peak stress in the Biphasic Plate 63% lower than the LCP-DF construct. The biphasic plating concept can be successfully incorporated into anatomically contoured distal femur plates while providing adequate flexibility and increasing implant strength.

The investigation of bone fracture healing under intramembranous and endochondral ossification

After trauma, fractured bone starts healing directly through bone union or indirectly through callus formation process. Intramembranous and endochondral ossification are two commonly known mechanisms of indirect healing. The present study investigated the bone fracture healing under intramembranous and endochondral ossification by developing theoretical models in conjunction with performing a series of animal experiments. Using experimentally determined mean bone densities in sheep tibia stabilized by the Locking Compression Plate (LCP) fixation system, the research outcomes showed that intramembranous and endochondral ossification can be described by Hill Function with two unique sets of function parameters in mechanical stimuli mediated fracture healing. Two different thresholds exist within the range of mechanical simulation index which could trigger significant intramembranous and endochondral ossification, with a relatively higher bone formation rate of endochondral ossification than that of intramembranous ossification. Furthermore, the increase of flexibility of the LCP system and the use of titanium LCP could potentially promote uniform bone formation across the fracture gap, ultimately better healing outcomes.

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.

Bridge Plate Design Effects on Yield and Fatigue in Distal Radius Fracture Model

Background  Bridge plating for distal radius fractures is indicated for complex fractures with comminution, extensive articular involvement, and/or cases requiring immediate weight bearing. Bridge plate fixation of distal radius fractures is a well-documented treatment method; however, failures have been reported with repetitive loading through the bridged distal radius fracture. Plate design is implicated as a cause of plate fracture in select clinical studies but few mechanical tests comparing bridge plate designs have been reported. This study sought to determine the impact of plate design on bridge plates intended to allow for immediate weight-bearing. Methods  Axial static ( n  = 3) and dynamic testing ( n  = 3) was performed on three distraction plates designs: bridge plate 1 (BP1) with central holes, bridge plate 2 (BP2) without central holes, and locking compression plate (BP3). Plates were loaded in axial compression with a simulated 10-mm fracture gap. Results  Significant static load differences were noted between all groups. Static load to failure for BP1, BP3, and BP2 were 240 ± 5 N, 398 ± 9 N, and 420 ± 3 N, respectively ( p  < 0.05). BP1 was the only plate series that failed during dynamic testing; all other plates achieved 100,000 cycles. Failure mode was a fracture occurring through the central screw hole of BP1. Finite element analysis demonstrated the effects of central screw holes on stress, strain, and plastic deformation under loading. Conclusion  Unused screw holes are the mechanical weak points; plates designed without these central screw holes are expected to survive greater load values. The threshold for clinical importance will need to be determined by future studies.

Improvement of clinical fracture healing - What can be learned from mechano-biological research?

The most significant predictors of reoperation following operative management of fractures are the presence of a third degree open fracture, remaining fracture gaps and a transverse fracture. However clinical studies provide no information regarding the involvement of various soft tissues or how the mechanical environment affects revascularisation and bone healing. Here the results of experimental and numerical mechano-biological studies on fracture healing are summarized to provide guidance toward clinical treatment of fractures. In experimental studies, isolated muscle crush appeared to only temporarily impair fracture healing, with no significant effect to the final bone healing, whereas a more severe muscle trauma significantly reduced callus formation and biomechanical properties of the healed bones. An intraoperative trauma can furthermore impede vascularization. Surgical removal of the haematoma or periosteum disturbs fracture healing. While reaming for intramedullary nailing reduced blood flow in the bone during the early phase of bone healing, it did not affect the stiffness or strength of the final bone healing. The optimal conditions for rapid vascularization and bone healing result from fracture fixation that minimizes shearing movements in the healing zone while allowing moderate compressive movements. Bone healing is increasingly delayed with increasing fracture gap size and critical-size defects do not heal sufficiently independent of the mechanical environment. The stiffness of fracture fixation systems like nails and external fixators applied in clinical treatments frequently display a too low stiffness, whereas plate systems often cause a too stiff fixation that suppresses bone healing.

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.

Effects of Bone-Plate Material on the Predicted Stresses in the Tibial Shaft Comminuted Fractures: A Finite Element Analysis

PURPOSE

In this research, low modulus carbon fiber (CF)-reinforced polyetheretherketone composite plates (CF-PEEK plates) were compared with traditional metal plates using finite element analysis to establish a reference for clinical application.

MATERIAL AND METHODS

Plates of stainless steel, titanium alloy (Ti6Al4V), or CF-PEEK with different carbon fiber reinforcement ratios (CF30, CF50, and CF60) were used to fix the tibial shaft comminuted fracture. The maximum stress, the maximum displacement of fracture and the stress shielding of cortex bone were analyzed.

RESULTS

Under 200 N axial compression, the maximum displacement was measured in the CF30 plate (4.62 mm) and the minimum in the stainless steel plate (0.23 mm). The stress shielding rates of stainless steel, titanium, CF30, CF50, and CF60 plates were 59.4%, 54.4%, 23.75%, 48.75% and 66.25%. Under 700 N axial compression, the internal fixation by the CF30 plate failed. Among the other 4 plates, the maximum displacement was measured in the CF50 plate (2.52 mm) and the minimum in the stainless steel plate (0.78 mm). The stress shielding rate of plates made of stainless steel, titanium, CF50, and CF60 were 57.1%, 52.0%, 48.1%, and 67.8%.

CONCLUSIONS

CF50 plates can be safely used in the tibial shaft comminuted fracture. The micromotion in the CF50 and CF60 plate was more beneficial to callus formation and fracture healing. The stress shielding of the cortex bone under the CF50 plate was the lowest. The finite element analysis indicated that the CF-PEEK material is worthy of further study because of its biomechanical advantages.

Imaging Modalities to Assess Fracture Healing

PURPOSE OF REVIEW

This review discusses imaging modalities for fracture repair assessment, with an emphasis on pragmatic clinical and translational use, best practices for implementation, and challenges and opportunities for continuing research.

RECENT FINDINGS

Semiquantitative radiographic union scoring remains the clinical gold standard, but has questionable reliability as a surrogate indicator of structural bone healing, particularly in early-stage, complex, or compromised healing scenarios. Alternatively, computed tomography (CT) scanning enables quantitative assessment of callus morphometry and mechanics through the use of patient-specific finite-element models. Dual-energy X-ray absorptiometry (DXA) scanning and radiostereometric analysis (RSA) are also quantitative, but technically challenging. Nonionizing magnetic resonance (MR) and ultrasound imaging are of high interest, but require development to enable quantification of 3D mineralized structures. Emerging image-based methods for quantitative assessment of bone healing may transform clinical research design by displacing binary outcomes classification (union/nonunion) and ultimately enhance clinical care by enabling early nonunion detection.

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.

Hardware considerations in infection and nonunion management: When and how to revise the fixation

The occurrence of both nonunion and fracture-related infection provides challenges for both the patient and the treating orthopaedic surgeon, with the potential need for complex reconstructive procedures to achieve union and/or eradicate infection. In addition to addressing the multiple different factors that often contribute to nonunion, surgeons are often forced to deal with difficult hardware issues at the time of revision surgery including infected hardware, loose or failing hardware, malaligned hardware, or inappropriate hardware constructs. This article reviews common causes of nonunions with emphasis on infection management and provides indications and techniques for hardware removal in the context of an algorithmic approach to nonunion management with illustrative case examples.