Failure of fracture plate fixation

Beyond Textbooks: Interactive Learning of Biomechanical Principles of Osteosynthesis with an Online Tool for Orthopaedic Residents

OBJECTIVES

This study aimed at evaluating the effectiveness of an online interactive biomechanical teaching tool called OSapp. Our main hypothesis was that through the presentation of appropriate science-based content in an interactive, self-directed learning environment familiar to residents the OSapp could significantly improve the knowledge, comprehension, and retention of clinically relevant biomechanical principles of osteosynthesis.

DESIGN

Thirty-one orthopaedic residents from the same institution were enrolled. Their knowledge of basic biomechanical principles of osteosynthesis was assessed using 24 multiple-choice questions, in 3 assessment rounds: at baseline; directly after a 1-week self-directed OSapp-based learning period; and 2 months later to measure retention. Results of the junior (1-3 years) and senior (4-5 years) resident groups were compared.

SETTING

Orthopaedics and Traumatology Department, Italian Hospital of Buenos Aires, Argentina.

PARTICIPANTS

Orthopaedic residents of the same Department at the time of investigation, including residency years 1 to 5.

RESULTS

Twenty-eight participants completed all 3 assessment rounds. Assessment scores significantly improved after the intervention compared to baseline (p < 0.05) and did not decline after 2 months (p > 0.99). Both juniors and seniors showed significant knowledge gain (p < 0.05) that was retained (p > 0.99). Although seniors were better than juniors at baseline (p ≤ 0.01) and postintervention (p < 0.05), after the intervention, juniors reached the level of baseline seniors (p > 0.21). No difference was observed between the 2 groups after 2 months (p > 0.21).

CONCLUSIONS

Self-directed learning with the interactive 3D models available in the freely available online tool OSapp led to a significant and sustained improvement of residents' knowledge and understanding of the biomechanical principles of osteosynthesis. Utilizing OSapp in surgical education could help to improve the efficiency and effectiveness of training and may thus lead to decreased fracture treatment complications including failure of osteosyntheses.

Mechanically compliant locking plates for diaphyseal fracture fixation: A biomechanical study

Axial micromotion between bone fragments can stimulate callus formation and fracture healing. In this study, we propose a novel mechanically compliant locking plate which achieves up to 0.6 mm of interfragmentary motion as flexures machined into the plate elastically deflect under physiological load. We investigated the biomechanical performance of three compliant plate variations in comparison to rigid control plates with small and large working lengths in a comminuted bridge plating scenario using humeral diaphysis surrogates. Under static axial loading, average interfragmentary motion was 6 times larger at 100 N (0.38 vs. 0.05 mm) and nearly three times larger at 350 N (0.58 vs. 0.2 mm) for compliant plates than rigid plates, respectively. Compliant plates delivered between 2.5 and 3.4 times more symmetric interfragmentary motion than rigid plates (p < 0.01). The bi-phasic stiffness of compliant pates provided 74%-96% lower initial axial stiffness up to approximately 100 N (p < 0.01), after which compliant plate stiffness was similar to rigid plates with increased working length (p > 0.3). The strength to failure of compliant plates under dynamic loading was on average 48%-55% lower than rigid plate groups (p < 0.01); however, all plates survived cyclic fatigue loading of 100,000 cycles at 350 N. This work characterizes the improvement in interfragmentary motion and the reduction in strength to failure of compliant plates compared to control rigid plates. Compliant plates may offer potential in comminuted fracture healing due to their ability to deliver symmetric interfragmentary motion into the range known to stimulate callus formation while surviving moderate fatigue loading with no signs of failure.

Increased risk of adverse events following the treatment of associated versus elementary acetabular fractures: a matched analysis of short-term complications

PURPOSE

This retrospective cohort study aims to compare short-term complication rates between patients receiving open reduction and internal fixation (ORIF) for associated versus elementary acetabular fractures, with a secondary objective of identifying independent risk factors for adverse outcomes.

METHODS

The American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) database was queried using current procedural terminology (CPT) codes to identify patients that underwent ORIF for associated acetabular (CPT 27228) or elementary acetabular fractures (CPT 27226, 27227) from 2010 to 2021. Propensity score matching was employed to account for baseline differences and the short-term complication rates were compared between the cohorts.

RESULTS

We identified 1,330 patients who underwent ORIF for an acetabular fracture between 2010 and 2021, including 868 patients with elementary fractures and 462 with associated fractures. After matching, there were 462 patients in each cohort. The matched associated acetabular fracture group experienced higher rates of any adverse event (AAE, p = 0.029), transfusion (p = 0.010), and reoperation (p = 0.049). Increased age, increased operative time, higher body mass index (BMI), and prolonged hospital length of stay (LOS) augmented the risk of any complication.

CONCLUSION

The findings of this study identify areas of greater risk of postoperative complications after ORIF in individuals with associated versus elementary acetabular fractures. Discussion of these heightened risks is critical to appropriate patient care. Understanding these risks plays an important role in the clinical decision-making process and may identify areas to monitor patients postoperatively.

Improving Patient Recall Following Operative Orthopaedic Trauma

BACKGROUND

Orthopaedic trauma patients may experience poor recall regarding their injury and treatment, impairing postoperative outcomes. We sought to evaluate the impact of a standardized postoperative educational protocol on patient recall, adherence to the treatment plan, and satisfaction.

METHODS

Two hundred and twenty adult, English-speaking patients with surgically treated lower-extremity fractures were prospectively included. One hundred and ten patients in the educational intervention cohort met with a non-physician study member after surgery but before hospital discharge. They were given a written questionnaire evaluating knowledge of key aspects of their injury and treatment plan. For incorrectly answered questions, the study team member told the patient the correct answer (e.g., "No, you broke your tibia."). Immediately after, the patient was verbally asked the question again (e.g., "Which bone did you break?"), repeating the process until the answer was correct. The 110 patients in the control cohort did not receive this "teach-back" protocol. During their first postoperative appointment, all 220 patients completed a follow-up questionnaire assessing recall, adherence to the treatment plan, and satisfaction.

RESULTS

The control cohort correctly answered 64% of recall-oriented questions versus 89% in the intervention cohort (p < 0.001). Eighty-two percent of control patients versus 89% patients in the intervention cohort adhered to postoperative weight-bearing restrictions (p = 0.09). Eighty-four percent of controls adhered to their deep venous thrombosis prophylaxis regimen versus 99% of the intervention cohort (p < 0.001). On a 5-point Likert scale, controls were less satisfied with their overall orthopaedic care compared with patients in the intervention cohort (mean of 4.38 ± 0.84 versus 4.54 ± 0.63 points; p = 0.02), although this difference was less than the minimal clinically relevant difference of 10% that was defined at study onset. On propensity score-weighted multivariable analysis, receipt of the postoperative educational intervention was the only modifiable factor associated with improvement in patient recall (26% improvement [95% confidence interval, 20% to 31%]; p < 0.001).

CONCLUSIONS

Some orthopaedic trauma patients' nonadherence to surgeon recommendations and dissatisfaction with care may be mitigated by postoperative education. This standardized postoperative educational protocol improves orthopaedic trauma patients' recall, adherence to their treatment plan, and satisfaction in a manner requiring minimal time.

LEVEL OF EVIDENCE

Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.

Influence of Screw Angulation on the Mechanical Properties on a Polyaxial Locking Plate Fixation

Polyaxial locking systems are widely used for strategic surgical placement, particularly in cases of osteoporotic bones, comminuted fractures, or when avoiding pre-existing prosthetics. However, studies suggest that polyaxiality negatively impacts system stiffness. We hypothesize that a new plate design, combining a narrow plate with asymmetric holes and polyaxial capabilities, could outperform narrow plates with symmetric holes. Three configurations were tested: Group 1 with six orthogonal screws, and Groups 2 and 3 with polyaxiality in the longitudinal and transverse axes, respectively. A biomechanical model assessed the bone/plate/screw interface under cyclic compression (5000 cycles) and torsion loads until failure. Screws were inserted up to 10° angle. None of the groups showed a significant loss of stiffness during compression (p > 0.05). Group 1 exhibited the highest initial stiffness, followed by Group 3 (<29%) and Group 2 (<35%). In torsional testing, Group 1 achieved the most load cycles (29.096 ± 1.342), while Groups 2 and 3 showed significantly fewer cycles to failure (6.657 ± 3.551 and 4.085 ± 1.934). These results confirm that polyaxiality, while beneficial for surgical placement, reduces biomechanical performance under torsion. Despite this, no group experienced complete decoupling of the screw-plate interface, indicating the robustness of the locking mechanism even under high stress.

Bicortical Compression and Construct Stability With Variable Pitch Locking Screws in Cadaveric Specimens

OBJECTIVES

A variable pitch locking screw is intended to provide interfragmentary compression combined with fixed angle stability of locking plate constructs. The objective of this study was to compare variable pitch locking screws (3.5-mm KreuLock Ti locking compression screws, Arthrex Inc., Naples, FL) with standard locking screws (from the same manufacturer) in bicortical fixation scenarios in cadaver bone by assessing (1) interfragmentary compression and plate-bone compression and (2) construct biomechanical stability.

METHODS

Nine matched pairs of fresh-frozen cadaveric specimens with an average age of 67.2 years (range, 37-83) were used. Interfragmentary compression and plate-bone compression associated with insertion of single bicortical screws were compared between the variable pitch and standard locking screws at increasing levels of torque. The specimens tested were distal tibiae having a simulated longitudinal fracture. Additionally, fibulae were osteotomized to create a stable longitudinal fracture pattern and were fixed with a 5-screw plate construct with either all variable pitch or all standard locking screws. One of the 5 screws was placed across the osteotomy without lagging. Fibulae were tested cyclically with axial with torsional loading to compare displacements, rotation, and loads at failure or tested in 4-point bending to compare construct stiffness and maximum force to failure.

RESULTS

Interfragmentary and plate-bone compression forces in the distal tibia model varied across specimens but were significantly higher with variable pitch locking screws compared with standard locking screws [512 N (SD = 324 N) vs. 79 N (SD = 64 N), P = 0.002, and 242 N (SD = 119 N) vs. 104 N (SD = 123 N), P = 0.028, respectively]. In cyclic loading of fibula constructs, no significant differences were detected in construct axial displacement or angular displacement (P > 0.05). In 4-point bending, no differences were detected in maximum force or bending stiffness (P > 0.05).

CONCLUSIONS

Variable pitch locking screws produced interfragmentary compression between cortices and plate-bone compression that was greater than that produced by standard locking screws. In a stable bicortical fibula fixation scenario under external loading, the stability of variable pitch locking screw constructs was similar to constructs with standard locking screws.

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

BACKGROUND AND OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Comparison of a 2.7-mm and 3.5-mm locking compression plate for ulnar fractures: a biomechanical evaluation

Objectives

Implant prominence after ulnar fracture fixation may be mitigated by the use of lower profile plates. The biomechanical strength and stability of 2.7-mm and 3.5-mm locking compression plates for fixation were compared.

Methods

Two fracture conditions, transverse (N = 10) and oblique (N = 10), were evaluated in an in vitro study. Half of the specimens for each condition were fixed with 2.7-mm plates and the other half with 3.5-mm plates, all fixed with conventional dynamic compression mechanisms. Specimens were loaded under ±2 Nm of cyclic axial torsion, then under 10 Nm of cyclic cantilever bending, and bending to failure. Interfragmentary motion and strain were analyzed to determine construct stability as a function of fracture pattern and plate size.

Results

Interfragmentary motion was significantly larger in all constructs fixed with 2.7-mm plates, compared with 3.5-mm plates (P < 0.01). The 2.7-mm constructs with transverse fractures had the greatest motion, ranging between 5° and 10° under axial rotation and 5.0-6.0 mm under bending. Motions were the lowest for 3.5-mm constructs with oblique fractures, ranging between 3.2 and 4.2 mm under bending and 2°-3.5° for axial rotation. For oblique fractures, the bending moment at ultimate failure was 31.4 ± 3.6 Nm for the 2.7-mm constructs and 10.0 ± 1.9 Nm for 3.5-mm constructs (P < 0.01). Similarly, for transverse fractures, the bending moment was 17.9 ± 4.0 Nm for the 2.7-mm constructs and 9.7 ± 1.3 Nm for the 3.5-mm constructs (P < 0.01).

Conclusions

Although 3.5-mm plates were more effective at reducing fracture motion, they were consistently associated with refracture at the distal-most screw hole under load to failure. By contrast, 2.7-mm plates plastically deformed despite excessive loads, potentially avoiding a subsequent fracture.

Level of Evidence

Level V.

Different internal fixation methods for Hoffa-like fractures of the tibial plateau: a finite element analysis

Due to the low incidence of posteromedial tibial plateau fractures and limited clinical data available, the optimal treatment for this type of fracture remains to be established. This type of fracture, also known as Hoffa-like fracture of the tibial plateau, shares a similar mechanism of injury with the Hoffa fracture of the femoral condyle. In the field of orthopedics, finite element analysis is considered a valuable method to guide clinical decision-making. In this study, four methods used for internal fixation of Hoffa-like fractures of the tibial plateau were compared using computer simulation and applying a finite element method (FEM). The methods compared were lateral L-plate fixation alone (Model A); lateral L-plate combined with posterior anti-slip plate (reconstruction plate/T-plate) fixation (Model B); lateral L-plate combined with posterior hollow nail fixation of the fracture block (Model C); and lateral L-plate combined with anterior hollow nail fixation of the fracture (Model D). The maximum displacement of the model and the maximum stress of the internal fixation material were analyzed by applying an axial load of 2,500 N. The results showed that, in the normal bone model, the maximum displacement of the fracture in Model A was 0.60032 mm, with improved stability through the addition of posterior lateral plate fixation in Model B and reduction of the displacement to 0.38882 mm. The maximum displacement in Model C and Model D was comparable, amounting to 0.42345 mm and 0.42273 mm, respectively. Maximum stress was 1235.6 MPa for Model A, 84.724 MPa for Model B, 99.805 MPa for Model C, and 103.19 MPa for Model D. In the internal fixation analysis of the osteoporotic fracture model, we observed patterns similar to the results of the normal bone model. The results indicated that Model B yielded the overall best results in the treatment of Hoffa-like fractures of the tibial plateau. The orthopedic surgeon may wish to implement these insights into the perioperative algorithm, thereby refining and optimizing clinical patient care. In addition, our findings pave the way for future research efforts.

Biomechanical evaluation of a healed acetabulum with internal fixators: finite element analysis

BACKGROUND

Treatment of complicated acetabular fracture with internal fixation usually has high risk of failure because of unbefitting fixation. However, evaluation of the biomechanical effect of internal fixation under physiological loading for fracture healing is still generally rarely performed. The purpose of this study is to analyze the biomechanical characteristics of a healed acetabulum with designed internal fixators under gait and to explore the biomechanical relationship between the healed bone and the internal fixator.

METHODS

A patient-specific finite element model of whole pelvis with designed internal fixators was constructed based on the tomographic digital images, in which the spring element was used to simulate the main ligaments of the pelvis. And the finite element analysis under both the combination loading of different phases and the individual loading of each phase during the gait cycle was carried out. The displacement, von Mises stress, and strain energy of both the healed bone and the fixation were calculated to evaluate the biomechanical characteristics of the healed pelvis.

RESULTS

Under the combination loading of gait, the maximum difference of displacement between the left hip bone with serious injury and the right hip bone with minor injury is 0.122 mm, and the maximum stress of the left and right hemi-pelvis is 115.5 MPa and 124.28 MPa, respectively. Moreover, the differences of average stress between the bone and internal fixators are in the range of 2.3-13.7 MPa. During the eight phases of gait, the stress distribution of the left and right hip bone is similar. Meanwhile, based on the acetabular three-column theory, the strain energy ratio of the central column is relatively large in stance phases, while the anterior column and posterior column of the acetabular three-column increase in swing phases.

CONCLUSIONS

The acetabular internal fixators designed by according to the anatomical feature of the acetabulum are integrated into the normal physiological stress conduction of the pelvis. The design and placement of the acetabular internal fixation conforming to the biomechanical characteristics of the bone is beneficial to the anatomical reduction and effective fixation of the fracture, especially for complex acetabular fracture.

The comparison of stress and strain between custom-designed bone plates (CDBP) and locking compression plate (LCP) for distal femur fracture

BACKGROUND

Distal femur fracture is considered one of the most common fractures due to high-energy traumas such as car accidents or low-energy traumas such as osteoporosis. Locking plates are orthopedic implants used for stabilized femur fracture. Thus, designing a bone plate fitted exactly with the patient's bone and correctly fixing bone segments are required for better fracture healing.

OBJECTIVES

This study aims to design a bone plate based on anthropometric characteristics of patients' femurs and compare performing custom-designed bone plates (CDBP) with the locking compression plate (LCP) by finite element method.

MATERIALS AND METHODS

In this analytical study, a 3D model of four patients' femur and CDBP were firstly designed in MIMICS 19.0 based on the patient's femur anatomy. After designing the bone plate, the CDBPs and LCP were fixed on the bone and analyzed by finite element method (FEM) in ANSYS, and stress and strain of bone plates were also compared.

RESULTS

The maximum principal stress for all 3D models of patients' fracture femur by CDBPs was stabilized better than LCP with a decrease by 39.79, 12.54, 9.49, and 20.29% in 4 models, respectively. Also, in all models, the strain of CDBPs is less than LCP. Among the different thicknesses considered, the bone plate with 5 mm thickness showed better stress and strain distribution than other thicknesses.

CONCLUSION

Customized bone plate designed based on patient's femur anatomical morphology shows better bone-matching plate, resulting in increasing the quality of the fracture healing and fails to any need for additional shaping.

TRIAL REGISTRATION NUMBER

Design and analysis of an implant were investigated in this study. There was no intervention in the diagnosis and treatment of patients and the study was not a clinical trial.

Outcomes of Locking Plate Fixation With Spine Cage for Unstable Proximal Humeral Fractures in Elderly Patients

OBJECTIVE

To compare the clinical and radiological results of locking plate fixation with and without spine cage for the treatment of unstable proximal humeral fractures in elderly patients.

DESIGN

Retrospective study.

SETTING

Level 1 Trauma Center.

PATIENTS/PARTICIPANTS

A total of 62 patients with a mean age of 72.68 (60-88) years were included. Thirty-nine patients were treated with only a locking compression plate (LCP group), whereas 23 patients were treated with a locking compression plate and a spine cage (SC group). The mean follow-up was 32.26 (24-46) months.

MAIN OUTCOME MEASURES

Radiological outcomes were assessed using the humeral head height and neck-shaft angle. The clinical results were evaluated using a visual analog scale for pain, the Constant-Murley score, the American Shoulder and Elbow score, and shoulder range of motion.

RESULTS

The average radiological changes in the humeral head height and neck-shaft angle were significantly higher in the LCP group than in the SC group ( P < 0.001 and P < 0.001, respectively). The final outcome scores were lower in the LCP group than in the SC group (Constant-Murley score of 73.26 vs. 78.91 [ P = 0.028] and American Shoulder and Elbow score of 72.36 vs. 78.57 [ P = 0.011]). The SC group showed better forward elevation ( P = 0.005) and abduction ( P = 0.001); however, no significant differences were observed for shoulder external or internal rotation. The number of complications was higher in the LCP group (38.5%) than in the SC group (13.0%) ( P = 0.033).

CONCLUSIONS

For unstable proximal humeral fractures with medial comminution in elderly patients, locking plate with an SC is a reasonable option to ensure satisfactory results and lower the postoperative complications.

LEVEL OF EVIDENCE

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

Difficult Management of a Femur Fracture in a Patient with Dyskeratosis Congenita: A Literature Review and Case Report

CASE

A 14-year-old boy with dyskeratosis congenita (DKC), status-post unrelated bone marrow transplant (BMT), sustained a femoral shaft fracture. Despite immediate fixation with the widest possible titanium elastic nails, fixation construct rigidity was insufficient and malunion occurred with refracture 5 years later. Revision fixation with rigid intramedullary nailing has maintained position for 1 year, although callus formation remains meager.

CONCLUSION

This is the first article to detail fracture care for a DKC patient. Although BMT increases lifespan, patients seemingly remain skeletally frail. Rigid intramedullary fixation is optimally durable and appears hematopoietically safe. Long-term follow-up is recommended.

A Unique Mode of Failure in the Noncontact Bridging Periprosthetic Plating System

Although lateral locking plates are often a preferred and successful fixation construct for the treatment of periprosthetic proximal and distal femur fractures, specific complications and modes of failure have been associated and well-described with their use. We present two cases of implant failure in the Non-Contact Bridge Periprosthetic Plating System (Zimmer Biomet) in which a nonlocked screw fretted through the annular seating of the plate. One case demonstrates failure in the setting of a proximal femur periprosthetic fracture, whereas the other demonstrates failure in the setting of a distal femur periprosthetic fracture. This unique mode of failure has not previously been reported in the literature.

Fracture Nonunion Treated with Low-Intensity Pulsed Ultrasound and Monitored with Ultrasonography: A Feasibility Study

The positive effect of low-intensity pulsed ultrasound (LIPUS) on bone fracture healing has been proved. However, during the period of LIPUS therapy, it is undetermined whether LIPUS promotes the formation of heterotopic ossification (HO), which usually occurs in muscle tissues after trauma such as bone fracture and spinal cord injury. Here, we used 6-week LIPUS therapy in a 42-year-old Chinese male patient with a fracture nonunion in combination with ultrasonography for monitoring fracture healing and HO formation. After the LIPUS therapy, the mineralized bone formation in the area of defect of the distal tibia was presented in an ultrasound image, which was consistent with the outcome of plain radiography showing callus formation and the blurred fracture line in the area exposed to LIPUS. In addition, ultrasound images revealed no evidence of HO development within soft tissues during the period of LIPUS therapy. This study suggests that ultrasonography is a potential tool to guarantee the performance of LIPUS therapy with monitoring HO formation. Easy to use, the integration of the handheld ultrasound scanner and the ultrasonic therapeutic apparatus is entirely dedicated to help orthopedists make high-quality care and diagnosis.

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.

From creative thinking to scientific principles in clinical practice

Stephan Perren's contributions to the understanding and application of the principles of bone pathobiology, healing, and fracture fixation to clinical care remain as a lasting legacy of a great creative mind. Less well appreciated perhaps were his important contributions to the dissemination and practical application of those principles through the use of technology as applied to the learning environment. This paper describes and pays tribute to a series of initiatives in which Perren was a leading mentor and collaborator in the development of methods and instruments through which the principles of bone mechano-pathobiology could be translated through active learning environments into the practical world of clinical musculoskeletal traumatology.

Contradictory working length effects in locked plating of the distal and middle femoral fractures-a biomechanical study

BACKGROUND

Working length have been reported to affect the plate stress and fixation stiffness. However, the results of previous studies have been controversial. The present study was to determine working length effects on different locations of femoral bone gap.

METHODS

Five composite femurs with wide bone gaps at five levels (G1, 2, 3, 5, and 7), were fixed with locking plates. G1-3, G5 and G7 represented gaps at distal femur, distal-middle femur and middle femur respectively. Strain gauges were applied near the screw holes. The plate-bone constructs were loaded through a hemicylinder on the femoral head with total constraints at the distal femur. The micro-strains, axial stiffness and interfragmentary motions were recorded. Then the locking screws were removed one by one and the tests were re-run. The working length effects were compared and correlated.

FINDINGS

In distal femurs (G1-3), long working length was negatively correlated with the highest strains (r = -0.97, -0.95 and - 0.95, p < 0.01) and axial stiffness (r = -1, -0.96 and -0.99, p < 0.01). In distal-middle femurs (G5), as the working length increased, the highest strain decreased initially and then increased (r = 0.81, p = 0.026) and the axial stiffness decreased (r = -0.98, p < 0.01). In middle femurs (G7), the highest strain and gap motions were much higher than that in the other groups and not significantly correlated with the working length change.

INTERPRETATION

Long working length could reduce the highest plate strain in distal femurs, but had no significant effects in middle femurs. The working length effects were markedly affected by the loading and boundary conditions.

Half-threaded holes markedly increase the fatigue life of locking plates without compromising screw stability

Aims

To determine whether half-threaded screw holes in a new titanium locking plate design can substantially decrease the notch effects of the threads and increase the plate fatigue life.

Methods

Three types (I to III) of titanium locking plates were fabricated to simulate plates used in the femur, tibia, and forearm. Two copies of each were fabricated using full- and half-threaded screw holes (called A and B, respectively). The mechanical strengths of the plates were evaluated according to the American Society for Testing and Materials (ASTM) F382-14, and the screw stability was assessed by measuring the screw removal torque and bending strength.

Results

The B plates had fatigue lives 11- to 16-times higher than those of the A plates. Before cyclic loading, the screw removal torques were all higher than the insertion torques. However, after cyclic loading, the removal torques were similar to or slightly lower than the insertion torques (0% to 17.3%), although those of the B plates were higher than those of the A plates for all except the type III plates (101%, 109.8%, and 93.8% for types I, II, and III, respectively). The bending strengths of the screws were not significantly different between the A and B plates for any of the types.

Conclusion

Removing half of the threads from the screw holes markedly increased the fatigue life of the locking plates while preserving the tightness of the screw heads and the bending strength of the locking screws. However, future work is necessary to determine the relationship between the notch sensitivity properties and titanium plate design.Cite this article: Bone Joint Res 2020;9(10):645-652.

Contouring Plates in Fracture Surgery: Indications and Pitfalls

Effective fracture surgery requires contouring orthopaedic implants in multiple planes. The amount of force required for contouring is dependent on the amount and type of material contained within the plane to be altered. The type of contouring used depends on the desired plate function; for example, buttress mode often requires some degree of undercontouring, whereas compression plating may require prebending. Other reasons to contour a plate include matching patient anatomy either to maximize fixation options or to reduce implant prominence. Precontoured plates can be convenient and help to facilitate soft-tissue friendly techniques but have the potential to introduce malreduction if the plate position and fit are not carefully monitored.

Clinical and patient-reported outcomes following Low Intensity Pulsed Ultrasound (LIPUS, Exogen) for established post-traumatic and post-surgical nonunion in the foot and ankle

BACKGROUND

Biophysical methods including Low Intensity Pulsed Ultrasound (LIPUS) are emerging as potential alternatives to revision surgery for treating established nonunions. We aim to prospectively review the clinical and patient-reported outcomes of patients treated with LIPUS following post-traumatic and post-surgical nonunions in the foot and ankle.

METHODS

Forty-seven consecutive patients underwent Exogen treatment. Patient-reported outcome scores included MOXFQ, EQ-5D and VAS. Patients were divided in to 3 groups: fractures (A), hindfoot procedures (B) and midfoot/forefoot procedures (C).

RESULTS

Thirty-seven patients (78.7%) clinically united, 4 patients (8.5%) noticed no significant improvement but did not want further intervention and 6 patients (12.8%) underwent revision surgery. The mean duration of Exogen treatment was 6 months. Union rates of 93%, 67% and 78% were noted in the three groups. Significant improvement in functional outcomes and potential cost savings were observed.

CONCLUSIONS

Exogen for established nonunion in the foot and ankle is a safe, valuable and economically viable clinical option as an alternative to revision surgery. We observed better results in the fracture and midfoot/forefoot groups and relatively poorer results in the hindfoot fusion group.

Evaluating the reoperation rate and hardware durability of three stabilizing implants for 105 malignant pathologic humerus fractures

INTRODUCTION

Many patients sustaining a malignant pathologic humerus fracture (MPHF) elect for surgical stabilization. Complications prompting reoperation can occur, leading to additional quality of life and financial cost. One common event preceding reoperation is a broken implant (BI). The purpose of this study was to identify the rate of reoperation following surgical stabilization of MPHF with three techniques - photodynamic bone stabilization (PBS), intramedullary nail (IMN), and cemented plate fixation (CPF) - and estimate to what extent improved implant durability might prevent reoperation.

MATERIALS AND METHODS

Retrospective data collection was performed, identifying 105 procedures (100 patients) who underwent non-articular MPHF surgery from 2010-2016: 19 PBS, 65 IMN, 21 CPF. All patients were followed for at least two years or until death.

RESULTS

Reoperation rates were similar at one year (10.5%,6.2%,4.8%, p = 737), two years (15.8%,6.2%,9.5%, p = 375), and final evaluation (15.8%,7.7%,14.3%, p = 248). The rate of BI for PBS, IMN, and CPF was 10.5%,0%, and 4.8% (p = 049 PBS/IMN) at one year, 15.8%,0%, and 9.5% (p = 010 PBS/IMN) at two years, and 15.8%,0%, and 14.3% (p = 010 IMN/PBS, p = 013 IMN/CPF) at final evaluation.

CONCLUSIONS

Reoperation rate was not significantly different at any time point. However, IMN surgery resulted in the lowest rate of broken implants (zero), statistically significant versus PBS at all time periods and versus CPF at final follow-up. PBS may eventually offer selected advantages for MPHF management, but current data suggests fragility must be thoughtfully considered.

Fibular strut allograft influences reduction and outcomes after locking plate fixation of comminuted proximal humeral fractures in elderly patients: a retrospective study

Background

Proximal humeral fractures (PHFs) are the third most commonly occurring fractures in elderly patients. Most of these fractures can be treated with conservative methods, but the optimal surgical treatment strategy for unstable fractures in elderly patients remains controversial. This study aimed to compare the radiological and clinical outcomes between locking compression plate (LCP) fixation and LCP fixation with fibular allograft implantation for the treatment of comminuted PHFs.

Methods

We retrospectively reviewed 60 patients (mean age, 72.75 years) with closed 3- or 4-part fractures, and a minimum of 2 years of follow-up. Fracture reduction was quantitatively determined by humeral head height (HHH) and neck-shaft angle (NSA). The clinical outcome was evaluated by Constant-Murley score (CMS) and American Shoulder and Elbow Surgeons (ASES) score.

Result

The average radiological changes were higher in the LCP group than in the locking plate with fibular allograft group (HHH of 4.16 mm vs 1.18 mm [p < 0.001] and NSA of 9.94° versus 3.12° [p < 0.001]) . The final average outcome scores were lower in the LCP group than in the FA group (CMS of 73.00 vs 78.96 [p = 0.024] and ASES score of 72.80 vs 78.64 [p = 0.022]). The FA group showed better forward elevation (p = 0.010) and abduction (p = 0.002); however, no significant differences were observed for shoulder external rotation or internal rotation. The number of complications was higher in the LCP group (28.57%) than in the FA group (1.2%) (p < 0.001).

Conclusion

For comminuted PHFs in elderly patients, LCP fixation combined with a fibular allograft is reasonable option to ensure satisfactory radiological and clinical outcomes.

Trial registration

ZDYJLY(2018)New-9. Name of registry: IEC for clinical Research of Zhongda Hospital, Affiliated to Southeast University. Date of registration: 2018-05-17.

A New Fastener With Improved Bone-To-Implant Interface Shows Superior Torque Stripping Resistance Compared With the Standard Buttress Screw

OBJECTIVE

The conventional AO buttress screw used for fracture fixation relies on a historic buttress thread design, which is prone to stripping at the bone-implant interface. We hypothesized that a new Bone-Screw-Fastener with an innovative interlocking thread design demonstrates increased resistance to torque stripping forces compared with the buttress screw, without compromising pullout strength.

METHODS

A biomechanical model was established in 6 matched pairs of adult human cadaveric tibiae to test torque resistance between the 3.5 mm Bone-Screw-Fastener and the 3.5 mm cortical AO buttress screw until failure. Uniaxial pullout testing of both screw types was performed as an internal control experiment.

RESULTS

The 3.5 mm Bone-Screw-Fastener had a significantly increased resistance to torque failure compared with the standard 3.5 mm AO buttress screw (P = 0.0145). In contrast to the buttress screws, none of the Bone-Screw-Fasteners stripped from the bone but rather failed at the screwdriver-implant interface in terms of a metal-on-metal failure. The internal control experiments revealed no significant difference in axial pullout strength between the 2 implants (P = 0.47).

CONCLUSIONS

These data demonstrate the superiority of the new Bone-Screw-Fastener over the conventional AO buttress screw regarding protection from torque stripping forces. In addition, the new thread design that interlocks to the bone does not sacrifice axial pullout resistance conveyed by the buttress screw. Future controlled trials will have to validate the in vivo relevance of these findings in a clinical setting.

Outcomes of locking plate fixation with fibular allograft augmentation for proximal humeral fractures in osteoporotic patients

Aims

The aim of this study was to evaluate the clinical and radiological outcomes of locking plate fixation, with and without an associated fibular strut allograft, for the treatment of displaced proximal humeral fractures in elderly osteoporotic patients.

Patients and Methods

We undertook a retrospective comparison of two methods of fixation, using a locking plate without an associated fibular strut allograft (LP group) and with a fibular allograft (FA group) for the treatment of these fractures. The outcome was assessed for 52 patients in the LP group and 45 in the FA group, with a mean age of 74.3 years (52 to 89), at a mean follow-up of 14.2 months (12 to 19). The clinical results were evaluated using a visual analogue scale (VAS) score for pain, the Constant score, the American Shoulder and Elbow Surgeons (ASES) score, and the range of movement. Radiological results were evaluated using the neck-shaft angle (NSA) and humeral head height (HHH).

Results

The mean forward elevation in the LP and FA groups was 125.3° (sd 21.4) and 148.9° (sd 19.8), respectively (p = 0.042), while other clinical factors showed no statistically significant differences between the groups. The changes in NSA and HHH immediately after the operation and at final follow-up were significantly better in the FA group than in the LP group (p = 0.015 and p = 0.021, respectively).

Conclusion

For comminuted proximal humeral fractures in osteoporotic patients, locking plate fixation with a fibular strut allograft shows satisfactory short-term results with respect to humeral head support and maintenance of reduction, and may reduce the incidence of complications associated with fixation using a locking plate alone. Cite this article: Bone Joint J 2019;101-B:260–265.

Malalignment in plate osteosynthesis

The aim for this review is to present general considerations in relation to malalignment after osteosynthesis with plate fixation and its consequences after fractures in adults in each of the following anatomical locations: humerus, forearm, femur, tibia. Recommendations for accepted malalignment in humerus diaphyseal fracture is varus <20 degrees, valgus <15 degrees, sagittal deformity <5 degrees and rotation <30 degrees. Recommendations when treating fractures of the forearm is anatomical reduction. Varus of ulna leads to loss of pronation. Valgus of ulna leads to loss of both pronation and supination. Recommendations for acceptable malalignment in femoral fractures is rotational deformity <15 degrees, increasing varus deformity in intertrochanteric fractures increases load on implant. Cortical-step-sign, profile of lesser trochanter, evaluation of ipsilateral neck anteversion are intraoperative methods to avoid rotational malalignment. Recommendations for accepted malalignment in the tibia is shortening <10mm, varus/valgus <5 degrees, sagittal deformity <10 degrees. Fixation of fibula leads to less rotational and valgus malalignment, but not enough to affect union rate of tibia, complications rate or functional score at 12 months. To avoid malalignment in plating, pre-contoured anatomical plates are available from most manufactures. Being aware that most such plates fit a 50-percentile Caucasian population is important in pre-surgical planning. Evaluation of the contralateral bone and the characteristics of the plate may help in planning additional bending of pre-shaped plates and bending tools should always be available when applying a plate, even a so-called anatomical one.

Modification of the screw hole structures to improve the fatigue strength of locking plates

BACKGROUND

The fatigue fracture of locking plates can substantially threaten fracture treatment results. In the present study, three measures for modifying the screw hole structures of plates were implemented to improve their fatigue strength.

MATERIALS

Custom-made identical titanium locking plates, except the screw hole configurations, were tested using four-point bending load. The three measures were partial removal of screw threads on the tension side of the plates, reduction of screw hole size, and modification of the thread radii. There were six types of plates: control (Type I), half of the threads removed (Type II) or one-third of the threads (Type III), smaller screw holes (Type IV), and increase of the thread root radii (Type V) or crest radii (Type VI).

FINDINGS

Compared with the control, Types II and III significantly improved the fatigue strength (14.5 and 10.1 times, respectively). Decreasing the size of the screw hole (Type IV) also yielded a higher fatigue strength (17.6%). Type VI significantly improved the fatigue strength (9.8 times). However, Type V decreased the fatigue strength (14%). For cyclic stiffness, Type IV was significantly higher than other types statistically. Failure analyses showed typical fatigue fracture in all plates and the cracks were always initiated at the thread crest.

INTERPRETATIONS

The fatigue strength of titanium locking plates can be significantly improved by structural changes in the screw holes. Removing the threads of the plates and increasing the crest radii of the threads were more effective measures than decreasing the size of the screw holes.

Placing a threaded plug in the hole of a locking plate at the fracture level can increase the resistance of the plate: A biomechanical study

Objectives: This study aimed to evaluate whether placing a threaded plug in the hole of a locking plate at the fracture level is beneficial for increasing the resistance of the plate. Methods: This experimental study analyzed load and compression forces in sheep tibia bone models. The following groups were assessed: Group 1 (n = 4), control bone samples; Group 2 (n = 4), samples of screw plate fixation without threaded plug in the hole at the fracture level; and Group 3 (n = 4), samples of screw plate fixation with a threaded plug in the hole at the fracture level. Elastic force, bending moment, elastic compression, and rigidity were evaluated using a three-point bending test. Results: Group 1 showed the greatest elastic force and the least amount of compression. The rigidity and elastic force were better in Group 3 than in Group 2. The mean elastic force in Group 3 was 22.4% of that in Group 1, whereas the mean elastic force in Group 2 was 19% of that in Group 1. Rigidity in Group 3 was 24.7% of that in Group 1, whereas rigidity in Group 2 was 18.3% of that in Group 1. Improved results were obtained in Group 3 when compared with Group 2. Conclusions: Our results suggest that placing a threaded plug in the hole of the plate at the fracture level provides additional rigidity and stability by improving resistance to loading forces, but the differences were not statistically significant.

Optimization of screw fixation in rat bone with extracorporeal shock waves

Screw fixation in osteoporotic patients is becoming an increasing problem in orthopaedic surgery as deterioration of cortical and cancellous bone hamper biomechanical stability and screw fixation. This might result in delayed weight-bearing or failure of instrumentation. We hypothesized that local peri-operative shock wave treatment can optimize osseointegration and subsequent screw fixation. In eight female Wistar rats, two cancellous and two cortical bone screws were implanted in both femora and tibiae. Immediately after implantation, 3.000 unfocused extracorporeal shock waves (energy flux density 0.3 mJ/mm² ) were applied to one side. The other side served as non-treated internal control. Evaluation of osseointegration was performed after 4 weeks with the use of microCT scanning, histology with fluorochrome labeling, and pull-out tests of the screws. Four weeks after extracorporeal shock wave treatment, treated legs exhibited increased bone formation and screw fixation around cortical screws as compared to the control legs. This was corroborated by an increased pull-out of the shock wave treated cortical screws. The cancellous bone screws appeared not to be sensitive for shock wave treatment. Formation of neocortices after shock wave therapy was observed in three of eight animals. Furthermore, de novo bone formation in the bone marrow was observed in some animals. The current study showed bone formation and improved screw fixation as a result of shock wave therapy. New bone was also formed at locations remote from the screws, hence, not contributing to screw fixation. Further, research is warranted to make shock wave therapy tailor-made for fracture fixation. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:76-84, 2018.

Influence of the number and position of stripped screws on plate-screw construct biomechanical properties

INTRODUCTION

Screw stripping is a common situation in fracture fixation, particularly in osteopenic bone treatment. Surgeons' perception of screw stripping is relatively poor and the real number of loose screws in every plate-screw construct is unknown. The biomechanical and clinical implications of the different possible screw-stripping situations are also unidentified. In this study, construct stiffness in different scenarios of stripped screws is investigated.

METHOD

A bone surrogate comminuted osteoporotic fracture was fixed with four screws in both sides of the fracture gap in 75 specimens. In four groups, one or two screws closest or distal to the gap were over-tightened and left in place in one part of the construct and the remaining screws were tightened with 0.3N m torque (four groups). In the fifth group (control), all the screws were tightened with 0.3N m torque. Construct stiffness was tested in terms of compression, bending, and torsion for 1000 cycles.

RESULTS

When one or two screws closest to the gap were stripped, stiffness only decreased by, respectively, 5.7% or 7.6% under compression and 4.7% or 6.7% under bending; however, stiffness in torsion was 15.1% or 32%, respectively, lower than the initial stiffness. When a screw distal to the gap was stripped, the stiffness decreased by 28% under bending and 10% under compression; no change was noted under torsion. When two screws distal to the gap were stripped, the stiffness decreased by 11% in compression, collapsed under bending, and decreased by 8% under torsion.

CONCLUSIONS

Position and number of stripped screws affect the biomechanical properties of a construct in different ways, depending on the acting forces.

Presence of Failed Fracture Implants in Association With Lower Extremity Long Bone Nonunion Does Not Portend Worse Outcome After Nonunion Repair

OBJECTIVE

The purpose of this study was to determine whether the finding of failed fracture implants in association with lower extremity long bone fracture nonunion portends worse clinical or functional outcome after surgical nonunion repair.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

Academic Medical Center.

PATIENTS

One hundred eighty-one patients who presented to our institution over a 10-year period and underwent surgical repair of a lower extremity fracture nonunion.

INTERVENTION

Surgical repair of lower extremity fracture nonunion.

MAIN OUTCOME MEASUREMENTS

Time to union, postoperative complications, visual analog scale pain scores, and Short Musculoskeletal Function Assessment scores after lower extremity nonunion repair. Data were analyzed to assess for differences in postoperative outcomes based on the integrity of fracture implants at the time of nonunion diagnosis. Implant integrity was defined using 3 groups: broken implants (BI), implants intact (II), and no implants (NI).

RESULTS

There was no significant difference in time to union after surgery between the BI, II, or NI groups (mean 8.1 months vs. 7.6 months vs. 6.2 months, respectively). Fourteen patients (7.7%) failed to heal, including 5 BI patients, 7 II patients, and 2 NI patients. One tibial nonunion patient in each of the 3 groups underwent amputation for persistent nonunion after multiple failed revision attempts at a mean of 4.8 years after initial injury. There was no difference in postoperative pain scores, the rate of postoperative complications, or functional outcome scores identified between the 3 groups.

CONCLUSIONS

The finding of failed fracture implants at the time of lower extremity long bone nonunion diagnosis does not portend worse clinical or functional outcome after surgical nonunion repair. Patients who present with failed fracture implants at the time of nonunion diagnosis can anticipate similar time to union, complication rates, and functional outcomes when compared with patients who present with intact implants or those with history of nonoperative management.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Treatment of comminuted proximal humeral fractures using locking plate with strut allograft

BACKGROUND

This study compared the radiologic outcome of fixation using locking plate only with fixation using locking plate with an endosteal strut allograft in the treatment of comminuted proximal humeral fracture.

METHODS

Among 52 patients with comminuted proximal humeral fracture, 32 patients underwent fixation with locking plate only, and 20 patients underwent fixation using locking plate with an endosteal strut allograft. The strut allograft was inserted into the intramedullary cavity of the humerus to support the humeral head and fixed with the locking plate. Immediate postoperative radiologic findings were compared with those of 6 months or more after the surgery, and loss of anatomic fixation was defined if the varus malalignment of neck-shaft angle (NSA) was more than 5° or if the change of humeral head height (HHH) was more than 3 mm.

RESULTS

In the locking plate-only group, 22 of 32 patients (69%) showed the change in NSA of more than 5°, with an average of 10.2°. The HHH change in 20 patients (62.5%) was more than 3 mm, with an average of 4 mm. Among 20 patients who underwent locking plate with the endosteal strut allograft, the average NSA and HHH change was 3° and 1 mm, respectively. Varus malalignment was evident in 2 patients (10%). The HHH change was more than 3 mm in 1 patient (5%).

CONCLUSION

Fixation using a locking plate with an endosteal strut allograft can be considered a reasonable option to maintain the anatomic reduction in elderly patients with comminuted proximal humeral fracture.

Are there too many screw holes in plates for fracture fixation?

Background

Implant breakage after the fixation of traumatic fractures is rare; however, when it occurs, it is debilitating for the patients and a challenge for surgeons. The purpose of this study was to analyze and identify the independent risk factors for implant breakage of traumatic fractures treated with plate osteosynthesis.

Methods

We reviewed the medical records of patients with a fracture to any part of their four extremities, clavicle, hand or foot, who underwent surgical plate osteosynthesis from January 2005 to January 2015, and who sustained a subsequent implant breakage. Kaplan–Meier univariate and multivariate Cox regressions were performed to identify independent associations of potential risk factors for implant breakage in this cohort.

Results

We identified 168 patients who underwent plate osteosynthesis surgery and had subsequent internal fixator breakage. The mean patient age was 40.63 ± 16.71 years (range, 3 to 78 years), with 72.0% (121) males and 28.0% (47) females. The average time between surgery and implant breakage was 12.85 ± 12.42 months (range, 1 to 60 months). In the final regression model, we show that inserting screws close to the fracture line is an independent predictive risk factor for implant breakage (HR, 2.165, 95%CI, 1.227 to 3.822; P = 0.008).

Conclusions

We found that inserting screws close to the fracture line is related to an increased risk of internal fixator breakage in patients treated with plate osteosynthesis after fracture. Plates with additional holes likely lead to an increased risk of implant breakage, presumably because surgeons cannot resist inserting extra screws into the holes adjacent to the fracture line, which reduces the stiffness of the plate. We have addressed this problem by designing a plate without holes adjacent to the fracture line.

Age-related optimization of screw placement for reduced loosening risk in locked plating

When using locked plating for bone fracture fixation, screw loosening is reported as one of the most frequent complications and is commonly attributed to an incorrect choice of screw configuration. Choosing a patient-optimized screw configuration is not straightforward as there are many interdependent variables that affect device performance. The aim of the study was to evaluate the influence that locking screw configuration has on loosening risk and how this is influenced by bone quality. This study uses finite element models that incorporate cortical bone heterogeneity, orthotropy, and geometrical nonlinearity to examine the effect of screw configuration on variables associated with loosening and interfragmentary motion. Strain levels within the bone were used as indicators of regions that may undergo loosening. The study found that, in healthy bone under axial loading, the most important variables influencing strain levels within the bone were the size of the bridging span (working length) and the plate rigidity. Unlike healthy bone, osteoporotic bone was found to be particularly sensitive to the spacing of the screws within the plate. Using two empty screw holes between the screws closest to the fracture was found to reduce the strain levels at the first screw by 49% in osteoporotic bone (compared to only 2.4% in healthy bone). The study also found that under torsional loading the total number of screws used was the most important variable with a 59% reduction in the strain around the screws closest to the fracture when using six rather than four screws in osteoporotic bone. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1856-1864, 2016.

Finite Element-Derived Surrogate Models of Locked Plate Fracture Fixation Biomechanics

Internal fixation of bone fractures using plates and screws involves many choices-implant type, material, sizes, and geometric configuration-made by the surgeon. These decisions can be important for providing adequate stability to promote healing and prevent implant mechanical failure. The purpose of this study was to develop mathematical models of the relationships between fracture fixation construct parameters and resulting 3D biomechanics, based on parametric computer simulations. Finite element models of hundreds of different locked plate fixation constructs for midshaft diaphyseal fractures were systematically assembled using custom algorithms, and axial, torsional, and bending loadings were simulated. Multivariate regression was used to fit response surface polynomial equations relating fixation design parameters to outputs including maximum implant stresses, axial and shear strain at the fracture site, and construct stiffness. Surrogate models with as little as three regressors showed good fitting (R ² = 0.62-0.97). Inner working length was the strongest predictor of maximum plate and screw stresses, and a variety of quadratic and interaction terms influenced resulting biomechanics. The framework presented in this study can be applied to additional types of bone fractures to provide clinicians and implant designers with clinical insight, surgical optimization, and a comprehensive mathematical description of biomechanics.

Biomechanical effect of the configuration of screw hole style on locking plate fixation in proximal humerus fracture with a simulated gap: A finite element analysis

BACKGROUND

Locking plate fixation for proximal humeral fractures is a commonly used device. Recently, plate breakages were continuously reported that the implants all have a mixture of holes allowing placement of both locking and non-locking screws (so-called combi plates). In commercialized proximal humeral plates, there still are two screw hole styles included "locking and dynamic holes separated" and "locking hole only" configurations. It is important to understand the biomechanical effect of different screw hole style on the stress distribution in bone plate.

METHODS

Finite element method was employed to conduct a computational investigation. Three proximal humeral plate models with different screw hole configurations were reconstructed depended upon an identical commercialized implant. A three-dimensional model of a humerus was created using process of thresholding based on the grayscale values of the CT scanning of an intact humerus. A "virtual" subcapital osteotomy was performed. Simulations were performed under an increasing axial load. The von Mises stresses around the screw holes of the plate shaft, the construct stiffness and the directional displacement within the fracture gap were calculated for comparison.

RESULTS

The mean value of the peak von Mises stresses around the screw holes in the plate shaft was the highest for combi hole design while it was smallest for the locking and dynamic holes separated design. The stiffness of the plate-bone construct was 15% higher in the locking screw only design (132.6N/mm) compared with the combi design (115.0N/mm), and it was 4% higher than the combi design for the locking and dynamic holes separated design (119.5N/mm). The displacement within the fracture gap was greatest in the combi hole design, whereas it was smallest for the locking hole only design.

CONCLUSIONS

The computed results provide a possible explanation for the breakages of combi plates revealed in clinical reports. The locking and dynamic holes separated design may be a better configuration to reduce the risk of plate fracture.

Role of the compression screw in the dynamic hip-screw system: A finite-element study

The dynamic hip-screw (DHS) system is a common implant for fixation of proximal femur fractures. During assembly, it has been recommended to remove the compression screw after initial compression has been obtained; however, related complications had been reported. So far, the role of compression screw in the reconstructed stability of hip fractures as well as the mechanical strength of the DHS system has rarely been mentioned. This study investigated the function of this screw in the DHS system during fracture healing. Based on the FE method, six numerical models of proximal femur were employed to analyze the mechanical response of a DHS implant with various fracture types and different fixation strategies (with or without a compression screw). The displacement of the femur head and peak von Mises stress were selected as indices of the stability of a fractured femur stabilized by a DHS device and of the risk of implant failure, respectively. Our results showed that a retained compression screw increased reconstructed structural stiffness, reducing the displacement of the femur head. This screw also helped to lessen mechanical failure of side plate by reducing the peak von Mises stress around the connection between the barrel and side plate. Both findings were evident in the proximal femur fracture involving the intertrochanteric part, and even more obvious in the setting of bony defects. Thus, we recommend the maintenance of compression screw in the DHS system while treating the intertrochanteric fracture, particularly in cases with bony defects.

Treatment of chronic (>1 year) fracture nonunion: heal rate in a cohort of 767 patients treated with low-intensity pulsed ultrasound (LIPUS)

BACKGROUND

Established fracture nonunions rarely heal without secondary intervention. Revision surgery is the most common intervention, though non-surgical options for nonunion would be useful if they could overcome nonunion risk factors. Our hypothesis is that low-intensity pulsed ultrasound (LIPUS) can enhance heal rate (HR) in fractures that remain nonunion after one year, relative to the expected HR in the absence of treatment, which is expected to be negligible.

METHODS

We collated outcomes from a prospective patient registry required by the U.S. Food & Drug Administration. Patient data were collected over a 4-year period beginning in 1994 and were individually reviewed and validated by a registered nurse. Patients were only included if they had four data points available: date when fracture occurred; date when LIPUS treatment began; date when LIPUS treatment ended; and a dichotomous outcome of healed vs. failed, assessed by clinical and radiological criteria. Data were used to calculate two derived variables: days to treatment (DTT) with LIPUS, and days on treatment (DOT) with LIPUS. Every validated chronic nonunion patient (DTT>365 days) with complete data is reported.

RESULTS

Heal rate for chronic nonunion patients (N=767) treated with LIPUS was 86.2%. Heal rate was 82.7% among 98 patients with chronic nonunion ≥5 years duration, and 12 patients healed after chronic nonunion >10 years (HR=63.2%). There was more patient loss to follow-up, non-compliance, and withdrawal, comparing chronic nonunion patients to all other patients (p<0.0001). Patient age was the only factor associated with failure to heal among chronic nonunions (p<0.004). Chronic nonunion patients averaged 3.1 surgical procedures prior to LIPUS, but some LIPUS-treated patients were able to heal without revision surgery. Among 91 patients who received LIPUS ≥90 days after their last surgery, HR averaged 85.7%, and the time from last surgery to index use of LIPUS averaged 449.6 days.

CONCLUSIONS

Low-intensity pulsed ultrasound enhanced HR among fractures that had been nonunion for at least 1 year, and even healed fractures that had been nonunion >10 years. LIPUS resulted in successful healing in the majority of nonunions without further surgical intervention.

Management of distal femur fractures with modern plates and nails: state of the art

Fractures of the distal femur, even those with articular extension, are well suited to surgical fixation with modern precontoured anatomic plates and nails. Numerous adjuvant techniques are available to the treating surgeon to obtain and maintain reduction while preserving fracture biology. Yet despite their proven track record and benefits over older implants, technical errors are common and must be overcome with proper preoperative planning and intraoperative attention to detail. This review summarizes the current state of the art regarding distal femur fractures, with an emphasis on relevant modern plate and nail surgical techniques, tempered by our current understanding of implant biomechanics, fracture healing, and long-term outcomes.

Functionalization of titanium implants using a modular system for binding and release of VEGF enhances bone-implant contact in a rodent model

AIMS

To test the immobilization of vascular endothelial growth factor (VEGF165 ) on the surface of titanium implants using DNA oligonucleotide (ODN) anchor strands for the ability to enhance periimplant bone formation.

MATERIALS AND METHODS

DNA oligonucleotides were anchored to the surface of sandblasted acid-etched (SAE) titanium screw implants and were hybridized with complementary strands of ODN conjugated to rhVEGF165 . The implants were tested against blank SAE implants and SAE implants with nano-anchored ODN. The implants were inserted into the tibiae of 36 Sprague-Dawley rats. Primary outcome parameters were bone-implant contact (BIC), amount of new bone formation and periimplant bone density (BD). density after 1, 4 and 13 weeks. Unit of analysis has been the individual implant.

RESULTS

Implants with rhVEGF165 hybridized to ODN anchor strands exhibited significantly increased average BIC after 1 month compared to blank implants and implants with anchored ODN strands.

CONCLUSIONS

It is concluded that rhVEGF165 immobilized on the surface of titanium implants through nano-anchored oligonucleotide strands can accelerate BIC of sandblasted and etched titanium implants to a certain extent. The radius of effect of the growth factor appears to be limited to tissue immediately adjacent to the implant surface.

Use of screw locking elements improves radiological and biomechanical results of femoral osteotomies

BACKGROUND

Dynamic compression plate (DCP) constructs provide inadequate fixation in cases of poor bone quality and early weight-bearing. Screw locking elements (SLE) are flat locking nuts placed at the end of the screw to prevent screw stripping from the bone, improving fixation stability. The purpose of this work was to compare biomechanical and radiological evaluations of femoral ovine osteotomies fixed using DCP constructs with and without SLE.

METHOD

A dyaphyseal femoral osteotomy was performed in sixteen adult sheep and fixed with a DCP and cortical screws. Half of the animals were operated on with a SLE on each side of the osteotomy and the rest without the addition of SLE. Four animals of each group were euthanized after 8 weeks, and the remaining after 16 weeks. Both femora of each animal were radiographed and mechanically tested in torsion.

RESULTS

Radiologically femoral malalignment or screw loosening was observed in six out of the eight animals operated on without SLE. In contrast, all animals subjected to the operation with SLE showed complete radiological consolidation of the osteotomy. Seven of these eight animals showed normal femoral alignment and no osteosynthesis failure. Stiffness of the bones fixed with SLE was among 145% and 177% the value of their contralateral non-operated femurs (all animals of this group showed greater stiffness on the operated bone than its contralateral non-operated femur). However, stiffness of the bones operated on without SLE was among 58% and 87% the value of the stiffness of their contralateral non-operated bone (all animals of this group showed greater stiffness on the non-operated bone than the osteotomized ones).

CONCLUSIONS

Use of SLE avoided loosening of the system and stimulated stronger osteotomy consolidation. Clinical application of this improved system may thus be a feasible and cost-effective alternative to other more rigid and expensive bone fixation techniques.

Experimental analysis of the minimally invasive plate osteosynthesis technique applied with non-locking screws and screw locking elements

Minimally invasive plate osteosynthesis (MIPO) is an effective surgical technique in the repair of humeral and tibial shaft fractures. There is some controversy as to the minimum number of screws required to ensure correct stability to promote healing, especially when dealing with low quality bones. This work compared different systems assembled on synthetic models simulating a comminuted fracture. Group 1 comprised a locking compression plate with four non-locking screws placed at the holes furthest from the fracture. Group 2 differed from group 1 only in the additional use of two screw locking elements (SLE). Group 3 had four rather than two SLE and, finally, Group 4 used 4 locking screws. The compression and torsion tests with static and cyclic loads showed that, in MIPO, two locking screws or two non-locking screws with SLE could be used per segment without any significant loss in stiffness after 1000 cycles, with system stability guaranteed in both cases. However, lower strength and significant loss of stiffness were observed when non-locking screws were used alone.

Mechanical behaviour of low-cost dynamic compression plates correlates with manufacturing quality standards

PURPOSE

This study compares the mechanical properties of low-cost stainless steel dynamic compression plates (DCPs) from developing-world manufacturers, adhering to varying manufacturing quality standards, with those of high-cost DCPs manufactured for use in the developed world.

METHODS

Standard-design ten-hole DCPs from six developing-world manufacturers and high-cost DCPs from two manufacturers in the developed world were studied. Nine plates from each manufacturer underwent mechanical testing: six in four-point monotonic bending to assess strength and stiffness and three in four-point bending fatigue. Statistical comparisons of the group means of monotonic bending test data were made, and a qualitative comparison was performed to assess failures in fatigue.

RESULTS

Low-cost DCPs from manufacturers with at least one manufacturing quality standard had significantly higher bending strength and fewer failures in fatigue than did those from low-cost manufacturers with no recognised quality standards. High-cost DCPs demonstrated greater bending strength than did those in both low-cost groups. There were no differences in stiffness and fatigue failure between high-cost DCPs and those low-cost DCPs with quality standards. However, high-cost DCPs were significantly less stiff and had fewer fatigue failures than low-cost DCPs manufactured without such standards.

CONCLUSION

Significant differences were found in the mechanical properties of ten-hole DCP plates from selected manufacturers in the developing and developed worlds. These differences correlated with reported quality certification in the manufacturing process. Mechanical analysis of low-cost implants may provide information useful in determining which manufacturers produce implants with the best potential for benefit relative to cost.

Evaluation of a new approach for modelling the screw–bone interface in a locking plate fixation: A corroboration study

Computational modelling of the screw–bone interface in fracture fixation constructs is challenging. While incorporating screw threads would be a more realistic representation of the physics, this approach can be computationally expensive. Several studies have instead suppressed the threads and modelled the screw shaft with fixed conditions assumed at the screw–bone interface. This study assessed the sensitivity of the computational results to modelling approaches at the screw–bone interface. A new approach for modelling this interface was proposed, and it was tested on two locking screw designs in a diaphyseal bridge plating configuration. Computational models of locked plating and far cortical locking constructs were generated and compared to in vitro models described in prior literature to corroborate the outcomes. The new approach led to closer agreement between the computational and the experimental stiffness data, while the fixed approach led to overestimation of the stiffness predictions. Using the new approach, the pattern of load distribution and the magnitude of the axial forces, experienced by each screw, were compared between the locked plating and far cortical locking constructs. The computational models suggested that under more severe loading conditions, far cortical locking screws might be under higher risk of screw pull-out than the locking screws. The proposed approach for modelling the screw–bone interface can be applied to any fixation involved application of screws.

Repeat LISS treatment for femoral shaft fractures due to hardware failure: a retrospective analysis of eleven cases

OBJECTIVE

To evaluate the effectiveness of a replating technique having a less-invasive stabilization system (LISS) for femoral shaft fractures due to LISS failure in adults.

PATIENTS AND METHODS

There were 11 patients with hardware failure of LISS for femoral shaft fractures, on an average of 50 days after the primary operation. The failed implants were removed, and the fractures were replated with a LISS following the rationale of biological osteosynthesis. Radiological fracture union and incidence of postoperative complications were employed to evaluate the effectiveness of this replating technique for femoral shaft fractures.

RESULTS

Operative duration including removing failed hardware and replating fractures averaged 81.5 min, with an average blood loss of 330 ml. Patients had an average follow-up of 25.7 months. Radiological evaluation indicated that fracture union occurred in an average of 4.4 months in all patients. The length and alignment of the affected limb were satisfactory, and hardware failure did not recur.

CONCLUSION

The replating technique with LISS for femoral shaft fractures due to hardware failure of LISS can obtain satisfactory results when the appropriate rationale of biological osteosynthesis and functional exercise is followed.