Advances in Dynamization of Plate Fixation to Promote Natural Bone Healing.

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

Effect of helmet design on impact performance of industrial safety helmets.

Background: Comparative studies of different helmet designs are essential to determine differences in helmet performance. The present study comparatively evaluated the impact performance of hardhat helmets, climbing-style safety helmets, and helmets with novel rotation-damping technologies to determine if advanced designs deliver improved protection. Methods: Six helmet designs from three categories of safety helmets were tested: two traditional hardhat helmets (HH Type I, HH Type II), two climbing-style helmets (CS Web, CS Foam), and two helmets with dedicated rotation-damping technologies (MIPS, CEL). Helmets were first evaluated in impacts of 31 J energy representing a falling object according to standard Z89.1-2014. Subsequently, helmets were evaluated in impacts representing a fall by dropping a helmeted head-neck surrogate at 275 J impact energy. The resulting head kinematics were used to calculate the probability of sustaining a head or brain injury. Results: Crown impacts representative of a falling object resulted in linear acceleration of less than 50 g in all six helmet models. Compared to crown impacts, front, side and rear impacts caused a several-fold increase in head acceleration in all helmets except HH Type II and CEL helmets. For impacts representative of falls, all helmets except the CEL helmet exhibited significantly increased head accelerations and an increased brain injury probability compared to the traditional HH Type I hardhat. Neck compression was 35%-90% higher in the two climbing-style helmets and 80% higher in MIPS helmets compared to the traditional HH type I hardhat. Discussion: Contemporary helmets do not necessarily deliver improved protection from impacts and falls compared to traditional hardhat helmets.

Impact Performance Comparison of Advanced Snow Sport Helmets with Dedicated Rotation-Damping Systems.

Rotational acceleration of the head is a principal cause of concussion and traumatic brain injury. Several rotation-damping systems for helmets have been introduced to better protect the brain from rotational forces. But these systems have not been evaluated in snow sport helmets. This study investigated two snow sport helmets with different rotation-damping systems, termed MIPS and WaveCel, in comparison to a standard snow sport helmet without a rotation-damping system. Impact performance was evaluated by vertical drops of a helmeted Hybrid III head and neck onto an oblique anvil. Six impact conditions were tested, comprising two impact speeds of 4.8 and 6.2 m/s, and three impact locations. Helmet performance was quantified in terms of the linear and rotational kinematics, and the predicted probability of concussion. Both rotation-damping systems significantly reduced rotational acceleration under all six impact conditions compared to the standard helmet, but their effect on linear acceleration was less consistent. The highest probability of concussion for the standard helmet was 89%, while helmets with MIPS and WaveCel systems exhibited a maximal probability of concussion of 67 and 7%, respectively. In conclusion, rotation-damping systems of advanced snow sport helmets can significantly reduce rotational head acceleration and the associated concussion risk.

Biomechanical models: key considerations in study design.

This manuscript summarizes presentations of a symposium on key considerations in design of biomechanical models at the 2019 Basic Science Focus Forum of the Orthopaedic Trauma Association. The first section outlines the most important characteristics of a high-quality biomechanical study. The second section considers choices associated with designing experiments using finite element modeling versus synthetic bones versus human specimens. The third section discusses appropriate selection of experimental protocols and finite element analyses. The fourth section considers the pros and cons of use of biomechanical research for implant design. Finally, the fifth section examines how results from biomechanical studies can be used when clinical evidence is lacking or contradictory. When taken together, these presentations emphasize the critical importance of biomechanical research and the need to carefully consider and optimize models when designing a biomechanical study.

Impact Performance Comparison of Advanced Bicycle Helmets with Dedicated Rotation-Damping Systems.

Bicycle helmets effectively mitigate skull fractures, but there is increasing concern on their effectiveness in mitigating traumatic brain injury (TBI) caused by rotational head acceleration. Bicycle falls typically involve oblique impacts that induce rotational head acceleration. Recently, bicycle helmet with dedicated rotation-damping systems have been introduced to mitigate rotational head acceleration. This study investigated the impact performance of four helmets with different rotation-damping systems in comparison to a standard bicycle helmet without a rotation-damping system. Impact performance was tested under oblique impact conditions by vertical drops of a helmeted headform onto an oblique anvil at 6.2 m/s impact speed. Helmet performance was quantified in terms of headform kinematics, corresponding TBI risk, and resulting brain strain. Of the four rotation-damping systems, two systems significantly reduced rotational head acceleration, TBI risk, and brain strain compared to the standard bicycle helmet. One system had no significant effect on impact performance compared to control helmets, and one system significantly increase linear and rotational head acceleration by 62 and 61%, respectively. In conclusion, results revealed significant differences in the effectiveness between rotation-damping systems, whereby some rotation-damping systems significantly reduced rotational head acceleration and associated TBI risk.

Evaluation of a novel bicycle helmet concept in oblique impact testing.

BACKGROUND: A novel bicycle helmet concept has been developed to mitigate rotational head acceleration, which is a predominant mechanism of traumatic brain injury (TBI). This WAVECEL concept employs a collapsible cellular structure that is recessed within the helmet to provide a rotational suspension. This cellular concept differs from other bicycle helmet technologies for mitigation of rotational head acceleration, such as the commercially available Multi-Directional Impact Protection System (MIPS) technology which employs a slip liner to permit sliding between the helmet and the head during impact. This study quantified the efficacy of both, the WAVECEL cellular concept, and a MIPS helmet, in direct comparison to a traditional bicycle helmet made of rigid expanded polystyrene (EPS). METHODS: Three bicycle helmet types were subjected to oblique impacts in guided vertical drop tests onto an angled anvil: traditional EPS helmets (CONTROL group); helmets with a MIPS slip liner (SLIP group); and helmets with a WAVECEL cellular structure (CELL group). Helmet performance was evaluated using 4.8 m/s impacts onto anvils angled at 30°, 45°, and 60° from the horizontal plane. In addition, helmet performance was tested at a faster speed of 6.2 m/s onto the 45° anvil. Five helmets were tested under each of the four impact conditions for each of the three groups, requiring a total of 60 helmets. Headform kinematics were acquired and used to calculate an injury risk criterion for Abbreviated Injury Score (AIS) 2 brain injury. RESULTS: Linear acceleration of the headform remained below 90 g and was not associated with the risk of skull fracture in any impact scenario and helmet type. Headform rotational acceleration in the CONTROL group was highest for 6.2 m/s impacts onto the 45° anvil (7.2 ± 0.6 krad/s2). In this impact scenario, SLIP helmets and CELL helmets reduced rotational acceleration by 22% (p = 0003) and 73% (p < 0.001), respectively, compared to CONTROL helmets. The CONTROL group had the highest AIS 2 brain injury risk of 59 ± 8% for 6.2 m/s impacts onto the 45° anvil. In this impact scenario, SLIP helmets and CELL helmets reduced the AIS 2 brain injury risk to 34.2% (p = 0.001) and 1.2% (p < 0.001), respectively, compared to CONTROL helmets. DISCUSSION: Results of this study are limited to a narrow range of impact conditions, but demonstrated the potential that rotational acceleration and the associated brain injury risk can be significantly reduced by the cellular WAVECEL concept or a MIPS slip liner. Results obtained under specific impact angles and impact velocities indicated performance differences between these mechanisms. These differences emphasize the need for continued research and development efforts toward helmet technologies that further improve protection from brain injury over a wide range a realistic impact parameters.

Biomechanics-Hot Topics Part I.

This study summarizes presentations of a symposium on biomechanically related hot topics of the 2015 Basic Science Focus Forum. Each topic emphasizes a biomechanical challenge common to all 4 of these presentations: an ideal fixation technique should deliver ample stability and sufficient flexibility to prevent fixation failure and to restore normal function.

Dynamic Fixation of Humeral Shaft Fractures Using Active Locking Plates: A Prospective Observational Study.

BACKGROUND: Rigid locked plating constructs can suppress fracture healing by inhibiting interfragmentary motion required to stimulate natural bone healing by callus formation. Dynamic fixation with active locking plates reduces construct stiffness, enables controlled interfragmentary motion, and has been shown to induce faster and stronger bone healing in vivo compared to rigid locking plates. This prospective observational study represents the first clinical use of active locking plates. It documents our early clinical experience with active plates for stabilization of humeral shaft fractures to assess their durability and understand potential complications. METHODS: Eleven consecutive patients with humeral shaft fractures (AO/OTA types 12 A-C) were prospectively enrolled at a level I and a level II trauma center. Fractures were stabilized by using active locking plates without supplemental bone graft or bone morphogenic proteins. The screw holes of active locking plates are elastically suspended in elastomer envelopes inside the plate, enabling up to 1.5 mm of controlled interfragmentary motion. Progression of fracture healing and integrity of implant fixation was assessed radiographically at 3, 6, 12, and 24 weeks post surgery. Patient-reported functional outcome measures were obtained at 6, 12, and 24 weeks post surgery. The primary endpoint of this study was plate durability in absence of plate bending or breakage, or failure of the elastically suspended locking hole mechanism. Secondary endpoints included fracture healing, complications requiring revision surgery, and functional outcome scores. RESULTS: The eleven patients had six simple AO/ OTA type 12A fractures, three wedge type 12B fractures, and two comminuted type 12C fracture, including one open fracture. All active locking plates endured the 6-month loading period without any signs of fatigue or failure. Ten of eleven fractures healed at 10.9 ± 5.2 weeks, as evident by bridging callus and pain-free function. One fracture required revision surgery 37 weeks post surgery due to late fixation failure at the screwbone interface in the presence of a atrophic delayed union. The average Disability of the Arm, Shoulder and Hand (DASH) score improved from 31 ± 22 at week 6 to 13 ± 15 by week 24, approaching that of the normal, healthy population (DASH = 10.1). By week 12, the difference between Constant shoulder scores, expressed as the difference between the affected and contralateral arm (8 ± 8), was considered excellent. By week 24, the SF-12 physical health score (44 ± 9) and mental health score (48 ± 11) approached the mean value of 50 that represents the norm for the general U.S. population. CONCLUSION: Absence of failure of the plate and locking holes suggests that dynamic fixation of humeral shaft fractures with active plates provides safe and effective fixation. Moreover, early callus bridging and excellent functional outcome scores suggest that dynamic fixation with active locking plates may promote increased fracture healing over standard locked plating.

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

BACKGROUND: Decreasing the stiffness of locked plating constructs can promote natural fracture healing by controlled dynamization of the fracture. This biomechanical study compared the effect of 4 different stiffness reduction methods on interfragmentary motion by measuring axial motion and shear motion at the fracture site. METHODS: Distal femur locking plates were applied to bridge a metadiaphyseal fracture in femur surrogates. A locked construct with a short-bridge span served as the nondynamized control group (LOCKED). Four different methods for stiffness reduction were evaluated: replacing diaphyseal locking screws with nonlocked screws (NONLOCKED); bridge dynamization (BRIDGE) with 2 empty screw holes proximal to the fracture; screw dynamization with far cortical locking (FCL) screws; and plate dynamization with active locking plates (ACTIVE). Construct stiffness, axial motion, and shear motion at the fracture site were measured to characterize each dynamization methods. RESULTS: Compared with LOCKED control constructs, NONLOCKED constructs had a similar stiffness (P = 0.08), axial motion (P = 0.07), and shear motion (P = 0.97). BRIDGE constructs reduced stiffness by 45% compared with LOCKED constructs (P < 0.001), but interfragmentary motion was dominated by shear. Compared with LOCKED constructs, FCL and ACTIVE constructs reduced stiffness by 62% (P < 0.001) and 75% (P < 0.001), respectively, and significantly increased axial motion, but not shear motion. CONCLUSIONS: In a surrogate model of a distal femur fracture, replacing locked with nonlocked diaphyseal screws does not significantly decrease construct stiffness and does not enhance interfragmentary motion. A longer bridge span primarily increases shear motion, not axial motion. The use of FCL screws or active plating delivers axial dynamization without introducing shear motion.

Dynamic Stabilization of Simple Fractures With Active Plates Delivers Stronger Healing Than Conventional Compression Plating.

OBJECTIVES: Active plates dynamize a fracture by elastic suspension of screw holes within the plate. We hypothesized that dynamic stabilization with active plates delivers stronger healing relative to standard compression plating. METHODS: Twelve sheep were randomized to receive either a standard compression plate (CP) or an active plate (ACTIVE) for stabilization of an anatomically reduced tibial osteotomy. In the CP group, absolute stabilization was pursued by interfragmentary compression with 6 cortical screws. In the ACTIVE group, dynamic stabilization after bony apposition was achieved with 6 elastically suspended locking screws. Fracture healing was analyzed weekly on radiographs. After sacrifice 9 weeks postsurgery, the torsional strength of healed tibiae and contralateral tibiae was measured. Finally, computed tomography was used to assess fracture patterns and healing modes. RESULTS: Healing in both groups included periosteal callus formation. ACTIVE specimens had almost 6 times more callus area by week 9 (P < 0.001) than CP specimens. ACTIVE specimens recovered on average 64% of their native strength by week 9, and were over twice as strong as CP specimens, which recovered 24% of their native strength (P = 0.008). Microcomputed tomography demonstrated that compression plating induced a combination of primary bone healing and gap healing. Active plating consistently stimulated biological bone healing by periosteal callus formation. CONCLUSIONS: Compared with compression plating, dynamic stabilization of simple fractures with active plates delivers significantly stronger healing.

Dynamic Stabilization with Active Locking Plates Delivers Faster, Stronger, and More Symmetric Fracture-Healing.

BACKGROUND: Axial dynamization of fractures can promote healing, and overly stiff fixation can suppress healing. A novel technology, termed active plating, provides controlled axial dynamization by the elastic suspension of locking holes within the plate. This prospective, controlled animal study evaluated the effect of active plates on fracture-healing in an established ovine osteotomy model. We hypothesized that symmetric axial dynamization with active plates stimulates circumferential callus and delivers faster and stronger healing relative to standard locking plates. METHODS: Twelve sheep were randomly assigned to receive a standard locking plate or an active locking plate for stabilization of a 3-mm tibial osteotomy gap. The only difference between plates was that locking holes of active plates were elastically suspended, allowing up to 1.5 mm of axial motion at the fracture. Fracture-healing was analyzed weekly on radiographs. After sacrifice at nine weeks postoperatively, callus volume and distribution were assessed by computed tomography. Finally, to determine their strength, healed tibiae and contralateral tibiae were tested in torsion until failure. RESULTS: At each follow-up, the active locking plate group had more callus (p < 0.001) than the standard locking plate group. At postoperative week 6, all active locking plate group specimens had bridging callus at the three visible cortices. In standard locking plate group specimens, only 50% of these cortices had bridged. Computed tomography demonstrated that all active locking plate group specimens and one of the six standard locking plate group specimens had developed circumferential callus. Torsion tests after plate removal demonstrated that active locking plate group specimens recovered 81% of their native strength and were 399% stronger than standard locking plate group specimens (p < 0.001), which had recovered only 17% of their native strength. All active locking plate group specimens failed by spiral fracture outside the callus zone, but standard locking plate group specimens fractured through the osteotomy gap. CONCLUSIONS: Symmetric axial dynamization with active locking plates stimulates circumferential callus and yields faster and stronger healing than standard locking plates. CLINICAL RELEVANCE: The stimulatory effect of controlled motion on fracture-healing by active locking plates has the potential to reduce healing complications and to shorten the time to return to function.

Treating Tibia Fractures With Far Cortical Locking Implants.

Compared with conventional plating, the relatively new technology of far cortical locking (FCL) allows for more flexible fixation. Increased flexibility of FCL constructs is thought to better stimulate secondary osteosynthesis and lead to improved healing for certain fracture patterns. We conducted a study to compare healing rates and complications of tibial fractures treated with FCL or standard plating techniques. Twenty-two patients with fractures of the tibia (Orthopaedic Trauma Association 41ABC, 42C, 43C) were included in the study. Twelve tibia fractures were treated with FCL and 10 with standard plating (locking or nonlocking). Mean follow-up was 47 weeks in the FCL group and 41 weeks in the control group. The fracture healing rate was 92% in the FCL group and 100% in the control group (difference not statistically significant). Of note, there were 2 open fractures in the FCL group and 0 in the control group. The groups had similar complication rates. Our study data suggest FCL implants are not inferior to conventional plating techniques. Given that FCL-treated fractures tended to be more complex, the groups' similar fracture healing rates may indicate improved fracture healing with FCL technology, but this possibility requires further investigation.

Biomechanical Concepts for Fracture Fixation.

Application of the correct fixation construct is critical for fracture healing and long-term stability; however, it is a complex issue with numerous significant factors. This review describes a number of common fracture types and evaluates their currently available fracture fixation constructs. In the setting of complex elbow instability, stable fixation or radial head replacement with an appropriately sized implant in conjunction with ligamentous repair is required to restore stability. For unstable sacral fractures with vertical or multiplanar instabilities, "standard" iliosacral screw fixation is not sufficient. Periprosthetic femur fractures, in particular Vancouver B1 fractures, have increased stability when using 90/90 fixation versus a single locking plate. Far cortical locking combines the concept of dynamization with locked plating to achieve superior healing of a distal femur fracture. Finally, there is no ideal construct for syndesmotic fracture stabilization; however, these fractures should be fixed using a device that allows for sufficient motion in the syndesmosis. In general, orthopaedic surgeons should select a fracture fixation construct that restores stability and promotes healing at the fracture site, while reducing the potential for fixation failure.

Elastically suspending the screw holes of a locked osteosynthesis plate can dampen impact loads.

Impact damping by elastic fixation is a principal engineering strategy to increase the durability of load-bearing structures exposed to prolonged dynamic loading. This biomechanical study evaluated axial impact damping provided by a novel dynamic locking plate. In this design, locking screw holes are elastically suspended within a silicone envelope inside the locking plate. Axial impact damping was assessed for 3 distinct fixation constructs applied to bridge a 10-mm fracture gap of a femoral diaphysis surrogate: a standard locking plate, a dynamic locking plate, and an Ilizarov ring fixator. First, the 3 fixation constructs were characterized by determining their axial stiffness. Subsequently, constructs were subjected to a range of axial impact loads to quantify damping of force transmission. Compared with standard locked plating constructs, dynamic plating constructs were 58% less stiff (P < .01) and Ilizarov constructs were 88% less stiff (P < .01). Impact damping correlated inversely with construct stiffness. Compared with standard plating, dynamic plating constructs and Ilizarov constructs dampened the transmission of impact loads by up to 48% (P < .01) and 74% (P < .01), respectively. In conclusion, lower construct stiffness correlated with superior damping of axial impact loads. Dynamic locking plates provide significantly greater impact damping compared with standard locking plates.

Dynamic locking plates provide symmetric axial dynamization to stimulate fracture healing.

Axial dynamization of an osteosynthesis construct can promote fracture healing. This biomechanical study evaluated a novel dynamic locking plate that derives symmetric axial dynamization by elastic suspension of locking holes within the plate. Standard locked and dynamic plating constructs were tested in a diaphyseal bridge-plating model of the femoral diaphysis to determine the amount and symmetry of interfragmentary motion under axial loading, and to assess construct stiffness under axial loading, torsion, and bending. Subsequently, constructs were loaded until failure to determine construct strength and failure modes. Finally, strength tests were repeated in osteoporotic bone surrogates. One body-weight axial loading of standard locked constructs produced asymmetric interfragmentary motion that was over three times smaller at the near cortex (0.1 ± 0.01 mm) than at the far cortex (0.32 ± 0.02 mm). Compared to standard locked constructs, dynamic plating constructs enhanced motion by 0.32 mm at the near cortex and by 0.33 mm at the far cortex and yielded a 77% lower axial stiffness (p < 0.001). Dynamic plating constructs were at least as strong as standard locked constructs under all test conditions. In conclusion, dynamic locking plates symmetrically enhance interfragmentary motion, deliver controlled axial dynamization, and are at least comparable in strength to standard locked constructs. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1218-1225, 2015.

Dynamic fixation of distal femur fractures using far cortical locking screws: a prospective observational study.

OBJECTIVES: Document fixation and healing of distal femur fractures stabilized by plate osteosynthesis using far cortical locking (FCL) screws. DESIGN: Prospective and observational. SETTING: Two level 1 and 1 level 2 trauma centers. PATIENTS: Thirty-two consecutive patients with 33 distal femur fractures (AO/OTA types 33A, 33C). INTERVENTION: Fractures were stabilized by plate osteosynthesis with MotionLoc FCL screws without supplemental bone graft or bone morphogenic proteins. Patients were followed up for a minimum of 1 year with functional and radiographic assessments obtained at postoperative weeks 6, 12, and 24 and computed tomography scans at week 12. If union was not confirmed within 1 year, follow-up was continued until union or revision surgery. MAIN OUTCOME MEASURES: The primary end point was fracture union in the absence of complications and secondary interventions. Fracture healing was defined by resolution of pain at the fracture site and cortical bridging on biplanar radiographs. Complications were defined by fixation failure, loss of reduction, implant breakage, infection, nonunion, and need for revision. RESULTS: Thirty-one fractures were available for follow-up. None of the 125 FCL screws used for diaphyseal fixation broke or lost fixation. One of the 31 fractures displaced into varus (ΔVarus = 5.8 degrees). Thirty of the 31 fractures healed within 15.6 ± 6.2 weeks. At an average follow-up of 17 ± 4 months, there were 2 revisions: one to correct a malrotation at day 5 and one to treat a nonunion at 6 months. CONCLUSIONS: Absence of implant and fixation failure suggests that dynamic plating of distal femur fractures with FCL screws provides safe and effective fixation.

Healing results of periprosthetic distal femur fractures treated with far cortical locking technology: a preliminary retrospective study.

INTRODUCTION: Periprosthetic distal femur fractures are severe injuries occurring in the often osteoporotic bone of the elderly. Far cortical locking (FCL) screws, which have been shown to promote increased callus formation in animal models, have recently become available for clinical use. The purpose of this study is to report preliminary healing and complication rates of periprosthetic distal femur fractures treated with FCL constructs. MATERIALS AND METHODS: A retrospective review of 20 patients who underwent open reduction and internal fixation of periprosthetic distal femur fractures using FCL constructs was performed. Healing was assessed radiographically and clinically at 6, 12 and 24 weeks post-operatively. Construct failure was defined as any hardware breakage or bone-implant dissociation leading to loss of reduction. RESULTS: Complete data through the 24 week study period was available for 18/20 patients. Bridging callus was identified in 16/18 patients by the 24 week follow up for a healing rate of 88.9%. In patients that healed, the average time to medial bridging callus formation was 10.7 ± 6.7 weeks, 11.0 ± 6.6 weeks for anterior fracture line and 13.4 ± 7.5 weeks for the posterior fracture line. both patients that failed to heal underwent revision surgery. DISCUSSION: The initial results of this study are comparable to results reported for distal femur periprosthetic fractures treated with locking plate fixation without FCL screws, although it was difficult to compare time to healing between previously published studies. It is the impression of the authors that callus appears earlier and is more robust and uniform between the three cortices in FCL cases compared to their previous experiences with traditional locking plate periprosthetic distal femur fractures. This work suggests that FCL screws may be superior to traditional locking constructs but further studies are needed to directly compare the two methods.

Angular Impact Mitigation system for bicycle helmets to reduce head acceleration and risk of traumatic brain injury.

Angular acceleration of the head is a known cause of traumatic brain injury (TBI), but contemporary bicycle helmets lack dedicated mechanisms to mitigate angular acceleration. A novel Angular Impact Mitigation (AIM) system for bicycle helmets has been developed that employs an elastically suspended aluminum honeycomb liner to absorb linear acceleration in normal impacts as well as angular acceleration in oblique impacts. This study tested bicycle helmets with and without AIM technology to comparatively assess impact mitigation. Normal impact tests were performed to measure linear head acceleration. Oblique impact tests were performed to measure angular head acceleration and neck loading. Furthermore, acceleration histories of oblique impacts were analyzed in a computational head model to predict the resulting risk of TBI in the form of concussion and diffuse axonal injury (DAI). Compared to standard helmets, AIM helmets resulted in a 14% reduction in peak linear acceleration (p<0.001), a 34% reduction in peak angular acceleration (p<0.001), and a 22-32% reduction in neck loading (p<0.001). Computational results predicted that AIM helmets reduced the risk of concussion and DAI by 27% and 44%, respectively. In conclusion, these results demonstrated that AIM technology could effectively improve impact mitigation compared to a contemporary expanded polystyrene-based bicycle helmet, and may enhance prevention of bicycle-related TBI. Further research is required.

Surgical stabilization of flail chest injuries with MatrixRIB implants: a prospective observational study.

BACKGROUND: Surgical stabilization of flail chest injury with generic osteosynthesis implants remains challenging. A novel implant system comprising anatomic rib plates and intramedullary splints may improve surgical stabilization of flail chest injuries. This observational study evaluated our early clinical experience with this novel implant system to document if it can simplify the surgical procedure while providing reliable stabilization. METHODS: Twenty consecutive patients that underwent stabilization of flail chest injury with anatomic plates and intramedullary splints were prospectively enrolled at two Level I trauma centres. Data collection included patient demographics, injury characterization, surgical procedure details and post-operative recovery. Follow-up was performed at three and six months to assess pulmonary function, durability of implants and fixation and patient health. RESULTS: Patients had an Injury Severity Score of 28±10, a chest Abbreviated Injury Score of 4.2±0.4 and 8.5±2.9 fractured ribs. Surgical stabilization was achieved on average with five plates and one splint. Intra-operative contouring was required in 14% of plates. Post-operative duration of ventilation was 6.4±8.6 days. Total hospitalization was 15±10 days. At three months, patients had regained 84% of their expected forced vital capacity (%FVC). At six months, 7 of 15 patients that completed follow-up had returned to work. There was no mortality. Among the 91 rib plates, 15 splints and 605 screws in this study there was no hardware failure and no loss of initial fixation. There was one incidence of wound infection. Implants were removed in one patient after fractures had healed. CONCLUSIONS: Anatomic plates eliminated the need for extensive intraoperative plate contouring. Intramedullary rib splints provided a less-invasive fixation alternative for single, non-comminuted fractures. These early clinical results indicate that the novel implant system provides reliable fixation and accommodates the wide range of fractures encountered in flail chest injury.