Nitinol, Stainless Steel, and Titanium Kirschner Wire Durability.

Kirschner wires (K wires) are a common fixation device in foot and ankle surgery, particularly in lesser-toe fixation. Fatigue failure is a known complication of this fixation. The material properties of the K wire are a factor in the strength and durability of the wire. The purpose of this study is to compare the durability of K wires made of stainless steel, titanium, and Nitinol. Ten samples each of stainless steel, titanium. and Nitinol underwent cyclic durability testing using a rotating beam approach, and S-N curves (applied stress vs the number of cycles to failure) were generated. The results demonstrate that, generally, Nitinol K wires have a shorter life for the same applied stress than the stainless steel or titanium wires. Titanium had a longer life at low stresses compared with stainless steel, and stainless steel had a longer life at higher stresses. This study provides comparative durability data for K wires made of different metals, which have not been previously reported. Although there was a statistically significant difference in durability for wires used in K wire fixation, all 3 metal types are reasonable choices for temporary K wire fixation.Levels of Evidence: Level 5: Mechanical study.

Bubble bilevel ventilation facilitates gas exchange in anesthetized rabbits.

BACKGROUND: Bubble continuous positive airway pressure is an established therapy for infants in respiratory distress. In resource-limited settings, few treatment options exist for infants requiring further respiratory support. A bubble bilevel device has been developed to provide nonelectric, time-cycled, pressure-limited respiratory support. We compared the efficacy of bubble bilevel ventilation with conventional mechanical ventilation in sedated rabbits. METHODS: Six adult rabbits under inhaled isoflurane general anesthesia were ventilated by alternating intervals of conventional and bubble bilevel ventilation for three 10-15-min periods. During each period, interval arterial blood gas (ABG) measurements were obtained after at least 10 min on the respective mode of ventilation. RESULTS: The bubble bilevel system was able to deliver the following pressures: 20/7, 15/5, 12/5, 8/5 cm H2O. The estimated differences in arterial blood gas values on bubble bilevel vs. ventilator were as follows (normalized values): pH 7.41 vs. 7.40, pCO2 37.7 vs. 40, pO2 97.6 vs. 80. In addition, the bubble bilevel ventilation delivered consistent pressure waveforms without interruption for over 60 min on two rabbits. CONCLUSION: This study demonstrates promising in vivo results on the efficacy of a novel bubble bilevel device, which may prove useful for infants in respiratory distress. IMPACT: Given the lack of personnel, funds or infrastructure to provide neonatal mechanical ventilation in resource-limited settings, additional low-cost, low-tech treatments are necessary to save infant lives. Bubble bilevel ventilation reliably delivers two levels of airway pressure to anesthetized rabbits resulting in normalization of blood gases comparable to those achieved on a traditional ventilator. If proven effective, simple technologies like this device have the potential to significantly impact neonatal mortality due to respiratory distress globally.

Bench Testing of a Bubble Noninvasive Ventilation Device in an Infant Lung Simulator.

BACKGROUND: Infant respiratory distress remains a significant problem worldwide, leading to more than one million neonatal deaths each year. The cost, maintenance, energy, and personnel required to implement ventilators have proven to be a barrier in many resource-limited settings. To address these barriers, a nonelectric bubble noninvasive positive pressure ventilation (NIV) device was developed. This study aims to benchmark the performance of this bubble NIV device against commercially available ventilators. METHODS: The delivered pressure waveforms and tidal volumes of the bubble NIV device were compared with those of 2 conventional ventilators (ie, Dräger Evita Infinity V500 and Hamilton G5) at the following pressure settings: 8/5, 12/5, and 15/5 cm H2O. To simulate the lung mechanics of an infant in respiratory distress, tests were conducted on the IngMar ASL 5000 Test Lung simulator. Resistance was set at 100 cm H2O/L/s, and compliance was tested at 0.5, 1.0, and 2.0 mL/cm H2O to simulate 3 different patients. RESULTS: The delivered pressure waveforms and compliance curves of the bubble NIV device are similar to those of the Hamilton and Dräger ventilators. The mean ± SD differences between delivered versus set pressure gradient (ie, the difference between the high delivered pressure and the low delivered pressure) for each treatment modality across the various values of compliance were -2 ± 8% for the bubble NIV device, 3 ± 4% for the Dräger ventilator, and 7 ± 10% for the Hamilton ventilator. CONCLUSIONS: The similarity of pressure waveforms and delivered tidal volumes in this simulated clinical scenario suggest that the bubble NIV device may provide comparable efficacy compared with traditional ventilator treatment for a range of patients. This may provide clinicians in resource-limited settings with an additional, simple, nonelectric treatment modality for the management of infant respiratory distress.

Feasibility of Transosseous Nonarticular Fixation of Lisfranc Injuries.

BACKGROUND: The optimal techniques for Lisfranc open reduction and internal fixation techniques remain debated. The purpose of the current study was to describe the joints involved in Lisfranc fixation and to determine if nonarticular transosseous internal fixation would be possible. METHODS: Twenty cadaver Lisfranc joints were dissected and the articular cartilage was quantified by calibrated digital imaging software. Utilizing CT data, a computational model of the foot was developed and the mean joint surface was mapped and nonarticular screw paths between bones was determined. RESULTS: For the medial-middle cuneiform (C1-C2) connection, 27.3% of the lateral face of C1 and 43.7% of the medial face of C2 was articular cartilage. Three variations of articular morphology were observed on C1 and 2 on C2. From the 3D models, it was determined that a joint-sparing, transosseous screw trajectory was possible between C1 and the second metatarsal and between C1 and C2. These screw paths were large enough to accommodate clinically useful screw diameters (>5 mm). The screw trajectories were roughly perpendicular to the long axis of the foot and take a plantar-medial to dorsal-lateral orientation. CONCLUSION: The articular surface of the Lisfranc joint was quantified for the first time and may be smaller than some surgeons realize. This study demonstrated the orientation required to minimize articular damage. CLINICAL RELEVANCE: The clinical significance of the current study was that a nonarticular screw trajectory was possible, and this information may help guide the placement of these screws.

The Effect of Pitch Variation and Diameter Variation on Screw Pullout.

Introduction: There are many screw and thread designs commercially available to surgeons for bone fixation. There is a paucity of literature on comparative mechanical properties of various screw and thread designs including variable pitch screws, and tapered screws. This purpose of this study was to test whether varying a screws thread pitch and/or tapering a screws core diameter alters the mechanical performance of screws. Methods: A mechanical pullout test was performed on 4 different screw designs, including a variable pitch screw, a constant pitch screw, and variations of these in a straight and tapered screw design. Three-dimensional printing technology was used to manufacture the metal screws in order to control for as many variables as possible. Results: The pullout strength of the constant pitch screws (304.9 ± 25.3 N, P < .001) was significantly greater than the variable pitch screws (259.7 ± 23.4 N). The pullout strength was also significantly greater for screws with a tapered diameter (305.4 ± 24.1 N) than a constant diameter (259.1 ± 23.5N, P < .001). Tapered diameter variable pitch screws had the largest stiffness overall, which was statistically significant against all other groups (P ⩽ .001). Conclusion: The pullout strength is significantly greater for screws with a tapered diameter than a constant diameter and greater for screws with a constant pitch than for a variable pitch. Results of stiffness testing is mixed depending on the screw taper. The clinical significance of this study is that it provides data on the effects that thread design and tapering have on the pullout strength of screws. Levels of Evidence: Level V: Mechanical study.

Development and Testing of a Bubble Bi-Level Positive Airway Pressure System.

BACKGROUND: Neonatal respiratory distress results in > 1 million annual deaths worldwide. Bubble CPAP is a simple, effective, and widely used therapy for infants in respiratory distress. In low-resource settings, more advanced respiratory support is limited by cost, technical expertise, and sporadic electricity. We sought to develop a safe, inexpensive, and simple solution to provide further respiratory support for these infants. METHODS: A standard bubble CPAP system was modified to provide 2 levels of positive airway pressure (bi-level positive airway pressure) by attaching a novel device. To demonstrate reliability, the system was run with continuous pressure monitoring on full-term and preterm neonatal mannikins with pressure targets of 8/5 cm H2O and 15/5 cm H2O to simulate 2 different modes of noninvasive ventilation (NIV). RESULTS: At a ventilation rate set between 30 and 45 cycles/min, by adjusting the leak rate of the device, the following mean pressures ± SD were demonstrated: term mannikin low-pressure NIV, 7.9 ± 0.2/5.3 ± 0.2 cm H2O; term mannikin high-pressure NIV, 15.1 ± 0.1/6.1 ± 0.1 cm H2O; preterm mannikin low-pressure NIV, 7.9 ± 0.2/5.3 ± 0.2 cm H2O; preterm mannikin high-pressure NIV, 16.5 ± 0.4/5.1 ± 0.1 cm H2O. CONCLUSIONS: The modified bubble CPAP system reliably provided alternating pressures similar to bi-level positive airway pressure modes of respiratory support in neonatal mannikins. The dual-pressure technology is a simple, single connection add-on that can readily be applied to existing bubble CPAP systems.

Ball and Socket Ankle: Mechanism and Computational Evidence of Concept.

The ball and socket ankle joint is a morphologically abnormal joint characterized by rounding of the articular surface of the talus. Other than anecdotal observation, little evidence has been presented to describe the development of this deformity. The purpose of the present study was to review ankle and subtalar joint mechanics and to kinematically examine the functional combination of these joints as a mechanism of the ball and socket ankle deformity. We reviewed functional representations of the ankle joint, subtalar joint, and ball and socket ankle deformity. A computational study of joint kinematics was then performed using a 3-dimensional model derived from a computed tomography scan of a ball and socket deformity. The joint kinematics were captured by creating a "virtual map" of the combined kinematics of the ankle and subtalar joints in the respective models. The ball and socket ankle deformity produces functionally similar kinematics to a combination of the ankle and subtalar joints. The findings of the present study support the notion that a possible cause of the ball and socket deformity is bony adaptation that compensates for a functional deficit of the ankle and subtalar joints.

Three-Dimensional Printing and Surgical Simulation for Preoperative Planning of Deformity Correction in Foot and Ankle Surgery.

A paucity of published data is available describing the methods for the integration of 3-dimensional (3D) printing technology and surgical simulation into orthopedic surgery. The cost of this technology has decreased and the ease of use has increased, making routine use of 3D printed models and surgical simulation for difficult orthopedic problems a realistic option. We report the use of 3D printed models and surgical simulation for preoperative planning and patient education in the case of deformity correction in foot and ankle surgery using open source, free software.

Effect of Real-Time Feedback on Screw Placement Into Synthetic Cancellous Bone.

OBJECTIVES: The objective of this study is to evaluate whether real-time torque feedback may reduce the occurrence of stripping when inserting nonlocking screws through fracture plates into synthetic cancellous bone. METHODS: Five attending orthopaedic surgeons and 5 senior level orthopaedic residents inserted 8 screws in each phase. In phase I, screws were inserted without feedback simulating conventional techniques. In phase II, screws were driven with visual torque feedback. In phase III, screws were again inserted with conventional techniques. Comparison of these 3 phases with respect to screw insertion torque, surgeon rank, and perception of stripping was used to establish the effects of feedback. RESULTS: Seventy-three of 239 screws resulted in stripping. During the first phase, no feedback was provided and the overall strip rate was 41.8%; this decreased to 15% with visual feedback (P < 0.001) and returned to 35% when repeated without feedback. With feedback, a lower average torque was applied over a narrower torque distribution. Residents stripped 40.8% of screws compared with 20.2% for attending surgeons. Surgeons were poor at perceiving whether they stripped. CONCLUSIONS: Prevention and identification of stripping is influenced by surgeon perception of tactile sensation. This is significantly improved with utilization of real-time visual feedback of a torque versus roll curve. This concept of real-time feedback seems beneficial toward performance in synthetic cancellous bone and may lead to improved fixation in cancellous bone in a surgical setting.

Biomechanical Evaluation of Strength and Stiffness of Subtalar Joint Arthrodesis Screw Constructs.

BACKGROUND: Subtalar arthrodesis is a common treatment for end-stage subtalar joint arthritis as well as many other clinical problems. The best method of subtalar arthrodesis fixation is unknown. The purpose of this study was to compare the strength of subtalar arthrodesis fixation methods including a single posterior screw (SP), 2 posterior minimally divergent screws (MD) and a 2 screw highly divergent screw (HD) construct for subtalar arthrodesis. METHODS: A biomechanical study was performed including the three different screw configurations (SP, MD, HD). These surrogate bone specimens were subjected to applied inversion and eversion torques about the subtalar joint axis on a servo-hydraulic load frame. Torsional stiffness of the construct and the maximum torque for each configuration were measured. Additionally, a cadaver study was performed using 5 fresh-frozen cadaver specimens. The perpendicular distance from the divergent screw guide-wire placement was measured from anatomic structures. RESULTS: The HD screw configuration was found to have the highest torsional stiffness in both inversion and eversion, followed by the MD construct and then the SP construct. Similarly, the HD construct had the highest maximum torque versus the MD and SP constructs. All between-group differences were statistically significant (P < .05). The mean distance from key structures to the divergent screw included the sural nerve (13 mm), peroneus brevis tendon (18 mm), tibialis anterior tendon (8 mm), and tibialis posterior tendon (21 mm). CONCLUSION: This biomechanical and cadaver study supports the use of 2 screws for fixation of subtalar arthrodesis over a single posterior screw. Additionally, we describe a biomechanically superior and potentially safe, alternative 2-screw divergent construct. CLINICAL RELEVANCE: This study gives biomechanical support for 2 screw, divergent fixation of subtalar arthrodesis or a single over a single screw or two screw minimally divergent construct.

The effect of load obliquity on the strength of locking and nonlocking constructs in synthetic osteoporotic bone.

The biomechanical performance of internal fracture fixation depends on several factors. One measure of performance is the strength of the construct. The objective of this biomechanical study was to identify the effect of load obliquity on the strength of locking and nonlocking plate and screw constructs. For this study, plates and screws were fixed to synthetic osteoporotic bone that had a 1 mm thick synthetic cortical shell. An 8-hole, 3.5 mm thick hybrid plate was fixed with either two 3.5 mm major diameter locking screws or two 4.0 mm major diameter cancellous screws. Forces were applied at 0, 45, and 90 degrees to the plate normal. Eight specimens were loaded to failure for each group. When loads were applied normal to the plate, the nonlocking construct failed initially at higher loads (123.2 ± 13.2 N) than the locking construct (108.7 ± 7.6 N, P = 0.020). For oblique loads, the locking construct failed at higher mean loads but the difference of means was not statistically significant (167.7 ± 14.9 N compared to 154.2 ± 9.4 N, P = 0.052). For loads parallel to the plate, the locking construct was much stronger than the nonlocking construct (1591 ± 227 N compared to 913 ± 237 N, P < 0.001). Stiffness and Energy outcomes are also compared.

The subtalar joint: biomechanics and functional representations in the literature.

The subtalar joint is important for gait and function of the foot and ankle. With few external landmarks, the joint is difficult to conceptualize and study in vivo. There have been several functional representations put forth in the literature which can be combined to give a broader understanding of the overall function and mechanics of the subtalar joint. This understanding is clinically important when considering the impact that disease has on the subtalar joint as well as how treatment of the subtalar joint impacts on the surrounding structures.

Surgeon perception of cancellous screw fixation.

OBJECTIVES: The ability of surgeons to optimize screw insertion torque in nonlocking fixation constructs is important for stability, particularly in osteoporotic and cancellous bone. This study evaluated screw torque applied by surgeons during synthetic cancellous fixation. It evaluated the frequency with which screws were stripped by surgeons, factors associated with screw stripping, and ability of surgeons to recognize it. METHODS: Ten surgeons assembled screw and plate fixation constructs into 3 densities of synthetic cancellous bone while screw insertion torque and axial force were measured. For each screw, the surgeon recorded a subjective rating as to whether or not the screw had been stripped. Screws were then advanced past stripping, and stripped screws were identified by comparing the insertion torque applied by the surgeon to the measured stripping torque. RESULTS: Surgeons stripped 109 (45.4%) of 240 screws and did not recognize stripping 90.8% of the time when it occurred. The tendency to strip screws was highly variable among individual surgeons (stripping ranging from 16.7% to 83.3%, P < 0.0001) and did not correlate with synthetic bone density in the range tested (P = 0.186) nor with the ranking of surgeons as resident or attending surgeon (P = 0.437). Screws that were correctly recognized as stripped retained a mean 55.0% of maximum torque, less than when stripping was not recognized (79.6%, P = 0.005). CONCLUSIONS: Surgeon perception is not reliable at preventing and detecting screw stripping at clinical torque levels in synthetic cancellous bone. Less aggressive insertion or standardized methods of insertion may improve the stability of nonlocking screw and plate constructs.

Subtalar arthrodesis alignment: the effect on ankle biomechanics.

BACKGROUND: The position, axis, and control of each lower extremity joint intimately affect adjacent joint function as well as whole-limb performance. A review of the literature finds little describing the biomechanics of subtalar arthrodesis and the effect on ankle biomechanics. The purpose of the current study was to establish this effect on sagittal plane ankle biomechanics. METHODS: A study was performed using a 3-dimensional, validated, computational model of the lower extremity. A subtalar arthrodesis was simulated from 20 degrees of varus to 20 degrees of valgus. At each arthrodesis position, the ankle dorsiflexor and plantarflexor muscles' fiber force, moment arm, and moments were calculated throughout a physiologic range of motion. RESULTS: Throughout ankle range of motion, plantarflexion and dorsiflexion strength varied with subtalar arthrodesis position. When the ankle joint was in neutral sagittal alignment, plantarflexion strength was maximized in 10 degrees of subtalar valgus, and strength varied by a maximum of 2.6% from the peak 221 Nm. In a similar manner, with the ankle joint in neutral position, dorsiflexion strength was maximized with a subtalar joint arthrodesis in 5 degrees of valgus, and strength varied by a maximum of 7.5% from the peak 46.8 Nm. The change in strength was due to affected muscle fiber force generating capacities and muscle moment arms. CONCLUSION: The significance of this study is that subtalar arthrodesis in a position of 5 to 10 degrees of subtalar valgus has a biomechanical advantage. CLINICAL RELEVANCE: This supports previous clinical outcome studies and offers a biomechanical rationale for their generally favorable outcomes.

The effect of clavicle malunion on shoulder biomechanics; a computational study.

BACKGROUND: Clavicle malunion affects the biomechanics of the shoulder joint. The purpose of this study is to establish the abduction, flexion, and internal (medial) rotation biomechanics of the shoulder after clavicle malunion. METHODS: A computational study was performed utilizing a three-dimensional, validated computational model of the upper extremity. Sequential shortening of the clavicle up to 20% was simulated. Muscle forces, moment arms, and moments were calculated for the surrounding musculature through a range of flexion, abduction, and internal rotation during the simulated shortening. FINDINGS: Shortening of the clavicle decreases the shoulder elevation moments of the upper extremity muscles during abduction. Internal rotation moments are also decreased with shortening. Flexion moments were affected less through physiologic range of motion. The observed effects are due to a combination of changes in moment arms of the individual muscles as well as a decrease in the force generating capacity of the muscles. Additionally, shortening of the clavicle increases coronal angulation of the clavicle at the sternoclavicular joint. INTERPRETATION: Shortening causes a decrease in the moment generating capacity as well as the total force generating capacity of the shoulder girdle muscles. The clinical significance of these computational results, which are consistent with recent clinical studies, is validation of the proposed functional deficit caused by clavicle malunion.

Galileo's contribution to modern orthopaedics.

INTRODUCTION: Galileo Galilei (1564-1642), world-renowned Italian mathematician, astronomer, physicist and philosopher, made many contributions to science. The objective of this study is to demonstrate that Galileo's discovery of scaling principles permitted others to define and advance orthopaedic research and clinical sciences. METHODS: The science and scaling principles of Galileo Galilei were extensively analyzed by reviewing his 1638 original work Discorsi e Demostrazioni Matematiche Intorno a Due Nuove Scienze. Works about Galileo's science were reviewed for the concept of the scaling principles and with the idea of shedding light on how his work influenced modern orthopaedics. RESULTS: Galileo strictly adhered to the Copernican heliocentric theory with the sun at the center of the universe, which caused him aggravation and made him the target of inquisition rage at the end of his prodigious life. With his attention away from the cosmos, Galileo--through the voices of Salviati, Sagredo and Simplicio in the Discourses on Two New Sciences--defined how scaling was important to the movement and function of objects. Galileo introduced important advances in scaling laws, which contributed to the development of the field of biomechanics. This discipline, in many ways, has defined modern clinical and research orthopaedics. DISCUSSION: Galileo, by introducing the principles of scaling, permitted their application to human physical capacity, to bone and tissue response after injury, and to clinical treatment of injuries. Galileo in this way made important contributions to the practice of modern orthopaedics.