Biomechanical Comparison of All-Suture, All-Inside Meniscus Repair Devices in a Human Cadaveric Meniscus Model

OBJECTIVE

Newer all-suture, all-inside meniscus repair devices utilize soft suture anchors. The purpose of this study was to compare the biomechanical performance of 4 meniscus repair devices in human cadaver menisci: the JuggerStitch (all-suture, all-inside), the FiberStitch (all-suture, all-inside), a polyether ether ketone (PEEK) all-inside, and an inside-out device.

DESIGN

Forty human cadaver menisci were tested after creating 20 mm longitudinal tears in the posterior meniscus. Each knee was randomized to 1 of 4 meniscus repair groups: JuggerStitch (all-suture, all-inside), FiberStitch (all-suture, all-inside), FAST-FIX 360 (PEEK-based anchor all-inside), and inside-out (with BroadbandTM tape meniscus needles). For each meniscus, 2 devices were used to prepare vertical mattress repair construct. The specimens were tested by pre-conditioning 20 cycles between 5 N and 30 N and then the tear diastasis was measured, followed by distraction to failure phase after imposing a displacement at a rate of 0.5 mm/s.

RESULTS

Ten menisci were tested in each of the 4 groups. After pre-conditioning, there was no significant difference in the gap formation among groups (P = 0.212). The average failure load for the JuggerStitch, FiberStitch, PEEK all-inside, and inside-out was 384 N, 311 N, 207 N, and 261 N, respectively, with a significant difference between groups (P = 0.034). Post hoc analysis showed the JuggerStitch failure load was higher than the PEEK all-inside and inside-out (P = 0.005, and P = 0.045, respectively). There was no significant difference between the failure load of the JuggerStitch and FiberStitch (P = 0.225).

CONCLUSION

The JuggerStitch all-suture device, FiberStitch all-suture device, PEEK all-inside, and inside-out devices have similar biomechanical properties for gapping and stiffness. The JuggerStitch all-suture, all-inside device has superior failure load compared with the PEEK all-inside and inside-out repair for longitudinal meniscus tear repair.

The Joystick Method: A Mini Open Technique for Repairing Patellar Osteochondral Fractures With Concomitant Medial Patellofemoral Ligament Reconstruction

Fixation of osteochondral fractures after patellar dislocation is typically done using an open approach due to the location of the defect. This is traditionally performed through a medial parapatellar arthrotomy to allow adequate visualization. By using the joystick method, adequate visualization is achieved with a smaller arthrotomy. Careful placement of the joystick in the planned anchor site of the medial patellofemoral ligament reconstruction reduces the number of drill sites in the patella.

How to Optimize Pedicle Screw Parameters for the Thoracic Spine? A Biomechanical and Finite Element Method Study

STUDY DESIGN

Pedicle screw study.

OBJECTIVE

The selection of pedicle screw parameters usually involves the surgeon's analysis of preoperative CT imaging along with anatomical landmarks and tactile examination. However, there is minimal consensus on a standardized guideline for selection methods on pedicle screws. We aimed to determine the effects of thoracic screw diameter to pedicle width on pullout strength determined by cortical bone purchase.

METHODS

Biomechanical study performed with human cadaveric thoracic vertebrae and experimentally validated three-dimensional finite element model instrumented with pedicle screws of various diameters. We used a variable (SD/PW) ratio to express the screw selection. We hypothesized a positive correlation between the pullout load determined by the bone purchase and the SD/PW. This relationship was first investigated in a validated finite element model considering bone purchase related to the strength of an upper thoracic vertebra. Then, the correlation to the entire spine is evaluated.

RESULTS

The failure load ranged from 371.3 to 1601.0 N, respectively, for 3 and 6 mm screws. The determinant coefficient was increased to R2=.421 when a linear relationship between pullout load and the SD/PW ratio was used. The peak loads of 1216 and 1288N were found for an SD/PW ratio of .83.

CONCLUSION

We have found that the screw pullout load is more correlated to SD/PW than other pedicle measures for a maximized SD/PW ratio of .83. This particular value should be considered the upper limit of the indicated SD/PW ratio and a means to determine the optimal screw diameter to enhance pullout strength.

In Vitro Evaluation of Lateral Femur Condyle Free Chondral Fragment Swelling after Soaking in Normal Saline

OBJECTIVE

After traumatic knee injuries, chondral fragments can avulse off bone with the progeny fragment becoming a loose body. The loose fragment may be larger than expected when trying to surgically repair the fragment back to its original site. The purpose of this study was to determine whether a loose chondral fragment from the lateral femur condyle would increase in size and weight after soaking in normal saline (NS) for 14 days.

DESIGN

Twelve 6-mm OAT (osteoarticular transfer) plugs were harvested from 6 cadaver knees on the lateral femoral condyle to simulate a chondral fragment. The chondral fragments were then placed inside an airtight specimen container with NS (0.9% sodium chloride) and were measured over 14 days.

RESULTS

After 14 days, the chondral fragments showed no increase in diameter as they measured an average of 5.567 ± 0.448 mm on Day 1 and 5.702 ± 0.253 mm on Day 14 (P = 0.183). The chondral fragments showed an increase in mass from an average of 0.058 ± 0.012 g on Day 1 to 0.073 ± 0.012 g on Day 14 (P < 0.001) and an increase in thickness from an average of 2.038 ± 0.346 mm on Day 1 to 2.229 ± 0.297 mm on Day 14 (P = 0.033).

CONCLUSIONS

Chondral fragments in NS increase in mass and thickness over time, but do not change in diameter. When surgeons are evaluating loose chondral fragments for fixation, they should consider that these fragments may appear thicker than the recipient location.

Acetabular Wall Weakening in Total Hip Arthroplasty: A Pilot Study

Total hip arthroplasty is a widely performed operation allowing disabled patients to improve their quality of life to a degree greater than any other elective procedure. Planning for a THA requires adequate patient assessment and preoperative characterizations of acetabular bone loss via radiographs and specific classification schemes. Some surgeons may be inclined to ream at a larger diameter thinking it would lead to a more stable press-fit, but this could be detrimental to the acetabular wall, leading to intraoperative fracture. In the attempt to reduce the incidence of intraoperative fractures, the current study aims to identify how increased reaming diameter degrades and weakens the acetabular rim strength. We hypothesized that there is proportionality between the reaming diameter and the reduction in acetabular strength. To test this hypothesis, this study used bone surrogates, templated from CT scans, and reamed at different diameters. The obtained bone surrogate models were then tested using an Intron 8874 mechanical testing machine (Instron, Norwood, MA) equipped with a custom-made fixture. Analysis of variance (ANOVA) was used to identify differences among reamed diameters while linear regression was used to identify the relationship between reamed diameters and acetabular strength. We found a moderate correlation between increasing reaming diameter that induced thinning of the acetabular wall and radial load damage. For the simplified acetabular model used in this study, it supported our hypothesis and is a promising first attempt in providing quantitative data for acetabular weakening induced by reaming.

Compressibility of Osteochondral Autograft Transfer Donor Grafts: A Comparison of Different Donor Regions and How Much Shortening Occurs of Plugs After Impaction

Background

Osteochondral autograft transfer (OAT) is a useful technique for full-thickness cartilage lesions of the distal femur. Various techniques recommend harvesting a plug 2 mm longer than the recipient hole to allow for graft impaction. Grafts with limited compressibility may not sit flush when impacted.

Purpose

To compare the compressibility/shortening of OAT donor plug regions from the distal femur of human cadaveric knees after impaction.

Study Design

Controlled laboratory study.

Methods

A total of 20 cadaveric knees (mean age, 70.3 ± 8.4 years) were divided into 4 donor regions: medial intercondylar (IC) notch, lateral IC notch, medial trochlea, and lateral trochlea. Each region was subdivided into 4 zones: far superior (FSZ), middle superior (MSZ), middle inferior (MIZ), and far inferior (FIZ). A total of 320 grafts (6-mm diameter, 15-mm depth) were extracted, and a custom-built machine was used to strike the graft 5 times using a predetermined energy of 0.11 J. The graft length was measured initially and after each impact. Statistical analysis of the compressibility for each of the 4 regions and all 16 zones was performed utilizing analysis of variance, with post hoc testing using the Fisher's least significant difference.

Results

Compression in the lateral IC notch, medial IC notch, medial trochlea, and lateral trochlea was 2.4 ± 1.5, 2.1 ± 0.7, 3.1 ± 2.2, and 2.1 ± 0.6 mm, respectively, with significant differences between the 4 regions (P < .01) and the most compression in the medial trochlea (P < .01). Subgroup analysis showed that the lateral trochlea had higher compressibility for FIZ versus MIZ (P = .02) and the lateral IC notch had higher compressibility for FSZ versus FIZ and MIZ (P < .05 for both).

Conclusion

Compressibility varied between OAT donor sites in the distal femur. OAT donor grafts showed the highest compressibility in the medial trochlea (3.1 mm) and lateral IC notch FSZ (3.0 mm).

Clinical Relevance

The lateral trochlea, medial IC notch, and the lower zones of the lateral IC notch grafts should not be oversized more than 2 mm in length, as these grafts may not compress adequately.

Experimental validation of a portable tidal volume indicator for bag valve mask ventilation

Introduction

Short-term emergency ventilation is most typically accomplished through bag valve mask (BVM) techniques. BVMs like the AMBU^® bag are cost-effective and highly portable but are also highly prone to user error, especially in high-stress emergent situations. Inaccurate and inappropriate ventilation has the potential to inflict great injury to patients through hyper- and hypoventilation. Here, we present the BVM Emergency Narration-Guided Instrument (BENGI) – a tidal volume feedback monitoring device that provides instantaneous visual and audio feedback on delivered tidal volumes, respiratory rates, and inspiratory/expiratory times. Providing feedback on the depth and regularity of respirations enables providers to deliver more consistent and accurate tidal volumes and rates. We describe the design, assembly, and validation of the BENGI as a practical tool to reduce manual ventilation-induced lung injury.

Methods

The prototype BENGI was assembled with custom 3D-printed housing and commercially available electronic components. A mass flow sensor in the central channel of the device measures air flow, which is used to calculate tidal volume. Tidal volumes are displayed via an LED ring affixed to the top of the BENGI. Additional feedback is provided through a speaker in the device. Central processing is accomplished through an Arduino microcontroller. Validation of the BENGI was accomplished using benchtop simulation with a clinical ventilator, BVM, and manikin test lung. Known respiratory quantities were delivered by the ventilator which were then compared to measurements from the BENGI to validate the accuracy of flow measurements, tidal volume calculations, and audio cue triggers.

Results

BENGI tidal volume measurements were found to lie within 4% of true delivered tidal volume values (95% CI of 0.53 to 3.7%) when breaths were delivered with 1-s inspiratory times, with similar performance for breaths delivered with 0.5-s inspiratory times (95% CI of 1.1 to 6.7%) and 2-s inspiratory times (95% CI of –1.1 to 2.3%). Audio cues “Bag faster” (1.84 to 2.03 s), “Bag slower” (0.35 to 0.41 s), and “Leak detected” (43 to 50%) were triggered close to target trigger values (2.00 s, 0.50 s, and 50%, respectively) across varying tidal volumes.

Conclusions

The BENGI achieved its proposed goals of accurately measuring and reporting tidal volumes delivered through BVM systems, providing immediate feedback on the quality of respiratory performance through audio and visual cues. The BENGI has the potential to reduce manual ventilation-induced lung injury and improve patient outcomes by providing accurate feedback on ventilatory parameters.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42490-022-00066-y.

Characterization of regional variation of bone mineral density in the geriatric human cervical spine by quantitative computed tomography

Background

Odontoid process fractures are among the most common in elderly cervical spines. Their treatment often requires fixation, which may include use of implants anteriorly or posteriorly. Bone density can significantly affect the outcomes of these procedures. Currently, little is known about bone mineral density (BMD) distributions within cervical spine in elderly. This study documented BMD distribution across various anatomical regions of elderly cervical vertebrae.

Methods and findings

Twenty-three human cadaveric C1-C5 spine segments (14 males and 9 female, 74±9.3 y.o.) were imaged via quantitative CT-scan. Using an established experimental protocol, the three-dimensional shapes of the vertebrae were reconstructed from CT images and partitioned in bone regions (4 regions for C1, 14 regions for C2 and 12 regions for C3-5). The BMD was calculated from the Hounsfield units via calibration phantom. For each vertebral level, effects of gender and anatomical bone region on BMD distribution were investigated via pertinent statistical tools.

Data trends suggested that BMD was higher in female vertebrae when compared to male ones. In C1, the highest BMD was found in the posterior portion of the bone. In C2, BMD at the dens was the highest, followed by lamina and spinous process, and the posterior aspect of the vertebral body. In C3-5, lateral masses, lamina, and spinous processes were characterized by the largest values of BMD, followed by the posterior vertebral body.

Conclusions

The higher BMD values characterizing the posterior aspects of vertebrae suggest that, in the elderly, posterior surgical approaches may offer a better fixation quality.

Variability in rod to bone distance needed in pelvic subcutaneous internal fixation to avoid nerve compression: A tridimensional population-based study

INTRODUCTION

Pelvic internal fixation has become a popular method for treatment of unstable pelvic ring injuries. Although successful, one complication is femoral nerve palsy from compression of the connecting rod. In light of this complication, this study was designed to evaluate sagittal inclinations of the rod and the feasibility of using a rod with a constant curvature.

HYPOTHESIS

It is hypothesized that that there is a connection between the sagittal inclination of the rod and the rod to bone distance, as well as single rod can be contoured with a constant curvature to be used in the majority of all patients.

METHODS

Three dimensional models of pelvis CTs from a single level 1 trauma center were created and imported into a program where software superimposed a pre-contoured rod in the sagittal planes upon the pelvic slices. The sagittal inclination was deemed acceptable is no interference occurred between the area of compression risk and the rod. For each pelvis and considered sagittal rod inclination, the rod radius of curvature (ROC), minimal rod to bone distance (RTB) and transverse inclinations (φ_L and φ_R) were measured at which the pedicle screws should be inserted to follow the direction of the smallest RTB.

RESULTS

The sagittal inclinations feasible for all subjects were between 15° to 30°. In this sagittal range, the average RTB varied in values ranging from 4.0±0.9mm to 25.4±11.4mm (p<0.01). Only 46% of subjects allowed a rod with constant curvature.

DISCUSSION AND CONCLUSION

Our study found that a rod to bone distance of 15mm was not safe for all models. As well, many subject models did not allow placement of pre-contoured rod. Patient specific templating of pelvic subcutaneous internal fixation is strictly needed to limit complications.

LEVEL OF EVIDENCE

VII; Basic Science.

Efficacy and safety testing of a COVID-19 era emergency ventilator in a healthy rabbit lung model

Background

The COVID-19 pandemic revealed a substantial and unmet need for low-cost, easily accessible mechanical ventilation strategies for use in medical resource-challenged areas. Internationally, several groups developed non-conventional COVID-19 era emergency ventilator strategies as a stopgap measure when conventional ventilators were unavailable. Here, we compared our FALCON emergency ventilator in a rabbit model and compared its safety and functionality to conventional mechanical ventilation.

Methods

New Zealand white rabbits (n = 5) received mechanical ventilation from both the FALCON and a conventional mechanical ventilator (Engström Carestation™) for 1 h each. Airflow and pressure, blood O₂ saturation, end tidal CO₂, and arterial blood gas measurements were measured. Additionally, gross and histological lung samples were compared to spontaneously breathing rabbits (n = 3) to assess signs of ventilator induced lung injury.

Results

All rabbits were successfully ventilated with the FALCON. At identical ventilator settings, tidal volumes, pressures, and respiratory rates were similar between both ventilators, but the inspiratory to expiratory ratio was lower using the FALCON. End tidal CO₂ was significantly higher on the FALCON, and arterial blood gas measurements demonstrated lower arterial partial pressure of O₂ at 30 min and higher arterial partial pressure of CO₂ at 30 and 60 min using the FALCON. However, when ventilated at higher respiratory rates, we observed a stepwise decrease in end tidal CO₂. Poincaré plot analysis demonstrated small but significant increases in short-term and long-term variation of peak inspiratory pressure generation from the FALCON. Wet to dry lung weight and lung injury scoring between the mechanically ventilated and spontaneously breathing rabbits were similar.

Conclusions

Although conventional ventilators are always preferable outside of emergency use, the FALCON ventilator safely and effectively ventilated healthy rabbits without lung injury. Emergency ventilation using accessible and inexpensive strategies like the FALCON may be useful for communities with low access to medical resources and as a backup form of emergency ventilation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42490-022-00059-x.

Medial Transmalleolar Portal Technique for Ankle Arthroscopic Headless Screw Fixation of Talar Osteochondritis Dissecans Lesions

This article describes a technique for arthroscopic fixation of an osteochondritis dissecans (OCD) lesion of the medial talar dome with headless compression screws. This technique involves creation of a medial transmalleolar portal using a guide and drill. The medial transmalleolar portal grants perpendicular access for screw fixation of OCD lesions in addition to the potential for osteochondral autograft transplantation (OAT). Advantages include access to the medial talar dome without performing a medial malleolar osteotomy. After completion of OCD fixation, an inverted osteochondral plug can be used to backfill the portal.

Ideal Donor Site for Osteochondral Autografting of the Distal Femur Using Radius of Curvature: A 3-Dimensional High-Resolution Scanner Comparison

OBJECTIVE

To compare radius of curvature (RoC) of distal femur osteochondral autograft transfer (OAT) donor sites from the intercondylar notch and trochlear ridge with recipient sites on the distal and posterior condyles and evaluate differences between recipient sites.

DESIGN

Nineteen cadaveric femurs were scanned with a 3-dimensional high-resolution sensor. Donor regions included the lateral (LTR) and medial trochlear ridges (MTR), and the lateral (LICN) and medial intercondylar notch (MICN). Recipient regions analyzed were the distal medial (DMFC), posterior medial (PMFC), distal lateral (DLFC), and posterior lateral femur condyle (PLFC). Six-millimeter OAT grafts were simulated, and average RoC of all regions was compared using an analysis of variance. Post hoc testing was performed using Fisher's least significant difference.

RESULTS

We found no significant differences in RoC of the LICN compared with all 4 recipient sites (P = 0.19, 0.97, 0.11, and 0.75 for DLFC, PLFC, DMFC, and PMFC, respectively) or the LTR and MTR to the posterior condyles (LTR vs. PLFC and PMFC; P = 0.72, 0.47, MTR vs. PLFC and PMFC P = 0.39, 0.22, respectively). Significant differences were found for RoC of the MICN compared with each recipient site (P < 0.001) and between distal and posterior femoral condyles (DLFC vs. PLFC, P = 0.016; DMFC vs. PMFC, P = 0.023).

CONCLUSION

The LICN is the ideal donor option for all recipient sites on the femoral condyles with respect to RoC of 6-mm OAT plugs. The MTR and LTR were acceptable donor sources for the posterior condyles, while the MICN was a poor match for all recipient sites. Additionally, the distal femur condyle and posterior femur condyle have different RoCs.

The Ideal Cortical Button Location on the Lateral Femur for Anterior Cruciate Ligament Suspensory Fixation is 30 mm Proximal to the Lateral Epicondyle

Purpose

To determine the ideal location for anterior cruciate ligament (ACL) suspensory cortical button placement on the lateral femur with the highest failure load and to establish the relationship of tunnel diameter and cortical thickness on load to failure.

Methods

Computed tomography (CT) data were obtained from 45 cadaveric distal femurs. A Cartesian coordinate system was established along the lateral femur with the lateral epicondyle (LE) as a reference point. Locations 0, 20 and 30 mm from the LE along lines 0°, 25°, 50°, and 75° posterioproximal from the axial plane were created. Tunnels connecting from each location to the center of the ACL footprint were simulated. Cortical thickness and long axis diameter of the oval cortical holes were determined for each location. Based on the CT data, custom drill guides were created and used to drill 4.5 mm tunnels at each lateral femur location to the ACL footprint on the cadaver femurs. Cortical buttons were placed at each location and pulled using a servohydraulic testing system. The correlation of tunnel diameter and cortical thickness to button failure load were analyzed using a regression analysis.

Results

Significant differences were found for failure load (P<.0001) and cortical thickness between the locations tested (P<.0001). The location 30 mm proximal from the LE and 75⁰ from the axial plane had the highest failure load of 573 N. A regression analysis (R² = .15) indicated that the cortical thickness was significantly correlated with load to failure (P <.0001), whereas the long-axis diameter was not (P = .33).

Conclusion

The ideal cortical button location on the lateral femur for ACL suspensory fixation was located 30 mm proximal from the lateral epicondyle, based on this area’s high failure load. Oblique tunnel drilling of this proximal location may cause a larger long-axis diameter cortical hole, but the cortex is also thicker, which is more closely correlated with failure load.

Clinical Relevance

Different ACL suspensory cortical button locations on the lateral femur have different failure loads based on the cortical thickness of the bone supporting the button. It is important for surgeons to understand which drilling techniques place the button in a proximal and posterior location, especially if the bone quality of the patient is of concern.

Salvaging Pull-Out Strength in a Previously Stripped Screw Site: A Comparison of Three Rescue Techniques

Screw stripping during bone fixation is a common occurrence during operations that results in decreased holding capacity and bone healing. We aimed to evaluate the rescue of the stripped screw site using screws of different dimensions. Five screw configurations were tested on cadaveric specimens for pull-out strength (POS). The configurations included a control screw tightened without stripping, a configuration voluntarily stripped and left in place, and three more configurations in which the stripped screws were replaced by a different screw with either increased overall length, diameter, or thread length. Each configuration was tested five times, with each screw tested once. The POS of the control screw, measured to be 153.6 ± 27 N, was higher than the POS measured after stripping and leaving the screw in place (57.1 ± 18 N, p = 0.001). The replacement of the stripped screw resulted in a POS of 158.4 ± 64 N for the screw of larger diameter, while the screws of the same diameter but increased length or those with extended thread length yielded POS values of 138.4 ± 42 and 185.7 ± 48 N, respectively. Screw stripping is a frequent intraoperative complication that, according to our findings, cannot be addressed by leaving the screw in place. The holding capacity of a stripped screw implanted in cancellous bone can successfully be restored with a different screw of either larger diameter, longer length, or extended thread length.

Role of the transverse ligament of the ulnar collateral ligament of the elbow: a biomechanical study

Background

The ulnar collateral ligament (UCL) complex of the elbow plays a primary role in valgus and posteromedial stability of the elbow. The anterior oblique ligament (AOL) of the UCL is believed to provide the majority of resistance to external forces on the medial elbow. The transverse ligament (TL) of the UCL is generally thought to have minimal contribution to the elbow’s overall stability. However, recent studies have suggested a more significant role for the TL. The primary aim of this study was to identify the TL’s contribution to the stability of the elbow joint in determining the joint stiffness and neutral zone variation in internal rotation.

Methods

Twelve cadaveric elbows, set at a 90° flexion angle, were tested by applying an internal rotational force on the humerus to generate a medial opening torque at the level of the elbow. The specimens were preconditioned with 10 cycles of humeral internal rotation with sinusoidal torque ranging from 0 to 5 Nm. Elbow stiffness measures and joint neutral zone were first evaluated in its integrity during a final ramp loading. The test was subsequently repeated after cutting the TL at 33%, 66%, and 100% followed by the AOL in the same fashion.

Results

The native UCL complex joint stiffness to internal rotation measured 1.52 ± 0.51 Nm/°. The first observable change occurred with 33% sectioning of the AOL, with further sectioning of the AOL minimizing the joint stiffness to 1.26 ± 0.32 Nm/° (P = .004). A 33% resection of the TL found an initial neutral zone variation of 0.376 ± 0.23° that increased to 0.771 ± 0.41° (P < .01) at full resection. These values were marginal when compared with the full resection of the AOL for which we have found 3.69 ± 1.65° (P < .01).

Conclusion

The TL had no contribution to internal rotation elbow joint stiffness at a flexion angle of 90°. However, sequential sectioning of the TL was found to significantly increase the joint neutral zone when compared with the native cadaveric elbow at a flexion angle of 90°. This provides evidence toward the TL having some form of contribution to the elbow’s overall stability.

Construction and Performance Testing of a Fast-Assembly COVID-19 (FALCON) Emergency Ventilator in a Model of Normal and Low-Pulmonary Compliance Conditions

INTRODUCTION

The COVID-19 pandemic has revealed an immense, unmet and international need for available ventilators. Both clinical and engineering groups around the globe have responded through the development of "homemade" or do-it-yourself (DIY) ventilators. Several designs have been prototyped, tested, and shared over the internet. However, many open source DIY ventilators require extensive familiarity with microcontroller programming and electronics assembly, which many healthcare providers may lack. In light of this, we designed and bench tested a low-cost, pressure-controlled mechanical ventilator that is "plug and play" by design, where no end-user microcontroller programming is required. This Fast-AssembLy COVID-Nineteen (FALCON) emergency prototype ventilator can be rapidly assembled and could be readily modified and improved upon to potentially provide a ventilatory option when no other is present, especially in low- and middle-income countries.

HYPOTHESIS

We anticipated that a minimal component prototype ventilator could be easily assembled that could reproduce pressure/flow waveforms and tidal volumes similar to a hospital grade ventilator (Engström CarestationTM).

MATERIALS AND METHODS

We benched-tested our prototype ventilator using an artificial test lung under 36 test conditions with varying respiratory rates, peak inspiratory pressures (PIP), positive end expiratory pressures (PEEP), and artificial lung compliances. Pressure and flow waveforms were recorded, and tidal volumes calculated with prototype ventilator performance compared to a hospital-grade ventilator (Engström CarestationTM) under identical test conditions.

RESULTS

Pressure and flow waveforms produced by the prototype ventilator were highly similar to the CarestationTM. The ventilator generated consistent PIP/PEEP, with tidal volume ranges similar to the CarestationTM. The FALCON prototype was tested continuously for a 5-day period without failure or significant changes in delivered PIP/PEEP.

CONCLUSION

The FALCON prototype ventilator is an inexpensive and easily-assembled "plug and play" emergency ventilator design. The FALCON ventilator is currently a non-certified prototype that, following further appropriate validation and testing, might eventually be used as a life-saving emergency device in extraordinary circumstances when more sophisticated forms of ventilation are unavailable.

Biomechanical Analysis of Patellar Tendon Repair With Knotless Suture Anchor Tape Versus Transosseous Suture

Background

Patellar tendon ruptures have routinely been repaired with transosseous suture tunnels. The use of knotless suture anchors for repair has been suggested as an alternative.

Purpose

To compare the load to failure and gap formation of patellar tendon repair at the inferior pole of the patella with knotless suture anchor tape versus transosseous sutures. A secondary objective was to investigate whether either technique shows an association between bone density and load to failure.

Study Design

Controlled laboratory study.

Methods

A total of 20 human tibias with attached patellar and quadriceps tendons were sharply incised at the bone-tendon junction at the inferior pole of the patella. A total of 10 tendons were repaired using 2 knotless suture anchors in the inferior pole of the patella and a single suture tape with 2 core sutures. The other 10 tendons were repaired using No. 2 suture passed through 3 transosseous tunnels. A distracting force was then applied through the suture in the quadriceps tendon. Gap distance through load cycling at the repair site and maximum load at repair failure were then measured. Bone density was measured using computed tomography scanning.

Results

No difference was found in the mean load to failure of knotless patellar tendon repair versus transosseous suture repair (367.6 ± 112.2 vs 433.9 ± 99 N, respectively; P = .12). After 250 cycles, the mean repair site gap distance was 0.85 ± 0.45 mm for the knotless patellar tendon repair versus 2.94 ± 2.03 mm for the transosseous suture repair (P = .03). A small correlation, although not statistically significant, was found between bone density and load to failure for the knotless tape repair (R ² = 0.228; P = .66). No correlation was found between bone density and load to failure for the transosseous repair (R ² = 0.086; P = .83).

Conclusion

Suture tape repair with knotless anchors for repair of patellar tendon rupture has comparable load to failure with less gap formation than transosseous suture repair. There is a small correlation between bone density and failure load for knotless anchor repair, which may benefit from further investigation.

Clinical Relevance

Using knotless suture anchors for patellar tendon rupture repair would allow for a smaller incision, less dissection, and likely shorter operating time.

Screw insertion torque as parameter to judge the fixation. Assessment of torque and pull-out strength in different bone densities and screw-pitches

BACKGROUND

Pull-out strength is a critical parameter to judge screw fixation in orthopaedic implants. However, the insertion torque is the main feeling in the hand of a surgeon relating to the strength of synthesis. The correlation between pull-out strength and torque is not completely understood. This creates uncertainty about the key-question: Should the torque be considered a valid parameter to judge the quality of fixation?

METHODS

Using the ASTM F543 as reference, three screws differing only in pitch (1.5, 2.1, 2.8 mm pitches) were tested in three foam-block densities (10, 15, and 20 pcf). The correlation was investigated by assessing the role of density and screw geometry.

FINDINGS

Torque was related to pull-out strength in all configurations (R = 0.979, P = 0.000). No difference in pull-out strength was found when screws were tightened to a range of 71.6%, SD = 7.6, of torque to fail (P > 0.05). Torque and pull-out strength were stratified according to density that influenced the two parameters up to 524% (P < 0.000). Pitch determined pull-out strength up to 33% (P < 0.000) while the 2.1 mm screw pitch showed the highest pull-out strength and torque in all configurations.

INTERPRETATION

Insertion torque was demonstrated to be a valid parameter to judge the quality of bone under fixation and therefore, the strength of the synthesis. Surgeons should not tighten the screws to values approaching torque to fail to obtain the highest pull-out strength. Density was the main factor influencing pull-out strength and torque. Pitch is another parameter deciding screw holding capacity.

Safe Supra-Acetabular Pin Insertion in Relation to Intraosseous Depth

In pelvic fractures, dysfunction of the pelvic ring is often stabilized with supra-acetabular pin insertion. In existing literature, there are heterogeneous indications on proper pins selection and inclinations. Therefore, this study aimed to quantify the narrowing of safe pin corridors in the transverse and sagittal planes with increments of intraosseous screw depths. A computer algorithm created cross-sections over three-dimensional pelvic reconstructions at sagittal inclinations from 45° cranial to 45° caudal in 5° increments. Templates of screw depths spanning 60-120 mm in 15 mm increments were disposed in the transverse plane from 45° medial to 45° lateral. Each intraosseous screw depth and transverse angle were evaluated for intraosseous containment to evaluate ranges narrowing with increasing screw depths. The 60-mm depth resulted in the largest sagittal range (60.9° ± 6.9°) and transverse range (27.5° ± 4.1°) at 30° caudal. Increasing depths by 15 mm resulted in ranges being significantly different from one another (p < 0.01). The sagittal plane of 20° cranial had the highest frequency of insertion for all depths, while transverse ranges were narrowed (p < 0.01). Bisecting angles were similar for sagittal planes 20° cranial to 30° caudal with an average of 27.9° ± 1.2° (p ≥ 0.115). In conclusion, while 60 mm depths can be inserted with the highest discretion, 15 mm increments in depth significantly reduce safe ranges. Screws depths above 90 mm have low frequencies of insertion, should be inserted more cranially and must be considered prone to breaching. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1790-1797, 2019.

Currently Adopted Criteria for Pedicle Screw Diameter Selection

Background

Transpedicular screw insertion has become widely accepted for the correction of spinal deformity as well as degenerative and traumatic injury, but adoption of this technique has remained less widespread in the thoracic compared to the lumbar spine. This is thought to be associated with the relative technical difficulty of screw insertion into the narrower widths of the thoracic pedicles and the neurologic and mechanical risks associated with breach of the pedicle wall. The surgical decision making involves determining the appropriate sized screw for maximum fixation strength while simultaneously respecting the structural integrity of the vertebral pedicles to prevent a breach and provide better fixation. This paper presents a systematic review of criteria for thoracic pedicle screw diameter (SD) selection in order to orient inexperienced surgeons on the impact of this selection on pedicle breaching and fixation strength.

Methods

We performed a systematic literature review focused on studies reporting SD selection in relation to pedicle dimensions, measures of fixation strength, and breach rate.

Results

Twenty-nine articles that measured fixation strength, breach rate, and/or provided SD in relation to pedicle width were selected for inclusion.

Conclusions

A commonly accepted criteria for pedicle SD selection has not yet been proposed. Screw diameters approximately 80% of the pedicle width have been adopted, but this proportion is rarely reported in the midthoracic vertebrae for which smaller pedicles and inadequate hardware specificity result in higher breach rates. Depending upon the insertion technique adopted, greater specificity in diameter selection by vertebral level should be pursued in order to maximally target cortical bone purchase.

Clinical Relevance

Based on this review of the literature, we believe that proper selection of the SD for individual vertebral level directly affects the insertion technique and the potential breach.

A novel technique with reduced computed tomography exposure to predict vertebral compression fracture: a finite element study based on rat vertebrae

Vertebral compression fractures are a significant clinical issue with an annual incidence of approximately 750,000 cases in the USA alone. Mechanical properties of vertebrae are successfully evaluated through finite element (FE) models based on vertebrae CT. However, clinical drawbacks associated to radiation transmission encouraged to explore the possibility to use selected or reduced portions of the vertebra. The objective of our study was to develop a new procedure to predict vertebral compression fracture from sub-volumes. We reconstructed rat vertebras from micro-CT of thoracic and lumbar groups. Each vertebra was partitioned into three sub-volumes of different axial thickness. FE simulating compression tests were performed on each model to evaluate their failure load and stiffness. Using a power function, a high correlation was found for stiffness and strength. The sub-volume with three fifths thickness had a failure load of 180.7 ± 19.2 N for thoracic and of 209.5 ± 27.4 N for the lumbar vertebra. These values were not significantly different from the values found for the entire vertebra (p > 0.05). Based on our findings, failure loads and stiffnesses obtained with reduced CT scans can be successfully used to predict full vertebral failure. This sub-region analysis and power relationship suggests that one can limit radiation exposure to patients when bone characterization is needed. Graphical abstract Estimated mechanical properties in relation to the extent of the computed tomography reconstruction.

Pedicle Screw With Increased Cortical Purchase Can Be Inserted With Same Accuracy as the Screw in Straightforward Trajectory Using 3D Modeling Landmarks

STUDY DESIGN

Comparison, in terms of insertion accuracy and biomechanical performance, between an increased cortical purchase and straightforward pedicle screw trajectory.

OBJECTIVE

This study aims to compare a trajectory with increased cortical purchase to the more common straightforward trajectory in terms of strength and insertion accuracy using real-time navigation.

SUMMARY OF BACKGROUND DATA

In previous studies, it was suggested that pedicle screw pullout strength is strongly correlated with bone mineral density, and using a more cortical tract allows a greater portion of the denser bone, the cortex, to be in contact with the screw. In light of this advantage, an insertion technique has been proposed more recently, to increase the cortical purchase to maximize screw thread contact with cortical bone. It is performed inserting the screw with reduced transverse inclination and results in cortical bone purchase in the lateral portion of the pedicle.

METHODS

Eight T1 and eight T3 vertebra models were reconstructed in Mimics Suite (Materialise, Leuven, Belgium) using CT data obtained with a Medtronic O-arm. Using a previously developed computer algorithm, we calculated all achievable safe trajectories for pedicle screw placement ensuring a minimal distance of 0.5 mm between screw and pedicle edges. For both vertebrae, among these, the straightest and the most convergent trajectories with the calculated insertion region greater than 15% of the total were selected to safely instrument the vertebrae, respectively, as ICP and straightforward techniques. The straightforward technique was planned with a transverse angle of 22.50° in both vertebrae whereas the ICP was planned with a transverse angle of 12.50° for T1 and 2.5° for T3. The screws were implanted by a surgeon experienced in straightforward insertion, and other independent investigators measured placement accuracy and mechanical performance.

RESULTS

The transverse screw angles for T1 and T3 with straightforward technique had average values of 24.93° ± 2.96° and 23.53° ± 2.70°, respectively. For the ICP technique, the average values were 15.60° ± 2.95° for T1 and 2.29° ± 1.55° for T3. The resultant errors associated with screw placement for T1 and T3 were not significantly different (p > .05). The pullout failure loads with straightforward techniques ranged from 756 ± 164 N in T1 to 703 ± 74 N in T3 and were not significantly different (p > .05) from the values of 699 ± 84 N for T1 and of 732 ± 113 N measured for the ICP.

CONCLUSIONS

For the upper thoracic vertebrae tested, despite the use of shorter screws, the insertion technique with increased cortical purchase, in biomechanical terms, is comparable with the straightforward trajectory. Using guidance, the proposed ICP technique was performed with the same accuracy as the popular straightforward technique.

LEVEL OF EVIDENCE

Level V.

Stability and Spine Pedicle Screws Fixation Strength-A Comparative Study of Bone Density and Insertion Angle

STUDY DESIGN

Analysis of insertion angle and bone density on the pedicle screw fixation strength with a novel testing protocol that accounts for the articular processes.

OBJECTIVE

To analyze the relationship between pedicle screw fixation strength and bone mineral density for different transverse screw insertion angles.

SUMMARY OF BACKGROUND DATA

The stability of the screw can become compromised by demineralization of the vertebral bone due to diseases such as osteoporosis. A weakening of the bone-screw interface, and therefore, a decrease in the fixation strength of the screw, leads to an increased probability of instrument failure, most commonly by screw loosening or screw pullout.

METHODS

Using the ASTM F543 as reference, we performed pullout tests with an Instron mechanical testing machine of a posterior fixation construct mimicking two pedicle screws connected at a distance of 40 mm as suggested by the ASTM F1717 on four densities of polyurethane foam in accordance with the ASTM F1839-08 standard to simulate bone densities ranging from osteoporotic (5 pcf) to higher than normal (20 pcf) in four transverse insertion angles.

RESULTS

A linear regression with two independent variables was found to be Y = -354.8812 + 91.8102 × X₁ - 6.8747 × X₂ (X₁ = density [pcf], X₂ = angle [degrees]), with a correlation coefficient of 0.95 for all the experimental data.

CONCLUSIONS

Pedicle screw insertion angle and bone density are critical to pullout strength. However, in osteoporotic bone, the insertion angle has only a marginal influence on pullout strength.

LEVEL OF EVIDENCE

V.

Validating a Modified Circle Theorem Method for the Measurement of Acetabular Cup Anteversion on Plain Radiography with Intra-Operative Data from Robotic Assisted Total Hip Arthroplasty

This study aims to validate a modified circle theorem method for the calculation of true version of the acetabular component on anteroposterior x-rays with intra-operative version data derived from robotic assisted total hip arthroplasty (THA). Planar anteversion measurements recorded intraoperatively in 80 THAs were correlated to measurements on anteroposterior radiographs. The mean anteversion of the cohort measured by the robotic system and on plain radiography was 21.2° ± 2.0° and 19.9° ± 3.4° respectively and 97.5% of cases were in a 30% relative error. The correlation between the true and planar measurements of anteversion on plain radiographs was strong (Pearson correlation coefficient of 0.9422). We conclude that the circle theorem method can be validated with data from robotic guided THA.

Role of posterior elements in the disc bulging of a degenerated cervical spine

BACKGROUND

Many studies have been developed to characterize the mechanical behavior of the intervertebral disc specifically for the lumbar spine and there have been limited studies done on the cervical spine with the goal to evaluate the strength of the cervical spine under compression without any information on the bulging of the intervertebral discs. The goal of the current study is to examine the deformation response of the cervical intervertebral disc classified with grade III or greater degeneration and analyze the relationship between axial deformation and anterior and posterior bulge under compression up to 550 N.

METHODS

Each specimen was compressed for 3 cycles to a maximum load of 550N in steps of 50 N. The bulge was measured using Linear Variable Differential Transformers (LVDTs on an intact spinal segment, spinal segment with post laminectomy, and spinal segment post facetectomy.

RESULTS

The anterior budge for an intact spinal segment shows a change of slope at loads of 262N±66N. For a physiological load of 250N the vertical displacement or spine segment height was reduced by 10.1% for an intact segment and 8.78% for the laminectomy and facetectomy configurations with F = 0.159 (Fcrit = 3.89) with no statistical difference observed. For the post laminectomy there was a decrease of 35% in anterior bulge compared to the intact specimen.

CONCLUSIONS

Our results show that for grade III disc degeneration the cervical segments bulging for both the laminectomy and facetectomy procedures are not significantly different. In post laminectomy the average anterior and posterior bulges are similar to the average anterior and posterior bulge post facetectomy.