Critical loss of primary implant stability in osteosynthesis locking screws under cyclic overloading

Primary implant stability, which refers to the stability of the implant during the initial healing period is a crucial factor in determining the long-term success of the implant and lays the foundation for secondary implant stability achieved through osseointegration. Factors affecting primary stability include implant design, surgical technique, and patient-specific factors like bone quality and morphology. In vivo, the cyclic nature of anatomical loading puts osteosynthesis locking screws under dynamic loads, which can lead to the formation of micro cracks and defects that slowly degrade the mechanical connection between the bone and screw, thus compromising the initial stability and secondary stability of the implant. Monotonic quasi-static loading used for testing the holding capacity of implanted screws is not well suited to capture this behavior since it cannot capture the progressive deterioration of peri‑implant bone at small displacements. In order to address this issue, this study aims to determine a critical point of loss of primary implant stability in osteosynthesis locking screws under cyclic overloading by investigating the evolution of damage, dissipated energy, and permanent deformation. A custom-made test setup was used to test implanted 2.5 mm locking screws under cyclic overloading test. For each loading cycle, maximum forces and displacement were recorded as well as initial and final cycle displacements and used to calculate damage and energy dissipation evolution. The results of this study demonstrate that for axial, shear, and mixed loading significant damage and energy dissipation can be observed at approximately 20 % of the failure force. Additionally, at this load level, permanent deformations on the screw-bone interface were found to be in the range of 50 to 150 mm which promotes osseointegration and secondary implant stability. This research can assist surgeons in making informed preoperative decisions by providing a better understanding of the critical point of loss of primary implant stability, thus improving the long-term success of the implant and overall patient satisfaction.

In-plane compressive responses and failure behaviors of composite sandwich plates with resin reinforced foam core

The paper presented an experimental study on the effect of the resin reinforced core configuration and core thickness on in-plane compressive responses and failure behaviors of composite sandwich specimens. Two resin reinforced core machining configurations were designed with three core thickness along. In-plane compressive load, displacement, strains on both sides, and failure morphology were closely monitored during the loading process. Meanwhile, the theoretical method also was supplementary to forecast the failures of sandwich structures. It was found that the enhancement of grooved, perforated holes and contour cut (GPC) core was better than double-side grooved and perforated hole (DGP) core to improve the in-plane compressive capacity of sandwich specimens for all thick cores. The core fracture or skin/core debonding failure of sandwich specimens resulted in an instant drop of in-plane compressive load, and the global buckling led to a slower reduction. The failure mode changed from global buckling to skin/core debonding at both sides as the core thickness increased for the Plain core sandwich specimen; switched from global buckling to a combined failure of core fracture and skin/core debonding at both sides, and then to skin/core debonding at both sides for the DGP core sandwich specimen; the skin/core debonding at the shallow side occurred for all GPC core specimens. The slight buckling trace of strains before the peak load probably triggered the skin/core debonding of sandwich specimens. The theoretical method could well forecast failure loads and corresponding failure modes of sandwich specimens with the 15 mm thick core, and reasonably predict failure loads for sandwich specimens with 30 mm and 45 mm thick cores.

Failure loads of heat-pressed versus milled lithium disilicate endocrowns

OBJECTIVES

This study aimed to compare the failure load of heat-pressed versus milled lithium disilicate endocrowns.

MATERIALS AND METHODS

Twenty extracted mandibular molars were sectioned 1.5 mm above the CEJ. Root canal treatment and endocrown preparation were done for all teeth. Samples were then divided into two groups: heat-pressed glass ceramic endocrowns (HP group) (n = 10) and milled endocrowns (CAD group) (n = 10). Cementation was done using self-adhesive resin cement, and a compressive load was applied on the occlusal surface of the specimens until failure occurred.

RESULTS

The mean failure loads were significantly higher in the HP group (2546.5 ± 339 N) compared to the CAD group (1759.9 ± 114.2) (p < 0.05), and majority of failures were due to fracture of the restoration.

CONCLUSIONS

Failure loads of heat-pressed lithium disilicate endocrown are superior to milled endocrown.

CLINICAL RELEVANCE

Molars restored with lithium disilicate endocrowns have higher failure loads than the maximum human bite force regardless of the fabrication method. Although heat-pressed endocrowns have superior failure loads to milled ones, both are indicated for restoring endodontically treated molar teeth.

Gait speed and spasticity are independently associated with estimated failure load in the distal tibia after stroke: an HR-pQCT study

This HR-pQCT study was conducted to examine bone properties of the distal tibia post-stroke and to identify clinical outcomes that were associated with these properties at this site. It was found that spasticity and gait speed were independently associated with estimated failure load in individuals with chronic stroke.

PURPOSE

(1) To examine the influence of stroke on distal tibia bone properties and (2) the association between these properties and clinical outcomes in people with chronic stroke.

METHODS

Sixty-four people with stroke (age, 60.8 ± 7.7 years; time since stroke, 5.7 ± 3.9 years) and 64 controls (age: 59.4 ± 7.8 years) participated in this study. High-resolution peripheral quantitative computed tomography (HR-pQCT) was used to scan the bilateral distal tibia, and estimated failure load was calculated by automated finite element analysis. Echo intensity of the medial gastrocnemius muscle and blood flow of the popliteal artery were assessed with ultrasound. The 10-m walk test (10MWT), Fugl-Meyer Motor Assessment (FMA), and Composite Spasticity Scale (CSS) were also administered.

RESULTS

The percent side-to-side difference (%SSD) in estimated failure load, cortical area, thickness, and volumetric bone mineral density (vBMD), and trabecular and total vBMD were significantly greater in the stroke group than their control counterparts (Cohen's d = 0.48-1.51). Isometric peak torque and echo intensity also showed significant within- and between-groups differences (p ≤ 0.01). Among HR-pQCT variables, the %SSD in estimated failure load was empirically chosen as one example of the strong discriminators between the stroke group and control group, after accounting for other relevant factors. The 10MWT and CSS subscale for ankle clonus remained significantly associated with the %SSD in estimated failure load after adjusting for other relevant factors (p ≤ 0.05).

CONCLUSION

The paretic distal tibia showed more compromised vBMD, cortical area, cortical thickness, and estimated failure load than the non-paretic tibia. Gait speed and spasticity were independently associated with estimated failure load. As treatment programs focusing on these potentially modifiable stroke-related impairments are feasible to administer, future studies are needed to determine the efficacy of such intervention strategies for improving bone strength in individuals with chronic stroke.

Failure load of the femoral insertion site of the anterior cruciate ligament in a porcine model: comparison of different portions and knee flexion angles

BACKGROUND

This study compared the failure load of the femoral insertion site of the anterior cruciate ligament between different portions and knee flexion angles.

METHODS

In total, 87 fresh-frozen, porcine knees were used in this study. Three knees were used for histological evaluation; the remaining 84 knees were randomly divided into 4 groups: anterior anteromedial bundle, posterior anteromedial bundle, anterior posterolateral bundle, and posterior posterolateral bundle groups (n=21 per group). The anterior cruciate ligament femoral insertion site was divided into these four areas and excised, leaving a 3-mm square attachment in the center of each bundle. Tibia-anterior cruciate ligament-femur complexes were placed in a material testing machine at 30°, 120°, and 150° of knee flexion (n=7), and the failure load for each portion was measured under anterior tibial loading (0.33 mm/s).

RESULTS

Histological study showed that the anterior cruciate ligament femoral insertion site consisted of direct and indirect insertions. Comparison of the failure load between the knee flexion angles revealed that all the failure loads decreased with knee flexion; significant decreases were observed in the failure load between 30 and 150° knee flexion in the posterior anteromedial bundle and posterior posterolateral bundle groups. Comparison of the failure load according to different portions revealed a significant difference between the anteromedial and posterolateral bundle groups at 150° of knee flexion, but no significant difference among the groups at 30° of flexion.

CONCLUSIONS

Although the failure load of the posterior portion decreased significantly in the knee flexion position, it (mainly consisting of indirect insertion) plays a significant role against anterior tibial load in the knee extension position; this appears to be related to the characteristics of the insertion site. Reflecting the complex structure and function of the ACL, this study showed that the failure load of the femoral insertion site varies with differences in positions and knee flexion angles.

Non-invasive prediction of the mouse tibia mechanical properties from microCT images: comparison between different finite element models

New treatments for bone diseases require testing in animal models before clinical translation, and the mouse tibia is among the most common models. In vivo micro-Computed Tomography (microCT)-based micro-Finite Element (microFE) models can be used for predicting the bone strength non-invasively, after proper validation against experimental data. Different modelling techniques can be used to estimate the bone properties, and the accuracy associated with each is unclear. The aim of this study was to evaluate the ability of different microCT-based microFE models to predict the mechanical properties of the mouse tibia under compressive load. Twenty tibiae were microCT scanned at 10.4 µm voxel size and subsequently compressed at 0.03 mm/s until failure. Stiffness and failure load were measured from the load-displacement curves. Different microFE models were generated from each microCT image, with hexahedral or tetrahedral mesh, and homogeneous or heterogeneous material properties. Prediction accuracy was comparable among models. The best correlations between experimental and predicted mechanical properties, as well as lower errors, were obtained for hexahedral models with homogeneous material properties. Experimental stiffness and predicted stiffness were reasonably well correlated (R2 = 0.53-0.65, average error of 13-17%). A lower correlation was found for failure load (R2 = 0.21-0.48, average error of 9-15%). Experimental and predicted mechanical properties normalized by the total bone mass were strongly correlated (R2 = 0.75-0.80 for stiffness, R2 = 0.55-0.81 for failure load). In conclusion, hexahedral models with homogeneous material properties based on in vivo microCT images were shown to best predict the mechanical properties of the mouse tibia.

Analysis of the influence of species, intervertebral disc height and Pfirrmann classification on failure load of an injured disc using a novel disc herniation model

BACKGROUND CONTEXT

Annular repair devices offer a solution to recurrent disc herniations by closing an annular defect and lowering the risk of reherniation. Given the significant risk of neurologic injury from device failure it is imperative that a reliable preclinical model exists to demonstrate a high load to failure for the disc repair devices.

PURPOSE

To establish a preclinical model for disc herniation and demonstrate how changes in species, intervertebral disc height and Pfirrmann classification impacts failure load on an injured disc. We hypothesized that: (1) The force required for disc herniation would be variable across disc morphologies and species, and (2) for human discs the force to herniation would inversely correlate with the degree of disc degeneration.

STUDY DESIGN

Animal and human cadaveric biomechanical model of disc herniation.

METHODS

We tested calf lumbar spines, bovine tail segments and human lumbar spines. We first divided individual lumbar or tail segments to include the vertebral bodies and disc. We then hydrated the specimens by placing them in a saline bath overnight. A magnetic resonance images were acquired from human specimens and a Pfirrmann classification was made. A stab incision measuring 25% of the diameter of the disc was then done to each specimen along the posterior intervertebral disc space. Each specimen was placed in custom test fixtures on a servo-hydraulic test frame (MTS, Eden Prarie, MN) such that the superior body was attached to a 10,000 lb load cell and the inferior body was supported on the piston. A compressive ramping load was placed on the specimen in load control at 4 MPa/sec stopping at 75% of the disc height. Load was recorded throughout the test and failure load calculated. Once the test was completed each specimen was sliced through the center of the disc and photos were taken of the cut surface.

RESULTS

Fifteen each of calf, human, and bovine tail segments were tested. The failure load varied significantly between specimens (p<.001) with human specimens having the highest average failure load (8154±2049 N). Disc height was higher for lumbar/bovine tail segments as compared to calf specimens (p<.001) with bovine tails having the highest disc height (7.1±1.7 mm). Similarly, human lumbar discs had a cross sectional area that was greater than both bovine tail/calf lumbar spines (p<.001). There was no correlation between disc height and failure load within each individual species (p>.05). Cross sectional area and failure load did not correlate with failure load for human lumbar spine and bovine tails (p>.05) but did correlate with calf spine (r=0.53, p=.04). There was a statistically significant inverse correlation between disc height and Pfirrmann classification for human lumbar spines (r=-0.84, p<.001). There was also a statistically significant inverse relationship between Pfirrmann classification and failure load (r=-0.58, p=.02).

CONCLUSIONS

We have established a model for disc herniation and have shown how results of this model vary between species, disc morphology, and Pfirrmann classification. Both hypotheses were accepted: The force required for disc herniation was variable across species, and the force to herniation for human spines was inversely correlated with the degree of disc degeneration. We recommend that models using human intervertebral discs should include data on Pfirrmann classification, while biomechanical models using calf spines should report cross sectional area. Failure loads do not vary based on dimensions for bovine tails.

CLINICAL SIGNIFICANCE

Our analysis of models for disc herniation will allow for quicker, reliable comparisons of failure forces required to induce a disc herniation. Future work with these models may facilitate rapid testing of devices to repair a torn/ruptured annulus.

Determinants of estimated failure load in the distal radius after stroke: An HR-pQCT study

Bone health is often compromised after stroke and the distal radius is a common site of fragility fractures. The macro- and mircoproperties of bone tissue after stroke and their clinical correlates are understudied. The objectives of the study were to use High-Resolution peripheral Quantitative Computed Tomography (HR-pQCT) to investigate the bone properties at the distal radius, and to identify the correlates of estimated failure load for the distal radius in people with chronic stroke. This was a cross-sectional study of 64 people with stroke (age: 60.8 ± 7.7 years, stroke duration: 5.7 ± 3.9 years) and 64 age- and sex-matched controls. Bilateral bone structural, densitometric, geometric and strength parameters of the distal radius were measured using HR-pQCT. The architecture, stiffness and echo intensity of the bilateral biceps brachii muscle and brachial artery blood flow were evaluated using diagnostic ultrasound. Other outcomes included the Fugl-Meyer Motor Assessment (FMA), Motor Activity Log (MAL), and Composite Spasticity Scale (CSS). The results revealed a significant side (paretic vs non-paretic for the stroke group, non-dominant vs dominant for controls) by group (stroke vs control) interaction effect for estimated failure load, cortical area, cortical thickness, trabecular number and trabecular separation, and all volumetric density parameters. Post-hoc analysis showed percent side-to-side differences in bone outcomes were greater in the stroke group than the control group, with the exception of trabecular thickness and intracortical porosity. Among the HR-pQCT variables, percent side-to-side difference in trabecular volumetric bone mineral density contributed the most to the percent side-to-side difference in estimated failure load in the stroke group (R² change = 0.334, β = 1.106). Stroke-related impairments (FMA, MAL, CSS) were found to be significant determinants of the percent side-to-side difference in estimated failure load (R² change = 0.233, β = -0.480). This was the first study to examine bone microstructure post-stroke. We found that the paretic distal radius had compromised bone structural properties and lower estimated failure load compared to the non-paretic side. Motor impairment was a determinant of estimated bone strength at the distal radius and may be a potential intervention target for improving bone health post-stroke.

Optimization of the failure criterion in micro-Finite Element models of the mouse tibia for the non-invasive prediction of its failure load in preclinical applications

New treatments against osteoporosis require testing in animal models and the mouse tibia is among the most common studied anatomical sites. In vivo micro-Computed Tomography (microCT) based micro-Finite Element (microFE) models can be used for predicting the bone strength non-invasively, after proper validation against experiments. The aim of this study was to evaluate the ability of different microCT-based bone parameters and microFE models to predict tibial structural mechanical properties in compression. Twenty tibiae were scanned at 10.4 μm voxel size and subsequently tested in uniaxial compression at 0.03 mm/s until failure. Stiffness and failure load were measured from the load-displacement curves. Standard morphometric parameters were measured from the microCT images. The spatial distribution of bone mineral content (BMC) was evaluated by dividing the tibia into 40 regions. MicroFE models were generated by converting each microCT image into a voxel-based mesh with homogeneous isotropic material properties. Failure load was estimated by using different failure criteria, and the optimized parameters were selected by minimising the errors with respect to experimental measurements. Experimental and predicted stiffness were moderately correlated (R² = 0.65, error = 14% ± 8%). Normalized failure load was best predicted by microFE models (R² = 0.81, error = 9% ± 6%). Failure load was not correlated to the morphometric parameters and weakly correlated with some geometrical parameters (R² < 0.37). In conclusion, microFE models can improve the current estimation of the mouse tibia structural properties and in this study an optimal failure criterion has been defined. Since it is a non-invasive method, this approach can be applied longitudinally for evaluating temporal changes in the bone strength.

Reference values and clinical predictors of bone strength for HR-pQCT-based distal radius and tibia strength assessments in women and men

Reference values for radius and tibia strength using multiple-stack high-resolution peripheral quantitative computed tomography (HR-pQCT) with homogenized finite element analysis are presented in order to derive critical values improving risk prediction models of osteoporosis. Gender and femoral neck areal bone mineral density (aBMD) were independent predictors of bone strength.

INTRODUCTION

The purpose was to obtain reference values for radius and tibia bone strength computed by using the homogenized finite element analysis (hFE) using multiple stacks with a HR-pQCT.

METHODS

Male and female healthy participants aged 20-39 years were recruited at the University Hospital of Bern. They underwent interview and clinical examination including hand grip, gait speed and DXA of the hip. The nondominant forearm and tibia were scanned with a double and a triple-stack protocol, respectively, using HR-pQCT (XCT II, SCANCO Medical AG). Bone strength was estimated by using the hFE analysis, and reference values were calculated using quantile regression. Multivariable analyses were performed to identify clinical predictors of bone strength.

RESULTS

Overall, 46 women and 41 men were recruited with mean ages of 25.1 (sd 5.0) and 26.2 (sd 5.2) years. Sex-specific reference values for bone strength were established. Men had significantly higher strength for radius (mean (sd) 6640 (1800) N vs. 4110 (1200) N; p < 0.001) and tibia (18,200 (4220) N vs. 11,970 (3150) N; p < 0.001) than women. In the two multivariable regression models with and without total hip aBMD, the addition of neck hip aBMD significantly improved the model (p < 0.001). No clinical predictors of bone strength other than gender and aBMD were identified.

CONCLUSION

Reference values for radius and tibia strength using multiple HR-pQCT stacks with hFE analysis are presented and provide the basis to help refining accurate risk prediction models. Femoral neck aBMD and gender were significant predictors of bone strength.

Comparison of failure loads and compressive stress in Press on metal and Press on Y-TZP copings

Objective:

The aim of the study was to assess the failure loads and compressive stresses among bilayered press on Y-TZP (POZ) and press on metal (POM) crowns with different core-veneer thickness.

Methods:

Thirty metal and Y-TZP copings were fabricated using CAD-CAM technology with specified thickness. All copings were veneered with ceramic materials using hot pressing technique, with 2mm and 2.5mm thickness. The different coping veneer thickness of crowns resulted in six study groups, including, POM: Coping/ veneer thickness of 0.7/2mm (Gp1), 0.7/2.5mm (Gp 2) and 1mm/2mm (Gp 3)-POZ: 0.7/2mm (Gp A), 0.7/2.5mm (Gp B) and 1mm/2mm (Gp C). Crowns were cemented to a standard implant analog and failure loads (FL) and compressive stress (CS) was ascertained by controlled load application in a universal testing machine. Data was analysed using ANOVA and multiple comparisons test.

Results:

The maximum FL were observed in the POM specimens with a C/V ratio of 1/2 (Group 3-1880.67± 256.78 N), however the lowest FL were exhibited by POZ crowns with 1/2 C/V ratio (Group C-611.89± 72.79 N). Mean FL and CS were significantly higher in POM compared to POZ crowns in respective groups. Increasing the coping-veneer thickness increased FL and CS among POM crowns. Increasing veneer and decreasing coping thickness improved FL and CS among POZ crowns.

Conclusions:

Press on metal specimen showed higher resistance to fracture than Press on Y-TZP specimens. Improved failure loads were observed in thin coping and thick veneers among Press on Y-TZP crowns.

The femoral posterior fan-like extension of the ACL insertion increases the failure load

PURPOSE

To examine the role of the posterior fan-like extension of the ACL's femoral footprint on the ACL failure load.

METHODS

Sixteen (n = 16) fresh frozen, mature porcine knees were used in this study and randomized into two groups (n = 8): intact femoral ACL insertion (ACL intact group) and cut posterior fan-like extension of the ACL (ACL cut group). In the ACL cut group, flexing the knees to 90°, created a folded border between the posterior fan-like extension and the midsubstance insertion of the femoral ACL footprint and the posterior fan-like extension was dissected and both areas were measured. Specimens were placed in a testing machine at 30° of flexion and subjected to anterior tibial loading (60 mm/min) until ACL failure.

RESULTS

The intact ACL group had a femoral insertion area of 182.1 ± 17.1 mm². In the ACL cut group, the midsubstance insertion area was 113.3 ± 16.6 mm², and the cut posterior fan-like extension portion area was 67.1 ± 8.3 mm². The failure load of the ACL intact group was 3599 ± 457 N and was significantly higher (p < 0.001) than the failure load of the ACL cut group 392 ± 83 N.

CONCLUSION

Transection of the posterior fan-like extension of the ACL femoral footprint has a significant effect on the failure load of the ligament during anterior loading at full extension. Regarding clinical relevance, this study suggests the importance of the posterior fan-like extension of the ACL footprint which potentially may be retained with remnant preservation during ACL reconstruction. Femoral insertion remnant preservation may allow incorporation of the fan-like structure into the graft increasing graft strength.

Influence of Bioactive, Resin and Glass Ionomer luting cements on the fracture loads of dentin bonded ceramic crowns

Objective:

To investigate the failure loads of dentin bonded all-ceramic crowns when luted with Bioactive, resin and glass ionomer cements (GIC) in an in-vitro setting.

Methods:

This study was conducted at King Saud University, Saudi Arabia, from Nov.2018 to March 2019. In this study, 60 premolar teeth were prepared for dentin-bonded ceramic crowns. Lithium disilicate ceramic crowns fabricated using CAD-CAM technique were cemented to teeth using Bioactive (ACITVA), Resin (Nexus 3 Gen) and GIC (Ketac Cem- Maxicap). Half of the bonded specimens in each group were thermocycled (50000 cycles), however the remaining half were not aged (n=10). Fracture loads of bonded crowns were assessed by exposing them to static axial occlusal loads (1mm/min) using a round ended metal probe in a Universal testing machine. Means and standard deviations among the study groups were compared with ANOVA and Tukey-Kramer multiple comparisons test.

Results:

Highest failure loads were observed in resin group without ageing (thermocycling) (689.13±89.41 N), however, the lowest loads were observed in GIC specimens with ageing (243.16±49.03 N). Among non-aged samples, failure loads for Bioactive (480.30±47.26 N) group were less than Resin (689.13±89.41 N) samples but higher than GIC (307.51±45.29 N) specimens respectively. Among the aged specimens, Bioactive (404.42±60.43 N) showed significantly higher failure loads than GIC (243.16±49.03 N), however lower failure loads than Resin (582.33±95.95 N) samples.

Conclusions:

Dentin boned crowns with resin cementation showed higher failure loads than Bioactive and GIC luted crowns. Crowns luted with Bioactive cement showed acceptable failure loads for use as restoration on anterior teeth.

A Biomechanical and Ease of Learning Comparison Study of Arthroscopic Sliding Knots

INTRODUCTION

This study aims to compare the biomechanical properties and ease of learning and tying of our novel knot (UM Knot) with other commonly used arthroscopic sliding knots.

MATERIALS AND METHODS

The Duncan, HU, SMC, Pretzel, Nicky's and square knots were selected for comparisons with UM knot. All knots were prepared with size 2 HiFi^® suture by a single experienced surgeon and tested with cyclic loading and load to failure tests. The ease of learning was assessed objectively by recording the time to learn the first correct knot and the total number of knots completed in 5 min by surgeons and trainees.

RESULTS

The UM knot average failure load is significantly superior to the HU knot (p < 0.05) and comparable to Duncan, SMC, Pretzel and Nicky's knots. According to the ease of learning assessment, UM, Duncan, SMC, Pretzel and Nicky's knots took statistically less time to learn than the HU knot. Although not significant, the failure count due to slippage is fewer in UM knot compared with other knots.

CONCLUSIONS

This study showed that UM knot is among the easiest knot to learn and tie, along with Duncan, SMC, Pretzel and Nicky's knots. Their biomechanical properties are comparable and their loads to failure were superior to the HU knot.

How much force is required to perforate a colon during colonoscopy? An experimental study

INTRODUCTION

Colonoscopy is a commonly-performed procedure to diagnose pathology of the large intestine. Perforation of the colon is a rare but feared complication. It is currently unclear how much force is actually required to cause such injury nor how this is altered in certain diseases. Our aim was to analyze the forces required to perforate the colon in experiments using porcine tissues.

METHODS

Using 3D printing technology, models of two commercially available colonoscope heads were printed under three configurations: straight (I), 90°- bent (L) and fully bent (U). Samples of porcine colon were assessed with the models and configurations under perpendicular and angular load application and these data compared to the maximum force typically exerted by experienced colonoscopists.

RESULTS

The force required for perforation was significantly lower for the I compared to the L of the larger colonoscope head configuration under angular loading (14.1 vs. 46.5 N). Similar differences were found for linear stiffness when loaded (I vs. L small when loaded perpendicular: 0.8 vs. 2.4 N/mm, I vs. L large when loaded angled 0.7 vs. 2.1 N/mm). The mode and site of failure varied significantly between the scopes, with delamination of the mucosa/submucosa below the sample (96%) for the I, blunt mucosa/submucosa/muscularis failure adjacent to the loading site (77%) for the L, and failure of all colon layers lateral to the loading site (59%) for the U configuration, respectively. Perpendicular and angulated loading resulted in similar load-deformation values. Maximum forces typically exerted by colonoscopists averaged 13.9-27.9 N, depending on the colonoscope model and head configuration.

DISCUSSION

The force required for colon perforation varies depending on the type mode of loading and is likely lower than the force an experienced colonoscopist would exert in daily practice. There is a real risk of perforation, especially when the end of the scope is advancing directly into the colonic wall. The given experimental setup allowed to obtain reliable data of the colon in a standardized scenario, forming the basis for further experiments.

Gap formation following primary repair of the anterior cruciate ligament: A biomechanical evaluation

BACKGROUND

Historically, inconsistent and unpredictable results of open primary anterior cruciate ligament (ACL) repair were reported. Recently, however, good results of arthroscopic primary ACL repair of proximal tears have been reported. Purpose of this study was to assess the direct postoperative gap formation and maximum failure load following simulated knee motion after primary ACL repair.

METHODS

Six matched-paired human cadaveric knees (mean age: 52years, range: 48 to 56years) were used. After primary proximal ACL repair with either suture button fixation or suture anchor fixation, knees were cycled five, 50 and 100 times with a simulated active quadriceps force. Gap formation between the femoral wall and ligament was measured using a digital caliper and maximum failure load was tested.

RESULTS

Gap formation after five, 50 and 100cycles of the knee were 0.30mm (±0.23), 0.75mm (±0.55) and 0.97mm (±0.70), respectively, with no significant differences between both fixation techniques. The overall maximum failure load was 243N (±143) with no difference between both techniques. Most common failure mode was slipping of suture from the fixation.

CONCLUSION

Following proximal ACL repair, gap formation of approximately one millimeter was measured after repetitious knee cycling with mean maximum failure load of 243N. These findings are likely to be sufficient for careful early active range of motion (ROM) when extrapolating from other available studies. Future studies with second-look arthroscopy are necessary to assess the gap formation and healing in patients treated with primary repair.

Mechanical properties of all-suture anchors for rotator cuff repair

Objectives

All-suture anchors are increasingly used in rotator cuff repair procedures. Potential benefits include decreased bone damage. However, there is limited published evidence for the relative strength of fixation for all-suture anchors compared with traditional anchors.

Materials and Methods

A total of four commercially available all-suture anchors, the ‘Y-Knot’ (ConMed), Q-FIX (Smith & Nephew), ICONIX (Stryker) and JuggerKnot (Zimmer Biomet) and a traditional anchor control TWINFIX Ultra PK Suture Anchor (Smith & Nephew) were tested in cadaveric human humeral head rotator cuff repair models (n = 24). This construct underwent cyclic loading applied by a mechanical testing rig (Zwick/Roell). Ultimate load to failure, gap formation at 50, 100, 150 and 200 cycles, and failure mechanism were recorded. Significance was set at p < 0.05.

Results

Overall, mean maximum tensile strength values were significantly higher for the traditional anchor (181.0 N, standard error (se) 17.6) compared with the all-suture anchors (mean 133.1 N se 16.7) (p = 0.04). The JuggerKnot anchor had greatest displacement at 50, 100 and 150 cycles, and at failure, reaching statistical significance over the control at 100 and 150 cycles (22.6 mm se 2.5 versus 12.5 mm se 0.3; and 29.6 mm se 4.8 versus 17.0 mm se 0.7). Every all-suture anchor tested showed substantial (> 5 mm) displacement between 50 and 100 cycles (6.2 to 14.3).

All-suture anchors predominantly failed due to anchor pull-out (95% versus 25% of traditional anchors), whereas a higher proportion of traditional anchors failed secondary to suture breakage.

Conclusion

We demonstrate decreased failure load, increased total displacement, and variable failure mechanisms in all-suture anchors, compared with traditional anchors designed for rotator cuff repair. These findings will aid the surgeon’s choice of implant, in the context of the clinical scenario.

Cite this article: N. S. Nagra, N. Zargar, R. D. J. Smith, A. J. Carr. Mechanical properties of all-suture anchors for rotator cuff repair. Bone Joint Res 2017;6:82–89. DOI: 10.1302/2046-3758.62.BJR-2016-0225.R1

Racial Differences in Bone Microarchitecture and Estimated Strength at the Distal Radius and Distal Tibia in Older Adolescent Girls: a Cross-Sectional Study

BACKGROUND

Previous studies have demonstrated that an individual's race and ethnicity are important determinants of their areal bone mineral density (aBMD), assessed by dual-energy X-ray absorptiometry. However, there are few data assessing the impact of race on bone microarchitecture and strength estimates, particularly in older adolescent girls and young adults. We hypothesized that bone microarchitecture and strength estimates would be superior in Blacks compared to White and Asian American adolescent girls and young adults of similar age based on reports of higher aBMD in Blacks.

METHODS

We assessed BMD using dual-energy X-ray absoptiometry (DXA), bone microarchitecture at the distal radius and distal tibia using high-resolution peripheral quantitative computed tomography (HRpQCT) and estimated measures of bone strength using micro-finite element analysis (FEA) in 35 White, 15 Asian American, and 10 Black girls 14-21 years.

RESULTS

After controlling for height, most DXA measures of aBMD and aBMD Z scores were higher in Black girls compared with Whites and Asian Americans. HRpQCT and FEA showed that at the distal radius, Blacks had greater cortical perimeter, cortical area, trabecular thickness, trabecular BMD, estimated failure load, and stiffness than the other two groups. For the distal tibia, trabecular number and BMD were higher in Blacks than Asian Americans.

CONCLUSIONS

Particularly at the distal radius, adolescent and young adult White and Asian American girls have less favorable bone microarchitecture and lower bone strength than Blacks, possibly explaining the lower risk of fracture seen in Blacks.

LEVEL OF EVIDENCE

Level II.

Influence of the resin cement thickness on the fatigue failure loads of CAD/CAM feldspathic crowns

OBJECTIVES

to evaluate the influence of the occlusal resin cement thickness on the cyclic loads-to-failure of feldspathic crowns and to compare the results to data from monotonic tests. A large range of cement thickness (50μm and 500μm) was tested, in order to better measure the influence of this variable.

METHODS

Feldspathic ceramic crowns (Vita Mark II blocks, Vita Zahnfabrik) were bonded to dentin analog dies (G10 (NEMA grade G10, International Paper), with occlusal resin cement thicknesses of 50μm and 500μm (Multilink Automix, Ivoclar). The dies were prepared with microchannels for water transport to the cement layer. After 96-h water storage, the specimens (n=20) were submitted to cyclic loads (500,000 cycles at 20Hz; initial maximum load=40% of monotonic load, from previous data) following a staircase sensitivity design (step size=25N). Failure loads at 500,000 cycles were compared to monotonic failure loads (from a previous study with specimens produced by the same author, using the same materials, specimen configuration and cementation protocol).

RESULTS

Crowns with an occlusal cement layer of 50μm were more resistant than those cemented with 500μm (246.4±22.9N vs. 158.9±22.9N), under wet cyclic testing conditions (p<0.001). The fatigue failure loads were reduced compared to monotonic loads: to 37% of monotonic for 50μm; to 53% of monotonic for 500μm.

SIGNIFICANCE

An occlusal cement thickness of 50μm was more favorable for the structural performance of feldspathic crowns than was 500μm. Cyclic fatigue reduced failure loads well below those found under monotonic loading.

Subject specific finite element modeling of periprosthetic femoral fracture using element deactivation to simulate bone failure

Subject-specific finite element (FE) modeling methodology could predict peri-prosthetic femoral fracture (PFF) for cementless hip arthoplasty in the early postoperative period. This study develops methodology for subject-specific finite element modeling by using the element deactivation technique to simulate bone failure and validate with experimental testing, thereby predicting peri-prosthetic femoral fracture in the early postoperative period. Material assignments for biphasic and triphasic models were undertaken. Failure modeling with the element deactivation feature available in ABAQUS 6.9 was used to simulate a crack initiation and propagation in the bony tissue based upon a threshold of fracture strain. The crack mode for the biphasic models was very similar to the experimental testing crack mode, with a similar shape and path of the crack. The fracture load is sensitive to the friction coefficient at the implant-bony interface. The development of a novel technique to simulate bone failure by element deactivation of subject-specific finite element models could aid prediction of fracture load in addition to fracture risk characterization for PFF.

Mechanical behavior of colonic anastomosis in experimental settings as a measure of wound repair and tissue integrity

AIM: To determine the mechanical properties of anastomotic colonic tissue in experimental settings and therefore give a measure of wound healing.

METHODS: Thirty-six male Wistar rats were used as experimental models of anastomotic tissue integrity. On the 5^th post-operative day, the tensile strength was measured by application of an axial force, providing a quantitative measure of anastomotic dehiscence and leakage.

RESULTS: Diagrams of the load as a function of the time [P = P (t)] and of the displacement also as a function of time [Δs = Δs (t)] were recorded for each test, permitting the design of the load versus the displacement diagram and thus providing significant data about the critical values of anastomotic failure. Quantitative data were obtained concerning the anastomotic strength of both control specimens (healthy rats), as well as specimens from non-healthy rats for comparison.

CONCLUSION: This experimental model provides an excellent method of measuring anastomotic strength. Despite the relative small number of specimens used, this method provides an accurate way of measuring wound repair. More experimental measurements need to be performed to correlate emerging tensile strength values to anastomotic failure.