Mechanical behaviors of CL-20 under an impact loading: A molecular dynamics study

Study on the dynamic process of CL-20 crystal under impact is critical for the safe utilization of energetic materials under extreme conditions. Herein, the mechanical and structural evolution of CL-20 under the impact of a diamond ball is investigated by using molecular dynamics simulation. The considerations are given to the effect of different impact velocity, impact direction and impact angle. It is found that a high impact velocity results in a large indentation depth and force, as well as more significant energy transition and the formation of a large number of molecular fragments. Moreover, CL-20 exhibits weak anisotropy along different impact directions due to the crystalline distribution anisotropy. Furthermore, the mechanical response of CL-20 is angle-dependent, which is caused by the discrepancy in local molecular re-arrangement. These results may enhance the understanding of the mechanical behavior of CL-20 and promote its wide applications.

Association of tibial acceleration during walking to pain and impact loading in adults with knee osteoarthritis

BACKGROUND

Higher impact loading during walking is implicated in the pathogenesis of knee osteoarthritis. Accelerometry enables the measurement of peak tibial acceleration outside the laboratory. We characterized the relations of peak tibial acceleration to knee pain and impact loading during walking in adults with knee osteoarthritis.

METHODS

Adults with knee osteoarthritis reported knee pain then walked at a self-selected speed on an instrumented treadmill for 3 min with an ankle-worn inertial measurement unit. Ground reaction forces and tibial acceleration data were sampled for 1 min. Vertical impact peaks, and average and peak instantaneous load rates were determined and averaged across 10 steps. Peak tibial acceleration was extracted for all steps and averaged. Pearson's correlations and multiple linear regression analyses assessed the relation of peak tibial acceleration to pain and impact loading metrics, independently and after controlling for gait speed and pain.

FINDINGS

Higher peak tibial acceleration was associated with worse knee pain (r = 0.39; p = 0.01), and higher vertical average (r = 0.40; p = 0.01) and instantaneous (r = 0.46; p = 0.004) load rates. After adjusting for gait speed and pain, peak tibial acceleration was a significant predictor of vertical average (R2 = 0.33; p = 0.003) and instantaneous (R2 = 0.28; p = 0.02) load rates, but not strongly associated with vertical impact peak.

INTERPRETATIONS

Peak tibial acceleration during walking is associated with knee pain and vertical load rates in those with knee osteoarthritis. Clinicians can easily access measures of peak tibial acceleration with wearable sensors equipped with accelerometers. Future work should determine the feasibility of improving patient outcomes by using peak tibial acceleration to inform clinical management.

Shock absorption capability of corrugated ring yield mount subjected to high impact loading

Various types of mechanical energy-absorbing devices are known that operate by plastic deformation. The corrugated ring mount that is used in this study relates to a device that absorbs energy by plastic deformation. This energy-absorbing device has reduced volumetric proportions, simple in design, and therefore has small overall dimensions and can be mass-produced at low cost. This study aims to determine the shock absorption capability and efficiency of this mount against impact loading. For this, Finite Element Method Analysis (FEA) and experimentation are done. The FEA is done using the Explicit Dynamics (AutoDyn) module of ANSYS Workbench and for experimentation Drop Test Machine (DTM) is used. In this study impact load from low g up to 85 g is applied and a very close agreement is found between FEA and experimental results. There is just a 5-10% deviation between the findings. The results show that this mount is plastically deformed to absorb the impact energy with a maximum efficiency of 70%. It concludes that it is a reliable and safer shock energy device.

An equivalent method of jet impact loading from collapsing near-wall acoustic bubbles: A preliminary study

Cavitation damage is a micro, high-speed, multi-phase complex phenomenon caused by the near-wall bubble group collapse. The current numerical simulation method of cavitation mainly focuses on the collapse impact of a single cavitation bubble. The large-scale simulation of the cavitation bubble group collapse is difficult to perform and has not been studied, to the best of our knowledge. In this study, the equivalent model of impact loading of acoustic bubble collapse micro-jets is proposed to study the cavitation erosion damage of materials. Based on the theory of the micro-jet and the water hammer effect of the liquid-solid impact, an equivalent model of impact loading of a single acoustic bubble collapse micro-jet is established under the principle of deformation equivalence. Since the acoustic bubbles can be considered uniformly distributed in a small enough area, an equivalent model of impact loading of multiple acoustic bubble collapse micro-jets in a micro-segment can be derived based on the equivalent results of impact loading of a single acoustic bubble collapse micro-jet. In fact, the equivalent methods of cavitation damage loading for single and multiple near-wall acoustic bubble collapse micro-jets are formed. The verification results show the law of cavitation deformation of concrete using equivalent loading is consistent with that of a micro-jet simulation, and the average relative errors and the mean square errors are insignificant. The equivalent method of impact loading proposed in this paper has high accuracy and can greatly improve the calculation efficiency, which provides technical support for numerical simulation of concrete cavitation.

Feasibility, tolerance and effects of adding impact loading exercise to pulmonary rehabilitation in people with chronic obstructive pulmonary disease: study protocol for a pilot randomised controlled trial

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a disorder linked with a multitude of extra pulmonary manifestations (also known as treatable traits), including low bone mineral density (BMD). To date, no specific guidelines exist for the management of BMD in this population. Impact loading exercise has been identified as an intervention that improves or maintains BMD in other populations. However, the feasibility of and tolerance to impact loading exercise has not been tested in people with COPD. The aim of the proposed study will be to investigate the feasibility and tolerance of adding impact loading exercise to a standard pulmonary rehabilitation programme (PRP) in people with COPD and report its effects on bone health, balance and falls risk.

METHODS

This is a protocol for a pilot feasibility and tolerance randomised controlled trial (RCT). Fifty-eight people with COPD will be randomly allocated, on a 1:1 ratio, to either the experimental or control group. Initially, participants in both groups will complete a standard 8-week (twice-weekly) PRP followed by a 32-week period of maintenance exercises. Over the initial 8-week period, participants allocated to the experimental group will also undertake targeted lower limb resistance exercises and commence a programme of impact loading exercises (e.g. bounding and drop jumps). On completion of the initial 8-week PRP, in addition to the standard maintenance exercises, participants in the experimental group will continue with home-based impact loading exercises, four times a week, for the extra 32 weeks. The primary outcome of this study is feasibility of and tolerance to impact loading exercises. Feasibility will be measured using data collected pertaining to recruitment, withdrawal and completion. Adherence to the exercises will be collected using exercise logs. Tolerance to the exercises will be determined using outcomes to assess pain, recording any adverse effects such as a fall and feedback from the participants in semi-structured interviews on completing of the trial. The effects of the 40-week experimental intervention on bone health, balance and falls risk will be reported.

DISCUSSION

This pilot RCT will test the feasibility and tolerance of an intervention that has never been trialed in people with COPD. It will also provide initial information regarding the size of the effect this intervention has on outcomes such as BMD, balance and falls risk. These data will be critical when designing a definitive RCT to advance this area of research.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry (ANZCTR): 12620001085965 (20/10/2020).

Effect of fatigue loading and rest on impact strength of rat ulna

Stress fracture is a common injury among athletes and military personnel and is associated with fatigue-initiated damage and impact loading. The recovery of bending strength has been shown to be a function of the rest days allowed after fatigue loading in rodents and the aim of this study was to investigate if similar results would occur under impact conditions. In this study, cyclic axial compression load was applied in vivo on the right forelimbs while left forelimbs served as controls. Two rest groups were used: one day of rest and seven days of rest. Afterwards, all ulnae were scanned using micro-Computed Tomography followed by impact testing. The micro-CT scan confirmed the formation of woven bone on loaded ulnae after seven days rest. The peak impact force was 37.5% higher in the control (mean = 174.96 ± 33.25 N) specimens compared to the loaded bones (mean = 130.34 ± 22.37 N). Fourier-transformed infrared spectroscopy analyses suggested no significant change of chemical composition in the cortical region between the loaded and control ulnae, but woven bone region had lower carbonate and amide I content than contralateral controls (p < 0.05). We find that cyclic fatigue loading had a negative effect on bone's impact response. Bones that experienced fatigue loading became less stiff, weaker, and more prone to fracture when subjected to impact. The formation of woven bone after seven days of rest did not restore the stiffness upon impact and confirm that rest time is crucial to the recovery of fatigue damage.

Bioinspired energy absorbing material designs using additive manufacturing

Nature provides many biological materials and structures with exceptional energy absorption capabilities. Few, relatively simple molecular building blocks (e.g., calcium carbonate), which have unremarkable intrinsic mechanical properties individually, are used to produce biopolymer-bioceramic composites with unique hierarchical architectures, thus producing biomaterial-architectures with extraordinary mechanical properties. Several biomaterials have inspired the design and manufacture of novel material architectures to address various engineering problems requiring high energy absorption capabilities. For example, the microarchitecture of seashell nacre has inspired multi-material 3D printed architectures that outperform the energy absorption capabilities of monolithic materials. Using the hierarchical architectural features of biological materials, iterative design approaches using simulation and experimentation are advancing the field of bioinspired material design. However, bioinspired architectures are still challenging to manufacture because of the size scale and architectural hierarchical complexity. Notwithstanding, additive manufacturing technologies are advancing rapidly, continually providing researchers improved abilities to fabricate sophisticated bioinspired, hierarchical designs using multiple materials. This review describes the use of additive manufacturing for producing innovative synthetic materials specifically for energy absorption applications inspired by nacre, conch shell, shrimp shell, horns, hooves, and beetle wings. Potential applications include athletic prosthetics, protective head gear, and automobile crush zones.

Design and Fabrication of a Drop Tower Testing Apparatus to Investigate the Impact Behavior of Spinal Motion Segments

Background

The vertebral column is the second most common fracture site in individuals with high-grade osteoporosis (30-50%). Most of these fractures are caused by falls. This information reveals the importance of considering impact loading conditions of spinal motion segments, while no commercial apparatus is available for this purpose. Therefore, the goal was set to fabricate an impact testing device for the measurement of impact behavior of the biological tissues.

Methods

In the present study, first, a drop-weight impact testing apparatus was designed and fabricated to record both force and displacement at a sample rate of 100 kHz. A load cell was placed under the sample, and an accelerometer was located on the impactor. Previous devices have mostly measured the force and not the deformation. Thereafter, the effect of high axial compression load was investigated on a biological sample, i.e., the lumbar motion segment, was investigated. To this end, nine ovine segments subjected to vertical impact load were examined using the fabricated device, and the mechanical properties of the lumbar segments were extracted and later compared with quasi-static loading results.

Results

The results indicated that the specimen stiffness and failure energy in impact loading were higher than those in the quasi-static loading. In terms of the damage site, fracture mainly occurred in the body of the vertebra during impact loading; although, during quasi-static loading, the fracture took place in the endplates.

Conclusion

The present study introduces an inexpensive drop-test device capable of recording both the force and the deformation of the biological specimens when subjected to high-speed impacts. The mechanical properties of the spinal segments have also been extracted and compared with quasi-static loading results.

Macroscopically healthy articular cartilage with fibrillar-scale early tissue degeneration subject to impact loading results in greater extent of cell-death

From previous investigations it has been shown that there exists healthy-appearing articular cartilage that contains collagen fibril network destructuring. It is hypothesised that such sub-micron scale destructuring not only presents an increased vulnerability to tissue scale damage following impact loading, but an increase in cell death as well. Cartilage-on-bone blocks from 12 patellae, six healthy (G0) and the other six with sub-micron fibrillar destructuring (G1), were obtained and subject to 2.3 J impact loading. Two sets of sub-samples were obtained for each block tested. One set was used to examine for the live/dead cell response using calcein-AM and propidium iodide staining, imaged with confocal microscopy. The tissue microstructural matrix was imaged from the other matched set, unstained and in its fully hydrated state, using differential interference contrast optical light microscopy. High speed imaging of the impact was used to calculate the velocity changes or coefficient of restitution (COR) and used as a proxy of energy that the tissue absorbed. A previously defined tissue matrix damage score was used to quantify the extent of fracturing and cracking in the matrix. The cell death (PCD) was counted and presented as a percentage against all cells live plus dead. The energy absorbed was 36.5% higher in G1 than in G0 (p = 0.034). However, the damage score and PCD of samples in the G1 group was much larger than the G0 group, ~300% and 161% respectively. Microscopy showed that cell death is associated to both matrix compaction and further fibrillar destructuring from the ECM to the territorial matrix regions of the chondron. Following impact loading, cartilage tissue that appears normal but contains sub-micron fibrillar matrix destructuring responds with significantly increased cell death.

Multi-laminate annulus fibrosus repair scaffold with an interlamellar matrix enhances impact resistance, prevents herniation and assists in restoring spinal kinematics

Focal defects in the annulus fibrosus (AF) of the intervertebral disc (IVD) arising from herniation have detrimental impacts on the IVD's mechanical function. Thus, biomimetic-based repair strategies must restore the mechanical integrity of the AF to help support and restore native spinal loading and motion. Accordingly, an annulus fibrosus repair patch (AFRP); a collagen-based multi-laminate scaffold with an angle-ply architecture has been previously developed, which demonstrates similar mechanical properties to native outer AF (oAF). To further enhance the mimetic nature of the AFRP, interlamellar (ILM) glycosaminoglycan (GAG) was incorporated into the scaffolds. The ability of the scaffolds to withstand simulated impact loading and resist herniation of native IVD tissue while contributing to the restoration of spinal kinematics were assessed separately. The results demonstrate that incorporation of a GAG-based ILM significantly increased (p < 0.001) the impact strength of the AFRP (2.57 ± 0.04 MPa) compared to scaffolds without (1.51 ± 0.13 MPa). Additionally, repair of injured functional spinal units (FSUs) with an AFRP in combination with sequestering native NP tissue and a full-thickness AF tissue plug enabled the restoration of creep displacement (p = 0.134), short-term viscous damping coefficient (p = 0.538), the long-term viscous (p = 0.058) and elastic (p = 0.751) damping coefficients, axial neutral zone (p = 0.908), and axial range of motion (p = 0.476) to an intact state. Lastly, the AFRP scaffolds were able to prevent native IVD tissue herniation upon application of supraphysiologic loads (5.28 ± 1.24 MPa). Together, these results suggest that the AFRP has the strength to sequester native NP and AF tissue and/or implants, and thus, can be used in a composite repair strategy for IVDs with focal annular defects thereby assisting in the restoration of spinal kinematics.

Shock absorbing ability in healthy and damaged cartilage-bone under high-rate compression

Articular cartilage is a soft tissue that distributes the loads in joints and transfers the compressive load to the underlying bone. At high rate and magnitudes of mechanical loading, cartilage and subchondral bone together are susceptible to damage. In addition, any disruption to the cartilage's structure, caused by injury, trauma or disorder such as osteoarthritis (OA), can alter the mechanism of load transfer from the cartilage to the underlying bone. Changes in the cartilage structure can also alter the ability of cartilage-bone to absorb and dissipate the impact energy. To investigate the effects of cartilage degradation on cartilage-bone shock absorption ability, the top 50% of the cartilage thickness was removed (modified cartilage) to mimic the cartilage thickness reduction in Grade III cartilage lesion and the remaining cartilage-bone unit (modified cartilage-bone) was compressed at high-rate (4% strain at 5 Hz). High-speed camera and microscope were used to capture microscopic deformation, and digital image correlation technique (DIC) employed to quantify the deformation of cartilage and bone. The mechanical properties (i.e. stiffness, strain, absorbed and dissipated energies) of cartilage and bone were calculated before and after the removal of the top 50% of the cartilage thickness, consisting of both the superficial tangential zone (STZ) and part of the middle zone of the cartilage. The results showed a significant degradation in the mechanical properties of the cartilage-bone unit after the removal of the top 50% cartilage thickness. The stiffness of the modified cartilage reduced significantly (by ~39%) and energy absorption in underlying bone increased by 32%, which can make the bone more vulnerable to damage in the modified cartilage-bone unit. In addition, the energy dissipation in the modified cartilage-bone unit was also increased by approximately 14%. These changes in mechanical properties suggest a crucial role of the STZ and middle zone (within the top 50% cartilage thickness) in protecting the underlying bone from the severe compressive impact loading. Results also indicated that under physiological contact stress of 7 MPa, strain in damaged cartilage was increased by 3.22% without affecting the mechanical behaviour of the underlying bone.

A Novel Competing Risk Analysis Model to Determine the Role of Cervical Lordosis in Bony and Ligamentous Injuries

OBJECTIVE

To determine role of lordosis in cervical spine injuries using a novel competing risk analysis model.

METHODS

The first subgroup of published experiments (n = 20) subjected upright human cadaver head-neck specimens to impact loading. The natural lordosis was removed. The second (n = 21) and third (n = 10) subgroups of published tests subjected inverted specimens to head impact loading. Lordosis was preserved in these 2 subgroups. Using axial force and age as variables, competing risks analysis techniques were used to determine the role of lordosis in the risk of bone-only, ligament-only, and bone and ligament injuries.

RESULTS

Bony injuries were focused more at 1 level to a straightened spine, and ligament injuries were spread around multiple levels. Age was not a significant (P < 0.05) covariate. A straightened spine had 3.23 times higher risk of bony injuries than a lordotic spine. The spine with maintained lordosis had 1.14 times higher risk of ligament injuries, and 2.67 times higher risk of bone and ligament injuries than a spine without lordosis (i.e., preflexed column).

CONCLUSIONS

Increased risk of bony injuries in a preflexed spine and ligament injuries in a lordotic spine may have implications for military personnel, as continuous use of helmets in the line of duty affects the natural curvature; astronauts, as curvatures are less lordotic after missions; and civilian patients with spondylotic myelopathy who use head protective devices, as curvatures may change over time in addition to the natural aging process.

Water depth effects on impact loading, kinematic and physiological variables during water treadmill running

PURPOSE

The purpose of this study was to compare impact loading, kinematic and physiological responses to three different immersion depths (mid-shin, mid-thigh, and xiphoid process) while running at the same speed on a water based treadmill.

METHODS

Participants (N=8) ran on a water treadmill at three depths for 3min. Tri-axial accelerometers were used to identify running dynamics plus measures associated with impact loading rates, while heart rate data were logged to indicate physiological demand.

RESULTS

Participants had greater peak impact accelerations (p<0.01), greater impact loading rates (p<0.0001), greater stride frequency (p<0.05), shorter stride length (p<0.01), and greater rate of acceleration development at toe-off (p<0.0001) for the mid-shin and mid-thigh compared to running immersed to the xiphoid process. Physiological effort determined by heart rate was also significantly less (p<0.0001) when running immersed to the xiphoid process.

CONCLUSION

Water immersed treadmill running above the waistline alters kinematics of gait, reduces variables associated with impact, while decreasing physiological demand compared to depths below the waistline.

Measurement of peak impact loads differ between accelerometers - Effects of system operating range and sampling rate

A wide variety of accelerometer systems, with differing sensor characteristics, are used to detect impact loading during physical activities. The study examined the effects of system characteristics on measured peak impact loading during a variety of activities by comparing outputs from three separate accelerometer systems, and by assessing the influence of simulated reductions in operating range and sampling rate. Twelve healthy young adults performed seven tasks (vertical jump, box drop, heel drop, and bilateral single leg and lateral jumps) while simultaneously wearing three tri-axial accelerometers including a criterion standard laboratory-grade unit (Endevco 7267A) and two systems primarily used for activity-monitoring (ActiGraph GT3X+, GCDC X6-2mini). Peak acceleration (gmax) was compared across accelerometers, and errors resulting from down-sampling (from 640 to 100Hz) and range-limiting (to ±6g) the criterion standard output were characterized. The Actigraph activity-monitoring accelerometer underestimated gmax by an average of 30.2%; underestimation by the X6-2mini was not significant. Underestimation error was greater for tasks with greater impact magnitudes. gmax was underestimated when the criterion standard signal was down-sampled (by an average of 11%), range limited (by 11%), and by combined down-sampling and range-limiting (by 18%). These effects explained 89% of the variance in gmax error for the Actigraph system. This study illustrates that both the type and intensity of activity should be considered when selecting an accelerometer for characterizing impact events. In addition, caution may be warranted when comparing impact magnitudes from studies that use different accelerometers, and when comparing accelerometer outputs to osteogenic impact thresholds proposed in literature.

Impact loading following quadriceps strength training in individuals with medial knee osteoarthritis and varus alignment

BACKGROUND

Greater impact loading at initial contact is postulated to play a role in the progression of osteoarthritis. Quadriceps weakness is common in individuals with knee osteoarthritis and may contribute to high impact loading. The purpose of this study was to examine the effects of quadriceps strengthening on impact loading parameters.

METHODS

Data from 97 individuals with knee osteoarthritis who participated in a randomized clinical trial examining effects of a 12-week quadriceps strengthening program was used to conduct this secondary exploratory analysis. Participants completed a three-dimensional gait assessment within 10% of 1.0m/s from which maximum rate of loading (Body Weight/second), average rate of loading (Body Weight/second), and peak vertical ground reaction force during early stance (Body Weight) were determined. Peak isometric quadriceps strength (Nm/kg) was also assessed.

FINDINGS

There was a significant increase in quadriceps strength in the training group (mean change (95%CI): 0.35(0.25, 0.045) Nm/kg, P=0.01) with no change in the control group (mean change (95%CI): 0.03(-0.39, 0.45) Nm/kg, P>0.05). There were no changes in impact loading variables. With data from both groups combined, changes in quadriceps strength explained 3% of variance in the change in maximum rate of loading. Change in quadriceps strength was not predictive of the change in peak vertical ground reaction force or average rate of loading.

INTERPRETATIONS

While change in strength was predictive of change in maximal loading rate, this explained only a small proportion of the variance. Future research examining the role parameters such as neuromuscular control play in impact loading are warranted.

Effect of unilateral and bilateral use of laterally wedged insoles with arch supports on impact loading in medial knee osteoarthritis

BACKGROUND

Increased impact loading is implicated in knee osteoarthritis development and progression.

OBJECTIVES

This study examined the impact ground reaction force (GRF) peak, its loading rate, its relative timing to stance phase timing, and walking speed during unilateral and bilateral use of laterally wedged insoles with arch supports.

STUDY DESIGN

Within-subject design.

METHODS

Thirty-three female patients with medial knee osteoarthritis were examined with (unilateral 6° and 11°, and bilateral 0°, 6°, and 11°) and without insole use.

RESULTS

Repeated measures MANOVA revealed that the impact force increased significantly in bilateral 11° versus unilateral 6° and without-insole conditions. The loading rate decreased significantly in unilateral 11° versus bilateral 6° insoles. The relative timing increased significantly in each of bilateral 6°, bilateral 11°, and unilateral 11° versus bilateral 0° insoles and in each of bilateral 11° and unilateral 11° versus without-insole condition. There were significant positive correlations between the walking speed and each of the force and loading rate. The Chi-square test revealed insignificant association between the insole condition and the presence of impact forces.

CONCLUSION

Unilateral 11° insoles are capable of reducing impact loading possibly through increasing foot pronation. Walking slowly is another possible strategy to reduce loading.

CLINICAL RELEVANCE

Unilaterally applied 11° laterally wedged insoles are capable of reducing and delaying the initial impact ground reaction forces and reducing their loading rates during walking in patients with medial knee osteoarthritis, thus reducing osteoarthritis progression. Walking slowly could also be used as a strategy to reduce impact loading.

A high-throughput model of post-traumatic osteoarthritis using engineered cartilage tissue analogs

OBJECTIVE

A number of in vitro models of post-traumatic osteoarthritis (PTOA) have been developed to study the effect of mechanical overload on the processes that regulate cartilage degeneration. While such frameworks are critical for the identification therapeutic targets, existing technologies are limited in their throughput capacity. Here, we validate a test platform for high-throughput mechanical injury incorporating engineered cartilage.

METHOD

We utilized a high-throughput mechanical testing platform to apply injurious compression to engineered cartilage and determined their strain and strain rate dependent responses to injury. Next, we validated this response by applying the same injury conditions to cartilage explants. Finally, we conducted a pilot screen of putative PTOA therapeutic compounds.

RESULTS

Engineered cartilage response to injury was strain dependent, with a 2-fold increase in glycosaminoglycan (GAG) loss at 75% compared to 50% strain. Extensive cell death was observed adjacent to fissures, with membrane rupture corroborated by marked increases in lactate dehydrogenase (LDH) release. Testing of established PTOA therapeutics showed that pan-caspase inhibitor [Z-VAD-FMK (ZVF)] was effective at reducing cell death, while the amphiphilic polymer [Poloxamer 188 (P188)] and the free-radical scavenger [N-Acetyl-L-cysteine (NAC)] reduced GAG loss as compared to injury alone.

CONCLUSIONS

The injury response in this engineered cartilage model replicated key features of the response of cartilage explants, validating this system for application of physiologically relevant injurious compression. This study establishes a novel tool for the discovery of mechanisms governing cartilage injury, as well as a screening platform for the identification of new molecules for the treatment of PTOA.

A longitudinal study of impact and early stance loads during gait following arthroscopic partial meniscectomy

People following arthroscopic partial medial meniscectomy (APM) are at increased risk of developing knee osteoarthritis. High impact loading and peak loading early in the stance phase of gait may play a role in the pathogenesis of knee osteoarthritis. This was a secondary analysis of longitudinal data to investigate loading-related indices at baseline in an APM group (3 months post-surgery) and a healthy control group, and again 2 years later (follow-up). At baseline, 82 participants with medial APM and 38 healthy controls were assessed, with 66 and 23 re-assessed at follow-up, respectively. Outcome measures included: (i) heel strike transient (HST) presence and magnitude, (ii) maximum loading rate, (iii) peak vertical force (Fz) during early stance. At baseline, maximum loading rate was lower in the operated leg (APM) and non-operated leg (non-APM leg) compared to controls (p ≤ 0.03) and peak Fz was lower in the APM leg compared to non-APM leg (p ≤ 0.01). Over 2 years, peak Fz increased in the APM leg compared to the non-APM leg and controls (p ≤ 0.01). Following recent APM, people may adapt their gait to protect the operated knee from excessive loads, as evidenced by a lower maximum loading rate in the APM leg compared to controls, and a reduced peak Fz in the APM leg compared to the non-APM leg. No differences at follow-up may suggest an eventual return to more typical gait. However, the increase in peak Fz in the APM leg may be of concern for long-term joint health given the compromised function of the meniscus.