Real time monitoring of screw insertion using acoustic emission can predict screw stripping in human cancellous bone

Background To develop experience, orthopaedic surgeons train their own proprioception to detect torque during screw insertion. This experience is acquired over time and when implanting conventional/non-locked screws in osteopenic cancellous bone the experienced surgeon still strips between 38 and 45%. Technology needs to be investigated to reduce stripping rates. Acoustic-Emission technology has the ability to detect stress wave energy transmitted through a screw during insertion into synthetic bone. Our hypothesis is Acoustic-Emission waves can be detected through standard orthopaedic screwdrivers while advancing screws through purchase and overtightening in cancellous human bone with different bone mineral densities replicating the clinical state. Methods 77 non-locking 4 mm and 6.5 mm diameter cancellous bone screws were inserted through to stripping into the lateral condylar area of 6 pairs of embalmed distal femurs. Specimens had varying degrees of bone mineral density determined by quantitative CT. Acoustic-Emission energy and axial force were detected for each test. Results The tests showed a significant high correlation between bone mineral density and Acoustic-Emission energy with R = 0.74. A linear regression model with the mean stripping load as the dependent variable and mean Acoustic-Emission energy, bone mineral densities and screw size as the independent variables resulted in r 2 = 0.94. Interpretation This experiment succeeded in testing real time Acoustic-Emission monitoring of screw purchase and overtightening in human bone. Acoustic-Emission energy and axial compressive force have positive high correlation to bone mineral density. The purpose is to develop a known technology and apply it to improve the bone-metal construct strength by reducing human error of screw overtightening

Incidental walking activity is sufficient to induce time-dependent conditioning of the Achilles tendon

The Achilles tendon has been seen to exhibit time-dependent conditioning when isometric muscle actions were of a prolonged duration, compared to those involved in dynamic activities, such as walking. Since, the effect of short duration muscle activation associated with dynamic activities is yet to be established, the present study aimed to investigate the effect of incidental walking activity on Achilles tendon diametral strain. Eleven healthy male participants refrained from physical activity in excess of the walking required to carry out necessary daily tasks and wore an activity monitor during the 24 h study period. Achilles tendon diametral strain, 2 cm proximal to the calcaneal insertion, was determined from sagittal sonograms. Baseline sonographic examinations were conducted at approximately 08:00 h followed by replicate examinations at 12 and 24 h. Walking activity was measured as either present (1) or absent (0) and a linear weighting function was applied to account for the proximity of walking activity to tendon examination time. Over the course of the day the median (min, max) Achilles tendon diametral strain was -11.4 (4.5, -25.4)%. A statistically significant relationship was evident between walking activity and diametral strain (P<0.01) and this relationship improved when walking activity was temporally weighted (AIC 131 to 126). The results demonstrate that the short yet repetitive loads generated during activities of daily living, such as walking, are sufficient to induce appreciable time-dependant conditioning of the Achilles tendon. Implications arise for the in vivo measurement of Achilles tendon properties and the rehabilitation of tendinopathy

Modelling activity dependent diametral strain in Achilles tendon

The Achilles tendon is a viscoelastic tissue that typically experiences 3500 ± 1700 cyclic loads per day from intermittent periods of ambulatory activity. Typically, peak tensile loads exceed three times body weight and average about 1500 N during stance, which lasts for approximately 0.6 s, followed by a 0.2 s unloaded swing phase. Viscoelastic materials respond to external load (stress) in a time-dependent manner commonly referred to as creep deformation (strain) and recover slowly when unloaded. This can be observed in vivo by monitoring changes in tendon diameter using quantitative ultrasonography and is referred to here as diametral strain. Diametral strains between −25% and +10% have been recorded over a 24 h period and are hypothesised to be associated with fluid movement within the tendon that corresponds with the creep and recovery histories. Changes in tendon diameter were taken at five times throughout a 24 h period in 11 subjects. Ambulatory activity was monitored as time stamped cadence periods by a Polar RS800sd module enabling time of day and activity duration to be used as indicators of creep and recovery histories. These archival records of diametral strain versus activity were then used to develop an adaptive non-linear viscoelastic model for interpolating tendon cross-sectional dimensions between observation points and from which, site specific volumetric flow rates can be estimated. This model has an error bound of less than 5% and has the potential for application to future studies linking fluid flow within the tissue to inherent biomechanical properties, injury status or pathological defects

Tendon rehabilitation: isolated eccentric loading invokes a greater reduction in Achilles tendon thickness than concentric loading

Eccentric calf muscle exercise has been advocated as the treatment of choice in Achilles tendinopathy. However, mechanisms underlying the efficacy of eccentric, as opposed to concentric, exercise remain unknown. This research investigated the acute change in the sagittal thickness of the Achilles tendon (AT) in response to bouts of isolated eccentric or concentric calf muscle exercise. Eleven healthy males, without AT pathology (age, 25.9 ± 4.9 years; mass, 74.2 ± 11.8 kg), completed an exercise protocol involving isolated eccentric loading of the AT (ankle dorsi-flexion), while the contra-lateral AT experienced isolated concentric loading (ankle plantar-flexion). Six sets of 15 repetitions were performed against body weight, with an additional 20% bodyweight added via a backpack. AT thickness 2 cm proximal to the calcaneal insertion was determined from sagittal sonograms taken immediately prior to and following exercise. Consistent with earlier research, calf muscle exercise resulted in an abrupt decrease in AT thickness. However, isolated eccentric loading induced a significantly greater decrease (−20.8 ± 5.5%) than concentric loading (−5.3 ± 4.7%, p = 0.013). It is hypothesised that eccentric muscle action may invoke a differential stress field within the AT that results in a localised increase in collagen strain and extrusion of water from the tendon. Shear stress arising from such fluid flow may, in turn, stimulate tenocytes to produce matrix proteins that promote tendon remodelling, as has been shown in other collagen-rich tissues. The findings of this research have broad implications for the treatment of tendinopathy and provide greater insight into the clinically perceived benefit of eccentric over concentric exercise in AT rehabilitation

Global patterns in small-scale cannabis growers’ distribution practices : Exploring the grower-distributor nexus

Background While the supply of cannabis is commonly assumed to be dominated by criminal gangs, a sizable share of the domestic cannabis supply is provided by small-scale growers. This article examines the nature and scope of small-scale growers’ distribution practices, with a particular focus on cross-country differences and variations between different types of grower-distributors, i.e., “non-suppliers”, “exclusive social suppliers”, “sharers and sellers” and “exclusive sellers”. Methods Based on a large convenience web survey sample of predominantly small-scale cannabis growers from 18 countries, this article draws on data from two subsamples. The first subsample includes past-year growers in all 18 countries who answered questions regarding their market participation (n = 8,812). The second subsample includes past-year growers in 13 countries, who answered additional questions about their supply practices (n = 2,296). Results The majority of the cannabis growers engaged in distribution of surplus products, making them in effect “grower-distributors”. Importantly, many did so as a secondary consequence of growing, and social supply (e.g., sharing and gifting) is much more common than selling. While growers who both shared and sold (“sharers and sellers”), and especially those who only sold (“exclusive sellers”), grew a higher number of plants and were most likely to grow due to a wish to sell for profits, the majority of these are best described as small-scale sellers. That is, the profit motive for growing was often secondary to non-financial motives and most sold to a limited number of persons in their close social network. Conclusion We discuss the implications of the findings on the structural process of import-substitution in low-end cannabis markets, including a growing normalization of cannabis supply