Comparison of three methods for identifying the heelstrike transient during walking gait

Impulsive, or high rate, loading contributes to cartilage degradation and is commonly identified via the heelstrike transient (HST) in the vertical ground reaction force (vGRF) during gait. Investigation of the HST may improve our understanding of knee osteoarthritis mechanical pathogenesis. However, the most appropriate method for objectively identifying the HST is unclear. Twenty-eight healthy subjects walked at a self-selected pace while vGRF data were captured. The efficacies of three HST identification methods (Radin, Hunt, and Modified Hunt) were evaluated using vGRF data lowpass filtered at three frequencies (raw/unfiltered, 75 Hz, and 50 Hz). Both the HST identification method and lowpass filter frequency influenced whether a HST was identified and whether a subject was classified as an “impulsive loader” (i.e. HST identified in 3 of 5 trials). The methods identified different phenomena in the vGRF, with the Radin and Modified Hunt methods identifying the HST 11-16 ms following ground contact and the Hunt method identifying the HST 83–122 ms following ground contact. Lowpass filtering the vGRF at 75 Hz and implementing the Radin method was the most effective approach for identifying the HST. Future longitudinal observations are necessary to determine if specific HST criteria are indicative of knee osteoarthritis development and progression.     

The influence of high-heeled shoes on strain and tension force of the anterior talofibular ligament and plantar fascia during balanced standing and walking

High-heeled shoes have the capability to alter the strain and tension of ligamentous structures between the foot and ankle, which may result in ankle instability. However, high-heeled shoes can also reduce the strain on plantar fascia, which may be beneficial for the treatment of plantar fasciitis. In this study, the influence of heel height on strain and tension force applied to the anterior talofibular ligament (ATL) and plantar fascia were investigated.A three-dimensional finite element model of coupled foot–ankle–shoe complex was constructed. Four heel heights were studied in balanced standing: 0 in. (0 cm), 1 in. (2.54 cm), 2 in. (5.08 cm), and 3 in. (7.62 cm). A walking analysis was performed using 2-in. (5.08 cm) high-heeled shoes.During balanced standing, the tension force on the ATL increased from 14.8 N to 97.0 N, with a six-fold increase in strain from 0 in. to 3 in. (0–7.62 cm). The tension force and the average strain on the plantar fascia decreased from 151.0 N (strain: 0.74%) to 59.6 N (strain: 0.28%) when the heel height increased from 0 in. to 2 in. (0–5.08 cm). When heel height reached 3 in. (7.62 cm), the force and average strain increased to 278.3 N (strain: 1.33%). The walking simulation showed that the fascia stretched out while the ATL loading decreased during push off. The simulation outcome demonstrated the influence of heel height on ATL alteration and plantar fascia strain, which implies risks for ankle injury and suggests guidance for the treatment of plantar fasciitis.     

A three-dimensional computed tomography study of distal femoral morphology in Japanese patients: Gender differences and component fit

BackgroundPrevious anthropometric studies have reported gender differences in distal femoral morphology. However, to date, very few studies have investigated the knee morphology of Japanese adults and possible gender differences. The purpose of this study was to examine the distal femoral morphology of Japanese patients, to characterize anatomical differences between male and female, and to evaluate the need to create gender-specific knee prostheses.Material and methodsWe evaluated 80 knees in 40 male and 40 female Japanese patients scheduled for total knee arthroplasty (TKA). The mediolateral (ML) and anteroposterior (AP) dimensions of the knees at different levels were measured preoperatively using three-dimensional computed tomography, and ML/AP aspect ratios were calculated.ResultsOn the distal femoral cut surface, the mean ML widths were 74.9 mm for male and 65.1 mm for female, and the mean AP lengths were 63.4 mm for male and 58.9 mm for female. Such values were generally smaller compared to data from European and North American studies. In this study, the mean ML/AP aspect ratios were 1.31 for male and 1.25 for female, higher than those from non-Asian regions. The ML/AP ratios of Japanese patients were negatively correlated with distal femoral AP length.ConclusionsJapanese female had a relatively narrower femoral width for a given AP length than male. Our study suggests the utility of Japanese-specific implants and provides useful insights for manufacturers to design components of appropriate sizes and aspect ratios for Japanese TKA patients.     

A new measure of the CoP trajectory in postural sway: Dynamics of heading change

The maintenance of upright stance requires the simultaneous control of posture in both the anterior–posterior (AP) and medial–lateral (ML) dimensions. Postural sway is typically measured by quantifying the movement of the center of pressure (CoP) in the AP and ML dimensions independently. Metrics such as path length and 95% ellipse area have been developed to take into account movement in both the AP and ML directions, but these metrics only quantify the magnitude of the CoP movement. The movement of the CoP is technically a vector quantity with both magnitude and direction characteristics. The direction of displacement, or heading, of the CoP may provide further insight into the control of posture. Accordingly, we present a novel variable that describes the rate of change in direction of CoP displacement in two dimensions, the heading change (Δϕ), which is derived from the CoP heading (ϕ). We then compared the standard deviation (SD) and the dynamic structure characterized by sample entropy (SampEn) of the heading change time series to previously examined metrics presented in the literature (SD and SampEn of the AP and ML time series, path length, SD and SampEn of the CoP resultant magnitude time series) during a 60 s single-leg stance performed by healthy participants and patients with a ruptured anterior cruciate ligament (ACL) prior to surgical intervention. Patients with an ACL rupture exhibited a different dynamic structure in Δϕ compared to healthy controls, t(14) = 2.44, p = 0.029, whereas none of the other metrics differed between groups (all p > 0.05). The novelty and utility of Δϕ is that it characterizes directional changes of the CoP, whereas previously documented postural control analyses describe only changes in magnitude.     

The effect of videotape augmented feedback on drop jump landing strategy: Implications for anterior cruciate ligament and patellofemoral joint injury prevention

BackgroundModification of high-risk movement strategies such as dynamic knee valgus is key to the reduction of anterior cruciate ligament (ACL) and patellofemoral joint (PFJ) injuries. Augmented feedback, which includes video and verbal feedback, could offer a quick, simple and effective alternative to training programs for altering high-risk movement patterns. It is not clear whether feedback can reduce dynamic knee valgus measured using frontal plane projection angle (FPPA).MethodsVertical ground reaction force (vGRF), two-dimensional FPPA of the knee, contact time and jump height of 20 recreationally active university students were measured during a drop jump task pre- and post- an augmented feedback intervention. A control group of eight recreationally active university students were also studied at baseline and repeat test.ResultsThere was a significant reduction in vGRF (p = 0.033), FPPA (p < 0.001) and jump height (p < 0.001) and an increase in contact time (p < 0.001) post feedback in the intervention group. No changes were evident in the control group.ConclusionAugmented feedback leads to significant decreases in vGRF, FPPA and contact time which may help to reduce ACL and PFJ injury risk. However, these changes may result in decreased performance.Clinical relevanceAugmented feedback reduces dynamic knee valgus, as measured via FPPA, and forces experienced during the drop jump task and therefore could be used as a tool for helping decrease ACL and PFJ injury risk prior to, or as part of, the implementation of injury prevention training programs.     

Sagittal plane body kinematics and kinetics during single-leg landing from increasing vertical heights and horizontal distances: Implications for risk of non-contact ACL injury

PurposeThis study identified kinematic and knee energetic variables that reduce the risk of non-contact anterior cruciate ligament (ACL) injury during single-leg landings from increasing vertical heights and horizontal distances.MethodsNine subjects performed single-leg landings from takeoff platforms with vertical heights of 20, 40, and 60 cm onto a force plate. Subjects also performed single-leg landings from a 40 cm high takeoff platform placed at horizontal distances of 30, 50 and 70 cm from a force plate. Kinematic and kinetic data were measured.ResultsVertical height had a significant and positive effect on peak vertical ground reaction force (VGRF) (p < 0.001), peak posterior ground reaction force (PGRF) (p = 0.004), knee flexion angle (p = 0.0043), trunk flexion angle (p = 0.03), knee power (p < 0.001) and knee work (p < 0.001). There was also a significant and positive effect of horizontal distance on peak PGRF (p < 0.001), ankle plantar flexion angle (p = 0.008), hip flexion angle (p = 0.007), and trunk flexion angle (p = 0.001). At increasing vertical height, peak VGRF was significantly correlated to ankle plantar flexion and knee flexion angles (r = − 0.77, p = 0.02 and r = − 0.78, p = 0.01, respectively). At increasing horizontal distance, peak PGRF was significantly correlated to ankle plantar flexion angle, knee power and knee work (r = − 0.85, p = 0.003; r = 0.67, p = 0.04; and r = 0.73, p = 0.02, respectively).Clinical RelevanceA better understanding of the risk factors to non-contact ACL injury during single-leg landings from increasing vertical heights and horizontal distances can aid in the design of injury prevention regimen.     

Proud osteochondral autograft versus synthetic plugs — Contact pressures with cyclical loading in a bovine knee model

PurposeTo determine whether proud synthetic and proud osteochondral plugs conform to native surrounding cartilage after cyclical loading and if there are differences in height and contact pressure after loading.MethodsSixteen bovine knees were used. Each received one osteochondral plug and one of two types of synthetic plugs (Smith & Nephew TruFit® BGS plug or Kensey Nash OsseoFit® plug). Plugs were placed in the center of each condyle's highest pressure area of articulation identified prior to defect creation (control). Static loads of 800 N were applied and contact pressures measured with Tekscan sensors.ResultsBoth types of synthetic grafts and the osteochondral grafts all subsided with cyclical loading (p < 0.001). The OsseoFit® plug displayed a greater reduction in height than the TruFit® plug compared to osteochondral grafts. The OsseoFit® plugs had significantly lower height than osteochondral grafts after both periods of cyclical loading (p < 0.001), while height of the TruFit® plugs was not significantly different than the heights of osteochondral grafts after either first (p = 0.387) or second (p = 0.261) periods of cyclical loading. Contact pressures for the OsseoFit® plugs were significantly lower than contact pressures for osteochondral grafts after both periods of cyclical loading (p < 0.001 for both). There was no difference between the pressures of TruFit® and osteochondral plugs after the first (p = 0.381) or second (p = 0.292) periods of cyclical loading.ConclusionsPrecision and accuracy are demanded to achieve flush osteochondral plug placement and OsseoFit synthetic plugs may subside more with less pressure than TruFit plugs if placed proud.     

An MRI compatible loading device for the reconstruction of clinically relevant plantar pressure distributions and loading scenarios of the forefoot

The purpose of this study is to demonstrate a new MRI compatible loading device capable of reconstructing realistic loading scenarios of the human foot for research in the field of foot biomechanics. This device has two different configurations: one used to compress the forefoot and one to bend the metatarsophalangeal joints. Required plantar pressure distribution under the metatarsal heads can be achieved by modifying the distribution of the dorsally applied forces. To validate the device, subject-specific plantar pressures were measured and then reconstructed using the device. For quiet stance the peak pressure reconstruction error was 3% while for mid-stance phase of gait it was 8%. The device was also used to measure the passive bending stiffness of the metatarsophalangeal joints of one subject with low intra-subject variability. A series of preliminary MRI scans confirmed that the loading device can be used to produce static weight-bearing images of the foot (voxel size: 0.23 mm × 0.23 mm × 1.00 mm).The results indicate that the device presented here can accurately reconstruct subject specific plantar pressure distributions and measure the foot's metatarsophalangeal passive stiffness. Possible future applications include the validation of finite element models, the investigation of the relationship between plantar pressure and internal stresses/strains and the study of the foot's inter-segmental passive stiffness.     

Comparison of eMAG™ versus NucliSENS® EasyMAG® performance on clinical specimens

BackgroundeMAG™ (bioMerieux) is a new nucleic acid extraction platform based on magnetic silica technology, like its predecessor, NucliSENS^® easyMAG^® (bioMerieux). Using the same reagents and disposables, eMAG™ adds further automation, allowing simultaneous extraction of 48 samples directly from primary tubes, and distribution of nucleic acid extracts on PCR strips or in tubes at the end of the extraction process.ObjectiveTo compare the performance of eMAG™ and easyMAG^® on various clinical specimens.Study designRespiratory (n = 199), whole blood (n = 50), plasma (n = 25) and urine (n = 25) specimens were extracted in parallel on both platforms. Both qualitative (respiratory virus, cell control, CMV, EBV, HHV6 and BKV detection) and quantitative (respiratory virus and cell control cycle thresolds, and CMV, EBV, HHV6 and BKV viral loads) results were compared.ResultsDetection of qualitative targets showed good agreement, ranging from 84.6% for whole blood to 95.9% for respiratory specimens. Correlations between quantitative results were good, with R² ranging from 0.802 to 0.995. Quantitative results showed average overall differences below 0.10 log₁₀ copies/mL between eMAG™ and easyMAG^®.ConclusionsThe two platforms showed comparable performance on the types of clinical specimen tested. With higher automation and throughput than easyMAG^®, the eMAG™ platform is likely to be advantageous for laboratories performing a large number of molecular analyses.     

Dosage plasmatique des D-dimères sur Integra 800® : comparaison avec le dosage sur Vidas® dans le diagnostic d'exclusion des maladies veineuses thromboemboliques

The D-dimer quantitative test is an exclusive screening tool used by the emergency departments for the exclusion of Deep Venous Thrombosis diseases (DVT). Its negative predictive value is closed to 100%. We compared the diagnostic performance of the D-dimer assay Tinaquant^® performed on an Integra 800^® to the reference Elisa D-dimer assay Vidas^®, which is routinely used in our laboratory as reference test. Interassay reproducibilility (CV) for Tinaquant^® is: 2.34% and 2.05% for levels of 1010 and 4830 ng/ml respectively. We investigated 250 patients with the two tests simultaneously. The correlation obtained through a linear regression (R = 0.86) gives the equation: Y (Integra^®) = 1.11 × (Vidas^®) – 72. The mean D-dimer Vidas^® are: 1337 ± 1700 ng/ml vs. Integra^®: 1496 ng/ml ± 2379. Ninety percent of the results are concordant at a cutoff of 500 ng/ml. Among the 25 discordant results, 18 are Vidas^®(+)/Tinaquant^®(–) showing a better specificity for the Tinaquant^® test, which is confirmed by imaging results for DVT diagnosis. Only 7 of the 25 give a better specificity for Vidas^®. Tinaquant^® D-dimer assay demonstrated interesting performances in this study regarding the practicability and the efficiency of the test. It appears to be suitable for the exclusion of DVT diseases and should be studied throughout a larger number of outpatients.     

Gender differences of the morphology of the distal femur and proximal tibia in a Korean population

PurposeWe conducted this study to determine whether the sizes of distal femurs and proximal tibiae in Korean men and women are different, and to assess suitability of the sizes of prostheses currently used in Korea.Materials and methodsWe performed morphological analysis of proximal tibia and distal femur on 115 patients (56 male, 59 female) using MRI to investigate a gender difference. Tibial mediolateral dimension (tMAP), tibial medial anteroposterior dimension (tMAP), tibial lateral anteroposterior dimension (tLAP) femoral mediolateral dimension (fML), femoral medial anteroposterior dimension (fMAP), and femoral lateral anteroposterior dimension (fLAP) were measured. The ratio of tMAP and tLAP to tML (plateau aspect ratio, tAP/tML × 100%), and that of fMAP and fLAP to fML (condylar aspect ratio, fAP/fML × 100%) were calculated. The measurements were compared with the similar dimensions of four total knee implants currently used.ResultsThe tML and tAP lengths showed a significant gender difference (P < 0.05). The plateau aspect ratio (tMAP/tML) revealed a significant difference between male (0.74 ± 0.05) and female (0.68 ± 0.04, P < 0.05). For morphotype of distal femur, males were found to have significantly large values (P < 0.05) in the parameters, except for fLAP. With regards to the ratio of the ML width to the AP length, the women showed a narrower ML width than the men. Both genders were distributed within the range of the dimensions of the prostheses currently used prostheses.ConclusionsKorean population revealed that women have smaller dimensions than male counterparts. In both genders, a relatively small size of prostheses matches distal femur and proximal tibia better among the implants currently used in Korea.     

Une alternative à la chromatographie pour la détection de la macroprolactine : calcul du rapport de deux immunodosages de la prolactine : Immulite 2000® et Kryptor®

Macroprolactin is a high molecular mass form of prolactin with minimal bioactivity in vivo. The presence of macroprolactin must be considered for the differential diagnosis of hyperprolactinemia because prolactin-immunoassays present various reactivity with macroprolactin. So we compared to the reference technique (size-exclusion chromatography) a new screening test: calculation of the ratio between results obtained from two prolactin assays: Immulite^® with high cross reactivity with macroprolactin and Kryptor^® with no reactivity. In this study, serums from 69 patients with various macroprolactinemia (between 8 and 88% with chromatography) were selected and the ratio of the results of two prolactin assays was calculated for 49 hyperprolactinemic serums (prolactinemia > 636 mUI/l, Immulite 2000^®). According to ROC curves analysis, a low Immulite^®/Kryptor^® ratio (< 1.45) indicates the presence of less than 20% of macroprolactin (sensitivity = 100% specificity = 85%), and a high ratio (> 1.80) indicates the presence of more than 50% of macroprolactin (sensitivity = 95%, specificity = 100%). However, this screening test must be confirmed by size-exclusion chromatography for the rare samples presenting an Immulite^®/Kryptor^® ratio between 1.45 and 1.80.     

Evaluation of the COBAS® AmpliPrep/COBAS® TaqMan® HCV Test,v2.0 and comparison to assays used in routine clinical practice in an international multicenter clinical trial: The ExPECT study

BackgroundThe COBAS^® AmpliPrep^®/COBAS^® TaqMan^® HCV Test, v2.0 (CAP/CTM2) is used for HCV RNA viral load monitoring.ObjectivesThe performance of the CAP/CTM2 was compared to other widely used tests, including a manual version of the assay (the COBAS^® TaqMan^® HCV Test, v2.0 for use with the High Pure System, HPS/CTM2) predominantly used during phase III clinical trials for the new direct acting antiviral therapies.Study designLow HCV RNA level comparisons were performed across tests (Abbott Realtime HCV Test, ART; COBAS^® AmpliPrep^®/COBAS^® TaqMan^® HCV Test, v1.0, CAP/CTM1; CAP/CTM2; and HPS/CTM2) using dilutions of the 2nd HCV WHO International Standard. Additionally, the clinical performance of the CAP/CTM2 was evaluated with 421 leftover HCV RNA-positive routine clinical samples.ResultsAll quantifiable WHO dilutions were within ±0.3 log₁₀ IU/mL of the expected results across tests and the analytical sensitivity resulted in a limit of detection of 12 IU/mL (95% confidence interval, 10, 15). When clinical samples were tested the results for 87% (367 of 421) of all sample comparisons were within ±0.5 log₁₀ IU/mL. When low viral load results (25–3500 IU/mL) were compared, values obtained by the ART assay were significantly lower (p < 0.0001) than those obtained with the CAP/CTM2.ConclusionsThe new CAP/CTM2 showed good accuracy with comparable sensitivity to comparator assays. The new kit is well-suited for use in the routine diagnostic laboratory, especially for accurate monitoring of patients receiving triple therapy or interferone-free regimens.     

Inter-rater reliability of the GNRB® knee arthrometer

BackgroundIn clinical settings, where arthrometers are mainly used by different clinicians, knowing the inter-rater reliability of the instrument is crucial in order for the results from different examiners to be accurately interpreted and limitations fully understood. The aim of this study was to evaluate the inter-rater reliability of the GNRB® knee arthrometer.MethodsKnee anterior laxity in both knees was tested in a group of young, uninjured subjects (N = 27, 13 females) by two examiners. Knee anterior laxity was calculated at test forces of 134 N and 250 N with values presented for the unstandardised and standardised conditions (relative to patellar stabilisation force).ResultsThe ICCs ranged from 0.220 to 0.424.ConclusionsThe inter-rater reliability of the GNRB® knee arthrometer is low.     

A quantitative in vitro method to predict the adhesion lifetime of diamond-like carbon thin films on biomedical implants

A quantitative method using Rockwell C indentation was developed to study the adhesion of diamond-like carbon (DLC) protective coatings to the CoCrMo biomedical implant alloy when immersed in phosphate-buffered saline (PBS) solution at 37 °C. Two kinds of coatings with thicknesses ranging from 0.5 up to 16 microns were investigated, namely DLC and DLC/Si-DLC, where Si-DLC denotes a 90 nm thick DLC interlayer containing Si. The time-dependent delamination of the coating around the indentation was quantified by means of optical investigations of the advancing crack front and calculations of the induced stress using the finite element method (FEM). The cause of delamination for both types of coatings was revealed to be stress-corrosion cracking (SCC) of the interface material. For the DLC coating a typical SCC behavior was observed, including a threshold region (60 J m^?2) and a “stage 1” crack propagation with a crack-growth exponent of 3.0, comparable to that found for ductile metals. The DLC/Si-DLC coating exhibits an SCC process with a crack-growth exponent of 3.3 and a threshold region at 470 J m^?2, indicating an adhesion in PBS at 37 °C that is about eight times better than that of the DLC coating. The SCC curves were fitted to the reaction controlled model typically used to explain the crack propagation in bulk soda lime glass. As this model falls short of accurately describing all the SCC curves, limitations of its application to the interface between a brittle coating and a ductile substrate are discussed.     

Intraoperative fluoroscopy shows better agreement and interchangeability in tibial tunnel location during single bundle anterior cruciate ligament reconstruction with postoperative three-dimensional computed tomography compared with an intraoperative image-free navigation system

BackgroundFluoroscopy and navigation systems provide an accurate and reproducible method of guiding anatomical tunnel positioning during anterior cruciate ligament reconstruction (ACLR). The aim was to evaluate the differences in tibial tunnel location assessed by both an intraoperative navigation system and fluoroscopy, validated using a one-week postoperative three-dimensional computed tomography (3DCT).MethodsThe tibial tunnel location in a consecutive series of 35 patients who received a single-bundle ACLR was evaluated by intraoperative navigation system, fluoroscopic image and compared with postoperative 3DCT position. The location to the anterior–posterior (AP) and medial–lateral (ML) direction were compared between all three methods.ResultsThe tibial tunnel locations were 46.7 ± 4.5%, 44.5 ± 1.9%, and 43.6 ± 2.4% in ML direction, and 42.8 ± 7.6%, 37.9 ± 3.8%, and 37.9 ± 3.7% in AP direction using an intraoperative navigation system, fluoroscopic image and postoperative 3DCT, respectively. Significant differences between the navigation system and fluoroscopic image (ML, P = 0.001; AP, P = 0.006), and the navigation system and 3DCT (ML, P = 0.001; AP, P < 0.001) were seen. However, there was no significant difference between fluoroscopy and 3DCT (ML, P = 0.315; AP, P = 0.999). There was a significant lack of agreement for analyses measured using a navigation system and 3DCT. Fluoroscopy and 3DCT demonstrated an acceptable agreement (ML, r_pt = − 0.21, P = 0.232; AP, r_pt = 0.04, P = 0.826).ConclusionsA tibial tunnel location assessed by intraoperative fluoroscopy shows better agreement and interchangeability with one-week postoperative 3DCT validation during single-bundle ACLR compared with an intraoperative image-free navigation system.     

Effect of addition of hyaluronic acids on the osteoconductivity and biodegradability of synthetic octacalcium phosphate

The present study was designed to investigate whether three sodium hyaluronic acid (HyA) medical products, Artz®, Suvenyl® and a chemically modified derivative of sodium HyA Synvisc®, can be used as suitable vehicles for an osteoconductive octacalcium phosphate (OCP). OCP granules (300–500 μm diameter) were mixed with these sodium HyAs with molecular weights of 90 × 10⁴ (Artz®), 190 × 10⁴ (Suvenyl®) and 600 × 10⁴ (Synvisc®) (referred to as HyA90, HyA190 and HyA600, respectively). OCP–HyA composites were injected using a syringe into a polytetrafluoroethylene ring, placed on the subperiosteal region of mouse calvaria for 3 and 6 weeks, and then bone formation was assessed by histomorphometry. The capacity of the HyAs for osteoclast formation from RAW264 cells with RANKL was examined by TRAP staining in vitro. Bone formation was enhanced by the OCP composites with HyA90 and HyA600, compared to OCP alone, through enhanced osteoclastic resorption of OCP. HyA90 and HyA600 facilitated in vitro osteoclast formation. The results suggest that the osteoconductive property of OCP was accelerated by the HyAs-associated osteoclastic resorption of OCP, and therefore that HyA/OCP composites are attractive bone substitutes which are injectable and bioactive materials.     

The statistical relationship between varus deformity,surgeon's experience,BMI and tourniquet time for computer assisted total knee replacements

The outcome of total knee arthroplasty (TKA) with severe pre-operative varus deformity is significantly worse than in well aligned knees. Computer navigated TKA has addressed some of the problems by ensuring accurate post-operative alignment. Our aims were to see if navigation could reproducibly correct a varus deformity to 3° of the mechanical axis and to investigate the relationships between the tourniquet time and severity of the preoperative deformity, BMI and a surgeon's experience.The 172 e.motion floating platform TKA's were implanted using the OrthoPilot^® Navigation system (B Braun-Aesculap, Tuttlingen, Germany). Pre-operative deformity and post-operative alignment were measured by the software. Tourniquet times were recorded automatically.All knees were corrected to within 3° of the neutral axis (mean 0.48°). Statistically significant relationships between tourniquet time (TT) and degree of pre-operative varus (p < 0.001), total number of previous e.motion TKA's performed (p < 0.001), and body mass index (p = 0.013) were found. A linear relationship between the variables can be expressed as a statistical formula:TT = 49.5 + PreOp Varus + 0.6(BMI) ? 0.1(total previous). Tourniquet time is measured in minutes and preoperative varus is measured in degrees from the mechanical axis. Total previous is the total number of navigated TKA's implanted by the surgeon.Tourniquet time is increased with larger pre-operative deformities and high BMI and decreased with surgical experience. The formula may give us a method of predicting the length of a procedure for a particular surgical team and may allow us to plan operating lists more accurately.     

Development of a shear measurement sensor for measuring forces at human–machine interfaces

Measuring shear force is crucial for investigating the pathology and treatment of pressure ulcers. In this study, we introduced a bi-axial shear transducer based on strain gauges as a new shear sensor. The sensor consisted of aluminum and polyvinyl chloride plates placed between quadrangular aluminum plates. On the middle plate, two strain gauges were placed orthogonal to one another. The shear sensor (54 mm × 54 mm × 4.1 mm), which was validated by using standard weights, displayed high accuracy and precision (measurement range, −50 to 50 N; sensitivity, 0.3 N; linear relationship, R² = 0.9625; crosstalk error, 0.635% ± 0.031%; equipment variation, 4.183). The shear force on the interface between the human body and a stand-up wheelchair was measured during sitting or standing movements, using two mats (44.8 cm × 44.8 cm per mat) that consisted of 24 shear sensors. Shear forces on the sacrum and ischium were almost five times higher (15.5 N at last posture) than those on other sites (3.5 N on average) during experiments periods. In conclusion, the proposed shear sensor may be reliable and useful for measuring the shear force on human–machine interfaces.     

Trans-scleral tactile tonometry: An instrumented approach

This article describes a feasibility study of a novel trans-scleral tonometer based on the use of an instrumented form of digital palpation tonometry. Similar to manual digital palpation tonometery, trans-scleral tonometer utilizes two force probes offset by a fixed distance. Force indentation data from these probes have been shown to correlate with the intraocular pressure (IOP) of the eye. Enucleated porcine eyes were used to experimentally validate the approach. The observed hysteresis in the force data was analyzed using an analytical model that accounts for the outflow of the aqueous humor. The predictions of the model indicate that the primary reason behind the observed hysteresis is stress relaxation (accommodation) in the visco-elastic corneo-scleral shell. Experimental data from eye distention and indentation tests were then used to infer the conditions under which the novel tonometer would be expected to have an accuracy of ±1 mmHg. Analysis of the data shows that indentation rates should be kept below 0.5 mm/s for a pressure range of 10–35 mmHg. Two commonly used pressure control protocols were tested in an effort to ensure accurate IOP values during the palpation tests. Due to the large increase of IOP during digital palpation, the trans-scleral (intra-vitreous) pressurization was found to be inadequate, leading to clogging of the line by the displaced vitreous. No such problems were identified when the eye was pressurized through the cornea and into the anterior chamber. Force data from multiple palpation experiments are used to generate calibration curves for a two-probe conceptual tonometer. The calibration showed that a 10 mN of force variation corresponds to 1 mmHg of IOP change. A possible implementation using a contoured facial mask is also presented.