Peter Worsley

Assessing contractile ability of the quadriceps muscle using ultrasound imaging

Muscle dimension changes on ultrasound imaging (USI) indicate contractile activity. Quadriceps force and rectus femoris (RF) dimensions were examined to assess USI for estimating contraction level. In 15 healthy males, mean age 24.8 years, isometric quadriceps force was measured in 90° knee flexion during submaximal and maximal voluntary contractions (MVCs) and at MVC in extension. Mid‐thigh cross‐sectional area (CSA), depth and width, and surface electromyography (EMG) of RF were recorded. Muscle width decreased curvilinearly as both force and EMG increased. At MVC, width was 3.2 ± 0.5 cm, 25% smaller than at rest (4.4 ± 0.7 cm), and similar to MVC in extension (−23%). CSA decreased linearly to −18% at MVC. RF thickness increased by only 10% (at 30% to MVC). Similar width changes at MVC in flexion and extension indicate the clinical potential of USI for assessing quadriceps contractility. Sensitivity is limited to assessing strength to within 25% of MVC in young males. Muscle Nerve, 2010

Predicted knee kinematics and kinetics during functional activities using motion capture and musculoskeletal modelling in healthy older people

Knowledge of joint forces and moments is essential for comparisons between healthy people and those with pathological conditions, with observed changes at joints providing basis for a particular intervention. Currently the literature analysing both kinematics and kinetics at the knee has been limited to small samples, typically of young subjects or those who have undergone joint arthroplasty. In this study, we examined tibiofemoral joint (TFJ) kinematics and kinetics during gait, sit-stand-sit, and step-descent in 20 healthy older subjects (aged 53-79 years) using motion capture data and inverse dynamic musculoskeletal models. Mean peak distal-proximal force in the TFJ were 3.1, 1.6, and 3.5 times body weight (N/BW) for gait, sit-stand, and step-descent respectively. There were also significant posterior-anterior forces, with sit-stand activity peaking at 1.6 N/BW. Moments about the TFJ peaked at a mean of 0.07 Nm/BW during the sit-stand activity. One of the most important findings of this study was variability found across the subjects, who spanned a wide age range, showing large standard deviations in all of the activities for both kinematics and kinetics. These data have provided an initial prediction for assessing kinematics and kinetics in the older population. Larger studies are needed to refine the database, in particular to reduce the variability in the results by studying sub-populations, to enable more robust comparisons between healthy and pathological TFJ kinematics and kinetics.

Development of a statistical model of knee kinetics for applications in pre-clinical testing

Pre-clinical computational testing of total knee replacements (TKRs) often only considers a single patient model with simplified applied loads. In studies of multiple patients, most only take into account geometric differences, especially in studies on the knee. Limited availability of kinetic data means that it is difficult to account for inter-patient variability. Principal component analysis (PCA) based statistical models have been used to capture the variation of a set of data and generate new instances of the data. This study presents a method to create a statistical model of kinetic waveform data. A PCA based statistical model was created of the tibiofemoral joint loads for level gait of preoperative TKR patients using data predicted from a musculoskeletal model. A reconstruction test showed that, using principal components (PCs) representing 95% variance, the median root-mean-squared (RMS) error was <0.1 body weight (BW) for the forces and <0.001 BWm for the moments. Leave-one-out tests were also performed and although the median RMS error increased for each load in comparison to the reconstruction error (maximum was 0.2 BW for the axial force and 0.012 BWm for the varus-valgus moment) these were considered within an acceptable limit. The purpose of creating a statistical model is to be able to sample a large set of data representing a population from a small set of clinical data. Such models can potentially be used in population based studies of TKRs incorporating inter-patient variability.

Neuromuscular electrostimulation via the common peroneal nerve promotes lower limb blood flow in a below-knee cast:a potential for thromboprophylaxis

Objectives We aimed to examine the characteristics of deep venous flow in the leg in a cast and the effects of a wearable neuromuscular stimulator (geko; FirstKind Ltd) and also to explore the participants’ tolerance of the stimulator. Methods This is an open-label physiological study on ten healthy volunteers. Duplex ultrasonography of the superficial femoral vein measured normal flow and cross-sectional area in the standing and supine positions (with the lower limb initially horizontal and then elevated). Flow measurements were repeated during activation of the geko stimulator placed over the peroneal nerve. The process was repeated after the application of a below-knee cast. Participants evaluated discomfort using a questionnaire (verbal rating score) and a scoring index (visual analogue scale). Results The geko device was effective in significantly increasing venous blood flow in the lower limb both with a plaster cast (mean difference 11.5 cm/sec-1; p = 0.001 to 0.13) and without a plaster cast (mean difference 7.7 cm/sec-1; p = 0.001 to 0.75). Posture also had a significant effect on peak venous blood flow when the cast was on and the geko inactive (p = 0.003 to 0.69), although these differences were less pronounced than the effect of the geko (mean difference 3.1 cm/sec-1 (-6.5 to 10)). The geko device was well tolerated, with participants generally reporting only mild discomfort using the device. Conclusion The geko device increases venous blood flow in the lower limb, offering a potential mechanical thromboprolylaxis for patients in a cast. Cite this article: Bone Joint Res 2013;2:179–85.

The physiological response of soft tissue to periodic repositioning as a strategy for pressure ulcer prevention

BACKGROUND Individuals who have reduced mobility are at risk of developing pressure ulcers if they are subjected to sustained static postures. To reduce this risk, clinical guidelines advocate healthcare professionals reposition patients regularly. Automated tilting mechanisms have recently been introduced to provide periodic repositioning. This study compared the performance of such a prototype mattress to conventional manual repositioning. METHODS Ten healthy participants (7 male and 3 female, aged 23-66 years) were recruited to compare the effects of an automated tilting mattress to standard manual repositioning, using the 30° tilt. Measures during the tilting protocols (supine, right and left tilt) included comfort and safety scores, interface pressures, inclinometer angles and transcutaneous gas tensions (sacrum and shoulder). Data from these outcomes were compared between each protocol. FINDINGS Results indicated no significant differences for either interface pressures or transcutaneous gas responses between the two protocols (P>0.05 in both cases). Indeed a small proportion of participants (~30%) exhibited changes in transcutaneous oxygen and carbon dioxide values in the shoulder during a right tilt for both protocols. The tilt angles at the sternum and the pelvis were significantly less in the automated tilt compared to the manual tilt (mean difference=9.4-11.5°, P<0.001). Participants reported similar comfort scores for both protocols, although perceived safety was reduced on the prototype mattress. INTERPRETATION Although further studies are required to assess its performance in maintaining tissue viability, an automated tilting mattress offers the ability to periodically reposition vulnerable individuals, with potential economic savings to health services.

Joint loading asymmetries in knee replacement patients observed both pre- and six months post-operation

BACKGROUND Studies have highlighted asymmetries in knee joint moments in individuals with osteoarthritis and joint replacements. However, there is a need to investigate the forces at the knee joints to establish the extent of loading asymmetries. METHODS Twenty healthy (mean age, 62; range, 55-79 years) and 34 pre- to post-knee arthroplasty (mean age, 64; range, 39-79 years) participants performed gait and sit-stand activities in a motion capture laboratory. Knee joint forces and moments were predicted using inverse dynamics and used to calculate peak loading and impulse data which were normalized to body weight. Comparisons were made between affected and contralateral limbs, and changes from pre- to post-knee arthroplasty. FINDINGS Pre-knee arthroplasty peak vertical knee forces were greater in the contralateral limb compared to the affected limb during both gait 3.5 vs. 3.2 ∗ body weight and sit-stand 1.8 vs. 1.5 ∗ body weight. During gait, peak knee adduction moment asymmetries significantly changed from pre- to post-knee arthroplasty (-0.3 to 0.8 ∗ % body weight ∗ m ∗ height), although differences in vertical knee forces remained. There were no significant changes in loading during sit-stand from pre- to post-knee arthroplasty. The healthy participants showed no noteworthy asymmetries. INTERPRETATION This study showed loading asymmetries in knee forces between affected and contralateral limbs both pre- and post-knee arthroplasty. Continued over reliance of the contralateral limb could lead to pathology.

New insights into the immediate outcome of collagenase injections for Dupuytren's contracture

Collagenase clostridium histolyticum is now established as an effective and safe option to treat patients with a single joint affected with Dupuytren’s contracture. We have extended its use to natatory and combined cords. In a prospective consecutive series of 298 cords in 237 patients, the mean total extension loss improved in cords crossing the metacarpophalangeal joint from 46° to 1°, in cords crossing the proximal interphalangeal joint from 56° to 7°, in natatory cords from 130° to 25° and in combined cords from 102° to 16°. The immediate correction of combined cords and natatory cords was less reliable than that obtained in cords crossing the metacarpophalangeal joint or proximal interphalangeal joint. Less severe pre-intervention contractures tended to correct better. We found a high complication rate, which may cause alarm. A total of 21% developed skin splits, with the risk of skin splits generally increasing with more severe pre-injection deformity. Blood blisters were only encountered after manipulation of the more severe contractures. A total of 23 patients (8%) had a spontaneous rupture and 57 patients (19%) had a partial spontaneous rupture. Only 4.9% needed a second injection. We noticed a learning curve, with seven of the first 20 cords (35%) needing a second injection to achieve a satisfactory correction and then only seven (2.5%) in the rest. Level of evidence: IV

Validity of measuring distal vastus medialis muscle using rehabilitative ultrasound imaging versus magnetic resonance imaging

UNLABELLED Objective quantification of muscle size can aid clinical assessment when treating musculoskeletal conditions. To date the gold standard of measuring muscle morphology is magnetic resonance imaging (MRI). However, theres a growing body of evidence validating rehabilitative ultrasound imaging (RUSI) against MRI. OBJECTIVE This study aimed to validate RUSI against MRI for the linear measurements of the distal fibres of vastus medialis muscle in the thigh. Twelve healthy male participants were recruited from a local university population. The distal portion of their right vastus medialis was imaged with the participant in long-sitting, using MRI and RUSI whilst the leg was in extension and neutral hip rotation. Cross sectional area (CSA) and three linear measures were taken from the MRI and these were compared with the same linear measures from RUSI. Statistical analysis included comparison of MRI and RUSI measures using the paired t-test and intra-class correlation coefficients (ICC 3,1). Mean differences between the linear measures taken from the MRI and RUSI were -0.5 mm to 2.9 mm (95% confidence intervals -0.6-8.3 mm), which were not statistically different (p > 0.05) and were highly correlated (ICCs 3,1 0.84-0.94). Correlations between the three linear measurements and muscle CSA ranged from r = 0.23 to 0.87, the greatest being muscle thickness. Multiplying the linear measures did not improve the correlation of 0.87 found for muscle thickness. Linear measures of vastus medialis depth made using RUSI were shown to be as valid as using MRI. Muscle thickness measures using RUSI could be used within an objective assessment of this muscle.

A Review of the Role of the Partial Pressure of Carbon Dioxide in Mechanically Loaded Tissues: The Canary in the Cage Singing in Tune with the Pressure Ulcer Mantra

Pressure ulcers (PUs) can occur in any situations where people are subjected to non-uniform distribution of pressure over a prolonged period. They can have devastating effects on the patients’ well-being and in extreme conditions can prove fatal. In addition to traditional wisdom implicating mechanically induced ischaemia, there is strong evidence that other mechanisms play a role in the cascade of events which can initiate the PU damage process at the cellular level. Some of these refer to a metabolic imbalance with compromised delivery of nutrients and accumulation of waste products in the local environment of the cells. The approach of much research has focused on the measure of oxygen in compressed tissues as a means of predicting early damage. However, the present review adopting a hierarchical approach, using length scales ranging from cells through to human models, has revealed compelling evidence which highlights the importance of carbon dioxide levels and associated concentration of other metabolites, such as lactate and purines. The temporal profiles of these metabolites have been monitored in the various models subjected to periods of mechanical-induced loading where the localized cells have converted to anaerobic metabolism. They reveal threshold levels of carbon dioxide which might be indicative of early tissue damage during both mechanical-induced ischaemia and subsequent reperfusion and an appropriate sensor could be used in a similar manner to the long-standing “canary in a cage” method to detect toxic gasses in enclosed mines.

An evaluation of fluid immersion therapy for the prevention of pressure ulcers

BACKGROUND Individuals with impaired mobility can spend prolonged periods on support surfaces, increasing their risk of developing pressure ulcers. Manufacturers have developed mattresses to maximise contact area. The present study evaluated both the biomechanical and physiological responses to lying postures on a Fluid Immersion Simulation mattress. METHODS Seventeen healthy participants were recruited to evaluate the mattress during three prescribed settings of immersion (high, medium and low). Parameters reflecting biomechanical and physiological responses, and the microclimate were monitored during three postures (supine, lateral and high-sitting) over a 90minute test session. Transcutaneous oxygen and carbon dioxide gas responses were categorised according to three criteria and data were compared between each condition. FINDINGS Results indicated that interface pressures remained consistent, with peak sacral values ranging from 21 to 27mmHg across all immersion settings and postures. The majority of participants (82%) exhibited minimal changes in gas tensions at the sacrum during all test conditions. By contrast, three participants exhibited decreased oxygen with increased carbon dioxide tensions for all three immersion settings. Supine and high sitting sacral microclimate values ranged between 30.1-30.6°C and 42.3-44.5% for temperature and relative humidity respectively. During lateral tilt there was a reduction of 1.7-2.5°C and 3.3-5.3% in these values. The majority of participants reported high comfort scores, although a few experienced bottoming out during the high-sitting posture at the high immersion setting. INTERPRETATION Fluid Immersion Simulation provides an intelligent approach to increase the support area. Further research is required to provide evidence based guidance on the use of personalised support surfaces.