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result(s) for
"Björkman, Anders"
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Alarming Plasmodium falciparum resistance to artemisinin-based combination therapy in Africa: the critical role of the partner drug
by
Gil, Pedro
,
Björkman, Anders
,
Alifrangis, Michael
in
Antiparasitic agents
,
Artemether
,
Artemisinin
2024
First-line treatment in the east African countries with emerging artemisinin resistance has been artemether–lumefantrine. When malaria transmission is high, frequent new reinfections can occur soon after treatment during the relatively long elimination phase of the partner drug, lumefantrine.2 Slowly decreasing concentrations of lumefantrine will result in the selection of P falciparum genotypes in the Pfmdr1 and Pfcrt genes, and possibly Pfmdr1 amplification, which are associated with lesser antiparasitic effects by lumefantrine (figure).2 The parasite population might be progressively selected towards lesser lumefantrine sensitivity, probably also enhanced by higher parasite fitness as most genotypes associated with lesser lumefantrine sensitivity are wild type.3,4 This progressive selection might even result in rare treatment failure of artemether–lumefantrine in an otherwise artemisinin sensitive infection (figure).5 A reduced effect of artemether–lumefantrine will however be much more considerable against parasites partly resistant to artemisinin and thus facilitate a concomitant emergence, selection, and spread of K13 mutations (figure). [...]while a reduced effect of an initially efficacious partner drug might evolve and spread after the occurrence of artemisinin resistance in southeast Asia,7 the opposite might be common in Africa with higher transmission rates.
Journal Article
Generalizable gesture classification of HDsEMG using volume representations of muscles averaged across multiple individuals
by
Björkman, Anders
,
Antfolk, Christian
,
Malesevic, Nebojsa
in
631/114/116/2392
,
631/114/116/2394
,
631/378/2632
2025
Human hands can perform far more gestures than the number of muscles controlling them, as most gestures result from coordinated combinations of muscle activations and relaxations. This complexity poses a key challenge for human-machine interfaces performing gesture classification based on electromyography (EMG). Rather than identifying all conceivable gestures, it may be simpler to instead identify the activity of the individual muscles which generate a variety of complicated gestures. Here we suggest a three-dimensional model with volume representations of individual digit extensor muscles, averaged across multiple individuals, and evaluate its application and performance in hand gesture classification. Time-domain peaks in high-density surface EMG data from different hand gestures were extracted and localized within the model, from which a gesture classification scheme was generated for both single and multi-label cases. The model was created and tested on a publicly available dataset with 19 participants, leveraging a leave-one-out approach to assess inter-subject generalizability, and multi-label data to assess generalizability to gestures not included in the creation of the model. For single-label classification performance, true positive rates were between 61.9 and 95.1%, with false positive rates between 0 and 24.1%, for different single-digit extensions. The multi-label test demonstrated some degree of generalizability in identifying completely new gesture compositions, while simultaneously maintaining the leave-one-out approach for inter-subject generalizability. A model generated with this approach could be used for gesture classification by anyone, without individual modelling data, with the potential to generalize to any number of gesture compositions.
Journal Article
Inferring position of motor units from high-density surface EMG
by
Björkman, Anders
,
Antfolk, Christian
,
Malesevic, Nebojsa
in
631/378/2632
,
639/166/985
,
Action potential
2024
The spatial distribution of muscle fibre activity is of interest in guiding therapy and assessing recovery of motor function following injuries of the peripheral or central nervous system. This paper presents a new method for stable estimation of motor unit territory centres from high-density surface electromyography (HDsEMG). This completely automatic process applies principal component compression and a rotatable Gaussian surface fit to motor unit action potential (MUAP) distributions to map the spatial distribution of motor unit activity. Each estimated position corresponds to the signal centre of the motor unit territory. Two subjects were used to test the method on forearm muscles, using two different approaches. With the first dataset, motor units were identified by decomposition of intramuscular EMG and the centre position of each motor unit territory was estimated from synchronized HDsEMG data. These positions were compared to the positions of the intramuscular fine wire electrodes with depth measured using ultrasound. With the second dataset, decomposition and motor unit localization was done directly on HDsEMG data, during specific muscle contractions. From the first dataset, the mean estimated depth of the motor unit centres were 8.7, 11.6, and 9.1 mm, with standard deviations 0.5, 0.1, and 1.3 mm, and the respective depths of the fine wire electrodes were 8.4, 15.8, and 9.1 mm. The second dataset generated distinct spatial distributions of motor unit activity which were used to identify the regions of different muscles of the forearm, in a 3-dimensional and projected 2-dimensional view. In conclusion, a method is presented which estimates motor unit centre positions from HDsEMG. The study demonstrates the shifting spatial distribution of muscle fibre activity between different efforts, which could be used to assess individual muscles on a motor unit level.
Journal Article
Asymptomatic low-density malaria infections: a parasite survival strategy?
2018
Of more interest is the longitudinal variation in parasite densities, although only 16 (7%) untreated infections evolved to parasite densities of more than 200 000 parasites per mL, above the detection limit of microscopy or rapid diagnostic tests. From previous studies, the main conclusion is that submicroscopic infections could be important contributors to transmission in areas with very low transmission intensity.1 A key question that remains is why P falciparum infections in individuals with no or low immunity can remain asymptomatic often without the development of high parasite densities. A new hypothesis might be that in a low-endemic environment, parasites that are less virulent might not be exposed to high competition from more virulent strains and might therefore persist at a low density, asymptomatic, undetected, and untreated allowing for further transmission over a long time period and therefore eventually selected.
Journal Article
Inflammatory and degenerative changes in the extensor pollicis longus muscle and tendon following ruptures caused by distal radius fractures
2025
Background
Rupture of extensor pollicis longus tendon (EPL) is a known complication following a distal radius fracture (DRF). Although the precise mechanisms behind these ruptures remain unclear, vascular impairment is thought to play a significant role. Additionally, the impact of an EPL rupture on microstructure of the tendon and muscle is not well understood, but such information could be important in guiding treatment strategies. This study aims to explore the histopathological changes in the EPL tendon and muscle in patients who have experienced an EPL rupture following a DRF.
Methods
Consecutive patients with an EPL rupture following a DRF were included and treated with an Extensor Indicis Proprius to EPL tendon transfer. Samples were taken from the distal part of EPL muscle and the proximal tendon from the musculotendinous junction to the rupture site as well as from the tendon distal to the rupture. The tendon specimens were analysed by standard histopathological techniques including immunohistochemistry. In cases of sufficient amount of muscle, fresh frozen specimens were analysed by enzyme- and immuno-histochemistry on cryostat sections.
Results
Thirteen patients (12 females, 1 male; median age 61, range 18–72 years) were included in the study. The EPL muscle in all participants showed extensive inflammatory changes, muscle fiber necrosis and regeneration, structural changes in the muscle fibers and slight interstitial fibrosis. The EPL tendon showed profound degenerative changes mainly in the central part of the tendon whereas there were regenerative changes in the periphery of the tendon. The pathological changes were present in all samples regardless of time between the DRF and the EPL rupture or the time between the diagnosis of the rupture and surgery.
Conclusions
The extensive inflammatory changes in the EPL muscle indicate that immune mediated mechanisms are involved in muscle degeneration following tendon rupture. The EPL tendon showed characteristic degenerative changes at the myotendinous junction, as well as proximally and distally to the rupture site. The reversibility and the clinical significance of the severe pathological changes seen in the EPL muscle alongside the healing potential of the tendon need further investigation.
Trial registration
Retrospectively registered the 2024–03-15 at Clinicaltrials.gov, ID: NCT06313489.
Journal Article
Automatic measurements of volar tilt and radial inclination of the distal radius on 3D models: validation against manual methods
2026
Assessing distal radius malunions traditionally relies on measuring volar tilt and radial inclination in 2D radiographs. Reliability of these parameters is limited by projection errors and landmark ambiguity. Using 3D models allows more precise quantification of these parameters. This study validated an algorithm for measuring volar tilt and radial inclination on 3D virtual models of malunited and healthy radii. The algorithm establishes a 3D coordinate system and anatomical landmarks replicating conventional 2D definitions to maintain clinical compatibility. Automatic 3D measurements on models from 16 participants were compared with manual measurements on 2D radiographs (by three surgeons in consensus) and on 3D models (by two independent raters). Agreement was assessed using Bland–Altman analysis, and landmark discrepancies were quantified. Mean differences between automatic 3D and manual 2D measurements were small: for volar tilt, 2.0° in malunited and 3.5° in healthy radii; for radial inclination, 1.5° and 2.3°, respectively. Strong agreement was also found between automatic and manual 3D measurements. Landmark deviations ranged from 0.5 to 2.8 mm, with an average longitudinal axis difference of 2.5°. This open-source algorithm provides a reproducible 3D assessment of distal radius alignment. By closely matching 2D standards, the algorithm has a high potential for clinical integration.
Journal Article
An exploratory study of the impact of CT slice thickness and inter-rater variability on anatomical accuracy of malunited distal radius models and surgical guides for corrective osteotomy
by
Axelsson, Peter
,
Gryska, Emilia
,
Libberecht, Katleen
in
Accuracy
,
Adult
,
Biology and Life Sciences
2024
High-resolution CT images are essential in clinical practice to accurately replicate patient anatomy for 3D virtual surgical planning and designing patient-specific surgical guides. These technologies are commonly used in corrective osteotomy of the distal radius. This study evaluated how the virtual radius models and the surgical guides’ surface that is in contact with the bone vary between experienced raters. Further, the discrepancies from the reference radius of surgical guides and radius models created from CT images with slice thicknesses larger than the reference standard of 0.625mm were assessed. Maximum overlap with radius model was measured for guides, and absolute average distance error was measured for radius models. The agreement between the lower-resolution guides surface and the raters’ guide surface was evaluated. The average inter-rater guide surface overlap was -0.11mm [95% CI: -0.13–0.09]. The surface of surgical guides designed on CT images with a 1mm slice thickness deviated from the reference radius within the inter-rater range (0.03mm). For slice thicknesses of 1.25mm and 1.5mm, the average guide surface overlap was 0.12mm and 0.15mm, respectively. The average inter-rater radius surface variability was 0.03mm [95% CI: 0.025–0.035]. The discrepancy from the reference of all radius models created from CT images with a slice thickness larger than the reference slice thickness was notably larger than the inter-rater variability but, excluding one case, did not exceed 0.2mm. The results suggest that 1mm CT images are suitable for surgical guide design. While 1.25mm slices are commonly used for virtual planning in hand and forearm surgery, slices larger than 1mm may approach the limit of clinical acceptability. Discrepancies in radius models were below 1mm, likely below clinical relevance.
Journal Article
Preclinical paired noninferiority study comparing in-house and commercially available 3D planning for corrective osteotomy of the distal radius
by
Axelsson, Peter
,
Gryska, Emilia
,
Libberecht, Katleen
in
639/166/985
,
692/1537/805
,
692/698/1671/63
2025
3D surgical planning and patient-specific guide design are becoming an established approach in complex skeletal surgery. Traditionally, this is outsourced to commercial companies, but an alternative is to establish an in-house hospital team for the process. This study aimed to compare the accuracy of in-house design with a commercial company. Sixteen patients with extra-articular distal radius malunions requiring surgery were included. A hospital-based team and a surgeon working with an external company independently planned surgery and designed guides for each patient. Accuracy was evaluated by comparing simulated corrections with the planned corrections using 3D-printed bone models. The null hypothesis was that the in-house guides were inferior to the externally purchased ones. Noninferiority margins of 5° for volar tilt and 2 mm for ulnar variance were set. The mean volar tilt error difference between the two guides was 2.3°, and the mean ulnar variance error difference was 0.38 mm, both within the noninferiority limits. The dimensional accuracy of the printed guides before and after sterilization showed minimal variation (less than 0.3 mm). The results demonstrated that in-house surgical planning and guide design for distal radius corrective osteotomies can achieve comparable accuracy to external commercial companies.
Journal Article
RTS,S/AS01 malaria vaccine—proven safe and effective?
2023
In October, 2021, WHO recommended that the RTS,S malaria vaccine, with its strong safety profile and high impact, be provided to children from age 5 months in regions with moderate to high Plasmodium falciparum malaria transmission. The evidence base included phase 3 trials in seven African countries and an ongoing malaria vaccine implementation programme (MVIP) in three African countries. We highlight problems with the MVIP mortality data, including potential confounding, inappropriate use of severe malaria as a surrogate marker, a statistically non-significant effect, and assessment after 2 years instead of the stipulated 4 years, which could have inflated the benefits and deflated the risks associated with the vaccine. We conclude that the claimed impact of the MVIP on mortality is not based on enough scientific evidence and that the MVIP findings do not rule out the possibility of increased mortality among vaccinated girls compared with vaccinated boys, as observed in the phase 3 studies. The MVIP should adhere fully to the planned analyses and the data should be made available for independent assessment. Roll-out of the vaccine elsewhere should include rigorous evaluation, especially of its safety.
Journal Article
The rubber hand illusion evaluated using different stimulation modalities
by
Svensson, Pamela
,
Björkman, Anders
,
Antfolk, Christian
in
Amputation
,
Annan medicinteknik
,
Clinical Medicine
2023
Tactile feedback plays a vital role in inducing ownership and improving motor control of prosthetic hands. However, commercially available prosthetic hands typically do not provide tactile feedback and because of that the prosthetic user must rely on visual input to adjust the grip. The classical rubber hand illusion (RHI) where a brush is stroking the rubber hand, and the user’s hidden hand synchronously can induce ownership of a rubber hand. In the classic RHI the stimulation is modality-matched, meaning that the stimulus on the real hand matches the stimulus on the rubber hand. The RHI has also been used in previous studies with a prosthetic hand as the “rubber hand,” suggesting that a hand prosthesis can be incorporated within the amputee’s body scheme. Interestingly, previous studies have shown that stimulation with a mismatched modality, where the rubber hand was brushed, and vibrations were felt on the hidden hand also induced the RHI. The aim of this study was to compare how well mechanotactile, vibrotactile, and electrotactile feedback induced the RHI in able-bodied participants and forearm amputees. 27 participants with intact hands and three transradial amputees took part in a modified RHI experiment. The rubber hand was stroked with a brush, and the participant’s hidden hand/residual limb received stimulation with either brush stroking, electricity, pressure, or vibration. The three latter stimulations were modality mismatched with regard to the brushstroke. Participants were tested for ten different combinations (stimulation blocks) where the stimulations were applied on the volar (glabrous skin), and dorsal (hairy skin) sides of the hand. Outcome was assessed using two standard tests (questionnaire and proprioceptive drift). All types of stimulation induced RHI but electrical and vibration stimulation induced a stronger RHI than pressure. After completing more stimulation blocks, the proprioceptive drift test showed that the difference between pre- and post-test was reduced. This indicates that the illusion was drifting toward the rubber hand further into the session.
Journal Article