The state of the art in telerehabilitation for musculoskeletal conditions

Real-time video telerehabilitation shows comparable satisfaction and similar or better attendance and adherence compared with in-person physiotherapy: a systematic review

QUESTION

How does physiotherapy delivered by real-time, video-based telerehabilitation compare with in-person delivery for the outcomes of attendance, adherence and satisfaction?

DESIGN

Systematic review of randomised control trials indexed in PubMed, CINAHL, Embase, Cochrane and PEDro on 12 March 2024.

PARTICIPANTS

Adults aged > 18 years.

INTERVENTION

Physiotherapy delivered via real-time video telerehabilitation.

OUTCOME MEASURES

Attendance, adherence and satisfaction.

RESULTS

Eight studies were included for attendance (n = 1,110), nine studies for adherence (n = 1,190) and 12 studies for satisfaction (n = 1,247). Telerehabilitation resulted in attendance at treatment sessions that was 8% higher (95% CI -1 to 18) and adherence to exercise programs that was 9% higher (95% CI 2 to 16) when compared with in-person physiotherapy. Satisfaction was similar with both modes of delivery (SMD 0.03 in favour of telerehabilitation, 95% CI -0.23 to 0.28). The level of certainty assessed by GRADE ranged from very low to low, primarily due to inconsistency and high risk of bias.

DISCUSSION

Attendance at appointments among participants assigned to telerehabilitation was somewhere between similar to and considerably higher than among control participants. Adherence to self-management with telerehabilitation was better than with in-person delivery, although with some uncertainty about the magnitude of the effect. Reported satisfaction levels were similar between the two modes of treatment delivery. Given the significance of attendance, adherence and satisfaction for successful outcomes, telerehabilitation offers a valuable alternative mode for physiotherapy delivery.

CONCLUSION

Real-time telerehabilitation has potentially favourable effects on attendance at treatment appointments and adherence to exercise programs, with similar satisfaction when compared with traditional in-person physiotherapy.

REGISTRATION

PROSPERO CRD42022329906.

Agreement and concurrent validity between telehealth and in-person diagnosis of musculoskeletal conditions: a systematic review

OBJECTIVES

To assess the concurrent validity and inter-rater agreement of the diagnosis of musculoskeletal (MSK) conditions using synchronous telehealth compared to standard in-person clinical diagnosis.

METHODS

We searched five electronic databases for cross-sectional studies published in English in peer-reviewed journals from inception to 28 September 2023. We included studies of participants presenting to a healthcare provider with an undiagnosed MSK complaint. Eligible studies were critically appraised using the QUADAS-2 and QAREL criteria. Studies rated as overall low risk of bias were synthesized descriptively following best-evidence synthesis principles.

RESULTS

We retrieved 6835 records and 16 full-text articles. Nine studies and 321 patients were included. Participants had MSK conditions involving the shoulder, elbow, low back, knee, lower limb, ankle, and multiple conditions. Comparing telehealth versus in-person clinical assessments, inter-rater agreement ranged from 40.7% agreement for people with shoulder pain to 100% agreement for people with lower limb MSK disorders. Concurrent validity ranged from 36% agreement for people with elbow pain to 95.1% agreement for people with lower limb MSK conditions.

DISCUSSION

In cases when access to in-person care is constrained, our study implies that telehealth might be a feasible approach for the diagnosis of MSK conditions. These conclusions are based on small cross-sectional studies carried out by similar research teams with similar participant demographics. Additional research is required to improve the diagnostic precision of telehealth evaluations across a larger range of patient groups, MSK conditions, and diagnostic accuracy statistics.

Patient Perceptions of Emergency Department Observation Care at Home

Introduction: The Virtual Observation Unit (VOU) utilizes telehealth and community paramedicine to provide observation-level care in patients' homes. Patients' experience of this novel program has not been reported. Methods: A phone-based patient experience survey was administered to the patients who were admitted to the VOU at an urban, academic Emergency Department in the Northeast United States. The survey asked about patient's perception of the program's quality of care (0 = worst care possible, 10 = best care possible). t Tests with a Bonferroni adjustment assessed for differences between patient demographic groups. Results: The survey response rate was 40% (124/307). Overall mean scores for perceived quality of care were very high (9.51 ± 1.19). There were no significant differences in patient's perception of quality of care between demographic cohorts of age, gender, race, or ethnicity. Conclusions: Patient experience with a novel VOU program was very positive and did not differ significantly by demographic cohort. Further research is warranted.

Comparing the Efficacy of Manual Therapy and Exercise to Synchronized Telerehabilitation with Self-Manual Therapy and Exercise in Treating Subacromial Pain Syndrome: A Randomized Controlled Trial

This study aimed to investigate the efficacy of manual therapy and exercise versus synchronized telerehabilitation with self-manual therapy and exercise in treating Subacromial Pain Syndrome (SAPS). Sixty individuals diagnosed with SPS, aged 18-50 years, were randomly assigned to home exercise (HE), manual therapy (MT), and telerehabilitation (TR) groups. Treatment protocols were administered over 8 weeks and included specific exercises and therapy interventions. Outcome measures included the Visual Pain Scale (VAS), shoulder range of motion (ROM) via goniometric measurements, Quick Disability Arm-Shoulder-Hand Problems Survey (Q-DASH), and patient satisfaction. Results revealed that both MT and TR groups exhibited reduced pain, increased ROM, lower Q-DASH scores, and higher patient satisfaction than the HE group. However, no significant differences were found between the MT and TR groups regarding pain levels, ROM, Q-DASH scores, or patient satisfaction. The study concludes that both telerehabilitation and manual therapy effectively alleviate pain and are well-received by patients with SPS. Additionally, manual therapy demonstrates superiority in enhancing functional levels compared to exercise-based interventions (Registration: NCT05200130).

Effectiveness of Telerehabilitation in Dizziness: A Systematic Review with Meta-Analysis

Dizziness can be a debilitating condition with various causes, with at least one episode reported in 17% to 30% of the international adult population. Given the effectiveness of rehabilitation in treating dizziness and the recent advancements in telerehabilitation, this systematic review aims to investigate the effectiveness of telerehabilitation in the treatment of this disorder. The search, conducted across Medline, Cochrane Central Register of Controlled Trials, and PEDro databases, included randomized controlled trials assessing the efficacy of telerehabilitation interventions, delivered synchronously, asynchronously, or via tele-support/monitoring. Primary outcomes focused on dizziness frequency/severity and disability, with secondary outcomes assessing anxiety and depression measures. Seven articles met the eligibility criteria, whereas five articles contributed to the meta-analysis. Significant findings were observed regarding the frequency and severity of dizziness (mean difference of 3.01, p < 0.001), disability (mean difference of -4.25, p < 0.001), and anxiety (standardized mean difference of -0.16, p = 0.02), favoring telerehabilitation. Telerehabilitation shows promise as a treatment for dizziness, aligning with the positive outcomes seen in traditional rehabilitation studies. However, the effectiveness of different telerehabilitation approaches requires further investigation, given the moderate methodological quality and the varied nature of existing methods and programs.

An Opportunity for Management of Fatigue, Physical Condition, and Quality of Life Through Asynchronous Telerehabilitation in Patients After Acute Coronavirus Disease 2019: A Randomized Controlled Pilot Study

OBJECTIVE

To compare the preliminary efficacy of asynchronous telerehabilitation in patients after acute coronavirus disease 2019 (COVID-19) on fatigue, physical condition, quality of life, and feasibility of this pilot study with that of a booklet format.

DESIGN

Randomized pilot study with 2 intervention arms: asynchronous telerehabilitation group and booklet-based rehabilitation group, with 2 follow-ups at 3 and 6 months.

SETTING

Hospital.

PARTICIPANTS

Patients discharged after COVID-19 were recruited and evaluated (N=35).

INTERVENTIONS

The intervention consisted of a 12-week multimodal rehabilitation program via telerehabilitation or by a booklet.

MAIN OUTCOME MEASURES

Fatigue as the main outcome and functional status, quality of life, and feasibility as secondary outcomes were evaluated.

RESULTS

After the intervention, there was no significant difference between groups in fatigue, but there were significant differences in favor of the asynchronous telerehabilitation group for the 6-Minute Walk Test (p=.008), the 30-Second Sit-to-Stand Test (p=.019), and physical quality of life (p=.035). These improvements were maintained throughout the 6-month follow-up. Telerehabilitation was shown to be a viable option, without incidents and with a higher adhesion (p=.028) than the booklet format.

CONCLUSIONS

A multimodal rehabilitation program by means of asynchronous telerehabilitation appears as a more effective option than traditional formats in improving post-acute COVID-19 sequelae.

Patient-Perceived Quality Assessment in Orthopedics and Traumatology Departments during COVID-19 Pandemic

The COVID-19 pandemic has led to significant disruptions in various healthcare systems. In Romania, the elective procedures in the orthopedic and traumatology specialty were one of the most affected. The study aims to investigate the influence of the COVID-19 pandemic on patient perceptions of quality in these departments. Standardized assessment tools were used, which consist of satisfaction questionnaires addressed to patients in order to assess the quality of health services in orthopedics and traumatology departments. Thus, a retrospective study was conducted using satisfaction questionnaires addressed to patients admitted to the orthopedics and traumatology departments of the County Clinical Emergency Hospital Bihor between January 2019 and December 2022. Eight reports, based on 746 questionnaires conducted during the studied period, were evaluated. To gauge patient satisfaction, Likert scales featuring five response options were used. A total of 627 questionnaires were valid, the exclusion criteria being incomplete questionnaires (the patients did not respond on all questions, n = 119). Four domains were analyzed: demographic data, hotel conditions, quality of medical care, and overall satisfaction. Demographic data highlight that patients exhibited an equitable distribution across residences, with 50.2% hailing from urban locales, while 53.5% (n = 333) were female. Regarding the overall impression, in 2020, there was a decline in the top rating of 5 compared to 2019, dropping to just 45.10% from 53.45%. Scores of 4 increased to 41.83%, while scores of 3 stayed under 8.5%. Scores of 2 and 1 were negligible. In 2021 and 2022, we can observe a sustained increase in the number of patients who awarded 5 points for overall impression and a decrease in the number of patients who awarded 4 points compared to previous years. The maximum difference between 2020 and 2021 and the period before and after this period was 27.24% (p-value < 0.001). The results indicate that while overall impressions of the hospital remained positive throughout the studied period, there were notable fluctuations in satisfaction levels during the pandemic. Patient satisfaction with attending physicians dipped in 2020 from 86.70% to 77.78% but recovered by 2022. The same trend can be observed with nurses and caregivers, as well as hotel services, during this period. These findings underscore the importance of addressing patient concerns and improving the quality of care delivery, particularly during times of crisis.

Therapists and patients perceptions of a mixed reality system designed to improve trunk control and upper extremity function

A prototype system aimed at improving arm function and trunk control after stroke has been developed that combines mixed-reality (MR) feedback with a mobile seat system (Holoreach). The purpose of this study was to assess the usability of Holoreach in a rehabilitation setting from both the patient and therapist perspective. Ten therapists (eight physiotherapists and two occupational therapists) used the device in their regular therapy programs for fifteen stroke patients with trunk control issues. Each patient received four individual therapy sessions with the device performed under the supervision of the therapist. Therapists and patients kept therapy diaries and used customized questionnaires. At the end of the study two focus groups were conducted to further assess usability. Generally, the prototype system is suitable for training trunk and arm control. The therapists expressed overall positive views on the impact of Holoreach. They characterized it as new, motivating, fresh, joyful, interesting, and exciting. All therapists and 80% of the patients agreed with the statement that training with Holoreach is beneficial for rehabilitation. Nonetheless, improvements are required in the hardware and software, and design. The prototype system contributes at various levels to the rapidly evolving advances in neurorehabilitation, particularly regarding the practical aspect of exercise delivery.

Enhancing automated lower limb rehabilitation exercise task recognition through multi-sensor data fusion in tele-rehabilitation

BACKGROUND

Tele-rehabilitation is the provision of physiotherapy services to individuals in their own homes. Activity recognition plays a crucial role in the realm of automatic tele-rehabilitation. By assessing patient movements, identifying exercises, and providing feedback, these platforms can offer insightful information to clinicians, thereby facilitating an improved plan of care. This study introduces a novel deep learning approach aimed at identifying lower limb rehabilitation exercises. This is achieved through the integration of depth data and pressure heatmaps. We hypothesized that combining pressure heatmaps and depth data could improve the model's overall performance.

METHODS

In this study, depth videos and body pressure data from an accessible online dataset were used. This dataset comprises data from 30 healthy individuals performing 7 lower limb rehabilitation exercises. To accomplish the classification task, three deep learning models were developed, all based on an established 3D-CNN architecture. The models were designed to classify the depth videos, sequences of pressure data frames, and combination of depth videos and pressure frames. The models' performance was assessed through leave-one-subject-out and leave-multiple-subjects-out cross-validation methods. Performance metrics, including accuracy, precision, recall, and F1 score, were reported for each model.

RESULTS

Our findings indicated that the model trained on the fusion of depth and pressure data showed the highest and most stable performance when compared with models using individual modality inputs. This model could effectively identify the exercises with an accuracy of 95.71%, precision of 95.83%, recall of 95.71%, and an F1 score of 95.74%.

CONCLUSION

Our results highlight the impact of data fusion for accurately classifying lower limb rehabilitation exercises. We showed that our model could capture different aspects of exercise movements using the visual and weight distribution data from the depth camera and pressure mat, respectively. This integration of data provides a better representation of exercise patterns, leading to higher classification performance. Notably, our results indicate the potential application of this model in automatic tele-rehabilitation platforms.

Usability of a visual feedback system to assess and improve movement disorders related to neck pain: Perceptions of physical therapists and patients

A prototype visual feedback system has been developed to assess and improve movement disorders related to neck pain. The aim of this study was to assess the usability of the prototype in a rehabilitation setting. Twelve physical therapists integrated the device into their regular therapy programs for 24 neck pain patients with movement disorders. Each patient performed three individual therapy sessions with the device under physical therapist supervision. Usability was assessed by the physical therapists and patients using therapy diaries, the System Usability Scale, and focus group or personal interviews. Based on an overall usability rating of marginally acceptable, the visual feedback system was generally found to be a device with the potential to assess and train neck pain patients but needs improvement. To become a useful adjunct to regular physical therapy, improvements in the hardware and software, and further system developments are required.

Effectiveness of Telemedicine for Musculoskeletal Disorders: Umbrella Review

BACKGROUND

Several systematic reviews (SRs) assessing the use of telemedicine for musculoskeletal conditions have been published in recent years. However, the landscape of evidence on multiple clinical outcomes remains unclear.

OBJECTIVE

We aimed to summarize the available evidence from SRs on telemedicine for musculoskeletal disorders.

METHODS

We conducted an umbrella review of SRs with and without meta-analysis by searching PubMed and EMBASE up to July 25, 2022, for SRs of randomized controlled trials assessing telemedicine. We collected any kind of patient-reported outcome measures (PROMs), patient-reported experience measures (PREMs), and objective measures, including direct and indirect costs. We assessed the methodological quality with the AMSTAR 2 tool (A Measurement Tool to Assess systematic Reviews 2). Findings were reported qualitatively.

RESULTS

Overall, 35 SRs published between 2015 and 2022 were included. Most reviews (n=24, 69%) were rated as critically low quality by AMSTAR 2. The majority of reviews assessed "telerehabilitation" (n=29) in patients with osteoarthritis (n=13) using PROMs (n=142 outcomes mapped with n=60 meta-analyses). A substantive body of evidence from meta-analyses found telemedicine to be beneficial or equal in terms of PROMs compared to conventional care (n=57 meta-analyses). Meta-analyses showed no differences between groups in PREMs (n=4), while objectives measures (ie, "physical function") were mainly in favor of telemedicine or showed no difference (9/13). All SRs showed notably lower costs for telemedicine compared to in-person visits.

CONCLUSIONS

Telemedicine can provide more accessible health care with noninferior results for various clinical outcomes in comparison with conventional care. The assessment of telemedicine is largely represented by PROMs, with some gaps for PREMs, objective measures, and costs.

TRIAL REGISTRATION

PROSPERO CRD42022347366; https://osf.io/pxedm/.

Care at a distance: Understanding lived experiences of people with MSK disorders receiving non-pharmacological interventions delivered through synchronous telehealth: A systematic rapid review

Background

Little is known about lived experience of synchronous telehealth in patients with musculoskeletal (MSK) disorders.

Objective

We conducted a rapid systematic review to answer: (1) what are the lived experiences and/or perspectives of people with MSK disorders receiving non-pharmacological interventions delivered through synchronous telehealth; and (2) what clinical implications can be inferred from qualitative studies focusing on lived experiences for how telehealth is delivered in the management of MSK disorders?

Data sources

A comprehensive search of MEDLINE, CINAHL, PsycINFO, ProQuest, and Google Scholar from June 2010 to July 2023. Eligible qualitative and mixed methods studies capturing lived experiences of adults with MSK disorders receiving non-pharmacological interventions via synchronous telehealth were included.

Study methods

Systematic rapid review conducted according to WHO guidelines. Titles and abstracts screened by reviewers independently, eligible studies critically appraised, and data was extracted. Themes summarized using the Consolidated Framework for Implementation Research (CFIR). GRADE-CERQual (Confidence in the Evidence from Reviews of Qualitative research) used to assess confidence in synthesis findings.

Results

We identified 9782 references, screened 8029, and critically appraised 22, and included 17 studies. There is evidence to suggest that the experience of telehealth prior to and during the pandemic was shaped by (1) patient perception of telehealth, (2) existing relationships with practitioners, (3) availability and accessibility of telehealth technologies, and (4) perceptions about the importance of the role of the physical exam in assessing and treating MSK disorders.

Conclusion

The five identified implications could be used to inform future research, policy, and strategy development.

Effectiveness of Functional or Aerobic Exercise Combined With Breathing Techniques in Telerehabilitation for Patients With Long COVID: A Randomized Controlled Trial

OBJECTIVE

The aim of this study was to compare the short-term clinical effects of 2 telerehabilitation programs, functional versus aerobic exercises (AEs), both combined with breathing techniques, regarding the improvement of long coronavirus disease 2019 (COVID-19) symptoms.

METHODS

A randomized controlled trial was conducted. The participants were assigned randomly to either the functional exercise (FE) group or AE group, both including breathing techniques. The interventions lasted for 8 weeks with 3 sessions per week, and they were conducted through the Fisiotrack mobile phone application. Assessments were performed at baseline and after treatment, including testing fatigue (Fatigue Assessment Scale), dyspnea (London Chest Activity of Daily Living Scale), functional performance (30 Seconds Standing Test), perceived stress (Perceived Stress Scale), anxiety and depression (Hospital Anxiety and Depression Questionnaire), and quality of life (European Quality of Life Scale). The perceived change after treatment (Patient Global Impression of Change Scale), the usability of the application (System Usability Scale), and the adherence to treatment were also examined after treatment.

RESULTS

In total, 43 participants (FE group, n = 21; AE group, n = 22; mean age = 42.4 [SD = 6.5] years) completed the study. In the intragroup comparison, the FE group showed improved fatigue (-6.7 points; 95% CI = -11.9 to -1.3), functional capacity (2.6 repetitions; 95% CI = 0.3 to 4.9), and perceived stress (-4.9 points; 95% CI = -9.1 to 0.8), while the AE group showed improved perceived stress (-6.2 points; 95% CI = -10.3 to -2.1). No significant differences in the intergroup effect were identified for the studied variables. Significant differences were observed in the Patient Global Impression of Change Scale in favor of the FE group compared to the AE group, and quality of life reached the minimal clinically important difference for both groups. The ease of use of the telerehabilitation tool was rated excellent in both groups.

CONCLUSIONS

Both telerehabilitation exercise modalities are effective at improving stress symptoms and quality of life in patients with long COVID-19. For improving fatigue and functional performance, FE shows more promising results.

IMPACT

FE or AE may be recommended depending on patients' symptoms, and both may improve quality of life and stress symptoms in patients with long COVID-19. Telerehabilitation may be an optimal intervention modality for the prescription of physical exercise in patients with long COVID-19.

Current challenges and potential solutions to the use of digital health technologies in evidence generation: a narrative review

Digital health is a field that aims to improve patient care through the use of technology, such as telemedicine, mobile health, electronic health records, and artificial intelligence. The aim of this review is to examine the challenges and potential solutions for the implementation and evaluation of digital health technologies. Digital tools are used across the world in different settings. In Australia, the Digital Health Translation and Implementation Program (DHTI) emphasizes the importance of involving stakeholders and addressing infrastructure and training issues for healthcare workers. The WHO's Global Task Force on Digital Health for TB aims to address tuberculosis through digital health innovations. Digital tools are also used in mental health care, but their effectiveness must be evaluated during development. Oncology supportive care uses digital tools for cancer patient intervention and surveillance, but evaluating their effectiveness can be challenging. In the COVID and post-COVID era, digital health solutions must be evaluated based on their technological maturity and size of deployment, as well as the quality of data they provide. To safely and effectively use digital healthcare technology, it is essential to prioritize evaluation using complex systems and evidence-based medical frameworks. To address the challenges of digital health implementation, it is important to prioritize ethical research addressing issues of user consent and addressing socioeconomic disparities in access and effectiveness. It is also important to consider the impact of digital health on health outcomes and the cost-effectiveness of service delivery.

Qualitative exploration of physical therapists' experiences providing telehealth physical therapy during COVID-19

BACKGROUND

Physical therapists are trained to provide treatment to patients through a mixture of strategies. The coronavirus (COVID-19) pandemic resulted in social distancing restrictions, and physical therapists, some without previous experience, adopted telehealth physical therapy modalities to treat their patients.

OBJECTIVES

The objective of this study was to explore physical therapists' experiences of providing telehealth physical therapy during the COVID-19 pandemic.

DESIGN AND METHODS

A multisite qualitative semi-structured interview study was conducted. Seventeen physical therapists were interviewed by videoconference or by phone, and the interviews were transcribed and analyzed thematically.

RESULTS

Three main themes emerged from the study. Firstly, physical therapists experienced professional challenges with diagnosing and treating patients hands-off and becoming more verbal. Secondly, telehealth physical therapy was perceived as not feasible or effective for certain patients, attesting to the digital care divide. Lastly, participants' perceptions of patient-therapist communication varied, expressing both communicative advantages and challenges.

CONCLUSIONS

Physical therapists who practiced telehealth physical therapy during the COVID-19 period experienced information and communication technology as professionally challenging. Physical therapists adapted positively to the use of telehealth physical therapy but perceived that not every patient could benefit from it. The study emphasized the need for a better understanding of physical therapists' hands-off skills for practicing telehealth physical therapy and considers the need to establish a patient classification for telehealth physical therapy.

Tele-Rehabilitation Interventions for Motor Symptoms in COVID-19 Patients: A Narrative Review

The COVID-19 pandemic brought new challenges to global healthcare systems regarding the care of acute patients and the delivery of rehabilitation programs to post-acute or chronic patients. Patients who survive severe forms of COVID-19 often report incomplete healing and long-term symptoms. The need of these patients for rehabilitation has been recognized as a public health problem. In this context, the application of tele-rehabilitation has been explored to reduce the burden on healthcare systems. The purpose of this narrative review is to present an overview of the state of the art regarding the application of remote motor rehabilitation programs for paucisymptomatic acute and post-acute COVID-19 patients, with a focus on the motor aspects of tele-rehabilitation. Following an extensive search on PubMed, the Web of Science, and Scopus, specific studies have been reviewed and compared in terms of study objectives and participants, experimental protocols and methods for home-based interventions, functional assessment, and rehabilitation outcomes. Overall, this review suggests the feasibility and the effectiveness of tele-rehabilitation as a promising tool to complement face-to-face rehabilitation interventions. However, further improvements are needed to overcome the limitations and the current lack of knowledge in the field.

Exercise Therapy for Knee and Hip Osteoarthritis: Is There An Ideal Prescription?

Purpose of review

Exercise therapy is the first line treatment for patients with knee and hip osteoarthritis (OA) but is consistently underutilized. In this review, we aim to provide health care professionals with an overview of the latest evidence in the areas of exercise therapy for OA, which can serve as a guide for incorporating the ideal exercise therapy prescription in the overall management plan for their patients with OA.

Recent findings

Evidence continues to be produced supporting the use of exercise therapy for all patients with knee or hip OA. Ample evidence exists suggesting exercise therapy is a safe form of treatment, for both joint structures and the patient overall. Several systematic reviews show that exercise therapy is likely to improve patient outcomes, regardless of disease severity or comorbidities. However, no single type of exercise therapy is superior to others.

Summary

Health care practitioners and patients should be encouraged to incorporate exercise therapy into treatment plans and can be assured of the safety profile and likelihood of improvement in important patient outcomes. Since no single exercise therapy program shows vastly superior benefit, patient preference and contextual factors should be central to the shared decision-making process when selecting and individualising appropriate exercise therapy prescriptions.