Effects of Systemic and Local Vibration Therapies on the Functional Capacity of Knee Osteoarthritis Individuals: A Systematic Review of Randomized Clinical Trials

Abstract

Knee osteoarthritis (KOA) is a growing health challenge with increasing prevalence. Early diagnosis and effective interventions are crucial to the management of KOA individuals. Vibration therapy has shown promise as an intervention for KOA. Systemic vibratory therapy (SVT) and local vibratory therapy (LVT) have gained interest in recent years. In these therapies, mechanical vibrations are transmitted to the body either systemically or locally. The current systematic review aims to comprehensively summarize SVT and LVT effects on the functional capacity of KOA individuals. Searches in PubMed, Web of Science, Scopus, PEDro, and EMBASE on 3 July 2024, including only randomized controlled trials, were performed. The data collected were participant characteristics, vibrating devices, intervention duration, and main findings. Risk of bias (RoB) was assessed with Cochrane tools, and methodological quality (MQ) was assessed via the Physiotherapy Evidence Database. Nine papers were selected from 922 articles: five on SVT and four on LVT, involving 352 individuals aged 40–80. SVT studies reported acute or chronic responses like increased muscle strength and improved functional capacity. LVT studies also indicated functional capacity improvements. RoB was classified as ‘high’ in three SVT studies and ‘low’ in two LVT studies. MQ was classified as ‘high’ in five SVT studies and one LVT study. Both SVT and LVT studies reported improvements in muscle strength, range of motion, and functional capacity. The current review revealed beneficial effects of both therapies on the functional capacity of KOA individuals. However, further well-designed studies are needed to reach definitive conclusions about the effect of SVT and LVT for KOA individuals.

1. Introduction

Mechanical vibration (MV) stimuli have been used in interventions, such as training or therapy, to improve biological parameters, including the functional capacity of individuals with different diseases [1]. In the context of therapy, the effects of MV may be explained in different ways, such as the tonic vibration reflex [2], via the central nervous system [3,4], and via mechanotransduction [5,6], where the mechanical stimuli lead to beneficial biological responses [5]. MV can be applied to the individual’s body systemically [7] or locally [8], depending on their specific clinical condition [9].

MV produced on the vibrating platform (VP) can be transmitted to individuals in contact with the base of the VP (e.g., orthostatic position, squat or sitting on an assistant chair positioned in front of the VP), generating the whole-body vibration (WBV) exercise in the SVT [5,10]. SVT has been considered safe and effective for the management of individuals with different clinical conditions [10,11]. When the individuals have difficulty in maintaining an orthostatic position, squat, or have undergone lower-limb surgery and may not have the benefits of the SVT, alternatively, the LVT can be used [12]. In LVT, the MV is delivered directly to a specific tendon or muscle region through a portable device, promoting physiological responses [8,9]. In recent decades, SVT and LVT have been used for the management of different diseases [13,14,15], such as KOA [16].

KOA is a chronic and degenerative disease with inflammatory characteristics, in which the knee joint is affected, leading to pain, instability, crepitus, tenderness, stiffness, and limited mobility, which together reduce functional capacity [17,18]. In consequence, KOA individuals often struggle to perform daily activities [19]. According to the Global Burden of Disease (GBD), KOA affects approximately 364.6 million people worldwide, an estimated 4.9% of the world’s population [20]. Aging is a major risk factor, with approximately 10% of individuals over 55 years affected, particularly women [18,21,22]. Furthermore, excess body load caused by obesity contributes to disease development and progression [23].

Clinically, KOA is diagnosed using knee radiographs, complementing the physical examination of the joint [24]. The Kellgren–Lawrence Scale [25] and Ahlbäck classification [26] are the most used tools to assess KOA severity. KOA has no cure, and treatment aims to relieve pain, restore joint function, and slow disease progression [27]. Accordingly, regular physical exercise helps strengthen muscles, improve joint stability, control body mass, and reduce pain [28,29]. However, individuals with KOA demonstrate difficulty to adhere to exercise programs due to disease-related comorbidities [20,30,31]. Both SVT and LVT show benefits in improving the knee extensor strength, physical function, pain reduction, and increase in the range of motion (ROM) in KOA individuals [13,14,32,33,34].

In this context, studies [35,36] have demonstrated favorable impacts of SVT and LVT on the functional capacity in KOA individuals. However, no systematic review has yet synthesized the evidence regarding these effects. Therefore, the aim of the current systematic review is comprehensively to summarize the literature related to the effects of SVT and LVT on the functional capacity of KOA individuals.

2. Material and Methods

2.1. Protocol and Registration

The current systematic review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA), and it was registered on the International prospective registry of systematic reviews (PROSPERO) with the number CRD42024546976.

2.2. Research Question

The current systematic review proposes to answer the following question: What effects can systemic and local vibratory interventions promote in the functional capacity of individuals with knee osteoarthritis? The PICO strategy was used to define the components of the research question: Participants (P) = individuals diagnosed with KOA; Interventions (I) = systemic or local vibration therapy; Comparison (C) = control group with no intervention practice or different types of intervention; Outcome (O) = functional capacity; Type of the study (S) = randomized clinical trials.

2.3. Eligibility Criteria

The inclusion criteria were (i) articles reporting original data about SVT or LVT; (ii) studies about investigations into the effects of SVT or LVT alone (without combined intervention) on functional capacity in KOA individuals; and (iii) interventional studies with inter- or intragroup comparisons.

The exclusion criteria were (i) papers out of scope; (ii) study protocols; (iii) reviews; and (iv) those not written in English.

2.4. Search Strategies

Five electronics databases—PubMed/MEDLINE, Physiotherapy Evidence Database (PEDro), Scopus, Embase, and Web of Science—were searched on 3 July 2024, following the strings shown in

Table 1. Search strategies for databases.

Databases	Search Strategies
PubMed/MEDLINE	(vibration OR “local muscle vibration” OR “vibration therapy” OR “whole body vibration” OR “orthotic device” OR “local vibration”) AND (“knee osteoarthritis” OR “knee osteoarthritides” OR “osteoarthritis of knee” OR “osteoarthritis of the knee”)
PEDro	“knee osteoarthritis” AND “vibration”
SCOPUS	(vibration OR “local muscle vibration” OR “vibration therapy” OR “whole body vibration” OR “orthotic device” OR “local vibration”) AND (“knee osteoarthritis” OR “knee osteoarthritides” OR “osteoarthritis of knee” OR “osteoarthritis of the knee”)
Embase	(‘knee osteoarthritis’/exp OR ‘knee osteoarthritis’) AND (‘vibration’/exp OR vibration)
Web of Science	(vibration OR “local muscle vibration” OR “vibration therapy” OR “whole body vibration” OR “orthotic device” OR “local vibration”) AND (“knee osteoarthritis” OR “knee osteoarthritides” OR “osteoarthritis of knee” OR “osteoarthritis of the Knee”)

. The authors P.M.L. and A.C.C.O. independently screened the titles and abstracts according to the eligibility criteria. In turn, if the eligibility was uncertain based on the title and abstract, the full-text version of the article was read to a final decision.

2.5. Data Extraction

After the search strategy, all the papers were exported to an Endnote^® file, and duplicates were removed. Two reviewers (P.M.L. and A.C.C.O.) independently applied the eligibility criteria and selected the studies for inclusion in the systematic review. Disagreements were solved by the analysis of a third author (A.L.B.D.C).

Data were extracted from each article and imported to an Excel spreadsheet containing (i) data regarding the selected publication (author and year); (ii) aim; (iii) participants/groups (sample size, age); (iv) body mass index; (v) vibrating device; (vi) exposure variable; (vii) period (days), bouts and rest time, parameters; (viii) methodological quality (Physiotherapy Evidence Database—PEDro—scale); and (ix) functional capacity outcomes. Two researchers (P.M.L and A.G.V.P) independently performed the data extraction. Disagreements were resolved by a third author (A.L.B.D.C).

2.6. Methodological Quality and Risk of Bias

The selected studies were independently appraised by two reviewers (P.M.L. and V.P.A.), and if there were any disagreements, a third reviewer (A.L.B.D.C.) was consulted. The issue was discussed until a consensus was reached. Afterwards, the methodological quality of the selected publication was evaluated according to the PEDro scale, which consists of ten items established based on an “expert consensus”, and this scale is specific to clinical trials of physical therapy interventions [37]. Then, the studies were classified as ‘high’ methodological quality (score of seven or greater), ‘fair’ methodological quality (score of five to six), and ‘poor’ methodological quality (score of four or below) [37].

The RoB in the included studies were evaluated by two reviewers (P.M.L. and S.G.D.), and if there were any disagreements, a third reviewer (A.L.B.D.C.) was consulted. The RoB of randomized controlled trials (RCT) was determined using a revised Cochrane risk-of-bias tool for randomized trials (RoB 2) [38]. Each domain was qualified as having a ‘low’ risk, ‘high’ risk of bias, and some concerns. Each judgment was represented by the colors green, red, and yellow, respectively.

3. Results

3.1. Search Results

A total of 922 papers were initially screened (Scopus = 310, EMBASE = 212, Web of Science = 173, PubMed = 152, PEDro = 31). After removing duplicates, a total of 439 records remained, and nine articles fulfilled the inclusion criteria in Figure 1.

3.2. Studies Characteristics

The nine selected studies were systematized by authors, year of publication, country, participants, age, body mass index (BMI), aim, vibrating device, exposure variable, intervention time, and the tools used to assess the functional capacity. The SVT results are summarized in Table 2, while the LVT results are summarized in Table 3.

All the nine selected papers were published between 2012 and 2023, and 40% of the studies were conducted in Europe (Italy, two studies; Poland, one study; Denmark, one study), 30% North (USA, one study) and South America (Brazil, two studies) and 30% in Asia (Iran, two studies; China, one study).

The selected studies included a total of 352 individuals (78.15% female) aged between 46 and 80 years, with BMIs between 18 and 44 kg/m², including people who had a diagnosis of unilateral or bilateral KOA and that underwent SVT or LVT.

In the SVT publications, the age of the individuals ranged from 47 [31] to 75 [34] years, and BMI varied from 23 [31] to 44 kg/m² [34], with a total of 226 individuals, of whom 179 were female. Considering the source of mechanical stimulation, the devices used varied, with 40% of studies employing the Novaplate^® Fitness Evolution (Novaplate, São Paulo, Brazil) (two studies) [34,39]; 20% using Xendon^® platform VibM (VibM, Xendon, Sweden) (one study) [31]; and 20% using Fitvibe^® Gymna Uniphy (Bilzen, Belgium) (one study) [40]; i-vib5050^® Sport Platform (China) (one study) [41]. The types of VP also differed: side-alternating displacement was used in studies by Trans et al. (2009) [31], Moreira-Marconi et al. (2020) [34], and Moura-Fernandes et al. (2020) [39], while vertical displacement was used by Abbasi et al. (2017) [40] and Lai et al. (2021) [41]. Furthermore, 80% of the studies (four records) established a study design with cumulative exposure, ranging from 4 to 8 weeks, with sessions varying from 2 to 3 days per week [31,39,40,41]. Training protocols varied widely, with the number of bouts per training session ranging from three [34] to fifteen [41] bouts, and the duration of time per day ranged from 5.5 [31] to 39 min [39]. In contrast, 20% of studies (one record) tested an acute protocol of one session in one day lasting 11 min [39]. Participants performed these protocols either barefoot [31,34,39,41] or wearing shoes [31] and in varying positions, from a semi-squatted position (knee angle from 30 to 60 degrees) [39,41] to sitting on a chair facing the VP, with the arms extended over the knees (knee angle from 100 to 120 degrees) [34,39].

Similarly, in LVT studies, the age of the individuals ranged from 46 [13] to 80 [14] years, and the BMI varied from 18 [33] to 36 km/m² [32], with 126 individuals, of whom 96 were female. The vibration devices varied, with 25% using vibratory unloader knee orthosis (one study) [33], 25% using RAM Vitberg© Base Module and Vitberg© Knee Module (Vitberg, Poland) (one study) [32], and 25% a pneumatic vibrator powered by compressed air (Bologna, Italy) (one study) [13], while Cro^®System (NEMOCO srl, Roma, Italy), was used in the remaining 25% (one study) [14]. Moreover, 75% of studies (three records) [13,32,33] employed cumulative exposure protocols (ranging from 2 to 6 weeks), with sessions varying to 5 h per week to 5 days/week. The number of bouts per session was one [13], with session durations ranging from 20 to 60 min [32]. One study does not report the number of bouts used but reported a time work per week of 300 min [33]. In contrast, 25% of the studies (one study) [14] employed acute protocol of three bouts over three consecutive days and session durations of 10 min. Notably, only one study [14] reported the rest time used between sessions (1 min). In relation to the muscles that received MV, the most reported were the vastus lateralis [13,14,33], vastus medialis, and rectus femoris muscles [13,14].

In the SVT, five studies [31,39,40,41] reported effects of cumulative and acute interventions on the functional capacity. To evaluate the functional capacity, a wide range of tools, such as timed up and go test (TUG), step test, 20 m walk test, anterior trunk flexion (ATF), isokinetic dynamometry, threshold for detection of passive movement (TDPM), five-repetition chair stand test (5CST), and 6 min walk distance test (6MWD), and questionnaires, such as Oswestry disability index (ODI), Lequesne’s functional index, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the measurement of perceived effort (BORG scale), were employed. Effects on the pain level and electromyographic profile were also reported. To assess the electromyographic profile, surface electromyography (sEMG) was used, and to evaluate the pain level, a visual analog scale (VAS) and WOMAC questionnaires were used.

In LVT, three studies [14,32,33] reported cumulative effects on the functional capacity. The tools used to assess the functional capacity were WOMAC, TUG, Knee Injury and Osteoarthritis Outcome Score (KOOS), Stair Climbing Test, knee range of motion (ROM), Short Physical Performance Battery (SPPB), Performance-Oriented Mobility Assessment (POMA), and a 6-camera Qualisys motion capture system to evaluate biomechanics were utilized. Effects on pain level and electromyographic profile were also reported, and to assess the pain level the VAS, Laitinen Questionnaire, and WOMAC were used. To evaluate the electromyographic profile, the sEMG was used.

Table 2. Summary of the main findings reported in the studies about the effects of the SVT in KOA individuals.

Authors/Year/Country	Participants/Groups/Mean Age (Years)	BMI (kg/m2–Mean ± SD)	Aim	Vibration Device	Exposure Variable	Period (Days) Bouts/Rest Time	Tools Used to Assess the Functional Capacity
Trans et al., 2009. [31] Denmark.	N: 52 Female WBVG: 61.5 ± 9.2 WBVBG: 58.7 ± 11 CG: 61.1 ± 8.5	WBVG 29.2 ± 6.1 WBVBG 29.1 ± 5.8 CG 30.2 ± 5.4	To verify the WBV exercise on muscle strength and proprioception.	Xendon® platform VibM, Sweden. Side-Alternating	f: 25 to 30 Hz A: n/d aPeak: n/d	8 weeks (2 days) 6 to 9 bouts: 30 s to 70 s/bout Rest: 30 s to 70 s	Isokinetic dynamometry TDPM WOMAC
Abbasi et al., 2017. [40] Iran.	N: 37 Male and Female WBVG: 63.6 ± 3 Placebo group: 68 ± 2.1 CG: 63.5 ± 4.8	WBVG: 28.4 ± 2.4 Placebo group: 29.8 ± 2 CG: 29.7 ± 1.8	To determine whether WBV is effective on electromyographic activity of the muscles of the lower limbs in KOA individuals.	Fitvibe® Gymna Uniphy NV, Bilzen, Belgium Vertical Vibration	f: 30 Hz A: 3 mm aPeak: 5.3 g	4 weeks (3 days) 6 to 15 bouts: 1 min/bout Rest: 1 min	sEMG
Moreira-Marconi et al., 2020. [34] Brazil.	N: 19 Male and Female WBVG: 64.1 ± 8.5 CG: 66.8 ± 8.5	WBVG: 34.9 ± 8.6 CG: 33.7 ± 6.9	To evaluate the effectiveness of WBV on the functionality of lower limbs by the electromyographic profile of the vastus lateralis muscles during the 5CST in KOA individuals.	Novaplate® Fitness Evolution, São Paulo, Brazil. Side-alternating	f: 5 to 14 Hz A: 1.25, 2.5, 3.75 mm aPeak: 0.12 to 2.95 g	5 weeks (2 days) 3 bouts: 3 min/bout Rest: 1 min	5CST sEMG
Moura-Fernandes et al., 2020. [39] Brazil.	N: 37 Male and Female WBVG: 62.3 ± 2.5 CG: 68 ± 2	WBVG: 34.7 ± 2.1 CG: 31.7 ± 1.2	To analyze the acute effects of WBV exercise on pain levels, functionality, and rating of exertion of elderly obese KOA individuals.	Nova Plate® Fitness Evolution, São Paulo, Brazil. Side-alternating	f: 5 to 14 Hz A: 1.25, 2.5, 3.75 mm aPeak: 0.12, 0.25, and 0.37 g	1 Day 3 bouts: 3 min/bout Rest: 1 min	ODI Lequesne’s Functional Index TUG BORG scale ATF
Lai et al., 2021. [41] China.	N: 81 Male and Female WBVG: 63.5 ± 4.9 Health Education: 63.6 ± 4.8 Strength Training: 64.8 ± 4	WBVG: 24.2 ± 2.7 Health Education: 23.4 ± 2.9 Strength Training: 23 ± 2.9	To investigate the therapeutic effect of WBV training on the neuromuscular function of KOA individuals.	i-vib5050® Sport Platform, China. Vertical vibration	f: 20 Hz A: 2 mm aPeak: 1.6 g	8 weeks (3 day) 6 to 15 bouts: 30 s to 1 min/bout Rest: 30 s to 60 s	TUG 6MWD

Amplitude, A; body mass index, BMI; control group, CG; Hertz, HZ; millimeter, mm; peak acceleration, aPeak; frequency, f; minute, min; not reported, N/R; whole-body vibration, WBV; whole-body vibration group, WBVG; whole-body vibration on balance group, WBVBG.

Table 2. Summary of the main findings reported in the studies about the effects of the SVT in KOA individuals.

Authors/Year/Country	Participants/Groups/Mean Age (Years)	BMI (kg/m2–Mean ± SD)	Aim	Vibration Device	Exposure Variable	Period (Days) Bouts/Rest Time	Tools Used to Assess the Functional Capacity
Trans et al., 2009. [31] Denmark.	N: 52 Female WBVG: 61.5 ± 9.2 WBVBG: 58.7 ± 11 CG: 61.1 ± 8.5	WBVG 29.2 ± 6.1 WBVBG 29.1 ± 5.8 CG 30.2 ± 5.4	To verify the WBV exercise on muscle strength and proprioception.	Xendon® platform VibM, Sweden. Side-Alternating	f: 25 to 30 Hz A: n/d aPeak: n/d	8 weeks (2 days) 6 to 9 bouts: 30 s to 70 s/bout Rest: 30 s to 70 s	Isokinetic dynamometry TDPM WOMAC
Abbasi et al., 2017. [40] Iran.	N: 37 Male and Female WBVG: 63.6 ± 3 Placebo group: 68 ± 2.1 CG: 63.5 ± 4.8	WBVG: 28.4 ± 2.4 Placebo group: 29.8 ± 2 CG: 29.7 ± 1.8	To determine whether WBV is effective on electromyographic activity of the muscles of the lower limbs in KOA individuals.	Fitvibe® Gymna Uniphy NV, Bilzen, Belgium Vertical Vibration	f: 30 Hz A: 3 mm aPeak: 5.3 g	4 weeks (3 days) 6 to 15 bouts: 1 min/bout Rest: 1 min	sEMG
Moreira-Marconi et al., 2020. [34] Brazil.	N: 19 Male and Female WBVG: 64.1 ± 8.5 CG: 66.8 ± 8.5	WBVG: 34.9 ± 8.6 CG: 33.7 ± 6.9	To evaluate the effectiveness of WBV on the functionality of lower limbs by the electromyographic profile of the vastus lateralis muscles during the 5CST in KOA individuals.	Novaplate® Fitness Evolution, São Paulo, Brazil. Side-alternating	f: 5 to 14 Hz A: 1.25, 2.5, 3.75 mm aPeak: 0.12 to 2.95 g	5 weeks (2 days) 3 bouts: 3 min/bout Rest: 1 min	5CST sEMG
Moura-Fernandes et al., 2020. [39] Brazil.	N: 37 Male and Female WBVG: 62.3 ± 2.5 CG: 68 ± 2	WBVG: 34.7 ± 2.1 CG: 31.7 ± 1.2	To analyze the acute effects of WBV exercise on pain levels, functionality, and rating of exertion of elderly obese KOA individuals.	Nova Plate® Fitness Evolution, São Paulo, Brazil. Side-alternating	f: 5 to 14 Hz A: 1.25, 2.5, 3.75 mm aPeak: 0.12, 0.25, and 0.37 g	1 Day 3 bouts: 3 min/bout Rest: 1 min	ODI Lequesne’s Functional Index TUG BORG scale ATF
Lai et al., 2021. [41] China.	N: 81 Male and Female WBVG: 63.5 ± 4.9 Health Education: 63.6 ± 4.8 Strength Training: 64.8 ± 4	WBVG: 24.2 ± 2.7 Health Education: 23.4 ± 2.9 Strength Training: 23 ± 2.9	To investigate the therapeutic effect of WBV training on the neuromuscular function of KOA individuals.	i-vib5050® Sport Platform, China. Vertical vibration	f: 20 Hz A: 2 mm aPeak: 1.6 g	8 weeks (3 day) 6 to 15 bouts: 30 s to 1 min/bout Rest: 30 s to 60 s	TUG 6MWD

Amplitude, A; body mass index, BMI; control group, CG; Hertz, HZ; millimeter, mm; peak acceleration, aPeak; frequency, f; minute, min; not reported, N/R; whole-body vibration, WBV; whole-body vibration group, WBVG; whole-body vibration on balance group, WBVBG.

Table 3. Summary of the main findings reported in the studies about the effects of the LVT on KOA individuals.

Authors/Year Country	Participants/Groups/Mean Age (Years)	BMI (kg/m2–Mean ± SD)	Aim	Vibration Device	Exposure Variable	Period (Days) Bouts Rest Time	Tools Used to Assess the Functional Capacity
Rabini et al., 2015. [14] Italy.	N: 50 Male and Female LVTG: 73.7 ± 5.2 CG: 75 ± 5.7	LVTG: >30 CG: >30	To evaluate the effects of local muscle vibration on physical functioning in patients with symptomatic KOA.	-Cro®System, NEMOCO srl, Italy (device)	f: 100 Hz A: 0.2–0.5 mm aPeak: 20.4 to 81.6 g	3 consecutive days. 3 bouts 10 min/ bout rest: 1 min	WOMAC SPPB POMA
Benedetti et al., 2017 [13] Italy.	N: 30 Male and Female LVTG: 61.8 ± 5.8 NMES: 55.7 ± 9.1	LVTG: 26.1 ± 2.9 NMES: 26 ± 2.8	To investigate the clinical effectiveness of high-frequency LVT on quadriceps muscle in patients with KOA and to disentangle, by means of surface electromyography (sEMG).	-Pneumatic vibrator powered by compressed air (Vibra Plus; A Circle s.p.a).	f: 150 Hz A: N/R aPeak: N/R	-2 weeks (5 days) 1 bout -20 min/bout -rest: 0 min	WOMAC ROM TUG Stair Climbing Test sEMG
Pasterczyk-Szczurek et al., 2023. [32] Poland.	N: 32 Male and Female LVTG: 63.6 ± 7.6 CG: 64.8 ± 10.8	LVTG: 31 ± 5.6 CG: 31.3 ± 5.5	To determine the impact of vibrations of variable frequency and low amplitude on pain perception and mobility in patients suffering from KOA.	-RAM Vitberg© Base Module and Vitberg© Knee Module.	f: 5–50 Hz A: 0–0.2 mm aPeak: 1.38 g	-3 weeks (5 days). 1 bout: 60 min/bout rest: N/R.	TUG KOOS questionnaire ROM sEMG
Barati et al., 2023. [33] Iran.	N: 14 Female Vibratory orthosis group: 55.6 ± 3.7 Conventional orthosis group: 57.2 ± 3.8	Vibratory orthosis group: 20.2 ± 2.2 Conventional orthosis group: 21.3 ± 2.1	To determine whether equipping an unloader knee orthosis with vibrators improves its effectiveness in pain, stiffness, function, and reducing the moment of knee adduction.	-Vibratory unloader knee orthosis.	f: 30 Hz A: 1.6 mm aPeak: 5.8 g	-6 weeks (5 h for week). -300 min/week rest: N/R.	WOMAC 6 camera Qualisys motion capture system

Amplitude, A; control group, CG; frequency, f; local vibratory therapy group, LVTG; Knee injury and Osteoarthritis Outcome Score, KOOS; peak acceleration, aPeak; Range of Motion, ROM; minute, min; not reported, N/R; osteoarthritis, OA; POMA, Performance Oriented Mobility Assessment; surface electromyography, sEMG. Timed up and go, TUG; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index.

Table 3. Summary of the main findings reported in the studies about the effects of the LVT on KOA individuals.

Authors/Year Country	Participants/Groups/Mean Age (Years)	BMI (kg/m2–Mean ± SD)	Aim	Vibration Device	Exposure Variable	Period (Days) Bouts Rest Time	Tools Used to Assess the Functional Capacity
Rabini et al., 2015. [14] Italy.	N: 50 Male and Female LVTG: 73.7 ± 5.2 CG: 75 ± 5.7	LVTG: >30 CG: >30	To evaluate the effects of local muscle vibration on physical functioning in patients with symptomatic KOA.	-Cro®System, NEMOCO srl, Italy (device)	f: 100 Hz A: 0.2–0.5 mm aPeak: 20.4 to 81.6 g	3 consecutive days. 3 bouts 10 min/ bout rest: 1 min	WOMAC SPPB POMA
Benedetti et al., 2017 [13] Italy.	N: 30 Male and Female LVTG: 61.8 ± 5.8 NMES: 55.7 ± 9.1	LVTG: 26.1 ± 2.9 NMES: 26 ± 2.8	To investigate the clinical effectiveness of high-frequency LVT on quadriceps muscle in patients with KOA and to disentangle, by means of surface electromyography (sEMG).	-Pneumatic vibrator powered by compressed air (Vibra Plus; A Circle s.p.a).	f: 150 Hz A: N/R aPeak: N/R	-2 weeks (5 days) 1 bout -20 min/bout -rest: 0 min	WOMAC ROM TUG Stair Climbing Test sEMG
Pasterczyk-Szczurek et al., 2023. [32] Poland.	N: 32 Male and Female LVTG: 63.6 ± 7.6 CG: 64.8 ± 10.8	LVTG: 31 ± 5.6 CG: 31.3 ± 5.5	To determine the impact of vibrations of variable frequency and low amplitude on pain perception and mobility in patients suffering from KOA.	-RAM Vitberg© Base Module and Vitberg© Knee Module.	f: 5–50 Hz A: 0–0.2 mm aPeak: 1.38 g	-3 weeks (5 days). 1 bout: 60 min/bout rest: N/R.	TUG KOOS questionnaire ROM sEMG
Barati et al., 2023. [33] Iran.	N: 14 Female Vibratory orthosis group: 55.6 ± 3.7 Conventional orthosis group: 57.2 ± 3.8	Vibratory orthosis group: 20.2 ± 2.2 Conventional orthosis group: 21.3 ± 2.1	To determine whether equipping an unloader knee orthosis with vibrators improves its effectiveness in pain, stiffness, function, and reducing the moment of knee adduction.	-Vibratory unloader knee orthosis.	f: 30 Hz A: 1.6 mm aPeak: 5.8 g	-6 weeks (5 h for week). -300 min/week rest: N/R.	WOMAC 6 camera Qualisys motion capture system

Amplitude, A; control group, CG; frequency, f; local vibratory therapy group, LVTG; Knee injury and Osteoarthritis Outcome Score, KOOS; peak acceleration, aPeak; Range of Motion, ROM; minute, min; not reported, N/R; osteoarthritis, OA; POMA, Performance Oriented Mobility Assessment; surface electromyography, sEMG. Timed up and go, TUG; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index.

3.3. Main Findings Related to the Functional Capacity

Considering the cumulative effects, from 3 to 8 weeks of exposure to mechanical vibration, relevant findings were observed that are considered favorable to the notion that the application of vibrating therapy improves the functional capacity, as summarized in Table 1 and Table 2.

In SVT studies, considering the cumulative effects, an increase in muscle strength [39,40] and a reduction in the time to perform the 5CST [35] were observed in the functional capacity parameter. Considering the acute effects of a 1- to 3-day period of mechanical vibration exposure, findings indicated favorable responses to this intervention. In SVT studies, beneficial results were observed in the functional capacity parameter, such as an increase in anterior trunk flexion and a reduction in the time to perform the TUG test [41].

Functional capacity improvements were observed in the cumulative effects in the LVT studies [13,14,32], increasing the range of motion of the knee [13,14] and decreasing the deleterious effect due to the orthosis in the biomechanic [32] of the gait. Moreover, beneficial results in functional capacity were observed in LVT studies in the acute effects, such as improvement of the functionality, mobility, and balance through the POMA and SPPB, as well as a reduction in joint stiffness and improvement of functionality in the WOMAC questionnaire [13].

3.4. Findings Related to Pain

Considering the acute effects, a study using SVT demonstrated a beneficial result in the reduction in the pain levels [41]. Furthermore, studies with a cumulative protocol (2 to 6 weeks) using LVT demonstrated a reduction in the pain perception. [13,14,32].

3.5. Methodological Quality

Considering the methodological quality assessed using the PEDro scale [42] (

Table 4. Assessment of the methodological quality of the SVT studies using the PEDro scale.

Reference	2	3	4	5	6	7	8	9	10	11	Score
Trans et al., 2009 [31]											7/10
Abbasi et al., 2017 [40]											8/10
Moreira-Marconi et al., 2020 [34]											6/10
Moura-Fernandes et al., 2020 [39]											7/10
Lai et al., 2021 [41]											8/10
	100%	60%	100%	60%	0%	0%	100%	100%	100%	100%

Assessment of the methodological quality of the included studies using the PEDro scale: (2) Subjects were randomly allocated to groups; (3) allocation concealed; (4) the groups were similar at baseline regarding the prognostic indicators; (5) blinding of all subjects; (6) blinding of all therapists who administered the intervention; (7) blinding of all assessors who measured at minimal one key outcome; (8) measures of at least one key outcome were obtained from more than 85% of the subjects firstly allocated to groups; (9) all subjects for whom outcome measures were disposable received the treatment or control condition as allocated, or, where this was not possible, data for at least one key outcome were analyzed by “intention to treat”; (10) the results of between-group statistical comparisons are reported for at minimal one key outcome; (11) the study gives both point measures and measures of variability for the minimal one key outcome.

and

Table 5. Assessment of the methodological quality of the LVT studies using the PEDro scale.

Reference	2	3	4	5	6	7	8	9	10	11	Score
Rabini et al. 2015 [14]											9/10
Benedetti et al. 2017 [13]											4/10
Barati et al. 2023 [33]											3/10
Pasterczyk-Szczurek et al. 2023 [32]											6/10
	100%	25%	25%	50%	0%	25%	75%	100%	50%	100%

Assessment of the methodological quality of the included studies using the PEDro scale: (2) Subjects were randomly allocated to groups; (3) allocation concealed; (4) the groups were similar at baseline regarding the prognostic indicators; (5) blinding of all subjects; (6) blinding of all therapists who administered the intervention; (7) blinding of all assessors who measured at the minimal one key outcome; (8) measures of at least one key outcome were obtained from more than 85%; of the subjects firstly allocated to groups; (9) all subjects for whom outcome measures were disposable received the treatment or control condition as allocated, or, where this was not possible, data for at least one key outcome were analyzed by “intention to treat”; (10) the results of between-group statistical comparisons are reported for at minimal one key outcome; (11) the study give both point measures and measures of variability for the minimal one key outcome.

), in the SVT studies, five studies [31,34,39,40,41] were considered with ‘good’ methodological quality (6 to 8 points). In the LVT, one study [13] was considered with ‘excellent’ methodological quality (9 to 10 points), one study [14] with ‘good’ methodological quality, and two studies [14,33] were considered to have ‘poor’ methodological quality (<4).

3.6. Risk of Bias

The results of the RoB of the included studies about SVT are shown in Figure 2A. The RoB 2.0 [43] tool was used to assess the risk of bias. In the bias arising from the randomization process (D1), 60% of studies (three studies) demonstrate a “low risk of bias” in the random allocation of individuals. The information due to deviations from the intended intervention (D2) demonstrates that 80% of studies (four studies) report a “low risk of bias” in relation to blinding of treated individuals and staff. In addition, regarding bias due to missing data (D3), 60% of studies (three studies) demonstrate a low loss of follow-up of study participants, presenting a low risk of bias. Furthermore, in relation to bias in measuring outcomes (D4), 40% of the studies (two studies) presented a “low risk of bias” in relation to the outcome due to knowledge of the intervention received. In terms of bias in outcome reporting (D5), 60% of studies (three studies) demonstrated a “low risk of bias” in outcome reporting due to multiple assessments or convenience. The RoB results of the included studies about LVT are shown in Figure 2B. In the bias D1, 100% of studies (four studies) demonstrate a “low risk of bias”. In addition, in D2, 50% of studies (two studies) demonstrate a “low risk of bias”, and in D3 bias, 100% of studies (four studies) demonstrate a “low risk of bias”. Likewise, D4 and D5 showed in 75% of studies (three studies) a “low risk of bias”.

4. Discussion

The main objective of this systematic review was to evaluate the effect of SVT and LVT on the functional capacity of individuals with KOA. After analyzing the included studies and considering their limitations, the results suggest that SVT and LVT may be beneficial interventions on functional capacity in individuals with KOA. The current systematic review provides a comprehension regarding the benefit influence of two different types of vibration interventions in functional capacity of KOA individuals. The findings of this study demonstrated that the SVT and LVT might be effective to improve the functional capacity of KOA individuals. The current review included nine studies, summarizing and discussing the effects of SVT and LVT on the functional capacity, indicating beneficial effects of vibration exposure on muscle strength, joint stiffness, balance, functional mobility, and in the range of motion and biomechanics of the gait. In addition, the effects of the SVT and LVT, reducing the level of pain and the improvement of the electromyographic profile, are also presented.

Regarding the KOA individuals in the selected studies, the age varied from 46 up to 80 years, and the BMI ranged between 18 and 44 kg/m², including people who had a diagnosis of unilateral or bilateral KOA submitted to SVT or LVT. From a total of 352 individuals, 78.15% were female, and these characteristics are in accordance with other authors that reported that the osteoarthritis is not only epidemiologically significant but also influenced by hormonal fluctuations [44,45]. Likewise, aging as obesity are a risk factor that increases the incidence of KOA [30]. It is important to highlight that the comprehension of these physiological and behavioral changes is crucial for tailoring effective management strategies for KOA individuals [35,45,46,47].

In the SVT studies [31,39,40,41], individuals were exposed to a cumulative intervention with frequencies ranging from 5 to 30 Hz, amplitudes from 1.25 to 3.75, and aPeak values ranging from 0.12 to 5.3 g (one study did not report amplitude and aPeak [31]). This range is in accordance with other studies, which use similar biomechanics parameters (f: 20 Hz, A: 2 mm, and aPeak:1.6 g/f: 35 Hz, A: 4–6 mm, and aPeak: 9.8–14.7 g) for the treatment of KOA individuals [14,32,33]. Furthermore, a previous meta-analysis showed that KOA individuals exposed to SVT at low or high frequencies had beneficial effects in functional capacity, considering the functional performance of the TUG test; the self-reported function used the WOMAC questionnaire, muscle strength, and reduced in pain [48]. Likewise, in the LVT studies [14,32,33], participants were exposed to cumulative MV by different devices (e.g., discharge prostheses with vibrating devices, pneumatic vibrator, and Vitberg) using a frequency range of 5 to 150 Hz, amplitude from 0.2 to 1.6, and aPeak ranging from 1.8 to 5.8 g (one study did not report amplitude and aPeak [14]). Furthermore, studies with the same population used similar frequencies: one study used a frequency of 50 Hz and an amplitude of 1.6 mm [48]; however, Kitay et al. [49] used a frequency alternating in cycles between 10, 27, and 42 Hz but did not report the amplitude used.

Concerning acute exposure, in one study using SVT, individuals were exposed to an acute vibration with progressive frequencies of 5 to 30 Hz; amplitudes of 1.25, 2.5, and 3.75 mm; and peak values ranging from 0.12, 0.25, to 0.37 g [42]. Furthermore, a study with similar parameters in an acute protocol for KOA individuals used a frequency of 35 Hz and an amplitude of 4 to 6 mm [50].

Concerning acute vibration exposure, one study using LVT used a fixed frequency of 100 Hz, an amplitude from 0.2 to 0.5 mm, and an aPeak from 20.4 to 81.6 g [13]. The frequency used in the study is corroborated by Souron et al., 2017, for recruitment of type Ia afferent fibers, being proportional from one-to-one to the range of 120 Hz [8].

Regarding functional capacity, the SVT studies [31,34,41] demonstrated an increase in the muscle strength in the lower limbs and increased functional mobility after exposure to cumulative MV (8 weeks). Petit et al. [50] also demonstrated, in KOA individuals exposed to SVT (6 weeks), increases in muscle strength and power. Additionally, a 3-week SVT protocol applied to moderately active women led to improvements in knee extensor muscle strength and flexibility compared to both the control group and baseline values [51]. These findings can be justified by the activation of type II fibers that are activated by SVT [10]. Likewise, the LVT studies reported reductions in pain perception [14,32,33], increases in functional capacity [14,32,33], and improvements in the ROM [14] and in biomechanics of the gait [32]. The results in the literature corroborate the findings of the current systematic review, where one study demonstrated a reduction in the level of pain and an increase in range of movement after intervention with LVT [52]. These variations in the mechanical vibration’s parameters and population characteristics across studies may help explain the heterogeneity observed in functional and symptomatic outcomes. Higher frequencies and amplitudes in SVT protocols appeared more often in studies reporting significant gains in muscle strength and functional mobility [35,39,40,50,51], while lower intensities were associated with subtler effects [41]. Similarly, differences in participants profiles, such as BMI and age ranges [31,44,45], may have influenced the response to vibration therapy, as metabolic and biomechanical constraints in older or obese individuals could attenuate improvements. The predominance of female participants also deserves consideration, as hormonal factors might modulate both pain perceptions and neuromuscular adaptation [44,45]. Finally, differences in vibration devices and intervention durations [13,14,32,33,40] likely contributed to the variability in reported effects, emphasizing the need for standardization in future studies and more precise stratification of outcomes by participant characteristics. However, few studies employed LVT protocols in this population, and further research is warranted.

The present study has some limitations. The high heterogeneity in study design, mechanical vibration parameters (e.g., frequency, amplitude, duration), and outcome measures (e.g., TUG, WOMAC, ROM) limited the possibility of direct comparison between SVT and LVT. Although both approaches demonstrated functional improvements, the lack of standardized protocols and consistent outcome metrics make it difficult to determine the relative efficacy of one modality over the other.

Despite promising preliminary evidence, the overall confidence in the findings is limited by the small number of high-quality randomized controlled trials and the moderate to high risk of bias in several studies. Therefore, the conclusions should be interpreted with caution, and future studies should aim to confirm these effects using a more rigorous methodological design.

A quantitative synthesis (e.g., meta-analysis) was not feasible due to the substantial methodological heterogeneity across studies. However, future systematic reviews might consider extracting standardized mean differences for more commonly reported outcomes when data availability permits. This could facilitate the generation of forest plots and comparative effect size estimates between SVT and LVT.

From a clinical perspective, SVT may be particularly suitable for individuals with moderate KOA and sufficient musculoskeletal capacity to tolerate higher vibration amplitudes, whereas LVT could be considered for frailer or older adults given its gentler mechanical profile. In low-resource settings, the feasibility of vibratory therapy should also account for equipment accessibility, and context-specific adaptations are necessary for effective implementation.

The strengths of the current study offer a comprehensive view of vibratory therapy, SVT, and LVT, demonstrating positive effects on the functional capacity of KOA individuals. Furthermore, the current systematic review might serve as a basis for clinical intervention protocols for vibrating therapies in KOA individuals.

5. Conclusions

In conclusion, the findings reported in the current systematic review suggest that SVT and LVT have potential effects on the functional capacity of KOA individuals. The current review revealed a promising but not conclusive effect of SVT on lower-limb muscle strength, pain, physical function, and improvement in range of motion. Additionally, LVT has demonstrated encouraging effects on pain, flexibility, stiffness, and balance. However, the current review highlights the need for more high-quality, standardized studies to confirm these findings and guide clinical application.