Effects of exercise combined with whole body vibration in patients with patellofemoral pain syndrome: a randomised-controlled clinical trial | BMC Musculoskeletal Disorders | Full Text

by fitness journalist

This study was a single-blind prospective randomised-controlled clinical trial, conducted between September and December 2019 at the AY360° Health and Sport Clinic (Seville, Spain).

The study was approved by the Ethical Research Committee of Jaen Province (project code 0916-N-19, approval date June 19, 2019) and prospectively registered (clinicaltrials.gov, Identifier NCT04031248). The Consolidated Standards of Reporting Trials (CONSORT) guidelines were followed. All participants provided written informed consent prior to being included in the study.

Adults who had reported anterior knee pain were recruited by a primary care physician in a public health centre in a province of southern Spain. In order to increase the sample size of participants for the study, it was decided to expand the lower limit of the age range registered in clinicaltrials.gov, from 30 to 65 years. Based previous studies [25, 27], those participants who met the following inclusion criteria were invited to participate in the study: i) insidious onset of anterior knee pain with a duration greater than 12 weeks; ii) self-reported patellofemoral pain intensity ≥30 mm on the 100 mm Visual Analogue Scale (VAS); iii) pain provoked by at least two of the following situations: prolonged sitting or kneeling, squatting, running, hopping or ascending or descending stairs.

Participants were excluded in cases of clinical history of patellofemoral dislocation or subluxation; knee osteoarthritis (confirmed with radiological tests); knee joint effusion; concomitant injury or pain from the hip, lumbar spine, or other knee structures (meniscus, ligaments, bursa, synovial plica, infrapatellar fat); traumatic lesions of soft tissues or previous orthopaedic surgery in lower limbs; having received knee injections of corticosteroids or hyaluronic acid; cognition or impaired communication; being involved in an ongoing medical-legal dispute.

In addition, the exclusion criteria included having any contraindication for using whole body vibration, such pacemakers, arrhythmias, cardiac valve dysfunction, pregnancy, epilepsy, recent acute thrombosis, infection and recent inflammation, malignant tumours, recent implants, recent fractures, acute disc pathology, acute tendinopathy, renal lithiasis or biliary and an acute episode in rheumatic pathology.

Patients were advised not to take analgesic medication from the beginning of the study, as well as not to receive other treatments, such as physiotherapy or injection therapy. Patients in both groups were required to participate in at least 80% of the programmed sessions (10 sessions) for the analysis.

Those participants who met the inclusion criteria were randomly assigned by a member of the research team to the experimental or control group following simple randomization procedures (using a random-number generator website http://www.randomization.com, and considering a 1:1 ratio distribution of participants in the study groups).

Study protocol

An external assistant collected all patient demographic and clinical data through interviews. A blind evaluator performed all measurements at baseline and immediately after the last treatment session for the entire sample, without knowing the group to which each participant belonged. A specific form for registering the demographic and clinical data of each participant was used. This form was filled out for each subject and codified in order to protect their privacy in accordance with the Organic Law 15/1999 on Protection of Personal Data, EU Regulation 2016/679 of the European Parliament and the Council of 27 April 2016 Data Protection as well as the Organic Law 3/2018, of December 5, on Protection of Personal Data and Guarantee of Digital Rights.

The research protocol was conducted in accordance with the Declaration of Helsinki statement of ethics, legal and regulatory principles in order to provide guidance for research related human health and all participants provided written informed consent prior to participating.

Outcome measures

Primary outcome measure for this study was pain intensity. In addition, knee range of movement and lower limb functionality were assessed at baseline and at 4 weeks (post-treatment) using standardised instruments and cross-culturally validated patient-reported outcome measures.

Pain intensity and neuropathic pain

For the assessment of pain intensity during activity, VAS of 10 cm was used, where 0 corresponds to ‘no pain’ and 100 represents the ‘worst pain imaginable’ [28]. Patient were asked to express the mean intensity of his/her knee pain over time, considering for this, the last 7 days. Minimal clinically important difference for the VAS was based on a reduction of 15 mm from the baseline or a 15–20% change after intervention [29].

In addition, to assess neuropathic pain (NP), the Spanish version of the Douleur Neuropathique-4 items (DN4) was used [30]. This questionnaire has 10 items, consisting of descriptions and signs of pain that are evaluated with 1 (yes) or 0 (no), indicating patients who have a high probability of having a neuropathic pain component. The evaluations of individual items were added to obtain a maximum total score of 10 with a cut-off point ≥4.

Knee flexion-extension range of movement (ROM)

For the knee flexion assessment, subjects lay in a supine position with 90 degrees of hip flexion. Hip positioning was guaranteed by the use of a thigh device that aided in the maintenance of the pre-set position. A universal goniometer was placed next to the femoral lateral epicondyle. The static handle of the goniometer was aligned with the thigh, using the femoral major trochanter as a reference, while the mobile handle aligned with the leg referencing the fibula lateral malleolus [31]. For the knee extension assessment, patients lay in a supine position and the limb being evaluated was raised by the heel, with knee stabilisation in contact with the stretcher. The instrument positioning in relation to the segment was the same as in the knee flexion measurement.

Lower limb functional assessment

The Spanish version of the Lower Extremity Functional Scale (LEFS) was used for the lower limb functional assessment [32]. This is a short self-reported questionnaire that has been proven to be a valid and reliable tool for assessing musculoskeletal dysfunction in the lower extremity. This scale consists of 20 items, with a score of 0 to 4, where the highest score represents the highest functionality of the lower limb. It has a high correlation with the Short Form Health Survey (SF-36), especially with the physical function and pain subscales [26]. The minimal clinically important LEFS difference in patients with lower extremity musculoskeletal conditions is 9 points [33].

Finally, the available Spanish version of the Kujala Patellofemoral Score was filled out by participants. This 13-item questionnaire represents a specific self-report measure of knee function in patients with PFP. Seven items have a maximal score of 10 and 6 with maximal 5 points. Total score ranges from 0 to 100, where the highest scores represent a better functional capacity [34]. The Kujala score has a reported minimum clinically important difference threshold of 9.5 points in a 4-week follow-up period [35].

Whole body vibration (WBV) training

In the present study, an axial (vertical) vibration platform was used (Power-Plate® Pro 5™ AIRdaptive TM HP, Power Plate North America, Inc., Northbrook, IL, USA). This device is annually reviewed by the technical unit of the company and complies with the international Medical Devices regulations (Devices Directive [MDD] 93/42/EEC [ISO 2631. 2011, Powerplate.com, 2013]). This model has a Class IIA certificate (MDD 553319/0086), which classifies it as having a medium low risk, ensuring that the device offers a therapeutic benefit under correct use (ISO 2631:2011, Powerplate.com, 2013).

The designed program consisted of a single bout of 18-exercise routine, executed on the vibration platform (Table 1). Graphic representation of the selected exercises is shown in Fig. 1.

Table 1 Exercise protocol of the study

Based on the scientific literature on exercise recommendations for patients with PFP [8, 36, 37], isometric and isotonic exercises that involve core, gluteal and quadriceps muscles were selected. We also based the WBV protocol on weight-bearing position considering the recommendations for patients with anterior knee pain and due to its greater functional transfer to daily living activities [10].

The frequency of the vibration platform was fixed at 40 Hz along the study and the amplitude of the vibration platform (peak-to-peak displacement) was set at 2 mm in the first two weeks, and 4 mm during the following two [38]. The acceleration peak for these parameters were 3.2G and 6.4G respectively. In terms of force (Newtons) developed for the participants to perform the exercises, this ranged from 748.5 N in a neutral environment (without vibration, control group), to 2395.2 N (intervention group, using 40 Hz, 2 mm, 3.2G) and 4790.4 N (when parameters in the intervention group were 40 Hz, 4 mm, 6.4 G).

Each session was structured following scheduled phases of warm-up, main active part and, finally, cool-down and stretching, as recommended by the American College of Sports Medicine [39]. The warm-up phase consisted of different lower limb active exercises to increase the blood flow, muscle temperature and to activate the central nervous system [40]. All exercises in the warm-up and conditioning phases were performed considering the time on the vibration platform in sets of 30 s, with 30 s of rest between repetitions. Finally, the cool-down period involved global stretching and trunk and lower limb relaxation, with exercises involving 60 s of work and 6 s of rest and 120 s of work with 12 s of rest, respectively. The total duration of the program was 22 min, following the general lines of high-intensity aerobic interval training, which establishes a rest period that is at least equal to that of the work period [10, 41]. Based on a modified pain monitoring model, pain or discomfort only was allowed during the exercise execution if was acceptable (< 4/10) and if returned to the same baseline level of pain as before starting exercises within 24 h. If this does not occur, the exercise should be modified by reducing load (time, exercise posture or vibration amplitude) [11].

The treatment protocol comprised 12 sessions conducted over 4 consecutive weeks (3 sessions per week) and each session was supervised by an experienced clinical physiotherapist. The aim was to avoid pain during all exercises and also to avoid unusual physical activity or other additional exercises [3]. The physiotherapist assisted each participant during these sessions, supervising and correcting their positions before beginning each exercise, as well as during its execution, indicating necessary adaptations if needed. The exercise program was performed using only body weight resistance without external weight. All participants performed the exercises wearing sports shoes.

Control group

The control group participants were instructed to do the same supervised exercise protocol but on a vibration platform while the system was off and did not transmit any vibration to the patient’s feet.

Statistical analysis

The statistical data processing was carried out using the PASW Advanced Statistics Package (SPSS Inc., Chicago, IL, USA), version 24.0. The data were reported as mean (standard deviation) and confidence intervals (95% CI). First, the normal distribution of the variables was verified by the Shapiro-Wilk test, following a descriptive analysis. The homogeneity of the variations was observed using the Levene test. Linearity was evaluated by bivariate scatter plots of residual values ​​observed against expected values. Comparisons between the baseline demographic and clinical data of the groups were made using the Student’s t-test for continuous data and the chi-square test for categorical data.

Separate 2 × (2) mixed-model analysis of variance (ANOVA) was used to evaluate interaction time × groups, including the time effects (baseline, post-treatment) and group effects (supervised exercise group vs WBV+ supervised exercise group) for each outcome measure. All analyses followed the intention-to-treat principle and groups were analyzed as randomized. Effect sizes were calculated using Square Eta (η2) was used to calculate the effect size (small, 0.01 ≤ η2 < 0.06, medium, 0.06 ≤ η2 < 0.14, and large, η2 > 0.14). The statistical significance was set at a value of p < 0.05.

The sample size calculation was based on the detection of: 1) a 15% change in the intensity of self-reported pain [29] and 2) a difference of > 9 points on the LEFS scale [33] and > 10 points on the Kujala scale in the comparison between groups after the intervention [35]. Taking into account the ANOVA analysis of repeated measures between factors (group x time), an alpha value of 0.05, a desired power of 90% and a medium effect size (f = 0.25), 46 participants in total were required for the study (G * Power, version 3.1.9.2).

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