Methods

Randomised controlled trial

Trial protocol registration: not reported

Participants

Country: Turkey

Setting: Hacettepe University, School of Physiotherapy and Rehabilitation, and Department of Orthopaedics and Traumatology, Ankara

Data collection period: not reported

Inclusion criteria: anterior knee pain (longer than 2 months), positive patellar compression test, age between 15 and 45 years, negative findings in the clinical examination of knee ligaments, bursae, menisci, synovial plicae, hamstring, quadriceps, and patellar tendons

Exclusion criteria: history or clinical evidence of patellofemoral dislocation, subluxation, or severe osteoarthritis, X‐rays showing lateral displacement of the patella

Mean duration of symptoms: 15.74 ± 9.31 months

62.5% of bilateral complaints, but only the most symptomatic knee was treated

Study participants: 44 people with patellofemoral pain assigned and 42 assessed

1. NMES + exercise: n = 22/available for analysis = 20

2. Only exercises: n = 22/available for analysis = 22

Mean age (SD): 39.0 (9.6) years

Gender (number of women/men): 31/13

Interventions

Comparison: NMES + other intervention (exercise) versus no NMES + same other intervention

Treatment duration: 6 weeks
Treatment setting: outpatient rehabilitation programme

Details of interventions:

1. NMES programme: Portable HVPGS, monophasic (twin‐peak pulse) waveform, pulse duration 65 to 75 µs, intensity amplitude ranges from 0 to 300 V, pulse frequency of 60 pulses per second. 2 self adhesive electrodes positioned over the VMO: the proximal electrode was placed 4 cm superior to the superomedial border of the patella, and the distal electrode 3 cm medial to this point. Participants in weight‐bearing position with a comfortable amount of knee flexion. The muscle was stimulated while the participant executed an active contraction of the quadriceps. The intensity of stimulation was adjusted to a level that induced a contraction as close as to a maximum voluntary contraction but without patellofemoral pain. Treatment duration: 10 minutes, 5 times a week.

2. Exercise programme: Both groups followed the same exercise programme (total of 30 sessions). First 2 weeks: quadriceps sets, straight leg raises, hip adductor strengthening exercises (to facilitate VMO contraction), eccentric quadriceps contraction by leg‐lowering exercises, leg pulls using a rubber tube. Weeks 2 to 4: bilateral shallow squats, toe rises on both feet, leg pulls using a rubber tube in a standing position, stretching exercises for iliotibial band, hamstring, quadriceps, and triceps surae muscles. Weeks 4 to 6: step‐downs, bilateral deep squats, 1‐legged shallow squats, exercises for lower extremity balance, cycling on a stationary bicycle, toe raises of 1 foot, hopping activities. The progression of load and exercises was individually prescribed according to the level of perceived pain. Ice was used after exercises to minimise latent soft‐tissue pain.

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee pain: VAS

2. Muscle strength: assessed through Lovett’s manual muscle test (graded between 0 and 5; higher scores indicating better muscle strength) (Kendall 2005):

   • zero indicates no contraction;

   • 1 indicates visible muscle contraction without joint movement;

   • 2‐ to 2+ indicates poor strength (ability to move through full active range of motion);

   • 3‐ to 3+ indicates fair strength (hold test position);

   • 4‐ to 4+ indicates good strength (hold test position against slight to moderate manual resistance);

   • 5 indicates normal strength (hold test position against strong manual resistance).

Follow‐up assessments: at 6 weeks (at end of treatment)

Notes

Description of condition: patellofemoral pain syndrome

The trial authors provided additional information on random sequence generation, allocation concealment, and blinding (participants, personnel, and assessors) via email (10 March 2015).

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "The subjects were randomly introduced into either HVPGS and exercise, or only exercise (control group)"

Authors' reply: "At the time of study, it was feasible for us to use coin tossing technique to assign patients to either HVPGS and exercise group, or only exercise (control group) in consecutively."

Allocation concealment (selection bias)

Unclear risk

Available information did not permit judgement.

Authors' reply: "Assigning patients to intervention groups was done by the first author with coin tossing technique to prevent second and third author/researcher from influencing concealing the allocation sequence in the study."

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Available information did not permit judgement.

Authors' reply: "Patients were also blinded to their intervention groups. Exercise programs were applied by physiotherapist (third researcher/author)"

However, since no sham/placebo was used, it is unlikely that the blinding was kept.

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Available information did not permit judgement.

Authors reply: "Pre and post treatment muscle strength and VAS measurements were evaluated by the same physiotherapist (second researcher) who is blind from the patient’s group"

Incomplete outcome data (attrition bias)
All outcomes

Unclear risk

Quote: “Two patients of the HVPGS group did not complete the study and their data results were excluded” (4.5% dropout)

No reasons were provided. We are uncertain of the potential effect of these missing data.

Selective reporting (reporting bias)

Unclear risk

No study protocol available. It is not clear if the results included all expected outcomes (e.g. retropatellar pain during activities: steps up and down and squatting). This study did not consider adverse event as an outcome.

Other bias

Low risk

The study appears to be free of other sources of bias. Baseline characteristics were balanced between groups.

Methods

Randomised controlled trial

Trial protocol registration: not reported

Participants

Country: Austria

Setting: Department of Physical Medicine and Rehabilitation, Wilhelminenspital Vienna and Core Unit for Medical Statistics and Informatics, Section of Clinical Biometrics, Medical University of Vienna

Data collection period: between June 2003 and August 2005

Inclusion criteria: bilateral anterior knee pain for 6 to 120 months and at least 3 of the following 4 clinical criteria: pain associated with prolonged sitting with bended knees, descending stairs, kneeling and squatting, or sports activities

Exclusion criteria: clinical evidence of patellar dislocation or subluxation, periarticular bursitis or tendonitis, ligamentous instability, or intra‐articular pathology. Before beginning therapy, all participants were thoroughly clinically examined. Those who did not reveal any obvious reason for a systemic disorder like patellar or lower‐extremity alignment problems or benign joint hypermobility syndrome were not excluded. To rule out osteoarthritic changes or hypoplastic femoral trochlea, radiographs were performed. Pregnancy, a history of knee surgery, or oral or intra‐articular administration of drugs within the last 3 months

Mean duration of symptoms: 14 months (6 to 24)

Only bilateral complaints (but did not clarify which knee was treated and assessed)

Study participants: 38 people with patellofemoral pain assigned and 29 assessed

1. NMES + exercise: n = 19/available for analysis after treatment = 18; and after 12 months = 13

2. Only exercises: n = 19/available for analysis after treatment = 18; and after 12 months = 16

Mean age (SD): 25.4 (6.7) years

Gender (number of women/men): 24/14

Interventions

Comparison: NMES + other intervention (exercise) versus no NMES + same other intervention

Treatment duration: 12 weeks
Treatment setting: at home

Details of interventions:

1. NMES programme: 2‐channel portable device, asymmetric biphasic pulses for a duration of 0.26 ms, duty cycle of 5:10, maximal amplitude 80 mA, frequency 40 Hz. Four self adhesive electrodes were placed respectively on both ends of the quadriceps muscles. Treatment duration: 2 20‐minute sessions with a minimum of 60‐minute rests between each session. The intensity of the stimulation was kept as high as possible; however, pain tolerance and participant discomfort were modifying factors.

2. Training programme: Both groups of participants followed the same exercise programme: isometric, concentric, excentric leg raises, stepping and squatting exercises. Balance exercises started from week 4 onward and consisted of standing on 1 leg for 2 minutes each. To increase the exercise demand, participants were instructed to draw circles in the air with the free contralateral leg from week 6 onward. From week 8 onward, participants had to do the 1‐legged balance exercises in a toe‐raised position with drawing circles with the contralateral leg in weeks 11 and 12. Static stretching exercises of the calf and thigh muscles consisted of 3 sets of 10‐second passive sustained stretching for each muscle group performed by the participants themselves at the end of each training session from weeks 4 to 12. Treatment duration: participants were instructed on daily training during the first 2 weeks and had a group session once a week under the supervision of the same physical therapist. From the third week on, they were instructed to train with higher loads 3 times a week for a total of 12 weeks.

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee pain: VAS, during activities (descending stairs, prolonged sitting, kneeling, or squatting) and during sport movements (walking, jogging, jumping)

2. Knee function: Kujala Patellofemoral Score

3. Muscle strength: Strength measurements were performed in a sitting position using a specifically designed chair. Strain gauges, connected in a full bridge circuit configuration, were placed on a lever near the centre of rotation and the output fed to a measurement amplifier. Participants were fixed with shoulder and hip straps and performed 3 maximal isometric contractions of the knee extensors of 10 seconds in 30° and 60° knee flexion with a 2‐minute rest between the contractions. The peak extension torque was recorded, and the best result of the 3 attempts was used for calculation.

Follow‐up assessments: at 12 weeks (at end of treatment) and 1 year

Notes

Description of condition: patellofemoral pain syndrome

The trial authors provided additional information on random sequence generation, allocation concealment and blinding (participants, personnel, and assessors) via email (16 March 2015).

Additionally, the trial authors provided information regarding which knee was treated and assessed (9 August 2016). Authors' reply: "EMS was applied on both knees"

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Authors' reply: "Random allocation of the patients to the 2 treatment groups was performed by using shuffled sealed envelopes”

Allocation concealment (selection bias)

Unclear risk

Authors' reply: "With sealed envelopes"

The authors did not mention if the envelopes were opaque.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Participants: probably not done because the interventions were different between groups.
Personnel: probably not done due to the nature of the intervention.

Authors' reply: No measures were used to ensure blinding.

Blinding of outcome assessment (detection bias)
All outcomes

High risk

Available information did not permit judgement.

Authors' reply: No measures were used to ensure blinding.

Incomplete outcome data (attrition bias)
All outcomes

High risk

Some participants did not complete the study (5.2% dropout at the end of the treatment and 19% dropout in the long term), and it is unclear how the authors dealt with these missing data.

Selective reporting (reporting bias)

Unclear risk

No study protocol available. It is not clear if the results included all expected outcomes. This study did not consider adverse event as an outcome.

Other bias

Unclear risk

The study appears to be free of other sources of bias. However, although baseline characteristics were balanced between groups, muscle strength before training was greater in the NMES group.

Methods

Randomised controlled trial

Trial protocol registration: not reported

Participants

Country: United Kingdom

Setting: Centre for Rehabilitation Science, Manchester Royal Infirmary, Manchester

Data collection period: not reported

Inclusion criteria: atraumatic peripatellar pain (greater than 6 months and not longer than 3 years); patellofemoral pain was provoked by 1 of the following alone or in combination: prolonged sitting, deep squatting, kneeling, ascending or descending stairs; quadriceps cross‐sectional area differences between affected and unaffected limb greater than 4%

Exclusion criteria: epilepsy, cancer, cardiac pacemaker, suspected heart problem, recent surgery (not including arthroscopy). In order to exclude abnormal foot and ankle pronation as the cause of patellofemoral pain, the participants were screened by kinetic gait analysis to detect abnormal values of mediolateral force. Pain from the lumbar spine and hip joint, severe leg length discrepancy, knee ligament, quadriceps tendon, and meniscal pathologies, Hoffa’s syndrome, medial plica syndrome, femoral anteversion and tibial torsion

Mean duration of symptoms: not reported

All unilateral complaints

Study participants: 16 people with patellofemoral pain assigned and 14 assessed

1. NMES (simultaneously delivered frequencies): n = 8/available for analysis = 7

2. NMES (sequentially delivered frequencies): n = 8/available for analysis = 7

Mean age (SD): 29.6 (5.9) years

Gender (number of women/men): 12/2

Interventions

Comparison: NMES (simultaneous mixed frequencies) versus control NMES (sequential mixed frequencies)

Treatment duration: 6 weeks
Treatment setting: at home

Details of interventions:

1. NMES with simultaneously combined high‐ and low‐frequency components: 2‐channel portable, asymmetrical biphasic pulse, maximum amplitude of 90 mA, duty cycle of 10:50, pulse duration 200 μs. Stimulation pattern: 3 simultaneously delivered components (a background low‐frequency component, a high‐frequency component superimposed on the background at regular intervals, and a ‘doublet’ of pulses delivered within the higher‐frequency burst). 2 self adhesive electrodes positioned over the quadriceps muscle group. Treatment duration: 60 minutes daily, for 6 weeks.

2. NMES with sequentially combined frequencies: 3‐channel stimulator, bipolar, biphasic asymmetrical rectangular pulses. Stimulation parameters and treatment duration: once a day, 5 days a week for the first 2 weeks (2 minutes at 8 Hz pulse width 250 μs; 20 minutes at 35 Hz pulse width 350 μs; 3 minutes at 3 Hz pulse width 250 μs), and then 3 times a week for weeks 3 and 4 and twice a week for the last 2 weeks (2 minutes at 8 Hz pulse width 250 μs; 20 minutes at 45 Hz pulse width 350 μs; 3 minutes at 3 Hz pulse width 250 μs). 2 self adhesive electrodes positioned over the quadriceps muscle group.

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee pain: VAS

2. Knee function: Kujala Patellofemoral Score

3. Adverse events: muscle fatigue rate assessed by bipolar electrode surface EMG (median frequency calculated at 1‐second intervals during a sustained 60‐second contraction at 60% of maximum)

4. Lower limb muscle function: functional performance tests: step‐up (the number of steps the participant could climb up onto a 25‐centimetre step), step‐down (the number of steps down a 25‐centimetre step), and squat flexion (the amount of knee flexion participants could achieve from a standing position until the onset of their patellar pain, measured by a universal goniometer)

5. Muscle strength: quadriceps isometric and isokinetic muscle strength measured through an isokinetic dynamometer (angular velocity at 90°/s)

Follow‐up assessments: 6 weeks (at end of treatment)

Notes

Description of condition: patellofemoral pain syndrome

The trial authors provided additional information on NMES parameters via email (9 March 2015).

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "Patients were randomly allocated by computer program to either the experimental stimulation or standard stimulation treatment regimes"

Allocation concealment (selection bias)

Unclear risk

Available information did not permit judgement.

Blinding of participants and personnel (performance bias)
All outcomes

Unclear risk

Participants: Available information did not permit judgement.
Personnel: Available information did not permit judgement.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

Available information did not permit judgement.

Incomplete outcome data (attrition bias)
All outcomes

High risk

2 participants (12% dropout) did not complete the study and were excluded from the analysis.

Selective reporting (reporting bias)

Low risk

No study protocol available. The authors considered only 1 adverse event (muscle fatigue); however, this is 1 of the most important adverse events in clinical practice.

Other bias

Unclear risk

Unable to judge because it is unclear if the groups were similar regarding relevant characteristics at baseline (age, gender, level of pain)

Methods

Randomised controlled trial

Trial protocol registration: not reported

Participants

Country: United Kingdom

Setting: Centre for Rehabilitation Science, Manchester Royal Infirmary, Manchester

Data collection period: not reported

Inclusion criteria: atraumatic peripatellar pain (greater than 6 months and not longer than 3 years), patellofemoral pain was provoked by 1 of the following alone or in combination: prolonged sitting, deep squatting, kneeling, ascending or descending stairs

Exclusion criteria: epilepsy, cancer, cardiac pacemaker, suspected heart problem, recent surgery (not including arthroscopy). In order to exclude abnormal foot and ankle pronation as the cause of patellofemoral pain, the participants were screened by kinetic gait analysis to detect abnormal values of mediolateral force. Presence of other lower extremity dysfunction that could account for the knee symptoms

Mean duration of symptoms: not reported

All unilateral complaints

Study participants: 80 people with patellofemoral pain assigned and 74 assessed

1. NMES (simultaneously delivered, mixed frequency): n = 38/available for analysis = 37

2. NMES (fixed frequency): n = 41/available for analysis = 37

Mean age (SD): 35 (11.4) years

Gender (number of women/men): 43/31

Interventions

Comparison: NMES (simultaneous mixed frequencies) versus control NMES (fixed frequency)

Treatment duration: 6 weeks
Treatment setting: at home

Details of interventions:

1. NMES device with simultaneously delivered, mixed frequency: 2‐channel portable, asymmetrical biphasic pulse, maximum amplitude of 90 mA, duty cycle of 10:50 delivering 90 impulses/min, pulse duration 200 μs. Stimulation pattern: simultaneously delivered frequency components of 83, 50, 2.5, and 2 Hz with a doublet of pulses (125 Hz) at the beginning of each pulse train. The pulse train was repeated once every minute and consisted of the following interpulse intervals: 8, 12, 20, 20, 20, 400, and 500 ms. 2 self adhesive electrodes over the quadriceps muscle group, 1 placed on the upper lateral thigh and the other on the lower medial thigh. Treatment duration: 60 minutes daily.

2. NMES device with fixed frequency: Asymmetric biphasic rectangular waveform, maximum amplitude 100 mA, duty cycle 10:50 delivering 350 impulses/min, pulse duration 300 μs, fixed frequency of 35 Hz. Four self adhesive electrodes were placed over the quadriceps muscle group. Treatment duration: daily stimulation periods lasting 60 minutes.

Stimulation intensity for both groups was the highest comfortably tolerable for all the participants.

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee pain: VAS

2. Knee function: Kujala Patellofemoral Score

3. Adverse events: muscle fatigue rate assessed by bipolar electrode surface EMG (median frequency calculated at 1‐second intervals during a sustained 60‐second contraction at 60% of maximum)

4. Lower limb muscle function: functional performance tests: step‐up (the number of steps the participant could climb up onto a 25‐centimetre step), step‐down (the number of steps down a 25‐centimetre step), and squat flexion (the amount of knee flexion participants could achieve from a standing position until the onset of their patellar pain, measured by a universal goniometer)

5. Muscle strength: quadriceps isometric and isokinetic muscle strength measured through an isokinetic dynamometer (angular velocity at 90°/s)

Follow‐up assessments: 6 weeks (at end of treatment)

Notes

Description of condition: patellofemoral pain syndrome
3 participants were excluded due to device failure.

The trial authors provided additional information on NMES parameters via email (9 March 2015).

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "Randomization was performed by consulting 4 computer‐generated randomization lists, 1 for each of the 4 stratified groups."

Allocation concealment (selection bias)

Unclear risk

Available information did not permit judgement.

Blinding of participants and personnel (performance bias)
All outcomes

Unclear risk

Participants: Available information did not permit judgement.
Personnel: Quote: "To preserve the blinding for the study, both devices were fully explained to and demonstrated on the patients by an independent investigator"

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Quote: "The lead investigator who examined and measured the patients was not part of the randomisation process, thus ensuring blindness to the stimulator allocation"

Incomplete outcome data (attrition bias)
All outcomes

High risk

Some participants did not complete the study (12% dropout), and their data were excluded from the analysis. Losses not balanced between groups.

Selective reporting (reporting bias)

Low risk

No study protocol available. The authors considered only 1 adverse event (muscle fatigue); however, this is 1 of the most important adverse events in clinical practice.

Other bias

Low risk

The study appears to be free of other sources of bias. Baseline characteristics were balanced between groups.

Methods

Double‐blinded, randomised sham‐controlled trial

Trial protocol registration: not reported

Participants

Country: United States

Setting: laboratory (single NMES session)

Data collection period: not described

Inclusion criteria: age between 15 and 65, atraumatic knee pain (greater than 3 months), pain with more than 2 of the following activities: jumping, kneeling, prolonged sitting, quadriceps contraction, running, squatting, or stair climbing or when pressure was placed on the patella. Participants were required to score less than 85 of 100 on the Anterior Knee Pain Scale.

Exclusion criteria: previous knee surgery, ligamentous instability, meniscal injury, or other sources of anterior knee pain, such as patellar tendinitis, bursitis, or patella subluxation. Contraindications to electrical stimulation: implanted biomedical devices, history of neuropathy, muscular abnormality, hypersensitivity to electrical stimulation, or active infection where the electrodes would be placed.

Mean duration of symptoms: not reported

People who presented bilateral complaints were included, but only the most symptomatic knee was treated.

Study participants: 22 people with patellofemoral pain assigned and assessed

1. NMES group: n = 11

2. Sham group: n = 11

Mean age (SD): 26.0 (7.9) years

Gender (number of women/men): 15/7

Interventions

Comparison: NMES versus placebo

Treatment duration: single session (15‐minute treatment)
Treatment setting: laboratory

Details of interventions:

1. NMES programme: PENS: biphasic asymmetric square‐wave pattern of 50‐hertz pulse frequency, 70‐microsecond phase duration, and 200‐millisecond stimulus train. 2 channels were used to deliver alternating patterns, mimicking the agonist‐antagonist muscle pattern that is seen in healthy people during functional tasks. Channel 1 consisted of 2 self adhesive electrodes positioned over the agonist muscles (gluteus medius and VMO), and channel 2 consisted of 2 electrodes positioned over the antagonist muscles (the middle of the adductor muscle group and the middle of the hamstrings muscle group). The patterned stimulus was a 200‐millisecond contraction to channel 1, a 200‐millisecond contraction to channel 2, and finally a 120‐millisecond contraction to channel 1. Participants were positioned on a treatment table with the hip and knee flexed to approximately 90º for the single 15‐minute treatment, which resulted in a strong motor contraction visible to the researcher.

2. Sham group: Participants received a single 15‐minute treatment (identical device settings were applied); however, the amplitude was only increased to 1 mA, which is the minimum stimulus allowed for the device display to light up and activate the timer to replicate a true treatment, even though no participant could perceive stimulation. The electrodes were placed at the same muscles as described above. Participants were instructed that they were receiving a "subsensory" treatment.

At the end of the intervention, the PENS electrodes were removed, and the participants were instructed to perform 2 functional movements. Outcome data were collected for both tasks.

• Single‐leg squat: the participant was instructed to stand on the injured leg and squat so that the knee was flexed to more than 60° and then return to the starting position. The participant was instructed to maintain the non‐standing limb at 90° of knee flexion for the duration of the task. The time to perform the task was standardised: 2 seconds to lower and 2 seconds to return to the starting position.

• Lateral step‐down: the participant stood on a step that was normalised to 10% of his or her height, lowered himself or herself until the contralateral heel touched a force plate, and then returned to the starting position. A 4‐second time period was also used for this task.

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee pain: VAS: participants placed a vertical mark on a 10‐centimetre VAS line for the pain they experienced during both tasks.

Follow‐up assessments: immediately at the end of the single‐session treatment (after completing the single‐leg squat and lateral step‐down)

Notes

Description of condition: patellofemoral pain

The trial authors provided additional information on random sequence generation, allocation concealment, and blinding (participants, personnel, and assessors) via email (12 August 2016).

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Available information did not permit judgement.

Allocation concealment (selection bias)

Unclear risk

Quote: "One researcher concealed treatment interventions in envelopes, which were randomly allocated to participants before enrolment."

The authors did not mention if the envelopes were sealed and opaque.

Blinding of participants and personnel (performance bias)
All outcomes

Unclear risk

Quote: "sham controlled laboratory study"

Since the authors did not exclude people who had received previous NMES therapy, it is difficult to affirm that the blinding was effective.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

Quote: "At the conclusion of the 15‐minute treatment, electrodes were removed, the blinded researcher left the laboratory, and the primary researcher returned to the laboratory to conduct post‐intervention assessments"

It is not clear if the outcome assessor was blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

All participants completed the study.

Selective reporting (reporting bias)

High risk

No study protocol available. It is unclear if the results included all expected outcomes. This study did not consider adverse event as an outcome. Another report of this study that included a subgroup of 15 females presented the same baseline characteristics (age, height, mass, anterior knee pain score, and VAS pain knee) as those for the 22 participants in the study.

Other bias

Unclear risk

Although the baseline characteristics were balanced between groups, we are uncertain whether these are correct. The pain scores (1.9 in both groups) were below the threshold ("more than 2") for inclusion in the trial.

Methods

Randomised controlled trial

Trial protocol registration: not reported

Participants

Country: Switzerland

Setting: Physical Medicine and Rehabilitation, Sion Hospital, Switzerland and Orthopaedic Hospital of Lausanne

Data collection period: not reported

Inclusion criteria: non‐traumatic retropatellar painful chondropathy, without radiological lesion, with or without Wiberg patellar dysplasia type I or II

Exclusion criteria: Wiberg dysplasia type III

Mean duration of symptoms: not reported

% of bilateral complaints not reported.

Study participants: 120 people with patellofemoral pain assigned and 94 assessed

1. NMES: n = 28 assessed

2. Isokinetic exercise: n = 40 assessed

3. Isometric exercise: n = 26 assessed

Mean age (SD): 26.4 (11.2) years
Gender (number of women/men): 50/44

Interventions

Comparison: NMES versus exercise (isokinetic) versus exercise (isometric)

Treatment duration: 4 weeks
Treatment setting: at home

Details of co‐interventions:

1. NMES programme: 4‐channel portable device, monophasic or biphasic rectangular waveform, pulse duration 200 μs, duty cycle of 15:45, frequency of 10 and 50 Hz. Stimulation pattern: 60 minutes at 10 Hz continuous, 30 minutes at 50 Hz with tetanic contractions, and 30 minutes at 10 Hz continuous. Electrodes were positioned over the VMO. Treatment duration: 2 hours, twice a day, daily.

2. Isokinetic exercise: Isokinetic exercises using an isokinetic dynamometer (Cybex II): flexion/extension (angular velocity between 30°/s and 300°/s). Series lasted 1 minute, with a break of 30 seconds to 2 minutes. Treatment duration: 25 to 30 minutes, 3 times a week.

3. Isometric exercise: Relaxation of the external passive structures, stretching the hamstrings and rectus, and a static proprioceptive rehabilitation. Treatment duration: 30 to 45 minutes, 3 times a week.

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee function: Arpège function scale

2. Muscle strength: quadriceps isometric and isokinetic strength using an isokinetic dynamometer (angular velocity at 30°/s and 300°/s)

Follow‐up assessments: 4 weeks (at end of treatment)

Notes

Description of condition: retropatellar chondropathy

It was not possible to obtain additional data on random sequence generation, allocation concealment, and blinding (participants, personnel, and assessors) after attempt to contact authors by email (9 March 2015).

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Available information did not permit judgement.

Allocation concealment (selection bias)

Unclear risk

Available information did not permit judgement.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Participants: probably not done because the interventions were different between groups.
Personnel: probably not done due to the nature of the intervention.

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Quote: "The evaluation of the isokinetic strength and Arpège criteria was performed by a neutral observer. This investigator does not belong to the rehabilitation team"

Incomplete outcome data (attrition bias)
All outcomes

High risk

Some participants did not complete the study (22% dropout) and it is unclear how the authors dealt with these missing data. Losses imbalanced between the groups.

Selective reporting (reporting bias)

Unclear risk

No study protocol available. It is unclear if the results included all expected outcomes. This study did not consider adverse event as an outcome.

Other bias

Unclear risk

This study provided no information on the side(s) affected, and it is unclear which knee was treated.

Methods

Randomised controlled trial

Trial protocol registration: not reported

Participants

Country: Turkey

Setting: Faculty of Medicine, Department of Sports Medicine, Hacettepe University, Ankara

Data collection period: not reported

Inclusion criteria: pain longer than 6 months, presence of retropatellar pain, crepitation and pain in patellar grinding, age between 18 to 40 years, no abnormalities on magnetic resonance imaging

Exclusion criteria: history or clinical evidence of patellofemoral dislocation, subluxation, or osteoarthritis, presence in the clinical examination of injury or dysfunction to the knee ligaments, bursae, menisci, and synovial plicae, history of lower extremity surgery, radiographic evidence of osteoarthritis in any compartments of the knee joint.

Mean duration of symptoms: not reported

All unilateral complaints

Study participants: 30 participants with patellofemoral pain assigned and assessed

1. NMES + exercises + patellar taping (n = 15)

2. Exercises + patellar taping (n = 15)

Mean age (SD): 42.7 (10.0) years

Gender (number of women/men): only women were included.

Interventions

Comparison: NMES + other intervention (exercise + taping) versus no NMES + same other intervention

Treatment duration: 6 weeks

Treatment setting: outpatient rehabilitation programme

Details of interventions:

1. NMES programme: Portable HVPGS, monophasic (twin‐peak pulse) waveform, pulse duration 65 to 75 µs, intensity amplitude ranges from 0 to 300 V, pulse frequency of 60 pulses per second. The proximal electrode was placed 4 cm superior to the superomedial border of the patella, and the distal electrode was placed 3 cm medial to the first point. Participants in sitting position with their knees extended were ordered to perform quadriceps isometric exercise with the stimulation. The intensity of stimulation was adjusted to produce a strong contraction without causing patellofemoral pain. Treatment duration: 20 minutes, 5 times a week.

2. Home exercise programme: Isometric quadriceps exercises in sitting, straight leg raise exercises (neutral position) with ankle weights, terminal knee extension exercises with ankle weights, wall squats with ball between the knees, split squats with elastic band (blue colour), step‐down exercises (backward, forward, and sideway), and single‐leg balance exercises in different knee angles with elastic band (blue colour). Stretching exercises included quadriceps, iliotibial band, hamstrings, and gastrocnemius muscles.

3. Patellar‐taping technique described by McConnell to correct patellar malposition. First a subtape was applied, while taking care not to place any tension on the participant’s skin. After the application of a subtape, a corrective tape was applied. Corrections were applied to obtain anterior tilt, medial glide, medial tilt, and unloading the fat pad until the participant’s pain was reduced by at least 50%.

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee pain: VAS

2. Knee function: Lower Extremity Functional Scale (LEFS)

Follow‐up assessments: short term (6 weeks)

Notes

Description of condition: patellofemoral pain syndrome

This trial had 3 treatment arms. Data from 1 group (NMES alone) were not included in this review.

It was not possible to obtain additional data on random sequence generation, allocation concealment, and blinding (participants, personnel, and assessors) after attempt to contact the authors by email (10 March 2015).

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Quote: “The patients were randomly allocated into three groups by the second author who was blinded in measurements and assessments”

The sentence above is unclear about the method used.

Allocation concealment (selection bias)

Unclear risk

Available information did not permit judgement.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Participants: probably not done because the interventions were different between groups.
Personnel: probably not done due to the nature of the intervention.

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Quote: “The patients were randomly allocated into three groups by the second author who was blinded in measurements and assessments”

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Quote: "All patients completed the rehabilitation program and all assessment procedures"

Selective reporting (reporting bias)

High risk

No study protocol available. It is unclear if the results included all expected outcomes. This study did not consider adverse event as an outcome. The conclusions for pain were contradicted by the data, raising doubts regarding their reliability.

Other bias

High risk

Baseline characteristics were balanced between groups, except for pain, which was significantly lower in the control group for all 3 functional activities.

Methods

Randomised controlled trial

Trial protocol registration: not reported

Participants

Country: Turkey

Setting: Hacettepe University, School of Physiotherapy and Rehabilitation, Sports Physiotherapy and Gulhane Military Medical Academy, Department of Orthopaedics and Traumatology, Ankara

Data collection period: not reported

Inclusion criteria: unilateral patellofemoral pain lasting more than 1 month

Exclusion criteria: history or clinical findings of patellar dislocation, meniscal or ligamentous injury, synovial plicae, knee surgery or trauma

Mean duration of symptoms: 1.8 years (range 1 month to 5 years)

All unilateral complaints

Study participants: 40 people with patellofemoral pain assigned and assessed

1. NMES + exercises + patellar taping + ice (n = 20)

2. Exercises + patellar taping + ice (n = 20)

Mean age (SD): 32.9 (7.3) years

Gender (number of women/men): no information

Interventions

Comparison: NMES + other intervention (exercise, taping, and ice) versus no NMES + same other intervention

Treatment duration: 3 weeks (total of 15 sessions)
Treatment setting: outpatient rehabilitation programme

Details of interventions:

1. NMES programme: Frequency of 30 Hz, duty cycle of 5:10, pulse duration 300 μs, pulse intensity: visible contraction. Electrode position was not reported. Stimulation session duration of 10 minutes.

2. Exercise programme: Terminal knee extension with elastic band, straight leg raise exercise, hip strengthening exercises with elastic band in standing position, lunge exercise, hamstring and iliotibial band stretching exercises with elastic band (2 times a day).

3. Patellar taping (not described).

4. Ice (not described).

Outcomes

Outcomes analysed in the study and used in this review:

1. Knee pain: VAS

2. Knee function: Cincinnati Knee Rating System

Follow‐up assessments: short term (3 weeks)

Notes

Description of condition: patellofemoral pain syndrome

This trial had 4 treatment arms. Data from 2 groups (NMES, ice, medial patellar glide and exercises; ice and home exercises) were not included in this review.

The trial authors provided additional information on NMES parameters and exercise programme via email, confirming that "same exercises were given to the all groups" (12 March 2015).

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Available information did not permit judgement.

Allocation concealment (selection bias)

Unclear risk

Available information did not permit judgement.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Participants: probably not done because the interventions were different between groups.
Personnel: probably not done due to the nature of the intervention.

Blinding of outcome assessment (detection bias)
All outcomes

High risk

Available information did not permit judgement, but seems unlikely given the nature of the intervention.

Incomplete outcome data (attrition bias)
All outcomes

Unclear risk

It is not clear if there were losses.

Selective reporting (reporting bias)

Unclear risk

No study protocol available. It is unclear if the results included all expected outcomes. This study did not consider adverse event as an outcome.

Other bias

Low risk

The study appears to be free of other sources of bias. Baseline characteristics were balanced between groups.