Table 10.

Details of Individual Studies on Use of NMES in PFPS

Author (Date), Study Design, and Study Size	Population Comparison Groups	Electrode Parameters: Size, Channels, Placement, and Limb Position	Stimulation Parameters: Waveform, Frequency, Pulse Duration, ON:OFF Time, and Amplitude	Treatment Schedule: Min/D Repetitions, D/Wk, and Total Wk Progression	Outcome Measures and Timing	Statistically Significant Results, NMES Compared with CON	Comments
Akarcali and colleagues (2002)128 RCT N=44 enrolled; N=44 or 42 analyzed (tables report 42 or 44) Included in SR131	PFPS>2 mo Aged 15–45 yr NMES (n=22): HVPC+Ex CON (n=22): Ex	4×4 cm 1 channel Electrodes: on VM 4 cm superior to and 3 cm medial to superomedial border patella Weight bearing with comfortable knee flex position	High-voltage PC 60 Hz 65–75 μs ON:OFF nr Amplitude max tolerable without pain Simultaneous voluntary contraction with NMES	10 min 5 d/wk 6 wk	Pain: VAS Strength: Lovett's manual muscle test @ 0, 3, and 6 wk	Less pain @ 3 wk No significant between-groups differences in all other outcomes	Parameters unlikely to increase strength (waveform combines rapid decay of intensity with very short pulse duration). Thus, equal increase in strength may be explained by Ex effects alone. Manual muscle test may be insensitive to improvement No blinding
Bily and colleagues (2008)122 RCT N=38 enrolled; N=36 analyzed @ 12 wk; N=29 analyzed @ 1 yr Included in SR131	PFPS NMES (n=19): NMES+Ex CON (n=19): Ex	5×13 cm 2 channels Electrodes: on prox and distal quads	Asymmetrical biphasic PC 40 Hz 260 μs ON:OFF 5:10 s Amplitude max tolerable No simultaneous voluntary contraction with NMES	20 min BID (160 contractions/d) 60 min rest between sessions 5 d/wk 12 wk	Pain: VAS max Function: Kujala PFPS Score Strength: seated isometric with strain gauges @ 0, 12 wk, and 1 yr	No between-groups differences	High number of repetitions, 800 contractions/wk, is typically used for training muscle endurance. However, the authors expected that quads strength would increase. No blinding Study was underpowered to detect change in pain.
Callaghan and Oldham (2004)123 RCT N=80 enrolled; N=79 treated; N=74 analyzed Included in SR131	PFPS NMES (n=38): Experimental device NMES (n=41): Conventional device	Conventional device: 5×9 cm 2 channels Electrodes: on quads; exact location nr Experimental device: 10×17 cm 1 channel Electrodes: on quads, upper lateral and distal medial	Conventional device: Asymmetrical biphasic PC 35 Hz 300 μs ON:OFF 10:50 s Experimental device: Asymmetrical balanced biphasic PC 200 μs 5 pulse train frequencies (125, 83, 50, 2.5, and 2 Hz) ON:OFF 10:50 s Amplitude set to highest comfortably tolerable No simultaneous voluntary contraction with NMES	60 min/d (60 contractions) 7 d/wk 6 wk	Lower extremity isometric and isokinetic torque @ 90°/s, Biodex Quads fatigue: EMG Knee flex in squatting: goniometer Patellar pain: VAS Step test: number until onset of pain Quads CSA: US imaging Function: Kujala PFPS Score @ 0 wk and within 1 wk after final NMES session Double blind	Similar improvements: Strength Fatigue Squatting Pain Step test CSA Function	Findings indicate that NMES is equally effective when delivered using mixed- vs. fixed-frequency pattern. This was a comparison between 2 types of NMES; with neither a CON nor a sham comparison, it is not possible to evaluate the effect of NMES. Short-term results
Callaghan and colleagues (2001)126 RCT N=16 enrolled; N=14 analyzed Included in SR131	PFPS 6 mo–3 yr NMES 1, experimental: simultaneous mixed frequency NMES 2, conventional: sequential mixed frequency	Electrodes: Size nr 2 channels Electrodes: on quads; exact location nr	NMES 1: Asymmetrical balanced biphasic PC Low-frequency background with superimposed pattern of high-frequency bursts 200 μs ON:OFF 10:50 s Amplitude max tolerable NMES 2: Asymmetrical biphasic PC Wk 1–4, 8 Hz×2 min, 35 Hz×20 min, 3 Hz×3 min; wk 5–6, 8 Hz×2 min, 45 Hz×20 min, 3 Hz×3 min 250–350 μs ON:OFF nr Amplitude nr No simultaneous voluntary contraction with NMES	NMES 1: 1 h/d (60 contractions) 7 d/wk 6 wk NMES 2: 1 h/d (60 contractions) Wk 1–2, 5 d/wk; wk 3–4, 3 d/wk; wk 5–6, 2 d/wk	Isometric and isokinetic ext torque: Biodex Muscle fatigue rate: EMG Pain: VAS Function: Kujala PFPS Score Step test Knee flex: max squat range Quads CSA: US scan @ 0, 7, 8, and 9 wk	Similar improvements: Strength Pain Function Step test Squat	Rationale was to improve both muscle fatigue (low Hz) and strength (high Hz). Findings indicated that NMES is equally effective when delivered using mixed sequential- vs. mixed simultaneous- frequency pattern. Small sample. No CON or sham group.

NMES=neuromuscular electrical stimulation; PFPS=patellofemoral pain syndrome; RCT=randomized controlled trial; SR=systematic review; HVPC=high-voltage pulsed current; Ex=exercise; CON=control; VM=vastus medialis; PC=pulsed current; nr=not reported; max=maximum; VAS=visual analog scale; prox=proximal; quads=quadriceps muscle; BID=2 times per day; flex=flexion; CSA=cross-sectional area; US=ultrasound; ext=extension; EMG=electromyography.