Table 9.

Summary of the Literature and Recommendations for Use of NMES in PFPS

Indication	Parameter Recommendations	Outcome Measures Demonstrating Benefit
PFPS	Electrode placement: No standardized location reported in the literature. Recommended placement is based on a critical review of the literature: 2 electrodes, 1 over the rec fem and vastus intermedius muscle bellies, the other over the VM.122,123 Recommendation is to position electrodes in line with the orientation of the muscle fibres.124,125 Limb position: No standardized location reported in the literature. From a clinical perspective, it is advisable to avoid the portion of the ROM that is provocative – i.e., position within the pain-free range. NMES waveform: low-frequency biphasic PC122,123,126,127 Frequency: 35–50 Hz122,123,126,127 Pulse duration: 250–500 μs122,123,126,127 Current amplitude: individual max tolerated intensity122,123,126–128 Work–rest cycle: ON:OFF 6–10:10–50 s; OFF times should be consistent with the treatment goals: shorter rest period (≤10 s) for endurance training, 30–50 s for strengthening purposes122,123,126–128 Treatment schedule: 12–15 contractions per session, as is typically reported in NMES literature relating to quads weakness98,99,102,103,108–110,112 Session frequency: ideally, 3 d/wk over 4–6 wk127	✓ Reduction in pain (VAS)123,126,128 ✓ Increased force-generating capacity (EMG)127 ✓ Deactivation of VL127
Rationale for recommended NMES protocol	In accordance with evidence for the importance of selective strengthening of VM,129 electrode placement should target VM and either rec fem and vastus intermedius or femoral nerve. Other recommended parameters are in accordance with those sufficient to elicit a strengthening effect. In contrast, using a short rest period and high number of reps (e.g., ≥60 reps/d) is thought to target muscle endurance rather than strength.130 Effects of an endurance-type protocol were shown by delayed onset of quads fatigue in PFPS using 35 Hz (main frequency) and 60 contractions daily, 7d/wk, for 6 wk.123,126
Physiological effect of NMES	NMES can assist in recruitment of motor fibres of VM, which are typically relatively weaker in PFPS than are other muscles of the quads mechanism. NMES activates sensory fibres; this may also be a factor in reducing PFPS pain.
Critical review of research evidence	Effectiveness has been examined in 1 SR131 consisting of 12 RCTs, of which 4 involved NMES for PFPS. The review was descriptive in nature. Authors of the SR concluded that combined NMES+Ex provided no added benefit than Ex alone for strengthening quads and noted that because Ex was part of the intervention, it was not possible to determine the possible benefits of NMES alone. In drawing conclusions, however, the authors did not consider whether NMES parameters in any of the RCTs were optimal for strengthening VM; potential parameters contributing to the lack of benefit include low frequency,122,123,126 low pulse charge,128 high number of daily contractions,122,123,126 and, in 1 study, use of an insensitive measure to assess change in muscle strength (manual muscle test).128 Interpretation of the literature is further complicated by comparison between 2 different forms of stimulation, sometimes without a sham group.126 Increased strength was shown in 2 RCTs that compared mixed versus fixed NMES frequency and low versus high NMES frequency.123,126These results cannot be interpreted as strong evidence because there was no CON group. NMES was applied for 6 wk without Ex in a controlled cohort study of 10 subjects with PFPS. The finding of increased force generation of the VM and decreased activation of VL using EMG as an outcome measure demonstrates the potential benefit of NMES.127 Feasibility has been demonstrated. No adverse effects have been associated with NMES in this population. The literature does not indicate that NMES is not effective in the management of PFPS; this has not been conclusively demonstrated.

NMES=neuromuscular electrical stimulation; PFPS=patellofemoral pain syndrome; rec fem=rectus femoris muscle; VM=vastus medialis; ROM=range of motion; PC=pulsed current; max=maximum; quads=quadriceps muscle; VAS=visual analog scale; EMG=electromyography; VL=vastus lateralis; reps=repetitions; SR=systematic review; RCT=randomized controlled trial; Ex=exercise; CON=control.