Table 11.

Summary of the Literature and Recommendations for Use of NMES in Knee OA

Indication	Parameter Recommendations	Outcome Measures Demonstrating Benefit
Knee OA	Electrode placement: large electrodes placed on quads muscle belly proximally on rec fem and distally on VM, VL, or both135–138 Limb position: sitting; hip flexed to 90°, knee flexed 60–90° 135,136,138 NMES waveform: low-frequency biphasic PC135–139 Frequency: 50 Hz135–139 Pulse duration: 250–300 μs135–140 Current amplitude: individual max tolerated intensity135,138,140 Work–rest cycle: ON:OFF 10:50 s (1:5 ratio)135,137,139 Treatment schedule: 15–20 contractions with Ex135–137,139 Session frequency: 3 d/wk, 4–8 wk135–140	✓ Strength (OHAUS dynamometer, Kin-Com, 1 RM, 10 RM)136,139,140 ✓ Improved self-reported function (WOMAC, SF-36)135–137,140,141 ✓ Improved function (SCT, 6MWT, 25-metre walk test, TUG)135,136,138–142 ✓ Pain (WOMAC)136
Rationale for recommended NMES protocol	NMES parameters for knee OA vary in the literature. A frequency of 50 Hz was used in 5 studies in Table 12; it was combined with an ON:OFF duration of 10:50 s in 3 studies and of 10:10 s or 10:30 s in 2 studies. Muscle strength increased in 3 of 4 studies that measured strength.136,139,140 Function and endurance increased in 3 (1 a marginal effect) of 4 studies that measured endurance.135,136,138 Pain decreased in 4 of 6 studies that measured pain.136–138,140 The recommended protocol is based on 5 studies.136–140 A further study used AC at 50 Hz burst rate with no resulting benefit for strength, pain, or function. This result may be due to using a protocol that consisted of a low number of contractions/wk (30) with neither supervised volitional Ex nor a self-management programme (e.g., home Ex, ROM).141 In contrast, NMES using 45 contractions/wk combined with Ex improved quads activation and strength after knee surgery.143 NMES using max tolerated amplitude at each session appears to have been the most effective. In contrast, amplitude, increased gradually up to 40% of MVIC over a 9-wk treatment period, increased strength but not more so than intensive Ex.136 A study that used an endurance type of protocol (25 Hz, 5:5 ON:OFF, 180 contractions 3 d/wk, max tolerated amplitude) showed increased strength and function.140 This protocol might be an alternative to the one recommended earlier, but additional study of this protocol is needed. Patterned NMES is not recommended because the single study using this approach showed results for the experimental groups that were not better than sham; furthermore, within-group benefits for the experimental group were seen at some measurement intervals but not others.142
Physiological effect of NMES	NMES can cause beneficial adaptations mediated by muscular and neural mechanisms. Tetanic contractions elicited by pulses of high intensity and short duration induce a high metabolic stress in the muscle, contribute to the reversal of inadequate motor unit recruitment, and improve the maximal capability of the neuromuscular system through increased force-generating capacity of the muscle and also through intensified voluntary activation.5
Critical review of research evidence	We reviewed the individual RCTs identified by our search protocol as well as 2 recent SRs.144,145 1 of the SRs examined NMES specifically for quads strengthening in elderly people with knee OA.144 6 studies met the criteria; although a meta-analysis was not possible, the authors stated that a best-evidence analysis showed moderate evidence in favour of NMES alone or combined with isometric quads Ex for strengthening. The literature on NMES in knee OA has some limitations. In some cases, randomization methods were not fully described, sample size was not calculated, or observed power was not reported. Some studies had high unexplained drop-out rates.135,138,140 Studies can also be criticized for risk of bias because subjects and therapists were not blinded to group allocation. This will almost always be the case in RCTs involving NMES because it is difficult to design sham NMES: Electrical current at amplitude less than contraction threshold (i.e., TENS-type current) would not suffice because TENS has been shown to reduce pain in knee OA, which might in turn affect function and quality of life. Interpretation of the literature is complicated by the use of a variety of NMES parameters and outcome measures. A recent large RCT135 showed significant effect of NMES on functional outcomes. Feasibility has been demonstrated. No adverse effects have been associated with NMES in this population.

NMES=neuromuscular electrical stimulation; OA=osteoarthritis; quads=quadriceps muscle; rec fem=rectus femoris muscle; VM=vastus medialis muscle; VL=vastus lateralis muscle; PC=pulsed current; max=maximum; Ex=exercise; RM=repetition maximum; WOMAC=Western Ontario and McMaster Universities Osteoarthritis Index; SF-36=Short Form (36) Health Survey; SCT=stair-climbing test; 6MWT=6-min walk test; TUG=timed up-and-go test; AC=alternating current; ROM=range of motion; MVIC=maximum voluntary isometric contraction; RCT=randomized controlled trial; SR=systematic review; TENS=transcutaneous electrical nerve stimulation.