Background

Patellofemoral pain syndrome, commonly known as anterior knee pain, is characterised by short- or long-term pain in the front part of the knee or behind the kneecap. Muscle stimulation has been proposed as a treatment for this condition. This involves the use of a device that produces a muscle contraction by placing electrodes on the skin of the leg. Muscle stimulation is often used together with exercises and other treatments but can also be used on its own.

Results of the search

We searched the medical literature up to May 2017 and found eight studies reporting results for a total of 345 participants who had anterior knee pain for at least one month, and sometimes over several years. Most of the participants were female. The average age of participants in the studies ranged from 25 to 43 years. All the studies were small and had flaws that meant they were at risk of bias. There was very little evidence on longer-term outcome. The results of one study that reported on immediate pain after a single 15-minute session of muscle stimulation are not reported here as these are of questionable clinical relevance.

Key results

Each of the seven remaining studies tested one of three comparisons.

Four studies compared a multiple-session muscle stimulation programme combined with exercise over several weeks with exercise on its own for the same period. All participants in two studies had adhesive tape applied across their knee cap, with ice also being applied in one study. We found very low-quality evidence that muscle stimulation with exercise may slightly reduce knee pain at the end of a treatment period of between 3 and 12 weeks better than exercise alone. However, very low-quality evidence did not show an effect on knee function. None of the studies reported on harms such as muscle fatigue and discomfort. There was very little useful information on longer-term effects.

One study compared muscle stimulation lasting four hours each day for four weeks with exercise. Very low-quality evidence showed no important difference between the two groups in knee function at the end of the four-week treatment. Of note is that the duration of muscle stimulation is much longer than used nowadays.

Two studies compared different types of muscle stimulation. Very low-quality evidence showed no important differences at the end of the six-week treatment programme between the different types of muscle stimulation.

Quality of the evidence

The overall quality of the evidence for all reported outcomes was very low. This means that we are very uncertain about the findings of these studies.

Conclusions

We found insufficient evidence to inform on the role of neuromuscular electrical stimulation for treating people with anterior knee pain. Further research is needed.