It seems that all but two of the included physical agents (MA and ultrasound therapy), exhibit statistically significant effects over placebo within 1–4 weeks, regardless of what doses and treatment procedures were being used. However, effect sizes for PEMF and SM, failed to reach the mean threshold for "minimal perceptible clinical improvement" for OAK as defined by Ehrich et al. . It cannot be ruled completely out that more studies may contribute to optimise PEMF treatment procedure and dosage, but at present MA, PEMF, US and SM cannot be recommended for rapid pain relief in OAK management.
For TENS, the above findings are at odds with previous reviews of TENS in chronic pain  and in chronic low back pain , but not in knee osteoarthritis .
The picture for acupuncture is mixed, and most studies with MA have been performed using fewer weekly treatment sessions than the other interventions. Consequently, the results at 4 weeks are similar to those of the placebo groups, while the effect at 8 weeks is statistically superior to placebo. In a systematic review of acupuncture reviews, it has been argued that the evidence in favour of acupuncture is weakened by lack of randomisation and lack of assessor or patient blinding . In this review, we have only included randomised and double-blinded (patient and assessor) trials, and the results are in line with a recent review of acupuncture OAK . However, the clinical relevance of the MA effect in OAK remains questionable, and the results infer that EA seems to be a better choice in OAK management.
For LLLT, a Cochrane review has found limited evidence in favour of LLLT in rheumatoid arthritis and inconclusive evidence in osteoarthritis . But we have previously pointed out that the findings in osteoarthritis could be caused by inherent methodological weaknesses  such as lack of adequate dose-response analyses. In line with the dosage recommendations from World Association for Laser Therapy, the findings above suggest that 904 nm is only effective with doses of 2–12 Joules and 830 nm with doses of 20–48 Joules when applied to 2–8 points over the joint capsule.
The small sample size of some trials on EA, TENS and LLLT may undermine the validity of our conclusions. It has been argued that evidence for most interventions lack sufficient statistical power to make valid conclusions . The Oxford pain research group suggests that reasonably robust conclusions can be be made from systematic reviews including 200 patients and/or more than 4 trials . Cochrane reviews offer positive conclusions for pharmacological interventions for pain based on the inclusion of 40 patients for neck pain  and 185 patients for OAK . The sample size for our total and subgroup analyses for optimal treatment for EA, TENS and LLLT met the criteria stated by the Oxford group (EA n = 242, LLLT n = 222, TENS n = 272). Nevertheless, we remain cautious in our conclusion until larger scale clinical trials are available to verify the results. Methodological trial quality also undermines review conclusions [36, 63], although the majority of trials on which our conclusions rest, were of acceptable quality.
The biological rationales for the observed effects seem somewhat clearer for EA, TENS and LLLT than for the interventions that demonstrated lesser effects. EA and TENS has been shown to inhibit ongoing nocicpetive transmission at a segmental level and that this is dose-dependent . The EA-trials included in the review delivered electrical stimulation with needles placed in the painful area, similar to that used for TENS. This is consistent with established physiological principles whereby stimulation in dermatomes and myotomes related to the pain are likely to elicit segmental analgesia mechanisms. It has been shown in experimental studies that electrical stimulation by both needle and skin electrode can produce similar analgesic effects . The observed similarities between TENS and EA in effect size and time-effect profiles after cessation of treatment, may be indices that similar physiological mechanisms are being induced by these two interventions. Adding the data from trials using acupuncture to trials using electrical stimulation in the form of EA, did not increase effect size over TENS to any appreciable extent.
During the last three years, controlled LLLT-trials have found dose-dependent anti-inflammatory effects under in vitro, in vivo, and in situ conditions [77, 78]. Another possible explanation for the observed positive LLLT effects may arise from local dose-dependent biostimulatory effects on cell activity which have been observed in controlled in vitro and vivo  trials with lower, but overlapping, dose intervals.
The value of standardising treatment procedures and dosage in the treatment with physical agents is highlighted by the finding that doses which work well in laboratory settings also can be extrapolated to induce better pain reduction in the clinical subgroups of EA, TENS and LLLT-trials with optimal treatment. But the heterogeneity of treatment procedures, application techniques and doses still call for careful interpretation of the results.
Until now, physical therapies have often been neglected in editorials and reviews of treatments for OAK [81, 82] and this may have resulted in the under-utilization of physical agents in OAK management . The safety of the physical therapies seems good as no serious adverse events were reported in the 36 RCTs reviewed. The advantage of physical agents is that they can be used in combination with drug therapy, thus reducing drug dosage and adverse effects. There is also some evidence that effects from adequately administered TENS, EA and LLLT remain clinically relevant even 1–2 months after the end of treatment. It may be difficult to directly compare the results of trials of physical agents with those of pharmacological interventions because of differences in the nature of the placebo's used in the trials.
In the pharmacological literature publication bias in favour of small trials with positive results has previously been detected. There seems to be no support for this tendency from asymmetry in the graphical plot . On the contrary, a small asymmetry towards publication bias in favour of small trials with negative results seems to be present for these physical interventions.
Exercise therapy, education and weight loss still remain the cornerstones of long-term OAK management , but our results suggest that EA, TENS and LLLT have potential to become useful adjuncts in OAK pain management.