When compared with other treatment modalities, most studies compared PNE with other needle interventions like dry needling, corticosteroid injections or placebo needling.

It's important to highlight that dry needling was often applied in different manners compared to PNE: Lopez-Royo et al50 applied both PNE and dry needling directly over the injured area (patellar tendon) following the same protocol blinded to the patient; Lopez Martos et al.27 and Al Boloushi et al49 applied both PNE and dry needling in the muscle trigger points; and Rodriguez Huget13,40 applied PNE at the injured tendon and dry needling at the trigger points of the related muscles. For this reason, the comparison between PNE and dry needling must be interpreted with caution since they are often not targeting the same tissue structures and may cause different therapeutical responses. One author31 compared the effects of PNE on different areas of the supraspinatus (tendon, muscle trigger points or combined), finding better results for the combined group.

Three studies have compared PNE with placebo needling27,47,50 with opposing outcomes. Lopez-Royo et al50 reported no differences between PNE and placebo needling. In this study, a sham needle was placed on the skin simulating the treatment procedure with the electrical current device turned off next to them and the therapist insisting on the whole therapeutic experience beyond the mere tactile stimulation. This is the only study in which blinding was assessed post-intervention and most patients included in the sham needle group could not guess what group they belonged to, while all patients included in the intervention group could guess they were receiving PNE. However, they did not show superior outcomes compared to the sham needling group. Two other studies showed superior outcomes with PNE compared to sham needling. Lopez-Martos et al27 designed a double-blinded study (only the principal investigator was blinded, not the therapist) applying a superficial skin puncture with the plastic cover in the sham needling group, and with the electrotherapy device simulating the same noise as with the PNE application. Finally, Fernandez-Rodriguez et al47 blinded both the patient and the therapist, performing the same needle intervention in both groups but turning off the ultrasonographic monitor so that the therapist could not see if an electrical current was being applied or not.

One study compared PNE with corticosteroid injection for plantar heel pain (Iborra-Marcos [48]), finding better outcomes in the PNE group for injury-related function, but no differences in pain or tissue structure in mid and long term.

Only eight studies used PNE in isolation for the intervention group. The vast majority combined PNE with different types of active exercise interventions; eccentric exercises,44,12,10,46,25,40,13,21,20,50 isoinertial strength protocols,45 stretching,12,49 rehab and reconditioning program17 or manual therapy combined with active physical exercise.29

Five studies compared PNE with active interventions. PNE showed better improvements in pain when used in combination or compared with strength only, especially in the mid-term (1-3 months), but this did not reflect in a better injury-related function for most studies except Arias-Buria.30 It's important to remark that the studies that compared PNE with strength interventions were applied in different pathologies and body regions for both upper and lower limbs: shoulder rotator cuff tendinopathy,29,30 patellar tendinopathy,46 soleus chronic injury21 and adductor enthesopathy.25 Strength protocols also differed between studies: twice a day, 3 sets of 12 repetitions for 4 to 5 weeks29,30; 3 sets of 15 repetitions (frequency not reported)46; 3 sets of 15 repetitions, 4 days a week for 4 weeks after dancing classes21; or a progression of exercises from isometric to eccentric to isoinertial eccentric.25

Since most studies targeting tendons combined PNE with different kinds of active exercise interventions (which remains the gold standard for tendinopathy management52,53), it's difficult to attribute all improvements to PNE, but it may be considered as an adjunct for pain management in some cases.

A recent systematic review by Gomez-Chiguano et al (2021),54 found moderate evidence of a positive effect of PNE on pain and pain-related disability in short, mid and long term for musculoskeletal conditions. However, the current body of evidence is scarce and difficult to interpret due to the differences in the way pain is measured across studies.

Different pain domains have been used, alone or in combination: maximum pain, minimal pain, average pain, pain at rest, pain on palpation, pain with muscle contraction, pain at work, pain during daily activities, pain during sport activities or pain with movement are some examples used in the studies included in this review. Three studies26,12,29 also measured the pressure pain threshold at the affected area using an algometer. Since different approaches were used to measure pain changes, and pain is subjective, it's difficult to establish clear comparisons between studies.

However, the best overall effects of PNE in our review were found for the pain domain, especially in shoulder-related tendinopathies at different time points.30,31,29,40 For other pathologies like plantar heel pain the results were conflicting: Fernandez-Rodriguez et al.47 reported a larger pain decrease with PNE compared to a placebo puncture in short, mid, and long term, while Al Boloushi et al49 and Iborra-Marcos48 didn't find any difference when PNE was compared to corticosteroid injection or dry needling. For patellar tendinopathy the results were conflicting as well; Abat46 reported superior effects of PNE combined with strength compared with strength only in the mid-term, but Lopez-Royo et al.50 reported PNE was not superior to dry needling or sham needling in mid and long term. For other pathologies, positive outcomes in terms of pain were found for temporomandibular joint dysfunction, epicondylalgia and soleus chronic injury, while conflicting or not superior outcomes were found for whiplash syndrome and adductor enthesopathy. Overall, better results on pain were found in short and mid-term (up to 3 months) compared to long term (more than 3 months).

Improvements in injury-related function with PNE were reported for subacromial pain by Arias-Buria et al.,30 compared to strength training at short and mid-term, and for plantar heel pain compared to sham needling47 and corticosteroid injections48 at different time points. However, some studies reported PNE did not have a superior effect on injury-related function compared to other treatment modalities or control groups for plantar heel pain,49 patellar tendinopathy,46,50 whiplash syndrome,26 soleus chronic injuries21 and adductor enthesopathy.25 For non-comparative studies there are also conflicting findings, with no improvements reported for patellar tendinopathy10,45 and positive effects found in achilles tendinopathy20 and groin pain function.24

However, functional scales may not necessarily reflect specific injury function in the same manner for different injury types. For example, VISA-P and VISA-A (used in all patellar and achilles tendon studies included in this review) are the gold standard for tendinopathy, while DASH (Disability of arm, shoulder, and hand) and SPADI (Shoulder Pain and Disability Index) (used in some rotator cuff tendinopathy and epicondylalgia studies) are not pathology-specific but general upper body functional scales.

As a summary, while there is evidence of a positive effect on PNE on pain, there is inconclusive evidence about the effectiveness of PNE for improving injury-related function.

Structural changes were measured by ultrasound in four comparative studies in patellar tendon,44 lateral epicondylalgia12 and plantar fasciitis,47,48 but no positive effects after PNE treatment were found.

Only Fernandez-Rodriguez et al47 documented a statistically significant decrease in plantar fascia thickness compared to the control group at 6 months. However, the authors acknowledged that a 0.3mm decrease may lack true relevance since changes below 0.7mm can be attributed to the intra-rater typical error.55 Other case series studies have reported improvements in tissue structure in patellar tendon12 and rectus femoris,17 but it's difficult to attribute those effects to PNE in the absence of a control group.

We can conclude that there isn't enough evidence to support the effect of PNE on promoting structural tissue changes.

Two RCT studies measured changes in range of motion for shoulder,31 and temporo-mandibular joint (TMJ)27; two studies assessed patient-reported perception of improvement or success,12,29 and two reported the patient satisfaction with the technique.10,45

For range of motion, PNE seems to improve shoulder mobility when applied in the infraspinatus muscle and tendon combined,31 and the same was observed for the TMJ when applied at the lateral pterygoid muscle.27 However, the small sample size of these studies and the magnitude of changes observed should prevent from extrapolating these effects to other pathologies and applications of the technique.

Between 79 and 88% of the subjects reported high satisfaction with the technique beyond 3 months,10,45 however no comparison can be made as there was no control group for these studies. A similar thing happens with the perception of success, which is reported as excellent by all patients in a case series study12 without a control group. Regarding the perception of improvement, more patients reported moderate to large improvements at 3 and 6 months in the PNE group compared with a control group in a shoulder RCT.29

Since there are many methodological limitations related to the use of subjective measures in low quality studies with small sample sizes, no clear conclusions can be extracted about the general effects of PNE in the patient perception of improvement and satisfaction.