In patients with hip fractures regional analgesic blocks are often useful.
A recent Cochrane review on nerve blockades in hip fractures, which included FNB and FIB, has shown high-quality evidence supporting a reduction in dynamic pain within 30 min of blockade. In this review the effect size was − 3,4 points on a scale from 0 to 10 . The cephalad spread of local anesthetic in FNB and FIB has been examined with magnetic resonance imagining. The ON is not widely covered. More importantly, the cephalad spread is unlikely to extend beyond the L5 level. Recent anatomical studies demonstrated that the articular branches from the FN, before innervating the hip capsule, enter the iliacus muscle at the L4–L5 levels and course deep to the psoas muscle and tendon between the AIIS and IPE. The AON courses deep to the medial aspect of psoas muscle around the L5 level, then it courses deep to the psoas around IPE to enter the anteromedial joint capsule [12, 13]. In contrast, the targets of the regional blockades described in our case series were the articular branches of AON and FN between AIIS and IPE. We are not able to affirm if the local anesthetic solution would spread medially enough to reach the plane between the pectineus and obturator externus muscles (subpectineal plane, SPP) where the articular branches of ON can be found. The SPP has been recently described by Nielsen et al.  as a target point for ON and its articular branches. Given the proximity of the SPP, it is conceivable that the local anesthetic may have spread to this plane. Anyway, dye injection studies are necessary to confirm this.
The median reduction of pain in our case series was 4,83 points in preoperative NRS at rest, and 6 points in dynamic state. Therefore, NRS was evaluated again 12 h after surgery, both in dynamic state and at rest. Interestingly, the patients in our case series presented different hip pathologies (intertrochanteric and subcapital fractures), and all of them reported significant preoperative pain relief and satisfactory postoperative analgesia. In addition, given that our technique targeted only the sensory branches, there was a potential motor-sparing effect compared with both the FIB and the FNB.
Nowadays there are no randomized controlled trials or other large-scale studies in literature regarding the PENG block. This is only a small case series and there are many limitations inherent to this type of study, such as danger of overinterpretation, lack of ability to generalize, publication bias and the retrospective nature of the design. But this type of publications also has some merits, such as the detection of novelties and generation of stimuli and hypotheses. There is room for improving the effect size of analgesia compared to the FIB and FNB, as discussed before. This case series shows a very impressive effect of this new blockade on the dynamic pain score and a good postoperative analgesia. This case series may help to consider a new approach of nerve blockades for patients with hip fracture with the better understanding of the anatomy for hip innervation and the planes where the nerves to the hip innervation run. We need more cadaveric studies, dye injection studies to confirm the spread of local anesthetics and randomized controlled trial to establish its efficacy, safety, and advantages over other regional analgesic techniques. Furthermore, in the near future, studies concerning optimal volume and type of local anestethics, any adjuvant drugs and particular populations, such as obese patients, will also be needed.