Ultrasound-guided gastrocnemius plane block: anatomical validation and clinical feasibility assessment

As a feasibility study, this study primarily aimed to assess the feasibility of conducting a future randomized controlled trial (RCT) on gastrocnemius plane block (GPB), including evaluation of the clinical application and safety profile of the technique.

The study comprised two phases: (1) anatomical validation with methylene blue staining in 8 supra-knee amputated limbs, followed by (2) clinical feasibility study in 20 patients undergoing foot surgery. This anatomical study was to assess the degree and length of staining in sciatic nerve branches. The clinical study evaluated the onset and duration of sensory block, motor function of the tibial and common peroneal nerves, the anatomical relationship between the popliteal artery and tibial nerve, and postoperative sensory and motor abnormalities.

The cadaveric study exhibited full or strong staining of the medial and lateral sural cutaneous nerves, common peroneal nerve and tibial nerve with methylene blue across all 8 specimens. The clinical study exhibited that the median onset time of sensory blockade for the tibial nerve, common peroneal nerve, superficial and deep peroneal nerves at Level 1 were all ≤ 20 min, and for Level 0 sensory blockade, the median onset time were all ≤ 40 min. Seventeen patients experienced full onset of sensory block in all branches of the sciatic nerve within one hour, whereas three patients experienced hypoalgesia within one hour and achieved full onset within 70 min. In all patients, both the tibial nerve and the common peroneal nerve exhibited motor block at 4 h postblock. At 32 h, all patients had no motor block in toe movements. Among the patients, the tibial nerve was located in the 9-12 o'clock arc (anterior-medial to the PA) in 10 patients (50%), at 9 o'clock (medial to the PA) in 5 patients (25%), at 12 o'clock (anterior to the PA) in 3 patients (15%), at the 6-9 o'clock arc (posterior-medial to the PA) in 1 patient (5%), and at 6 o'clock (posterior to the PA) in 1 patient (5%). One month after surgery, telephone follow-up revealed no sensory abnormalities or motor dysfunction in any patient.

Ultrasound-guided gastrocnemius plane block has the potential to offer a new postoperative analgesic option for foot and ankle surgeries in clinical settings. The findings from this feasibility study provide critical information for the design of subsequent definitive trials. Future large-scale randomized controlled trials (RCTs) can be conducted to confirm the efficacy of the GPB.