The 5-in-2 Ankle Block for Outpatient Foot Surgery: the FIT Block Study

Foot surgery is frequently performed using regional anesthesia (RA). The ultrasound guided popliteal sciatic nerve block seems the gold standart technique. Improved ultrasound resolution and the development of early rehabilitation in outpatient surgery have led to the development of more distal RA techniques, at the ankle.

The ankle blocks are well described and provide similar anesthetic quality and surgical comfort than the popliteal sciatic nerve block. However, it has been reported that successful surgical anesthesia with ankle block was not reached in 14% to 16% of patients scheduled for hallux valgus surgery. Interestingly, these distal blocks preserve extrinsic motor function of the foot, enabling the patient to ambulate while minimizing the risk of falling.

Distal blocks using repeated punctures close to the periostum are painful during the RA performance. Sensitivity is greater at limbs extremities, as evidenced by Penfield's homonculus and the size of the brain surface devoted to extremities. As a result, it is frequently necessary to sedate the patient during the regional anesthesia procedure. The position of the ankle tourniquet may also require sedation if the surgery is to be prolonged.

For foot surgery under ankle blocks, it is necessary to anesthetize all distal branches of the sciatic nerve, i.e. the superficial and deep fibular nerves, the tibial nerve and the sural nerve. The saphenous nerve, coming from the lumbar plexus, is anesthetized with an ankle skin infiltration.

In the classical approaches, the tibial nerve is blocked at the medial aspect of the ankle, in the medial retro-malleolar region, posterior to tibial vessels. The sural nerve is blocked superficially in the lateral retro-malleolar region, between the calcaneal tendon and the lateral malleolus. The deep fibular nerve is located on the anterior surface of the instep, next to the periosteum, particularly painful when encountered by the needle. The superficial fibular nerve is located on the anterolateral aspect of the leg, where it is already divided into its two distal branches. Sometimes not visualized on ultrasound, these branches can be blocked by subcutaneous infiltration. This presents a risk of failure due to the anatomical variability of their emergence, explaining the risk of sensory blockade failure, as well as a theoretical risk of accidental injury during infiltration.

Optimized ultrasound guided approach for the FIT Block will be used, based on optimal nerve anatomical locations. A one puncture proximal approach for the fibular nerves is used, while maintaining the benefit of preserved extrinsic motricity. Another one puncture approaches the sural nerve laterally, after the block of the tibial nerve during the same puncture and then the subcutaneous infiltration of the saphenous nerve. An anatomical proof of concept study has been done before the exploratory clinical study.

These approaches permit a surgical anesthetic block for foot surgery using 2 punctures (instead of 5) with a single patient's body position, compatible with sedation.