Ultrasound-Guided Biceps Femoris Short Head (BiFeS) Block: A Novel Regional Anesthesia Technique for the Posterolateral Knee.

Objective: We introduce a novel intervention for posterolateral knee pain termed the Biceps Femoris Short Head (BiFeS) Block, which targets the articular branches innervating the posterolateral aspect of the joint. We describe a two-part proof-of-concept study to validate the BiFeS block: A cadaveric study evaluating injectate spread and a retrospective case series assessing analgesic efficacy.

Methods: In the cadaveric study, 25 mL of dye solution was applied at the interface between the BiFeS and the lateral supracondylar line of the femur following bone contact. For the retrospective cases, we present five patients with posterolateral knee pain following total knee arthroplasty (TKA) who underwent a BiFeS block with 25 mL of 0.25% bupivacaine.

Results: In all cadaveric specimens, a distinct dye spread was observed deep to the BiFeS, extending both medial and lateral to the lateral supracondylar line and along the facies poplitea. In all specimens, the superior lateral genicular nerve and the lateral branch of the nerve to the vastus intermedius were stained. The anterior branch of the common fibular nerve was stained in 2 out of 6 specimens where it could be identified. In the clinical cases, the median(IQR) NRS score decreased from 6.5(6-7) pre-block to 3(2-3) post-intervention.

Conclusion: Our preliminary data demonstrate that the BiFeS block achieves complete blockage of the posterolateral knee capsule. This technique may serve as a complementary, motor-sparing regional anesthesia method, particularly for postoperative pain management following TKA. Advantages include a low risk of complications, avoidance of vascular and neural structures, feasibility in the supine position.