Sonographic Location of Distal A1 Pulley by Means of a Bony Acoustic Landmark on the Proximal Phalanx: An Anatomic Study

Abstract

To identify the anatomic relationship between the distal extent of the A1 pulley and the distalmost insertion point of the palmar plate into the base of the proximal phalanx at a metaphyseal bony ridge, the "P1 peak" (P1P), which is a bony acoustic landmark easily identifiable on sonography of the finger. We studied 48 fingers (no thumbs) from 12 fresh frozen cadavers with high-resolution ultrasound. A 20-gauge hypodermic needle was directed perpendicular to the long axis of the tendon sheath along a plumb line drawn at the level of the bony flare of the proximal metaphyseal-diaphyseal junction of the proximal phalanx, or the P1P, under high-resolution ultrasound guidance. Dissection was then performed, and the distance of the needle barrel and the actual distance of the P1P from the distal edge of the A1 pulley were recorded. The study demonstrated that accurate placement of the needle within 1 mm of the actual P1P was possible using ultrasound guidance and that the P1P was within 1 mm of the distal edge of the actual A1 pulley in all specimens studied. In all the specimens studied, we found that the P1P may be used as a clearly identifiable sonographic reference landmark to identify the distal extent of the A1 pulley. Using the P1P landmark as a guide to judge the completeness of ultrasound-guided percutaneous trigger finger release may reduce the risks of incomplete distal release and inadvertent release of the A2 pulley.