Ultrasound-guided injection of the rotator interval synovial lining: A cadaveric validation

Ultrasound-guided injections of the rotator interval (RI) are commonly performed in clinical practice targeting the anatomical interface between the long head of the biceps tendon (LHBT) and the biceps reflection pulley (BRP). Herewith, cadaveric validation of the exact placement of the injectate inside the synovial compartment of the RI is lacking in the pertinent literature. The purpose of this study was to investigate the correct placement and the spread patterns of different dye volumes within the synovial space of the RI of the shoulder in cadaveric samples.

The RI of both shoulders of two cadavers (1 male, 1 female, Thiel's embalming technique) was injected with blue-colored dye under ultrasound guidance, using the in-plane technique and lateral-to-medial approach. Targeting the LHBT-BRP interface, 0.5 mL and up to 1.5 mL of blue dye were injected, respectively, in both cadavers. The bursal tissue overlying the RI was also injected in both cadavers using 1.0 mL of yellow dye. Subsequently, a layer-by-layer anatomical dissection was performed to test the placement and spread of the blue dye within the synovial space of the RI.

The blue dye was correctly placed within the synovial sheath of the RI in all cadaveric shoulders (4/4), and no communication with the overlying bursal cavity was identified. A distal spread of the dye around the extracapsular portion of the LHBT was observed in all cadaveric samples. Notably, proximal spread of the blue dye inside the (capsular space and the synovial cavity of the) glenohumeral joint was identified only in shoulders which were injected with 1.5 mL of volume (2/4). The anatomical exploration of the RI demonstrated the presence of a double-layer synovial lining with an inner lumen and a fenestrated proximal edge located below the BRP. Three-dimensional and multiplanar reconstruction computed tomography (CT) scans demonstrated a mean value of 32.5 mm for the length of the capsular tunnel (CaT) of the LHBT.

Under ultrasound guidance, the double-layered synovial sheath of the shoulder RI can be injected. The mixture may spread distally, around the extracapsular segment of the LHBT, and proximally inside the capsulosynovial space of the glenohumeral joint.

Basic Science, Level V; Cadaveric/Anatomy Study.