# Cadaveric analyses of injectate distribution patterns in ultrasound-guided rotator interval, dual-target, and posterior glenohumeral injections

## TL;DR

This study compares how different injection techniques spread dye in the shoulder, showing that each method targets specific areas, which can help guide treatment for shoulder conditions.

## Contribution

The study introduces a dual-target injection technique that reliably infiltrates the subdeltoid bursa and anterior capsule.

## Key findings

- Rotator interval and dual-target injections consistently stain the biceps tendon sheath and anterior capsule.
- Posterior glenohumeral injections most reliably stain the posterior capsule.
- Dual-target injections ensure subdeltoid bursal infiltration not seen in other techniques.

## Abstract

Intra-articular corticosteroid injection is a standard treatment for adhesive capsulitis and is commonly performed via the rotator interval or posterior glenohumeral approaches, with prior evidence favoring the former. Injectate distribution varies by technique. Additionally, a dual-target approach combining rotator interval and subdeltoid bursal injections has been proposed for subacromial impingement. This study compared dye distribution among rotator interval, dual-target, and posterior glenohumeral injection techniques.

This cadaveric study evaluated dye spread in 18 shoulders from nine embalmed cadavers. Three ultrasound-guided techniques were assessed: rotator interval injection (15 mL), dual-target injection (10 mL rotator interval + 5 mL subdeltoid bursa), and posterior glenohumeral injection (15 mL). Following the injection, systematic dissection was performed. Staining of the subdeltoid bursa, long head of the biceps tendon sheath, anterior glenohumeral capsule, and posterior glenohumeral capsule was graded as absent, partial, or extensive.

Extensive staining of the biceps tendon sheath and anterior glenohumeral capsule was observed in all shoulders receiving rotator interval or dual-target injections, whereas posterior glenohumeral injections showed inconsistent coverage of these structures. Reliable subdeltoid bursal infiltration occurred only in the dual-target group (5/6 shoulders). The posterior glenohumeral capsule was most consistently and extensively stained following posterior glenohumeral injection (6/6), with moderate coverage in the rotator interval and dual-target groups. Infraspinatus infiltration was uncommon and observed only after posterior glenohumeral injection.

The injection technique markedly influences shoulder injectate distribution. Rotator interval and dual-target approaches preferentially address anterior structures, the dual-target technique ensures subdeltoid bursal coverage, and the posterior approach most consistently infiltrates the posterior glenohumeral capsule. Technique selection should be guided by the predominant pathological target in adhesive capsulitis and related disorders.

Dual-target and rotator interval approaches reliably infiltrate the anterior capsule, making them suitable for adhesive capsulitis with biceps long head pathology, whereas the posterior glenohumeral approach primarily covers the posterior capsule and is less suitable for concomitant anterior shoulder disorders.

The injection technique determines the injectate distribution in the shoulder.Dual-target and rotator interval injections ensure anterior capsule infiltration.The posterior approach best targets the posterior capsule.

The injection technique determines the injectate distribution in the shoulder.

Dual-target and rotator interval injections ensure anterior capsule infiltration.

The posterior approach best targets the posterior capsule.