Appropriate techniques for deltoid intramuscular injections in Japanese nursing-home residents: A multi-centric observational study using ultrasonography

Objective: The appropriate technique for administering deltoid intramuscular (IM) injections in older populations with thin muscle layers remains unclear. This study aimed to ascertain the optimal needle length (ONL) and injection site for IM administration into the deltoid muscle by assessing the thickness of the subcutaneous fat layer and the deltoid muscle via ultrasonography. Methods: This study involved 151 nursing home residents (NHRs) from 4 facilities. Using ultrasonography, we measured deltoid muscle thickness and the subcutaneous fat layer at 3 standardized locations: 5.0, 7.5, and 10.0 cm below the acromion. Measurements were obtained with the transducer positioned perpendicular to the skin surface, both in the resting state and with the muscle-bunching technique (manual compression of the deltoid between both hands). ONL was determined from the measurement of the distance from the skin to the midpoint of the deltoid. Results: The subcutaneous fat layer was the thickest at 10.0 cm, followed by 7.5 cm and 5.0 cm (p <.001). The deltoid was thicker at the 5.0- and 7.5-cm points than at the 10.0-cm point (p <.001). The median ONL at the 3 subacromial points was 12.3, 12.8, and 12.1 mm, respectively. The muscle-bunching technique resulted in approximately double the thickness of the deltoid muscle layer. Conclusions: In Japanese NHRs, IM injection into the deltoid is deemed appropriate at distances of 5.0 and 7.5 cm below the acromion, utilizing a 16-mm needle. The muscle-bunching technique is recommended for underweight patients.