Does obesity prevent the needle from reaching muscle in intramuscular injections?

This paper is a report of a study to measure subcutaneous tissue thickness at the dorsogluteal and ventrogluteal sites and to determine optimal needle length for dorsogluteal and ventrogluteal intramuscular injections in adults with a body mass index of more than 24.9 kg/m2.

Problems can arise if drugs designed to be absorbed from muscle are only delivered into subcutaneous tissue. Increasing obesity in all developed and many developing countries makes this an increasing concern.

Ultrasound measurements were made of the subcutaneous tissue of overweight, obese and extremely obese people at the dorsogluteal and ventrogluteal sites with the probe held at a 90 degrees angle to the plane of the injection site. Subcutaneous tissue thickness was measured in 119 adults whose body mass index was >or=25 kg/m2. The data were collected in 2005-2006.

Mean subcutaneous tissue thickness at the dorsogluteal site was 34.5 mm for overweight adults, 40.2 mm for obese adults and 51.4 mm for extremely obese adults, and at the ventrogluteal site was 38.2 mm for overweight adults, 43.1 mm for obese adults and 53.8 mm for extremely obese adults.

Intramuscular injections administered at the dorsogluteal site in 98% of women and 37% of men, and at the ventrogluteal site in 97% of women and 57% of men, would not reach the muscles of the buttock. A needle longer that 1.5 inches should be used in women whose body mass index is more than 24.9 kg/m2, the dorsogluteal site may be used in all overweight and obese men, and the ventrogluteal site may be used in overweight men only.