Computed tomographic measurement of gluteal subcutaneous fat thickness in reference to failure of gluteal intramuscular injections.

OBJECTIVE: Casual observation of gluteal region fat thickness on computed tomography (CT) of the pelvis leads to the hypothesis that, in some individuals, intended intramuscular injections are not properly deposited in the gluteal muscle. We gathered and analyzed data to determine whether this hypothesis was true.
METHODS: CT scans of the pelvis were analyzed over an 18-day period in the fall of 2005. The thickness of gluteal region subcutaneous fat was measured in a standardized manner.
RESULTS: Measurement of gluteal region subcutaneous fat thickness was performed for 298 pelvic CT scans. There were 150 male subjects and 148 female subjects. The average gluteal fat thickness for female subjects was 33.2 mm, whereas the average for male subjects was 23.1 mm. Analysis revealed a significant difference in gluteal region fat thickness between male and female subjects. A 37-mm needle, allowing for 6-mm penetration of the gluteal muscle, would not have entered the gluteal muscle fibres in 81 of 148 female subjects (54.7%), in 21 of 150 male subjects (14%), and in 102 of the 298 total sample (34.2%). Analysis revealed a significant difference between male and female subjects with regard to gluteal muscle needle penetration. CONCLUSION AND RECOMMENDATION: An overall predicted failure rate of 34% was identified for intended gluteal intramuscular injections when the standard technique was used. This is important information for care providers who inject medications in the gluteal region. In a significant number of patients, the medications will be injected subcutaneously and not into the gluteal musculature, possibly altering the pharmacokinetics of the administered medication. An alternative injection site should probably be chosen to increase the success rate of intramuscular deposition of medications and vaccines in unselected adults.