Injection granulomas. Intramuscle or intrafat?

OBJECTIVES: Intramuscular injection is a commonly used route of parenteral drug administration. We studied the fat vs muscle location, the depth of calcified buttock granulomas, and the thickness of subcutaneous fat. Data were assessed with respect to the length of a needle commonly used in intramuscular buttock injections. DESIGN: Three hundred thirty-eight sequential pelvic computed tomographic scans were studied. Subcutaneous fat thickness was measured for each patient at the upper outer quadrant of the buttock. The location and depth of each calcified granuloma were also recorded. SETTING: Tertiary care academic teaching hospital. RESULTS: One hundred sixty-four calcified granulomas were found in 67 patients. One hundred fifty-two of these granulomas were in fat and 12 were in muscle; this was statistically significant using a single-sample binomial distribution (P < .001;95% confidence interval, 0.04 to 0.13). The mean (+/- SD) subcutaneous fat thickness at the upper outer quadrant of the buttock was 5.0 +/- 1.9 cm, with female patients having a mean subcutaneous fat thickness of 5.7 +/- 1.8 cm vs 4.4 +/- 1.7 cm for male patients. CONCLUSIONS: The finding that buttock subcutaneous fat thickness exceeds the length of the most commonly used needle for intramuscular buttock injection (3.8 cm), together with the preponderance of calcified granulomas found in the fat of female patients, suggests that the currently used injection technique may not be therapeutically optimal. We suggest that longer needles be used for intramuscular buttock injections in adults.