Assessment of gluteus maximus muscle area with different image analysis programs.

OBJECTIVE To determine the effectiveness of a percutaneous gluteal stimulation system (GSTIM) by comparing assessments of axial computed tomography (CT) scans for the pelvic area. DESIGN Comparing the measurements of the cross-sectional area (CSA) of the gluteus maximus muscle between raters and 2 image analysis programs. SETTING Retrospective axial CT scans of the pelvic area. PARTICIPANTS Men (N=9) with complete (below T6) spinal cord injury (SCI) and at least 2 years postinjury participated in the study (range, 29-75y; mean age, 51.8y). INTERVENTION Comparing gluteus maximus CSA before and after a period of GSTIM. MAIN OUTCOME MEASURE Measurements made by 2 expert and 2 nonexpert raters were used to compare the repeatability and reliability of measuring muscle CSA. The longitudinal study presented is from repeated CT scans obtained over a 2-year period for 1 representative participant who received a GSTIM system. RESULTS For repeatability, nonexpert raters measured a mean CSA of 35.2 cm2 (range, 20-45 cm2), while experts measured 21 cm2 (range, 10-35 cm2). A composite of all raters using the same program had SDs of 2.5 to 2.6 cm2 for a program available through the National Institutes of Health and 2.5 to 4.4 cm2 for a commercially available program. For reliability, differences between the 2 programs had mean differences in SD between 2.2 and 3.7 cm2. CONCLUSIONS The same rater and program (preferably the more reliable ImageJ) is recommended for the course of a longitudinal study. Otherwise, significant error would be introduced. Furthermore, significant increases in the CSA of gluteal muscle compared with preintervention (baseline) measurements were observed for the participant receiving GSTIM.