ORIGINAL ARTICLE Assessment of Gluteus Maximus Muscle Area With Different Image Analysis Programs Gary A. Wu, MS, Kath Bogie, DPhil ABSTRACT. Wu GA, Bogie K. Assessment of gluteus maximus muscle area with different image analysis programs. Arch Phys Med Rehabil 2009;90:1048-54. 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 35.2cm 2 (range, 20 – 45cm 2 ), while experts mea- sured 21cm 2 (range, 10 –35cm 2 ). A composite of all raters using the same program had SDs of 2.5 to 2.6cm 2 for a program available through the National Institutes of Health and 2.5 to 4.4cm 2 for a commercially available program. For reli- ability, differences between the 2 programs had mean differ- ences in SD between 2.2 and 3.7cm 2 . 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 intro- duced. Furthermore, significant increases in the CSA of gluteal muscle compared with preintervention (baseline) measure- ments were observed for the participant receiving GSTIM. Key Words: Electric stimulation; Rehabilitation; Spinal cord injuries. Published by Elsevier Inc on behalf of the American Con- gress of Rehabilitation Medicine. M USCLE ATROPHY IS CAUSED by paralysis of mus- cles in patients with complete SCI as a result of loss of the ability to communicate command signals from the central nervous system to muscles below the level of injury. Rapid widespread loss of muscle mass has been found to occur in the first 6 weeks after SCI 1 and continues for up to 18 months postinjury before the muscle mass eventually plateaus. Muscle atrophy leads to an average of 45% to 80% reduction in muscle CSA after SCI. 2 An estimated 20% to 30% of these patients have a history of pressure ulcers by 5 to 10 years postinjury. 3,4 The prevalence, together with high economic and sociologic costs of pressure ulcers, demonstrates the importance of iden- tifying risk factors, preventing pressure ulcer occurrence, and developing cost-effective interventions. The finding that a pre- vious incidence of pressure ulcer is the most significant factor in predicting development of future pressure ulcers suggests that preventive methods must be made a priority. 5 The use of GSTIM can provide a means for varying the pressure under bony prominences and minimize the loss of muscle bulk. While sitting, GSTIM can contract 1 side of the buttocks at a time, simulating weight-shifting strategies and redistributing pressure. 6,7 Tissue viability is improved when mechanical occlusion of blood flow is alleviated, increasing blood and lymph flow. Additionally, the repeated rhythmic muscle contractions may act as a pump, increasing oxygen supply in the muscle tissue. 8,9 Longer-term studies have shown that continued use produces an increase in weight-shifting efficacy. 10 Minimizing the loss of muscle bulk also decreases the risk of pressure ulcer development. It has been shown that electrical stimulation of paralyzed muscles affected by SCI can increase muscle bulk, 11 condition the muscle, and decrease fatigability. 12 Previous studies have shown an increase in gluteal lean muscle mass after 6 months of stimulation in patients with acute SCI. 11 CSA measurements of stimulated muscle were used as an indication of the effectiveness of stimulation. The primary goal of the current study was to evaluate 2 image analysis techniques in CSA measurements of the gluteal region anatomy. The hypothesis was that measurements from 2 different image analysis programs and different raters were repeatable and reliable. The secondary goal was to determine changes over time in gluteal muscle CSA with use of the GSTIM. Because of the long-term nature of the study, it was also important to minimize the number of scans and confine them to the specific area of interest in order to minimize radiation exposure. CT imaging techniques met these goals and minimized the risk of compromising the GSTIM. From the Departments of Biomedical Engineering (Wu) and Orthopaedics (Bogie), Case Western Reserve University; and Cleveland Functional Electrical Stimulation Center, Louis Stokes Cleveland Department of Veterans Affairs Medical Center (Wu, Bogie), Cleveland, OH. Supported by the Veterans Administration Rehabilitation Research and Develop- ment Service (grant no. B4664). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organi- zation with which the authors are associated. Reprint requests to Kath Bogie, DPhil, Dept of Orthopaedics, Case Western Reserve University, 2109 Adelbert Rd, BRB 336, Cleveland, OH 44106, e-mail: kmb3@case.edu. 0003-9993/09/9006-00760$36.00/0 doi:10.1016/j.apmr.2008.12.009 List of Abbreviations CSA cross-sectional area CT computed tomography GSTIM percutaneous gluteal stimulation system MRI magnetic resonance imaging SCI spinal cord injury 1048 Arch Phys Med Rehabil Vol 90, June 2009