3D anatomy and deformation of the seated buttocks.
OBJECTIVE
To describe the 3D anatomy and deformation of the buttocks during sitting.


METHODS
The buttocks of 4 able-bodied individuals and 3 individuals with spinal cord injury were scanned sitting in a FONAR Upright MRI. T1-weighted Fast Spin Echo scans were collected with the individuals seated on a custom wheelchair cushion to unload the ischial tuberosities (ITs) and seated on a 3 inch foam cushion. Multi-planar scans were analyzed, and the muscle, bone and adipose tissue was manually segmented for 3D rendering and analysis of the quantity, geometry, and location of tissues.


RESULTS
The gluteus maximus was positioned lateral and posterior to the IT, covering the inferior portion of the IT for only 2 able-bodied participants. Adipose thickness directly under the IT did not differ by diagnosis, nor did it have a consistent response to loading. However, the envelopment of the IT by the surrounding adipose tissue was much greater in two of the participants with spinal cord injuries. These two subjects also had the most curved skin surface as the tissue wrapped around the IT. Tissue strains around the ischium were most visible in the adipose and connective tissue. The gluteus maximus displaced and distorted upwards, posterior and lateral, away from the inferior IT.


CONCLUSIONS
Multi-planar imaging is necessary to investigate anatomy and deformation of the buttocks. 5 out of 7 participants did not sit directly on muscle. The tissue beneath their ITs was predominantly composed of fat and connective tissue, suggesting that these tissues might be most vulnerable to injury.
School of Applied Physiology, Georgia Institute of Technology, 490 10th Street NW, Atlanta, GA 30318, USA. Electronic address: sharon.sonenblum@coa.gatech.edu.
Sharon Eve
SE
Sonenblum
Schools of Applied Physiology and Industrial Design, Georgia Institute of Technology, 490 10th Street NW, Atlanta, GA 30318, USA. Electronic address: stephen.sprigle@coa.gatech.edu.
Stephen H
SH
Sprigle
School of Health Sciences, University of Ulster, Shore Road, Jordanstown, Newtownabbey, County Antrim BT38 0QB, Northern Ireland, United Kingdom. Electronic address: j.cathcart@ulster.ac.uk.
John McKay
JM
Cathcart
Institute of Nursing and Health Research, School of Health Sciences, University of Ulster, Shore Road, Newtownabbey BT37 0QB, United Kingdom. Electronic address: rj.winder@ulster.ac.uk.
Robert John
RJ
Winder
D000293:Adolescent; D000328:Adult; D002081:Buttocks / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D013119:Spinal Cord Injuries / Q000473:pathology; D055815:Young Adult
Anatomy; MRI; Pressure ulcer; Sitting; Tissue deformation