Use of MRI images to measure tissue thickness over the ischial tuberosity at different hip flexion

Abstract

The goal of this experiment was to investigate changes in the thickness of the soft tissue overlying the ischial tuberosity (IT) due to changes in hip flexion angle and the addition of a sitting load. Eleven healthy subjects were tested. An apparatus constructed from foam blocks and an air bladder was used to position the subjects in different postures within an MRI tube. MRI images of the buttocks and thigh were obtained for four postures: Supine, 45° Hip Flexion, Non-Weight-Bearing 90° Hip-Flexion, and Weight-Bearing 90° Hip-Flexion. The thickness of muscle, adipose tissue, and skin was measured between the IT tip and skin surface, perpendicular to the cushion placed beneath the thighs. The tissue overlying the IT was found to be significantly (P < 0.001) thinner in 90° Hip-Flexion (73.8 ± 9.0 mm) than in the supine position (135.9 ± 8.1 mm). Muscle thickness decreased significantly from Supine to Non-Weight-Bearing 90° Hip-Flexion (59.1 ± 8.5%, P < 0.001), and further decreased from Non-Weight-Bearing to Weight-Bearing 90° Hip-Flexion (46.2 ± 7.9%, P < 0.001). Under Weight-Bearing 90° Hip-Flexion, the muscle tissue deformed significantly (P < 0.001) more than the adipose tissue and skin. We concluded that the tissue thickness covering the IT significantly decreased with hip flexion, and further decreased by nearly half during loading caused by sitting. In addition, the muscle tissue experienced the largest deformation during sitting. The results of this study may improve our understanding of risk factors for pressure ulcer development due to changes in tissue padding over the IT in different postures.

Factors that influence soft tissue thickness over the greater trochanter: Application to understanding hip fractures

“…Specifically, Makhsous et al (2011) found that nonweight-bearing hip flexion decreased the thickness of the tissues overlying the ischial tuberosity by up to 44.1% relative to a supine position. Interestingly, though, our findings contrast with several reports that soft tissue thickness in the pelvic region increases as muscle activation increases (Hodges et al, 2003;Makhsous et al, 2011).…”

“…, respectively, than in the supine position (Makhsous et al, 2011). Additionally, ultrasonography has been used to demonstrate that muscle thickness (across the tibialis anterior, biceps brachii, brachialis, transversus abdominis, obliquus internus abdominis, and obliquus externus abdominus) increases with activation level (Hodges et al, 2003).…”

“…While soft tissue thickness in some body regions is influenced by joint posture, muscle activation, and gender (Ley et al, 1992;Hodges et al, 2003;Makhsous et al, 2011), investigations have been limited to anatomical position or supine posture (in vivo), or in isolation (in cadaveric studies), rather than postures associated with falling configurations. For example, soft tissue thickness overlying the ischial tuberosity is 31% and 44% lower at hip flexion angles of 45 and 90…”

Skin thickness on bony prominences measured by ultrasonography in patients with spinal cord injury

“…The authors concluded that this was likely because the skin is the thinnest of the three layers. 8 It is known that high-frequency sonography can visualize tiny measurements like skin thickness that simply cannot be shown by standard MRI scans. 23 High-resolution ultrasound also has great advantages for the diagnostic evaluation of deep tissue injury.…”

“…7 Recent studies using MR images have examined deep tissue deformations and physiological characteristics of the skin, subcutaneous fat and muscle in weight-bearing and supine positions. 8,9 However, there have been no controlled studies comparing differences in skin thickness over bony prominences between patients with SCI and control subjects using ultrasonographic measurements. The aim of this study was to evaluate the differences in the thickness of the skin overlying the greater trochanter, ischial tuberosity, and sacrum between individuals with SCI and volunteers without SCI.…”