Adaptation of a MR imaging protocol into a real-time clinical biometric ultrasound protocol for persons with spinal cord injury at risk for deep tissue injury:A reliability study

Background: High strain in soft tissues that overly bony prominences are considered a risk factor for pressure ulcers (PUs) following spinal cord impairment (SCI) and have been computed using Finite Element methods (FEM). The aim of this study was to translate a MRI protocol into ultrasound (US) and determine between-operator reliability of expert sonographers measuring diameter of the inferior curvature of the ischial tuberosity (IT) and the thickness of the overlying soft tissue layers on able-bodied (AB) and SCI using real-time ultrasound. Material and methods: Part 1: Fourteen AB participants with a mean age of 36.7 ± 12.09 years with 7 males and 7 females had their 3 soft tissue layers in loaded and unloaded sitting measured independently by 2 sonographers: tendon/muscle, skin/fat and total soft tissue and the diameter of the IT in its short and long axis. Part 2: Nineteen participants with SCI were screened, three were excluded due to abnormal skin signs, and eight participants (42%) were excluded for abnormal US signs with normal skin. Eight SCI participants with a mean age of 31.6 ± 13.6 years and all male with 4 paraplegics and 4 tetraplegics were measured by the same sonographers for skin, fat, tendon, muscle and total. Skin/fat and tendon/muscle were computed. Results: AB between-operator reliability was good (ICC = 0.81–0.90) for 3 soft tissues layers in unloaded and loaded sitting and poor for both IT short and long axis (ICC = −0.028 and −0.01). SCI between-operator reliability was good in unloaded and loaded for total, muscle, fat, skin/fat, tendon/muscle (ICC = 0.75–0.97) and poor for tendon (ICC = 0.26 unloaded and ICC = −0.71 loaded) and skin (ICC = 0.37 unloaded and ICC = 0.10). Conclusion: A MRI protocol was successfully adapted for a reliable 3 soft tissue layer model and could be used in a 2-D FEM model designed to estimate soft tissue strain as a novel risk factor for the development of a PU.