Application of tissue ultrasound palpation system (TUPS) in objective scar evaluation

One of the characteristics of hypertrophic scarring is its raised appearance. Its maturation often results in increased thickness. Therapists usually rely on subjective observation and palpation to document scar thickness. The result of these subjective assessments may reflect only the superficial scar thickness but is unable to measure the whole scar volume and thickness under the skin surface. Measurement of scar thickness using ultrasound imaging has been previously reported, but has not been commonly used in clinics due to its complex operation method and high cost. In this study, we have adopted a newly developed and user-friendly Tissue ultrasound palpation system (TUPS) for the assessment of scar thickness. It consists of a finger size palpation probe, connected to an ultrasound transducer and an in-series load cell to measure the thickness of the soft tissue over the human body. The method of operation is easy and it can be used to measure skin thickness on various parts of the body, thus reflecting the skin thickness. The reliability of the TUPS in clinical application was tested on 30 subjects with a hypertrophic scar at a local hospital. Three raters implemented two assessments on each subject to study its test-retest and inter-rater reliabilities. It was then used to assess 100 subjects with various severity of hypertrophic scar caused by trauma, scald, burn or surgery. They were assessed using TUPS as well as the Vancouver Scar Scale (VSS) for rating scar thickness, pliability, pigmentation and vascularity. Two-way mixed intra-class correlation showed a high test-retest reliability with Intraclass Correlation Coefficient (ICC)=0.98 and inter-rater reliability ICC=0.84. Fair positive correlations with VSS thickness score and VSS total score r=0.34 (p<0.05) and 0.42 (p<0.05), respectively. A significant difference between two scar type groups (50 burn scald scars and 50 surgical scars) was demonstrated (d.f.=52.94, t=3.99, p<0.01). TUPS was proved to have high inter-rater, test-retest reliability and it had a moderate correlation with the VSS that clinicians used for assessment of the scar. This system is recommended for clinical assessment of scar thickness.