The minimal important change (MIC) and minimal clinically important difference (MCID) of the patient and observer scar assessment scale (POSAS) 2.0.

Background: The Patient and Observer Scar Assessment Scale (POSAS) is frequently used to assess scar quality after burns. It is important to be aware of the minimal important change (MIC) and the minimal clinically important difference (MCID) to establish if a POSAS score represents a clinically relevant change or difference. The aim of this study is to explore the MIC and MCID of POSAS version 2.0.

Methods: This prospective study included 127 patients with deep dermal burns that underwent split thickness skin grafting with a mean age of 44 years (range 0 - 87) and total body surface area burned of 10 % (range 0.5 - 55). POSAS data was obtained for one burn scar area at three, six, and 12 months after split skin grafting. At the second and third visits, patients rated the degree of clinical change in scar quality in comparison to the previous visit. At 12 months, they completed the POSAS for a second burn scar area and rated the degree of clinical difference between the two scar areas. Two anchor-based methods were used to determine the MIC and MCID.

Results: MIC values of the patient POSAS ranged from - 0.59 to - 0.29 between three and six months and from - 0.75 to - 0.38 between six and 12 months follow-up. Both had a poor discriminatory value. MCID values ranged from - 0.39 and - 0.08, with a better discriminatory value.

Conclusion: Results suggest that patients consider minor differences (less than 0.75 on the 1-10 scale) in POSAS scores as clinically important scar quality changes. MCID values can be used to evaluate the effects of burn treatment and perform sample-size calculations.