Is the visibility of standardized inflicted bruises improved by using an alternate ('forensic') light source?

AIM

To study the visibility of standardized inflicted bruises by using an alternate ('forensic') light source compared to a white light source.

METHODS

Bruises were inflicted on the flexor site of the forearm (halfway in the middle) in 76 adults, by suddenly allowing a cylindrical metal object (400g) with rounded edges to drop for 1m in a vertically positioned tube. At 0.25, 1, 2, 7 and 14days after this blunt force impact, the impact site on the forearm was photographed with a white light source and subsequently with an alternate light source at 415nm. Visibility of bruises on 170 randomized photographs was assessed on a calibrated monitor by 10 forensic medical specialists (physicians and pathologists) independently in two sessions: (1) with white light source photographs, and (2) after a mean of 11days with greyscale converted alternate light source photographs. Bruise visibility was expressed as a report mark between 1 (very bad) and 10 (excellent), or as 'no visible bruise'. To determine intra-rater agreement, 10 of 170 photographs were assessed twice (untold to the assessors). In total 3600 (180×10×2) photographs were assessed.

RESULTS

39 of 73 (53%) participants who completed the study, developed a visible bruise (women more often than men, p<0.001). Inter-rater agreement between assessors was high (mean inter-class coefficient, ICC, for white light source 0.66 (SD 0.14) and for alternate light source ICC 0.73 (0.09)). Intra-rater agreement was excellent (mean ICC 0.88 (SD 0.09)). Mean report marks for bruise visibility, recorded independently by 10 assessors on 170 unique photographs per light source, were significantly higher with an alternate light source than with a white light source, at 1 and 2days after impact: 4.4 (SD 2.0) vs 3.8 (1.8) (p<0.01) and 4.9 (2.1) vs 4.5 (2.0) (p<0.05), respectively. However, these differences were small, as the mean difference (effect size) in report marks were 0.6 (0.5) and 0.4 (0.3), at 1 and 2days after impact, respectively. The other time points showed no statistical significant differences in report marks.

CONCLUSIONS

Bruises after standardized blunt force impact were slightly better visible with an alternate light source than with a white light source after 1 and 2 days, but not after 0.25, 7 and 14 days. The value of using an alternate light source at 415nm to improve bruise visibility was limited in this study.