Reliability of the Pulp Nail Bone (PNB) classification for fingertip injuries

Evans and Bernardis proposed the ‘PNB classification’, by which a fingertip injury is classified according to each structure: pulp P, nail N, bone B. The objective of this study was to assess the inter-observer reliability, repeatability and accuracy of PNB. One hundred patients presenting with a fingertip injury were included prospectively, photographed, then classified in randomly chosen orders by nine independent observers. A third were drawn randomly and classified a second time to measure repeatability. A reference classification was also provided by one of the authors of the PNB system. Classifications agreed with the reference in 59% of injuries for P, 55% for N and 54% for B. The Kappa values for inter-observer agreement were 0.520 for P, 0.512 for N, and 0.504 for B; for intra-observer agreement, they were 0.616 for P, 0.658 for N, and 0.577 for B. Although levels of agreement are comparable with results found for other classifications, they are insufficient for use of the PNB classification without improvement.