Reliability of subluxation and articular involvement measurements during the assessment of bony mallet finger

The aim of this study was to investigate the reliability of distal interphalangeal joint (DIPJ) subluxation and articular surface involvement measurements during the assessment of bony mallet finger. Two observers measured articular involvement, subluxation ratio and rated joint congruency on 30 lateral radiographs of patients with bony mallet finger on two separate occasions. All measurements and ratings were done on magnified digital radiographs on a workstation. The intraclass correlation coefficient (ICC) and kappa statistics were used to establish relative agreement between observers. The intra-observer reliability for articular involvement and subluxation ratio were good for Observer A (ICCs 0.888 and 0.775) and excellent for Observer B (ICCs 0.958 and 0.910) on both occasions. However, the subluxation rating was moderate for both observers (kappa 0.772 and 0.780, respectively). Inter-observer reliability for articular involvement (ICC 0.884) and the subluxation ratio (ICC 0.818) was good on the first measurement. Although the subluxation rating was perfect for the first measurement (kappa 0.927), it was moderate for the second (kappa, 0.619). The reliability of articular involvement (%) and subluxation ratio (%) measurement was good and excellent. However, the decision on whether the DIPJ is congruent or incongruent was only moderately reproducible. These findings show us that surgeons should be cautious when assessing subluxation, which is the most important criterion for choosing the appropriate treatment.