Background: Treatment decisions regarding volar base fractures of the middle phalanx depend on whether the proximal interphalangeal (PIP) joint is reduced. Our aim was to study the agreement among hand surgeons in determining whether the PIP joint fractures are subluxated and to study the factors associated with subluxation of these fractures. Methods: In this retrospective chart review, 413 volar base fractures of the middle phalanx were included. Demographic and injury-related factors were gathered from medical records and radiographs. Using a Web-based survey, interobserver agreement was determined among 105 hand surgeons on the assessment of PIP joint subluxation of a series of 26 cases. Using the cohort of 413 fractures, a threshold for percent articular involvement and relative fracture displacement that corresponds with subluxation of the PIP joint was analyzed. Results: We found moderate to substantial agreement between hand surgeons on subluxation (κ = 0.59, P <.0001) and an overall percent agreement of 85%. Percent articular involvement and relative fracture displacement were independently associated with subluxation of the PIP joint (P <.001). Percent articular involvement of 35% had a specificity of 90% and a negative predicting value (NPV) of 92% for joint subluxation. Relative fracture displacement of 35% had a specificity of 92% and an NPV of 94% for joint subluxation. Conclusions: Surgeons generally agree on whether a PIP joint is subluxated. Percent articular involvement and relative fragment displacement are objective measurements that can help characterize joint stability and assist with decision-making.