Grading of proximal interphalangeal joint instability

Grade 1 Distal avulsion of volar plate from base of middle phalanx.
Hyperextension of PIP joint. (swan-neck deformity)
Proximal avulsion of checkreins less common and can cause pseudoboutonniere deformity
Grade 2 Volar plate injury extends to collateral ligaments.
Dorsal subluxation produces more instability.
Volar plate tilting with detachment of collateral ligament
Grade 3Fracture-dislocation of distal attachment of volar plate.
Stable injury: fragment involves <40% of articular surface with integrity of collateral ligament attachment
Unstable: dorsal subluxation with larger fracture fragment