screw fixation

Concept

1. Initial press fit with mechanical stability

Mechanism

Direct blow

- most common

Indirect

- forced knee flexion with foot fixed / maximally contracted quadriceps

Types

1.  Vertical

2.  Transverse

Meyers & McKeever classification

Type I:   Undisplaced avulsion fracture

Type II:  Anterior portion displaced & hinged

Type IIIA:   Displaced

Type IIIB:   Displaced & Rotated