Medial marginal fracture of the patella following patellar dislocation.

Among patients with patellar dislocation, a small fragment is occasionally found along the medial border of the patella. However, the detailed pathology of this fracture has not been clearly described, especially in relation to the medial patellofemoral ligament (MPFL). The purpose of this study was to describe the pathology of this fracture in relation to the MPFL. The subjects were seven patients with an acute primary patellar dislocation showing a medial marginal fracture of the patella. An open exploration was performed to confirm the relationship between the fragment and the MPFL. The MPFL was repaired by re-attachment to the patella with anchors. The patellar fracture site was determined by the location of anchors in the post-operative plain radiograph. The fragments were continuous with the thick and taut MPFL in all cases. Re-attachment of the MPFL stabilized the patella against lateral shift by manual force improving the tracking. All patients returned to their pre-injury activity level without any episodes of recurrent dislocation or subluxation at the final follow up (av. 31 months). Medial marginal fracture of the patella was an avulsion fracture of the MPFL that occurred at the middle one-third of the patella.