Atraumatic Extra-articular Patellar Dislocation with Vertical Axis Rotation: A Case Study

Abstract

Introduction: Acute patellar dislocation is a common injury usually associated with a significant traumatic mechanism resulting in lateral displacement. Vertical axis rotation following dislocation is a rare variant of this type of injury and can prevent closed reduction in the acute setting.

Case presentation: A 32-year old gentleman presented with an irreducible patella dislocation following an unusual atraumatic mechanism. Following attempts at closed reduction under sedation and regional nerve block, eventual open reduction and soft tissue reconstruction was required under general anesthetic. During the open reduction procedure, it was noted that the patella had dislocated into a lateral extra-articular position and rotated around its vertical axis. Following patella reduction, the medial patellar retinaculum was repaired. Examination under anesthetic revealed satisfactory tracking of patella following repair.

Conclusion: A review of the literature suggests dislocations such as the current presentation, are extremely rare and although have been described to occur with minor trauma, have never been described to occur following a largely atraumatic event. In such cases, closed reduction may be impossible even with adequate analgesia due to patella position and soft tissue obstruction. Open reduction is essential in these situations.

Keywords: Patellar Reduction; Patellar dislocation; vertical axis rotation.

Figure 1

Antero – posterior radiograph demonstrating lateral patella dislocation.

Figure 2

Lateral radiograph of the right knee demonstrating rotation of patella

Figure 3

Intraoperative Antero-posterior florous copy image following successful reduction

Figure 4

Lateral radiograph of the right knee following surgery in knee splint