A third of patients with multiligament knee injuries exhibit radiological signs of patella dislocation

Multiligament knee injury (MLKI) is considered major trauma. What is currently undescribed is the incidence of concomitant patella dislocation in a setting of MLKI, which is needed for a better understanding of concomitant injuries that are a consequence of the dislocated patella - rupture of the medial patellofemoral ligament (MPFL) and cartilage lesions. The present study aimed to investigate the incidence of patellar dislocation in the MLKI setting.

Magnetic resonance imaging (MRI) and operative note review of two major trauma centres for 2016-2023 were performed. MLKIs, defined as a disruption of at least two major knee ligaments, are classified as either ACL- or PCL-based or cruciate. All cases had a preoperative MRI and were treated surgically. Patella dislocation on MRI was defined as: (1) dislocated patella, (2) lateralization >2/3 with a bone bruise/cartilage injury, (3) bony or intrasubstance MPFL rupture with or without a bone bruise/cartilage injury. Note was also made on whether the patella was displaceable during surgery. The incidence of MPFL reconstructions was noted via the operative notes.

A total of 364 MKLIs were included. Mean age was 36.0 ± 13.4 years, 131 patients were female (36.0%). Observed incidence of patella instability was 29.7%: disruption of the MPFL was 75 cases (20.6%), lateralization of the patella in combination with bone bruise/cartilage injury in 30 cases (8.2%) as well as one case of a dislocated patella on MRI (0.27%). MPFL reconstruction was performed in 14 cases, and in 2 cases, a repair was performed (4.4%).

The present study demonstrates that the incidence of patella dislocation in the setting of MLKI can be as high as 29.1%. The clinical relevance of currently diagnosing and managing patellar dislocation in the setting of MLKI requires further research.

Level III, retrospective study.