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

PURPOSE: 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.

METHODS: 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.

RESULTS: 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%).

CONCLUSION: 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 OF EVIDENCE: Level III, retrospective study.