Poster 284: Investigating the Frequency and Extent of Articular Cartilage Injury Following Patellar Dislocation: A Comparison of Recurrent vs. First-Time Dislocations
Authors: Sonnier John , Reddy Manoj , Ciccotti Michael , SAUCEDO SAMUEL , Avendano John , Cohen Steven , Tjoumakaris Fotios , Freedman Kevin , Campbell Michael 
Published: August 2023

Objectives: In cases of patellar dislocation, surgical intervention is typically reserved for patients with recurrent instability, unless a chondral or osteochondral fragment is identified following the initial dislocation. There is concern that multiple dislocation events may result in a higher incidence of articular cartilage injury. The purpose of this study is to compare the incidence of articular cartilage damage in patients with a single patellar dislocation to those with multiple patellar dislocations, and secondarily to compare the location and severity of chondral injury between the groups. Methods: Patients diagnosed with patellar dislocation were retrospectively identified by ICD-9 & ICD-10 codes from 2017-2021. Inclusion criteria were patients with a documented history of patellar dislocation with an MRI of the affected knee available for review. Patients with articular cartilage injury prior to dislocation event were excluded. Medical records were reviewed to determine the number of previous patellar dislocations. Articular cartilage injury was graded using a validated system, AMADEUS (mean total Area Measurement And DEpth & Underlying Structures, a scale from 0 to 100; 100 = no injury). Parametric continuous data was calculated by performing t tests. Nonparametric continuous data was calculated by performing Mann-Whitney tests. Chi-Square or Fisher’s Exact tests were used to calculate p values for categorical data. Results: After chart and imaging review, 233 patients were included: 117 with a primary dislocation and 116 with recurrent dislocations. Fifty-one (43.6%) of the primary dislocations and 68 (58.6%) of the recurrent dislocations were found to have articular cartilage injuries (p=0.068). When comparing the primary and recurrent groups, there was no difference in age, BMI, race, or laterality, but the recurrent group contained a significantly larger proportion of females (46.2% vs. 65.5%, P=0.004). There was no difference in lesion size, subchondral bone defect, presence of bone edema, or total AMADEUS score between groups (p=0.231). Subgroup analysis revealed that when cartilage damage is present, patients from the primary group had significantly more full-thickness lesions (p<0.001) and lower AMADEUS scores (p=0.016). The primary group had an increased proportion of medial facet and lateral femoral condyle lesions (p=0.026). Conclusions: There is a high percentage of cartilage injury in patients with a history of primary and recurrent patellar instability, with 43.6% and 58.6% of patients respectively, showing articular cartilage injury on MRI. Chondral injury primarily affected the medial and lateral patellar facets, and the lateral femoral condyle in both the primary and recurrent dislocation groups. However, the primary group demonstrated an increased number of full thickness lesions and subchondral bone defects. There was no difference in lesion size, presence of bone edema, or total AMADEUS score between the primary and recurrent groups. [Table: see text][Table: see text]