Paper 35: Number of Patellar Dislocation Events are Associated with Increased Chondral Damage of the Trochlea: data from the JUPITER group
Authors: Bram Joshua , Lijesen Emilie , Green Daniel , Veerkamp Matthew , Propp Bennett , Heyworth Benton , Brady Jacqueline , JUPITER Study Group  , Stein Beth Shubin , Parikh Shital 
Published: October 2024

Objectives:

Patellofemoral instability (PFI) is frequently associated with chondral injuries to the patella and trochlea. Though several radiographic and intra-operative studies have demonstrated a link between patellar dislocation and chondral injury, the influence of the number of patellar dislocation events on the presence of chondral wear and severity is not established. This study aimed to understand the association between the number of patellar instability events and chondral damage observed directly in a large patient population undergoing patellar stabilization procedures.

Methods:

This was a retrospective review of the prospective multi-center Justifying Patellar Instability Treatment by Results (JUPITER) cohort. All patients undergoing primary surgical procedures to address PFI from 12/2016 to 9/2022 with a recorded number of patellar dislocations and detailed intra-operative assessment of the articular cartilage were included. Cartilage lesions were classified using the International Cartilage Repair Society (ICRS) classification, where ICRS grades 2 to 4 are defined as abnormal or severely abnormal. The number of dislocation events was grouped into 1-2, 3-5, and >5 dislocations. Continuous and categorical variables were compared using independent t-tests and chi-squared tests, respectively with multivariable regressions used to control for demographic characteristics potentially influencing cartilage wear. A significance threshold of p<0.05 was used.

Results:

A total of 938 patients at mean age 16.2 ± 3.8 years (range 5.1-35.0 years, 61.4% female patients) undergoing PFI procedures were included. Of these, 580 (61.8%) demonstrated a chondral injury. The most commonly affected region was the patella (n = 498, 53.1%) followed by the femoral condyles (n = 148, 15.8%), and trochlea (n = 109, 11.6%), with 83 (8.8%) patients having lesions located on both the patella and trochlea (Table 1). MPFL reconstruction was performed in 861 (91.8%) cases (Table 2), with other commonly performed procedures including patellofemoral chondroplasty (n = 388, 41.4%) and lateral retinacular lengthening or release (n = 255, 27.2%). Patients with fewer dislocations more frequently underwent fixation of an osteochondral fragment (1-2: 19.5%, 3-5: 7.6%, >5: 1.7%, p<0.001). There were no differences in the presence (p=0.209) or grade (p=0.716) of patellar chondral lesions based on dislocation number (Table 3). Patients with >5 patellar dislocations more frequently had a trochlear chondral lesion (19.8%) compared to the groups with fewer dislocations (1-2: 8.4%, 3-5: 13.0%, p<0.001). A greater number of dislocations was also associated with a higher proportion of abnormal (ICRS grades 2-4) trochlear lesions (>5: 15.3%, 3-5: 11.7%, 1-2: 7.6%, p=0.009), and the mean trochlear ICRS grade was significantly greater for the highest dislocator group (>5, mean 0.45 ± 0.99, p=0.023) compared to those with fewer dislocations (1-2: mean 0.24 ± 0.84, 3-5: mean 0.34 ± 0.93). Combined patellar and trochlear lesions were also higher in the most frequent dislocation group (>5 dislocations: 15.8%, 3-5: 9.9%, 1-2: 6.1%, p<0.001). In multivariable regression accounting for age, sex, BMI, and dislocation count, a dislocation count >5 was the only variable significantly predictive of the presence of a trochlear chondral lesion (OR 2.16, 95% CI 1.36-3.43, p=0.001). Both age in years (OR 1.11, 95% CI 1.06-1.16, p<0.001) and BMI (OR 1.05, 95% CI 1.02-1.07, p<0.001) were predictive of a patellar lesion, while both age in years (OR 1.07, 95% CI 1.01-1.13, p=0.017) and dislocation count >5 (OR 2.25, 95% CI 1.35-3.75, p=0.002) were predictive of the presence of both a patellar and trochlear lesion.

Conclusions:

This study demonstrates that an increased number of patellofemoral dislocation events is associated with more frequent trochlear and combined patellar/trochlear chondral damage with higher injury severity. Specifically, a dislocation count >5 is associated with a greater than 2-fold increase in the number of trochlear chondral injuries, which are of higher severity potentially requiring surgical management. Conversely, patients with fewer dislocation events were more likely to undergo osteochondral fracture fixation, which may have driven earlier operative intervention in this group. This is the first, large prospective study to demonstrate that multiple patellar dislocations can result in increased and more severe chondral damage.