Purpose or Case Report: Prior to maturity, a secondary physis surrounding the patella defines an area of potential weakness. We seek to understand how age, sex, and physeal status affect the prevalence and degree of patellar osteochondral injury and medial patellofemoral ligament (MPFL) injury after acute patellar dislocation.
Methods & Materials: A retrospective review of the EMR and PACS from January 2016 to July 2019 identified 130 knees MRIs (from 126 patients, 4 with bilateral imaging) performed within 30 days of a first-time patellar dislocation. Patients with prior knee surgery and articular disorders were excluded. MRIs and associated reports were reviewed to evaluate the distal femoral physis (open, partially closed vs. closed), grade of patellar osteochondral injury (0-5, with grade 0 representing no visible injury and grade 5 representing exposed subchondral bone), presence of femoral osteochondral injury, presence and location of MPFL injury (patellar vs. femoral third), and presence of MPFL avulsion fracture. Statistical correlations with age, sex, and physeal status were measured with point-biserial correlation, 2-tailed z-test, and chi-square test.
Results:
Study population
130 evaluated knees aged 9-20 comprised 45% male and 55% female. The distal femoral physis was open in 42% (age 9-17), partially closed in 27% (age 13-17), and closed in 30% (age 16-20).

Injury prevalence
Patellar osteochondral injury: 45% (58/130) including 5% grade 4 and 16% grade 5.
MPFL injury: 56% (73/130) including 38% at the patellar third, 22% at the femoral third and 5% at both.
Patellar MPFL avulsion fracture: 15% (20/130).
Femoral osteochondral injury: 15% (20/130) including 8% purely chondral injury and 8% osseous and chondral injury.

Data analysis
Boys more often had grade 5 patellar osteochondral injury (24% vs. 10%, p=0.030) and MPFL injury (69% vs. 44%, p=0.007). Patients with open physes more often had MPFL injury than those with closed or partially closed physes (77% vs. 58%, p=0.030). Age had a positive biserial correlation with patellar osseous and chondral (grade 4 or 5) injury (p=0.029). Physeal status did not correlate with osteochondral injury grade. Age, sex, and physeal status did not correlate with the location of MPFL injury, presence of patellar MPFL avulsion fracture, or presence of femoral osteochondral injury.
Conclusions: Our data demonstrate that male sex and increasing age, but not physeal status, is associated with higher grades of osteochondral injury. MPFL injury is associated with male sex and an open physis.