Differences in the Severity and Location of Patellofemoral Cartilage Damage Between Instability Patients With and Without Patella Alta.

Background: Patella alta is a risk factor for recurrent patellar instability. Differences in chondral injury in patients with patellar instability between patella alta and patella norma have not been evaluated. Purpose: To analyze whether preoperative cartilage damage differs in severity and location between patellar instability patients with and without patella alta. Study Design: Cohort study; Level of evidence, 3. Methods: Patients with patellar instability who underwent patellar realignment surgery at a single institution with preoperative magnetic resonance imaging (MRI) scans were included. After measurement of Caton-Deschamps index (CDI) on MRI, patients were divided into patella alta (CDI ≥1.3) and patella norma groups. The area measurement and depth and underlying structures (AMADEUS) score was used to quantify cartilage defect severity on MRI. Results: A total of 121 patients were divided into patella alta (n = 50) and patella norma (n = 71) groups. The groups did not differ significantly in sex ratio, age at MRI, body mass index, mean reported number of previous dislocations, or mean interval between first reported dislocation and date of MRI. A total of 34 (68%) of the patella alta group and 44 (62%) of the patella norma group had chondral defects ( Conclusion: Patients with patella alta had less severe cartilage injury after patellar instability, including a lower proportion with full-thickness defects and better overall cartilage grade. The location of injury when present was similar between alta and norma, with most defects affecting the medial facet, lateral facet, and lateral femoral condyle in descending frequency.