Patellar morphology is different in patellofemoral instability: An MRI comparative case-control study

Purpose

Although patellofemoral instability (PFI) affects both femoral and patellar compartments, literature provided little attention for the patellar morphology contribution on PFI. This study evaluates the patellar morphology patterns on MRI to establish their contribution in PFI.

Methods

This study retrospectively analyzes patellar MRI and X-ray measurements performed between 2018 and 2022. 50 knees with recurrent patellar dislocation were matched with 50 matched knees of ACL-reconstruction candidates with no history of patellar dislocation based on age and gender. Caton-Deschamps’ index, Wiberg’s patellar morphotype, Dejour’s trochlear dysplasia classification, sagittal patellofemoral engagement index and additional patellar cartilage and bone parameters and their relative ratio measurements were assessed in both groups.

Results

Study patients present differences in patellar morphology; a wider lateral facet (p = 0,019) and a narrower medial facet compared to the control group (p < 0,001). The subchondral patellar crest is medialized compared to the control group (p < 0,001). The cartilaginous crest measurements of the patella were not significantly different in both groups yet PFI group presents a wider Wiberg angle (p < 0,001), thus a flatter patella, compared to the control group.

Conclusion

The patella in PFI patients presents a larger lateral facet, a narrower medial facet, a flatter surface and a medialized patellar crest compared with the control group. In PFI, a rather medial patellar crest might predispose towards a greater patellar tilt and destabilize the already compromised patellar-trochlear groove congruence. PFI is a multifactorial disease and both trochlea and patella play a role in its manifestation, thus, literature should address patellar morphotype contribution in patellofemoral instability.

Level of Evidence: Level III.