The Relationship of patella to trochlear groove
The groove helps to keep the patella within its walls during knee motion, so that the patella does not sublux or dislocate.
If there is mal-alignment, so that the patellar tendon does not align well with the groove, the patient can experience pain from over-pressure on one side of the patella, or instability.
Peer-reviewed papersQuote from peer-reviewed paper:
"Dysplasia of the femoral trochlea is a major predisposing factor for instability of the patellofemoral joint."
Citation: Fahlbusch H, Krivec L, Müller S, Reiter A, Frosch KH, Krause M. Arthrofibrosis is a common but poorly defined complication in multiligament knee injuries: a systematic review. Arch Orthop Trauma Surg. 2023 Aug;143(8):5117-5132. doi: 10.1007/s00402-022-04730-9. Epub 2022 Dec 15. PMID: 36520199; PMCID: PMC10374851.
Trochlear dysplasia
In some people the groove may be abnormally flat at the upper end, or may even be a bump rather than a groove, making it easy for the patella to jump up and out of this constraint - subluxation or dislocation.
Peer-reviewed papersQuote from peer-reviewed paper:
"....Currently expert consensus suggests a conservative treatment after first time dislocation...."
Citation: Dejour DH, Mesnard G, Giovannetti de Sanctis E. Updated treatment guidelines for patellar instability: "un menu à la carte". J Exp Orthop. 2021 Nov 26;8(1):109. doi: 10.1186/s40634-021-00430-2. PMID: 34837157; PMCID: PMC8626553.