The Faroese Knee Cohort: Etiology and Long-term Implications of Trochlear Dysplasia and Patellar Dislocations.

The Faroese Knee Cohort aims to consist of all persons in the Faroe Island between 15-20 years old with patellar instability* (PI) or a knee injury.

Special focus will be on PI, Patella dislocation (PD) and Trochlear Dysplasia (TD), a condition where the femoral trochlea has a dysplastic shape and lacks the lateral support of the patella. The diagnosis will be set by MRI of the knees and is in this study defined as the presence of one of the following: Crossing sign on a true lateral x-ray, lateral trochlear inclination angle < 11 degrees or a trochlear depth < 3 mm.

The hypothesis is that abnormal values in the following measures will be associated with increased risk of patellar dislocation and worse patient reported outcome: Caton-Deschamps index, Lateral Trochlear Inclination, Trochlear Facet Asymmetry, Trochlear Depth, Tuberostias Tibia - Trochlear Groove distance, Patello-trochlear index and Tuberositas Tibia - Posterior Cruciate Ligament distance.

Furthermore, we expect pivoting sports to be a behavioral risk factor.

The primary endpoint is measured by the number of patellar dislocations or near-dislocation the patient experiences (daily, weekly, monthly, yearly).

The secondary endpoint is the patient reported outcome measures.

*Definition: Patellar instability (PI) is the overall term encompassing both 1) recurrent patella dislocations and 2) recurrent episodes of a clear sensation of the kneecap riding on the outer border/aspect of the knee before popping back in track. The episodes must be a severe complaint for the patient. PI usually follows after a first time patellar dislocation.

Inclusion criteria

• Age between 15-20 years at the start of patient enrolment.
• The feeling of patellar instability, or patellar dislocation/near-dislocation.
• The person has to be from the Faroe Islands.
• All persons under the age of 18 must get written consent by their parents

Exclusion criteria

• Terminal illness
• Mental disabilities and illness, meaning that the patient cannot independently answer the PROM´s and cooperate to the clinical investigation.