High Femoral Antetorsion Is a Major Risk Factor for Anterior Knee Pain whereas Trochlea Dysplasia Predisposes for Patella Dislocation

PURPOSE OF THE STUDY Patellofemoral stability and congruency are influenced by different parameters. Their contribution to anterior knee pain and instability is not fully understood. We investigated, if isolated femoral antetorsion of more than 25 degrees leads to patellofemoral instability. MATERIAL AND METHODS We analyzed 90 knees in patients with patellofemoral complaints and correlated clinical and radiological characteristics. Patients presenting at our center between January 2018 and December 2020 because of patellofemoral pain or instability were included, provided that there was no previous surgical intervention done. RESULTS The severity of trochlea dysplasia classified using the Oswestry-Bristol classification significantly correlated with events of patellofemoral dislocations. (chi=8.152, p=0.043, phi=0.288). All males with a history of patella dislocation had at least a mild trochlea dysplasia. The majority of females complaining about patellofemoral symptoms in general had a dysplastic trochlea. Patella alta is more frequently found in patients with trochlea dysplasia than in patients with a normal femoral trochlea anatomy. DISCUSSION The majority of unstable patellofemoral joints showed a dysplastic trochlea. A high femoral antetorsion was found to be an additional minor factor contributing to instability. Isolated high femoral antetorsion without trochlea dysplasia rather leads to anterior knee pain without patella dislocation. Furthermore, no direct significant correlation between patella alta and patellofemoral instability was found. Patella alta can therefore rather be seen as a result of a dysplastic trochlea than a primary major risk factor for patellofemoral instability. CONCLUSIONS Trochlea dysplasia is the major risk factor for patellofemoral instability. Patella alta can rather be seen as a result of a dysplastic trochlea than as a primary risk factor for patella instability or pain. Isolated high femoral antetorsion often leads to patellofemoral pain syndrome but not to patella dislocations.