Abstract

To assess anatomical risk factors in patients after lateral patellar dislocation (LPD) and controls using MRI. MR images of 186 knees after LPD and of 186 age- and gender-matched controls were analysed. The presence of trochlear dysplasia was assessed by evaluation of trochlear inclination, facet asymmetry, and trochlear depth; patella alta was evaluated by the Insall-Salvati index and Caton-Deschamps index; the lateralised force vector was measured by the tibial tuberosity-trochlear groove (TT-TG) distance. Compared with controls, dislocators had significantly lower values for all three parameters of trochlear dysplasia (-32 %, -32 %, -44 %) and significantly higher values for patella alta (+14 %,+13 %) and TT-TG (+49 %) (all P < 0.001). Trochlear dysplasia was observed in 112 dislocators (66 %), of whom 61 (36 %) additionally had patella alta and 15 (9 %) an abnormal TT-TG. As isolated risk factors, patella alta (15 %) and abnormal TT-TG (1 %) were rare. Only 25 dislocators (15 %) had no anatomical risk factors. Trochlear dysplasia in conjunction with abnormal TT-TG or patella alta is associated with a 37- and 41-fold higher risk. Most dislocators have anatomical risk factors, varying in severity and constellation.

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