Prevalence and patterns of anatomical risk factors in patients after patellar dislocation: a case control study using MRI
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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.
• Magnetic resonance imaging provides unique information about anatomical variation within the knee.
• Anatomical variants increase the risk for lateral patellar dislocation (LPD)
• Trochlear dysplasia is the main risk factor for LPD.
• Patellar alta and abnormal tibial tuberosity-trochlear groove distance may be additional factors.
• Patient-specific evaluation of risk factors following LPD may help future management.
KeywordsPatellar dislocation Patellar instability Trochlear dysplasia Patella alta TT-TG
Edzard Wiener and Gerd Diederichs contributed equally to this article.
Two additional research projects were carried out in subgroups of this cohort: (1) One subgroup of the cohort received additional scans for rotational alignment of the lower limb. The manuscript with the title “MRI analysis of rotational alignment in patients with patellar dislocation” is accepted for publication in the American Journal of Sports Medicine. (2) Another subgroup was analysed for cartilage defects. This article entitled “Prevalence of cartilage lesions and early osteoarthritis in patients with patellar dislocation” was already published in European Radiology (DOI 10.1007/s00330-012-2493-3).
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