An analysis of knee anatomic imaging factors associated with primary lateral patellar dislocations.

PURPOSE: Various knee anatomic imaging factors have been historically associated with lateral patellar dislocation. The characterization of these anatomic factors in a primary lateral patellar dislocation population has not been well described. Our purpose was to characterize the spectrum of anatomic factors from slice imaging measurements specific to a population of primary lateral patellar dislocation. A secondary purpose was to stratify these data by sex/skeletal maturity to better detail potential dimorphic characteristics.
METHODS: Patients with a history of primary lateral patellar dislocation between 2008 and 2012 were prospectively identified. Ten MRI measurements were analysed with results stratified by sex/skeletal maturity. A '4-factor' analysis was performed to detail the number of 'excessive' anatomic factors within a single individual.
RESULTS: This study involved 157 knees (79 M/78 F), and 107 patients were skeletally mature. The measurements demonstrate more anatomic risk factors in this population than historical controls. Patella height and trochlear measurements are the most common 'dysplastic' anatomic factors in this population. There were differences based on sex for some patellar height measurements and for TT-TG; there were no differences based on skeletal maturity.
CONCLUSION: Primary lateral patellar dislocation patients have MRI measurements of knee anatomic factors that are generally more dysplastic than the normal population; however, there is a broad spectrum of anatomic features with no pattern predominating. Characterizing knee anatomic imaging factors in the patient with a primary lateral patellar dislocation is a necessary first step in characterizing the (potential) differences between the primary and recurrent patellar dislocation patient. LEVEL OF EVIDENCE: IV.