MRI analysis of anatomic structures related to the patellofemoral joint instability

Abstract

Objective To assess the principle anatomic factors contributing to the incidence of patellofemoral joint instability. Methods Knee MRI evaluations of 20 patients who had the clinical diagnosis of patellofemoral joint instability in the Third Affiliated Hospital of Sun Yat-sen University from September 2010 to September 2012 were selected as patellar instability group[8 males, 12 females, the average age was (24±8) years], including the patellar dislocation and injury of medial patellar retinaculum. The criteria for exclusion were any history of a multiple-ligament injury to the knee joint, an accompanying knee fracture, massive hydrarthrosis or a history of knee surgery. The MRI images of 69 asymptomatic subjects were selected as the asymptomatic group[31 males, 38 females, the average age was (25±5) years]. None of these subjects had symptoms or objective pathologic findings related to the patellofemoral, fractures and ligament injury of knee. Patellar height, sulcus angle, sulcus lateral facet ratio, and the tibial tubercle trochlear groove (TT-TG) distance were measured in both groups. Independent-samples t test and logistic regression were used for statistic analysis. Results The mean values of patellar height, sulcus lateral facet ratio, sulcus angle, and TT-TG in asymptomatic group were 1.02±0.15, 0.63±0.13 , 145°±8°, (1.15±0.24) cm, respectively; and the mean values of patellar height, sulcus lateral facet ratio, sulcus angle, and TT-TG in patellar instability group were 1.16±0.14, 0.44±0.13, 152°±8°, (1.69±0.27) cm, respectively. Significant differences were observed between asymptomatic group and patellar instability group for all variables (t=3.728, t=5.755, t=3.446, t=8.614, all P values<0.01). Significant correlations between patellar instability and anatomic factors (TT-TG, sulcus lateral facet ratio, and sulcus angle) were observed by logistic regression (all P values<0.05). Sulcus lateral facet ratio, the standardized partial regression coefficient were -78.221, 0.277 and 0.026, respectively. Conclusions Patients with patellar instability show higher values of patellar height, TT-TG, and sulcus angle, and lower value of sulcus lateral facet ratio. TT-TG and sulcus lateral facet ratio may be the principal factors of patellar instability in Chinese population. Key words: Patellofemoral joint; Magnetic resonance imaging; Trochlear dysplasia; Tibial tubercle trochlear groove