The Application Of The Upright Weight-bearing MRI In The Diagnosis Of Patellar Instability

Objective:1. TO obtain the MRI images of the knee joint by the patients with patellar instability and normal group,who respectively had supine (0°) and weight-bearing (90°)knee MRI(Magnetic Resonance Imaging) examination.2.To measure the each index matching degree on joint response to patellofemoral instability in the cross-sectional MRI images. TO measure, analyze and compare each measurement data of supine (0°)and weight-bearing (90°)of patellar instability group and normal group. To investigate the diagnostic value of weight-bearing MRI to patellar instability.Materials and methods:1.To collect the 33 cases of patellar instability patient’s images data Materials which was performed in the supine position (0°) and weight-bearing (90°) of knee joint MRI examination in our hospital. And which was confirmed by knee joint arthroscopy arthroscopic surgery. Remove those with knee injury, knee joint synovitis, Cruciate ligament tearing, rheumatism, rheumatoid or tuberculosis of knee joint disease or with knee surgery.2. To recruit the graduate and undergraduate students in our college of 15 volunteers (30 knees), which without knee symptoms, surgery and trauma history and the knee surgeons performed physical examination confirmed that the positive signs were no patellar instability. The two groups did the same conditions of supine (0°) and weight-bearing (90°) of knee joint MRI examination.3. The Femoral trochlear angle, lateral patellofemoral angle, femoral trochlear depth and Patella tilt angle Were measured in the knee joint Spin Echo T1 sequence MRI cross-sectional image in the supine and weight-bearing stations.4. To test the 4 index’s difference of supine and weight-bearing by using independent sample t test or non parametric test. Respectively Drawing ROC curves of supine and weight-bearing condition, observed the area under the curve of each index, compared with supine and weight-bearing indexes for the diagnosis of patellar instability sensitivity and specificity, and Youden index (Youden, Index, YI) the maximum value point as the diagnostic value.result:The figure of the FTA, FTD,PTA and LPA, of the Patellar instability group were 141.1°±7.0°、(3.84±1.59)mm,15.1°±8.9° and 3.0°in Supine position. And the figure of the normal control group were 137.5°±3.7°、(6.63±0.90) mm、9.2°±2.9° and 7.8° respectively. Patients compared with normal group, the differences were statistically significant (t=-2.538、8.591、-3.484, Z=-5.540, P< 0.05).The figure of the FTA, FTD,PTA and LPA, of the Patellar instability group were 141.1°±6.9°、 (3.84±1.58) mm.18.2°±8.6° and-2.4° in upright position. And the figure of the normal control group were 137.5°±3.8°、(6.63±0.92) mm 9.6°±2.9°nd 7.8° respectively. Patients compared with normal control group, the differences were statistically significant (t=-2.559、8.589、-5.248, Z=-6.052, P< 0.05). The difference of FTA and FTD before and after loading was not statistically significant (Z=-0.487 and -0.010, P> 0.05), but the PTA and LPA’s difference figure in weight-bearing and supine were significant differences, have statistical significance (Z=-2.839 and -3.589, P< 0.05). Supine and weight-bearing area of femoral FTA of the ROC curve were 0.679 and 0.676, the area under the ROC curve of FTD were 0.929 and 0.927, There was no difference between FTA and FTD area curve with supine and weight-bearing. The PTA area under the curve of 0.695 and 0.834 respectively in the supine and the weight-bearing position.The area under the curve of LPA were 0.893 and 0.930.The area under the MRI curve of weight-bearing was significantly greater than the supine position. In the supine position of FTA, LPA,PTA and FTD diagnosis value were> 143.92°、< 4.56°、> 15.28°、< 4.83mm, the diagnostic sensitivity was 42.1%、71.1%、44.7 and 73.7% respectively, The specificity was 100%、 90%、100% and 100%. The diagnostic values of these four parameters were > 139.49°、< 3.35°、>12.72°、< 4.78mm in weight-bearing stations. The diagnostic sensitivity was 65.8%、71.1%、81.6% and 73.7%, the diagnostic specificity was 76.7%、100%、83.3% and 100% respectively.Conclusion:No matter in supine or weight-bearing stations, the Femoral trochlear angle, lateral patellofemoral angle, femoral trochlear depth and Patella tilt angle are all effective in diagnosis of patellar instability. But lateral patellofemoral angle and patellar tilt angle in weight-bearing MRI station compared to supine station have changed obviously, and the difference is statistically significant. And According to ROC curve, the effective diagnostic value of the upright weight-bearing MRI to patellar instability was observed.