 Hello, everyone. I am Dr. Aniket Verma, junior resident of department of radio diagnosis, JN Medical College, Aligarh. My topic of presentation is case presentation on particular instability. 18-year-old male presented with a complaint of recurrent dislocation of right knee cap following the trauma two years back. There is difficulty in squatting and sitting cross-leg on inspection. We can see there is an old heel scar mark of 1-2 cm over the right knee. The patella dislocates while flexing of the right knee and reduces back on extension. Following the mild drag, there is a reverse jet drag and the critical angle was found to be 50 degrees. This is a plain radiograph APN lateral view, showing the INSAL-SALVATI index as 1.2 and Modify INSAL-SALVATI index as 1.6. Skyline-Noran view depicting the circle angle as 144 degrees and later there is lateral patella displacement. And we can see there is a small vertically oriented medial patella facets. So it is a type 3 patella. Lateral patella femoral angle was calculated as 13.3 degrees and on axial MR cuts, the trochlea phasored asymmetry came out to be 49%. Patella tochlea index is calculated on the sagittal MR images as came out to be 0.25 and patella high ratio was 1.66 and Modify INSAL-SALVATI index as 1.86. This all suggests that there is a high riding patella, that is patella alta. TTTG came out to be as 12.7 and lateral trochlea inclination and trochlea depth was came out to be as 4.3. Now the brief introduction about the patella instability. Most patients are young and active individuals, high risk for women in the second decade. The prevalence is 6 to 77 per 1 lakh. Nearly half of all the patients with the first time dislocation will sustain the further dislocation after initial conservative management. During the recovery period, the restrictive mobility and two-third of them report limitations in the strainer's activities. Chronic instability and recurrent dislocation may lead to progressive cartilage damage and severe arthritis if not treated adequately. MR imaging is highly sensitive for detecting capsular, ligamentus, cartilaginous and bone injuries associated with patella dislocation. MR has now replaced the diagnostic orthoscopic as the primary diagnostic modality. Most important factors predisposing to the patella instability include trochlea dysplasia, patella alta, excessive litterization of the t-viltiprosity, quantification of these anatomical anomalies will help the orthosurgeon to choose the optimal treatment. The aim of the surgery is two-fold to repair the knee damage caused by the patella dislocation and to correct those anomalies that are known to contribute to the future dislocations. Patella dislocation is characterized by the complete loss of contact between the patella femoral joint surfaces. In almost all the cases, the patella dislocation literally most common mechanism of the first-time patella dislocation is flex position of the knee with internal rotation on a planted foot with a valgus component. In addition, a traumatic component in the form of a mild to severe external force may be involved which results in disruption of the medial ligaments. Now the risk factors for the patella instability and assessment with the MRM is first came as a trochlea dysplasia. It identifies one of the main factor contributing to the chronic patella femoral instability. Trochlea joint surface is flattened proximally and the concavity is less pronounced distally. This combination results in considerable loss of the lateral patella tracking and in the lateral dislocation of the patella at the initiation of the flexion. The classic criteria for the diagnosing trochlea dysplasia are the crossing sign and double contour sign. Crossing sign is line represented by the deepest part of the trochlea groove crossing the anterior aspect of the condyles assessed from the lateral radiograph. Double contour sign is double line at the anterior aspect of the condyles and is present if the medial condyles is hyperplastic. The jar had proposed the distinguishing four morphological types of the trochlea dysplasia. In the type A, the morphological structures are preserved as we can see in the image A. In the type B, there is flat horizontally oriented trochlea joint surface. In type C, there is flat and obliquely oriented trochlea joint surface with a facet asymmetry. In the type D, type D is the same as type C but with a prominent bone protrusion on the parasiteal view giving the cliff pattern. Another Weber classification of the patella shape. It describes mainly on the asymmetry between the patella medial and lateral facets on the axial views of the patella, increasing number of types indicating the larger degree of the asymmetry. In the type 3, there is maximum asymmetry. In the type 1, roughly symmetrical facets are there and they are concave facets and equal sized. Although it is presumed as the ideal shape of the patella, it is in fact rather uncommon occurring in 10% of the general population. The type 2 or B, the slightly smaller medial facet is there and there is concave shaped lateral facet. In the type 3 Weber, the markedly smaller facet of the medial facet and more vertically oriented, quantitative method for diagnosing the trochlear dysplasia. Lateral trochlear inclination, most superior section showing the trochlear cartilage, in selected from the axial data set, the inclination angle is less than 11 degrees indicating the trochlear dysplasia. Lateral trochlear inclination, assessed on the axial fat saturation T2 MR images, a line drawn along the sub-continental bone of the lateral trochlear facet and the second line is drawn along the posterior aspect of the femoral condyles and we measure the angle between them, it is less than 11 degrees trochlear dysplasia. Second comes here, a trochlear facet asymmetry. Here again, we measure the length of the medial trochlear facet to the length of the lateral trochlear facet ratio measured at the 3 cm above the Tb femoral joint graft. A trochlear facet ratio of less than 40% is identified indicating the dysplasia and with the sensitivity of the 100% and specificity of the 96%. The trochlear depth, the deepest point of the sulcus is determined at the same level as a trochlear facet asymmetry is determined. The trochlear dysplasia is assumed if the trochlear depth is 3 mm or less, the sensitivity of the 100% specificity of 96%. Let's depict in the images. Facet, we measure the length of the medial facet and the lateral facet. Then we use it to divide the medial facet length upon the lateral facet length into 100%. If it is less than 40%, it indicates the dysplasia there. And trochlear depth is measured by the first we draw a reference line which is at the posterior aspect of the femoral condyne at the 3 cm above the Tb femoral joint graft. Then we draw the largest anterior posterior diameter of the lateral and the medial condyne like this A and C. Then we draw the deepest point of the sulcus and we use the formula of A plus C upon 2 minus B. That is, we take the mean of A and C and then subtract it from the B. So if the trochlear depth is 3 mm or less, it is assumed to be indicating the dysplasia. Now patella ulta or high-riding patella. As we discussed, if the patella is too high above the trochlear fossa and occurs when the patella tendon is too long. If patella ulta, the degree of the flexion needs to be higher for the patella to engage in the trochlea compared with the normal lean. This problem leads to the reduced patella contact area and decrease bone stability in the shallow degrees of flexion. Patella height ratio is calculated as the length of the patella tendon measured posteriorly from the apex of the patella to its attachment to the tibial tuberosity and divided by the longest supereo inferior diameter of the patella, that is, in salvati index, the normal patella height ratio is reported as a 1.1 with a standard deviation of 0.1 and patella ulta is defined as the patella height ratio of more than 1.3 which is the normal ratio plus the two standard deviation. The patella trochlea index has recently been proposed as the more accurate reflection of the functional height of the patella. This index is a measure of patella feborel contact data determined from the sagittal MR images. Here, in the sagittal MR image, we can see how we measure the patella height ratio or in salvati index. We take the longest supereo inferior diameter of the patella and we measure the length of the patella tendon. Then we use a formula A upon V, that is, the length of the patella tendon and the longest diameter of the supereo inferior diameter of the patella. If normally, as we can discuss, the normal has a value of 1.1 with a standard deviation of 0.1 and if it is more than 1.3, then we take it as the patella ulta. Now, last comes here TTTG. We measure a distance from the t-wheel to vertical to the trochlea group on the axial fast T2 MR image. The distance from the deepest point of the trochlea, that is the line B is drawn and to the middle of the t-wheel to vertical, we measure the distance between them. If this distance is less than 15 mm, it is considered as normal. If the distance is 15 to 20 mm, it is coming up to the borderline and distance of more than 20 mm indicates the marked lateralization of the tribrosity. Now, the repair techniques are MPFL reconstruction, medial capsular plication and lateral capsular release, trochleoplasty and t-wheel tribrosity transfers. Now, coming back to our case, there is borderline trochlea dysplasia with a circle angle of 144 degrees and trochlea depth is 4.3. MTTTG came out 12.7 with asymmetrical trochlea facets, so it came out to 49%. There is pteroalta as we have discussed and verbac type 3 ptero. So considering all these things, the MPFL reconstruction was done using a semitrendinosis graph. Thank you.