## 4 Discussion  
The key finding that can be derived from this study is that there are differences in the TL/PL ratio between genders. Further, the TL/PL ratio is significantly higher in females than in males. However, there is no difference in the patellar alta and baja between the 2 SD method and the extreme value method. The joint-reaction-force on the patellofemoral joint is associated with the patellar height. Patellar alta is a condition related with malalignment of patellofemoral joint and a reduced patellofemoral contact area; it leads to patellofemoral pain and instability [22; 23]. Patellar baja is related with restricted motion of the knee, called Osgood-Schlatter disease, and patellofemoral arthritis [24; 25]. Realignment yields a satisfactory outcome in the cases of patellar malalignment or malposition [26]. It is important to shift the tendon insertion both medially and distally in order to perform a patellar-tendon transfer for patellar subluxation [27]. Patellofemoral arthritis may occur if the patellar tendon is rerouted too far distally as the articular surface of the patella is forced against the femoral condyles. Patellar tendon transfer must be performed only when the patellar height is clearly abnormal. Therefore, there is a requirement for a clear definition of the normal patellar position in the knee. Several techniques have been developed for performing radiological evaluation of patellar height [4; 8; 9; 10]. The Insall-Salvati ratio is independent of the degree of knee flexion and is a simple method to evaluate [18]. In the Blackburne-Peel method, there is no consideration of patellar ligament when assessing the patellar  
Figure 2: The distribution of the Insall–Salvati index (ISI) for the whole sample: a symmetrical curve; the thick solid line shows the mean (0.92), the thin solid lines show the normal range from the previous study (0.8, 1.20) [9], the broken lines show the normal range using 2 SD from the mean (0.64, 1.20), and the dotted line shows the normal range using the extreme 2.5% at each end of the distribution (0.65, 1.19). height [4]. In general, squatters have a higher range of knee flexion. The presence of the quadricipital groove that results from patellar ligament pressure against the upper end of the tibia makes projecting a forward line along the tibial plateau difficult [28]. It yields different results for squatters. Thus, grading the patellar level in relation to the tibial plateau is not appropriate for assessing the patellar position in squatters. By comparing the Insall-Salvati ratio measurements on MRIs to those on radiographs, it has been demonstrated that the ratio can be measured more precisely on MRIs [18]. Based on the previously conducted studies, the size of abnormal patellar to length of patellar tendon, defined by the Insall-Salvati ratio, is too frequent to be regarded as abnormal [5]. It led to measurement of the Insall-Salvati ratio in a large population that was referred for clinical knee MRI examination. In addition to lateral radiographs, MRIs are increasingly being used for analyzing patellofemoral anatomy in patients with patellofemoral instability. Orthopedic surgeons use MRIs to evaluate the patellar height, but traditional cutoff values of patellar height ratios based on lateral radiographs are not comparable to these MRI values. Our study yields a TL/PL ratio that is smaller than those reported in previously conducted studies [5; 6; 8; 18]. Only two previous studies, similar to our study, yielded a TL/PL ratio less than one [29; 30]. TL/PL ratios in the study conducted by [PERSON] et al. and our study were \(0.961\pm 0.14\) and \(0.92\pm 0.14\), respectively [29]. As previously mentioned, morphometric characteristics are determined by sociocultural, environmental, and genetic conditions and by functional, health, and lifestyle status. In addition, the patellar positions in the population of South China are 15-20% higher than that in the population of West China [31].