Different Patellar Indices and Their Role in Decision-Making: An MRI-Based Study

Abstract

Magnetic resonance imaging (MRI) of knee has become the integral part of knee evaluation, hence any MRI based study adds more value if it helps in the decision-making process, especially for surgery in treating patellofemoral pain. We tried to determine normal patellar indices using knee MR images and the correlation between them and also compared the results with different ethnic population. We analyzed the prospectively collected MR images of 117 knees/patients, and Insall–Salvati (IS) index, modified IS index, patellotrochlear (PT) index, and patellophyseal (PP) index were calculated. Two standard deviations from the mean were used to define the normal and abnormal patellar position. Cohen's kappa values were used to assess the agreement between the indices and the correlation between them was analyzed using Pearson's correlation. The mean values for IS index, modified IS index, PT index, and PP index were 1.00, 1.53, 0.40, and 0.58, respectively. There was very good agreement between PT index and PP index. There was weak correlation between all the indices except the one between PT and PP indices which had a strong negative correlation. Based on commonly used methodology, there were 4% of asymptomatic patients who were outside the standardized cut-off values and different indices classified different knees as abnormal. This indicates patellar position should be one among the many other factors, not as a sole factor when making a surgical decision in patellofemoral pain. We also noted that the indices compared fairly with other populations. Further research is needed to determine the clinical applicability of these indices.

Association between quadriceps fat pad edema and patellofemoral osteoarthritis: a quantitative Q-Dixon-based magnetic resonance imaging (MRI) analysis

“…IFPE is related to several PF maltracking parameters, including the TT-TG, LTI, and PTA, especially the ISR or MISR, which indicate the patella alta ( 11 , 35 ). We used MISR instead of ISR to avoid the influence of patellar morphology ( 36 , 37 ). IFPE may be caused by PF maltracking, which triggers OA progression ( 38 ).…”

Association between the most superior point of patella-entrance of femoral trochlea distance ratio (SP-ET index) and chondromalacia patella: an investigation via magnetic resonance imaging

“…The distance from the most superior point of the patellar chondral surface to the most superior point of the trochlear cartilage divided by the whole length of articular cartilage of the patella is known as the patellophyseal index, which is used in the assessment of patella height by some researchers [ 19 , 27 , 28 ]. This method has some similarities with SP-ET index; however, only one plane (the sagittal cross-sectional image with the greatest craniocaudal diameter of the patella) is required to perform the measurement, and this situation minimises the effect of axial patellar displacement.…”

Association among peripatellar fat pad edema and related patellofemoral maltracking parameters: a case-control magnetic resonance imaging study

“…The most common method is the ISR since it is simple to measure and unaffected by knee flexion; however, it can be influenced by patellar morphology [ 29 ]. The MISR eliminates this disadvantage by measuring only a particular cartilage length and is more reproducible than the ISR; however, it can be affected by varied subchondral bone geometry [ 16 ]. The PTI truly represents patella-trochlear articulation since it quantifies the patella-trochlear contraction.…”

“…2 f). The MISR [ 16 ] was measured as the ratio between the distance from the distal end of the patellar cartilage to the tibial tuberosity and the length of the patellar cartilage (Fig. 2 g).…”

“…2 g). The PTI [ 16 ] was measured as the ratio between the vertical patellar cartilage distance and the distance of trochlear cartilage contacted with the patella (Fig. 2 h).…”