This study was to determine the reliability and validity of manual measurements of patellar height to standard radiographic measurements in 30 knees of 15 subjects. Patellar height was measured using manual and radiographic methods. The manual measurements were performed by two examiners using digital vernier calipers with the subject sitting and the knees in 30° of flexion. The radiographic measurements were performed in the same position. The reliability of the manual measurements was assessed by means of intraclass correlation coefficients [ICC(3,1)], and the validity was investigated using the Pearson’s product-moment correlation coefficient and an independent t-test. The intra- and inter-rater reliabilities of the manual measurement of patellar height were excellent (ICC=.86 and .88 respectively). The validity of patellar height measured manually compared to the radiographic method was good (Pearson’s r=.69). In conclusion, the manual method is an objective, qualitative measurement of patella height.

The purpose of this study was to assess the influence of patellar height on quadriceps muscles' electromyography (EMG) activity during a squat exercise in adults with patella baja. For the study, we recruited 15 volunteers who had patella baja on the right side. We measured the EMG activity of the right rectus femoris, vastus medialis oblique, and vastus lateralis muscles during squat exercises under two conditions, specifically with and without an infra-patellar strap. The infra-patellar strap was applied below the tested patella to elevate the patella to a normal height. A paired t-test was used to compare the effects of patella height on EMG activity of the quadriceps muscles. The EMG activity of the rectus femoris (RF), vastus medialis oblique (VMO), and vastus lateralis (VL) muscles were significantly decreased during the squat exercise with the infra-patellar strap compared to the same exercise without the infra-patellar strap (p<.05), while the VMO/VL ratio was not different significantly between two conditions (p>.05). The findings of this study suggest that an infra-patellar strap may benefit people with patellar baja, as changes in patellar height could improve the efficiency of the quadriceps muscles.