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Variability of Measurement of Patellofemoral Indices with Knee Flexion and Quadriceps Contraction: An MRI-Based Anatomical Study

View Article: PubMed Central - PubMed

ABSTRACT

Purpose: The purpose of this study was to investigate the impact of varying knee flexion and quadriceps activity on patellofemoral indices measured on magnetic resonance imaging (MRI).

Materials and methods: MRI of the knee was performed in 20 patients for indications other than patellar or patellofemoral pathology. Axial and sagittal sequences were performed in full extension of the knee with the quadriceps relaxed, full extension of the knee with the quadriceps contracted, 30° flexion of the knee with the quadriceps relaxed, and 30° flexion with the quadriceps contracted. Bisect offset, patella tilt angle, Insall-Salvati ratio and Caton-Deschamps index were measured.

Results: With the knee flexed to 30° and quadriceps relaxed, the mean values of patellar tilt angle, bisect offset, Insall-Salvati ratio and Caton-Deschamps index were all within normal limits. With the knee extended and quadriceps contracted, the mean patellar tilt angle (normal value, <15°) was 14.6° and the bisect offset (normal value, <65%) was 65%, while the Caton-Deschamps index was 1.34 (normal range, 0.6 to 1.3). With the knee extended and quadriceps relaxed, the mean Caton-Deschamps index was 1.31.

Conclusions: MRI scanning of the knee in extension with the quadriceps contracted leads to elevated patellofemoral indices. MRI taken with the knee in 30° of flexion allows more reliable assessment of the patellofemoral joint and minimises the confounding effect of quadriceps contraction.

No MeSH data available.


Bisect offset.
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Mentions: Axial and sagittal MRI sequences were performed with the knee fully extended and quadriceps contracted; knee fully extended and quadriceps relaxed; knee flexed 30° with quadriceps contracted; and knee flexed 30° with quadriceps relaxed. A triangular wedge was placed under the patient’s knee to reproducibly create 30° of flexion. When quadriceps contraction was required, subjects were given a rest period between MRI sequences to prevent muscle fatigue. Bisect offset27) and patellar tilt angle28) were measured on axial MRI images using the slice showing the widest view of the patella. The Insall-Salvati index and Caton-Deschamps index were measured on the sagittal view using the slice showing the widest view of the patella. Four measurements were used on both axial and sagittal MRI images to determine pathology. Bisect offset (Fig. 1) was determined by drawing a line connecting the posterior femoral condyles and a perpendicular line was then drawn through the deepest point of the trochlea groove to where it intersects the patellar width line. In cases where the trochlea was flattened, the perpendicular line was drawn at the midpoint between the posterior femoral condyles. The bisect offset is defined as the proportion of the patella lying lateral to the midline as a percentage of the whole patellar width. Subjects were considered having excessive bisect offset if they had values over 65%. Patellar tilt was defined as the angle between a line connecting the posterior femoral condyles and the maximum patellar width (Fig. 2). The Insall-Salvati ratio was determined by comparing the length of the patellar tendon with the length of the patella. The Caton-Deschamps index was defined as the ratio of the distance between the lower edge of the patellar joint surface and the upper edge of the tibial plateau to the length of the patellar articular surface (Fig. 3).


Variability of Measurement of Patellofemoral Indices with Knee Flexion and Quadriceps Contraction: An MRI-Based Anatomical Study
Bisect offset.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5134784&req=5

f1-ksrr-28-297: Bisect offset.
Mentions: Axial and sagittal MRI sequences were performed with the knee fully extended and quadriceps contracted; knee fully extended and quadriceps relaxed; knee flexed 30° with quadriceps contracted; and knee flexed 30° with quadriceps relaxed. A triangular wedge was placed under the patient’s knee to reproducibly create 30° of flexion. When quadriceps contraction was required, subjects were given a rest period between MRI sequences to prevent muscle fatigue. Bisect offset27) and patellar tilt angle28) were measured on axial MRI images using the slice showing the widest view of the patella. The Insall-Salvati index and Caton-Deschamps index were measured on the sagittal view using the slice showing the widest view of the patella. Four measurements were used on both axial and sagittal MRI images to determine pathology. Bisect offset (Fig. 1) was determined by drawing a line connecting the posterior femoral condyles and a perpendicular line was then drawn through the deepest point of the trochlea groove to where it intersects the patellar width line. In cases where the trochlea was flattened, the perpendicular line was drawn at the midpoint between the posterior femoral condyles. The bisect offset is defined as the proportion of the patella lying lateral to the midline as a percentage of the whole patellar width. Subjects were considered having excessive bisect offset if they had values over 65%. Patellar tilt was defined as the angle between a line connecting the posterior femoral condyles and the maximum patellar width (Fig. 2). The Insall-Salvati ratio was determined by comparing the length of the patellar tendon with the length of the patella. The Caton-Deschamps index was defined as the ratio of the distance between the lower edge of the patellar joint surface and the upper edge of the tibial plateau to the length of the patellar articular surface (Fig. 3).

View Article: PubMed Central - PubMed

ABSTRACT

Purpose: The purpose of this study was to investigate the impact of varying knee flexion and quadriceps activity on patellofemoral indices measured on magnetic resonance imaging (MRI).

Materials and methods: MRI of the knee was performed in 20 patients for indications other than patellar or patellofemoral pathology. Axial and sagittal sequences were performed in full extension of the knee with the quadriceps relaxed, full extension of the knee with the quadriceps contracted, 30° flexion of the knee with the quadriceps relaxed, and 30° flexion with the quadriceps contracted. Bisect offset, patella tilt angle, Insall-Salvati ratio and Caton-Deschamps index were measured.

Results: With the knee flexed to 30° and quadriceps relaxed, the mean values of patellar tilt angle, bisect offset, Insall-Salvati ratio and Caton-Deschamps index were all within normal limits. With the knee extended and quadriceps contracted, the mean patellar tilt angle (normal value, <15°) was 14.6° and the bisect offset (normal value, <65%) was 65%, while the Caton-Deschamps index was 1.34 (normal range, 0.6 to 1.3). With the knee extended and quadriceps relaxed, the mean Caton-Deschamps index was 1.31.

Conclusions: MRI scanning of the knee in extension with the quadriceps contracted leads to elevated patellofemoral indices. MRI taken with the knee in 30° of flexion allows more reliable assessment of the patellofemoral joint and minimises the confounding effect of quadriceps contraction.

No MeSH data available.