Ultrasound assessment of patellar ligament length in athletes and non-athletes

Determining the length of patellar ligament is important both clinically and in research where it has been linked to various knee pathologies including patellar dislocation & instability. Within published literature; plain film radiography, magnetic resonance imaging (MRI) and computerised tomography have been used to study/asses the patellar ligament. Ultrasound has been proposed as a non-invasive, low-cost alternative but there is currently no consensus as to the techniques employed and questions remain about inter-operator variability. This study aims to evaluate variations in patellar ligament length (PLL) between athletes and non-athletes and address inter-operator variability through the use of ultrasound. Each ligament was measured following a modified form of a recently published technique by two investigators; blinded to each other’s results; using a GE LOGIQ e system with a 12L-RS transducer. Once the technique was clearly delineated there was no statically significant difference between the measurements obtained from the two investigators. Average PLL was found to be 47.1±7.8 mm and 45.1±4.0 mm in athletes and non-athletes respectively with no significant difference in means between the two groups regardless of limb dominance, gender or height. The difference in the PLL between the two limbs was significantly affected by body mass index value (BMI) (H(2)=9.577, p=0.008), specifically between the normal and overweight groups (p=0.007). Previous work has related patellar ligament length to force output rather than age but our findings show no significant correlation between the two. This study validates a pre-existing ultrasound technique with specific modifications to control inter-operator variability.