Reliability of ultrasound strain elastography in the assessment of the quadriceps and patellar tendon in healthy adults

Objective
To report the intra- and inter-operator reliability of ultrasound strain elastography measures in the assessment of quadriceps and patellar tendons.

Materials and methods
Forty tendons were investigated of 20 healthy volunteers. Five anatomical sites were examined and analysed by three operators of differing levels of experience. Ultrasound was performed over two measures, employing three sonoelastography measurement techniques using a GE S8 with linear probe (L6–15 MHz). The percentage of exact agreement, Cohen's kappa and ICC 2,1 were performed to assess intra- and inter-operator reliability.

Results
The patellar tendon is more reliably measured across all techniques compared to the quadriceps tendon, particularly the distal region. Colour scoring was the most reliable method of sonoelastography. Colour scoring intra- and inter-operator reliability was better for patella tendon sites across all operators (60–95% agreement range), and greatest for experienced operators. Elasticity index intra-operator reliability was greatest for the most experienced operator compared with the least (ICC range 0.35–0.72 and ICC 0.17–0.60). Elasticity ratio intra-operator reliability of the patella tendon was fair–excellent for the experienced operator (ICC range 0.43–0.91), excluding the mid patellar region (ICC 0.13). Poor–fair inter-operator reliability was observed for elasticity ratio (ICC range 0.0–0.54) and elasticity index (ICC range 0.0–0.57).

Conclusions
Strain elastography of the patellar tendon is more reliable than the quadriceps tendon. Intra- and inter-operator reliability was better when undertaken by more experienced operators. Colour scoring was more reliable than elasticity ratio and index methods. Poor–fair intra- and inter-operator reliability of the elasticity ratio and elasticity index was observed.