Purpose: The purpose of this study is to see if changes in patient positioning result in significant changes in Doppler findings.
Materials and methods: 30 consecutive patients with jumper's knee in the proximal portion of the patellar tendon formed the study group. The patellar tendon was scanned in the longitudinal plane with colour and spectral Doppler with the knee fully extended as well as, flexed at 15 degrees and 20 degrees . All subjects were randomised to either extension or 20 degrees flexion as the initial position. The amount of colour Doppler activity inside the tendon was expressed with the colour fraction (colour pixels/total pixels) in the proximal portion of the tendon. With spectral Doppler, the resistive index was measured ((peak systolic velocity--end-diastolic velocity)/ peak systolic velocity).
Results: The mean (+/- SE) colour fraction in the fully extended position and 20 degrees flexion was 36.7 +/- 3.4% and 13.3 +/- 3.4%, respectively (p<0.0001). The mean resistive index was 0.607 +/- 0.036 with full extension and 0.914 +/- 0.036 with 20 degrees flexion (p<0.0001). On an individual patient basis, a decrease in colour fraction was observed in all 30 patients (100%), whereas an increase in resistive index was observed in 29 patients (97%). Maximum perfusion was seen in all positions when flexion was the initial position.
Conclusion: We advocate that for the examination of the patellar tendon by Doppler sonography, the patients should have fully extended and relaxed knees. Otherwise, the colour Doppler findings will underestimate the flow, and the spectral Doppler will overestimate peripheral vascular resistance.