Fig. 3. Effects of continuous posterior lumbar plexus block ropivacaine concentration on hip flexor strength after hip arthroplasty. Muscle strength was evaluated using a dynamometer to measure maximum voluntary isometric contractions (MVIC). Data are expressed as median (horizontal bar ) with 25th–75th (box ) and 10th–90th (whiskers ) percentiles for patients randomly assigned to receive 0.1% ropivacaine (basal 12 ml/h, 4-ml bolus) or 0.4% ropivacaine (basal 3 ml/h, 1-ml bolus). The 95% confidence intervals for the estimated group differences fell within prespecified tolerances and were therefore deemed equivalent. POD = postoperative day.