Peripheral nerve block is one of the many options available to reduce pain after total knee arthroplasty. Among the various kinds of peripheral nerve block procedure, femoral nerve block (FNB) using ropivacaine is a very effective method for reducing pain. However, it has been known to cause weakness in the quadriceps femoris, resulting in an increased risk of fall during ambulation after surgery. The purpose of this study was to compare the effectiveness of FNB on pain and muscle strength with different concentrations of ropivacaine.

Our study was performed on 120 patients with knee osteoarthritis who had undergone total knee arthroplasty between January 2016 and December 2016. Patients were divided to 3 groups depending on the concentration of ropivacaine: Group 1 received 0.125% ropivacaine 6 ml FNB; group 2 received 0.2% ropivacaine 6 ml FNB; group 3 received normal saline 6 ml FNB. FNB with 1% lidocaine 10 ml and 0.75% ropivacaine 10 ml was performed to all groups at 3 hours after surgery. From the day after surgery, each group of patients were injected 4 times with FNB on their own designated concentration of ropivacaine with an interval of 6 hours. The severity of pain was estimated by visual analogue scale (VAS) and the strength of quadriceps femoris was measured using medical research council (MRC) grade and knee extension angle.

VAS score in group 3 was significantly higher compared to other groups; MRC grade in group 2 was significantly lower than in other grades, and knee extension angle in group 2 was significantly lower than in other groups at 6 pm on the day of and at 6 am on the day after surgery. VAS score, MRC grade, and extension angle of all groups showed no significantly difference at other times.

FNB with 0.125% ropivacaine after total knee arthroplasty shows effective reduction of pain without inducing quadriceps femoris weakness.