Adverse effect of femoral nerve blockade on quadriceps strength and function after ACL reconstruction

The purpose of this study was to determine if quadriceps strength and functional outcomes were similar at 6 months following anterior cruciate ligament [ACL] reconstruction in patients receiving a continuous 48-hour femoral nerve blockade for postoperative analgesia (FNB group) versus patients with no FNB (control group). A retrospective cohort was designed including athletes who underwent primary ACL reconstruction with patellar tendon autograft between 2005 and 2010 at our institution with identical rehabilitation protocols. The FNB group included 96 patients with an average age of 21 years and the control group included 100 patients with an average age of 20 years. At 6 months following ACL reconstruction, isokinetic strength (slow and fast activation) and functional tests including vertical jump, single hop, triple hop, and return to sport were analyzed with an α value < 0.05 as significant. Multivariate regression models were used to compare these outcomes between the FNB and control groups after adjusting for gender and competitive athlete status. At 6 months, fast extension isokinetic strength was inferior in the FNB group (78 vs. 85%; p < 0.01). After adjusting for gender and competitive athlete status, fast (p = 0.002) and slow extension strength (p = 0.01), vertical jump (p = 0.03) and single jump (p = 0.02) were also inferior in the FNB group. There were no significant differences in full return to sport between the two groups (86% at 7.5 months in the FNB group vs. 93% at 7.3 months in the control group). In this retrospective comparative study, the hypothesis that patients treated with continuous FNB for postoperative analgesia following ACL reconstruction with patellar tendon autograft will have inferior knee extension (quadriceps) strength and function at 6 months follow-up was affirmed. However, no differences were observed in return to sport, bringing into question whether these statistical differences translate into meaningful clinical consequences after ACL reconstruction. The level of evidence was level III, retrospective case-control series.