Femoral nerve block is associated with persistent strength deficits at 6 months after anterior cruciate ligament reconstruction in pediatric and adolescent patients

Background: Femoral nerve block (FNB) has become a popular method of postoperative analgesia for anterior cruciate ligament (ACL) reconstruction in pediatric and adolescent patients. Successful rehabilitation after surgery involves return of quadriceps and hamstring strength. Purpose: To compare knee strength and function 6 months after ACL reconstruction in pediatric and adolescent patients who received FNB versus patients with no nerve block. Study Design: Cohort study; Level of evidence, 3. Methods: Patients 18 years or younger who underwent primary ACL reconstruction between 2000 and 2010 at a single institution were identified. If the patient was skeletally immature, a transphyseal ACL reconstruction was performed. Of these patients, 68% underwent reconstruction with a patellar tendon autograft, and in 32% of patients a hamstring autograft was utilized. There were 124 patients who met the study inclusion criteria, including 62 in the FNB group (31 males, 31 females) and 62 patients in the control group (25 males, 37 females). All study patients participated in a comprehensive rehabilitation program that included isokinetic strength and functional testing at 6 months postoperatively. Results: Univariate analysis showed a significantly higher deficit at 6 months in the FNB group with respect to fast isokinetic extension strength (17.6%vs 11.2%; P = .01) as well as fast (9.9%vs 5.7%; P = .04) and slow (13.0% vs 8.5%; P = .03) isokinetic flexion strength. There was no difference in slow isokinetic extension strength deficit between the 2 groups (FNB, 22.3% vs control, 18.7%; P = .20).With respect to function, there were no differences in deficit for vertical jump (FNB, 9.4% vs control, 11.3%; P = .30), single hop (7.6% vs 7.5%; P = .96), or triple hop (8.0% vs 6.6%; P = .34) between the 2 groups. A significantly higher percentage of patients in the control group met functional and isokinetic criteria for return to sports at 6 months (90.2% vs 67.7%; odds ratio, 4.37; P = .002). Conclusion: Pediatric and adolescent patients treated with FNB for postoperative analgesia after ACL reconstruction had significant isokinetic deficits in knee extension and flexion strength at 6 months when compared with patients who did not receive a nerve block. Patients without a block were 4 times more likely to meet criteria for clearance to return to sports at 6 months.