Femoral Nerve Blockade is Associated with Persistent Strength Deficits at Six Months Post ACL Reconstruction in Pediatric and Adolescent Patients

OBJECTIVES: Femoral nerve blockade has become a popular method of postoperative analgesia for anterior cruciate ligament (ACL) reconstruction in pediatric and adolescent patients. Successful rehabilitation after ACL reconstruction involves return of quadriceps and hamstring strength and dynamic knee stability. The objective of this study was to compare strength and function six months after ACL reconstruction in pediatric and adolescent patients who received a femoral nerve block versus a control group of patients with no nerve block. METHODS: A search of our institutional database was performed to identify patients 17 years of age or younger who underwent primary ACL reconstruction between 2001 and 2010. Revision ACL surgeries and previous contralateral and ipsilateral knee surgeries were excluded. Based on institutional protocol, the patients participated in a comprehensive rehabilitation program and underwent isokinetic strength testing (slow and fast activation) and functional testing (vertical jump, single hop, triple hop) at six months after ACL reconstruction. RESULTS: There were 127 patients that met the inclusion criteria, including 63 patients in the NB group (32 males, 31 females) and 64 patients in the control group (26 males, 38 females). There were no significant differences between the NB group and the control group with respect to age (15.7 ± 1.4 vs. 15.5 ± 1.4, p = 0.26), sex (p = 0.29), BMI (23.7 ± 3.6 vs. 23.8 ± 3.6, p = 0.91), or type of graft used (67% patellar tendon autograft, 33% hamstring autograft vs. 70% patellar tendon autograft, 30% hamstring autograft, p = 0.85). Univariate analysis showed a significantly higher deficit at six months in the NB group with respect to fast isokinetic extension strength (17.6% vs. 11.3%, p = 0.008), as well as fast (12.8% vs. 8.3%, p = 0.029) and slow (9.9% vs. 5.5%, p = 0.029) isokinetic flexion strength. There was no difference in slow extension isokinetic strength deficit between the two groups (NB 22.1% vs. control 18.9%, p = 0.246).. With respect to function, there were no differences in deficit for vertical jump (NB 9.3% vs. control 11.3%, p = 0.267), single hop (NB 7.5% vs. control 7.6%, p = 0.970), or triple hop (NB 7.9% vs. control 6.5%, p = 0.375) between the two groups. A higher percentage of patients in the control group met criteria for return to sports at six months. (88.9% vs. 68.3%, p = 0.008). CONCLUSION: Pediatric and adolescent patients treated with a femoral nerve block for postoperative pain control after ACL reconstruction had significant isokinetic deficits in knee extension (quadriceps) and flexion (hamstring) strength at six months when compared to patients who did not receive a nerve block. No differences in the results of functional testing were observed between the two groups. A significantly higher percentage of patients in the group who did not receive a block were cleared to return to sports at six months following ACL reconstruction.