Paper 41: Increased Knee Valgus and Hip Adduction Moments after Hamstring Autograft compared to Quadriceps Autograft in Adolescents 6 Months after Anterior Cruciate Ligament Reconstruction

Abstract

Objectives: Evidence is limited related to the effects of autograft type on functional performance during gait lab-based functional testing after ACL reconstruction (ACLR), especially the quadriceps autograft. The goal of this study was to compare biomechanical outcomes as measured by 3D motion analysis during the drop vertical test between quadriceps autograft with bone block (QB), quadriceps autograft without bone block (Q), hamstring autograft (HS), and bone-patellar tendon-bone autograft (BTB) six-months postoperatively in an adolescent population. We hypothesized that the quadriceps groups would demonstrate decreased knee extension moments as compared to the hamstring autograft group without other significant differences. Methods: Patients aged 8-18 years who underwent primary ACLR were included. Patients with previous history of ipsilateral knee surgery were excluded. Kinematic and kinetic data collected during a drop vertical jump test in a formal gait lab using a computerized video-based system (Motion Analysis Corp. CORTEX software) was collected six months after ACLR and compared to the uninjured contralateral limb. The Kruskal Wallis test and subsequent pairwise comparisons were carried out for each studied parameter. Primary outcomes included transverse plane hip power, hip internal rotation moment, knee valgus angles, and knee extensor moments between the graft types. Secondary outcomes included hip abduction moment, knee valgus moment, and knee external rotation moment. Results: A total of 155 subjects’ charts were included for review, with 54, 40, 35, and 26 subjects in the HS, QB, Q, and BTB groups respectively. There were no significant differences in terms of age, sex, or affected leg (p > 0.1973). Athletic activity for each subject was also noted when appropriate, including soccer (37), basketball (34), and American football (30). The QB group had smaller knee extension moments maximums (-0.97 N*m/kg vs. -0.35 N*m/kg, p = 0.0323) and smaller knee extension moment averages (-0.12 N*m/kg vs. -0.03 N*m/kg, p = 0.0265) as compared to the HS group. The Q group demonstrated smaller knee extension moment averages (-0.13 N*m/kg vs. -0.03 N*m/kg, p = 0.459) as compared to the HS group. Analysis of secondary outcomes revealed that the HS group demonstrated larger knee valgus moments at initial contact (0.28 N*m/kg vs -0.35 N*m/kg, p = 0.0254) as compared to the Q group. The HS group demonstrated significantly larger hip adduction moment maximums (0.30 N*m/kg vs -0.04 N*m/kg, p = 0.0426) and smaller knee external rotation moment averages (-0.02 N*m/kg vs 0.02 N*m/kg, p = 0.0206) as compared to the QB group. No other secondary outcomes were statistically significant between any of the groups. Conclusions: The findings of this study suggest that the quadriceps autograft may confer improved knee coronal plane biomechanics in regard to ACL reinjury rates when compared to a hamstring autograft at 6 months after ACLR in adolescent patients performing a drop vertical jump. The hamstring autograft group was significantly associated with larger knee valgus moments at initial contact as compared to the quadriceps autograft without bone block and significantly larger hip adduction moments compared to the quadriceps autograft with bone block. Both quadriceps grafts were shown to demonstrate significantly decreased knee extension moments as compared to a hamstring autograft. Further long-term clinical studies may be useful in determining whether the apparent biomechanical differences seen between autograft types are correlated with reinjury rates.