Hamstring Tendon Grafts Result in Altered Muscle Activity 1-Year After ACL Reconstruction

Abstract

The semitendinosus/gracilis graft (ST/G) is one of the most common grafts used for anterior cruciate ligament reconstruction (ALCR). While the ST/G tendon provides a stable graft and muscle morphology is not compromised, little is known about how harvesting the ST/G influences muscle activity. PURPOSE: The purpose of this study was to compare muscle activity of patients who received ST/G to those who received a bone-patellar tendon-bone (BPTB) autograft, and allograft (Allo). METHODS: One year after ACLR, 35 athletes (18 ST/G, 5 BPTB, 12 Allo) completed biomechanical analysis of gait with EMG recorded from the involved limb medial and lateral hamstrings (MH and LH), rectus femoris (RF), vastus medialis and lateralis (VM and VL). EMG were filtered and amplitude normalized, with the mean activity calculated for each phase of stance: weight acceptance (WA), mid-stance (MS), Terminal stance (TS). Repeated measures ANOVAs (Graft x Phase) were performed to compare muscle activity and co-activity of muscle pairs (MH-LH, MH-VM, VM-VL). Post-hoc tests were performed in the presence of interactions; alpha ≤ 05. RESULTS: A significant Graft x Phase interaction was observed for MH activity during WA (p=.022), with greater MH activity in the ST/G group (17.3±6.3%) compared to BPTB (8.3±5.4%; p=.021). A significant Graft x Phase interaction was also observed at WA for RF activity (p<.001), with less RF activity in the ST/G (6.8±4.9%) compared to BPTB (20.7±22.5%; p=.006) and during MS compared to Allo (ST/G: 2.9±3.8%; Allo: 7.6±7.0%; p=.032). There were significant Graft X Phase interactions for co-activity of the MH-LH (p=.003) and for MH-VM (p=.008). Post hoc analyses revealed greater MH-LH coactivity during WA in the ST/G (21.9±8.8%) compared to Allo (11.2±6.8%; p=.002), but not compared to BPTB (14.8 ±6.8%; p≥.106). The ST/G also exhibited less MH-VM coactivity (3.3±.2.8) during TS compared to Allo (17.6±17.7%; p=.003), but not compared to BPTB (14.3±16.6%; p=.083). CONCLUSIONS: Muscle activity differences were observed in the ST/G group compared to BPTB and Allo groups, one year after ACLR, suggesting the use of ST/G during ACLR may result in altered hamstring activity patterns and function. Further work is needed to examine the effects of these differences to knee function and the relation with to knee flexor strength.