Background and objectives: Anterior cruciate ligament reconstruction (ACLR) often results in quadricep atrophy. The purpose of this study was to compare the bilateral thickness of each quadricep component before and after ACLR. Materials and Methods: Cross-sectional study design. In 14 patients who underwent ACLR, bilateral quadricep muscle thicknesses were measured using a portable ultrasound device, 1 h before and 48–72 h after ACLR. Two-way analysis of variance (ANOVA) was used to compare muscle thickness pre- and post-ACLR between the limbs. Results: The primary finding was that the vastus intermedius (VI) muscle was significantly smaller in the reconstructed limb after ACLR compared to that in the healthy limb (Reconstructed limb; RCL = Pre-operated (PRE): 19.89 ± 6.91 mm, Post-operated(POST): 16.04 ± 6.13 mm, Healthy limb; HL = PRE: 22.88 ± 6.07, POST: 20.90 ± 5.78 mm, F = 9.325, p = 0.009, η²p = 0.418). Conclusions: The results represent a selective surgical influence on the quadricep muscle thickness. These findings highlight the need of advanced strengthening exercises in order to restore VI thickness after ACLR.

Emerging evidence suggests that lower quadriceps rate of torque development (RTD) following anterior cruciate ligament reconstruction (ACLR) may be associated with altered landing mechanics. However, the influence of quadriceps RTD magnitude and RTD limb symmetry on landing mechanics limb symmetry remains unknown. To assess the influence of quadriceps RTD magnitude and RTD limb symmetry on sagittal plane landing mechanics limb symmetry in females with and without ACLR during functional landing tasks. Cross-Sectional Laboratory Thirty-eight females (ACLR=19, 19.2±1.8 years-old, 164.1±7.0 cm, 63.8±7.6 kg, Time after surgery: 20.1±9.5 months; Control=19, 21.1±3.3 years-old, 167.3±7.3 cm, 67.3±9.3 kg). Landing mechanics were assessed during double-leg and single-leg jump-landing tasks (DL and SL), and a side-cut task (SC). Quadriceps RTD was collected during isometric muscle contractions. Separate stepwise multiple linear regression models determined the amount of variance in limb symmetry in sagittal plane knee moment at initial contact (IC), peak vertical ground reaction force (vGRF), and loading rate that could be explained by quadriceps RTD magnitude or RTD limb symmetry, group (ACLR or Control), and their interaction. In ACLR females, greater quadriceps RTD limb symmetry was associated with greater symmetry in sagittal plane knee moment at IC during DL (P=.004). Peak vGRF and loading rate could not be predicted by quadriceps RTD magnitude or RTD limb symmetry, group, or their interaction during all tasks. Developing greater quadriceps RTD symmetry, but not RTD magnitude, likely enables more symmetrical sagittal plane knee landing mechanics during double-leg task in ACLR females, and thus may reduce the risk of a second ACL injury. Such protective effect was not found during single-leg tasks that may not allow for a compensatory landing mechanism of shifting load to the uninvolved limb as is possible during a double-leg task.

Lower explosive quadriceps strength, quantified as rate of torque development (RTD), may contribute to landing mechanics associated with anterior cruciate ligament (ACL) injury risk. However, the association between quadriceps RTD and landing mechanics during high demand tasks remains unclear. Therefore, this study investigated the influence of quadriceps RTD on sagittal plane landing mechanics during double-leg jump landings (DLJL) and single-leg jump cuts (SLJC) in females with and without ACL reconstruction (ACLR). Quadriceps RTD was measured during isometric muscle contractions. Landing mechanics were collected during DLJL and SLJC tasks. Separate stepwise multiple linear regression models determined the amount of variance in sagittal plane landing mechanics that could be explained by quadriceps RTD, group (ACLR or Control), and their interaction. The results indicate that greater quadriceps RTD is associated with lower loading rate (p = 0.02) and longer time to peak vertical ground reaction force (p = 0.001) during SLJC, regardless of ACLR status. As greater loading rate may lead to higher risk of ACL injuries and post-traumatic knee osteoarthritis post-ACLR, explosive muscle strength interventions might be useful for individuals with and without ACLR to facilitate the use of safer landing mechanics.