Long-term gait biomechanics in level, uphill, and downhill conditions following anterior cruciate ligament reconstruction

Walking speed differentially affects lower extremity biomechanics in individuals with anterior cruciate ligament reconstruction compared to uninjured controls

BACKGROUND

Walking biomechanics are commonly affected after anterior cruciate ligament reconstruction and differ compared to uninjured controls. Manipulating task difficulty has been shown to affect the magnitude of walking impairments in those early after knee surgery but it is unclear if patients in later phases post-op are similarly affected by differing task demands. Here, we evaluated the effects of manipulating walking speed on between-limb differences in ground reaction force and knee biomechanics in those with and without anterior cruciate ligament reconstruction.

METHODS

We recruited 28 individuals with anterior cruciate ligament reconstruction and 20 uninjured control participants to undergo walking assessments at three speeds (self-selected, 120%, and 80% self-selected speed). Main outcomes included sagittal plane knee moments, angles, excursions, and ground reaction forces (vertical and anterior-posterior).

FINDINGS

We observed walking speed differentially impacted force and knee-outcomes in those with anterior cruciate ligament reconstruction. Between-limb differences increased at fast and decreased at slow speeds in those with anterior cruciate ligament reconstruction while uninjured participants maintained between-limb differences regardless of speed (partial η2 = 0.13-0.33, p < 0.05). Anterior cruciate ligament reconstruction patients underloaded the surgical limb relative to both the contralateral, and uninjured controls in GRFs and sagittal plane knee moments (partial η2 range = 0.13-0.25, p < 0.05).

INTERPRETATION

Overall, our findings highlight the persistence of walking impairments in those with anterior cruciate ligament reconstruction despite completing formal rehabilitation. Further research should consider determining if those displaying larger changes in gait asymmetries in response to fast walking also exhibit poorer strength and/or joint health outcomes.

Dynamic knee stiffness during walking is increased in individuals with anterior cruciate ligament reconstruction

Individuals with anterior cruciate ligament (ACL) reconstruction often display abnormal gait mechanics reflective of a "stiff-knee" gait (i.e., reduced knee flexion angles and moments). However, dynamic knee stiffness, which is the dynamic relationship between the position of the knee and the moment acting on it, has not been directly examined during walking in individuals with ACL reconstruction. Here, we aimed to evaluate dynamic knee stiffness in the involved compared to the uninvolved limb during weight-acceptance and mid-stance phases of walking. Twenty-six individuals who underwent ACL reconstruction (Age: 20.2 ± 5.1 yrs., Time post-op: 7.2 ± 0.9 mo.) completed an overground walking assessment using a three-dimensional motion capture system and two force plates. Dynamic knee stiffness (Nm/°) was calculated as the slope of the regression line during weight-acceptance and midstance, obtained by plotting the sagittal plane knee angle versus knee moment. Paired t-tests with Bonferroni corrections were used to compare differences in dynamic stiffness, knee excursions, and moment ranges between limbs during both stance phases. Greater dynamic knee stiffness was found in the involved compared with the uninvolved limb during weight-acceptance and mid-stance (p < 0.01). Knee flexion and extension excursions were reduced in the involved limb during both weight-acceptance and mid-stance, respectively (p < 0.01). Sagittal plane knee moment ranges were not different between limbs during weight-acceptance (p = 0.1); however, the involved limb moment range was reduced relative to the uninvolved limb during mid-stance (p < 0.01). These results indicate that individuals with ACL reconstruction walk with a stiffer knee throughout stance, which may influence knee contact forces and could contribute to the high propensity for post-traumatic knee osteoarthritis development in this population.

The 6DOF knee kinematics of healthy subjects during sloped walking compared to level walking

BACKGROUND

Level Walking is a frequent functional movement during daily life. However, sloped walking is also common. Exploring 6DOF knee kinematics during sloped walking is important. It provides a reference for the rehabilitation, safety, and knee health of patients with knee diseases walking on sloped surfaces.

RESEARCH QUESTION

The study aimed to explore 6DOF knee kinematics characteristics during sloped walking compared to level walking. We hypothesized that tibial anteroposterior translation and flexion angle (the sagittal plane) were significantly different from those of level walking.

METHODS

One hundred young, healthy adults (50 males and 50 females) were recruited for this study. A three-dimensional gait analysis system was used to collect 6DOF knee kinematics during level and sloped walking. The slope was set to ± 15% when the sloped walking was performed.

RESULTS

Sloped walking mainly increased knee flexion angle (upslope, 2.5-26.2°, 1-100% gait cycle (GC), p < 0.05; downslope, 1.7-11.9°, 15-95% GC, p < 0.05) and anterior tibial translation (upslope, 0.7-4.1 mm, 3-54% GC & 0.6-2.1 mm, 80-94% GC; downslope, 1.0-2.2 mm, 21-69% GC) in the participants' knees. However, participants' other 4DOF knee kinematics during sloped walking were significantly different from those during level walking (p < 0.05). Participants had 'drastically changeable' knee kinematic alterations in the transverse and coronal plane (the other 4DOF knee kinematics) during sloped walking compared to level walking.

SIGNIFICANCE

Our results confirmed the hypothesis. Sloped walking significantly increased anterior tibial translation (in most GC) and flexion angle. These kinematic changes in healthy subjects should be evaluated and further explored for patients with knee diseases, such as anterior cruciate ligament deficiency. Our findings are meaningful for their rehabilitation or safety or knee health while walking on sloped surfaces. Our study may provide a pilot reference for the 6DOF knee kinematic exploration of sloped walking.

Aberrant gait biomechanics in individuals with ACL reconstruction are magnified during treadmill walking

Aberrant gait biomechanics following anterior cruciate ligament reconstruction (ACLR) likely contribute to post-traumatic osteoarthritis (PTOA) development. Gait biomechanics are typically assessed overground, but the use of instrumented/force-measuring treadmills is increasingly common. The purpose of this study was to compare gait biomechanics overground and on an instrumented treadmill in individuals with ACLR and healthy controls. Twenty-four individuals with ACLR and 24 healthy controls completed overground and gait biomechanics assessments. Biomechanical outcomes included peak vertical ground reaction force (vGRF), internal knee extension (KEM) and abduction (KAM) moments, and knee flexion (KFA) and adduction angles; KFA at heel strike; knee flexion displacement; and inter-limb symmetry for each outcome. Peak KEM (P < 0.001, 95%CI [-0.016, -0.007 xBW*Ht]) and vGRF (P < 0.001, 95%CI [-0.09. -0.03 xBW]) were significantly less symmetrical in the ACLR group compared to the control group on the treadmill but not overground. Additionally, peak KEM was smaller in the ACLR limb compared to the contralateral limb both overground (P = 0.005, 95%CI [-0.010, -0.001 xBW*Ht]) and on the treadmill (P < 0.001, 95%CI [-0.015, -0.007 xBW*Ht]), but this difference was 1.8x larger on the treadmill compared to overground. Peak KFA (P = 0.001, 95%CI [-4.2, -1.2°]) and vGRF (P < 0.001, 95%CI [-0.07, -0.03 xBW]) were smaller in the ACLR limb on the treadmill but not overground. These findings suggest aberrant gait biomechanics are exacerbated during treadmill walking post-ACLR and that evaluating kinematics and kinetics on instrumented treadmills may be valuable for assessing risk factors of PTOA development.