Determine the vertical ground reaction forces and knee mechanics with different gait inclinations in the sheep model

Abstract

Our current understanding of knee mechanics and anterior cruciate ligament (ACL) function is predominately based on data recorded during simulations of clinical examinations or the application of nonphysiologic loads and motions. These methodologies provide little information on knee and ACL mechanics during activities of daily living (ADLs). Additionally, researchers have not directly measured knee kinetics, knee contact pressures, and ACL forces, and it is unknown how these parameters change with different activities. This study quantified the effects of activity level on vertical ground reaction forces, knee kinematics, and joint and ligament forces during in vivo motions. Five female Suffolk sheep were walked twice weekly on a treadmill during level (0°), inclined (+6°), and declined (−6°) gait for 12 weeks. Electromagnetic (EM) trackers were surgically implanted onto the left distal femur and the left proximal tibia, and in vivo motions were recorded for all activities. Following sacrifice, the in vivo motions were applied to their respective knees using a serial robot with a multi‐axis load cell. In vitro simulations were repeated to measure (a) total knee forces, (b) contact pressure maps, and (c) ACL‐only forces. Declining the gait surface led to increased posterior translation during the swing phase and decreased flexion at hoof‐strike, decreased medial contact pressure at push‐off, decreased ACL force at hoof‐strike and increased ACL force at push‐off. This study established a system that can be used to examine knee mechanics and ACL forces during ADLs for different knee states to define design requirements for ACL reconstruction techniques.

Biomechanical gait analysis in sheep: kinematic parameters

“…Also, kinetic parameters should be considered, taking into account the studies already conducted by ( Duda et al, 1998 ; Seebeck et al, 2005 ; Spatholt et al, 2023 ). During the sheep’s gait cycle, the interaction between vertical ground reaction forces (VGRF) and joint kinematics is crucial for the animal’s efficient movement.…”

“…During the sheep’s gait cycle, the interaction between vertical ground reaction forces (VGRF) and joint kinematics is crucial for the animal’s efficient movement. At the moment of IC, the VGRF is low, but as the sheep’s body weight is transferred to the paw in contact with the ground, the VGRF gradually increases ( Duda et al, 1998 ; Spatholt et al, 2023 ). Simultaneously, the hip and knee joints extend, providing stability and support to the limb and the sheep’s body weight.…”

“…In the middle of the support phase, the sheep carries all its weight on the paws that are on the ground, and the VGRF reaches its peak. At this point, the VGRF of the hind limbs is about 60% of the sheep’s body weight ( Duda et al, 1998 ; Spatholt et al, 2023 ). As the TO moment approaches, the sheep begins to lift its legs off the ground with a simultaneous flexion in the hip, knee, and ankle extension.…”

“…During the swing phase, the joints remain flexed (with the knee reaching its maximum flexion during midswing and the hip reaching its maximum flexion just before the next IC), allowing the paws to move forward to start the next gait cycle. Meanwhile, the weight of the sheep’s body is supported by the other paws in contact with the ground ( Duda et al, 1998 ; Spatholt et al, 2023 ).…”

“…Thus, the kinetic and kinematic values were described, but through an invasive evaluation method (Tapper et al, 2006). Another study examined the relationships between kinematics, knee kinetics, contact pressures, and ligament loads for multiple ADLs and, as expected, the results demonstrated that declining gait decreases flexion of the knee at hoof strike and increases flexion during push off (Spatholt et al, 2023).…”