Estimates of Cruciate Ligament Forces Resulting from Anterior Tibial Translation During Simulated Flexion Motion of the Human Knee

Cruciate ligaments are main stabilizers of the joint in the sagittal plane. Anterior cruciate ligament is one of the most injured ligaments, particularly during strenuous activities. Integrity of these ligaments is examined clinically by estimating appropriate relative movements of the connected bones. Experiments on cadaver knees provide laxity measurements. However, determination of corresponding ligament forces is either difficult or not possible due to several challenges. In the present study, a mathematical model is used to simulate such laxity tests and estimate cruciate ligament forces when the lower leg at the knee is translated anterior to thigh, thus, stretching the anterior cruciate ligament. The simulation is repeated at several joint positions and with different forces that cause translation. The model calculations showed general agreement with experimental measurements in the literature. For example, the lower leg translated 6, 6.1, and 5.9 mm, respectively, at 30, 45, and 60° flexion with 150 N anterior translating load on the tibia. This is similar to the patterns reported in the literature from in vitro studies. The model helped in gaining further insight in the joint behavior with estimation of corresponding forces developed in the ligament for each simulation. The analysis suggests that 30–60° flexion may be appropriate range for clinical estimation of the ligament integrity as at these joint positions, the laxity is higher, while the ligament forces are not highest in comparison to other flexion angles.