# Loads on the Knee Joint Ligaments during Stair Climbing
###### Abstract  
Background. Stair climbing is often performed by people in daily life and requires considerable energy and muscle effort. This task has been widely described in the literature, but the role of the knee joint ligaments has not been sufficiently investigated. This could be relevant for planning ligament reconstruction surgery, for providing suggestions to subjects with partial ligament injuries, and for identifying compensatory strategies for reducing ligament loads. Methods. A dynamic musculoskeletal model was used to analyse the relationship between ligament loads and muscle forces during stair climbing. Results. The most loaded ligaments were the posterior cruciate ligament and the deep fibres of the medial collateral ligament, particularly during the mid-swing phase, where the knee was maximally flexed and the hamstring muscles contracted. The anterior cruciate ligament was recruited during the stance phase to compensate for the anteriorly-directed force applied to the tibia by the vasti muscles; the collateral ligaments stabilized the knee joint during the swing phase. The tibiotemporal contact force, resulting from all external and internal forces applied to the knee, was in good agreement with data provided in the literature. Conclusions. This study represents a forward step in the knowledge of ligament loads during stair climbing, which could be useful for providing informed recommendations to subjects with ligament injuries.  
Keywords:stair climbing; knee joint ligaments; musculoskeletal model; dynamic simulation; knee joint biomechanics +
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and can even lead to risk of damage. Several studies have analysed the loads at the tibiofemoral interface and at the patellofemoral joint [20; 21; 22; 23; 24; 25; 26], but, as far as we are aware, none of them has described the role of the ligaments in stair climbing and the forces they support to keep the joint congruent. Actually, some attempts to measure ligament strain in vivo have been made [27; 28] by means of a strain-gauge device (DVRT). In particular, [PERSON] et al. [29] measured the strain of the Anterior Cruciate Ligament in vivo during stair climbing. This method only measures the deformation of a few ligaments, and, from these measurements, it is difficult to obtain the load distribution among several ligaments. In this sense, musculoskeletal models represent an innovative method for studying the biomechanics of complex structures, having the potential to simulate the movement, to apply the muscular forces, and to estimate the loads in all internal structures of a joint. Since knowledge of ligament loads can be useful for providing suggestions to subjects with partial injuries of the ligaments and for identifying any compensatory strategies for the reduction of these loads, we have deemed it important to deepen understanding of the relationship between ligament loads and muscle forces. For this purpose, we have adapted a previously developed musculoskeletal model [30] to the analysis of stair climbing. This work is based on a single, exemplary subject, and does not pretend to represent any specific population. The aims of this study were to assess how the different knee-joint ligaments are loaded in an intact knee during stair climbing and to explain how ligament tensions are affected by the muscle forces produced in this specific task. Deeper investigation will be devoted to analysing how the muscle forces should be modulated to reduce the risk of ligament damage.