Simulation of surface strain in tibiofemoral cartilage during walking for the prediction of collagen fibre orientation

The collagen fibres in the superficial layer of tibiofemoral articular cartilage exhibit distinct patterns in orientation revealed by split lines. In this study, we introduce a simulation framework to predict cartilage surface loading during walking to investigate if split line orientations correspond with principal strain directions in the cartilage surface. The two-step framework uses a multibody musculoskeletal model to predict tibiofemoral kinematics which are then imposed on a deformable model to predict surface strains. The deformable model uses absolute nodal coordinate formulation (ANCF) shell elements to represent the articular surface and a system of spring-dampers and internal pressure to represent the underlying cartilage. Simulations were performed to predict surface strains due to internal pressure, loading induced by walking, and the combination of both loading due to pressure and walking. Peak femoral and tibial cartilage deflections were slightly greater than 1 mm during simulated walking. First principal strain magnitudes within the cartilage surface ranged up to 3%. Time-averaged first principal strains agreed best with split line maps from the literature when surface loading due to internal cartilage pressure was included. This result suggests there may be a connection between pressure-induced surface strain patterns and the collagen fibre orientation patterns that emerge.

胫股关节软骨浅层的胶原纤维呈现出由裂隙线（split lines）所揭示的独特取向模式。本研究提出一种仿真框架，用于预测行走过程中的软骨表面载荷，以探究软骨裂隙线的取向是否与软骨表面的主应变方向相符。该两步框架首先通过多体肌肉骨骼模型预测胫股关节运动学参数，随后将其施加于可变形模型以预测表面应变。可变形模型采用绝对节点坐标公式（absolute nodal coordinate formulation, ANCF）壳单元表征关节面，并通过弹簧-阻尼系统与内部压力模拟下方的软骨组织。本研究开展了三类仿真，分别预测内部压力引发的表面应变、行走诱发的表面应变，以及压力与行走载荷共同作用下的表面应变。仿真行走过程中，股骨与胫骨软骨的最大变形量略大于1 mm。软骨表面的第一主应变幅值最高可达3%。当纳入软骨内部压力引发的表面载荷时，时间平均第一主应变分布与文献中的软骨裂隙线图谱匹配度最佳。该结果表明，压力诱发的表面应变模式与所观测到的胶原纤维取向模式之间可能存在关联。