Eckstein F, Merz B, Schön M, Jacobs C R, Putz R
Anatomische Anstalt der Ludwig Maximilians Universität München, Germany.
Anat Embryol (Berl). 1999 Jan;199(1):85-97. doi: 10.1007/s004290050212.
In the present study, we tested the hypothesis that tension and bending, rather than compression alone, determine the functional adaptation of subchondral bone in incongruous joints. We investigated whether tensile stresses in the subchondral bone of the humero-ulnar articulation are affected by the direction of muscle and joint forces, and whether the tensile stresses are large enough to cause microstructural adaptation, specifically a preferential alignment of the trabeculae and the subchondral collagen fibres. Using a previously validated finite element model of the human humero-ulnar joint, we calculated the contact pressure, the principal compressive and tensile stresses, and the strain energy density in the subchondral bone for various flexion angles. A bicentric (ventro-dorsal) pressure distribution was found in the joint at 30 degrees to 120 degrees of flexion, with contact pressures of up to between 2.5 and 3 MPa in the ventral and dorsal aspects of the ulnar joint surface, but less than 0.5 MPa in the centre. The principal tensile stress in the subchondral bone of the trochlear notch quantitatively exceeded the principal compressive stress at low flexion angles (maximum 8.2 MPa), and the distribution of subchondral strain energy density differed substantially from that of the contact stress (r=-0.72 at 30 degrees and r=+0.58 at 90 degrees of flexion). No important tensile stress was computed in the trochlea humeri. On contact radiography, we found sagittally orientated subarticular trabeculae in the notch, running tangential to the surface. Furthermore, we observed sagittally orientated split lines in the subchondral bone of the notch of 20 cadaver joints, suggesting a ventro-dorsal orientation of the collagen fibres. The trochlea humeri, on the other hand, did not show a preferential direction of the subchondral split lines, these findings confirming the predictions of tensile stresses in the model. We conclude that, due to the important contribution of tension to subchondral bone stress, the distribution of subchondral density cannot be directly employed for assessing the long term distribution of joint pressure at the cartilage surface. The magnitude of the tensional stress varies considerably with the direction of the muscle and joint forces, and it appears large enough to cause functional adaptation of the subchondral bone on a microstructural level.
在本研究中，我们验证了一个假设，即张力和弯曲而非单纯的压缩决定了不协调关节中软骨下骨的功能适应性。我们研究了肱尺关节软骨下骨中的拉应力是否受肌肉和关节力方向的影响，以及这些拉应力是否大到足以引起微观结构适应性变化，特别是小梁和软骨下胶原纤维的优先排列。使用先前验证过的人体肱尺关节有限元模型，我们计算了不同屈曲角度下的接触压力、主压应力和拉应力以及软骨下骨中的应变能密度。在30度至120度屈曲时，关节中发现了双中心（腹背）压力分布，尺骨关节面腹侧和背侧的接触压力高达2.5至3兆帕，但中心处小于0.5兆帕。在低屈曲角度下，滑车切迹软骨下骨中的主拉应力在数量上超过了主压应力（最大值8.2兆帕），软骨下应变能密度的分布与接触应力的分布有很大差异（屈曲30度时r = -0.72，屈曲90度时r = +0.58）。在肱骨滑车中未计算出重要的拉应力。在接触放射成像中，我们在切迹中发现了矢状排列的关节下小梁，与表面相切。此外，我们在20个尸体关节切迹的软骨下骨中观察到矢状排列的分裂线，表明胶原纤维的腹背方向。另一方面，肱骨滑车未显示软骨下分裂线的优先方向，这些发现证实了模型中拉应力的预测。我们得出结论，由于张力对软骨下骨应力的重要贡献，软骨下密度分布不能直接用于评估软骨表面关节压力的长期分布。拉应力的大小随肌肉和关节力的方向有很大变化，并且似乎大到足以在微观结构水平上引起软骨下骨的功能适应性变化。
