Rapperport D J, Carter D R, Schurman D J
J Orthop Res. 1985;3(4):435-46. doi: 10.1002/jor.1100030406.
Two-dimensional finite element analyses were conducted of the normal hip using contact elements at the joint surface. The models studied were constructed for a slice through the pubis, acetabulum, and ilium. In the analyses the proximal femur was pressed into the acetabulum and intraarticular pressures and principal stresses in the joint region were determined for different load magnitudes and directions and various boundary conditions. Three sets of boundary conditions were examined: (a) deformable pubic symphysis, (b) rigid pubic symphysis, and (c) simulations of experimental studies. In the deformable model the pubic symphysis was free to displace in the sagittal plane and rotate. In the rigid model the pubic symphysis was rigidly fixed. Superoposterior loading resulted in high-contact pressures at the acetabular dome for all sets of boundary conditions. For the deformable model subject to a more medially directed load the acetabulum closed in such a manner as to squeeze the head of the femur creating high-contact pressures superiorly and inferiorly. This resulted in significant compressive stresses in the superior dome cancellous bone and inferior cancellous bone. The cumulative effect of this squeezing action with normal biological remodeling may cause elongation of the femoral head resulting in asphericity and incongruity of the unloaded hip joint articular surfaces. Rigidly fixing the pubic symphysis stiffened the model and resulted in principal stress patterns that did not reflect trabecular density or orientations as well as those of the deformable pubic symphysis model. Finite element simulations of previous experimental studies modeled the close proximity of the fixation to the excised acetabulum. These boundary conditions prevented the squeezing caused by pelvis deformations. The resulting contact areas, pressure distributions, and bone stresses were very different from those of the more anatomic, deformable pubic symphysis model. These findings demonstrate the sensitivity of hip contact pressures and stresses to imposed boundary conditions and indicate that care should be taken to simulate anatomic conditions in experimental and theoretical studies.
使用关节表面的接触单元对正常髋关节进行了二维有限元分析。所研究的模型是针对通过耻骨、髋臼和髂骨的切片构建的。在分析中，将股骨近端压入髋臼，并针对不同的载荷大小和方向以及各种边界条件确定关节区域内的关节内压力和主应力。研究了三组边界条件：(a) 可变形耻骨联合，(b) 刚性耻骨联合，以及 (c) 实验研究的模拟。在可变形模型中，耻骨联合在矢状面内可自由位移并旋转。在刚性模型中，耻骨联合被刚性固定。对于所有边界条件组，后上方向加载都会导致髋臼穹顶处产生高接触压力。对于承受更向内侧方向载荷的可变形模型，髋臼以挤压股骨头的方式闭合，从而在上方和下方产生高接触压力。这导致上方穹顶松质骨和下方松质骨中出现显著的压应力。这种挤压作用与正常生物重塑的累积效应可能会导致股骨头伸长，从而导致未加载髋关节关节面的非球形和不协调。刚性固定耻骨联合使模型变硬，并导致主应力模式不能像可变形耻骨联合模型那样反映小梁密度或方向。先前实验研究的有限元模拟对固定装置与切除髋臼的紧密接近程度进行了建模。这些边界条件防止了骨盆变形引起的挤压。由此产生的接触面积、压力分布和骨应力与更符合解剖学的可变形耻骨联合模型有很大不同。这些发现证明了髋关节接触压力和应力对施加的边界条件的敏感性，并表明在实验和理论研究中应注意模拟解剖条件。
