Wasielewski Ray C
Ohio State University Hospitals, Columbus, 43214, USA.
Clin Orthop Relat Res. 2002 Nov(404):232-46. doi: 10.1097/00003086-200211000-00037.
Wear of the insert backside occurs ostensibly because of micromotion at the undersurface articulation that occurs with loading. When a cyclic axial load was applied to contemporary knee implants, all inserts tested moved 2 to 25 microm in the shear plane relative to the metal backing suggesting that undersurface motion may be inevitable. Variables that increase the forces between the insert and metal backing can worsen relative micromotion and backside wear. Forces at the undersurface articulation, created during physiologic loading, are influenced by insert type, articular design, and surgical technique. Increasing articular insert constraint can cause forces at the main articulation to be resisted and transferred to this and the other interfaces. Designs with a cam post mechanism that force rollback at a certain flexion angle create a significant force in this shear plane. Inserts with highly conforming articular geometries can have a similar affect if used to inhibit anteroposterior or mediolateral motion of the femur on the tibial insert. Component alignment and position, and ligament balance also may influence backside wear as suggested by the great variability of wear patterns seen on like insert retrievals and by kinematic differences observed in fluoroscopic studies of the same implant design. Only by understanding these potential causes of backside motion and subsequent wear, can backside wear be mitigated.
垫片背面的磨损表面上似乎是由于加载时在关节面下表面发生的微动所致。当对当代膝关节植入物施加周期性轴向载荷时，所有测试的垫片相对于金属背板在剪切平面内移动了2至25微米，这表明关节面下表面的运动可能是不可避免的。增加垫片与金属背板之间力的变量会加剧相对微动和背面磨损。生理加载过程中在关节面下表面产生的力受垫片类型、关节设计和手术技术的影响。增加关节垫片的约束会导致主关节处的力被抵抗并转移到此处和其他界面。具有凸轮柱机制且在特定屈曲角度强制后滚的设计会在该剪切平面内产生显著的力。如果用于抑制股骨在胫骨垫片上的前后或内外侧运动，具有高度贴合关节几何形状的垫片可能会有类似影响。组件对齐和位置以及韧带平衡也可能影响背面磨损，这从类似垫片取出物上看到的磨损模式的巨大变异性以及对相同植入物设计的荧光透视研究中观察到的运动学差异可以看出。只有通过了解背面运动和后续磨损的这些潜在原因，才能减轻背面磨损。
