Imaging Research Laboratories, Robarts Research Institute, 100 Perth Drive, London, ON, N6A 5K8, Canada.
Clin Orthop Relat Res. 2012 Jul;470(7):1847-54. doi: 10.1007/s11999-011-2143-0.
To accurately quantify polyethylene wear in retrieved arthroplasty components, the original geometry of the component must be estimated accurately using a reference geometry such as a computer-aided design (CAD) model or a never-implanted insert. However, differences may exist between the CAD model and manufactured inserts resulting from manufacturing tolerances.
QUESTIONS/PURPOSES: We quantified the deviations between CAD models and newly manufactured inserts and determined how these deviations compared with using a never-implanted insert as a reference geometry.
We obtained five cruciate-retaining (CR) and five posterior-stabilizing (PS) tibial inserts and their CAD models. The inserts were scanned and reconstructed using microcomputed tomography (micro-CT). Differences in volume and surface geometry were measured among (1) the individual inserts; (2) between the inserts and a CAD model; and (3) between the inserts and a reference geometry constructed from multiple scanned inserts averaged together.
The micro-CT volumes were, on average, 0.4% smaller (34-178 mm(3)) than the CAD model volumes. The mean deviation between the CAD model and insert surface geometry was 25.7 μm smaller for CR and 36.8 μm smaller for PS. The mean deviation between the inserts and an averaged reference geometry was 1.4 μm larger for CR and 0.4 μm smaller for PS.
Deviations exist between manufactured tibial inserts and CAD models that could cause errors in wear measurements. Scanned inserts may better represent the preimplantation geometry of worn inserts than CAD models, depending on the manufacturing variability between lots.
The magnitude of the error in estimation of the preimplantation geometry of a retrieved component could add or subtract the equivalent of 1 year of wear.
为了准确地量化从关节置换假体中取出的聚乙烯磨损量，必须使用参考几何形状（如 CAD 模型或未植入的插入物）准确估计组件的原始几何形状。然而，由于制造公差，CAD 模型和制造的插入物之间可能存在差异。
问题/目的：我们量化了 CAD 模型和新制造的插入物之间的偏差，并确定了这些偏差与使用未植入的插入物作为参考几何形状相比的情况。
我们获得了五个十字韧带保留（CR）和五个后稳定（PS）胫骨插入物及其 CAD 模型。使用微计算机断层扫描（micro-CT）对插入物进行扫描和重建。在以下方面测量了体积和表面几何形状的差异：（1）单个插入物之间；（2）插入物与 CAD 模型之间；（3）插入物与由多个扫描插入物平均构建的参考几何形状之间。
micro-CT 体积平均比 CAD 模型体积小 0.4%（34-178mm³）。CR 的 CAD 模型和插入物表面几何形状之间的平均偏差小 25.7μm，PS 的平均偏差小 36.8μm。CR 的插入物和平均参考几何形状之间的平均偏差大 1.4μm，PS 的平均偏差小 0.4μm。
制造的胫骨插入物与 CAD 模型之间存在偏差，这可能导致磨损测量中的误差。扫描的插入物可能比 CAD 模型更好地代表磨损插入物的植入前几何形状，具体取决于批次之间的制造可变性。
对取回组件的植入前几何形状的估计误差的大小可能会增加或减少相当于 1 年的磨损量。
