Nadorf Jan, Klein Simon B, Gantz Simone, Jakubowitz Eike, Kretzer Jan Philippe, Bischel Oliver E
Laboratory of Biomechanics and Implant Research, Clinic for Orthopedics and Trauma Surgery, Center for Orthopedics, Trauma Surgery and Spinal Cord Injury, Heidelberg University Hospital, Schlierbacher Landstr. 200A, Heidelberg, Germany.
Biometrics Consulting and Project Management, University Heidelberg, Im Neuenheimer Feld 130, Heidelberg, Germany.
Knee. 2017 Oct;24(5):1016-1024. doi: 10.1016/j.knee.2017.07.010. Epub 2017 Aug 6.
Aseptic loosening is the major reason for failure of distal femoral replacement using current modular megaprostheses. Although the same stems are used for proximal and distal replacement, survival rates in clinical studies with distal reconstruction were lower within the same system compared to proximal reconstruction. We analyzed whether primary stability as presupposition for long-term fixation can be achieved with a current tapered stem design. Additionally, we hypothesized that stem length affects primary stability depending on bone defect situations.
A modular tumor system (Megasystem-C®, Link GmbH, Hamburg, Germany) with two different tapered stems (100 and 160mm) was implanted in eight Sawbones® in two consecutively created defect situations (10 and 20cm proximal to knee joint level). Primary rotational stability was investigated by measuring relative micromotions between implant and bone to identify the main fixation areas and to characterize the fixation pattern.
The fixation differed between the two stem lengths and with respect to both defect situations; however in each case the main fixation area was located at or close to the femoral isthmus. Highest relative micromotions were measured with the 160-mm stem at the distal end within small bone defects and at the proximal end when defects were increased.
The analyzed design seemed to create sufficient primary stability along the main fixation areas of the implant. Based on these results and with respect to oncologic or potential revision situations, we suggest the use of the shorter stem to be more favorable in case of primary implant fixation.
无菌性松动是目前使用模块化大型假体进行股骨远端置换失败的主要原因。尽管近端和远端置换使用相同的柄，但在同一系统中，与近端重建相比，远端重建临床研究中的生存率较低。我们分析了采用当前的锥形柄设计能否实现作为长期固定前提的初始稳定性。此外，我们假设柄的长度会根据骨缺损情况影响初始稳定性。
将一个带有两种不同长度锥形柄（100毫米和160毫米）的模块化肿瘤系统（Megasystem-C®，德国汉堡的Link GmbH公司）植入八具Sawbones®模型中，设置两种连续的骨缺损情况（膝关节水平近端10厘米和20厘米处）。通过测量植入物与骨之间的相对微动来研究初始旋转稳定性，以确定主要固定区域并描述固定模式。
两种柄长度之间以及在两种骨缺损情况下固定情况均不同；然而，每种情况下主要固定区域均位于或靠近股骨干峡部。在小骨缺损时，160毫米柄在远端测得的相对微动最高，而当骨缺损增大时，在近端测得的相对微动最高。
所分析的设计似乎在植入物的主要固定区域产生了足够的初始稳定性。基于这些结果，并考虑到肿瘤学或潜在翻修情况，我们建议在初次植入固定时，使用较短的柄更为有利。
