Laboratory of Biomechanics, Justus-Liebig-University Giessen, Klinikstrasse 29, 35392 Giessen, Germany.
Laboratory of Biomechanics, Justus-Liebig-University Giessen, Klinikstrasse 29, 35392 Giessen, Germany.
Clin Biomech (Bristol). 2021 Feb;82:105283. doi: 10.1016/j.clinbiomech.2021.105283. Epub 2021 Jan 26.
Revision reverse shoulder arthroplasty (RSA) poses considerable surgical challenges. We hypothesized that a newly developed press-fit stem, which is modeled on the medullary canal of the supracondylar region of the distal humerus by a slight distal bend, achieve both correct fit and sufficient primary stability and that additional distal fixation by interlocking screws is favorable in case of advanced humeral bone loss.
A modular tapered press-fit stem was implanted in 16 Sawbone humeri in three consecutively created defect situations (200 mm (experimental group type 3°), 160 mm (type 4°) and 120 mm (type 5°) bone length above the epicondylar line. In experimental groups type 4° and 5°, additional distal interlocking screw fixation with one to three screws was tested. Primary stability was investigated by measuring micromotions with a high-precision rotational setup.
Highest relative micromotions were noted at the proximal end in experimental groups type 3° and type 4°, whereas in type 5° highest micromotions could be seen at the distal end. Overall micromotions were significantly lower in type 3° and increased with extended defect size. In experimental group type 5°, micromotions increased with reduced additional distal screw fixation.
The examined press-fit stem did not provide sufficient primary rotational stability in all constructs without additional support. Advanced distal humeral bone loss had a strong impact on primary fixation. In experimental group type 5° with 120 mm bone remaining, it might be beneficial to use three distal interlocking screws in the supracondylar region in order to neutralize torque and to avoid early loosening.
翻修反肩关节置换术（RSA）带来了相当大的手术挑战。我们假设一种新开发的压配合柄，其通过轻微的远端弯曲模仿肱骨干远端的髁上区域髓腔，既能实现正确的适配，又能提供足够的初始稳定性，并且在肱骨干严重骨量丢失的情况下，通过锁定螺钉进行额外的远端固定是有利的。
在连续创建的三种缺损情况下（200mm（实验分组 3°）、160mm（实验分组 4°）和 120mm（实验分组 5°）在髁上线以上的骨长度），在 16 个模拟肱骨干中植入了一种模块化锥形压配合柄。在实验分组 4°和 5°中，测试了额外的远端锁定螺钉固定，使用 1 至 3 颗螺钉。通过高精度旋转设置测量微运动来研究初始稳定性。
在实验分组 3°和 4°中，近端的相对微运动最大，而在实验分组 5°中，远端的微运动最大。总体微运动在实验分组 3°和 4°中较低，随着缺损尺寸的增加而增加。在实验分组 5°中，随着额外的远端螺钉固定减少，微运动增加。
在没有额外支撑的情况下，所检查的压配合柄在所有结构中都不能提供足够的初始旋转稳定性。严重的远端肱骨干骨量丢失对初始固定有很大影响。在实验分组 5°中，剩余 120mm 骨的情况下，在髁上区域使用三根远端锁定螺钉可能是有益的，以中和扭矩并避免早期松动。
