Department of Trauma, Hand, Plastic and Reconstructive Surgery, Julius-Maximilians-University Wuerzburg, Wuerzburg, Germany; Department of Traumatology and Hand Surgery, St. Vincentius Clinic, Karlsruhe, Teaching Hospital Albert-Ludwigs-University Freiburg, Freiburg, Germany.
Department of Research and Development, Arthrex Inc., Munich, Germany.
J Shoulder Elbow Surg. 2021 Jun;30(6):1257-1265. doi: 10.1016/j.jse.2020.09.009. Epub 2020 Oct 1.
Proximal humeral fractures in elderly patients are frequently treated with reverse total shoulder arthroplasty, and tuberosity healing improves clinical outcome and patient satisfaction. So far reverse prostheses with different humeral inclination (HI) angles have been used. However, it has not been investigated yet if the HI angle affects the primary stability of the tuberosity fixation in primary reverse total shoulder arthroplasty for proximal humeral fractures in a biomechanical setting.
A 4-part fracture was created in 7-paired human cadaver proximal humeri after preceding power analysis. After randomization in a pairwise fashion, reverse prostheses with either 135° (n = 7) or 155° (n = 7) were implanted. The tuberosities were reduced anatomically to the metaphysis of the prostheses and were fixed with 3 suture cerclages in a standardized technique. Tightening was performed with a cerclage tension device with 50 Newton meter (N m). Before biomechanical testing, the initial vertical and horizontal gap formation was measured. The humeri were placed in a custom-made test setup enabling internal and external rotation. Cyclic loading with a gradually increasing load magnitude was applied with a material testing machine starting with 20 N m and increasing by 5 N m after each 100th cycle until failure (>15° rotation of the tuberosities). Any motion of the tuberosities was measured with a 3-dimensional camera system.
Overall, the 155° group reached an average of 1460 ± 270 cycles and the 135° group of 1900 ± 271 cycles (P = .048). In contrast to the 135° group, in the 155° group, a mean initial vertical (0.3 ± 0.7 mm) and horizontal (2.7 ± 3.3 mm) gap formation could be observed before cyclic loading. After 1100 cycles, the 155° group showed increased rotation of both lesser and greater tuberosities in all 3 axes around the humeral shaft compared with the 135° group.
Primary stability of the reattached tuberosities is significantly increased, whereas rotational movements are decreased in prostheses with an anatomic HI of 135° compared with a 155° HI according to the original Grammont design. In addition, a 135° HI allows an exact anatomic reposition of the tuberosities, whereas this was not possible for the 155° design. However, transferability and clinical relevance of these biomechanical results have to be verified with clinical studies.
老年人肱骨近端骨折常采用反式全肩关节置换术治疗，结节愈合可改善临床疗效和患者满意度。目前已经使用了具有不同肱骨倾斜（HI）角度的反式假体，但在生物力学环境下，对于肱骨近端骨折的初次反式全肩关节置换术，HI 角度是否会影响结节固定的初始稳定性尚未得到研究。
在先前的功率分析之后，在 7 对人体尸体肱骨近端创建了 4 部分骨折。随机两两分组，分别植入 HI 为 135°（n = 7）或 155°（n = 7）的反式假体。结节解剖复位至假体干骺端，采用标准化技术用 3 根缝线环扎固定。使用 50 牛顿米（N m）的环扎张力装置进行紧固。在生物力学测试之前，测量初始垂直和水平间隙形成。将肱骨置于定制的测试装置中，以实现内旋和外旋。采用材料试验机施加逐渐增加的载荷大小进行循环加载，起始载荷为 20 N m，每 100 次循环增加 5 N m，直到失效（结节旋转>15°）。使用三维摄像系统测量结节的任何运动。
总体而言，155°组平均达到 1460±270 个循环，而 135°组达到 1900±271 个循环（P =.048）。与 135°组相比，在 155°组中，在循环加载之前可以观察到平均初始垂直（0.3±0.7 mm）和水平（2.7±3.3 mm）间隙形成。在 1100 次循环后，与 135°组相比，155°组在所有 3 个围绕肱骨轴的方向上，较小和较大结节的旋转均增加。
与原始 Grammont 设计的 155°HI 相比，具有解剖学 HI 为 135°的假体可显著增加再附着结节的初始稳定性，同时减少旋转运动。此外，135°HI 可实现结节的精确解剖复位，而 155°设计则无法实现。然而，这些生物力学结果的可转移性和临床相关性还需要通过临床研究来验证。
