Reeves Jacob M, Spangenberg Gregory W, Elwell Josie A, Stewart Ben, Vanasse Tom, Roche Chris, Faber Kenneth J, Langohr G Daniel G
Department of Mechanical and Materials Engineering, The University of Western Ontario, London, ON, Canada.
The Roth | McFarlane Hand and Upper Limb Centre, London, ON, Canada.
JSES Int. 2023 Jul 24;7(6):2445-2453. doi: 10.1016/j.jseint.2023.06.023. eCollection 2023 Nov.
Shoulder arthroplasty humeral stem design has evolved to include various shapes, coatings, lengths, sizes, and fixation methods. While necessary to accommodate patient anatomy characteristics, this creates a surgical paradox of choice. The relationship between the surgeon's selection of short-stem implant size and construct stiffness, resistance to subsidence and micromotion has not been assessed.
Eight paired cadaveric humeri were reconstructed with surgeon-selected (SS) and 2-mm diametrically larger (SS+2) short-stemmed press-fit implants. Each reconstruction was subjected to 2000 cycles of 90° forward flexion loading, and stem subsidence and micromotion were measured using optical tracking. Compressive stiffness of the stem-bone reconstruction was then assessed by applying a load in-line with the stem axis that resulted in 5 mm of stem subsidence.
Increasing stem size by 2 mm resulted in the construct stiffness more than doubling compared to SS stems (-741 ± 243 N/mm vs. -334 ± 120 N/mm; = .003; power = 0.971). These larger stems also subsided significantly less than their SS counterparts (SS: 1.2 ± 0.6 mm; SS+2: 0.5 ± 0.5 mm; = .029; power = 0.66), though there were no significant changes in micromotion (SS: 169 ± 59 μm; SS+2: 187 ± 52 μm; = .506; power = 0.094).
The results of this study highlight the importance of proper short-stem sizing, as a relatively small 2 mm increase in diametral size was observed to significantly impact construct stiffness, which could increase the risk of stress shielding and implant loosening. Future work should focus on developing tools that objectively quantify bone quality and aid surgeons in selecting the appropriate size short-stem humeral implants for a particular patient.
肩关节置换术中肱骨干假体的设计不断发展，包括各种形状、涂层、长度、尺寸和固定方法。虽然这些设计对于适应患者的解剖特征是必要的，但这也带来了手术选择的难题。外科医生选择的短柄植入物尺寸与结构刚度、下沉阻力和微动之间的关系尚未得到评估。
使用外科医生选择的（SS）和直径大2毫米（SS + 2）的短柄压配合植入物对八对尸体肱骨进行重建。每次重建都要承受2000次90°前屈加载循环，并使用光学跟踪测量假体下沉和微动。然后通过沿假体轴线施加导致假体下沉5毫米的载荷来评估假体 - 骨重建的压缩刚度。
与SS假体相比，直径增加2毫米导致结构刚度增加一倍以上（-741±243 N/mm对-334±120 N/mm；P = 0.003；检验效能 = 0.971）。这些更大的假体下沉也明显少于其SS对应物（SS：1.2±0.6毫米；SS + 2：0.5±0.5毫米；P = 0.029；检验效能 = 0.66），尽管微动没有显著变化（SS：169±59微米；SS + 2：187±52微米；P = 0.506；检验效能 = 0.094）。
本研究结果强调了正确选择短柄尺寸的重要性，因为观察到直径相对较小地增加2毫米会显著影响结构刚度，这可能会增加应力遮挡和植入物松动的风险。未来的工作应集中在开发能够客观量化骨质量并帮助外科医生为特定患者选择合适尺寸的短柄肱骨头植入物的工具上。
