Division of Sports Medicine, Department of Orthopaedic Surgery, New England Baptist Hospital, Boston, MA, USA.
Department of Orthopaedic Surgery, Novant Health, Huntersville, NC, USA.
J Shoulder Elbow Surg. 2020 Nov;29(11):2395-2405. doi: 10.1016/j.jse.2020.04.004. Epub 2020 Jun 9.
The purpose was to analyze the influence of deltoid lengthening due to different implant designs and anatomic variations of the acromion and scapular spine (SS) in the parasagittal plane on strain patterns after reverse shoulder arthroplasty (RSA).
Ten cadaveric shoulders with strain rosettes placed on the surface of the acromial body (Levy II) and SS (Levy III) were tested using a shoulder simulator. RSA using humeral onlay (+3, +5, +8, +10, +13 mm) and glenosphere lateralization (0, +6 mm) was performed. Arm lengthening and magnitude of strain on acromion/SS were measured. The length of deltoid was assessed using validated computer modeling. Anatomic variance of the SS angle and position of acromion in relation to the scapular plane was examined. For comparison of strain as a function of deltoid lengthening, 25 mm was used as a threshold value for comparison based on previous literature demonstrating a decrease in Constant score and active anterior elevation in patients with arm lengthening >25 mm.
At maximal deltoid lengthening (30.8 mm), average strains were 1112 με (acromion) and 1165 με (SS) (P < .01). There was an 82.6% increase in acromial strain at maximum lengthening compared with 25 mm (P = .02) and a strain increase of 79 με/mm deltoid lengthening above a threshold of 25 mm. The strain results delineated 2 anatomic groups: 5 of 10 specimens (group A) showed higher strain on SS (1445 με) vs. acromion (862 με, P = .02). Group A had a more posteriorly oriented acromion, whereas group B was anteriorly oriented (P < .001).
Deltoid lengthening above 25 mm produced large strains on the acromion/SS. Anatomic variation may indicate that as the acromion is more posteriorly oriented, the SS takes more strain from the deltoid vs. the acromion. Our study's data may help surgeons identify a high-risk population for increased strain patterns after RSA.
本研究旨在分析在矢状位上，由于不同的植入物设计和肩峰及肩胛脊柱（SS）解剖变异导致的三角肌延长对反肩关节置换（RSA）后应变模式的影响。
使用肩部模拟器对表面贴有应变花的 10 具尸体肩部（Levy II 肩峰体和 Levy III SS）进行测试。采用肱骨上置（+3、+5、+8、+10、+13mm）和肱骨头外侧化（0、+6mm）进行 RSA。测量肩峰/SS 的臂长延长和应变幅度。使用经过验证的计算机建模评估三角肌的长度。检查 SS 角度和肩峰相对于肩胛平面的位置的解剖变异。为了比较三角肌延长与应变的关系，根据先前的文献，将 25mm 作为阈值，因为该文献表明在臂长延长>25mm 的患者中，Constant 评分和主动前抬高都会降低，因此将 25mm 作为阈值用于比较。
在三角肌最大延长（30.8mm）时，平均应变分别为 1112με（肩峰）和 1165με（SS）（P<0.01）。与 25mm 相比，最大延长时肩峰的应变增加了 82.6%（P=0.02），三角肌延长超过 25mm 时，应变增加 79με/mm。应变结果将 10 个标本分为 2 个解剖组：5 个标本（A 组）的 SS（1445με）的应变明显高于肩峰（862με，P=0.02）。A 组的肩峰更向后倾斜，而 B 组则向前倾斜（P<0.001）。
三角肌延长超过 25mm 会在肩峰/SS 上产生较大的应变。解剖变异可能表明，随着肩峰向后倾斜，SS 从三角肌中承受的应变比肩峰更大。我们的研究数据可以帮助外科医生识别 RSA 后应变模式增加的高危人群。
