Haislup Brett D, Ashmyan Roman, Johnston Peter S, Wright Melissa A, Abbasi Pooyan, Murthi Anand M
Department of Orthopaedic Surgery, MedStar Union Memorial Hospital, Baltimore, MD, USA.
Georgetown University School of Medicine, Washington, DC, USA.
JSES Int. 2022 Sep 13;6(6):884-888. doi: 10.1016/j.jseint.2022.08.010. eCollection 2022 Nov.
Small changes in deltoid tension and moment arm due to glenosphere lateralization may be associated with an increase in acromion or scapular spine strain in reverse shoulder arthroplasty (RSA), which can lead to stress fracture. The coracoacromial ligament (CAL) may be protective and lower the strain seen on the acromion or scapular spine. This biomechanical study investigated the impact of glenosphere lateralization and CAL integrity on acromion and scapular spine strain after RSA.
Ten cadaveric specimens were tested on a custom dynamic shoulder frame. Acromial and scapular spine strain were measured at 0°, 30°, and 60° of abduction using strain rosettes fixed to the acromion (Levy Type 2) and the scapular spine (Levy Type 3). Specimens were first tested with a standard commercially available RSA implant with zero lateralization and then subsequently with the +3 and +6 lateralizing glenospheres for that implant. The CAL was then cut in each specimen and testing was repeated with the 0, +3, and +6 glenospheres. Maximal strain was recorded at both the acromion and scapular spine and analysis of variance compared strain across various abduction angles and glenospheres with and without CAL transection.
In the intact CAL group, maximal strain decreased significantly at the acromion with abduction from 0° to 30° and 0° to 60°, however, at the scapular spine abduction did not significantly impact strain. Maximal strain decreased significantly with increasing abduction from 0 to 30 and 0 to 60 at both the acromion and scapular spine in the cut CAL group. Average strain at the acromion was significantly higher in the cut group (844.7 με) versus the intact group (580.3 με), a difference of 31.3% ( = .0493). Average strain at the scapular spine, did not differ in the cut group (725 με) compared with the intact group (787 με) ( = .3666). There were no statistically significant differences in acromial or scapular spine strain between various levels of glenosphere lateralization in either the cut or intact state.
In this biomechanical study, arm abduction decreased acromial and scapular spine strain following RSA. Cutting the CAL significantly increased strain at the acromion, and did not significantly alter strain at the scapular spine for all angles of abduction, differing from prior literature. Glenosphere lateralization did not have a significant effect on strain at the levels studied regardless of CAL status. Continued study of the complexion relationship between surgical and implant factors on strain following RSA is needed.
在反肩关节置换术（RSA）中，由于关节盂球窝外移导致三角肌张力和力臂的微小变化，可能与肩峰或肩胛冈应变增加有关，这可能导致应力性骨折。喙肩韧带（CAL）可能具有保护作用，并降低肩峰或肩胛冈上的应变。本生物力学研究探讨了关节盂球窝外移和CAL完整性对RSA术后肩峰和肩胛冈应变的影响。
在定制的动态肩部框架上对10个尸体标本进行测试。使用固定在肩峰（Levy 2型）和肩胛冈（Levy 3型）上的应变片，在0°、30°和60°外展角度测量肩峰和肩胛冈的应变。首先使用零外移的标准市售RSA植入物对标本进行测试，然后使用该植入物的+3和+6外移关节盂球窝进行后续测试。然后在每个标本中切断CAL，并使用0、+3和+6关节盂球窝重复测试。记录肩峰和肩胛冈的最大应变，并通过方差分析比较在有和没有CAL横断的情况下，不同外展角度和关节盂球窝的应变。
在完整CAL组中，随着外展角度从0°增加到30°和从0°增加到60°，肩峰处的最大应变显著降低，然而在肩胛冈处外展并未显著影响应变。在切断CAL组中，随着外展角度从0°增加到30°和从0°增加到60°，肩峰和肩胛冈处的最大应变均显著降低。切断组肩峰处的平均应变（844.7με）显著高于完整组（580.3με），相差31.3%（P = 0.0493）。切断组肩胛冈处的平均应变（725με）与完整组（787με）相比无差异（P = 0.3666）。在切断或完整状态下，不同程度关节盂球窝外移之间，肩峰或肩胛冈应变无统计学显著差异。
在本生物力学研究中，手臂外展可降低RSA术后肩峰和肩胛冈的应变。切断CAL显著增加了肩峰处的应变，并且在所有外展角度下均未显著改变肩胛冈处的应变，这与先前的文献不同。无论CAL状态如何，在所研究的水平上，关节盂球窝外移对应变均无显著影响。需要继续研究RSA术后手术和植入物因素与应变之间的复杂关系。
