Coats-Thomas Margaret S, Marra Guido, Ludvig Daniel, Garg Ankur, Perreault Eric J, Seitz Amee L
Biomedical Engineering, Northwestern University, Evanston, Illinois.
Shirley Ryan AbilityLab, Chicago, Illinois.
JB JS Open Access. 2024 Jan 9;9(1). doi: 10.2106/JBJS.OA.23.00053. eCollection 2024 Jan-Mar.
Patients with persistent glenohumeral osteoarthritis symptoms despite nonoperative management may pursue anatomic total shoulder arthroplasty (TSA). TSA revision rates are higher in patients with preoperative eccentric (asymmetric posterior erosion) compared with concentric (symmetric) glenoid deformity. If posterior rotator cuff deficiency demonstrated preoperatively in patients with eccentric deformity persists after TSA, it may manifest as relative weakness in external compared with internal rotation secondary to deficient activity of the shoulder external rotator muscles. Persistent posterior rotator cuff deficiency is hypothesized to contribute to TSA failures. However, it remains unknown whether rotational strength is impaired after TSA in patients with eccentric deformity. Our goal was to determine if patients with eccentric deformity exhibit relative external rotation weakness that may be explained by posterior rotator cuff deficiency after TSA.
Patients who were >1 year after TSA for primary glenohumeral osteoarthritis and had had preoperative eccentric or concentric deformity were prospectively recruited. Torque was measured and electromyography was performed during maximal isometric contractions in 26 three-dimensional direction combinations. Relative strength in opposing directions (strength balance) and muscle activity of 6 shoulder rotators were compared between groups.
The internal (+) and external (-) rotation component of strength balance did not differ in patients with eccentric (mean internal-external rotation component of strength balance: -7.6% ± 7.4%) compared with concentric deformity (-10.3% ± 6.8%) (mean difference: 2.7% [95% confidence interval (CI), -1.3% to 6.7%]; p = 0.59), suggesting no relative external rotation weakness. Infraspinatus activity was reduced in patients with eccentric (43.9% ± 10.4% of maximum voluntary contraction [MVC]) compared with concentric (51.3% ± 10.4% of MVC) deformity (mean difference: -7.4% [95% CI, -13.4% to -1.4%] of MVC; p = 0.04).
A relative external rotation strength deficit following TSA was not found, despite evidence of reduced infraspinatus activity, in the eccentric-deformity group. Reduced infraspinatus activity suggests that posterior rotator cuff deficiencies may persist following TSA in patients with eccentric deformities. Longitudinal study is necessary to evaluate muscle imbalance as a contributor to higher TSA failure rates.
Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
尽管采用了非手术治疗，但仍有持续性盂肱关节骨关节炎症状的患者可能会选择解剖型全肩关节置换术（TSA）。与同心（对称）型盂肱关节畸形患者相比，术前存在偏心（不对称后侵蚀）型盂肱关节畸形的患者TSA翻修率更高。如果术前在偏心畸形患者中表现出的后方肩袖缺损在TSA术后持续存在，可能会表现为由于肩部外旋肌活动不足，导致外旋相对于内旋出现相对无力。持续的后方肩袖缺损被认为是导致TSA失败的原因。然而，对于存在偏心畸形的患者，TSA术后旋转力量是否受损尚不清楚。我们的目标是确定存在偏心畸形的患者是否表现出相对的外旋无力，这可能是由TSA术后后方肩袖缺损所导致的。
前瞻性招募原发性盂肱关节骨关节炎接受TSA术后超过1年且术前存在偏心或同心畸形的患者。在26种三维方向组合的最大等长收缩过程中测量扭矩并进行肌电图检查。比较两组之间相反方向的相对力量（力量平衡）和6条肩部旋转肌的肌肉活动。
偏心畸形患者（力量平衡的平均内 - 外旋转分量：-7.6%±7.4%）与同心畸形患者（-10.3%±6.8%）相比，力量平衡的内（+）和外（-）旋转分量没有差异（平均差异：2.7%[95%置信区间（CI），-1.3%至6.7%]；p = 0.59），表明不存在相对的外旋无力。与同心畸形（最大自主收缩[MVC]的51.3%±10.4%）相比，偏心畸形患者的冈下肌活动减少（MVC的43.9%±10.4%）（平均差异：-7.4%[95%CI，-13.4%至-1.4%]的MVC；p = 0.04）。
在偏心畸形组中，尽管有冈下肌活动减少的证据，但未发现TSA术后存在相对的外旋力量不足。冈下肌活动减少表明，存在偏心畸形的患者TSA术后后方肩袖缺损可能持续存在。有必要进行纵向研究以评估肌肉失衡是否是导致TSA更高失败率的一个因素。
预后水平III。有关证据水平的完整描述，请参阅作者指南。
