De Wilde L F, Audenaert E A, Berghs B M
Department of Orthopaedic Surgery, Physical Medicine & Rehabilitation, Ghent University Hospital, De Pintelaan 185, B-9000, Belgium.
J Orthop Res. 2004 Nov;22(6):1222-30. doi: 10.1016/j.orthres.2004.03.010.
Painful cuff tear arthropathy (CTA) affects the independence of the elderly. Surgical treatment often consists of joint replacement, the functional outcome of which remains variable. Knowledge of the biomechanical properties of the different prosthetic designs can guide the orthopaedic surgeon in the choice of implant to predict its clinical result. A 3-D computer model of the glenohumeral joint is used to analyse the moment of the deltoid muscle in the scapular plane. A geometrical 3-D ball-and-socket model of the shoulder joint was used to calculate (1) the angle-force relationships, (2) the moment arm of the deltoid muscle and (3) the moment of the deltoid muscle components, for increasing degrees of arm elevation in the scapular plane. In this 3-D model, a clinical thoraco-scapular rhythm analysis was implemented, based on measurements in normal subjects, patients treated with an anatomical prosthesis and patients treated with an inversed delta III prosthesis. These data were compared for 10 different prosthetic treatment options.
Muscle angle-force curves show a favourable slope in non-anatomical prosthetic designs, where the centre of rotation of the glenohumeral joint is medialized, the deltoid muscle is elongated and the humeral shaft is lateralized. On the contrary, anatomical prosthetic designs do not perform well in this computer analysis.
From a biomechanical point of view, a shoulder prosthesis which medializes the centre of rotation, lengthens the deltoid muscle and increases the deltoid lever arm, results in a significantly more powerful abduction of the shoulder, despite complete loss of rotator cuff function.
This study explains why a successful functional outcome can be expected in CTA with a reversed prosthesis.
疼痛性肩袖撕裂关节病（CTA）影响老年人的独立性。手术治疗通常包括关节置换，但其功能结果仍存在差异。了解不同假体设计的生物力学特性可以指导骨科医生选择植入物，以预测其临床效果。使用三维计算机模型分析肩胛平面中三角肌的力矩。使用肩关节的几何三维球窝模型来计算（1）角度-力关系，（2）三角肌的力臂，以及（3）三角肌各部分的力矩，以评估在肩胛平面中手臂抬高程度增加时的情况。在这个三维模型中，基于对正常受试者、接受解剖型假体治疗的患者和接受反三角Ⅲ型假体治疗的患者的测量，进行了临床胸肩节律分析。对10种不同的假体治疗方案进行了这些数据的比较。
在非解剖型假体设计中，肌肉角度-力曲线显示出有利的斜率，其中肱盂关节的旋转中心向内侧移位，三角肌拉长，肱骨干向外侧移位。相反，在这种计算机分析中，解剖型假体设计表现不佳。
从生物力学角度来看，一种使旋转中心向内侧移位、拉长三角肌并增加三角肌力臂的肩关节假体，尽管肩袖功能完全丧失，但能显著增强肩部的外展力量。
本研究解释了为什么使用反置假体治疗CTA可预期获得成功的功能结果。
