Shoulder prostheses treating cuff tear arthropathy: a comparative biomechanical study.

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. RESULTS: 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. CONCLUSIONS: 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. RELEVANCE: This study explains why a successful functional outcome can be expected in CTA with a reversed prosthesis.     

Scapulothoracic and glenohumeral kinematics following an external rotation fatigue protocol

STUDY DESIGN: Repeated-measures experimental design. OBJECTIVE: To determine the effects of shoulder external rotator muscle fatigue on 3-dimensional scapulothoracic and glenohumeral kinematics. BACKGROUND: The external rotator muscles of the shoulder are important for normal shoulder function. Impaired performance of these muscles has been observed in subjects with impingement syndrome and it is possible that external rotator muscle fatigue leads to altered kinematics of the shoulder girdle. METHODS AND MEASURES: Twenty subjects without a history of shoulder pathology participated in this study. Three-dimensional scapulothoracic and glenohumeral kinematics were determined from electromagnetic sensors attached to the scapula, humerus, and thorax. Surface electromyographic (EMG) data were collected from the upper and lower trapezius, serratus anterior, anterior and posterior deltoid, and infraspinatus muscles. Median power frequency (MPF) values were derived from the raw EMG data and were used to indicate the degree of local muscle fatigue. Kinematic and EMG measures were collected prior to and immediately following the performance of a shoulder external rotation fatigue protocol. RESULTS: After completing the fatigue protocol subjects demonstrated less external rotation of the humerus. Additionally, they had less posterior tilt of the scapula in the beginning phase of arm elevation, and more scapular upward rotation and clavicular retraction in the mid ranges of arm elevation. CONCLUSIONS: Performance of an external rotation fatigue protocol results in altered scapulothoracic and glenohumeral kinematics. Further studies are needed to investigate the effects of external rotator muscle fatigue on scapulothoracic and glenohumeral kinematics in subjects with shoulder pathology.     

Influence of humeral prosthesis height on biomechanics of glenohumeral abduction. An in vitro study

BACKGROUND: During shoulder replacement surgery, the normal height of the proximal part of the humerus relative to the tuberosities frequently is not restored because of differences in prosthetic geometry or problems with surgical technique. The purpose of the present study was to determine the effect of humeral prosthesis height on range of motion and on the moment arms of the rotator cuff muscles during glenohumeral abduction. METHODS: Tendon excursions and abduction angles were recorded simultaneously in six cadaveric specimens during passive glenohumeral abduction in the scapular plane. Moment arms were calculated for each muscle by computing the slope of the tendon excursion-versus-glenohumeral abduction angle relationship. The experiments were carried out with the intact joint and after replacement of the humeral head with a prosthesis that was inserted in an anatomically correct position as well as 5 and 10 mm too high. RESULTS: Insertion of the prosthesis in positions that were 5 and 10 mm too high resulted in significant and marked reductions of the maximum abduction angle of 10 degrees (range, 5 degrees to 18 degrees ) and 16 degrees (range, 12 degrees to 20 degrees ), respectively. In addition, the moment arms of the infraspinatus and subscapularis decreased by 4 to 10 mm. This corresponded to a 20% to 50% decrease of the abduction moment arms of the infraspinatus and an approximately 50% to 100% decrease of the abduction moment arms of the subscapularis, depending on the abduction angle and the part of the muscle being considered. CONCLUSIONS: If a humeral head prosthesis is placed too high relative to the tuberosities, shoulder function is impaired by two potential mechanisms: (1) the inferior capsule becomes tight at lower abduction angles and limits abduction, and (2) the center of rotation is displaced upward in relation to the line of action of the rotator cuff muscles, resulting in smaller moment arms and decreased abduction moments of the respective muscles. Clinical Relevance: In patients managed with shoulder replacement surgery, limitation of range of motion, loss of abduction strength, and overload with long-term failure of the supraspinatus tendon are potential consequences of positioning the humeral head of the prosthesis proximal to the anatomic position.     

Hemiarthroplasty in rotator cuff tear arthropathy

Rotator cuff tear arthropathy results in a painful glenohumeral joint with poor function. Loss of the stabilizing effect of the rotator cuff allows superior subluxation of the humeral head. The poor mechanical advantage of the deltoid muscle creates a weak, poorly functioning shoulder. Hemiarthroplasty with a large humeral head component can relieve pain and retain some of the mechanical advantage of the deltoid by lateralizing the center of rotation of the humeral head and regaining deltoid length. A larger-than-anatomic humeral head decreases the risk of further superior subluxation of the humeral head by decreasing wear. Stability is regained by retensioning the deltoid muscle envelope. This article reviews the technique of large head hemiarthroplasty in this difficult reconstructive problem.     

The reverse shoulder prosthesis (Delta III) in acute shoulder fractures: technical considerations with respect to stability

The reverse shoulder prosthesis reverses the relationship between the scapular and humeral component, resulting in a mechanical advantage as the deltoid muscle is able to compensate for the rotator cuff deficiency. Based on this mechanical advantage, the reverse shoulder prosthesis has become an accepted alternative for the treatment of complex proximal humeral fractures. The purpose of this article is to discuss technical considerations related to stability in the use of the reverse shoulder prosthesis in acute shoulder fractures, based on clinical experience.     

Rehabilitation of shoulder joint instabilities

The overall goal of the rehabilitation period is a return to full range of motion and a strengthening of the muscles that have a role in protecting the shoulder from injury. Rehabilitation is accomplished gradually and is performed initially in a limited range that excludes the terminal 30 degrees at either end. Two key muscle groups are to be strengthened. One group is for the glenohumeral joint: the deltoid, latissimus dorsi, pectoralis major, and the rotator cuff muscles--especially the subscapularis muscle for internal rotation and the infraspinatus and the teres minor muscles for external rotation. The second group, the trapezius, rhomboids, and serratus anterior muscles, is strengthened for scapular control. Finally, general conditioning and trunk flexibility exercises are critical for a return to former competitive levels.     

反式全肩关节假体置换治疗巨大不可修复肩袖撕裂

目的探讨反式全肩关节置换术（reverse total shoulder arthroplasty,RTSA）治疗巨大不可修复肩袖撕裂的临床治疗效果。 方法对南京中医药大学附属医院2018年5月至2020年1月收治的采取RTSA治疗的13例巨大不可修复肩袖撕裂患者的临床资料进行回顾性分析。记录术前及最后一次随访时患者的肩关节前屈、外展、外旋活动,美国肩肘外科协会评分（American shoulder and elbow surgeons score,ASES）及美国加州大学洛杉矶分校（University of California at Los Angeles,UCLA）评分评估患者肩关节功能。并记录患者发生并发症的情况及影像学检查结果。术前行MR确定肩袖脂肪浸润程度,CT评价肩胛盂骨质情况及有无缺损,术后使用X线评估假体情况。 结果13例患者均随访至少12个月以上。统计术前与术后12个月数据之间的关系,术后12个月肩关节前屈、外展、外旋活动,ASES评分和UCLA评分较术前明显提高,差异具有统计学意义（P<0.01）。随访期内13例患者中有1例患者因局部血肿在术后1周行切开血肿清除引流术,所有患者功能恢复良好。 结论RTSA治疗巨大不可修复肩袖撕裂临床效果良好。     

Shoulder arthroplasty: evolving techniques and indications

The development of modern shoulder replacement surgery started over half a century ago with the pioneering work done by CS Neer. Several designs for shoulder prostheses are now available, allowing surgeons to select the best design for each situation. When the rotator cuff is intact, unconstrained prostheses produce reliable and reproducible results, with prosthesis survival rates of 97% after 10 years and 84% after 20 years. In patients with three- or four-part fractures of the proximal humerus, the outcome of shoulder arthroplasty depends largely on healing of the greater tuberosity, which is therefore a major treatment objective. Factors crucial to greater tuberosity union include selection of the optimal prosthesis design, flawless fixation of the tuberosities, and appropriate postoperative immobilization. The reverse shoulder prosthesis developed by Grammont has been recognized since 1991 as a valid option for patients with glenohumeral osteoarthritis. Ten-year prosthesis survival rates are 91% overall (including trauma and revisions) and 94% for glenohumeral osteoarthritis with head migration. These good results are generating interest in the reverse shoulder prosthesis as a treatment option in situations where unconstrained prostheses are unsatisfactory (primary glenohumeral osteoarthritis with marked glenoid cavity erosion; comminuted fractures in patients older than 75 years; post-traumatic osteoarthritis with severe tuberosity malunion or nonunion; massive irreparable rotator cuff tears with pseudoparalysis; failed rotator cuff repair; and proximal humerus tumor requiring resection of the rotator cuff insertions).     

Simulated joint and muscle forces in reversed and anatomic shoulder prostheses

Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0 degrees to 150 degrees of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90 degrees of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.     

Replacement arthroplasty of the rotator cuff deficient shoulder

The rotator cuff is often severely damaged in arthritis of the shoulder and there is no satisfactory technique for its repair. patients with a ruptured cuff and an eroded glenohumeral joint may have intractable pain, and standard methods of joint replacement are then inappropriate. A ball and socket prosthesis has been designed to replace the function of both the rotator cuff and the glenohumeral joint. Mechanical testing has shown that the scapular cup can be securely fixed. The outcome in 71 shoulders operated upon since 1973 is reported.     

Painful Shoulder After Surgery for Rotator Cuff Disease

Persistent shoulder pain after surgery for rotator cuff disease may be caused by conditions that are either extrinsic or intrinsic to the shoulder. Extrinsic causes of persistent shoulder pain include cervical radiculopathy, suprascapular neuropathy, abnormalities of scapular rotation (due to long-thoracic or spinal-accessory neuropathy), and adjacent or metastatic neoplasms. Causes of persistent pain that are intrinsic to the shoulder include both intra-articular conditions (e.g., glenohumeral osteoarthritis, adhesive capsulitis, recurrent anterior subluxation, and labral and bicipital tendon abnormalities) and extra-articular conditions (e.g., persistent subacromial impingement, persistent or recurrent rotator cuff defects, acromioclavicular arthropathy, and deltoid muscle deficiency). Successful management requires an accurate diagnosis, maximal rehabilitation, judicious use of surgical intervention, and a well-motivated patient. The results of revision surgery in patients with persistent subacromial impingement, with or without an intact cuff, are inferior to reported results after primary acromioplasty or rotator cuff repair.     

?Terrible triad�� der Schulter

A total of 22 patients with diverse lesions of the brachial plexus (18 of those with deltoid paralysis) had complete range of motion of the glenohumeral joint, contrary to the commonly accepted notion of the deltoid as the ??prime mover?? of the glenohumeral joint. Favorable results were obtained by rotator cuff reconstruction in 71 patients, in whom cuff tears were associated with various lesions of the brachial plexus, including 43 cases of ?? terrible triad?? and of these 8 cases with irreversible paralysis of the deltoid muscle. Based on these observations, the authors conclude that the supraspinatus muscle and the rotator cuff as a whole must be considered as the ??prime mover?? of the glenohumeral joint. The importance of early diagnosis of the condition of the rotator cuff (rupture or nerve lesion) and reconstruction of a ruptured cuff in these complex lesions of the shoulder is emphasized.     

Muscle and Joint Function After Anatomic and Reverse Total Shoulder Arthroplasty Using a Modular Shoulder Prosthesis

Changes in joint architecture and muscle loading resulting from total shoulder arthroplasty (TSA) and reverse total shoulder arthroplasty (RSA) are known to influence joint stability and prosthesis survivorship. This study aimed to measure changes in muscle moment arms, muscle lines of action, as well as muscle and joint loading following TSA and RSA using a metal‐backed uncemented modular shoulder prosthesis. Eight cadaveric upper extremities were assessed using a customized testing rig. Abduction, flexion, and axial rotation muscle moment arms were quantified using the tendon‐excursion method, and muscle line‐of‐force directions evaluated radiographically pre‐operatively, and after TSA and revision RSA. Specimen‐specific musculoskeletal models were used to estimate muscle and joint loading pre‐ and post‐operatively. TSA lateralized the glenohumeral joint center by 4.3 ± 3.2 mm, resulting in small but significant increases in middle deltoid force (2.0%BW) and joint compression during flexion (2.1%BW) (p < 0.05). Revision RSA significantly increased the moment arms of the major abductors, flexors, adductors, and extensors, and reduced their peak forces (p < 0.05). The superior inclination of the deltoid significantly increased while the inferior inclination of the rotator cuff muscles decreased (p < 0.05). TSA using an uncemented metal‐backed modular shoulder prosthesis effectively restores native joint function; however, lateralization of the glenoid component should be minimized intra‐operatively to mitigate increased glenohumeral joint loading and polyethylene liner contact stresses. Revision RSA reduces muscle forces required during shoulder function but produces greater superior joint shear force and less joint compression. The findings may help to guide component selection and placement to mitigate joint instability after arthroplasty. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1988–2003, 2019     

Use of the reverse shoulder prosthesis for the treatment of failed hemiarthroplasty in patients with glenohumeral arthritis and rotator cuff deficiency

We report the use of the reverse shoulder prosthesis in the revision of a failed shoulder hemiarthroplasty in 19 shoulders in 18 patients (7 men, 11 women) with severe pain and loss of function. The primary procedure had been undertaken for glenohumeral arthritis associated with severe rotator cuff deficiency. Statistically significant improvements were seen in pain and functional outcome. After a mean follow-up of 44 months (24 to 89), mean forward flexion improved by 26.4 degrees and mean abduction improved by 35 degrees . There were six prosthesis-related complications in six shoulders (32%), five of which had severe bone loss of the glenoid, proximal humerus or both. Three shoulders (16%) had non-prosthesis related complications. The use of the reverse shoulder prosthesis provides improvement in pain and function for patients with failure of a hemiarthroplasty for glenohumeral arthritis and rotator cuff deficiency. However, high rates of complications were associated with glenoid and proximal humeral bone loss.     

The biomechanics of the rotator cuff in health and disease – A narrative review

The rotator cuff has an important role in the stability and function of the glenohumeral joint. It is a complex anatomic structure commonly affected by injury such as tendinopathy and cuff tears. The rotator cuff helps to provide a stabilising effect to the shoulder joint by compressing the humeral head against the glenoid cavity via the concavity compression mechanism. To appreciate the function of the cuff it is imperative to understand the normal biomechanics of the cuff as well as the mechanisms involved in the pathogenesis of cuff disease.The shoulder joint offers a wide range of motion due to the variety of rotational moments the cuff muscles are able to provide. In order for the joint to remain stable, the cuff creates a force couple around the glenohumeral joint with coordinated activation of adjacent muscles, which work together to contain the otherwise intrinsically unstable glenohumeral joint and prevent proximal migration of the humerus. Once this muscular balance is lost, increased translations or subluxation of the humeral head may result, leading to changes in the magnitude and direction of the joint reaction forces at the glenohumeral joint. These mechanical changes may then result in a number of clinical presentations of shoulder dysfunction, disease and pain.This narrative review aims to highlight the importance of functional rotator cuff biomechanics whilst assessing the kinetics and kinematics of the shoulder joint, as well as exploring the various factors involved in cuff disease.     

Analysis of the scapulo-humeral rhythm for periarthritis scapulohumeralis

To clarify the scapulo-humeral rhythm in twenty-five patients with periarthritis scapulo-humeralis, the movements of the scapula and the humerus during arm elevation were measured and analysed using a fluoroscope and a computer, and the rhythm of five patient with rotator cuff tear was compared with that of seven normal subjects. The ratio of scapular movement to humeral one in the patients with severe shoulder contracture due to periarthritis scapulohumeralis was greater than that of patients with mild contracture and that of normal subjects. In the patients with rotator cuff tear, wider range of scapular rotation was observed in the early phase of the motion. During the early phase of arm elevation, the humeral head moved to the upper direction by means of gliding in the patients with severely contracted shoulder and rotator cuff tear, and in the patients with mildly contracted shoulder the humeral head moved to the upper direction by means of ball rolling. In the normal subjects no such upward movement of the humeral head was observed. We believe that the restriction of the glenohumeral joint motion and dysfunction of the rotator cuff, which were caused by periarthritis scapulohumeralis, may break down the scapulohumeral rhythm.     

A New Surgical Technique for Extensive Exposure of the Proximal Humerus and Shoulder

Different techniques have been described for surgical exposure of the shoulder and proximal humerus. However, the neurovascular and muscular anatomy in the proximity of the humerus precludes the use of a “safe” extensive approach. We here present a new technique for extensive exposure of the proximal humerus and shoulder for wide resection of tumors. By reflecting the deltoid with its origin as an osteomyocutaneous flap downwards and backwards, the entire shoulder, including the rotator cuff and proximal humerus, are exposed with minimal damage to the blood supply and function of the deltoid muscle. This approach, which is a logical combination of anterior, transacromial and deltoid splitting approaches, was used in 17 patients, 11 achieving satisfactory functional results. Our new surgical approach reduces intraoperative damage to the blood supply of the deltoid and results in better function of the shoulder postoperatively because both the powerful intermediate muscle fibers of the deltoid and its acromial origin remain intact.     

Analysis of the scapulohumeral rhythm

The movement of the shoulder complex was once aptly described by Codman as the "scapulohumeral rhythm". To demonstrate this rhythm, 20 normal men and four patients with rotator cuff rupture were asked to elevate their arms smoothly in approximately three seconds and five seconds in front of a fluoroscope with or without load. The X-ray was irradiated perpendicularly in the scapular plane. The movements were calculated using a computer. In the normal men, the ratio of the scapular movements to humeral movements was not constant during scapular abduction. The movements of the instant center of the humerus occurred in a small area during abduction, and the result suggested that the movement of the glenohumeral joint was almost rotational. The movements of the instant center of the scapula occurred in a relatively large area during abduction. The movements of the shoulder complex with cuff rupture were quite different from those of normal men.     

Optimal positioning of the humeral component in the reverse shoulder prosthesis

Introduction

Total reverse shoulder arthroplasty is becoming more and more the standard therapeutic practice for glenohumeral arthropathy with massive lesions of the rotator cuff. The biomechanical principle of this prosthesis is represented by the reversion of the normal anatomy of the shoulder joint. This non-anatomical prosthesis leads to a medialization of the rotation centre of the glenohumeral joint and also to a distalization of the humeral head. All that causes a deltoid tension increasing so allowing a larger abduction of the arm. Main complications of the reverse shoulder prosthesis are due to the joint instability, the scapular notching and the wear of the polyethylene insert.

Purpose

The main goal of the present work is to study the effect of the positioning of the humeral component on the intrinsic stability of the reverse shoulder prosthesis. In particular, through finite element method simulations, the variation of the stability ratio of the shoulder joint has been calculated for both vertical and horizontal dislocating loads depending on the humeral stem version angle. Moreover, in order to estimate the wear of the polyethylene cup, some analyses have been developed to calculate the pressures on the polyethylene insert.

Results

The obtained results demonstrate the dislocation of a shoulder prosthesis and the wear of the polyethylene insert can be prevented or limited by conveniently varying the version angle of the humeral component.     

复杂肱骨近端骨折人工肱骨头置换术中肩袖重建的长期疗效观察

目的探讨Neer 3、4部分肱骨近端骨折人工肱骨头置换术中肩袖重建的远期临床效果。方法回顾性分析自2001-01—2012-12采用人工肱骨头置换术治疗的25例Neer 3、4部分肱骨近端骨折。术前测量健侧大结节最低点至肱骨头最高点的距离,术中尽量解剖复位肱骨大、小结节,合理控制假体高度及后倾角度,尽可能修复重建损伤肩袖,术后分阶段康复锻炼。结果本组22例获得有效随访,随访时间平均120(49~190)个月。末次随访时ASES评分为80~92(86.28±3.36)分,肩关节内旋至T10水平,患肢主动前屈上举125°~135°,外旋36°~42°。1例合并臂丛神经损伤者术后肩关节功能恢复满意。结论对于骨折端无法良好复位、肱骨头缺血性坏死可能性大的复杂肱骨近端骨折,人工肱骨头置换同时进行精细的肩袖重建可以获得无痛和良好运动范围的肩关节。