Thoracohumeral muscle activity alters glenohumeral joint biomechanics during active abduction.

Normal function of the glenohumeral joint depends on coordinated muscle forces that stabilize the joint while moving the shoulder. These forces can either provide compressive forces to press the humeral head into the glenoid or translational forces that may destabilize the glenohumeral joint. The objective of this study was to quantify the effect of pectoralis major and latissimus dorsi muscle activity on glenohumeral kinematics and joint reaction forces during simulated active abduction. Nine fresh-frozen whole upper extremities were tested using a dynamic shoulder testing apparatus. Seven muscle force combinations were examined: a standard combination and 10%, 20%, or 30% of the deltoid force applied to the latissimus dorsi or pectoralis major tendon, respectively. Pectoralis major and latissimus dorsi muscle activity decreased the maximum angle of glenohumeral abduction and external rotation, and increased the maximum horizontal adduction angle compared to the standard muscle combination. Thoracohumeral muscle activity also created a more anteriorly directed joint reaction force that resulted in anterior translation compared to the standard muscle combination. Therefore, the ratio between anteriorly directed translational forces and compressive forces increased during abduction due to this muscle activity, suggesting that thoracohumeral muscle activity may decrease glenohumeral stability based on the joint position and applied loads. A better understanding of the contribution of muscle forces to stability may improve rehabilitation protocols for the shoulder aimed at maximizing compression and minimizing translation at the glenohumeral joint.     

Influence of rotator cuff tears on glenohumeral stability during abduction tasks

One of the main goals in reconstructing rotator cuff tears is the restoration of glenohumeral joint stability, which is subsequently of utmost importance in order to prevent degenerative damage such as superior labral anterior posterior (SLAP) lesion, arthrosis, and malfunction. The goal of the current study was to facilitate musculoskeletal models in order to estimate glenohumeral instability introduced by muscle weakness due to cuff lesions. Inverse dynamics simulations were used to compute joint reaction forces for several static abduction tasks with different muscle weakness. Results were compared with the existing literature in order to ensure the model validity. Further arm positions taken from activities of daily living, requiring the rotator cuff muscles were modeled and their contribution to joint kinetics computed. Weakness of the superior rotator cuff muscles (supraspinatus; infraspinatus) leads to a deviation of the joint reaction force to the cranial dorsal rim of the glenoid. Massive rotator cuff defects showed higher potential for glenohumeral instability in contrast to single muscle ruptures. The teres minor muscle seems to substitute lost joint torque during several simulated muscle tears to maintain joint stability. Joint instability increases with cuff tear size. Weakness of the upper part of the rotator cuff leads to a joint reaction force closer to the upper glenoid rim. This indicates the comorbidity of cuff tears with SLAP lesions. The teres minor is crucial for maintaining joint stability in case of massive cuff defects and should be uprated in clinical decision‐making. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1628–1635, 2016.     

An anatomic study of the humeral insertion of the inferior glenohumeral capsule

To define inferior humeral capsular anatomy better, 12 cadaveric shoulders were dissected and an inferior capsular shift was performed. Two types of inferior humeral attachments were identified. In 7 specimens, the anterior capsular insertion bifurcated at the 8-o'clock position (on a right specimen) into a superior internal fold adjacent to the articular cartilage and an inferior external fold on the humeral surgical neck. In 5 specimens, the capsular insertion did not split but inserted over a broad area on the surgical neck. In all specimens, there was a re-confluence of the two folds at the 4-o'clock position. The inferior humeral capsular attachment may extend as far as 2 cm inferior to the articular surface and can be divided into two distinct types, split and broad, each with distinct internal and external folds of the capsule. Failure to release both of these folds limits the ability to shift the capsule superiorly by tethering the capsule inferiorly.     

肩关节置换术后关节不稳的生物力学研究进展

肩关节是人体活动范围最大的关节,属球窝关节。正常肩关节的被动活动范围取决于喙肩弓的外形和结构,以及在关节极度旋转时的关节囊紧张程度[1]。其稳定性取决于过关节的静力性结构(包括韧带和肌腱)和动力性结构(肌肉收缩)之间复杂的相互作用,而关节面对合、关节翻转、关节腔负压及关节面的黏附和内聚作用在维持肩关节的稳定性中也起辅助作用[2]。在重建时,要想保持关节的静力和动力的微妙平衡关系是相当困难的,严重的软组织和骨质解剖改变使得在软组织松解和恢复关节方位时很难保持关节稳定性[3]。并发症包括感染、神经损伤、术中骨折、关节…     

Effects of the glenoid labrum and glenohumeral abduction on stability of the shoulder joint through concavity-compression : an in vitro study.

BACKGROUND: Although the glenohumeral joint is the most mobile articulation of the human body, it is known to exhibit ball-and-socket kinematics. Compression into the glenoid labral concavity keeps the humeral head centered. The purpose of the present study was to determine the effects of joint position on glenohumeral stability through concavity-compression. METHODS: Ten cadaveric shoulders were tested. The glenoid was mounted horizontally onto a six-component load-cell while the humerus was clamped to a vertically unconstrained slide. An x-y stage translated the load-cell with the glenoid underneath the humeral head in eight different directions. Compressive loads of 20, 40, and 60 N were applied. The tests were repeated in 0 degrees, 30 degrees, 60 degrees, and 90 degrees of glenohumeral abduction with and without the labrum. Relative translations between the glenoid and the humeral head and the forces resisting translation were recorded. Then the stability ratio, defined as the peak translational force divided by the applied compressive force, was calculated. RESULTS: The average stability ratio was higher in the hanging-arm position than it was in glenohumeral abduction. The highest stability ratio was detected in the inferior direction (59.8% 7.7%) when the labrum was intact and in the superior direction (53.3% 7.9%) when the labrum had been resected. Under both conditions, the anterior direction was associated with the lowest stability ratio (32.0% 4.4% with the labrum and 30.4% 4.1% without the labrum). Resection of the glenoid labrum resulted in an average decrease in the stability ratio of 9.6% 1.7%. With increasing compressive load, the average stability ratio slightly decreased. CONCLUSIONS: Glenohumeral stability through concavity-compression was greater in the hanging-arm position than it was in glenohumeral abduction. The average contribution of the labrum to glenohumeral stability through concavity-compression was approximately 10%, about one-half of the value previously reported. With the labrum intact, the glenohumeral joint was most stable in the inferior direction. Without the labrum, it was most stable in the superior direction. Under both conditions, it was least stable in the anterior direction. Glenohumeral joint stability through concavity-compression decreases with higher compressive loads.     

The glenohumeral micromotion and influence of the glenohumeral ligaments during axial rotation in varying abduction angle

BackgroundThe patients with shoulder instability or disorders in overhead athletes have been considered to have an abnormal micromotion at the glenohumeral joint. However, the normal range of the micromotion has not been available during axial rotation with various abduction angles, especially above 90° abduction. This study aimed to investigate the glenohumeral translation and influence of the glenohumeral ligaments during axial rotation with up to maximum abduction.MethodsFourteen healthy volunteers performed active axial rotations at 0°, 90°, 135°, and maximal abduction angles. The positions of the humeral head center relative to the glenoid at maximally external, neutral, and maximally internal rotations (ER, NR, IR, respectively) for each abduction angle were evaluated using two- (2D) and three-dimensional (3D) shape matching registration techniques. The shortest pathway and its length between the origin and insertion of the superior, middle, and inferior glenohumeral ligaments (SGHL, MGHL, and IGHL, respectively) were calculated for each position.ResultsThe glenohumeral joint showed 3.1 mm of superoinferior translation during axial rotation at 0° abduction (P < 0.0001), and 2.6 mm and 4.5 mm anteroposterior translation at 135° and maximal abduction (P < 0.0001), respectively. The SGHL and MGHL reached a maximum length at ER with 0° abduction, and the anterior and posterior bands of the IGHL reached a maximum at ER with 90° abduction and IR with 0° abduction.ConclusionsThese findings indicated that the SGHL played a role as an inferior suppressor at 0° abduction, while the anterior band of IGHL played a role as an anterior stabilizer at 90° abduction. Every glenohumeral ligament did not get taut and the anteroposterior translation became greater with increasing abduction angle, above 90°. These results could be used as a reference when comparing with the pathological shoulders in the future study.     

Influence of fall height and impact surface on biomechanics of feet-first free falls in children

OBJECTIVE: The objectives of our study were to assess biomechanics associated with feet-first free falls in 3-year-old children and to investigate the influence of impact surface type and fall height on key biomechanical measures associated with injury risk. METHODS: Repeatable feet-first free fall experiments were conducted in a laboratory mock-up environment using an instrumented Hybrid II 3-year-old test dummy. Impact surface type and fall height were varied to examine their influence on biomechanical measures. RESULTS: Feet-first falls from short distances (27 in.) (0.69 m) were found to have a low risk of contact-type head injury, regardless of impact surface type. When comparing different types of impact surfaces in a 27 in. (0.69 m) fall, head acceleration associated with falls onto playground foam was significantly less than that associated with falls onto wood, linoleum or padded carpet. For falls onto playground foam, femoral compressive loads and bending moments were found to significantly increase as fall height increased. CONCLUSIONS: Impact surface type and fall height were found to influence biomechanics associated with injury risk in feet-first free falls as assessed through experimental mock-ups using an instrumented child test dummy. Feet-first falls from short distances (27 in.) (0.69 m) were associated with a low risk of contact-type head injury as assessed using HIC, irrespective of impact surface type.     

肩关节外展过程中盂肱韧带长度变化的体内三维分析

下移的作用.外展60°时,中盂肱韧带稳定着盂肱关节的前方.外展120°时,下盂肱韧带前束发挥了主要的前方稳定作用.当外展至180°时,腋囊维持着盂肱关节前方的稳定,同时下盂肱韧带后束维持着下方的稳定.     

Anterior instability of the glenohumeral joint with humeral avulsion of the glenohumeral ligament. A review of 41 cases

We studied retrospectively a consecutive series of 547 shoulders in 529 patients undergoing operation for instability. In 41, the cause of instability was considered to be lateral avulsion of the capsule, including the inferior glenohumeral ligament, from the neck of the humerus, the HAGL lesion. In 35, the lesion was found at first exploration, whereas in six it was noted at revision of a previous failed procedure. In both groups, the patients were older on average than those with instability from other causes. Of the primary cases, in 33 (94.3%) the cause of the first dislocation was a violent injury; six (17.4%) had evidence of damage to the rotator cuff and/or the subscapularis. Only four (11.4%) had a Bankart lesion. In patients undergoing a primary operation in whom the cause of the first dislocation was a violent injury, who did not have a Bankart lesion and had no suggestion of multidirectional laxity, the incidence of HAGL was 39%.     

Influence of T-shift capsulorrhaphy on rotation and translation of the glenohumeral joint: An experimental study

To evaluate changes in the response of capsuloligamentous restraints to translatory forces and rotation torques caused by experimental capsulorrhaphy (T-shift modification of Bankart repair), eight cadaveric shoulders were tested. Measurements were taken in intact and vented specimens, after severance of the anterior capsule at the glenoid rim (creating an artificial Bankart lesion), T-shaped incision of the anterior capsule, and refixation of the capsule (with a standard Bankart procedure) combined with tightening by T-shift. Rotation torques and translatory forces were applied in different positions of abduction with a specifically designed mounting apparatus that had four degrees of freedom. Dynamic and static measurements were performed with a tracking sysem that had six degrees of freedom. T-shift capsulorrhaphy restored the resistance of the capsuloligamentous restraints to translatory forces in all directions. This restoration was confirmed when we compared these results with data obtained from intact joints. No significant alteration of the centering mechanism resulting from rotation torques was observed, although the extent of external and internal rotation was remarkably decreased. This T-shift modification seems to produce a symmetric reduction of the volume of the capsule without significant displacement of the humeral head.     

Load-bearing capacity of the tibial component of the total condylar knee prosthesis. An in vitro study

The load-bearing capability of the tibial component of total knee prostheses is affected by the coverage of the osteotomized tibial surface by the tibial component. An anthropometric study of the proximal tibia indicated that standard total condylar tibial knee components may significantly underutilize the available weight-bearing tibial surface. The unloaded area values ranged from 6% to 43% in males and from 1% to 25% in females. An experimental study of the load-bearing capability of both standard tibial components and tibial components custom-fitted to conform to the periphery of the upper tibial surface was performed. Improvement in single load to failure with the conforming prosthesis averaged 29% in females with stemless prosthesis, 21% in females with stemmed prostheses, 41% in males with stemless prostheses, and 89% in males with stemmed prostheses. Post-test examination of the failed tibiae with conforming implants indicated failure by major fragmenting of the proximal tibia rather than cancellous bone crushing, suggesting that the maximal load-bearing ability of the upper tibial surface was more nearly being achieved. The results demonstrate the benefit to be gained by fully utilizing the available tibial surface for load transmission across the joint and suggest that use of custom-fitted tibial components has considerable merit.     

Translation of the humeral head on the glenoid with passive glenohumeral motion

We have demonstrated that certain passive motions of the glenohumeral joint are reproducibly accompanied by translation of the head of the humerus on the glenoid. We investigated the relationship of these translations to the position of the glenohumeral joint and to applied torques and forces in seven isolated glenohumeral joints from fresh cadavera, using a six-degrees-of-freedom position sensor and a six-axis force and torque transducer. Reproducible and significant translation occurred in an anterior direction with glenohumeral flexion and in a posterior direction with extension. We also observed translation with cross-body movement. The translation occurring with flexion was obligate in that it could not be prevented by the application of an oppositely directed force of thirty to forty newtons. Operative tightening of the posterior portion of the capsule increased the anterior translation on flexion and cross-body movement and caused it to occur earlier in the arc of motion compared with the intact glenohumeral joint. Operative tightening of the posterior part of the capsule also resulted in significant superior translation with flexion of the glenohumeral joint.     

Lesions in different types of anterior glenohumeral joint dislocation. An experimental study

Three different kinds of anterior shoulder joint dislocation were studied in an experimental setup including 15 shoulder joint specimens. Lesion to the anterior-inferior part of the capsule was the most frequent finding in anterior dislocation. In anterior-superior dislocation lesions to the anterior-inferior part of the capsule and the posterior part of the cuff were equally prominent. Anterior-inferior dislocation was associated with lesions to all capsular structures including the glenohumeral ligament and both the anterior and posterior part of the cuff. From a clinical point of view, the study indicates that in some types of anterior dislocation a severe lesion of the posterior part of the capsule and cuff must also be considered.     

The HAGL lesion: An arthroscopic technique for repair of humeral avulsion of the glenohumeral ligaments

Glenoid avulsion of the capsulolabral complex and associated capsular laxity are well-described results of traumatic anterior dislocation. A less common consequence of traumatic anterior instability is the humeral avulsion of the glenohumeral ligaments (HAGL) lesion. An understanding of the arthroscopic pathoanatomy of the HAGL lesion will assist the surgeon in recognizing this uncommon entity. We describe a suture anchor technique for arthroscopic repair of HAGL lesions that anatomically reapproximates the torn edge of the glenohumeral ligament complex to its humeral head insertion. The technique is technically straightforward and does not require special equipment beyond that typical for arthroscopic labral repairs.     

Recurrent disassembly of a modular humeral prosthesis. A case report.

A modular prosthesis for shoulder arthroplasty can be complicated by disassembly of the bearing surface from the humeral stem. Glenohumeral instability and increased humeral translation may be associated with this complication.