A larger critical shoulder angle requires more rotator cuff activity to preserve joint stability

Shoulders with rotator cuff tears (RCT) tears are associated with significantly larger critical shoulder angles (CSA) (RCT CSA = 38.2°) than shoulders without RCT (CSA = 32.9°). We hypothesized that larger CSAs increase the ratio of glenohumeral joint shear to joint compression forces, requiring substantially increased compensatory supraspinatus loads to stabilize the arm in abduction. A previously established three dimensional (3D) finite element (FE) model was used. Two acromion shapes mimicked the mean CSA of 38.2° found in patients with RCT and that of a normal CSA (32.9°). In a first step, the moment arms for each muscle segment were obtained for 21 different thoracohumeral abduction angles to simulate a quasi‐static abduction in the scapular plane. In a second step, the muscle forces were calculated by minimizing the range of muscle stresses able to compensate an external joint moment caused by the arm weight. If the joint became unstable, additional force was applied by the rotator cuff muscles to restore joint stability. The model showed a higher joint shear to joint compressive force for the RCT CSA (38.2°) for thoracohumeral abduction angles between 40° and 90° with a peak difference of 23% at 50° of abduction. To achieve stability in this case additional rotator cuff forces exceeding physiological values were required. Our results document that a higher CSA tends to destabilize the glenohumeral joint such that higher than normal supraspinatus forces are required to maintain modeled stability during active abduction. This lends strong support to the concept that a high CSA can induce supraspinatus (SSP) overload. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:961–968, 2016.     

Glenohumeral joint reaction forces increase with critical shoulder angles representative of osteoarthritis—A biomechanical analysis

Osteoarthritis (OA) of the glenohumeral joint constitutes the most frequent indication for nontraumatic shoulder joint replacement. Recently, a small critical shoulder angle (CSA) was found to be associated with a high prevalence of OA. This study aims to verify the hypothesis that a small CSA leads to higher glenohumeral joint reaction forces during activities of daily living than a normal CSA. A shoulder simulator with simulated deltoid (DLT), supraspinatus (SSP), infraspinatus/teres minor (ISP/TM), and subscapularis (SSC) musculotendinous units was constructed. The DLT wrapping on the humerus was simulated using a pulley that could be horizontally adjusted to simulate the 28° CSA found in OA or the 33° CSA found in disease‐free shoulders. Over a range of motion between 6° and 82° of thoracohumeral abduction joint forces were measured using a six‐axis load cell. An OA‐associated CSA yielded higher net joint reaction forces than a normal CSA over the entire range of motion. The maximum difference of 26.4 N (8.5%) was found at 55° of thoracohumeral abduction. Our model thus suggests that a CSA typical for OA predisposes the glenohumeral joint to higher joint reaction forces and could plausibly play a role in joint overloading and development of OA. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1047–1052, 2016.     

Electromyographic activity of the biceps brachii muscle in shoulders with anterior instability

Purpose: The purpose of this study was to evaluate the activity of the biceps muscle in the vulnerable abduction and external rotation position of the shoulder in patients with anterior instability. Type of Study: This experimental study included a prospective analysis of the electromyographic (EMG) data on a group of patients with traumatic unilateral anterior instability of the shoulder. The EMG data of the unstable shoulders was compared with those of the opposite shoulders as control. The optimal sample size for the case-control study was calculated using an nQuery Advisor program (nQuery Advisor 3.0, Statistical Solutions, Cork, Ireland). Methods: The EMG analyses were conducted in 76 shoulders in 38 patients who had a traumatic anterior instability in 1 shoulder. The EMG records were obtained at different positions of the shoulder, which included 0°, 45°, 90°, and 120° of shoulder abduction. In each angle of shoulder abduction, the arms were placed in an external rotation as tolerated by the anterior apprehension. The paired-sample t test was used to compare the difference of the root mean square (RMS) voltages between the stable and unstable shoulders in each degree of arm position. Results: The RMS voltage of the biceps muscle was significantly greater in the unstable shoulder than the opposite stable shoulder in all positions of the arm (P =.00). The RMS voltage of the biceps was maximal at 90° and 120° of external rotation in the unstable shoulder (P <.05). The RMS voltage of the supraspinatus muscle revealed no differences in any of the test conditions (P =.904,.506,.119, and.781 in 0°, 45°, 90°, and 120°, respectively). Conclusions: In the vulnerable abduction and externally rotated position, the biceps muscle plays an active compensatory role in the unstable shoulder but not in the stable shoulder.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 8 (October), 2001: pp 864–868     

Shoulder electromyography in multidirectional instability

We studied shoulder muscle activity in multidirectional instability (MDI) and multidirectional laxity (MDL) of the shoulder, our hypothesis being that altered muscle activity plays a role in their pathogenesis. Six muscles (supraspinatus, infraspinatus, subscapularis, anterior deltoid, middle deltoid, and posterior deltoid) were investigated by use of intramuscular dual fine-wire electrodes in 7 normal shoulders, 5 MDL shoulders, and 6 MDI shoulders. Each subject performed 5 types of exercise (rotation in neutral, 45 degrees of abduction, 90 degrees of abduction, flexion/extension, and abduction/adduction) on an isokinetic muscle dynamometer at two rates, 90 degrees /s and 180 degrees /s. After filtering, rectification, and smoothing, the electromyography signal was normalized by using the peak voltage of the movement cycle. In subjects with MDI, compared with normal subjects, activity patterns of the anterior deltoid were different during rotation in neutral and 90 degrees of abduction, whereas those of the middle and posterior deltoid were different during rotation in 90 degrees of abduction. In subjects with MDL, the posterior deltoid showed increased activity compared with normal subjects during adduction. Activity patterns of the supraspinatus, infraspinatus, and subscapularis appeared similar in both groups. Dual fine-wire electromyography offers insight into the complex role of shoulder girdle muscle function in normal movement and in instability. Altered patterns of shoulder girdle muscle activity and imbalances in muscle forces support the theory that impaired coordination of shoulder girdle muscle activity and inefficiency of the dynamic stabilizers of the glenohumeral joint are involved in the etiology of MDI. Interestingly, the abnormalities are in the deltoid rather than the muscles of the rotator cuff.     

Dynamic ultrasonography to evaluate coracoacromial ligament displacement during motion in shoulders with supraspinatus tendon tears

We evaluated coracoacromial ligament (CAL) displacement during motion in shoulders with supraspinatus tendon tears by dynamic ultrasonography (US). Twenty subjects with unilateral, full‐thickness supraspinatus tendon tears (SST group) and 20 subjects with intact supraspinatus tendons (control group) underwent dynamic US. The CAL displacement in their bilateral shoulders was measured in the transverse US view during passive and active shoulder abduction and internal rotation (SAIR). In the SST group, the CAL displacement was significantly greater in the affected shoulders than in the intact ones (1.9 mm ± 0.8 mm vs. 1.5 mm ± 0.5 mm, p = 0.01) during passive SAIR, but was not significantly different between the shoulders (1.7 mm ± 0.7 mm vs. 1.7 mm ± 0.4 mm, p = 0.81) during active SAIR. In the control group, no difference in the CAL displacement between the shoulders was noted during passive and active SAIR. Thus, dynamic US revealed greater CAL displacement in shoulders with supraspinatus tendon tears than in intact ones during passive SAIR. Dynamic US may help to detect abnormal kinematics in shoulders with such injury. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1430–1434, 2012     

Experimental investigation of reaction forces at the glenohumeral joint during active abduction

Reaction forces at the glenohumeral joint counterbalance the mass moment of the upper extremity during shoulder motion and are directly related to the activity of muscles across the joint. Because stability of the glenohumeral joint depends on compression of the humeral head into the glenoid, reaction forces constitute an important aspect of shoulder biomechanics. The objective of this study was to measure reaction forces at the glenohumeral joint during active scapula plane abduction. Furthermore, to clarify the relationship between the deltoid and supraspinatus muscles throughout abduction, this study investigated the effect of 4 variations of applied muscle forces on the magnitude and direction of glenohumeral reaction forces. We used a dynamic shoulder testing apparatus equipped with a force-moment sensor to directly measure reaction forces. Joint reaction forces increased throughout abduction and peaked at approximately 90 degrees for all testing conditions. The largest reaction forces occurred when the ratio of applied forces favored the supraspinatus tendon, whereas simulated paralysis of the supraspinatus resulted in a significant decrease in joint compression. There were no differences in direction of the reaction force between testing conditions. The results of this study indicate that the magnitude of glenohumeral joint reaction forces varies according to the ratio of forces between the supraspinatus and deltoid muscles. Thus, conditions characterized by either deltoid or supraspinatus dysfunction may result in abnormal loading mechanics at the glenohumeral joint. Understanding the relationship between rotator cuff function and glenohumeral reaction forces will aid in clarifying the importance of muscular activity to shoulder stability and strength as it relates to compression of the humeral head.     

Effect of glenohumeral abduction angle on the mechanical interaction between the supraspinatus and infraspinatus tendons for the intact,partial‐thickness torn,and repaired supraspinatus tendon conditions

Rotator cuff tears are difficult to manage because of the structural and mechanical inhomogeneity of the supraspinatus tendon. Previously, we showed that with the arm at the side, the supraspinatus and infraspinatus tendons mechanically interact such that conditions that increase supraspinatus tendon strain, such as load or full‐thickness tears, also increase infraspinatus tendon strain. This suggests that the infraspinatus tendon may shield the supraspinatus tendon from further injury while becoming at increased risk of injury itself. In this study, the effect of glenohumeral abduction angle on the interaction between the two tendons was evaluated for supraspinatus tendon partial‐thickness tears and two repair techniques. Principal strains were quantified in both tendons for 0°, 30°, and 60° of glenohumeral abduction. Results showed that interaction between the two tendons is interrupted by an increase in abduction angle for all supraspinatus tendon conditions evaluated. Infraspinatus tendon strain was lower at 30° and 60° than at 0° abduction angle. In conclusion, interaction between the supraspinatus and infraspinatus tendons is interrupted with increase in abduction angle. Additionally, 30° abduction should be further evaluated for management of rotator cuff tears and repairs as it is the angle at which both supraspinatus and infraspinatus tendon strain is decreased. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:846–851, 2010     

The effect of rotator cuff tears on reaction forces at the glenohumeral joint.

The rotator cuff muscles maintain glenohumeral stability by compressing the humeral head into the glenoid. Disruption of the rotator cuff compromises concavity compression and can directly affect the loads on the glenohumeral joint. The purpose of this study was to quantify the effect of rotator cuff tears on the magnitude and direction of glenohumeral joint reaction forces during active shoulder abduction in the scapular plane using nine cadaveric upper extremities. Motion of the full upper extremity was simulated using a dynamic shoulder testing apparatus. Glenohumeral joint reaction forces were measured by a universal force-moment sensor. Five conditions of rotator cuff tears were tested: Intact, Incomplete Supraspinatus Tear, Complete Supraspinatus Tear, Supraspinatus/Infraspinatus Tear, and Global Tear. Reaction forces at the glenohumeral joint were found to steadily increase throughout abduction and peaked at maximum abduction for all conditions tested. There were no significant differences in reaction force magnitude for the intact condition (337 +/- 88 N) or those involving an isolated incomplete tear (296 +/- 83 N) or complete tear (300 +/- 85 N) of the supraspinatus tendon. Extension of tears beyond the supraspinatus tendon into the anterior and posterior aspect of the rotator cuff led to a significant decrease in the magnitude of joint reaction force (126 +/- 31 N). Similarly, such tears resulted in a significant change in the direction of the reaction force at the glenohumeral joint. These results suggest that joint reaction forces are significantly affected by the integrity of the rotator cuff, specifically, by the transverse force couple formed by the anterior and posterior aspects of the cuff. The quantitative data obtained in this study on the effect of rotator cuff tears on magnitude and direction of the reaction force at the glenohumeral joint helps clarify the relationship between joint motion, joint compression and stability.     

Outcome of pectoralis major transfer for the treatment of irreparable subscapularis tears

BACKGROUND: Chronic tears of the subscapularis tendon with or without associated tears of the supraspinatus and infraspinatus tendons may lead to pain and dysfunction of the shoulder. If conservative treatment fails and repair of the musculotendinous unit is impossible, transfer of the pectoralis major tendon can be attempted to substitute for lost subscapularis function. METHODS: Twenty-eight patients underwent a total of thirty consecutive pectoralis major transfers at an average age of fifty-three years. There were twelve isolated subscapularis tears and eighteen subscapularis tears associated with a tear of the supraspinatus or the supraspinatus and infraspinatus. All patients were examined clinically and with standard radiographs. RESULTS: The mean relative Constant score increased from 47% preoperatively to 70% at an average of thirty-two months postoperatively (p < 0.0001). The mean Constant scores for pain (p = 0.0009) and activities of daily living (p < 0.0001), the range of forward flexion (p < 0.05), and abduction strength (p = 0.001) also improved. Thirteen patients (14 shoulders) were very satisfied, ten patients (eleven shoulders) were satisfied, two patients (two shoulders) were disappointed, and three patients (three shoulders) were dissatisfied with the result. The average subjective shoulder value increased from 23% preoperatively to 55% postoperatively (p = 0.0009). In patients with a massive tear, the outcome was less favorable when the torn supraspinatus tendon was irreparable, as determined preoperatively or intraoperatively, than when it was reparable (average relative Constant scores, 49% and 79%, respectively; p = 0.002). CONCLUSIONS: Pectoralis major transfer results in improvement for patients with an irreparable subscapularis tear with or without an associated reparable supraspinatus tear. If an irreparable subscapularis tear is associated with an irreparable supraspinatus tear, the results are less favorable, and pectoralis major transfer may not be warranted.     

Effects of Abduction Pillows on Rotator Cuff Repair: A Biomechanical Analysis

Background

After rotator cuff repair, some surgeons use abduction pillows to unload or protect the repair construct, while others do not.

Question/Purpose

The aim of this study was to determine which type of sling—one with a small or large abduction pillow or one without a pillow—places the repaired rotator cuff in the best position to reduce tension on the supraspinatus.

Methods

An X-ray study was performed on asymptomatic subjects to determine what position the shoulder is placed in when wearing a sling with or without an abduction pillow. Positions were then reproduced in human cadaveric shoulders using a custom-made testing jig, and tension on the repaired supraspinatus was measured.

Results

X-rays showed that abduction of the glenohumeral joint with a sling was only 4°, with a sling with a small pillow was 13°, and with a sling with a large abduction pillow was 25°. Placing the cadaveric shoulders in the position of a sling with a small abduction pillow caused a reduction in tension on the supraspinatus of 27% anteriorly and 55% posteriorly compared to placing the shoulder in the position of a sling without an abduction pillow; a large abduction pillow caused a further reduction in tension, of 42% anteriorly and 56% posteriorly.

Conclusion

These findings show that abduction pillows reduce tension on the repaired supraspinatus tendon.

     

Disruption of the anterior–posterior rotator cuff force balance alters joint function and leads to joint damage in a rat model

The rotator cuff assists in shoulder movement and provides dynamic stability to the glenohumeral joint. Specifically, the anterior–posterior (AP) force balance, provided by the subscapularis anteriorly and the infraspinatus and teres minor posteriorly, is critical for joint stability and concentric rotation of the humeral head on the glenoid. However, limited understanding exists of the consequences associated with disruption of the AP force balance (due to tears of both the supraspinatus and infraspinatus tendons) on joint function and joint damage. We investigated the effect of disrupting the APforce balance on joint function and joint damage in an overuse rat model. Twenty‐eight rats underwent 4 weeks of overuse to produce a tendinopathic condition and were then randomized into two surgical groups: Detachment of the supraspinatus only or detachment of the supraspinatus and infraspinatus tendons. Rats were then gradually returned to their overuse protocol. Quantitative ambulatory measures including medial/lateral, propulsion, braking, and vertical forces were significantly different between groups. Additionally, cartilage and adjacent tendon properties were significantly altered. These results identify joint imbalance as a mechanical mechanism for joint damage and demonstrate the importance of preserving rotator cuff balance when treating active cuff tear patients. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:638–644, 2014.     

Glenoid cartilage mechanical properties decrease after rotator cuff tears in a rat model

Rotator cuff repairs are commonly performed to reduce pain and restore function. Tears are also treated successfully without surgical intervention; however, the effect that a torn tendon has on the glenohumeral cartilage remains unknown. Clinically, a correlation between massive rotator cuff tears and glenohumeral arthritis has often been observed. This may be due to a disruption in the balance of forces at the shoulder, resulting in migration of the humeral head and subsequently, abnormal loading of the glenoid. Our lab previously demonstrated changes in ambulation and intact tendon mechanical properties following supraspinatus and infraspinatus rotator cuff tendon tears in a rat model. Therefore, the purpose of this study was to investigate the effects of supraspinatus and infraspinatus rotator cuff tears on the glenoid cartilage. Nine rats underwent unilateral detachment of the supraspinatus and infraspinatus tendons and were sacrificed after 4 weeks. Cartilage thickness significantly decreased in the antero‐inferior region of injured shoulders. In addition, equilibrium elastic modulus significantly decreased in the center, antero‐superior, antero‐inferior, and superior regions. These results suggest that altered loading after rotator cuff injury may lead to damage to the joint with significant pain and dysfunction. Clinically, understanding the mechanical processes involved with joint damage will allow physicians to better advise patients. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1435–1439, 2012     

Muscle and joint‐contact loading at the glenohumeral joint after reverse total shoulder arthroplasty

The purposes of this study were to determine the contributions of each shoulder muscle to glenohumeral joint force during abduction and flexion in both the anatomical and post‐operative shoulder and to identify factors that may contribute to the incidence of glenoid component loosening/failure and joint instability in the shoulder after reverse shoulder arthroplasty (RSA). Eight cadaveric upper extremities were mounted onto a testing apparatus. Muscle lines of action were measured, and muscle forces and muscle contributions to glenohumeral joint forces were determined during abduction and flexion of the pre‐operative anatomical shoulder and of the shoulder after arthroplasty. Muscle forces in the middle deltoid during abduction and those in the middle and anterior deltoid during flexion were significantly lower in the reverse shoulder than the pre‐operative shoulder (p < 0.017). The resultant glenohumeral joint force in the reverse shoulder was significantly lower than that in the pre‐operative shoulder; however, the superior shear force acting at the glenohumeral joint was significantly higher (p < 0.001). Reverse total shoulder arthroplasty reduces muscle effort in performing lifting and pushing tasks; however, reduced joint compressive force has the potential to compromise joint stability, while an increased superior joint shear force may contribute to component loosening/failure. Because greater superior shear force is generated in flexion than in abduction, care should be taken to avoid excessive shoulder loading in this plane of elevation. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1850–1858, 2011     

Contact pressure of the coracoacromial arch in shoulders with joint contracture: A cadaveric study

Backgrounds

There have been many reports describing that the capsular fibrosis of the shoulder joint is the main cause of frozen shoulder, whereas others reported the significance of subacromial impingement as an etiological factor. The purpose of this study was to investigate the contact pressure between the coracoacromial arch and the rotator cuff tendons to clarify the contact phenomenon in shoulders with joint contracture.

冈上肌腱撕裂查体试验的诊断价值研究

目的:探讨6种常用查体试验对冈上肌腱撕裂的诊断价值,并评估这6种临床查体是否可以区分冈上肌腱部分或全层撕裂.方法:选择2017年6月至2020年9月因肩关节疾病行肩关节镜下手术治疗的91例患者,其中男49例,女42例;年龄31～68(50.8±11.0)岁;右侧70例,左侧21例.术前采用Hug-up试验、Jobe试验...     

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.     

Functional outcome after shoulder arthroplasty for primary osteoarthritis: a multicenter study

Shoulder arthroplasty outcomes have been reported in many case series. Typically, these series have followed either a single prosthesis used to treat a variety of arthritic disorders of the shoulder or experience in a single institution. In contrast, this report of a prospective study summarizes the experience of several surgeons with a single prosthetic design for treatment of primary osteoarthritis of the shoulder. A prospective, multicenter clinical outcome study evaluated 176 shoulders in 160 patients with primary osteoarthritis. This study evaluated a single prosthetic design (Global Shoulder) used by 19 contributing surgeons. Enrollment included 133 total shoulder replacements and 43 humeral head replacements (hemiarthroplasty) in 98 men and 62 women. Neither age nor sex affected whether hemiarthroplasty or total shoulder arthroplasty was performed. Patients with full-thickness cuff tears preferentially had hemiarthroplasty. The decision to perform total shoulder arthroplasty or hemiarthroplasty was based on the surgeon's preference. There were significant improvements (P <.001) in all evaluated and self-assessed outcome parameters from the preoperative baseline for both total shoulder arthroplasty and hemiarthroplasty. The results confirm that prosthetic arthroplasty leads to dramatic improvement in pain, function, and patient satisfaction. Intraoperative complications occurred in 5.4% of cases, and postoperative complications occurred in 7.8%. The most common intraoperative complications were intraoperative fractures, occurring in 9 cases. The most common postoperative complications were glenoid component loosening and humeral head subluxation. Almost all cases of humeral head instability were associated with rotator cuff tears or glenoid component loosening (or both). Seven shoulders underwent 9 additional surgeries during the 5-year study period. Thirteen shoulders in 11 patients were lost as a result of death unrelated to the procedure; 2 shoulders in 1 patient were lost within 3 days/3 months after the bilateral replacements as a result of death from pulmonary embolism. Nine percent of the shoulders (16/176) had full-thickness rotator cuff tears. Eight of the 16 shoulders with full-thickness supraspinatus cuff tears had hemiarthroplasty. All of these tears were isolated to the supraspinatus tendon, and all were repairable. There were no differences in postoperative pain, function, American Shoulder and Elbow Surgeons scores, or range of motion. There were no differences between total shoulder arthroplasty and hemiarthroplasty in those patients with a reparable rotator cuff tear. Total shoulder arthroplasty and hemiarthroplasty for treatment of primary osteoarthritis result in good or excellent pain relief, improvement in function, and patient satisfaction in 95% of cases. Avoiding intraoperative humeral shaft fractures through use of an uncemented, canal-filling prosthetic stem requires careful attention to reaming and component sizing. Postoperative humeral head subluxation is often associated with other factors including rotator cuff tears or glenoid component loosening.     

Die Auswirkung definierter Varusdeformitäten am proximalen Humerus auf die Elevationskräfte des Armes

Objectives

This study investigated the hypothesis that different varus deformities of the humeral head decrease the efficiency of the M. supraspinatus (SSP) and increase the deltoid elevation forces.

Methods

A varus deformity model of the proximal humerus was developed with an intact rotator cuff and deltoid muscle in human specimens. Three groups were differentiated per random distribution: group I (n=8): 45° varus deformity, group II (n=8): 20° varus deformity, and a control group (n=8). The effect of different varus malunions (20° and 45° varus) on the SSP efficiency and on the arm elevation forces was analyzed with a robot-assisted shoulder simulator and a force-controlled hydraulic system in three defined phases of elevation: 0–30°, 30–60°, and 60–90°.

Results

The SSP efficiency (i.e., the degree of elevation per unit muscle force) was 0.12±0.03°/N in group I, 0.18±0.05°/N in group II, and 0.24±0.10°/N in the control group and was significantly lesser in group I than in group II (p=0.036) and in the control group (p=0.039). Under physiological loading of the rotator cuff, the deltoid elevation force per elevation angle was significantly greater in groups l and ll compared to the control group in the elevation phases between 0–30° and 60–90°. In case of an unloaded SSP (i.e., simulation of a SSP tear), the elevation forces were significantly greater in group l than in group ll (p=0.040), and in the control group (p=0.004) in the elevation phase between 60° and 90°.

Conclusion

Varus deformities of the humeral head significantly decreased the SSP efficiency (45° varus), and significantly increased the arm elevation forces (≥20° varus in the elevation phases 0–30° and 60–90°). The hypothesis of our study could be confirmed.     

Surgical exposure of the stiff knee

A proprioceptive deficit is an important determinant of disability in various shoulder disorders, such as instability and osteoarthrosis. In 15 patients with impingement syndrome stage II (Neer 1983), who were treated by arthroscopic subacromial decompression, we measured movement sense by determining threshold levels for the perception of motion of the shoulder. The patients were placed in a specially designed chair allowing continuous passive motion of the shoulder joint, while avoiding cutaneous, auditory and visual stimuli. To assess movement detection thresholds, passive abduction movements of the shoulder were performed at a starting angle of 60°, an amplitude of 10° and an angular velocity of 1.3°/s. Before surgery, all patients had higher threshold levels for the perception of motion in their affected shoulders then in the other side. After decompression, proprioception had improved on the decompressed side, but was unchanged on the other side.     

Persistent hemarthrosis of the shoulder joint with a rotator-cuff tear in the elderly

Summary Three elderly patients developed persistent hemarthrosis of the shoulder joint without having suffered injury. Complete tears of the rotator cuff, attrition of the undersurface of the acromion, and instability were noted in the affected shoulders. Synovial fluids examined from two patients contained many alizarin red S-positive microspheroids. The synovium obtained at surgery from two patients showed hypervascularity, vasodilatation, and severe degenerative changes of collagenous tissues. The tendon of the m. supraspinatus showed infiltrations of multinucleated giant cells around calcified deposits consisting of hydroxyapatite crystals. Anatomical and mechanical derangements, and possible biological reactions following phagocytosis of hydroxyapatite crystals, may have contributed to the persistent hemorrhage in the shoulder joints.