Neck and shoulder pain

Neck and shoulder pains are presenting or incidental symptoms in a large variety of conditions. There may be similarities in the anatomicophysiological mechanism of pain production and in the clinical picture in many of these conditions. Many of the vague and refractory cases of neck and shoulder pain and of migraine may be due to cervical disc disease. Scalenus anticus syndrome and cardiac disease can be diagnosed or differentiated from cervical disc syndrome only by thorough investigation. Proper treatment of neck and shoulder pain is dependent upon correct diagnosis through complete history, physical examination and laboratory tests, as described in this presentation.     

A genome-wide association study identifies 5 loci associated with frozen shoulder and implicates diabetes as a causal risk factor

Frozen shoulder is a painful condition that often requires surgery and affects up to 5% of individuals aged 40–60 years. Little is known about the causes of the condition, but diabetes is a strong risk factor. To begin to understand the biological mechanisms involved, we aimed to identify genetic variants associated with frozen shoulder and to use Mendelian randomization to test the causal role of diabetes. We performed a genome-wide association study (GWAS) of frozen shoulder in the UK Biobank using data from 10,104 cases identified from inpatient, surgical and primary care codes. We used data from FinnGen for replication and meta-analysis. We used one-sample and two-sample Mendelian randomization approaches to test for a causal association of diabetes with frozen shoulder. We identified five genome-wide significant loci. The most significant locus (lead SNP rs28971325; OR = 1.20, [95% CI: 1.16–1.24], p = 5x10^-29) contained WNT7B. This variant was also associated with Dupuytren’s disease (OR = 2.31 [2.24, 2.39], p<1x10^-300) as were a further two of the frozen shoulder associated variants. The Mendelian randomization results provided evidence that type 1 diabetes is a causal risk factor for frozen shoulder (OR = 1.03 [1.02–1.05], p = 3x10^-6). There was no evidence that obesity was causally associated with frozen shoulder, suggesting that diabetes influences risk of the condition through glycemic rather than mechanical effects. We have identified genetic loci associated with frozen shoulder. There is a large overlap with Dupuytren’s disease associated loci. Diabetes is a likely causal risk factor. Our results provide evidence of biological mechanisms involved in this common painful condition.     

Three-dimensional scapular kinematics and scapulohumeral rhythm in patients with glenohumeral osteoarthritis or frozen shoulder

We aimed to describe 3D scapular kinematics and scapulohumeral rhythm (SHR) in glenohumeral (GH) osteoarthritis shoulders compared to unaffected shoulders and to compare the abnormal scapular kinematic schema for GH osteoarthritis with that for frozen shoulder. Thirty-two patients with stiff shoulder (16 with GH osteoarthritis and 16 with frozen shoulder) performed maximal arm elevation in two planes, sagittal and frontal. Scapular rotations and humeral elevation of the affected and unaffected shoulders were measured by the Polhemus Fastrak electromagnetic system. Patients with GH osteoarthritis were older, had longer disease duration (p<0.001) and less restricted humeral elevation in the frontal plane (p=0.01). Protraction was significantly lower for the affected shoulders except for arm elevation in the frontal plane in the GH osteoarthritis group. Furthermore, protraction was lower with frozen shoulder than GH osteoarthritis during arm elevation in the frontal plane. Scapular lateral rotation and SHR were significantly higher for the affected shoulders in both groups whatever the plane of elevation. SHR showed a fair to moderate negative correlation with maximal humeral elevation in both groups and appears to be higher with frozen shoulder than GH osteoarthritis. In addition, SHR of the affected shoulder showed a fair to moderate correlation with disease duration only with GH osteoarthritis. Scapular tilt did not differ between affected and unaffected sides and was not influenced by type of disease. In conclusion, the increased scapular lateral rotation described in frozen shoulder is also observed in GH osteoarthritis. SHR of the affected shoulder is inversely related to severity of limitation of shoulder range of motion, which suggests a compensatory pattern.     

MRI in shoulder joint instability

The paper provides the results of MRI studies in 100 patients having complaints of pain and impaired movements in the shoulder joint in order to establish a diagnosis. Sixty-three patients were found to have MRI signs of shoulder joint instability (SJI). The paper presents and states the found MRI symptoms of SJI. The author concludes that MRI of the shoulder joint in its instability should be used appropriately as it may early reveal changes in the articular osseous, cartilaginous, and soft tissues, which is useful in diagnosing and choosing a treatment.     

MRI in shoulder joint instability

The paper provides the results of MRI studies in 100 patients having complaints of pain and impaired movements in the shoulder joint in order to establish a diagnosis. Sixty-three patients were found to have MRI signs of shoulder joint instability (SJI). The paper presents and states the found MRI symptoms of SJI. The authors concludes that MRI of the shoulder joint in its instability should be used appropriately as it may early reveal changes in the articular osseous, cartilaginous, and soft tissues, which is useful in diagnosing and choosing a treatment.     

Improvements in measuring shoulder joint kinematics

For many clinical applications it is necessary to non-invasively determine shoulder motion during dynamic movements, and in such cases skin markers are favoured. However, as skin markers may not accurately track the underlying bone motion the methods currently used must be refined. Furthermore, to determine the motion of the shoulder a model is required to relate the obtained marker trajectories to the shoulder kinematics. In Wu et al. (2005) the International Society of Biomechanics (ISB) proposed a shoulder model based on the position of bony landmarks. A limitation of the ISB recommendations is that the reference positions of the shoulder joints are not standardized. The aims of this research project were to develop a method to accurately determine shoulder kinematics using skin markers, and to investigate the effect of introduction of a standardized reference configuration. Fifteen subjects, free from shoulder pathology, performed arm elevations while skin marker trajectories were tracked. Shoulder kinematics were reconstructed using a chain model and extended Kalman filter. The results revealed significant differences between the kinematics obtained with and without introduction of the reference configuration. The curves of joint angle tended towards 0° for 0° of humerus elevation when the reference configuration was introduced. In conclusion, the shoulder kinematics obtained with introduction of the reference configuration were found to be easier to interpret than those obtained without introduction of the reference configuration.     

Significance of shoulder function in the reconstruction of prehension with double free-muscle transfer after complete paralysis of the brachial plexus

Reconstruction of shoulder stability and movement in cases with complete paralysis of the brachial plexus was performed to improve the outcomes for universal function of prehension after double free-muscle transfer (Doi's procedure). In cases in which the C5 or C6 nerve root was available as a donor, neurotization of the supra-scapular nerve was performed with a nerve graft. If the C5 or C6 nerve root was not available, then the contralateral C7 nerve root was chosen as the donor motor nerve and was transferred to the suprascapular nerve by using a vascularized ulnar nerve graft. Seven cases with ipsilateral C4, C5, or C6 nerve root transfer to the suprascapular nerve and one with contralateral C7 transfer were evaluated, and the functional outcomes for the range of shoulder motion were compared with those for patients who had undergone arthrodesis of the humeroscapular joint or had undergone no procedures for shoulder function reconstruction. The patients who underwent supra-scapular nerve repair demonstrated statistically significantly better ranges of motion for flexion and abduction of the shoulder, compared with the other two groups. Shoulder function is important for achieving prehensile function among patients with complete paralysis of brachial function, when they undergo double free-muscle transfer.     

Dynamic shoulder dynamometry: a way to develop delay onset muscle soreness in shoulder muscles

A dynamic shoulder dynamometer has been designed to develop a vertical downward force over a measured range of motion, i.e. scapular elevation. The dynamometer is force-controlled to apply a required force within the range of motion. Calibration procedures were performed to assess the reliability of the force and displacement measurements. The system is designed to operate in isometric or eccentric conditions. For eccentric exercise the dynamometer has, for the first time, provided possibilities to elicit delay onset muscle soreness in shoulder muscles. In future, the apparatus will enable investigations of sensory-motor interactions in the shoulder region.     

Morphometric affinities of the human shoulder

To analyze differences between apes and monkeys and the affinities of man, we have studied the shoulder girdle of 327 specimens of anthropoid primates. The scapula, clavicle and humerus are viewed as an integrated functional complex on the basis of 18 measurements. Several varieties of multivariate analysis show that man is clearly closer to other hominoids than to the included monkey taxa (whether terrestrial or arboreal, Old World or New World). The marked shoulder differences between apes and monkeys and similarities between apes and man correlate with the muscular anatomy, which in hominoids allows the motions involved in their locomotion and feeding behavior. As the hominid-pongid correspondence in shoulder morphology is especially detailed regarding the functionally important joint surfaces, it is consistent with a fairly recent period of common ancestry and behavior. No hypothetical evolutionary pathway or ancestral form of the human shoulder need look far beyond the model afforded by extant pongids. In contrast with previous studies on the primate shoulder, these results agree with information accumulating from other systems—comparative anatomy, primate behavior, and molecular biology — in suggesting very close relationship between man and extant African pongids.     

An entropy-assisted musculoskeletal shoulder model

Optimization combined with a musculoskeletal shoulder model has been used to estimate mechanical loading of musculoskeletal elements around the shoulder. Traditionally, the objective function is to minimize the summation of the total activities of the muscles with forces, moments, and stability constraints. Such an objective function, however, tends to neglect the antagonist muscle co-contraction. In this study, an objective function including an entropy term is proposed to address muscle co-contractions. A musculoskeletal shoulder model is developed to apply the proposed objective function. To find the optimal weight for the entropy term, an experiment was conducted. In the experiment, participants generated various 3-D shoulder moments in six shoulder postures. The surface EMG of 8 shoulder muscles was measured and compared with the predicted muscle activities based on the proposed objective function using Bhattacharyya distance and concordance ratio under different weight of the entropy term. The results show that a small weight of the entropy term can improve the predictability of the model in terms of muscle activities. Such a result suggests that the concept of entropy could be helpful for further understanding the mechanism of muscle co-contractions as well as developing a shoulder biomechanical model with greater validity.     

Muscle activation in the contralateral passive shoulder during isometric shoulder abduction in patients with unilateral shoulder pain.

Studies have shown an increased muscle activation at the opposite passive side during unilateral contractions. The purpose of the present study was to examine the influence of pain on muscle activation in the passive shoulder during unilateral shoulder abduction. Ten patients with unilateral rotator tendinosis of the shoulder and nine healthy controls performed unilateral maximal voluntary contractions (MVC) and sustained submaximal contractions with and without subacromial injections of local anaesthetics of the afflicted shoulder. Muscle activation was recorded by electromyography (EMG) from the trapezius, deltoid, infraspinatus and supraspinatus muscles in both shoulders. During MVCs, the EMG amplitude from muscles of the passive afflicted side was not different in patients and controls, and was not influenced by pain alterations. In contrast, the EMG amplitude from the muscles of the passive unafflicted side was lower in the patients and increased after pain reduction. During the sustained submaximal contraction the EMG amplitude increased gradually in the passive shoulder to 15-30% of the EMG amplitude observed during MVC. This response was not influenced by differences in pain. We conclude that muscle activation of the passive shoulder was closely related to the activation of the contracting muscles and thus related to central motor drive, and not directly influenced by changes in pain.     

The architecture of the shoulder in some mammals

A series of nine features of the shoulder girdle, chosen as having functional significance in relation to the movements of the shoulder in arboreal locomotion, have been studied in 1188 specimens of 194 genera of mammals. The features were defined metrically and examined by means of a multivariate statistical technique: viz. canonical analysis. The study has shown that those mammals which are nonarboreal differ considerably among themselves and form the arboreal forms. But the myriad shapes of the shoulder girdle in a wide range of mammals (e.g. some marsupials, edentates, rodents, carnivores and primates) which climb or forage in trees, can be summarized mathematically by a very small number of similar canonical variates. This information correlates well with that of a previous series of studies carried out on the primates alone. The biological information that was postulated as being reflected by the individual canonical variates for the primates is also apparent for the arboreal mammals. The different variates separate the forms in ways which are consonant with what is known about the function of the shoulder in locomotion. Aspects of the shape of the shoulder defined by the analysis appear to be discernible from an examination of the contribution of the original variables to each individual canonical variate. This seems to confirm that the shape of the shoulder girdle within a very wide range of mammals is limited by a very small number of underlying factors of biological significance. One interpretation of the results suggests that the genetic model of the mammalian shoulder may have been sufficiently fixed at an early stage in the evolution of the class as to place considerable constraints upon the subsequent evolution of the shoulder in the different Orders.     

The role of the biceps brachii in shoulder elevation.

The biceps brachii is a bi-articular muscle affecting motion at the shoulder and elbow. While its' action at the elbow is well documented, its role in shoulder elevation is less clear. Therefore, the purpose of this project was to investigate the influence of shoulder and elbow joint angles on the shoulder elevation function of the biceps brachii. Twelve males and 18 females were tested on a Biodex dynamometer with the biceps brachii muscle selectively stimulated at a standardized level of voltage. The results indicated that both shoulder and elbow joint angles influence the shoulder joint elevation moment produced by the biceps brachii. Further analysis revealed that the elevation moment was greatest with the shoulder joint at 0 degrees and the elbow flexed 30 degrees or less. The greatest reduction in the elevation moment occurred between shoulder angles of 0 degrees and 30 degrees . The shoulder elevation moment was near zero when shoulder elevation reached or exceeded 60 degrees regardless of elbow angle. These results clarify the role of the biceps in shoulder elevation, as a dynamic stabilizer, and suggest that it is a decelerator of the arm during the throwing motion.     

Recent advances in shoulder research

Shoulder pathology is a growing concern for the aging population, athletes, and laborers. Shoulder osteoarthritis and rotator cuff disease represent the two most common disorders of the shoulder leading to pain, disability, and degeneration. While research in cartilage regeneration has not yet been translated clinically, the field of shoulder arthroplasty has advanced to the point that joint replacement is an excellent and viable option for a number of pathologic conditions in the shoulder. Rotator cuff disease has been a significant focus of research activity in recent years, as clinicians face the challenge of poor tendon healing and irreversible changes associated with rotator cuff arthropathy. Future treatment modalities involving biologics and tissue engineering hold further promise to improve outcomes for patients suffering from shoulder pathologies.     

Effect of a pathological scapular tilt after total shoulder arthroplasty

Total shoulder arthroplasty (TSA) is an accepted and most successfully used treatment for different shoulder pathologies. Different risk factors for the failure of the prosthesis are known. A pathological scapular orientation, observed in elderly people or in patients suffering from neuromuscular diseases, could be a cause of failure, which has not been investigated yet. To test this hypothesis, a numerical musculoskeletal model of the glenohumeral joint was used to compare two TSA cases: a reference normal case and a case with a pathological anterior tilt of the scapula. An active abduction of 150° was simulated. Joint force, contact pattern, polyethylene and cement stress were evaluated for both cases. The pathological tilt slightly increased the joint force and the contact pressure, but also shifted the contact pattern. This eccentric contact increased the stress level within the polyethylene of the glenoid component and within the surrounding cement layer. This adverse effect occurred mainly during the first 60° of abduction. Therefore, a pathological orientation of the scapula may increase the risk of a failure of the cement layer around the glenoid component. These preliminary numerical results should be confirmed by a clinical study.     

Analysis of glenoid fixation for a reversed anatomy fixed-fulcrum shoulder replacement

The restoration of pain-free stable function in gleno-humeral arthritic cases in various situations such as rotator cuff deficiency, old trauma and failed total shoulder arthroplasty is a challenging clinical dilemma. The Bayley-Walker shoulder has been designed specifically for very difficult cases where surface replacement devices do not provide sufficient stability. This device is a fixed-fulcrum reverse anatomy implant where the centre of rotation is placed medially and distally with respect to the normal shoulder, to increase the lever arm of the abductor muscles. An important problem in devices of this type is obtaining secure and long-lasting fixation of the glenoid component. In this design, fixation is achieved using a tapered screw for engagement with cortical bone and HA coating for subsequent osseointegration. This study presents the results from a three-dimensional finite element analysis conducted on this component for two load cases at 60 degrees and 90 degrees abduction. The results showed that most of the forces were transmitted from the component to the cortical bone of the scapula, the remaining load being transmitted through cancellous bone. Histology from a retrieved case shows evidence of bone remodelling. The retrieval case obtained some time after implantation showed new bone formation had occurred around the threads onto the HA coating. Fixing the component in this way at multiple locations in cortical bone may overcome the problems of glenoid loosening historically associated with cemented constrained devices.     

A regression model predicting isometric shoulder muscle activities from arm postures and shoulder joint moments

Tissue overloading is a major contributor to shoulder musculoskeletal injuries. Previous studies attempted to use regression-based methods to predict muscle activities from shoulder kinematics and shoulder kinetics. While a regression-based method can address co-contraction of the antagonist muscles as opposed to the optimization method, most of these regression models were based on limited shoulder postures. The purpose of this study was to develop a set of regression equations to predict the 10th percentile, the median, and the 90th percentile of normalized electromyography (nEMG) activities from shoulder postures and net shoulder moments. Forty participants generated various 3-D shoulder moments at 96 static postures. The nEMG of 16 shoulder muscles was measured and the 3-D net shoulder moment was calculated using a static biomechanical model. A stepwise regression was used to derive the regression equations. The results indicated the measured range of the 3-D shoulder moment in this study was similar to those observed during work requiring light physical capacity. The r² of all the regression equations ranged between 0.228 and 0.818. For the median of the nEMG, the average r² among all 16 muscles was 0.645, and the five muscles with the greatest r² were the three deltoids, supraspinatus, and infraspinatus. The results can be used by practitioners to estimate the range of the shoulder muscle activities given a specific arm posture and net shoulder moment.     

Evaluation of regression-based 3-D shoulder rhythms

The movements of the humerus, the clavicle, and the scapula are not completely independent. The coupled pattern of movement of these bones is called the shoulder rhythm. To date, multiple studies have focused on providing regression-based 3-D shoulder rhythms, in which the orientations of the clavicle and the scapula are estimated by the orientation of the humerus. In this study, six existing regression-based shoulder rhythms were evaluated by an independent dataset in terms of their predictability. The datasets include the measured orientations of the humerus, the clavicle, and the scapula of 14 participants over 118 different upper arm postures. The predicted orientations of the clavicle and the scapula were derived from applying those regression-based shoulder rhythms to the humerus orientation. The results indicated that none of those regression-based shoulder rhythms provides consistently more accurate results than the others. For all the joint angles and all the shoulder rhythms, the RMSE are all greater than 5°. Among those shoulder rhythms, the scapula lateral/medial rotation has the strongest correlation between the predicted and the measured angles, while the other thoracoclavicular and thoracoscapular bone orientation angles only showed a weak to moderate correlation. Since the regression-based shoulder rhythm has been adopted for shoulder biomechanical models to estimate shoulder muscle activities and structure loads, there needs to be further investigation on how the predicted error from the shoulder rhythm affects the output of the biomechanical model.     

Morphoclinal variation in the anthropoid shoulder.

A morphocline in the organization of the shoulder joint is demonstrated among anthropoid primates. This metrical test supports the view that hominoid distinctions are monophyletic in origin. The primates that are behaviorally and functionally convergent on hominoids are only partially convergent or are not convergent in shoulder morphology.