Dynamic upper limb proprioception in multidirectional shoulder instability

Shoulder proprioception changes in postmastectomy patients: an observational study

PURPOSE

Breast cancer surgery can cause changes in the anatomical structure of the shoulder and in shoulder mobility, leading to the increased possibility of long-term arm morbidity such as lymphedema. This study aims to evaluate the active shoulder joint position sense (AJPS) with and without lymphedema in postmastectomy patients.

METHODS

A total of 66 women, including 22 patients with lymphedema, 22 patients without lymphedema, and 22 healthy controls, were enrolled in the study. Pain severity was evaluated with the Numeric Pain Scale and edema severity was measured with circumferentially at 10 cm intervals. The normal range of motion of the shoulder joint was evaluated with the universal goniometer and the AJPS was assessed by active position repetition testing at 55°, 90°, and 125° shoulder flexion targets using the smartphone application "Clinometer."

RESULTS

AJPS at 55°, 90°, and 125° shoulder flexion target angles with and without lymphedema were different in all target angles compared to healthy controls (p < 0.01). There was a difference between the absolute error value of AJPS at 55° flexion (p < 0.05), and no difference at 90° and 125° flexion between the with and without lymphedema groups (p > 0.05).

CONCLUSION

This study shows that the AJPS was negatively affected in with and without lymphedema postmastectomy patients compared to healthy controls. This result emphasizes the importance of adding personalized methods for the restoration of joint position sense in addition to rehabilitation programs generally applied to the patient group.

Relationship between pain and proprioception among individuals with rotator cuff-related shoulder pain

BACKGROUND

Individuals with rotator cuff-related shoulder pain (RCRSP) have altered proprioception. The relationship between shoulder pain and proprioception is not well understood.

PURPOSE

This study aimed to investigate the relationship between shoulder pain and proprioception.

STUDY DESIGN

This was a cross-sectional comparative study.

METHODS

Twenty-two participants with RCRSP (mean age 27.6 ± 4.8 years) and 22 matched pain-free participants (23.4 ± 2.5 years) performed two upper limb active joint position sense tests: (1) the Upper Limb Proprioception Reaching Test (PRO-Reach; reaching toward seven targets) in centimeters and (2) Biodex System at 90% of maximum internal rotation in degrees. Participants performed three memorization and three reproduction trials blindfolded. The proprioception error (PE) is the difference between the memorized and estimation trials. Pain levels were captured pre- and post-evaluation (11-point Likert Numerical Pain Rating Scale). Relationships between PE and pain were investigated using independent t-tests and Spearman rank correlations.

RESULTS

Overall, 22.7% RCRSP participants indicated an increase in pain following the PRO-Reach (X̅ increase of 1.4 ± 1.5 points), while 59% did so with the Biodex (X̅ increase of 2.3 ± 1.8 points), reflecting a clinically important increase in pain. Weak-to-moderate correlations between pain and PEs were found with the Biodex (r = 0.39-0.53) and weak correlations with the PRO-Reach (r = -0.26 to 0.38). Concerning PEs, no significant differences were found between groups with the Biodex (p = 0.32, effect size d = -0.31 [-0.90 to 0.29]). The RCRSP participants demonstrated lower PEs with the PRO-Reach in elevation compared to pain-free participants (global X̅ = 4.6 ± 1.2 cm vs 5.5 ± 1.5 cm; superior 3.8 ± 2.1 cm vs 5.7 ± 2.9 cm; superior-lateral nondominant targets 4.3 ± 2.2 cm vs 6.1 ± 2.8 cm; p = 0.02-0.05, effect size d = 0.72-0.74 [0.12-1.3]).

CONCLUSIONS

Individuals with RCRSP demonstrated better upper limb proprioception in elevation, suggesting a change to interoception (sensory reweighting) in the presence of pain.

Measuring upper limb active joint position sense: Introducing a new clinical tool - The Upper Limb Proprioception Reaching Test

BACKGROUND

Proprioception is our sense of body awareness, including the sub-category of active joint position sense (AJPS). AJPS is fundamental to joint stability and movement coordination. Despite its importance, there remain few confident ways to measure upper limb AJPS in a clinic.

OBJECTIVE

To assess a new AJPS clinical tool, the Upper Limb Proprioception Reaching Test (PRO-Reach; seven targets), for discriminant validity, intra-rater and absolute reliability.

DESIGN

Cross-sectional measurement study.

METHODS

Seventy-five healthy participants took part in a single session with 2 consecutive evaluations (E1 and E2) (within-day reliability). Twenty participants were randomly selected to perform a dominant shoulder fatigue protocol (discriminant validity), whereafter a third evaluation was repeated (E3). The PRO-Reach was analyzed with paired t tests (discriminant validity), intra-class correlation coefficients (ICCs) and minimal detectable change [MDC]) (intra-rater: within-day and between-trial relative and absolute reliability).

RESULTS

The PRO-Reach supports moderate (mostly superior targets) to excellent (mostly inferior targets) reliability. Between-trial ICCs (T1/T2/T3) varied between 0.72 and 0.90, and within-day (E1/E2) ICCs between 0.45 and 0.72, with associated MDC95 values (3.9-5.0 cm). The overall scores (seven targets) supported the strongest within-day reliability (ICC = 0.77). The inferior targets demonstrated the highest between-trial and within-day reliability (ICCs = 0.90 and 0.72). A fatigue effect was found with the superior and superior-lateral targets (P < .05).

CONCLUSIONS

The inferior targets and overall scores demonstrate the strongest reliability. The use of the PRO-Reach tool may be suitable for clinical use upon further psychometric testing amongst pathological populations.

LEVEL OF EVIDENCE

Level III cross-sectional study.

Advances in the Non-Operative Management of Multidirectional Instability of the Glenohumeral Joint

Multidirectional instability (MDI) of the glenohumeral joint refers to symptomatic subluxations or dislocations in more than one direction. The aetiology of MDI is multifactorial, which makes the classification of this condition challenging. A shoulder rehabilitation program is the initial recommended treatment for MDI, however available rehabilitation programs have varying levels of evidence to support their effectiveness. In 2016, we published the details of an evidence-based program for MDI that has been evaluated for efficacy in two single-group studies and a randomised controlled trial. In 2017, we published a clinical commentary on the aetiology, classification, and treatment of this condition. The aim of this paper is to provide an update on the components of these publications with a particular focus on new advances in the non-operative management of this condition.

Evidence of distorted proprioception and postural control in studies of experimentally induced pain: a critical review of the literature

OBJECTIVES

Deficits in proprioception and postural control are common in patients with different musculoskeletal pain syndromes. It has been proposed that pain can negatively affect proprioception and postural control at a peripheral level, however research is limited to animal studies. Human studies have shown that it is more likely, that the link between pain and proprioceptive deficits, lies within changes in the central nervous system where noxious and non-noxious stimuli may overlap. In clinical studies, causality cannot be determined due to other factors which could confound the assessment such as pathophysiological features of the underlying musculoskeletal disorder and different psycho-social influences especially in patients with chronic pain. On the other hand, experimentally induced pain in healthy participants is able to control most of these confounding factors and perhaps offers an assessment of the effects of pain on proprioception and postural control. The aim of this paper is to critically appraise the literature related to the effect of experimentally induced pain on proprioception and postural control. Results from these studies are discussed and limitations are highlighted for future research.

METHODS

A search of databases (Medline, Scopus, PubMed) was conducted as well as reference check from relevant articles published since 2000. Fifteen studies which explored the effect of experimentally induced pain on postural control and ten studies which explored the effect of experimentally induced pain on proprioception were included.

RESULTS

We found that in the majority of the studies, postural control was negatively affected by experimentally induced pain. Results for proprioception were mixed depending on the body region and the way the painful stimuli were delivered. Kinesthesia was negatively affected in two studies, while in one study kinesthesia was enhanced. Joint position sense was not affected in four out of five studies. Finally, force sense was affected in three out of four studies.

CONCLUSIONS

From a clinical point of view, findings from the available literature suggest that experimentally induced pain impairs postural control and could potentially increases the risk for falls in patients. Interventions aiming to reduce pain in these patients could lead to preservation or improvement of their balance. On the other hand, the same conclusion cannot be drawn for the effect of experimentally induced pain on kinesthesia and joint position sense due to the limited number of studies showing such an effect.

The acute effects of vibratory stimuli during exercise on the sensorimotor control of the shoulder complex: A pilot study

BACKGROUND

Functional stability of the shoulder requires a balance of active forces, passive forces, and control subsystems of the joint complex. Although whole-body vibration enhances shoulder muscle function and proprioception, the impact of vibration on the sensorimotor control of the shoulder joint remains unclear.

OBJECTIVE

To investigate the acute effect of vibratory stimuli on the sensorimotor control of the shoulder joint.

METHODS

Fifteen male participants (age, 22.7 ± 2.3 years) were included and performed the exercise in a modified push-up position with partial weight-bearing on a vibration platform with and without vibratory stimuli. The vibration protocol included six sets lasting for 30 s each with a 30-s rest between sets. The main outcome measures included the upper limb static stability test, Upper Quarter Y Balance Test (UQYBT), and electromyography data of the upper limb.

RESULTS

Vibratory stimuli resulted in an increased UQYBT score (all directions; P< 0.01) and infraspinatus, serratus anterior, and lower trapezius muscle activity (P< 0.05) between pre- and post-exercise versus the control condition. Stabilometric parameters showed no significant interaction between condition and time.

CONCLUSIONS

Vibratory stimuli could maximize training benefits while limiting injury risk for athletes. Our findings could guide the development of rehabilitation programs for patients with shoulder instability.

Comparison of the effects of conventional physiotherapy and proprioception exercises on pain and ankle proprioception in patients with lumbar radiculopathy

BACKGROUND

Lumbar radiculopathy is characterized by a significant amount of backache causing loss of workforce and is a significant health problem frequently seen in the general population.

OBJECTIVE

The purpose of this study was to compare the effects of conventional physiotherapy (CT) and proprioception exercises (PE) on ankle proprioception and lumbar pain between patients with lumbar radiculopathy and a healthy control group.

METHODS

In this randomized clinical trial, 89 patients referred to the Physical Medicine and Rehabilitation outpatient clinic were selected through convenience sampling. They were randomly assigned to three groups: CT (n= 27), PE (n= 31), CT&PE (n= 31). Thirty healthy volunteers were included in the study as the control group. Proprioception measurements were made with an isokinetic dynamometer at 10∘ dorsiflexion (DF), 11∘, and 25∘ plantarflexion (PF) angles. Lumbar pain was assessed by using the Numerical Pain Rating Scale (NPRS). The data were analyzed by IBM SPSS Statistics version 22.0 via the Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

There was a statistically significant difference between the groups in terms of ankle proprioception and NPRS measurements in post-treatment evaluations (p< 0.05). Statistically significant differences were found between CT and PE groups and CT&PE and control groups. There was no statistically significant difference in comparing CT and PE groups and CT&PE and control groups within themselves (p> 0.05).

CONCLUSION

The combined use of CT and PE is an effective method that can be used in the clinic to reduce angular differences in ankle proprioception which is one of the primary factors of balance and coordination and lumbar pain.

Is Thumb Proprioception Decreased in Patients With Trapeziometacarpal Joint Osteoarthritis?

Proprioception is thought to be essential for normal joint homeostasis, and its decreased function has been associated with an increased risk of joint diseases. However, only a few studies have been performed on the association between proprioceptive function in the trapeziometacarpal joint (TMCJ) and osteoarthritis. The purpose of this study was to compare TMCJ proprioceptive function in elderly women with radiographic TMCJ osteoarthritis relative to age-matched control women without osteoarthritis. We enrolled 19 women (mean age, 66 years) with symptomatic, radiographic Eaton and Littler grade 2, 3, and 4 TMCJ osteoarthritis and 19 age-matched control women without osteoarthritis. We evaluated thumb proprioception by using a joint-position reproduction test and compared the reposition error (RE) between the groups. We carried out a multivariate analysis for factors potentially associated with increased RE, such as age, body mass index, hand dominance, the presence of diabetes, pain level, and the presence of osteoarthritis. Also, a logistic regression analysis was performed for factors associated with the occurrence of TMCJ osteoarthritis. Patients with TMCJ osteoarthritis had greater RE than did the control patients in the joint-position reproduction test at 20°, 30°, and 40° of thumb palmar abduction. The multivariate analysis indicated that increased RE was associated with the presence of osteoarthritis, but not with the other factors assessed. The occurrence of TMCJ osteoarthritis was associated with increased RE at 20°, 30°, and 40° of thumb palmar abduction. This study showed that decreased proprioceptive function was associated with the presence of osteoarthritis in the TMCJ, although the causality remains unknown. Further studies on the role of proprioception in the pathogenesis of TMCJ osteoarthritis and the potential role of its training for disease prevention or treatment are required.

The effect of neck muscle fatigue on shoulder humeral rotation joint position sense

INTRODUCTION

Cervical extensor muscle (CEM) fatigue causes decrements in upper limb proprioceptive accuracy during constrained single-joint tasks. This study used a novel humeral rotation joint position sense (JPS) measurement device to compare JPS accuracy in participants who received acute CEM fatigue vs. non-fatigued controls.

METHODS

Participants had vision occluded and were passively guided into postures of internal humeral rotation from a baseline posture before and after a CEM fatigue or control protocol. Mixed model repeated measures ANOVAs were used to verify fatigue and compared absolute, constant, and variable JPS error between groups.

RESULTS

CEM fatigue was verified via pre-post reduction in CEM strength, and myoelectric indicators of fatigue. However, between-group comparisons of absolute, constant, and variable JPS error were not statistically significant, despite having large effect sizes.

DISCUSSION

Contrary to prevailing literature, unconstrained humeral rotation JPS did not appear to be affected by CEM fatigue in this study. However, between-group differences in JPS error were dwarfed by inter-trial variability, which likely arose due to the unconstrained nature of this task, conflating chances for a Type II error. Future research should perform a kinematic analysis of task constraints to highlight potential compensatory mechanisms obscuring significant findings in this otherwise robust effect.

Preoperative and postoperative shoulder position sense in patients who underwent arthroscopic Bankart repair for traumatic shoulder joint instability

Background

Proprioceptive feedback is a reflex dislocation prevention mechanism that contributes to shoulder joint stability. In patients with Bankart lesions, the anteroinferior glenohumeral ligament complex is damaged and reduces the likelihood of tensile stress. As a result, proprioceptive feedback does not work, which leads to instability. Surgical reconstruction is indicated to restore proprioception, but the details of recovery after arthroscopic surgery are unknown. The purpose of this study is to investigate whether arthroscopic Bankart repair can improve the position sense of the shoulder.

Methods

We used the isokinetic dynamometer Biodex System 3 (Biodex, Shirley, NY, USA) to investigate preoperative and postoperative joint position sense in 140 shoulders (137 men, 3 women) undergoing arthroscopic Bankart repair for traumatic shoulder joint instability. The control subjects comprised 40 shoulders of healthy volunteers (all men). Active position sense was measured by setting the shoulder external rotation to 75° based on 90° abduction and neutral internal/external rotation position. Reproductive angle inaccuracy (RAI) was measured thrice, and the mean value was calculated. The RAI was measured preoperatively, 6 months and 1 year postoperatively, and at the final observation (range, 16-96 months; mean, 31.5 months).

Results

Mean RAI was significantly higher (6.4°) preoperatively in the traumatic shoulder instability group than in the control group (5.0°). Mean postoperative RAI changed to 5.0, 4.9, and 4.7° at 6 months, 1 year, and final observation, respectively (mean, 31.5 months). RAI recovered to the same level as the control group at 6 months after the surgery and was maintained the same level until final observation.

Conclusion

Position sense was significantly worse in patients with traumatic shoulder joint instability than in healthy volunteers, and a significant improvement in position sense was observed after reconstruction of the anteroinferior glenohumeral ligament complex by arthroscopic Bankart repair. Therefore, arthroscopic Bankart repair is a favorable procedure that can improve the position sense of the shoulder in patients with traumatic shoulder instability.

Quantifying the three-dimensional joint position sense of the shoulder

Joint position sense is important for performing activities of daily living and recreational activities. The objective of this study was to develop new insights into the proprioceptive capabilities of the shoulder using a novel virtual reality paradigm where participants actively recreated shoulder positions in all three dimensions. This allows for better identification of changes in joint position sense across different shoulder postures. Ten males and ten female healthy adults matched a cursor controlled by shoulder rotations calculated from motion capture tracking, to a target shoulder position presented in a virtual environment with the use of a virtual reality headset. Four elevation angles, three plane of elevation angles, and three rotation angles were investigated, totaling thirty-six angles that encompassed the range of motion of the shoulder. Joint position sense was enhanced as the elevation angle was increased, and further enhanced when the arm was more externally rotated and elevated. As elevation angle increased to 90°, joint position sense significantly increased. There was also a significant interaction of external rotation on elevation angle. As elevation angle increased, participants were more accurate when the arm was externally, but exhibited greater variability. These improvements in joint position sense are likely produced by increased tension in muscles and capsuloligamentous mechanoreceptors within the shoulder. As many sports and activities of daily living require joint position sense to complete a task, the ability to elevate and externally rotate is important for adequate shoulder proprioception and control.

Bilateral shoulder proprioception deficit in unilateral anterior shoulder instability

HYPOTHESIS AND BACKGROUND

Proprioception is an important element of shoulder dynamic stability. It has been shown to be affected in cases of capsular or labral injuries of the glenohumeral joint. Therefore, this study was conducted to investigate bilateral shoulder proprioception by active reproduction of joint position both in patients with post-traumatic recurrent unilateral shoulder instability and in normal healthy volunteers.

METHODS

We compared 41 patients, comprising 11 female and 30 male patients with an average age of 25.6 years (range, 18-39 years), with post-traumatic unilateral anterior shoulder instability with a control group of 27 healthy volunteers with no history of shoulder problems and with normal shoulder function during examination. All patients were examined using a high-accuracy computer-controlled electronic goniometer (Propriometer). The error of active reproduction of joint position (EARJP) was measured in abduction, flexion, external rotation, and internal rotation in both shoulders.

RESULTS

We observed a significant deficit in the EARJP in the unstable shoulders within the instability group. Surprisingly, similar results were recorded for the contralateral, unaffected shoulders within this group of patients compared with the control group. Joint acuity increased with higher elevation of the arm position.

CONCLUSION

Unilateral shoulder injuries, resulting in instability, affect proprioception in both shoulders, as demonstrated by an increased EARJP. This is the first report of unilateral shoulder instability coexisting with inferior proprioception in both shoulders.

Multidirectional instability of the glenohumeral joint: Etiology, classification, assessment, and management

Multidirectional instability of the shoulder is a type of glenohumeral joint shoulder instability. There are discrepancies in the definition and classification of this condition, which can make diagnosis and treatment selection challenging. Knowledge of contributing factors, the typical clinical presentation, and current best evidence for treatment options can assist in the diagnosis and appropriate treatment selection for this pathology. The purpose of this article is to present an overview of the current literature regarding the etiology, classification, assessment, and management of multidirectional instability of the glenohumeral joint.

Translational movement within the glenohumeral joint at different rotation velocities as seen by cine MRI

BACKGROUND

The glenohumeral joint is subjected to opposing forces when the direction of shoulder motion is changed, accelerating and decelerating to make the movements. The influence of motion velocity or acceleration on translation of the humeral head has not been evaluated although direction and distance of humeral head translation has been analyzed in real time in normal shoulders. We hypothesized that, in a normal shoulder, the humeral head does not deviate significantly or suddenly during active shoulder rotation regardless of motion velocity. The purpose of this study was to clarify normal intraarticular kinematics of humeral head position and translation during axial shoulder rotation with the arm by the side of the body at different rotational velocities using cine magnetic resonance imaging (MRI).

METHODS

Both shoulders of ten healthy adults (mean age group between 27.80 ± 6.05 years) were used in this study. Prior to MRI scan, dynamic glenohumeral stability was confirmed by physical examination. The glenohumeral joint was scanned during active shoulder rotation at three angular velocities (low, medium and high velocities), with the arm by the side of the body by real-time cine MRI while recording with the help of a video camera. Translation of the humeral head and rotation angles on MR imaging and video camera were measured to match shoulder rotational positions.

RESULTS

There were no statistical differences of the humeral head position and translation among three rotation velocities (p > 0.05). Translation of the humeral head was distributed from 1.44 ± 2.45 mm anteriorly to 0.65 ± 1.84 mm posteriorly at low velocity, from 0.74 ± 1.92 mm anteriorly to 0.75 ± 2.17 mm posteriorly at medium velocity, and from 2.62 ± 2.19 anteriorly to 1.17 ± 1.44 mm posteriorly at high velocity.

CONCLUSIONS

Translation of the humeral head was shown to undergo no significant change throughout the ranges of internal and external rotation, or among different rotational velocities in dynamic stability of the glenohumeral joint.

Multidirectional Shoulder Instability: Treatment

Background:

The treatment of multidirectional instability of the shoulder is complex. The surgeon should have a clear understanding of the role of hiperlaxity, anatomical variations, muscle misbalance and possible traumatic incidents in each patient.

Methods:

A review of the relevant literature was performed including indexed journals in English and Spanish. The review was focused in both surgical and conservative management of multidirectional shoulder instability.

Results:

Most patients with multidirectional instability will be best served with a period of conservative management with physical therapy; this should focus in restoring strength and balance of the dynamic stabilizers of the shoulder. The presence of a significant traumatic incident, anatomic alterations and psychological problems are widely considered to be poor prognostic factors for conservative treatment. Patients who do not show a favorable response after 3 months of conservative treatment seem to get no benefit from further physical therapy.

When conservative treatment fails, a surgical intervention is warranted. Both open capsular shift and arthroscopic capsular plication are considered to be the treatment of choice in these patients and have similar outcomes. Thermal or laser capsuloraphy is no longer recommended.

Conclusion:

Multidirectional instability is a complex problem. Conservative management with focus on strengthening and balancing of the dynamic shoulder stabilizers is the first alternative. Some patients will fare poorly and require either open or arthroscopic capsular plication.

Multidirectional Instability: Natural History and Evaluation

Background:

Multidirectional instability (MDI) represents a great challenge to the orthopedic surgeon. When treating these patients we must be aware that instability refers to a symptomatic situation, thus multidirectional instability is defined as symptomatic involuntary instability in two or more directions, and should be clearly differentiated from asymptomatic hyperlaxity.

It may be associated with hyperlaxity, either congenital or acquired following repetitive stress, but also may be present without hyperlaxity, which is rare.

Methods:

We searched in the online data bases and reviewed the relevant published literature available.

Results:

Many differences can be seen in the current literature when identifying these patients, unclear definitions and criteria to be included in this patient group are common.

Conclusion:

Understanding the complex shoulder biomechanics as well as being aware of the typical clinical features and the key examination signs, which we review in this article, is of paramount importance in order to identify and classify these patients, allowing the best treatment option to be offered to each patient.

Shoulder position sense in volleyball players with infraspinatus atrophy secondary to suprascapular nerve neuropathy

Isolated infraspinatus atrophy (IIA) is a common condition among overhead-activity athletes, which affects the hitting shoulder and is caused by suprascapular nerve injury. As the suprascapular nerve is a mixed nerve, such damage could lead to reduced afferent proprioceptive information and impaired shoulder sensorimotor control. This study aimed to evaluate the proprioception of the shoulder with IIA, through the assessment of shoulder position sense. The shoulder position sense was assessed in 24 professional volleyball players (12 players with IIA and 12 healthy players) with a blind dynamic shoulder repositioning test (all participants were blindfolded during the test). Three functional glenohumeral movements were tested as follows: abduction, forward flexion, and a combination of abduction and external rotation. In all three tested movements, the affected shoulder of players with isolated infraspinatus atrophy showed significantly higher hand position error than the healthy contralateral (P<10^-3 , for all movements) and the healthy control group hitting shoulder (P<10^-3 , for abduction and flexion; P=.02, for combined movement of abduction and external rotation). The study highlights a reduced sense of position of the hitting shoulder in professional volleyball players with IIA secondary to suprascapular nerve palsy. The higher hand position error of the pathologic shoulder suggests an impairment of the shoulder sensorimotor control system, which likely results from reduced afferent proprioceptive information. Deficient afferent proprioceptive information may result in poor accuracy in descending motor commands and impairment of the shoulder neuromuscular function, leading to reduced shoulder functional stability and increased risk of injury.

Errors in Shoulder Joint Position Sense Mainly Come from the Glenohumeral Joint

While synchronous movement of the glenohumeral and scapulothoracic joints has been emphasized in previous kinematics studies, most investigations of shoulder joint position sense have treated the shoulder complex as a single joint. The purposes of this study were to investigate the joint position sense errors of the humerothoracic, glenohumeral, and scapulothoracic joints at different elevation angles and to examine whether the errors of the glenohumeral and scapulothoracic joints contribute to the errors of the humerothoracic joint. Fifty-one subjects with healthy shoulders were recruited. Active joint position sense of the humerothoracic, glenohumeral, and scapulothoracic joints was measured at 50°, 70°, and 90° of humerothoracic elevation in the scapular plane. The results showed that while scapulothoracic joint position sense errors were not affected by target angles, there was an angle effect on humerothoracic and glenohumeral errors, with errors decreasing as the target angles approached 90° of elevation. The results of a multiple regression analysis revealed that glenohumeral errors explained most of the variance of the humerothoracic errors and that scapulothoracic errors had a weaker predictive relationship with humerothoracic errors. Therefore, it may be necessary to test scapular joint position sense separately in addition to the assessment of the overall shoulder joint position sense.

Upper limb joint position sense during shoulder flexion in healthy individuals: a pilot study to develop a new assessment method

BACKGROUND

Altered shoulder joint position sense (JPS) following shoulder injury has been demonstrated in the literature and may increase the risk of injury. A JPS assessment targeting the shoulder will provide the clinician with an objective marker. The present study aimed to develop an assessment method of JPS using an active relocation test (ART).

METHODS

In total, 40 healthy participants were recruited. A laser-pointer attached to the index finger during an ART allowed measurement (mm) of JPS by measuring the distance between the target and relocated position. Participants were blindfolded and stood an arm's length (approximately 1 m) away from the wall. Whilst keeping the wrist in neutral and elbow extended, the participant actively moved to the target position (90° glenohumeral flexion), held for 5 seconds, returned their arm to their side and actively returned to the target position. A mean was calculated from three trials to provide an ART score.

RESULTS

The mean (SD) dominant and nondominant ART score was 89.2 (SD 35.5) mm (95% confidence interval = 77.87 mm to 100.5 mm) and 94.1 (34.5) mm (95% confidence interval = 83.1 mm to 105.2 mm), respectively. Arm dominance did not significantly affect ART scores.

CONCLUSIONS

No significant difference was demonstrated between the dominant and nondominant arm using an ART assessing JPS acuity. Further studies are needed to establish inter-rater and intra-rater reliability.

The role of the peripheral and central nervous systems in rotator cuff disease

Rotator cuff (RC) disease is an extremely common condition associated with shoulder pain, reduced functional capacities, and impaired quality of life. It primarily involves alterations in tendon health and mechanical properties that can ultimately lead to tendon failure. RC tendon tears induce progressive muscle changes that have a negative impact on surgical reparability of the RC tendons and clinical outcomes. At the same time, a significant base of clinical data suggests a relatively weak relationship between RC integrity and clinical presentation, emphasizing the multifactorial aspects of RC disease. This review aims to summarize the potential contribution of peripheral, spinal, and supraspinal neural factors that may (1) exacerbate structural and functional muscle changes induced by tendon tear, (2) compromise the reversal of these changes during surgery and rehabilitation, (3) contribute to pain generation and persistence of pain, (4) impair shoulder function through reduced proprioception, kinematics, and muscle recruitment, and (5) help explain interindividual differences and response to treatment. Given the current clinical and scientific interest in peripheral nerve injury in the context of RC disease and surgery, we carefully reviewed this body of literature with a particular emphasis on suprascapular neuropathy that has generated a large number of studies in the past decade. Within this process, we highlight the gaps in current knowledge and suggest research avenues for scientists and clinicians.

Upper limb kinematics after arthroscopic and open shoulder stabilization

BACKGROUND

Shoulder joint stability mediated by proprioception is often quantified by arm repositioning tests (i.e., static end-position accuracy), overlooking ongoing movement quality. This study assessed movement quality by adopting smoothness-related kinematic descriptors. We compared performance of healthy controls with that of patients in arthroscopic shoulder stabilization and open shoulder stabilization groups. We hypothesized that arm kinematics after arthroscopic intervention would more closely resemble healthy movements compared with patients after open shoulder stabilization surgery.

METHODS

Healthy controls (N = 14) were compared with patients after arthroscopic shoulder stabilization (N = 10) and open shoulder stabilization (N = 12). Right-hand dominant subjects (the affected side in patients) performed 135 unconstrained 3-dimensional pointing movements toward visual targets (seen through pinhole goggles; i.e., no arm vision). Arm kinematic data were recorded and offline analyzed to obtain hand tangential velocity profiles further used to compute the acceleration-to-movement time ratio, peak-to-mean velocity ratio, and number of velocity peaks ("symmetry," "proportion," and "fragmentation" features, respectively). Parametric and nonparametric statistics were used for comparisons (P ≤ .05).

RESULTS

Control and arthroscopic shoulder stabilization groups presented similar acceleration-to-movement time ratio and peak-to-mean velocity ratio. Both groups differed from the open shoulder stabilization group (P = .001). Distributions of velocity peaks for control and arthroscopic shoulder stabilization groups were similar, whereas open shoulder stabilization and control subjects differed significantly (P = .028).

CONCLUSIONS

Movement quality mediated by proprioception in arthroscopic shoulder stabilization patients matches that of healthy controls, whereas performance in open shoulder stabilization patients seems inferior compared with that in healthy controls, as assessed by smoothness-related measures (less symmetrical, more fragmented movements).

Multidirectional instability of the shoulder: biomechanics, clinical presentation, and treatment strategies

Multidirectional instability (MDI) of the shoulder is a condition where the dislocation occurs in more than one direction with minimal or no causative trauma. Its pathoanatomy is complex and characterized by a redundant capsule, resulting in increased glenohumeral joint volume. The fact that several further factors may contribute to symptom onset complicates the diagnosis and hampers the identification of a therapeutic approach suitable for all cases. There is general agreement that the initial treatment should be conservative and that surgery should be reserved for patients who have not responded to an ad hoc rehabilitation program. We review the biomechanics, clinical presentation, and treatment strategies of shoulder MDI.

The effect of experimentally-induced subacromial pain on proprioception

Shoulder injuries may be associated with proprioceptive deficits, however, it is unknown whether these changes are due to the experience of pain, tissue damage, or a combination of these. The aim of this study was to investigate the effect of experimentally-induced sub-acromial pain on proprioceptive variables. Sub-acromial pain was induced via hypertonic saline injection in 20 healthy participants. Passive joint replication (PJR) and threshold to detection of movement direction (TTDMD) were assessed with a Biodex System 3 Pro isokinetic dynamometer for baseline control, experimental pain and recovery control conditions with a starting position of 60° shoulder abduction. The target angle for PJR was 60° external rotation, starting from 40°. TTDMD was tested from a position of 20° external rotation. Repeated measures ANOVAs were used to determine differences between PJR absolute and variable errors and TTDMD for the control and experimental conditions. Pain was elicited with a median 7 on the Numeric Pain Rating Scale. TTDMD was significantly decreased for the experimental pain condition compared to baseline and recovery conditions (≈30%, P = 0.003). No significant differences were found for absolute (P = 0.152) and variable (P = 0.514) error for PJR. Movement sense was enhanced for the experimental sub-acromial pain condition, which may reflect protective effects of the central nervous system in response to the pain. Where decreased passive proprioception is observed in shoulders with injuries, these may be due to a combination of peripheral tissue injury and neural adaptations that differ from those due to acute pain.

The effects of shoulder injury on kinaesthesia: a systematic review and meta-analysis

The aim of this systematic review was to synthesize the evidence for changes for proprioceptive variables consisting of movement and position sense in participants with glenohumeral musculoskeletal disorders. Five databases were searched until 13th August 2013. Methodological quality was assessed and meta-analyses were performed for active and passive joint reposition sense (AJPS and PJPS) and movement sense, determined with threshold to detection of passive motion (TTDPM). The search yielded 17 studies, four of which were classified as having high methodological quality, seven as moderate and six as low quality. For participants with post-traumatic glenohumeral instability, pooled findings indicate moderate evidence for higher TTDPM for involved shoulders compared to control groups and the contralateral uninvolved side, indicating decreased movement sense. For AJPS and PJPS there was moderate to limited evidence for significant increased errors for involved compared to uninvovled shoulders, but not when compared to the control groups. Limited evidence was found for decreased AJPS acuity for patients with chronic rotator cuff pain and for patients with unspecified shoulder pain compared to healthy controls. Movement sense is most likely to be impaired after shoulder injury involving post-traumatic instability when compared to the contralateral shoulder and to controls, while deficits for AJPS and PJPS are more likely to be evident compared to the contralateral shoulder in participants with glenohumeral musculoskeletal disorders.

Movement control in patients with shoulder instability: a comparison between patients after open surgery and nonoperated patients

BACKGROUND

Open surgery to correct shoulder instability is deemed to facilitate recovery of static and dynamic motor functions. Postoperative assessments focus primarily on static outcomes (e.g., repositioning accuracy). We introduce kinematic measures of arm smoothness to assess shoulder patients after open surgery and compare them with nonoperated patients. Performance among both groups of patients was hypothesized to differ. Postsurgery patients were expected to match healthy controls.

METHODS

All participants performed pointing movements with the affected/dominant arm fully extended at fast, preferred, and slow speeds (36 trials per subject). Kinematic data were collected (100 Hz, 3 seconds), and mixed-design analyses of variance (group, speed) were performed with movement time, movement amplitude, acceleration time, and model-observed similarities as dependent variables. Nonparametric tests were performed for number of velocity peaks.

RESULTS

Nonoperated and postsurgery patients showed similarities at preferred and faster movement speeds but not at slower speed. Postsurgery patients were closer to maximally smoothed motion and differed from healthy controls mainly during slow arm movements (closer to maximal smoothness, larger movement amplitude, shorter movement time, and lower number of peaks; i.e., less movement fragmentation).

CONCLUSIONS

Arm kinematic analyses suggest that open surgery stabilizes the shoulder but does not necessarily restore normal movement quality. Patients with recurrent anterior shoulder instability (RASI) seem to implement a "safe" but nonadaptive mode of action whereby preplanned stereotypical movements may be executed without depending on feedback. Rehabilitation of RASI patients should focus on restoring feedback-based movement control. Clinical assessment of RASI patients should include higher order kinematic descriptors.

Acute spontaneous atraumatic bilateral anterior dislocation of the shoulder joint with Hill-Sachs lesions: first reported case and review of literature

The anatomy of the shoulder joint comprises a relatively large humeral head with a shallow glenoid cavity allowing a remarkable range of motion at the expense of inherent instability. Despite anterior shoulder dislocations being the most common type encountered, bilateral dislocations are rare and almost always posterior. The aetiology is usually direct or indirect trauma related to sports, seizures, electric shock or electroconvulsive therapy. We present the first reported case of atraumatic bilateral acute anterior shoulder dislocations with associated Hill-Sachs lesions in a young, fit and well patient with no comorbidities. MRI illustrated the Hill-Sachs lesions with superior labral tear from anterior to posterior, and confirmed the acute nature of the injury by demonstrating the bone marrow oedema. The patient was treated surgically with arthroscopic anterior stabilisation. At 6 months following surgery, the patient has a pain free full range of movement of both shoulders with no further dislocations and has returned to work.

Shoulder Joint Position Sense in Injured and Noninjured Judo Athletes

Context:

A reduction in joint position sense (JPS) is sometimes a consequence of shoulder injury that may adversely affect the ability to maintain dynamic joint stability.

Objective:

To compare shoulder JPS between previously injured and noninjured judokas.

Design:

Cohort study.

Participants:

Twenty-nine noninjured subjects (10.93 ± 3.45 years) and eleven injured subjects (15.09 ± 3.39 years).

Main Outcome Measures:

JPS was tested at 45° and 80°of shoulder external rotation at 90° of abduction.

Results:

No signifcant difference in JPS was found between previously injured and noninjured judokas at either joint position.

Conclusion:

Despite evidence that JPS acuity decreases following shoulder injury, this study did not demonstrate a difference in average error between previously injured and noninjured judokas. Uncontrolled confounding factors, such as age and time since injury, may have affected the results. Sport-specifc shoulder joint loading patterns may also be an important factor that affects JPS.

The relationship between anterior glenohumeral laxity and proprioception in collegiate baseball players

OBJECTIVE

To determine if a relationship exists between anterior glenohumeral (GH) laxity and proprioception.

DESIGN

Cross-sectional study.

SETTING

University biomechanics laboratory.

PARTICIPANTS

Thirty asymptomatic collegiate baseball players.

INDEPENDENT VARIABLES

Anterior GH laxity.

MAIN OUTCOME MEASURES

Proprioception (active joint position sense) at positions of 75 degrees of external rotation, 30 degrees of external rotation, and 30 degrees of internal rotation were measured using an isokinetic dynomometer. Anterior GH laxity was measured using an instrumented arthrometer.

RESULTS

Linear regression analyses showed that there were no relationships between anterior GH laxity and active joint position sense at 30 degrees of GH internal rotation and 30 degrees of GH external rotation (r = 0.21, P = 0.13). However, there was a moderate positive relationship between anterior GH laxity and joint position sense at 75 degrees of shoulder external rotation (r = 0.56, P = 0.001).

CONCLUSIONS

These results suggest that shoulder proprioception in 75 degrees of external rotation decreases as anterior GH laxity increases. These results may prove beneficial in the prevention, evaluation, and treatment of various shoulder injuries associated with GH laxity.

Joint position sense is not altered during shoulder medial and lateral rotations in female assembly line workers with shoulder impingement syndrome

This study evaluated joint position sense (JPS) during medial and lateral rotations of the shoulder in female workers with and without shoulder impingement syndrome (SIS). Three groups were assessed. The case group consisted of 15 female assembly line workers (35.5, SD 5.8 years) with unilateral SIS. Control group 1 consisted of 15 female assembly line workers asymptomatic for SIS (34.4, SD 5.5 years) and control group 2 consisted of 15 female subjects (33.1, SD 6.2 years) asymptomatic for SIS and with no exposure to activities with the upper limbs. The JPS was evaluated bilaterally during passive (2°/sec) and active (5°/sec) repositioning tests using an isokinetic dynamometer. The target angles were 45° of lateral rotation (achieved by medially rotating the shoulder from 90° of lateral rotation) and 75° of lateral rotation (achieved by laterally rotating the shoulder from neutral rotation). There were no differences between sides for all groups (p  >  0.05). There were no differences in any of the variables between the case group and the control groups (p  >  0.05). The results of this study suggest that JPS during medial and lateral rotations of the shoulder is not altered in female assembly line workers with SIS.

Measurement of active shoulder proprioception: dedicated system and device

Proprioception is an essential part of shoulder stability and neuromuscular control. The purpose of the study was the development of a precise system of shoulder proprioception assessment in the active mode (Propriometr). For that purpose, devices such as the electronic goniometer and computer software had been designed. A pilot study was carried out on a control group of 27 healthy subjects, the average age being 23.8 (22–29) in order to test the system. The result of the assessment was the finding of the error of active reproduction of the joint position (EARJP). EARJP was assessed for flexion, abduction, external and internal rotation. For every motion, reference positions were used at three different angles. The results showed EARJP to range in 3–6.1°. The proprioception evaluation system (propriometr) allows a precise measurement of active joint position sense. The designed system can be used to assess proprioception in both shoulder injuries and treatment. In addition, all achieved results of normal shoulders may serve as reference to be compared with the results of forthcoming studies.

Management of multidirectional instability of the shoulder

Multidirectional shoulder instability is defined as symptomatic instability in two or more directions. Instability occurs when static and dynamic shoulder stabilizers become incompetent due to congenital or acquired means. Nonspecific activity-related pain and decreased athletic performance are common presenting complaints. Clinical suspicion for instability is essential for timely diagnosis. Several examination techniques can be used to identify increased glenohumeral translation. It is critical to distinguish increased laxity from instability. Initial management begins with therapeutic rehabilitation. If surgical management is required, capsular plication has been used successfully. Advanced arthroscopic techniques offer several advantages over traditional open approaches and may have similar outcomes. The role of rotator interval capsular plication is controversial, but it may be used to augment capsular plication in patients with specific patterns of instability. Despite encouraging results, outcomes remain inferior to those associated with traumatic unidirectional instability.

Recurrent anterior shoulder instability associated with bony defects

Mobility of the glenohumeral joint is facilitated through the complex interplay of soft tissue and osseous anatomy. Arthroscopic shoulder stabilization is commonly used in the surgical management of shoulder instability. However, the management of the unstable shoulder associated with bony defects (glenoid, humeral, or combined) can be challenging. Adequate recognition of bony defects is paramount to successful treatment and entails a careful history, clinical examination, and advanced radiographic imaging. Nonoperative methods of treatment are often insufficient for treating patients with large bony defects. Bony procedures, as opposed to soft procedures, may yield better outcomes in this patient population. However, respective surgical techniques used to address these defects are technically challenging with a significant learning curve and may lead to significant morbidity. This represents a paradigm shift in treatment and replaces the old paradigm of "open vs arthroscopic" instability surgery.

Evaluation and treatment of shoulder instability

The shoulder joint has a wide range of motion as a result of a complex interplay of soft tissue and bone structures. It is also the most frequently dislocated joint in the body. Shoulder dislocations are generally classified as traumatic and nontraumatic. There are many specific causes, each of which necessitate individualized treatment modalities. Accurate diagnosis requires a careful history and physical examination. Arthroscopic surgery and advances in imaging have expanded our understanding of anatomy and pathology relevant to shoulder instability and its treatment. Surgery is the treatment of choice for recurrent traumatic instability. Surgery may also be indicated in some first-time traumatic dislocations in young contact athletes, whereas rehabilitation is the initial treatment of choice in older patients with initial instability and in those with nontraumatic dislocations. Results of arthroscopic capsulolabral repair now equal those of open capsulolabral repair and have become the surgical treatment of choice for most patients. However, in cases of recurrent instability and significant bone deficiency of either the glenoid or humeral head, open bone reconstructive procedures are often necessary to ensure successful outcomes.

Arthroscopic rotator interval closure by purse string suture for symptomatic inferior shoulder instability

Multidirectional instability of the shoulder is a complex condition that can be difficult to diagnose and treat. Clinically, it is characterized by symptomatic global laxity of the glenohumeral joint and may present either traumatically or atraumatically, unilaterally or bilaterally, and with or without generalized joint laxity. Capsular plication is a primary treatment option in these patients and is used to tension the redundant or lax capsule. We evaluated the role of rotator interval closure in restoring stability as a primary procedure in patients with multidirectional instability and a positive and painful sulcus sign.Twenty adult patients (16 men and 4 women) presenting with multidirectional instability were evaluated clinically and radiologically to assess the degree and direction of instability, were treated by arthroscopic rotator interval closure and inferior capsular plication, and were followed up for a minimum of 2 years. Clinical and functional results were excellent at 2-year follow-up. The results of the study indicate that the closure of the rotator interval in patients with symptomatic inferior instability will have a long-lasting effect on the stability and function of the shoulder, as the closure improves not only the static restraints but also the dynamic restraints of the shoulder through the improved proprioception secondary to restoration of the rotator interval structures.

Recovery of shoulder strength and proprioception after open surgery for recurrent anterior instability: a comparison of two surgical techniques

BACKGROUND

Previous studies have documented a decrease in proprioceptive capacity in the unstable shoulder. The degree to which surgical approach affects recovery of strength and proprioception is unknown.

MATERIALS AND METHODS

The recovery of strength and proprioception after open surgery for recurrent anterior glenohumeral instability was compared for 2 surgical procedures. A prospective analysis of 55 consecutive patients with posttraumatic unilateral recurrent anterior glenohumeral instability was performed. Thirty patients (group 1) underwent an open inferior capsular shift with detachment of the subscapularis, and 25 (group 2) underwent an anterior capsulolabral reconstruction.

RESULTS

Mean preoperative proprioception and strength values were significantly lower for the affected shoulders in both groups. At 6 months after surgery, there were no significant differences for mean strength and proprioception values between the unaffected and operative sides for group 2 patients. In group 1 patients, however, there were still significant deficits in mean position sense and strength values. Complete restoration of proprioception and strength, however, was evident by 12 months in group 1.

CONCLUSION

This study demonstrates that there are significant deficits in both strength and proprioception in patients with posttraumatic, recurrent anterior glenohumeral instability. Although both are completely restored by 1 year after surgery, a subscapularis-splitting approach allows for complete recovery of strength and position sense as early as 6 months postoperatively. Detachment of the subscapularis delays recovery of strength and position sense for up to 12 months after surgery.

Unconstrained shoulder joint position sense does not change with body orientation

Our knowledge of the role of muscle activation on proprioception is incomplete. Previous work has either focused on comparing active and passive motions or manipulated both muscle activation and joint angles simultaneously. We conducted an experiment at the shoulder in which subjects' trunks were tilted backwards to decouple joint angle from joint torque. Twenty three healthy subjects underwent testing in an unconstrained joint position sense task. Kinematics were measured with a magnetic tracking device. The joint position sense task consisted of subjects moving their arms to a predetermined orientation in space with the help of visual feedback from the magnetic tracking device presented to the subjects through a head-mounted display. Subjects were then asked to reproduce the presented joint position in the absence of visual feedback. The protocol was performed under two tilts: upright and trunk tilted back 45 degrees. This allowed for a comparison of joint position sense at different joint angles (at the same resistive torque) and at different resistive torques (at the same joint angles). When comparing these two tilts, we found that matching based on elevation angle demonstrated no significant difference, while matching based on torques did find differences. These results implicate elevation angle at the shoulder as playing a more important role in modulating joint position sense than joint torque.

Sensorimotor deficits remain despite resolution of symptoms using conservative treatment in patients with tennis elbow: a randomized controlled trial

OBJECTIVES

To evaluate the time course of sensorimotor deficits in lateral epicondylalgia (LE; tennis elbow) and how these deficits may be influenced by common conservative treatments.

DESIGN

Single-blind randomized controlled trial.

SETTING

University laboratory, Australia.

PARTICIPANTS

A total of 198 participants with unilateral LE of a minimum 6 weeks duration and normative data from a group of 40 healthy participants.

INTERVENTIONS

Participants with LE were randomly assigned to physical therapy, corticosteroid injection, or a wait-and-see approach with ergonomic advice.

MAIN OUTCOME MEASURES

Upper-limb reaction time (simple, 1-choice and 2-choice reaction time) and speed of movement were assessed at baseline and 6 and 52 weeks of follow-up.

RESULTS

Patients with LE exhibited delayed reaction times (P<.001) and slower movement speeds (P<.001) for both the affected and unaffected arm at baseline, compared with normative data. Despite some improvement over time, significant bilateral deficits remained compared with healthy participants, with no significant differences between the affected and unaffected arm. Overall, there was no significant difference between the 3 treatment groups over time.

CONCLUSIONS

Sensorimotor deficits remain relatively unchanged over time and are present bilaterally in patients with unilateral LE. Treatment did not influence the time course of the sensorimotor deficits. This prompts conjecture as to the relationship and clinical relevance of sensorimotor deficits in LE. It should be noted that treatment evaluated in this study did not specifically target sensorimotor function, and further investigation into the significance of sensorimotor deficits in patients with LE is required.

[Early failure of anterior bone block in multidirectional shoulder instability: a case report]

We report the case of a 47-year-old female patient who developed predominantly anterior multidirectional glenohumeral instability. After rehabilitation, this patient was treated surgically with an anterior coracoid bone block using the Latarjet technique. The second postoperative day, the control scan revealed posterior glenohumeral dislocation. The patient underwent a second operation for a posterior iliac block. At last clinical follow-up (six years), the patient had normal shoulder motion; shoulder function was considered excellent using the clinical scores. We recall the pathogenic hypotheses explaining multidirectional shoulder instability and discuss the proposed treatments. This case illustrates the difficult diagnosis and therapeutic management of multidirectional instability. Under general anesthesia, examination showed that posterior laxity predominated while paradoxically, the patient presented predominantly anteromedial dislocations. This case is also exceptional by the development of posterior dislocation, an unusual postoperative complication after an anterior bone block; we describe the therapeutic options. In the event of multidirectional instability with bone injuries, we recommend a block in the direction of the instability. Preoperative examination under general anesthesia can be helpful in understanding the mechanism of residual postoperative instability, which would require complementary surgical stabilization.

Open and arthroscopic treatment of multidirectional instability of the shoulder

Multidirectional instability of the shoulder can be a difficult diagnostic and therapeutic dilemma for orthopaedic surgeons. First described by Neer and Foster, the mainstay of treatment is usually conservative, with most patients doing very well with nonoperative management. In patients with recalcitrant symptoms, surgical treatment primarily has been aimed at addressing the pathologically increased capsular volume. Newer studies suggest that the pathology also includes abnormal labral morphology and perhaps inadequate neuromuscular control. The arthroscopic treatment of multidirectional instability has come to have comparable results to open techniques when the multifactorial nature of the disease is recognized and the multiple techniques are used in combination to fully treat all pathology. Thermal capsulorrhaphy cannot be recommended at this time, except perhaps as an adjunct to other capsular plication or capsulorrhaphy techniques. The advantages of a less invasive procedure make arthroscopic capsular plication attractive, but it is associated with increased technical difficulty and a steep learning curve. Further studies are needed to distinguish a clear advantage of one over the other. Regardless of the technique used, the key to success is addressing the capsular laxity and redundancy to restore anatomic capsuloligamentous tension without overconstraining the shoulder.

Sensorimotor contribution to shoulder stability: effect of injury and rehabilitation

Shoulder joint stability is the humeral head remaining or promptly returning to proper alignment within the glenoid fossa. This is mediated by both mechanical and dynamic restraint mechanisms. Coordination of these restraint systems is required for shoulder joint stability. The sensorimotor system is defined as all of the sensory, motor, and central integration and processing components involved in maintaining joint stability. The sensorimotor system is comprised of several components including proprioception, joint position sense, kinesthesia, sensation of force, and neuromuscular control. With joint injury, not only are the mechanical restraints disrupted (joint capsule, glenoid labrum, etc.) but also, the sensorimotor system is affected. Restoration of the sensorimotor system has been shown to occur through both surgical and conservative intervention and rehabilitation. Surgery has been shown to restore both mechanical restraints and the sensorimotor system. Specific rehabilitation techniques have also been effective at improving the sensorimotor system in healthy and pathological patients.

Shoulder joint position sense improves with elevation angle in a novel, unconstrained task

Proprioception, encompassing the submodalities of kinesthesia and joint position sense, is important in the maintenance of joint stability, especially in the shoulder. The purpose of this study was to examine the effects of plane and elevation angle on unconstrained shoulder joint position sense. Twenty-two subjects (12 male, 10 female) without a history of shoulder pathology were recruited from a university campus. Subjects attempted to replicate, with respect to plane and elevation angles, various target positions. Target positions consisted of five plane angles at 90 degrees of arm elevation and five arm elevation angles in the scapular plane. All target positions were tested twice to assess the reliability of the measurement. Intraclass correlation coefficients were generally low across target positions, possibly owing to the novelty and demanding nature of the task. No differences in repositioning errors were observed between plane angles (p = 0.255). Repositioning errors decreased linearly as the elevation angle increased from 30 degrees to 90 degrees (p = 0.007) and increased again from 90 degrees to 110 degrees of elevation (p = 0.029). Our results suggest that unconstrained joint position sense may be enhanced with increased muscular activation levels. Further, afferent feedback from musculotendinous mechanoreceptors may dominate over that from capsuloligamentous sources in unconstrained movements.

Atypical shoulder muscle activation in multidirectional instability

OBJECTIVE

Surface and intramuscular electromyography was used to investigate shoulder muscle activity in subjects with multidirectional instability (MDI).

METHODS

Subjects (seven MDI, 11 control) performed repetitive shoulder abduction/adduction, flexion/extension and internal/external rotation movements on an isokinetic dynamometer. The activity of the deltoid, infraspinatus, supraspinatus, latissimus dorsi, and pectoralis major muscles were recorded using double-differential surface and intramuscular fine-wire electrodes. A repeated measures analysis of variance evaluated group differences in the amplitude, onset, termination and duration of the muscle activity.

RESULTS

Significant activation parameter differences for the supraspinatus, infraspinatus, posterior deltoid and pectoralis major muscles were found in the subjects with MDI. The rotator cuff and posterior deltoid muscles demonstrated abbreviated periods of activity when performing internal/external rotation, despite activation amplitudes that were similar to the controls. In contrast, the activation of the pectoralis major differed from the control group in both the amplitude and time domains when performing shoulder extension.

CONCLUSIONS

MDI is associated with atypical patterns of muscle activity that occur even when highly constrained movements are used to elicit the activity.

SIGNIFICANCE

In addition to glenohumeral hyperlaxity, the results suggest that dysfunctional neuromuscular control of the rotator cuff is also a contributing factor to the pathoetiology of MDI.