Radiographic and Advanced Imaging Evaluation of Posterior Shoulder Instability

PURPOSE OF REVIEW

Posterior shoulder instability is an uncommon but important cause of shoulder dysfunction and pain which may occur as the result of seizure, high energy trauma, or repetitive stress related to occupational or sport-specific activities. This current review details the imaging approach to the patient with posterior shoulder instability and describes commonly associated soft tissue and bony pathologies identified by radiographs, CT, and MR imaging.

RECENT FINDINGS

Advances in MR imaging technology and techniques allow for more accurate evaluation of bone and soft tissue pathology associated with posterior shoulder instability while sparing patients exposure to radiation. Imaging can contribute significantly to the clinical management of patients with posterior shoulder instability by demonstrating the extent of associated injuries and identifying predisposing anatomic conditions. Radiologic evaluation should be guided by clinical history and physical examination, beginning with radiographs followed by CT and/or MRI for assessment of osseous and soft tissue pathology. Synthesis of a patient's clinical history, physical exam findings, and radiologic examinations should guide clinical management.

SECEC Didier Patte Prize 2023: the ABC classification of posterior shoulder instability

BACKGROUND

The ABC classification has recently been proposed as a comprehensive classification system for posterior shoulder instability (PSI). The purpose of this study was to analyze the comprehensiveness as well as inter-rater and intrarater reliability of the ABC classification.

METHODS

All consecutive patients presenting with unidirectional PSI from June 2019 to June 2021 were included in a prospective study. No patients were excluded, leaving a consecutive series of 100 cases of PSI in 91 patients. All recorded clinical and imaging data were used to create anonymized clinical case vignettes, which were evaluated twice according to the ABC classification at the end of the recruitment period in random sequential order by 4 independent raters (2 experienced shoulder surgeons and 2 orthopedic residents) to analyze the comprehensiveness as well as inter-rater and intrarater reliability of the ABC classification for PSI and to describe differences in characteristics among subtypes. Group A was defined as a first-time singular PSI event <3 months in the past regardless of etiology and is further subdivided into type 1 and type 2 depending on the occurrence of a subluxation (A1) or dislocation (A2). Group B comprises recurrent dynamic PSI regardless of time since onset and is further subdivided by the cause of instability into functional (B1) and structural (B2) dynamic PSI. Group C includes chronic static PSI with posterior humeral decentering that can be either constitutional (C1) or acquired (C2).

RESULTS

None of the cases was deemed unsuitable to be classified based on the proposed system by the observers. After consensus agreement between the 2 expert raters, 16 cases were attributed to group A (8 type A1 and 8 type A2); 64, to group B (33 type B1 and 31 type B2); and 20, to group C (11 type C1 and 9 type C2). The expert raters agreed on the classification subtypes in 99% and 96% of the cases during the first rating and second rating, respectively (intraclass correlation coefficients [ICCs], 0.998 and 0.99, respectively). The intraobserver reliability was excellent for both raters. The beginners reached the same conclusion as the consensus agreement in 94% of the cases (ICC, 0.99) and 89% of the cases (ICC, 0.97) during the first round and 94% each (ICC, 0.97) during the second round. The intraobserver reliability was excellent for both beginners. Overall, discrepancies between raters were found between groups B1 and B2 (n = 14), groups B2 and C2 (n = 4), groups B1 and C1 (n = 1), and groups A1 and B2 (n = 1). In general, each subtype showed distinctive clinical and imaging characteristics that facilitated the diagnosis.

CONCLUSION

The presented ABC classification for PSI is a comprehensive classification with a high reliability and reproducibility. However, a gradual transition and potential progression between the subtypes of PSI must be considered. The reliable distinction between different subtypes of PSI based on etiology and pathomechanism provides a standardized basis for future investigations on treatment recommendations.

Retrospective analysis of decision-making in post-traumatic posterior shoulder instability

PURPOSE

This study aims to assess the clinical outcomes in the management of post-traumatic posterior shoulder instability (PSI) with a focus on the decision-making process for operative and conservative treatments.

INTRODUCTION

PSI can result from traumatic events, impacting a patient's quality of life. This study delves to better indicate decision-making for operative indication of post-traumatic PSI patients.

METHODS

Patients who sustained posterior shoulder dislocations were selected from a single surgeon's database within a five-year period. Cases of degenerative or genetically caused PSI were excluded, resulting in a cohort of 28. Patients were initially managed conservatively but indicated for surgery if they were unable to actively stabilize the shoulder or exhibited bony or cartilage defects confirmed through imaging. If conservative treatment did not yield significant improvements, it was classified as a failure, and operative intervention was recommended. The WOSI Score, ROM, and X-ray were employed to evaluate the success of treatment.

RESULTS

Out of the 28 patients, 11 received conservative, seven immediate surgeries, and ten transitioned from conservative to operative treatment. The overall success rate showed 25 good to excellent results. In the persistent conservative treatment group, the initial WOSI score was significantly lower compared to the operative group.

CONCLUSION

This study suggests that post-traumatic PSI can be successfully managed conservatively with initial low clinical symptoms (low WOSI score) and in the absence of absolute indications for operative treatment. When surgery is necessary, arthroscopic procedures proved effective in achieving good to excellent results in 16 out of 17 cases.

Open treatment of posterior glenoid bone loss and bipolar bone loss

Posterior glenohumeral instability is an increasingly common and challenging orthopaedic problem. While an arthroscopic soft tissue stabilization procedure (i.e., reverse Bankart repair) is effective in treating most cases of posterior instability, this procedure may be inadequate in shoulders with critical posterior glenoid bone loss (GBL), or in cases of an engaging reverse Hill-Sachs lesion. Thus, the purpose of the present manuscript was to report contemporary surgical approaches, techniques, and outcomes for the open treatment of glenoid or humeral head bone loss in posterior instability to help guide clinical decision making. Open osteoarticular augmentation procedures have emerged as a popular option to treat posterior bone loss, with bony auto- and allografts utilized from a variety of donor sites including iliac crest, scapular spine, acromion, distal clavicle, and distal tibia. The combination of glenoid retroversion and bone loss can be addressed with a posterior glenoid opening wedge osteotomy. Bipolar bone loss may be treated with a combination of the aforementioned techniques, in addition to a reverse remplissage, a modified McLaughlin procedure, or various arthroplasty-related options. Although short and mid-term outcomes are dependable, studies reporting long-term outcomes are sparse. Moreover, there is no current consensus regarding the most effective treatment of posterior shoulder instability in the setting of bone loss, and open surgical techniques continue to evolve. Further research is necessary to determine long-term effectiveness of these surgical options.

Posterior Shoulder Instability in Tennis Players: Aetiology, Classification, Assessment and Management

Background

Micro-traumatic posterior shoulder instability (PSI) is an often missed and misdiagnosed pathology presenting in tennis players. The aetiology of micro-traumatic PSI in tennis players is multifactorial, including congenital factors, loss of strength and motor control, and sport-specific repetitive microtrauma. Repetitive forces placed on the dominant shoulder, particularly combinations of flexion, horizontal adduction, and internal rotation contribute to the microtrauma. These positions are characteristic for kick serves, backhand volleys, and the follow-through phase of forehands and serves. The aim of this clinical commentary is to present an overview of the aetiology, classification, clinical presentation, and treatment of micro-traumatic PSI, with a particular focus on tennis players.

Level of Evidence

5.

Posterior stability of the shoulder depends on acromial anatomy: a biomechanical study of 3D surface models

PURPOSE

Primary glenohumeral osteoarthritis is commonly associated with static posterior subluxation of the humeral head. Scapulae with static/dynamic posterior instability feature a superiorly and horizontally oriented acromion. We investigated whether the acromion acts as a restraint to posterior humeral translation.

METHODS

Five three-dimensional (3D) printed scapula models were biomechanically tested. A statistical shape mean model (SSMM) of the normal scapula of 40 asymptomatic shoulders was fabricated. Next, a SSMM of scapular anatomy associated with posterior subluxation was generated using data of 20 scapulae ("B1"). This model was then used to generate three models of surgical correction: glenoid version, acromial orientation, and acromial and glenoid orientation. With the joint axially loaded (100N) and the humerus stabilized, an anterior translation force was applied to the scapula in 35°, 60° and 75° of glenohumeral flexion. Translation (mm) was measured.

RESULTS

In the normal scapula, the humerus translates significantly less to contact with the acromion compared to all other configurations (p < .000 for all comparisons; i.e. 35°: "normal" 8,1 mm (± 0,0) versus "B1" 11,9 mm (± 0,0) versus "B1 Acromion Correction" 12,2 mm (± 0,2) versus "B1 Glenoid Correction" 13,3 mm (± 0,1)). Restoration of normal translation was only achieved with correction of glenoid and acromial anatomy (i.e. 75°: "normal" 11 mm (± 0,8) versus "B1 Acromion Correction" 17,5 mm (± 0,1) versus "B1 Glenoid Correction" 19,7 mm (± 1,3) versus "B1 Glenoid + Acromion Correction" 11,5 mm (± 1,1)).

CONCLUSIONS

Persistence or recurrence of static/dynamic posterior instability after correction of glenoid version alone may be related to incomplete restoration of the intrinsic stability that is conferred by a normal acromial anatomy.

LEVEL OF EVIDENCE V

biomechanical study.

Mid-term to long-term results of open posterior bone block grafting in recurrent posterior shoulder instability: a clinical and CT-based analysis

Background

There is little consensus on the best treatment after failed conservative management of recurrent posterior shoulder instability. The purpose of this study was to analyze our clinical and radiological mid-term to long-term results of an open, posterior bone block procedure for the treatment of recurrent posterior shoulder instability.

Methods

From 1999 to 2015, 14 patients were included in the study and available for clinical and radiographic follow-up (FU). FU included a standardized physical examination, assessment of the Constant-Murley-Score, subjective shoulder value, American Shoulder and Elbow Surgeons score, and Western Ontario Shoulder Instability Index. Conventional radiographs and a computed tomography (CT)-scan were performed preoperatively and at latest FU. Glenohumeral arthropathy was classified as per Samilson and Prieto. The CT scans were used to evaluate the structure of the graft (resorption, union), graft positioning, glenoid version, centering of the humeral head, and glenoid erosion and morphology.

Results

The median age at the time of surgery was 26 years (range 16-41 years) and the median FU period was 9 years (range 4-20 years). The rate of reported dynamic postoperative subluxation and instability was 46% (n = 6) and the rate of dynamic posterior instability during clinical testing at FU was 31% (n = 4). The tested instability rate in the traumatic group was 14% (n = 1) compared to the atraumatic group with 50% (n = 3) during clinical FU. The mean Constant-Murley-Score increased from preoperatively (77 ± 11 points) to postoperatively (83 ± 14 points, P = .158). The last FU showed an American Shoulder and Elbow Surgeons score of 85 ± 12; the Western Ontario Shoulder Instability Index score was 715 ± 475 points. The mean subjective shoulder value increased from 58% ± 19 preoperatively to 73% ± 17 at final FU (P = .005). Degenerative changes increased by at least one grade in 67% of the patients. Mean preoperative glenoid retroversion (CT) was 7.5° ± 6°. The position of the graft was optimal in 86% (n = 12). In 62% of the cases, a major resorption of the graft (Zhu grade II) was observed.

Conclusion

The rate of tested recurrent instability at last FU was as high as 31% (n = 4, atraumatic [n = 3] vs. traumatic [n = 1]) after a median FU of 9 years. Given the moderate improvement of clinical outcome scores, shoulder stability and the increase of degenerative joint changes by at least one grade (Samilson/Prieto) in 67% of patients, a posterior bone block procedure is not a uniformly satisfying treatment option for recurrent posterior shoulder subluxation, especially in cases of atraumatic posterior instability.

Understanding Batter's Shoulder: Diagnosis, Treatment, and Outcomes

PURPOSE OF REVIEW

Though most of the attention in recent literature on baseball injuries has been paid to throwers, one often overlooked aspect of the game is the effect of the batter's swing on the shoulder. It is well known that the batter's lead shoulder can experience significant translational forces during the player's swing, and that these are increased following a missed swing. The purpose of this paper is to review the background and pathophysiology as well as clinical presentation and treatment of players with Batter's shoulder.

RECENT FINDINGS

Recent studies demonstrate that while nonoperative treatment of Batter's shoulder is still a viable first line of treatment, favorable outcomes have been reported with arthroscopic posterior labral repair for high level athletes. Batter's injury can cause significant pain and dysfunction in baseball hitters, especially during the follow through phase of swing. While conservative care can be attempted early, outcomes following arthroscopic posterior labral repair are favorable with a high rate of return to play.

Dynamic Posterior Instability Test: A New Test for Posterior Glenohumeral Instability

Background

Recurrent posterior shoulder instability has become an increasingly recognized cause of shoulder disability, especially among athletes. The presentation can be vague and therefore its clinical diagnosis is often overlooked. Few diagnostic tests exist and these tests are difficult to perform in an anxious and apprehensive patient. Many also lack high specificity and do not effectively distinguish posterior labral tears from other shoulder pathologies. As a result, the authors worked to develop a new test, the dynamic posterior instability test (DPIT). The purpose of this study was to describe the DPIT as well as a modified DPIT test and to evaluate the accuracy of these tests in detecting posterior labral pathology. It was hypothesized that the dynamic posterior instability test (DPIT) would improve accuracy in the evaluation of posterior labral tears.

Methods

For a 9-month period, the DPIT and modified DPIT tests were performed on all patients evaluated for posterior instability of the shoulder. The records of all patients who had undergone a posterior labral repair (type VIII SLAP and posterior labral tears) were reviewed. The results of the DPIT and modified DPIT tests were compared to intra-operative findings. Anterior glenohumeral instability patients were also evaluated with these tests to serve as a control.

Results

Fifty-one patients had a positive and 3 patients had a negative DPIT test. Of the anterior instability patients, there was 1 positive and 19 negative test results. The sensitivity of the DPIT test was 94.4%, specificity 95%, the positive predictive value 0.98, and the negative predictive value 0.86. The results of the modified DPIT were the same as the DPIT test.

Conclusions

The DPIT and modified DPIT tests provide a valuable new tool when combined with history and other physical examination findings improve the accuracy of diagnosis of posterior shoulder instability.

Conservative treatment of acute traumatic posterior shoulder dislocations (Type A) is a viable option especially in patients with centred joint, low gamma angle, and middle or old age

PURPOSE

Purpose of this study was to evaluate the mid- to long-term outcome after conservatively treated first-time posterior shoulder dislocations and to determine structural defects associated with failure.

METHODS

In this multi-centric retrospective study, 29 shoulders in 28 patients with first-time acute posterior shoulder dislocation (Type A1 or A2 according to the ABC classification) and available cross-sectional imaging were included. Outcome scores as well as radiological and magnetic resonance imaging were obtained at a mean follow-up of 8.3 ± 2.7 years (minimum: 5 years). The association of structural defects with redislocation, need for secondary surgery, and inferior clinical outcomes were analysed.

RESULTS

Redislocation occurred in six (21%) shoulders and nine shoulders (31%) underwent secondary surgery due to persistent symptoms. The posttraumatic posterior glenohumeral subluxation was higher in the redislocation group compared to the no redislocation group; however, statistical significance was not reached (61.9 ± 12.5% vs. 50.6 ± 6.4%). Furthermore, a higher adapted gamma angle was observed in the failed conservative treatment group versus the conservative treatment group, similarly without statistically significant difference (97.8° ± 7.2°, vs. 93.3° ± 9.7°). The adapted gamma angle was higher than 90° in all patients of failed conservative therapy and the redislocation group. An older age at the time of dislocation showed a significant correlation with better clinical outcomes (SSV: r = 0.543, p = 0.02; ROWE: r = 0.418, p = 0.035 and WOSI: r = 0.478, p = 0.045). Posterior glenohumeral subluxation after trauma correlated with a worse WOSI (r = - 0.59, p = 0.02) and follow-up posterior glenohumeral decentring (r = 0.68, p = 0.007). The gamma angle (r = 0.396, p = 0.039) and depth of the reverse Hill-Sachs lesion (r = 0.437, p = 0.023) correlated significantly with the grade of osteoarthritis at follow-up.

CONCLUSION

Conservative treatment is a viable option in patients with an acute traumatic posterior shoulder dislocation with good outcome after mid- and long-term follow-up especially in patients with centred joint, low gamma angle, and middle or old age.

LEVEL OF EVIDENCE

IV.

Does the posterior glenoid osteotomy reduce the rate of recurrence in patients with posterior shoulder instability - A systematic review

BACKGROUND

Posterior shoulder instability (PSI) is becoming an increasingly recognised condition. A number of different treatment modalities exist to treat PSI including arthroscopic or open surgeries when non-operative treatment has failed. The primary aim of this systematic review was to analyse the rate of recurrent instability after posterior glenoid osteotomy (PGO) for recurrent PSI, while secondary aim was to identify complication rate and the amount of retroversion correction.

PATIENTS AND METHODS

A review of the online databases MEDLINE and Embase was conducted on 1 November 2019 according to PRISMA guidelines. The review was registered prospectively in the PROSPERO database (Registration No. CRD42020161984). Clinical studies reporting either the recurrence rate, complications or amount of retroversion correction after PGO for PSI were included. The studies were appraised using the Methodological Index for Non-Randomized Studies (MINORS) tool.

RESULTS

The search strategy identified 9 studies eligible for inclusion. Of the 9 studies, 4 showed an improvement in retroversion with a mean change in retroversion of 10^o. All 9 studies reported on recurrence rate with an overall rate of 22%. Complications were discussed in only 7 of the studies with overall rate of 18.3%. The most common complication reported in the studies were degenerative changes of the glenohumeral joint (7.3%) and iatrogenic fractures (5.5%).

CONCLUSION

PGO is a viable option in patients with recurrent PSI that have increased retroversion and have failed non-operative or arthroscopic treatment. It does however carry a significant risk of complications.

LEVEL OF EVIDENCE

IV; Systematic review.

Similar scapular morphology in patients with dynamic and static posterior shoulder instability

Background

There is evidence that specific variants of scapular morphology are associated with dynamic and static posterior shoulder instability. To this date, observations regarding glenoid and/or acromial variants were analyzed independently, with two-dimensional imaging or without comparison with a healthy control group. Therefore, the purpose of this study was to analyze and describe the three-dimensional (3D) shape of the scapula in healthy and in shoulders with static or dynamic posterior instability using 3D surface models and 3D measurement methods.

Methods

In this study, 30 patients with unidirectional posterior instability and 20 patients with static posterior humeral head subluxation (static posterior instability, Walch B1) were analyzed. Both cohorts were compared with a control group of 40 patients with stable, centered shoulders and without any clinical symptoms. 3D surface models were obtained through segmentation of computed tomography images and 3D measurements were performed for glenoid (version and inclination) and acromion (tilt, coverage, height).

Results

Overall, the scapulae of patients with dynamic and static instability differed only marginally among themselves. Compared with the control group, the glenoid was 2.5° (P = .032), respectively, 5.7° (P = .001) more retroverted and 2.9° (P = .025), respectively, 3.7° (P = .014) more downward tilted in dynamic, respectively, static instability. The acromial roof of dynamic instability was significantly higher and on average 6.2° (P = .007) less posterior covering with an increased posterior acromial height of +4.8mm (P = .001). The acromial roof of static instability was on average 4.8° (P = .041) more externally rotated (axial tilt), 7.3° (P = .004) flatter (sagittal tilt), 8.3° (P = .001) less posterior covered with an increased posterior acromial height of +5.8 mm (0.001).

Conclusion

The scapula of shoulders with dynamic and static posterior instability is characterized by an increased glenoid retroversion and an acromion that is shorter posterolaterally, higher, and more horizontal in the sagittal plane. All these deviations from the normal scapula values were more pronounced in static posterior instability.

Return to sport after surgical treatment for posterior shoulder instability: a systematic review

Purpose

To report the rate of return to sport after surgical treatment for posterior shoulder instability among athletes.

Methods

A systematic review of the literature regarding rate of return to sport after surgical treatment for posterior shoulder instability was undertaken. The primary outcome measure was return to sport. The secondary outcome measures included rate of return to sport to preinjury level, time to return to sport, injury type, reoperations after primary surgery, and objective patient-reported outcome data. Data is summarized with ranges and tables.

Results

A total of 23 studies met inclusion criteria. The rate of return to sport ranged from 57.9%-100%. The rate of return to sport to the preinjury level ranged from 47.4%-100%. Time to return to sport ranged from 4.3-7.7 months. Furthermore, 66% of subjects had an acute traumatic injury and 34% were of insidious onset. The most commonly reported outcome measures were American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) scores and visual analog scale (VAS) pain scores. At a minimum of 1-year follow-up, ASES and VAS pain scores improved. Revision rates ranged from 0%-36.8%.

Conclusion

The systematic review demonstrated high rates of return to sport and relatively high rates of return to preinjury level of sport among all athletes who underwent surgical treatment for posterior shoulder instability. Objective patient-reported outcome metrics improved postoperatively whereas revision rates remained low.

No difference in outcomes of surgical treatment for traumatic and atraumatic posterior shoulder instability

BACKGROUND

Posterior shoulder instability is a rare pathology and accounts for 2-10% of all shoulder instabilities. The purpose of this study was to compare pain and functional scores following surgical treatment of traumatic and atraumatic PSI.

HYPOTHESIS

The authors hypothesize that patients with traumatic PSI are at greater risks of residual pain and recurrent subluxation.

MATERIAL AND METHODS

The records of 150 patients operated for PSI between 2000 and 2015 at 10 different centers were analysed. Inclusion criteria were symptomatic PSI (subluxation and/or pain) with radiographic signs of posterior glenoid erosion or fracture, posterior labral tears, or reverse Hill Sachs lesions. One hundred and seventeen patients were eligible, of which 84% presented symptoms of subluxation and/or dislocation, and 16% were painful without clinical symptoms of subluxation and/or dislocation. Patients were evaluated at 48±33months (range: 12-159) using the Constant, Walch-Duplay and Rowe scores, with pain on Visual Analogic Scale (pVAS).

RESULTS

Compared to atraumatic PSI, traumatic PSI was more prevalent in men (84.4% vs 61.9%, p=0.031), and tended to have fewer pain symptoms (15.8% vs 23.8%, n.s). Atraumatic PSI was more likely to affect the dominant arm, although the difference was not significant (81.0% vs 59.4%, n.s.). Traumatic PSI did not differ from atraumatic PSI in terms of preoperative lesional characteristics, procedures performed, or postoperative pain and instability. Although these differences were not statistically significant, it is worth noting that traumatic PSI patients experienced more recurrence of instability (15.6% vs 4.8%, p=0.298), and lower pain on VAS (1.5±2.3 vs 2.6±3.0, n.s.) compared to atraumatic PSI.

DISCUSSION

Functional scores did not significantly differ between traumatic and atraumatic PSI after surgery, although traumatic PSI patients tended to have a higher recurrence of instability, while atraumatic PSI patients tended to remain more painful.

LEVEL OF EVIDENCE

IV, retrospective cohort study.

Glenoid retroversion is an important factor for humeral head centration and the biomechanics of posterior shoulder stability

PURPOSE

Glenoid retroversion is a known independent risk factor for recurrent posterior instability. The purpose was to investigate progressive angles of glenoid retroversion and their influence on humeral head centration and posterior translation with intact, detached, and repaired posterior labrum in a cadaveric human shoulder model.

METHODS

A total of 10 fresh-frozen human cadaveric shoulders were investigated for this study. After CT- canning, the glenoids were aligned parallel to the floor, with the capsule intact, and the humerus was fixed in 60° of abduction and neutral rotation. Version of the glenoid was created after wedge resection from posterior and fixed with an external fixator throughout the testing. Specimens underwent three conditions: intact, detached, and repaired posterior labrum, while version of the glenoid was set from + 5° anteversion to - 25° retroversion by 5° increments. Within the biomechanical setup, the glenohumeral joint was axially loaded (22 N) to center the joint. At 0° of glenoid version and intact labrum, the initial position was used as baseline and served as point zero of centerization. After cyclic preloading, posterior translation force (20 N) was then applied by a material testing machine, while start and endpoints of the scapula placed on an X-Y table were measured.

RESULTS

The decentralization of the humeral head at glenoid version angles of 5°, 10°, 15°, and 20° of retroversion and 5° of anteversion was significantly different (P < 0.001). Every increment of 5° of retroversion led to an additional decentralization of the humeral head overall by (average ± SD) 2.0 mm ± 0.3 in the intact and 2.0 mm ± 0.7 in the detached labrum condition. The repaired showed significantly lower posterior translation compared to the intact condition at 10° (P = 0.012) and 15° (P < 0.01) of retroversion. In addition, CT measured parameters (depth, diameter, and native version) of the glenoid showed no correlation with angle of dislocation of each specimen.

CONCLUSION

Bony alignment in terms of glenoid retroversion angle plays an important role in joint centration and posterior translation, especially in retroversion angles greater than 10°. Isolated posterior labrum repair has a significant effect on posterior translation in glenoid retroversion angles of 5° and 10°. Bony correction of glenoid version may be considered to address posterior shoulder instability with retroversion > 15°.

Incidence of posterior shoulder instability and trends in surgical reconstruction: a 22-year population-based study

BACKGROUND

The incidence of posterior shoulder instability (PSI) in the general population is not well defined. This study aimed to define the population-based incidence of PSI and describe trends in incidence and surgery rates.

METHODS

The study population included 143 patients (16 females, 127 males) diagnosed with new-onset PSI between January 1, 1994, and December 31, 2015. Medical records were reviewed to extract patient data. Age- and sex-specific incidence rates were calculated and adjusted to the 2010 United States population. Poisson regression was performed to examine trends by timeline, sex, and age.

RESULTS

Age- and sex- adjusted annual incidence of PSI was 4.64 per 100,000 person-years, and posterior dislocation was 1.30 per 100,000 person-years. Peak PSI incidence for males and females was at 14 to 19 years (31.82 and 5.23 per 100,000 person-years). PSI incidence was higher in males than females (8.86 vs. 1.07 per 100,000 person-years, P < .001). The 5-year cumulative risk of surgery for patients with PSI was 53.1% between 1996 and 2002, 59.9% between 2003 and 2008, and 87.5% between 2009 and 2015. Patients with PSI between 2009 and 2015 had a significantly increased rate of surgery (hazard ratio, 2.2; 95% confidence interval, 1.4-3.6; P = .001) compared with those between 1996 and 2002.

CONCLUSION

The age- and sex- adjusted incidence of PSI in the general population was 4.64 per 100,000 person-years. There is a significantly greater incidence of PSI in males than females, with both sexes peaking at 14 to 19 years and incidence rates remaining elevated throughout the third and fourth decades of life. The incidence of PSI remained stable over time; however, the rate of surgical intervention increased significantly, from 53.1% of patients between 1996 and 2002 to 87.5% of patients between 2009 and 2015.

Biomechanics of posterior shoulder instability - current knowledge and literature review

Posterior instability of the shoulder is a rare condition and represents about 10% of shoulder instability. It has become more frequently recognized in the last year, even though it is more difficult to diagnose than anterior shoulder instability. As this form of shoulder pathology is somewhat rare, biomechanical knowledge is limited. The purpose of our study was to perform an extensive literature search, including PubMed and Medline, and to give an overview of the current knowledge on the biomechanics of posterior shoulder instability. The PubMed/Medline databases were utilized, and all articles related to posterior shoulder instability and biomechanics were included to form a comprehensive compilation of current knowledge. A total of 93 articles were deemed relevant according to our inclusion and exclusion criteria. As expected with any newly acknowledged pathology, biomechanical studies on posterior shoulder instability remain limited in the literature. Current biomechanical models are performed in a static manner, which limits their translation for explaining a dynamic pathology. Newer models should incorporate dynamic stabilization of both the rotator cuff and scapulothoracic joint. There is a current lack of knowledge with regards to the pathomechanism of posterior shoulder instability, with no consensus on appropriate treatment regimens. Further investigation is therefore required at both basic science and clinical levels.

[The ABC guide for the treatment of posterior shoulder instability]

BACKGROUND

Posterior glenohumeral instability (PGHI) is an often unrecognized or misdiagnosed type of shoulder instability due to its heterogenic clinical and radiological presentation.

CLASSIFICATION

The ABC classification for PGHI is based on the different pathomechanisms and recommended treatment standards and is therefore a guide to finding the correct diagnosis and therapy for affected patients. There are different types of PGHI: A (first time), B (dynamic), C (static). These groups are further classified based on pathomechanical principles: A1: subluxation, A2: dislocation; B1: functional, B2: structural; C1: constitutional, C2: acquired.

THERAPY

In patients with type 1 PGHI (A1, B1, C1) conservative treatment is recommended while in patients with type 2 PGHI (A2, B2, C2) surgical treatment can be considered based on structural defects, clinical symptoms, chronicity, age, functional demand, and patient-specific health status. In addition it has to be considered, that there is the possibility of coexisting or overlapping subtypes as well as the chance of progression from one category into another over time.

Arthroscopic posterior bone block stabilization-early results of an effective procedure for the recurrent posterior instability

PURPOSE

In the current study the clinical outcome of an arthroscopic posterior bone block augmentation in combination with a posterior capsular repair was investigated.

METHODS

Twenty-four shoulders (18 patients) with unidirectional posterior shoulder instability were treated with an arthroscopic posterior bone block and capsular reconstruction. The mean follow up period was 26 months. The patients were examined pre- and postoperatively using the Constant-Murley score, the Rowe score, Walch-Duplay score and Western Ontario Shoulder index.

RESULTS

At the follow up examination 21 shoulders were classified to be stable, while one patient reported a single redislocation and two further patients reported recurrent posterior subluxation or posterior apprehension. Thus, the recurrence rate was defined to be 12.5%. The Rowe-Score significantly improved from 50 points preoperatively to 75 points postoperatively (p = 0.0003). The WOSI-score significantly improved from 37% preoperatively to 66% postoperatively (p = 0.0001). Revision surgery commonly was required for screw removal.

CONCLUSION

The early clinical results of this arthroscopic bone block augmentation and capsular repair are promising.

LEVEL OF EVIDENCE

IV.

Painful posterior shoulder instability: Anticipating and preventing failure. A study in 25 patients

BACKGROUND

Painful posterior shoulder instability (PPSI) is the least common of the three clinical patterns of posterior shoulder instability. PPSI is defined as pain combined with anatomical evidence of posterior instability but no instability events.

MATERIAL AND METHOD

We studied a multicentre cohort of 25 patients with PPSI; 23 were identified retrospectively and had a follow-up of at least 2 years and 2 patients were included prospectively. Most patients engaged in sports.

RESULTS

All 25 patients underwent surgery, which usually consisted in arthroscopic capsulo-labral reconstruction. The outcome was excellent in 43% of patients; another 43% had improvements but reported persistent pain. The pain remained unchanged or worsened in the remaining 14% of patients. Causes of failure consisted of a missed diagnosis of shoulder osteoarthritis with posterior subluxation, technical errors, and postoperative complications. The main cause of incomplete improvement with persistent pain was presence of cartilage damage.

CONCLUSION

Outcomes were excellent in patients who were free of cartilage damage, bony abnormalities associated with posterior instability (reverse Hill-Sachs lesion, erosion or fracture of the posterior glenoid), technical errors, and postoperative complications.

ABC classification of posterior shoulder instability

Posterior glenohumeral instability (PGHI) is a commonly under- and misdiagnosed pathology owing to its variety of clinical presentations. In order to facilitate diagnosis and treatment, the simple yet comprehensive ABC classification for PGHI is based on the underlying pathomechanical principles and current standard of treatment. Three main groups of PGHI are distinguished based on the type of instability: A (first time), B (dynamic), C (static). Two subtypes further differentiate these groups in terms of their specific pathomechanism and provide a guideline in the choice of appropriate treatment: A (1, subluxation; 2, dislocation), B (1, functional; 2, structural), C (1, constitutional; 2, acquired). While conservative treatment is warranted in most patients with type 1 PGHI (A1, B1, C1), surgical treatment should be considered on an individual basis in patients with type 2 PGHI (A2, B2, C2), while keeping in mind that the different groups and subtypes can overlap, co-exist, or even progress from one to another over time. Of course the necessity for surgical treatment depends on the extent of the structural defects, on the severity of symptoms, on the chronicity, as well as on patient-specific functional demand, age, and health status. Nonetheless, the ABC classification helps to correctly diagnose the type of PGHI and provides a guideline for the generally recommended type of treatment.

Use of shoulder pacemaker for treatment of functional shoulder instability: Proof of concept

Background

Functional shoulder instability (polar type III) is caused by underactivity of rotator cuff and periscapular muscles, which leads to subluxation or dislocation during shoulder movement. While surgical treatment has shown no benefits, aggravates pain, and frequently diminishes function even further, conservative treatment is often ineffective as well.

Objectives

The aim was to investigate the effectiveness of a “shoulder pacemaker” device that stimulates underactive muscles in patients with functional instability during shoulder movement in order to re-establish glenohumeral stability.

Patients and methods

Three patients with unsuccessfully treated functional shoulder instability causing pain, emotional stress, as well as limitations during daily activities and sports participation were enrolled in this pilot project. The device was used to stimulate the external rotators of the shoulder and retractors of the scapula. Pain level, subjective shoulder instability, range of motion, visible aberrant muscle activation, and signs of dislocation were compared when the device was switched on and off.

Results

No changes were observed when the device was attached but switched off. When the device was switched on, all patients were able to move their arms freely without pain, discomfort, or subjective or objective signs of instability. All patients rated this as an excellent experience and volunteered to train further with the device. No complications were observed.

Conclusion

The electric stimulation of hypoactive rotator cuff and periscapular muscles by means of the shoulder pacemaker successfully re-establishes stability in patients with functional shoulder instability during the time of application.

 Video online

The online version of this article (doi: 10.1007/s11678-017-0399-z) contains the video: “The Shoulder-Pacemaker: treatment of functional shoulder instability with pathological muscle activation pattern”. Video by courtesy of P. Moroder, M. Minkus, E. Böhm, V. Danzinger, C. Gerhardt and M. Scheibel, Charité Universitätsmedizin Berlin 2017, all rights reserved

Results of an open posterior bone block procedure for recurrent posterior shoulder instability after a short- and long-time follow-up

PURPOSE

The aim of the present study was to analyse and compare the clinical and radiological results after open posterior bone block procedure at long- (LT) and short-term (ST) follow-up. The hypothesis was that placement of a bone block at the posterior glenoid rim in a technique of extending the glenoid surface will create permanent joint stability even in cases with hyperlaxity without a clinically relevant loss of motion or increase in osteoarthritis.

METHODS

Fifteen consecutive shoulders with recurrent posterior dislocation were evaluated clinically and radiologically. The Rowe score, Western Ontario Shoulder Index, Walch-Duplay score and the Constant-Murley score were used for clinical evaluation. The patients were categorized according to their follow-up period as either ST follow-up (min 12 months) or LT follow-up (min 42 months).

RESULTS

The clinical results showed no significant difference between ST (9) and LT (6) with good to very good overall results in the subjective as well as the objective scores (CS, RS, WDS). At LT, most patients felt mild to minor pain under strain. The difference in pain between the groups was not significant. Active ranges of motion and strength assessments were normal in all cases. In one case, recurrent dislocations occurred after bone graft resorption 6 months post-operatively. Only one patient presented mild osteoarthritis, without further progress at follow-up.

CONCLUSION

The open posterior bone block procedure can be a successful treatment option for recurrent posterior shoulder instability at ST and LT follow-up. This series showed a low rate of recurrent dislocations without development or progression of osteoarthritis. Since soft tissue procedures do not always provide satisfying results, the posterior bone block augmentation presents a reliable technique for the treatment of symptomatic posterior instability.

LEVEL OF EVIDENCE

Case Series, Treatment Study, Level IV.

Bone block procedures in posterior shoulder instability

PURPOSE

Posterior shoulder dislocation is often associated with bone defects. Surgical treatment is often necessary to address these lesions. The aim of the present systematic review was to analyse the available literature concerning bone block procedures in the treatment of bone deficiencies following posterior dislocation. In addition, the methodology of the articles has been evaluated through the Coleman methodology score.

METHODS

A systematic review of the literature was performed using the keywords "posterior shoulder instability", "posterior shoulder dislocation", "bone loss", "bone defect", "bone block", and "bone graft" with no limit regarding the year of publication. All English-language articles were evaluated using the Coleman methodology score.

RESULTS

Fifty-four articles were identified, and 13 articles met inclusion criteria. The initial cohort included 208 shoulders, and 182 were reviewed at an average follow-up of 72.7 months (±55.2). The average Coleman score was 57.2 (±8.0). The most lacking domains were the size of study population, the type of study, and the procedure for assessing outcomes. All the articles showed an increase in the outcome scores. Radiographic evaluation revealed degenerative changes such as osteoarthritis and graft lysis in most of the series.

CONCLUSIONS

This review confirms the lack of studies with good methodological quality. However, bone grafting is a reliable option since significant improvement in all scores is reported. Although a low incidence of recurrence is generally described, there are concerns that the results may deteriorate over time as evidenced by graft lysis and glenohumeral osteoarthritis in up to one-third of patients.

LEVEL OF EVIDENCE

Systematic review, Level IV.

The split portal: Description of a new accessory posterior portal for arthroscopic shoulder instability procedures

PURPOSE

Open approach to the posterior shoulder during bone block for posterior shoulder instability is challenging. Anatomical study was performed to identify landmarks of a portal, avoiding soft tissue damage, between the infraspinatus (IS) and teres minor (TM) muscles and distant from the supra-scapular nerve (SSN) for arthroscopic shoulder bone block.

METHODS

Eight fresh-frozen cadaveric shoulder specimens were used. The arthroscope was introduced through the soft point (SP). A guide wire was placed through the SP, in the rotator interval direction. A posterior open dissection exposed the split between the IS and TM. A new guide wire was placed into the split, parallel to the first wire, to locate the new posterior arthroscopic approach. Ten distances were measured to define the safe position.

RESULTS

The mean values were: SP to split IS-TM: 2 ± 0.2 (2-2.8); spinal bone to split IS-TM: 5 ± 0.5 (3-6.2); split IS-TM to posterior glenoid 6 o'clock: 1.3 ± 0.3 (0.6-1.6), 9 o'clock: 1.5 ± 0.3 (1-1.9), and 12 o'clock: 2 ± 0.1 (2.1-2.4); SSN to posterior glenoid 6 o'clock: 2.4 ± 0.2 (2.1-2.6), 9 o'clock: 1.7 ± 0.1 (1.5-1.8), and 12 o'clock: 1.5 ± 0.3 (1.2-2.1); and SSN to split IS-TM: 2 ± 0.3 (1.2-2.1).

CONCLUSION

This preliminary anatomical study described a posterior arthroscopic portal located 2 cm under the SP, parallel to the SP portal direction, and finishing between 7 and 8 o'clock at the posterior rim of the glenoid. For arthroscopic shoulder bone block, this portal can avoid muscle and SSN lesions.

Posterior Shoulder Instability in Overhead Athletes

Posterior shoulder instability in overhead athletes presents a unique and difficult challenge. Often, this group has an inherent capsular laxity and/or humeral retroversion to accommodate the range of motion necessary to throw. This adaptation makes the diagnosis of posterior capsulolabral pathology challenging, as the examiner must differentiate between adaptive capsular laxity and pathologic instability. Further complicating matters, the intraoperative surgeon must find the delicate balance of achieving stability while still allowing the necessary range of motion.

Posterior shoulder instability in the athletic population: Variations in assessment, clinical outcomes, and return to sport

Posterior instability of the shoulder is becoming an increasingly recognized shoulder injury in the athletic population. Diagnostic elements, such as etiology, directionality, and degree of instability are essential factors to assess in the unstable athletic shoulder. Concomitant injuries and associated pathologic lesions continue to be a significant challenge in the surgical management of posterior shoulder instability. Return to sport and previous level of play is ultimately the goal for every committed athlete and surgeon, thus subpopulations of athletes should be recognized as distinct entities requiring unique diagnostic, functional outcome measures, and surgical approaches.

Posterior shoulder instability in the contact athlete

Historically, posterior shoulder instability has been a challenging problem for contact athletes and orthopedic surgeons alike. A complete understanding of the normal shoulder anatomy and biomechanics and the pathoanatomy responsible for the instability is necessary for a successful clinical outcome. In addition, the surgeon must be familiar with the diagnostic imaging and physical examination maneuvers required for the correct diagnosis without missing any other concurrent abnormalities. This understanding will allow orthopedists to plan and execute the appropriate management, whether this may involve conservative or surgical intervention. The goal should always be to correct the abnormality and have the patient return to play with full strength and no recurrent instability.