Posterior glenoid rim deficiency in recurrent (atraumatic) posterior shoulder instability

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.

Risk Factors Associated with First Time and Recurrent Shoulder Instability: A Systematic Review

Background

Shoulder instabilities constitute a large proportion of shoulder injuries and have a wide range of presentations. While evidence regarding glenohumeral dislocations and associated risk factors has been reported, less is known regarding the full spectrum of instabilities and their risk factors.

Purpose

The purpose of this systematic review was to identify modifiable risk factors to guide patient management decisions with regards to implementation of interventions to prevent or reduce the risk of shoulder instability.

Study Design

Systematic Review.

Methods

A systematic, computerized search of electronic databases (CINAHL, Cochrane, Embase, PubMed, SportDiscus, and Web of Science) was performed. Inclusion criteria were: (1) a diagnosis of shoulder instability (2) the statistical association of at least one risk factor was reported, (3) study designs appropriate for risk factors, (4) written in English, and (5) used an acceptable reference standard for diagnosed shoulder instability. Titles and abstracts were independently screened by at least two reviewers. All reviewers examined the quality studies using the Newcastle-Ottawa Scale (NOS). At least two reviewers independently extracted information and data regarding author, year, study population, study design, criterion standard, and strength of association statistics with risk factors.

Results

Male sex, participation in sport, hypermobility in males, and glenoid index demonstrated moderate to large risk associated with first time shoulder instability. Male sex, age \<30 years, and history of glenohumeral instability with concomitant injury demonstrated moderate to large risk associated with recurrent shoulder instability.

Conclusion

There may be an opportunity for patient education in particular populations as to their increased risk for suffering shoulder instability, particularly in young males who appear to be at increased risk for recurrent shoulder instability.

Level of Evidence

Level III.

Differences in Osseous Shoulder Morphology, Scapulothoracic Orientation, and Muscle Volume in Patients With Constitutional Static Posterior Shoulder Instability (Type C1) Compared With Healthy Controls

BACKGROUND

Constitutional static posterior humeral decentering (type C1 according to ABC Classification) has been recognized as a pre-osteoarthritic deformity that may lead to early-onset posterior decentering osteoarthritis at a young age. Therefore, it is important to identify possible associations of this pathologic shoulder condition to find more effective treatment options.

PURPOSE

To perform a comprehensive analysis of all parameters reported to be associated with a C1 shoulder-including the osseous shoulder morphology, scapulothoracic orientation, and the muscle volume of the shoulder girdle in a single patient cohort.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A retrospective, comparative study was conducted analyzing 17 C1 shoulders in 10 patients who underwent magnetic resonance imaging (MRI) with the complete depiction of the trunk from the base of the skull to the iliac crest, including both humeri. The mean age of the patients was 33.5 years, and all patients were men. To measure and compare the osseous shoulder morphology (glenoid version, glenoid offset, humeral torsion, anterior acromial coverage, posterior acromial coverage, posterior acromial height, and posterior acromial tilt) and scapulothoracic orientation (scapular protraction, scapular internal rotation, scapular upward rotation, scapular translation, scapular tilt, and thoracic kyphosis), these patients were matched 1 to 4 according their age, sex, and affected side with shoulder-healthy patients who had received positron emission tomography (PET)-computed tomography. To measure and compare the muscle volume of the shoulder girdle (subscapularis, infraspinatus/teres minor, supraspinatus, trapezius, deltoid, latissimus dorsi/teres major, pectoralis major, and pectoralis minor), patients were matched 1 to 2 with patients who had received PET-MRI. Patients with visible pathologies of the upper extremities were excluded.

RESULTS

The C1 group had a significantly higher glenoid retroversion, increased anterior glenoid offset, reduced humeral retrotorsion, increased anterior acromial coverage, reduced posterior acromial coverage, increased posterior acromial height, and increased posterior acromial tilt compared with controls (P < .05). Decreased humeral retrotorsion showed significant correlation with higher glenoid retroversion (r = -0.742; P < .001) and higher anterior glenoid offset (r = -0.757; P < .001). Significant differences were found regarding less scapular upward rotation, less scapular tilt, and less thoracic kyphosis in the C1 group (P < .05). The muscle volume of the trapezius and deltoid was significantly higher in the C1 group (P < .05).

CONCLUSION

Patients with C1 shoulders differ from healthy controls regarding osseous scapular and humeral morphology, scapulothoracic orientation, and shoulder girdle muscle distribution. These differences may be crucial in understanding the delicate balance of glenohumeral centering.

A Posterior Acromial Bone Block Augmentation Is Biomechanically Effective at Restoring the Force Required To Translate the Humeral Head Posteriorly in a Cadaveric, Posterior Glenohumeral Instability Model

PURPOSE

To assess the biomechanical utility of a posterior acromial bone block (PABB) for the treatment of posterior glenohumeral instability.

METHODS

Ten fresh-frozen cadaveric specimens were obtained based upon an a priori power analysis. A 2.5-cm scapular spine autograft was harvested from all shoulders. A custom robot device was used to apply a 50-N compressive force to the glenohumeral joint. The humeral head was translated 10 mm posteroinferiorly at 30 degrees from the center of the glenoid at a rate of 1.0 mm/s in 6 consecutive conditions: (1) intact specimen, (2) intact with PABB, (3) posterior capsulolabral tear, (4) addition of the PABB, (5) removal of the PABB and repair of the capsulolabral tear (LR), and (6) addition of the PABB with LR. The maximum force required to obtain this translation was recorded. Paired t tests were performed to compare relevant testing conditions.

RESULTS

Ten cadavers with a mean ± SD age of 54.4 ± 13.1 years and mean ± SD glenoid retroversion of 6.5 ± 1.0 degrees were studied. The PABB provided greater resistance force to humeral head translation compared to the instability state (instability, 29.3 ± 15.3 N vs PABB, 47.6 ± 21.0 N; P = .001; 95% confidence interval [CI], -27.6 to -10.0). When comparing PABB to LR, the PABB produced higher resistance force than LR alone (PABB, 47.6 ± 21.0 N; LR, 34.2 ± 20.5 N; P = .012; 95% CI, -23.4 to -4.1). An instability lesion treated with the PABB, with LR (P = .056; 95% CI, -0.30 to 20.4) or without LR (P = .351; 95% CI, -6.8 to 15.7), produced resistance forces similar to the intact specimen.

CONCLUSIONS

A PABB is biomechanically effective at restoring the force required to translate the humeral head posteriorly in a cadaveric, posterior glenohumeral instability model. A posterior acromial bone block is a biomechanically feasible option to consider in patients with recurrent posterior instability.

CLINICAL RELEVANCE

Augmentation of the posterior acromion may be a biomechanically feasible option to treat posterior shoulder instability.

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.

Rotator Cuff Tears to Shoulder Instability: The Relationship Between Acromial Morphology and Shoulder Pathology

» The acromion is a well-studied region of the scapula that has demonstrated substantial relationships to various shoulder pathologies.» Abnormal acromial morphology is associated with rotator cuff pathology, and our understanding of this risk factor inspired acromioplasty as an adjunctive treatment for rotator cuff tears.» The acromion is linked closely to shoulder kinematics and biomechanics, as it serves as the origin for the deltoid muscle.» In degenerative shoulder disease, eccentric glenohumeral osteoarthritis has been associated with a higher, flatter acromial roof.» Increasing literature is emerging connecting morphology of the acromion with shoulder instability.

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.

Glenoid Bone Loss Pattern in Patients With Posterior Instability Versus Anterior Instability: A Matched Cohort Study

Background

The pattern of glenoid bone loss (GBL) in anterior glenohumeral instability is well described. It was recognized recently that posterior GBL after instability has a posteroinferior pattern.

Purpose/Hypothesis

The purpose of this study was to compare GBL patterns in a matched cohort of patients with anterior versus posterior glenohumeral instability. The hypothesis was that the GBL pattern in posterior instability would be more inferior than the GBL pattern in anterior instability.

Study Design

Cohort study; Level of evidence, 3.

Methods

In this multicenter retrospective study, 28 patients with posterior instability were matched with 28 patients with anterior instability by age, sex and number of instability events. GBL location was defined using a clockface model. Obliquity was defined as the angle between the long axis of the glenoid and a line tangent to the GBL. Superior and inferior GBL were measured as areas and defined relative to the equator. The primary outcome was the 2-dimensional characterization of posterior versus anterior GBL. The secondary outcome was a comparison of the posterior GBL patterns in traumatic and atraumatic instability mechanisms in an expanded cohort of 42 patients.

Results

The mean age of the matched cohorts (n = 56) was 25.2 ± 9.87 years. The median obliquity of GBL was 27.53° (interquartile range [IQR], 18.83°-47.38°) in the posterior cohort and 9.28° (IQR, 6.68°-15.75°) in the anterior cohort (P < .001). The mean superior-to-inferior bone loss ratio was 0.48 ± 0.51 in the posterior cohort and 0.80 ± 0.55 (P = .032) in the anterior cohort. In the expanded posterior instability cohort (n = 42), patients with traumatic injury mechanism (n = 22), had a similar GBL obliquity compared to patients with an atraumatic injury mechanism (n = 20) (mean, 27.73° [95% CI, 20.26°-35.20°] vs 32.20° [95% CI, 21.27°-43.14°], respectively) (P = .49).

Conclusion

Posterior GBL occurred more inferiorly and at an increased obliquity compared with anterior GBL. This pattern is consistent for traumatic and atraumatic posterior GBL. Bone loss along the equator may not be the most reliable predictor of posterior instability, and critical bone loss may be reached more rapidly than a model of loss along the equator may predict.

Accuracy of MR arthrography in the detection of posterior glenoid labral injuries of the shoulder

OBJECTIVE

The purpose of this study is to evaluate the accuracy of MR arthrography in detecting isolated posterior glenoid labral injuries using arthroscopy as the reference standard.

METHODS

MR arthrograms of 97 patients with isolated posterior glenoid labral tears by arthroscopy and those of 96 age and gender-matched controls with intact posterior labra were reviewed by two blinded radiologists for the presence and location of posterior labral abnormalities. The sensitivity and specificity of detection of posterior labral tears were calculated as well as the prevalence of associated pathologies. Medical records were reviewed for demographics, history and direction of shoulder instability, and prior surgery.

RESULTS

Posterior labral pathology was detected by MR arthrography with sensitivities of 76% and 84% for readers 1 and 2, and a specificity of 88% for both readers. Kappa value for interreader agreement was 0.91. Twenty-two of twenty-three (96%) tears isolated to the posteroinferior quadrant on arthroscopy were correctly identified on MRI. Commonly associated pathologies included paralabral cyst (38%), humeral fracture (7%), and glenoid fracture (2%). Fifteen of ninety-seven (16%) patients with posterior tears on both arthroscopy and MRI had glenoid rim deficiency on imaging versus no patients with intact posterior labra (p < 0.001). Forty of ninety-seven (41%) patients with posterior tears on arthroscopy had a history of posterior instability versus none without posterior tears. There was no significant difference in tear length on MRI between those with a history of instability and those without (p = 0.56).

CONCLUSION

MR arthrography is accurate in detecting posterior glenoid labroligamentous injuries.

Reverse total shoulder arthroplasty in patients with type B2, B3, and type C glenoids: comparable clinical outcome to patients without compromised glenoid bone stock-a matched pair analysis

BACKGROUND

Primarily posterior bone deficient (dysplastic) (Walch type C) or secondarily eroded (Walch type B2 or B3) glenoids represent a surgical challenge for shoulder arthroplasty. Due to the posteriorly static decentered head, reverse total shoulder arthroplasty (RTSA) is often considered as the treatment of choice. The purpose of this study is to report the clinical and radiographic outcomes, complications and reoperations of RTSA for posteriorly deficient glenoids.

MATERIALS AND METHODS

All patients who underwent RTSA for osteoarthritis secondary to underlying glenoid deficiency (Walch type B2, B3 and C) between 2005 and 2018 (study group), were identified from our institutional shoulder arthroplasty database and gender- and age-matched to a cohort of patients with normal glenoid bone stock (control group). Longitudinal pre- and postoperative clinical [Constant-Murley (CS) score, Subjective Shoulder Value (SSV)] and radiographic outcomes were assessed.

RESULTS

We included 188 patients (94 in each group). The median follow-up was 43 ± 26 (24-144) months in the study group and 59 ± 32 (24-124) months in the control group. The glenoid deficiency was addressed by using glenoid bone reconstruction. The surgical site complication and revision rate of RTSA in patients with bony deficient glenoids were 17% and 7%. Although glenoid loosening was slightly higher in the study group (5 vs. 2), overall no significant differences were found between the study and control groups in satisfaction scores, preoperative and postoperative absolute and relative Constant scores, complication and revision rates, respectively.

CONCLUSION

Reverse total shoulder arthroplasty (RTSA) seems to be a valuable treatment option for patients with primary (dysplasia) or secondary (wear) posterior glenoid deficiency. Although severe glenoid bone loss seems to be a risk factor for glenoid component failure, the overall complication and revision rates as well as clinical and radiographic outcome are comparable to RTSA in patients without compromised glenoid bone stock.

LEVEL OF EVIDENCE

Level III: case-control study.

Arthroscopic Posterior Articular Coverage and Shift (PACS) Procedure for Treatment of Preosteoarthritic Constitutional Static Posterior Shoulder Instability (Type C1)

BACKGROUND

Different joint-preserving techniques for treatment of preosteoarthritic, constitutional static (type C1) posterior shoulder instability (PSI) have been proposed, including posterior glenoid open wedge osteotomy and bone graft augmentation. However, the techniques are demanding, the reported complication and reoperation rates are high, and posterior decentering cannot reliably be reversed.

PURPOSE

To assess the clinical and radiological longitudinal outcomes of patients with type C1 PSI after arthroscopic posterior articular coverage and shift (PACS) surgery.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

We performed a retrospective analysis of a prospective database with longitudinal follow-up including 14 shoulders in 13 patients who underwent an arthroscopic PACS procedure for symptomatic preosteoarthritic constitutional static posterior instability (type C1) with previous failed nonoperative treatment. Patients were clinically evaluated before surgery and at 3, 6, 12, and 24 months postoperatively in terms of satisfaction and pain levels as well as standardized physical examination, Subjective Shoulder Value (SSV), Western Ontario Shoulder Instability Index (WOSI) score, Constant score, and Rowe score. Preoperative, postoperative, and follow-up magnetic resonance imaging scans were obtained in all patients. A paired 2-sample t test was used to compare changes in continuous variable parameters over time. Correlation analyses were performed using the Pearson correlation coefficient.

RESULTS

All outcome scores and the pain level improved significantly from preoperatively to postoperatively, and the improvement was sustained over the follow-up period of 2 years (pain level, 6.4 preoperatively vs 3.3 at 2 years, P < .001; SSV, 40 vs 70, P = .001; WOSI, 33 vs 56, P = .001; Constant, 70 vs 79, P = .049; Rowe, 52 vs 76, P < .001). The mean glenohumeral and scapulohumeral subluxation indices were significantly lower in the early postoperative period compared with preoperative measurements (glenohumeral, 52% ± 6% vs 58% ± 10%, P = .02; scapulohumeral, 70% ± 8%; vs 77% ± 9%, P = .002, respectively); however, they returned to baseline values at follow-up (57% ± 7% vs 58% ± 10%, P = .7; 75% ± 6% vs 77% ± 9%, P = .4, respectively). A high scapulohumeral subluxation index, excessive glenoid retroversion, and increased posterior positioning of the humeral head in relation to scapular blade axis and older age were correlated with worse clinical outcomes.

CONCLUSION

Over the follow-up period of 2 years, the PACS procedure significantly improved outcome scores in patients who had preosteoarthritic constitutional static posterior shoulder instability, especially in younger patients with less severe glenoid retroversion and posterior decentering of the humeral head. However, similar to other techniques, the PACS procedure needs to be considered a symptomatic therapy that does not reverse the underlying cause or stop the progressive pathology.

Imaging Posterior Instability of the Shoulder

Posterior instability of the shoulder is much less common than anterior instability with a clinical presentation that is often less obvious, making the diagnosis more challenging and more easily missed. We describe the imaging findings of posterior instability so the radiologist can make the diagnosis and provide a detailed description, enabling the surgeon to make more informed decisions regarding management and surgery.

Prospective Evaluation of Posterior Glenoid Bone Loss After First-time and Recurrent Posterior Glenohumeral Instability Events

BACKGROUND

Although posterior glenohumeral instability is becoming an increasingly recognized cause of shoulder pain, the role of posterior glenoid bone loss on outcomes remains incompletely understood.

PURPOSES

To prospectively determine the amount of bone loss associated with posterior instability events and to determine predisposing factors based on preinstability imaging.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A total of 1428 shoulders were evaluated prospectively for ≥4 years. At baseline, a subjective history of shoulder instability was ascertained for each patient, and bilateral noncontrast magnetic resonance imaging (MRI) scans of the shoulders were obtained regardless of any reported history of shoulder instability. The cohort was prospectively followed during the study period, and those who were diagnosed with posterior glenohumeral instability were identified. Postinjury MRI scans were obtained and compared with the screening MRI scans. Glenoid version, perfect-circle-based bone loss was measured for each patient's pre- and postinjury MRI scans using previously described methods.

RESULTS

Of the 1428 shoulders that were prospectively followed, 10 shoulders sustained a first-time posterior instability event and 3 shoulders sustained a recurrent posterior instability event. At baseline, 11 of 13 shoulders had some amount of glenoid dysplasia and/or bone loss. The change in glenoid bone loss was 5.4% along the axis of greatest loss (95% CI, 3.8%-7.0%; P = .009), 4.4% at the glenoid equator (95% CI, 2.7%-6.2%; P = .016), and 4.2% of total glenoid area (95% CI, 2.9%-5.3%; P = .002). Recurrent glenoid instability was associated with a greater amount of absolute bone loss along the axis of greatest loss compared with first-time instability (recurrent: 16.8% ± 1.1%; 95% CI, 14.6%-18.9%; first-time: 10.0% ± 1.5%; 95% CI, 7.0%-13.0%; P = .005). Baseline glenoid retroversion ≥10° was associated with a significantly greater percentage of bone loss along the axis of greatest loss (≥10° of retroversion: 13.5% ± 2.0%; 95% CI, 9.6%-17.4%; <10° of retroversion: 8.5% ± 0.8%; 95% CI, 7.0%-10.0%; P = .045).

CONCLUSIONS

Posterior glenohumeral instability events were associated with glenoid bone loss of 5%. The amount of glenoid bone loss after a recurrent posterior glenohumeral instability event was greater than that after first-time instability. Glenoid retroversion ≥10° was associated with a greater amount of posterior glenoid bone loss after a posterior instability event.

Comprehensive management of posterior shoulder instability: diagnosis, indications, and technique for arthroscopic bone block augmentation

Recurrent posterior glenohumeral instability is an entity that demands a high clinical suspicion and a detailed study for a correct approach and treatment. Its classification must consider its biomechanics, whether it is due to functional muscular imbalance or to structural changes, volition, and intentionality.

Due to its varied clinical presentations and different structural alterations, ranging from capsule-labral lesions and bone defects to glenoid dysplasia and retroversion, the different treatment alternatives available have historically had a high incidence of failure.

A detailed radiographic assessment, with both CT and MRI, with a precise assessment of glenoid and humeral bone defects and of glenoid morphology, is mandatory.

Physiotherapy focused on periscapular muscle reeducation and external rotator strengthening is always the first line of treatment. When conservative treatment fails, surgical treatment must be guided by the structural lesions present, ranging from soft tissue repair to posterior bone block techniques to restore or increase the articular surface.

Bone block procedures are indicated in cases of recurrent posterior instability after the failure of conservative treatment or soft tissue techniques, as well as symptomatic demonstrable nonintentional instability, presence of a posterior glenoid defect >10%, increased glenoid retroversion between 10 and 25°, and posterior rim dysplasia. Bone block fixation techniques that avoid screws and metal allow for satisfactory initial clinical results in a safe and reproducible way.

An algorithm for the approach and treatment of recurrent posterior glenohumeral instability is presented, as well as the author’s preferred surgical technique for arthroscopic posterior bone block.

Glenoid Version Assessment When the CT Field of View Does Not Permit the Friedman Method: The Robertson Method

Background:

To improve spatial resolution, current clinical shoulder cross-sectional imaging studies reduce the field of view of the shoulder, excluding the medial scapula border and preventing glenoid version measurement according to the Friedman method.

Purpose:

To evaluate a method to accurately and reliably measure glenoid version on cross-sectional shoulder images when the medial scapula border is not included in the field of view, and to establish measurements equivalent to the Friedman method.

Study Design:

Controlled laboratory study.

Methods:

Sixty-five scapulae underwent computed tomography (CT) scanning with an optimal shoulder CT-positioning protocol. Glenoid version was measured on CT images of the full scapula using the Friedman method. We developed a measurement method (named the Robertson method) based on the glenoid vault version from partial scapula images, with a correction angle subtracted from the articular-surface-glenoid vault measurement. Comparison with the Friedman method defined the accuracy of the Robertson method. Three observers tested inter- and intraobserver reliability of the Robertson method. Accuracy was statistically evaluated with t tests and reliability with the intraclass correlation coefficient (ICC).

Results:

The statistical distribution of glenoid version was similar to published data,–0.5° ± 3° [mean ± SD]. The initial measurement using the Robertson method resulted in a more retroverted angle compared with the Friedman method, and a correction angle of 7° was then applied. After this adjustment, the difference between the 2 methods was nonsignificant (0.1° ± 4°; P > .65). Reliability of the Robertson method was excellent, as the interrater ICC was 0.77, the standard error of measurement (SEM) was 1.1° with P < .001. The intrarater ICC ranged between 0.84 and 0.92, the SEM ranged between 0.9° and 1.2° with P < .01.

Conclusion:

A validated glenoid version measurement method is now available for current clinical shoulder CT protocols that reliably create Friedman-equivalent values.

Clinical Relevance:

Friedman-equivalent values may be made from common clinical CTs of the shoulder and compared with prior and future Friedman measurements of the scapula.

Long-term results after posterior open glenoid wedge osteotomy for posterior shoulder instability associated with excessive glenoid retroversion

BACKGROUND

Treatment of posterior shoulder instability (PSI) associated with excessive glenoid retroversion is a rare, challenging problem in shoulder surgery. One proposed technique is posterior open wedge glenoid osteotomy to correct excessive glenoid retroversion as described by Scott. However, this operation is rarely performed, and limited long-term outcomes using this approach are available. The goal of this study was to analyze the long-term outcomes of posterior open wedge glenoid osteotomy for PSI associated with excessive glenoid retroversion.

METHODS

Six consecutive patients (7 shoulders) with a mean age of 24 years (range 19-34) were treated with posterior open wedge glenoid osteotomy for PSI associated with a glenoid retroversion greater than 15° and followed up clinically and radiographically at a mean age of 15 years (range 10-19).

RESULTS

Recurrent, symptomatic PSI was observed in 6 of 7 shoulders (86%). One necessitated revision with a posterior (iliac crest) bone block procedure and was rated as a failure and excluded from functional analysis. One patient rated his result as excellent, 3 as good, 1 as fair, and 1 as unsatisfactory. Mean relative Constant Score (CS%) was unchanged from preoperation to final follow-up (CS% = 72%) and pain did not significantly decrease (Constant Score = 7-10 points; P = .969). The mean Subjective Shoulder Value (SSV) improved postoperatively, but with 6 patients the improvement did not reach statistical significance (SSV = 42%-67%, P = .053) and the total Western Ontario Shoulder Instability Index averaged 30% at the final follow-up. Mean glenoid retroversion of all 7 shoulders was corrected from 20° (range 16°-26°) to 3° (range -3° to +8°) (P = .018). In the 5 shoulders with preoperative static posterior subluxation of the humeral head, the humeral head was not recentered. All 7 shoulders showed progression of glenoid arthritic changes.

CONCLUSIONS

Posterior open wedge glenoid osteotomy for PSI associated with excessive glenoid retroversion neither reliably restored shoulder stability nor recentered the joint or prevent progression of osteoarthritis. Alternative treatments for PSI associated with excessive glenoid retroversion have to be developed and evaluated.

Posterior Open-wedge Osteotomy and Glenoid Concavity Reconstruction Using an Implant-free, J-shaped Iliac Crest Bone Graft in Atraumatic Posterior Instability with Pathologic Glenoid Retroversion and Dysplasia: A Preliminary Report

BACKGROUND

Atraumatic posterior shoulder instability in patients with pathologic glenoid retroversion and dysplasia is an unsolved problem in shoulder surgery.

QUESTIONS/PURPOSES

In a preliminary study of a small group of patients with atraumatic posterior shoulder instability associated with glenoid retroversion ≥ 15° and glenoid dysplasia who underwent posterior open-wedge osteotomy and glenoid concavity reconstruction using an implant-free, J-shaped iliac crest bone graft, we asked: (1) What proportion of the patients had persistent apprehension? (2) What were the improvements in patient-reported shoulder scores? (3) What were the radiographic findings at short-term follow-up?

METHODS

Between 2016 and 2018, we treated seven patients for atraumatic posterior shoulder instability. We performed this intervention when posterior shoulder instability symptoms were unresponsive to physiotherapy for at least 6 months and when it was associated with glenoid retroversion ≥ 15° and dysplasia of the posteroinferior glenoid. All seven patients had a follow-up examination at a minimum of 2 years. The median (range) age at surgery was 27 years (16 to 45) and the median follow-up was 2.3 years (2 to 3). Apprehension was assessed by a positive posterior apprehension and/or posterior jerk test. Patient-reported shoulder scores were obtained and included the subjective shoulder value, obtained by chart review (and scored with 100% representing a normal shoulder; minimum clinically important difference [MCID] 12%), and the Constant pain scale score (with 15 points representing no pain; MCID 1.5 points). Radiographic measurements included glenohumeral arthropathy and posterior humeral head subluxation, bone graft union, correction of glenoid retroversion and glenoid concavity depth, as well as augmentation of glenoid surface area. All endpoints were assessed by individuals not involved in patient care.

RESULTS

In four of seven patients, posterior apprehension was positive, but none reported resubluxation. The preoperative subjective shoulder value (median [range] 40% [30% to 80%]) and Constant pain scale score (median 7 points [3 to 13]) were improved at latest follow-up (median subjective shoulder value 90% [70% to 100%]; p = 0.02; median Constant pain scale score 15 points [10 to 15]; p = 0.03). Posterior glenoid cartilage erosion was present in four patients (all four had Walch Type B1 glenoids) preoperatively and showed no progression until the final follow-up examination. The median (range) humeral head subluxation index decreased from 69% (54% to 85%) preoperatively to 55% (46% to 67%) postoperatively (p = 0.02), and in two of four patients with preoperative humeral head subluxation (> 65% subluxation), it was reversed to a centered humeral head. CT images showed union in all implant-free, J-shaped iliac crest bone grafts. The median preoperative retroversion was corrected from 16° (15° to 25°) to 0° postoperatively (-5° to 6°; p = 0.02), the median glenoid concavity depth was reconstructed from 0.3 mm (-0.7 to 1.6) preoperatively to 1.2 mm (1.1 to 3.1) postoperatively (p = 0.02), and the median preoperative glenoid surface area was increased by 20% (p = 0.02). No intraoperative or postoperative complications were recorded, and no reoperation was performed or is planned.

CONCLUSION

In this small, retrospective series of patients treated by experienced shoulder surgeons, a posterior J-bone graft procedure was able to reconstruct posterior glenoid morphology, correct glenoid retroversion, and improve posterior shoulder instability associated with pathologic glenoid retroversion and dysplasia, although four of seven patients had persistent posterior apprehension. Although no patients in this small series experienced complications, the size and complexity of this procedure make it likely that as more patients have it, some will develop complications; future studies will need to characterize the frequency and severity of those complications, and we recommend that this procedure be done only by experienced shoulder surgeons. The early results in these seven patients justify further study of this procedure for the proposed indication, but longer term follow-up is necessary to continue to assess whether it is advantageous to combine the reconstruction of posterior glenoid concavity with correction of pathological glenoid retroversion and increasing glenoid surface compared with traditional surgical techniques such as the posterior opening wedge osteotomy or simple posterior bone block procedures.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Risk Factors for Failure of Nonoperative Treatment of Posterior Shoulder Labral Tears on Magnetic Resonance Imaging

INTRODUCTION

There are no reports in the literature describing risk factors for failure of nonoperative treatment of patients with posterior labral tears on magnetic resonance imaging (MRI). The purpose of this study is to identify risk factors for failure of nonoperative treatment in patients with an isolated posterior glenoid labral tear identified on MRI only. Patients with posterior labral tears on MRI who fail to improve with nonoperative treatment likely share a constellation of clinical history, physical exam, and radiographic findings.

METHODS

One hundred and fifty-nine active duty military service members under the age of 40 with a posterior labral tear seen on MRI and who were clinically evaluated by a musculoskeletal trained physician were identified. We retrospectively evaluated their records ensuring a minimum of 2 years follow-up after MRI to identify surgical intervention for the posterior labral tear during this time period. Patients were stratified into two groups, those treated with any combination of nonoperative modalities and those treated with posterior labral repair surgery during the 2 years after the MRI. The electronic medical records were reviewed for clinical presentation and physical exam results. We measured multiple radiographic parameters, including glenoid version, size of the tear, and bone loss on MRI. Qualitative and quantitative data were compared between groups using Fisher's exact test and Student's t-test, respectively. This study was conducted under institutional review board approval.

RESULTS

Of the 157 patients' shoulders in our study, 52% (n = 82) of patients with posterior labral tears underwent nonoperative treatment while 48% (n = 75) underwent surgery. The significant risk factors associated with surgery were a history of a specific injury, primary presenting complaint of instability, patient reported history of subluxation, inability to trust their shoulder with overhead activity, decreased strength with weight lifting, positive posterior load/shift exam, positive anterior apprehension, increased osseous glenoid retroversion, increased humeral head subluxation ratio, and anterior labral height (P < 0.05). Patients with a chief complaint of pain were much more likely to succeed with nonoperative treatment while those with instability underwent surgery more often. Ten (12.5%) of the surgical procedures included an anterior and posterior labral repair/stabilization procedure.

CONCLUSION

Patients with an MRI confirmed posterior labral tear, which present with subjective complaints and physical exam maneuvers consistent with instability, appear less likely to be treated nonoperatively. Increased glenoid retroversion and posterior humeral head subluxation may also predispose patients toward surgical treatment. Additionally, posterior labral tears may extend into the anterior labrum more frequently than is recognized on MRI.

Glenoid Orientation and Profile in Atraumatic or Microtraumatic Posterior Shoulder Instability: Morphological Analysis Using Computed Tomography Arthrogram

Background:

Posterior shoulder instability (PSI) is a relatively uncommon condition that occurs in about 10% of patients with shoulder instability. PSI is usually associated with dislocations due to acute trauma and multidirectional instability, but it can also occur with or without recognizable recurrent microtrauma. The infrequency of atraumatic or microtraumatic PSI and the lack of a full understanding of the pathoanatomy and the knowledge of management can lead to misdiagnosis or delayed diagnosis.

Purpose:

To evaluate the morphologic factors of the glenoid that are associated with atraumatic or microtraumatic PSI.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Enrolled in this study were patients who underwent arthroscopic posterior labral repair between January 2013 and March 2017 and were diagnosed with posterior glenohumeral instability by means of preoperative computed tomography arthrography (CTA) (n = 39; PSI group). These patients did not have any significant dislocation or subluxation episodes. The morphologic factors of the glenoid as revealed using CTA were compared with the CTA images from a sex-matched control group (n = 117) of patients without PSI who had been diagnosed with adhesive capsulitis in an outpatient clinic. The glenoid version and shape were evaluated between the 2 groups using the CTA findings, and the degree of centricity of the humeral head to the glenoid was assessed in the PSI group. Multivariate logistic regression analysis was performed to identify factors associated with PSI.

Results:

The results of the multivariate logistic regression analysis indicated no statistically significant difference between the PSI and control groups regarding glenoid version or a flat-shaped glenoid. However, statistically significant between-group differences were found regarding convex glenoid shape, with an odds ratio of 5.39 (95% CI, 1.31-23.35; P = .0207). The proportion of eccentricity was significantly higher in the PSI group (21/39; 54%) versus the control group (47/117; 40%) (P = .031).

Conclusion:

The presence of convex glenoid shape was significantly associated with atraumatic or microtraumatic PSI. Humeral head eccentricity accounted for a high percentage of convex glenoid shape. However, there was no significant correlation between PSI and glenoid retroversion.

[Double internal fixations of clavicle and scapula and intraoperative reduction of glenopolar angle for treatment of floating shoulder injuries]

Objective

To investigate the effectiveness of double internal fixations of clavicle and scapula and intraoperative reduction of glenopolar angle in the treatment of floating shoulder injuries.

Methods

Between January 2010 and June 2019, 13 patients with floating shoulder injury were treated with double internal fixation of clavicle and scapula and intraoperative reduction of glenopolar angle. There were 11 males and 2 females with an average age of 48 years (range, 25-65 years). The causes of injury included falling from height in 2 cases, traffic accident injury in 3 cases, heavy object injury in 2 cases, and other injuries in 6 cases. There were 2 cases of Ⅰ-B-3 type, 1 case of Ⅰ-C-2 type, 1 case of Ⅰ-C-3 type, 3 cases of Ⅱ-B-2 type, 1 case of Ⅱ-B-3 type, 1 case of Ⅱ-B-4 type, 2 cases of Ⅱ-C-2 type, 1 case of Ⅱ-C-4 type, and 1 case of Ⅱ-D-3 type according to the classification of floating shoulder injury. All patients had unilateral clavicle fracture with scapular neck fracture, 1-4 superior shoulder suspensory complex (SSSC) injuries. The time from injury to operation was 7-17 days, with an average of 12 days. The glenopolar angle, subacromail space, anteroposterior inclination angle of scapular glenoid, scapular glenoid up and down angle were measured before and after operation; Constant-Murly score and Herscovici score were used to evaluate the recovery of shoulder joint function.

Results

All incisions healed by first intention, and there was no early postoperative complications such as infection. All 13 cases were followed up 12-48 months, with an average of 25.2 months. Both the clavicle and the scapula had bone union, and the average healing time was 6 months and 4 months respectively. There were no complications such as nonunion, shoulder deformity, plate fracture or failure of internal fixation, acromion impingement syndrome, and frozen shoulder. At last follow-up, the glenopolar angle, subacromail space, anteroposterior inclination angle of scapular glenoid, and scapular glenoid up and down angle were all corrected significantly ( P<0.05). The pain, function, activity, muscle strength scores, and total score in Constant-Murly score were significantly improved when compared with preoperative scores ( P<0.05). According to the Herscovici scoring standard, the shoulder joint function was evaluated as excellent in 8 cases, good in 3 cases, and fair in 2 cases. The excellent and good rate was 84.6%.

Conclusion

Double internal fixation of clavicle and scapula to stabilize SSSC and reduct glenopolar angle during operation is an effective method for treating the floating shoulder injury.

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.

A New Method for Measuring Glenoid Version on Standard Magnetic Resonance Imaging

Background

The most effective method and modality for measuring glenoid version for different shoulder conditions is uncertain. Computed tomography (CT) imaging exposes the patient to radiation, and standard magnetic resonance imaging (MRI) does not consistently image the entire scapula. This study investigates the reliability of a new method for assessing glenoid version using routine shoulder MRI.

Methods

MRI images of 20 patients undergoing arthroscopy for shoulder instability were independently assessed by 3 clinicians for osseous and chondrolabral glenoid version. To assess glenoid version, a line was drawn from medial corner of the glenoid body to midpoint of the glenoid face. A line perpendicular to this was the reference against which to measure glenoid version. Measurements were repeated after 3 months to assess intra- and interobserver reliability. Reliability was determined using intraclass correlation coefficients (ICCs).

Results

Interclass correlation coefficients showed at least good reliability for most estimates of intraobserver reliability (ICC ≥ .66) and excellent reliability for most estimates of interobserver reliability (ICC ≥ .84), with the exception of some inferior glenoid measurements where ICC was poor (ICC ≤.41).

Discussion

We propose that this new method of measuring glenoid on standard axial MRI can be used as a simple, practical, and reliable method in shoulder instability patients, which will reduce the requirement for CT in this group.

Difference in glenoid retroversion between two-dimensional axial computed tomography and three-dimensional reconstructed images

Background

The glenoid version of the shoulder joint correlates with the stability of the glenohumeral joint and the clinical results of total shoulder arthroplasty. We sought to analyze and compare the glenoid version measured by traditional axial two-dimensional (2D) computed tomography (CT) and three-dimensional (3D) reconstructed images at different levels.

Methods

A total of 30 cases, including 15 male and 15 female patients, who underwent 3D shoulder CT imaging was randomly selected and matched by sex consecutively at one hospital. The angular difference between the scapular body axis and 2D CT slice axis was measured. The glenoid version was assessed at three levels (midpoint, upper one-third, and center of the lower circle of the glenoid) using Friedman’s method in the axial plane with 2D CT images and at the same level of three different transverse planes using a 3D reconstructed image.

Results

The mean difference between the scapular body axis on the 3D reconstructed image and the 2D CT slice axis was 38.4°. At the level of the midpoint of the glenoid, the measurements were 1.7°±4.9° on the 2D CT images and −1.8°±4.1° in the 3D reconstructed image. At the level of the center of the lower circle, the measurements were 2.7°±5.2° on the 2D CT images and −0.5°±4.8° in the 3D reconstructed image. A statistically significant difference was found between the 2D CT and 3D reconstructed images at all three levels.

Conclusions

The glenoid version is measured differently between axial 2D CT and 3D reconstructed images at three levels. Use of 3D reconstructed imaging can provide a more accurate glenoid version profile relative to 2D CT. The glenoid version is measured differently at different levels.

Posterior Shoulder Instability: What to Look for

Posterior shoulder instability is often hard to diagnose with clinical examination. Patients generally present with vague pain, weakness, and/or joint clicking but less frequently complaining of frank sensation of instability. Imaging examinations, especially MR imaging and magnetic resonance arthrography, have a pivotal role in the identification and management of this condition. This review describes the pathologic micro/macrotraumatic magnetic resonance features of posterior shoulder instability as well as the underlying joint abnormalities predisposing to this condition, including developmental anomalies of the glenoid fossa, humeral head, posterior labrum, and capsular and ligamentous structures.

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°.

Location of the Glenoid Defect in Shoulders With Recurrent Posterior Glenohumeral Instability

BACKGROUND

Posterior glenoid bone deficiency is an increasingly recognized entity in the setting of recurrent posterior shoulder instability; however, little is known about the subject. Due to the paucity of literature on posterior bone loss, historical comparisons with anterior bone loss may not be fully accurate.

PURPOSE

To systematically describe the morphology of posterior bone defects in the setting of recurrent posterior shoulder instability based on several quantitative parameters, including the mean location, orientation, and extent of bone loss on a clockface model, as well as the angle of the defect relative to the long axis of the glenoid.

STUDY DESIGN

Cross-sectional study; Level of evidence, 4.

METHODS

Three-dimensional reconstructed computed tomography scans of serially collected patients with a history of recurrent posterior shoulder instability were evaluated by 3 separate reviewers. The posterior glenoid bone defect was characterized using the following measures: (1) the mean lesion location and orientation based on a clockface model with 6 o'clock denoted as inferior and 9 o'clock as directly posterior for all patients; (2) the total extent of the posterior bone defect based on the clockface; and (3) the average angle of the bone loss relative to the long axis of the glenoid.

RESULTS

A total of 70 male patients and 1 female patient with a mean age of 29.3 years (range, 24.4-35.1 years) were included in the analysis. The mean clockface location of the posterior glenoid defect originated at 6:44 (range, 4:16-8:12) and extended to a mean of 9:28 (range, 7:02-10:38). The mean extent of the posterior glenoid defect was 2:43 (range, 1:08-4:50), which corresponds to a mean total bone loss arc of 81.5° (range, 34.2°-144.9°), nearly 1 quadrant of the glenoid. Posterior bone loss occurred in a posteroinferior direction at a mean angle of 30.7° (range, 8.0°-80.0°) relative to the long axis of the glenoid.

CONCLUSION

Posterior bone defects in the setting of posterior shoulder instability most commonly occur in the posteroinferior quadrant of the glenoid and extend on average from 6:44 to 9:28 (81.5° total degrees of arc) on a clockface model. Posterior bone loss occurs at a mean of 30° off the long axis of the glenoid in a posteroinferior direction, which is historically different from anterior bone loss, which occurs parallel to the long axis of the glenoid. This study serves to highlight the location and orientation of bone loss that one can expect in a patient with recurrent posterior shoulder instability, although additional work is needed to assess why this develops.

Is the version angle of the glenoid different in bone and cartilage? An MRI study

Background/aim

To determine whether or not there is a difference between the version of the bone and cartilage surfaces of the glenoid. Axial magnetic resonance imaging (MRI) slices were examined in order to evaluate the measurements taken based on both the cartilage and bone joint surfaces.

Materials and methods

A retrospective evaluation was made of the MRI scans of 182 patients. All of the reviewers independently measured the glenoid version angles of all of the patients from 1–182. The process was then repeated, with each reviewer taking second measurements of the angles from 1–182. Pearson correlation coefficient analysis was applied to evaluate the interaction and relationships between the measurements taken from the bone and cartilage. The intra- and interobserver interclass correlation coefficients (ICCs) were assessed. Analysis of variance was applied to determine any interobserver significant differences.

Results

The mean glenoid version was determined as –3.58 ± 4.08° in the bone-based measurements and –5.81 ± 4.30° in the cartilage-based measurements. The cartilage- and bone-based measurements were found to have inter- and intraobserver reliability. A statistically significant difference was observed between the mean cartilage-based version and the mean bone-based version. Changes in the cartilage- and bone-based measurements were correlated; however, this change was not linear.

Conclusion

The cartilage-based version showed a significant difference from the bone- based version. Therefore, in the preoperative planning and evaluation of glenoid-based pathologies, it would be more appropriate to evaluate both the bone and cartilage surface on MRI.

Characterization of Posterior Glenoid Bone Loss Morphology in Patients With Posterior Shoulder Instability

PURPOSE

To systemically describe posterior bone defects in the setting of posterior shoulder instability based on several parameters, including surface area, slope and version, defect height from the base of the glenoid, and extent of bone loss at equal intervals along the long axis of the fossa.

METHODS

A total of 40 young, active individuals with recurrent posterior shoulder instability and a bony injury confirmed on either computed tomography (n = 18; mean age, 26.3 ± 4.0 years) or magnetic resonance imaging (n = 22; mean age, 20.0 ± 4.9 years) were identified. The posterior glenoid bone defect was characterized using the following measures: (1) percentage of bone loss, (2) glenoid vault version, (3) slope of the posterior defect relative to the glenoid surface, (4) superior-inferior length of the defect, and (5) anterior-posterior width of the defect at 5 intervals along the glenoid fossa.

RESULTS

The mean age of the 40 patients was 22.9 ± 5.5 years (range, 14.9-35.5 years). The mean surface area of glenoid bone loss was 9.7% ± 4.7%. Glenoid version measured at 5 equal intervals along the inferior two-thirds of the glenoid was 12.8° ± 4.9°, 11.9° ± 5.0°, 10.1° ± 6.3°, 10.5° ± 6.5°, and 8.7° ± 7.2° from superior to inferior. The mean slope of the posterior defect relative to the glenoid fossa was 26.8° ± 11.5°. The mean superior-inferior height of the bony defect was 21.9 ± 0.4 mm. The anterior-posterior sloped width of the defect at 5 equal intervals along the glenoid fossa was 0.9 ± 1.5 mm, 2.8 ± 2.4 mm, 4.0 ± 1.7 mm, 4.0 ± 2.1 mm, and 2.9 ± 2.6 mm from superior to inferior. Low-grade (<10%) bone loss was diagnosed in most shoulders (23 of 40 evaluated), whereas 15 had moderate bone loss (10% to <20%) and 2 had high-grade bone loss (≥20%).

CONCLUSIONS

Posterior glenoid bone loss is characterized by a loss of posterior bony concavity, increased slope from anterior to posterior, and increased posterior version. The most anterior-posterior sloped width was quantified at the third and fourth intervals of 5 equal intervals from superior to inferior. This study highlights that patients with posterior instability have bone loss that is sloped relative to the glenoid fossa and suggests that management must be appropriately tailored given the distinctiveness of posterior bone loss.

LEVEL OF EVIDENCE

Level IV, case series.

Posterior Acromial Morphology Is Significantly Associated with Posterior Shoulder Instability

BACKGROUND

The purpose of this paper was to determine whether acromial morphology influences anteroposterior shoulder stability. We hypothesized that a more horizontal and higher position of the acromion in the sagittal plane would be associated with posterior instability.

METHODS

In this retrospective study, patients with unidirectional posterior instability were age and sex-matched to a cohort of patients with unidirectional anterior instability. Both cohorts were compared with a control group of patients with no instability and no degenerative glenohumeral (rotator cuff and/or joint surface) or acromial changes. Measurements on radiographs included posterior acromial tilt, anterior and posterior acromial coverage (AAC and PAC), posterior acromial height (PAH), and the critical shoulder angle (CSA).

RESULTS

The number of patients enrolled in each instability group was 41, based on a priori power analysis. The control group consisted of 53 shoulders. Of the measured anatomic factors, PAH showed the most significant association with posterior instability (odds ratio [OR] = 1.8; p < 0.001) in the logistic regression model. PAH was significantly greater in the posterior instability group compared with the anterior instability group (30.9 versus 19.5 mm; p < 0.001). With a cutoff value of PAH of 23 mm, the OR for posterior instability was 39. Shoulders with posterior instability were also significantly different from normal shoulders with regard to PAH (p < 0.001), AAC (p < 0.001), and PAC (p < 0.001) whereas, in the shoulders with anterior instability, all of these values except the AAC (p = 0.011) did not differ from those of normal shoulders.

CONCLUSIONS

Specific acromial morphology is significantly associated with the direction of glenohumeral instability. In shoulders with posterior instability, the acromion is situated higher and is oriented more horizontally in the sagittal plane than in normal shoulders and those with anterior instability; this acromial position may provide less osseous restraint against posterior humeral head translation. A steep "Swiss chalet roof-type" acromion virtually excluded recurrent posterior instability in an albeit relatively small cohort of patients. Additional investigation is needed to determine the relevance of these findings for future treatment.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Increased Glenoid Retroversion Is Associated With Increased Rotator Cuff Strength in the Shoulder

BACKGROUND

The rotator cuff muscles are critical secondary stabilizers in the shoulder. Increased glenoid retroversion and rotator cuff strength have been associated with the risk of posterior shoulder instability; however, the effect of increased glenoid retroversion on rotator cuff strength remains unclear.

PURPOSE/HYPOTHESIS

The purpose was to examine the association between glenoid version and rotator cuff strength in the shoulder in a young and healthy population with no history of shoulder instability. The hypothesis was that increased glenoid retroversion would be associated with increases in rotator cuff muscle strength.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A prospective cohort study was conducted over a 4-year period within a high-risk population to identify the risk factors for shoulder instability. Analyzed participants included 574 freshmen entering a United States service academy. Baseline data collected upon entry into the study included magnetic resonance imaging measurements of glenoid version. Rotator cuff strength was also assessed at baseline using a handheld dynamometer. Internal and external rotation strength were assessed with the glenohumeral joint positioned in neutral and in 45° of abduction. The current study represents an analysis of the baseline data from this cohort.

RESULTS

The mean age, height, and weight of participants was 18.77 ± 0.97 years, 176.81 ± 8.48 cm, and 73.80 ± 12.45 kg, respectively. The mean glenoid version at baseline was 7.79°± 4.85° of retroversion. Univariate linear regression analyses demonstrated that increased glenoid retroversion was associated with increased internal and external rotation strength of the rotator cuff in neutral and 45° of abduction (P < .001). Similar results were observed in multivariable models controlling for important confounding variables.

CONCLUSION

The results of this study demonstrate that as glenoid retroversion increases, internal and external rotation strength of the rotator cuff also increase in a young and healthy athletic population. These compensatory changes may contribute to increased glenohumeral dynamic stability in the presence of worse static stability with increasing retroversion.

Shoulder measurements on MRI: Statistical analysis of patients without and with rotator cuff tears and predictive modeling

This study aims to determine significant differences between various measurements of shoulder structures and relationships in patients with and without rotator cuff tears and identify a subset of these measurements that may merit further investigation. Shoulder MRIs of 120 patients with rotator cuff tears (RCT group) and 80 patients with normal examinations (No RCT group) were retrospectively identified. Numerous measurements of shoulder anatomy and relationships and pathology characterization were performed for each study. The mean and ranges of measurements for each group were identified, and P-values were calculated to assess differences between the two groups. Classification and Regression Tree (CART) identified prediction models for separating the two groups based on these shoulder MRI measurements. Statistically significant differences were observed for 9 of 18 of the shoulder measurements between the two groups (P < 0.05). Using long head of biceps tendon tear, tendinosis, and subacromial-subdeltoid bursal fluid, the prediction model from CART demonstrated 99.5% accuracy in separating the two groups. Subacromial distance, subacromial spur size, and acromioclavicular osteophyte could also separate the two groups with 97.5% accuracy. Other measures less commonly associated with impingement and rotator cuff tears could also be used to separate the two groups with up to 81.5% accuracy. This study introduces new measures and clarifies ranges for existing measurements on shoulder MRI. Abnormalities of some of these measurements may be associated with subacromial impingement, and combinations of these parameters may be useful for separating patients with or without rotator cuff tears. Clin. Anat. 33:173-186, 2020. © 2019 Wiley Periodicals, Inc.

The role of bone in glenohumeral stability

Shoulder stability depends on several factors, either anatomical or functional. Anatomical factors can be further subclassified under soft tissue (shoulder capsule, glenoid rim, glenohumeral ligaments etc) and bony structures (glenoid cavity and humeral head).

Normal glenohumeral stability is maintained through factors mostly pertaining to the scapular side: glenoid version, depth and inclination, along with scapular dynamic positioning, can potentially cause decreased stability depending on the direction of said variables in the different planes. No significant factors in normal humeral anatomy seem to play a tangible role in affecting glenohumeral stability.

When the glenohumeral joint suffers an episode of acute dislocation, either anterior (more frequent) or posterior, bony lesions often develop on both sides: a compression fracture of the humeral head (or Hill–Sachs lesion) and a bone loss of the glenoid rim. Interaction of such lesions can determine ‘re-engagement’ and recurrence.

The concept of ‘glenoid track’ can help quantify an increased risk of recurrence: when the Hill–Sachs lesion engages the anterior glenoid rim, it is defined as ‘off-track’; if it does not, it is an ‘on-track’ lesion. The position of the Hill–Sachs lesion and the percentage of glenoid bone loss are critical factors in determining the likelihood of recurrent instability and in managing treatment.

In terms of posterior glenohumeral instability, the ‘gamma angle concept’ can help ascertain which lesions are prone to recurrence based on the sum of specific angles and millimetres of posterior glenoid bone loss, in a similar fashion to what happens in anterior shoulder instability.

Cite this article: EFORT Open Rev 2018;3:632-640. DOI: 10.1302/2058-5241.3.180028

Etiology of Shoulder Arthritis in Young Patients

The manifestation of glenohumeral arthritis in the young adult is a devastating occurrence that can be difficult to manage. This review details the many underlying etiologies including genetic causes, congenital abnormalities, glenohumeral instability, posttraumatic lesions, postcapsulorraphy arthropathy, osteonecrosis, intraarticular pain pump postoperative use, radiofrequency/thermal capsulorraphy treatments, septic arthritis/infection, and inflammatory arthropathies. Although each of these potential causes have been well-studied, their contributions to the development of glenohumeral arthritis in the young person has not been described extensively.

Characterization of the dysplastic Walch type C glenoid

Aims

The Walch Type C dysplastic glenoid is characterized by excessive retroversion. This anatomical study describes its morphology.

Patients and Methods

A total of 29 shoulders with a dysplastic glenoid were analyzed. CT was used to measure retroversion, inclination, height, width, radius-of-curvature, surface area, depth, subluxation of the humeral head and the Goutallier classification of fatty infiltration. The severity of dysplasia and deficiency of the posterior rim of the glenoid were recorded.

Results

A type C glenoid occurred in 1.8% of shoulders referred to our tertiary centres. The mean retroversion, inclination, height, width, radius-of-curvature, surface area, and depth of the glenoid were 37°, 3°, 46 mm, 30 mm, 37°, 1284 mm3, and 16 mm, respectively. The mean posterior subluxation was 90%. The Goutallier class was < 2 in 25 shoulders (86%). Glenoid dysplasia was mild in four, moderate in 14, and severe in 11 shoulders. The typical appearance of the posterior glenoid rim had a rounded or ‘lazy J’ morphology. The glenoid neck was deficient in 18 shoulders (62%).

Conclusion

A dysplastic Type C glenoid characteristically has a uniconcave retroverted morphology, a deficient posteroinferior rim and scapular neck, and a reduced depth. These findings help to define the unique anatomical variations and may aid the planning of surgery and the development of components for these patients. Cite this article: Bone Joint J 2018;100-B:1074–9.

Posterior Shoulder Instability

Posterior shoulder instability is a relatively uncommon condition, occurring in ∼10% of those with shoulder instability. Because of the rarity of the condition and the lack of knowledge in treatment, it is often misdiagnosed or patients experience a delay in diagnosis. Posterior instability typically affects athletes participating in contact or overhead sports and is usually the result of repetitive microtrauma or blunt force with the shoulder in the provocative position of flexion, adduction, and internal rotation, leading to recurrent subluxation events. Acute traumatic posterior dislocations are rare injuries with an incidence rate of 1.1 per 100,000 person years. This rate is ∼20 times lower than that of anterior shoulder dislocations. Risk factors for recurrent instability are: (1) age below 40 at time of first instability; (2) dislocation during a seizure; (3) a large reverse Hill-Sachs lesion; and (4) glenoid retroversion. A firm understanding of the pathoanatomy, along with pertinent clinical and diagnostic modalities is required to accurately diagnosis and manage this condition.

Glenoid osteotomy for atraumatic posteroinferior shoulder instability associated with glenoid dysplasia

Aims

We report the clinical results of glenoid osteotomy in patients with atraumatic posteroinferior instability associated with glenoid dysplasia.

Patients and Methods

The study reports results in 211 patients (249 shoulders) with atraumatic posteroinferior instability. The patients comprised 63 men and 148 women with a mean age of 20 years. The posteroinferior glenoid surface was elevated by osteotomy at the scapular neck. A body spica was applied to maintain the arm perpendicular to the glenoid for two weeks postoperatively. Clinical results were evaluated using the Rowe score and Japan Shoulder Society Shoulder Instability Score (JSS-SIS); bone union, osteoarthrosis, and articular congruity were examined on plain radiographs.

Results

The Rowe score improved from 36 to 88 points, and the JSS-SIS improved from 47 to 81 points. All shoulders exhibited union without progression of osteoarthritis except one shoulder, which showed osteoarthritic change due to a previous surgery before the glenoid osteotomy. All but three shoulders showed improvement in joint congruency. Eight patients developed disordered scapulohumeral rhythm during arm elevation, and 12 patients required additional open stabilization for anterior instability.

Conclusion

Good results can be expected from glenoid osteotomy in patients with atraumatic posteroinferior instability associated with glenoid dysplasia. Cite this article: Bone Joint J 2018;100-B:331–7.

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.

Arthroscopic treatment of posterior shoulder instability in patients with and without glenoid dysplasia: a comparative outcomes analysis

BACKGROUND

The purpose of this study was to evaluate the influence of glenoid dysplasia on outcomes after isolated arthroscopic posterior labral repair in a young military population.

METHODS

Thirty-seven male patients who underwent arthroscopic posterior labral repair for symptomatic posterior shoulder instability were evaluated at a mean duration of 3.1 years. A comparative analysis was performed for those with glenoid dysplasia and without dysplasia. Additional factors analyzed included military occupational specialty (MOS), preoperative mental health clinical encounters and mental health medication use, and radiographic characteristics (version, posterior humeral head subluxation, and posterior capsular area) on a preoperative standard shoulder magnetic resonance arthrogram. The groups were analyzed with regard to shoulder outcome scores (subjective shoulder value [SSV], American Shoulder and Elbow Surgeons [ASES] rating scale, Western Ontario Shoulder Instability Index [WOSI]), need for revision surgery, and medical separation from the military.

RESULTS

Of 37 patients, 3 (8.1%) underwent revision surgery and 6 (16%) underwent medical separation. Overall outcome assessment demonstrated a mean SSV of 67.9 (range, 25-100) ± 22.1, mean ASES of 65.6 (range, 15-100) ±  22, and mean WOSI of 822.6 (range, 5-1854) ± 538. There were no significant differences in clinical outcome scores between the glenoid dysplasia and no dysplasia groups (SSV, P = .55; ASES, P = .57; WOSI, P = .56). MOS (P = .02) and a history of mental health encounters (P = .04) were significantly associated with diminished outcomes.

CONCLUSIONS

The presence or absence of glenoid dysplasia did not influence the outcome after arthroscopic posterior labral repair in a young military population. However, a history of mental health clinical encounters and an infantry MOS were significantly associated with poorer clinical outcomes.

[Diagnostics and treatment of posterior shoulder instability]

Posterior shoulder instability has a markedly lower incidence than anterior shoulder instability. It has a wide spectrum of clinical symptom manifestations and the overwhelming number of patients lack a traumatic primary dislocation. In addition to a detailed medical history, a specific clinical examination with the help of standardized provocation tests is essential for the diagnostics. For the detection of structural posterior capsule and labral lesions in cases of chronic courses, magnetic resonance imaging (MRI) should be used with an intra-articular contrast agent. Relevant bony defects of the humeral head (reverse Sachs-Hill lesion) are frequent, whereas critical posterior defects of glenoid cavity are relatively rare. Both lesions should be quantified using 3D computed tomography. The choice of therapeutic procedure should be based on the underlying pathology of the defect. Conservative therapy is useful in patients with scapular dyskinesis, voluntary dislocation and pathological muscle patterning. In isolated soft tissue pathologies, arthroscopic labrum fixation and capsule plication are the standard treatment. In the case of insufficient soft tissue relations or critical posterior glenoid defects, bony stabilization of the glenoid using an iliac crest bone graft is the recommended therapy.

The Posterior Unstable Shoulder: Natural History, Clinical Evaluation and Imaging

Background:

There is a low incidence of posterior instability which is present in only 2% to 10% of all unstable shoulders. The posterior instable shoulder includes different manifestations like fixed dislocation, recurrent subluxation or dislocation.

Methods:

Research and online content related to posterior instability is reviewed. Natural history, clinical evaluation and imaging are described.

Results:

An awareness of the disorder, together with a thoughtful evaluation, beginning with the clinical history, usually leads to proper diagnosis. An appropriate physical exam, taking in account hyperlaxity and specific tests for posterior instability should be done.

Conclusion:

Posterior shoulder instability is an uncommon condition and is challenging to diagnose. There is not a single injury that is responsible for all cases of recurrent shoulder dislocation or subluxation, and the presence of soft tissue lesions or bone alterations should be evaluated, with the use of adequate simple radiology and multiplanar imaging.

Critical Findings on Magnetic Resonance Arthrograms in Posterior Shoulder Instability Compared With an Age-Matched Controlled Cohort

BACKGROUND

Posterior shoulder instability is less common and potentially more difficult to diagnose clinically and radiographically compared with anterior shoulder instability. Radiographic findings including posterior labral tears, increased retroversion, presence of glenoid dysplasia, and increased capsular area are associated with symptomatic recurrent posterior shoulder instability.

PURPOSE

This study aimed to determine the prevalence and severity of associated radiographic parameters found on magnetic resonance arthrograms (MRAs) in patients with arthroscopically confirmed isolated posterior labral tears and symptomatic recurrent posterior shoulder instability, compared with an age-matched cohort of patients without posterior instability or labral injury confirmed with shoulder arthroscopy.

STUDY DESIGN

Cross-sectional study, Level of evidence, 3.

METHODS

Patients who received a preoperative standard shoulder MRA at an academic institution over a 5-year period and had symptomatic posterior instability and received a repair of an arthroscopically confirmed posterior labral tear (n = 63) were identified. These patients were compared with an age-matched control group of patients without posterior instability (n = 49) who underwent an isolated arthroscopic distal clavicle resection that included an arthroscopic glenohumeral joint evaluation. Glenoid version, posterior humeral head subluxation, glenoid dysplasia, and linear and capsular area measurements were evaluated between the 2 groups. Interobserver reliability for continuous and categorical variables was assessed for all measurements.

RESULTS

Multivariate logistic regression revealed that the presence of increased glenoid retroversion (P = .0018), glenoid dysplasia (P = .03), and increased axial posterior capsular cross-sectional area (P = .05) were significantly associated with posterior labral tears and symptomatic posterior shoulder instability compared with the age-matched control group. Posterior humeral head subluxation was found to be a statistically significant variable with univariate analysis (P = .001) for posterior shoulder instability but not with multivariate logistic regression (P = .53). Interobserver reliability was good to very good for all measurements (intraclass correlation coefficient [ICC] = 0.74-0.85; κ = 0.64) but was moderate for total capsular area and sagittal capsular area measurements (ICC = 0.43-0.56).

CONCLUSION

The presence of increased glenoid retroversion, glenoid dysplasia, and increased posterior capsular area on MRA are significantly associated with posterior labral tears and symptomatic posterior shoulder instability. Identification of these critical radiographic variables on magnetic resonance arthrography assists in the accurate diagnosis and management of clinically significant posterior shoulder instability.

The Role of CT Arthrography in Shoulder Instability

Computerized Tomography (CT) and CT arthrography are useful tools in evaluating both the osseous structures and the soft tissues in patients with shoulder instability. A variety of osseous injuries can be accurately depicted, such as Hill-Sachs lesions, glenoid rim fractures, or glenoid bone loss. CT arthrography further allows precise evaluations of labral and chondral defects. Further, CT is a simple modality for performing anatomical measurements in the shoulder such as glenoid version or for the assessment of osseous deficiencies of the posterior glenoid. Finally, CT is also be beneficial for assessing patients in the postoperative situation.

Advanced Imaging of Glenohumeral Instability: It May Be Less Complicated than It Seems

Glenohumeral joint instability is usually an intimidating topic for most radiologists due to both the complexity of related anatomical and biomechanical considerations and the increasing number of classifications and acronyms reported in the literature in association with this condition. In this short review, we aim to demystify glenohumeral instability by first focusing on the relevant anatomy and pathophysiology. Second, we will review what the important imaging findings are and how to describe them for the clinician in the most relevant yet simple way. The role of the radiologist in assessing glenohumeral instability lesions is to properly describe the stabilizing structures involved (bone, soft-tissue stabilizers, and their periosteal insertion) to localize them and to attempt to characterize them as acute or chronic. Impaction fractures on the glenoid and humeral sides are important to specify, locate, and quantify. In particular, the description of soft-tissue stabilizers should include the status of the periosteal insertion of the capsulo-labro-ligamentous complex. Finally, any associated cartilaginous or rotator cuff tendon lesion should be reported to the clinician.

Reliability of measurements performed on two dimensional and three dimensional computed tomography in glenoid assessment for instability

PURPOSE

The main purpose of this study is to establish which of two methods is more reliable in glenoid assessment for instability in pre-operative planning. Accordingly, we have studied the intra- and inter-observer reliability of glenoid parameters with the use of two-dimensional (2D) and three-dimensional (3D) reconstructed computed tomography (CT) images.

METHODS

One hundred glenoids were measured with the use of 2D-CT and 3D-CT (in 3D orientation) by two independent observers (one experienced and one inexperienced). Measurements were repeated after one week for 30 randomly selected glenoids.

RESULTS

The intra-class correlation coefficient (ICC) for inter-observer reliability was significantly greater for 3D-CT (0.811 to 0.915) than for 2D-CT (0.523 to 0.925). All intra-observer reliability values for 3D-CT were near perfect (0.835 to 0.997), while those for 2D-CT were less reliable (0.704 to 0.960). A dependent t-test showed that, for both observers, almost all glenoid parameters (except R and d) differed significantly (p < 0.05) between 2D and 3D measurement methods.

CONCLUSIONS

Therefore, it can be concluded that 3D glenoid reconstructions are more reliable for glenoid bone loss assessment than 2D-CT. The results suggest that quantifying a glenoid defect with the use of 2D image only-even if performed by an experienced orthopaedic surgeon-is prone to errors. Differences in measurements between and within observers can be explained by plane setting and identifying glenoid rim in 2D-CT. Accordingly, we recommend that glenoid measurements should be performed in 3D orientation using 3D reconstruction obtained from CT images for pre-operative assessments, which are crucial for surgical planning.

Glenoid version and its relationship to glenohumeral instability and labral tears

BACKGROUND

Evidence suggests a relationship between glenoid retroversion and posterior instability, but no literature exists comparing glenoid version referencing the scapular body versus the endosteal vault. This study evaluated glenoid version and its relationship to unidirectional instability and labral tears.

METHODS

Glenoid version in patients with unidirectional instability or labral tears was measured with magnetic resonance imaging by either the Friedman method or the Poon and Ting method. Analyses of variance followed by independent t tests were used to compare 3 groups: anterior instability or labral tears (anterior pathology group, n = 33); posterior instability or labral tears (posterior pathology group, n = 34); and stable controls (n = 30). The referencing error for 2-dimensional axial images was evaluated for variance by imaging facility. Interobserver and intraobserver reliability scores were calculated.

RESULTS

With the Friedman method, the posterior pathology group (-9°) was more retroverted than the control group (-4°) (P = .0005) and the anterior pathology group (-5°) (P = .0104) but there was no difference between the control group and anterior pathology group (P = .38). The referencing error in the sagittal plane averaged 23° and varied by facility (P = .0365). The coronal-plane error averaged 1° and did not vary by facility (P = .7180). Intraclass correlation coefficient scores showed good to excellent intrarater and inter-rater reliability.

CONCLUSION

The posterior pathology group had 5° more retroversion than controls using the Friedman method. Glenoid version using the Poon and Ting method or the Friedman method did not predict anterior instability or labral tears. Axial magnetic resonance images were constructed with a referencing error in the sagittal plane that varied by magnetic resonance imaging facility and has implications for improving 2-dimensional axial imaging protocols.

Glenoid Dysplasia: Pathophysiology, Diagnosis, and Management

➤Subtle forms of glenoid dysplasia may be more common than previously thought and likely predispose some patients to symptomatic posterior shoulder instability. Severe glenoid dysplasia is a rare condition with characteristic radiographic findings involving the posteroinferior aspect of the glenoid that often remains asymptomatic.➤Instability symptoms related to glenoid dysplasia may develop over time with increased activities or trauma. Physical therapy focusing on rotator cuff strengthening and proprioceptive control should be the initial management.➤Magnetic resonance imaging and computed tomographic arthrograms are useful for detecting subtle glenoid dysplasia by revealing the presence of an abnormally thickened or hypertrophic posterior part of the labrum, increased capsular volume, glenoid retroversion, and posteroinferior glenoid deficiency.➤Open and arthroscopic labral repair and capsulorrhaphy procedures have been described for symptomatic posterior shoulder instability. Glenoid retroversion of >10° may be a risk factor for failure following soft-tissue-only procedures for symptomatic glenoid dysplasia.➤Osseous procedures are categorized as either glenoid reorientation (osteotomy) or glenoid augmentation (bone graft), and no predictable results have been demonstrated for any surgical strategy. Glenoid osteotomies have been described for increased retroversion, with successful results, although others have noted substantial complications and poor outcomes.➤In severe glenoid dysplasia, the combination of bone deficiency and retroversion makes glenoid osteotomy extremely challenging. Bone grafts placed in a lateralized position to create a blocking effect may increase the risk of the development of arthritis, while newer techniques that place the graft in a congruent position may decrease this risk.