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.

The role of bone in glenohumeral stability.

Surgical treatment of shoulder instability caused by anterior glenoid bone loss is based on a critical threshold of the defect size. Recent studies indicate that the glenoid concavity is essential for glenohumeral stability. However, biomechanical proof of this principle is lacking. The aim of this study was to evaluate whether glenoid concavity allows a more precise assessment of glenohumeral stability than the defect size alone. The stability ratio (SR) is a biomechanical estimate of glenohumeral stability. It is defined as the maximum dislocating force the joint can resist related to a medial compression force. This ratio was determined for 17 human cadaveric glenoids in a robotic test setup depending on osteochondral concavity and anterior defect size. Bony defects were created gradually, and a 3D measuring arm was used for morphometric measurements. The influence of defect size and concavity on the SR was examined using linear models. In addition, the morphometrical-based bony shoulder stability ratio (BSSR) was evaluated to prove its suitability for estimation of glenohumeral stability independent of defect size. Glenoid concavity is a significant predictor for the SR, while the defect size provides minor informative value. The linear model featured a high goodness of fit with a determination coefficient of R2 = 0.98, indicating that 98% of the SR is predictable by concavity and defect size. The low mean squared error (MSE) of 4.2% proved a precise estimation of the SR. Defect size as an exclusive predictor in the linear model reduced R2 to 0.9 and increased the MSE to 25.7%. Furthermore, the loss of SR with increasing defect size was shown to be significantly dependent on the initial concavity. The BSSR as a single predictor for glenohumeral stability led to highest precision with MSE = 3.4%. Glenoid concavity is a crucial factor for the SR. Independent of the defect size, the computable BSSR is a precise biomechanical estimate of the measured SR. The inclusion of glenoid concavity has the potential to influence clinical decision-making for an improved and personalised treatment of glenohumeral instability with anterior glenoid bone loss.

/pdf/glenoid-concavity-has-a-higher-impact-on-shoulder-stability-39dv0ym5es.pdf

Glenoid concavity has a higher impact on shoulder stability than the size of a bony defect.

Purpose: Glenohumeral joint compatibility and bone morphology are among the most critical factors in shoulder stabilization. Our study investigated the effect of the bone morphological structure of the shoulder joint on anterior shoulder dislocation. Methods: In our study, people with a history of shoulder dislocation were selected as the patient group. In the control group, patients with shoulder MRIs for any reason and no history of shoulder dislocation were included. Those who have a fracture around the shoulder, a congenital deformity in the shoulder region, arthrosis of the shoulder, those whose MRI images cannot be measured, those with Hill-Sachs lesion, connective tissue diseases (such as Ehler Danlos), who are unsure of their diagnosis, or who have incomplete and incorrect suspicious information in their patient file have been excluded. In our retrospective case-control study, glenoid width, glenoid height, glenoid’s height-to-width ratio, glenoid’s depth, glenoid’s version, glenoid’s inclination, humerus radius of curvature, glenoid radius of curvature, and bony shoulder stability ratio were measured on MRI images of the patients. The sample size for each group was determined using a power analysis method. The intra-class coefficient (ICC) assessed interobserver and intraobserver reliability. Results: A total of 80 patients, 40 each in the control and patient groups, were included in the study. Glenoid width was measured as 24.27 ± 1.58 in the patient group, 25.61 ± 1.72 in the control group; glenoid height was as measured 36.49 ± 2.26 in the patient group, 36.74 ± 1.99 in the control group; height-to-width ratio was measured as 1.5 ± 0.08 in the patient group, 1.43 ± 0.05 in the control group; glenoid version was as measured −0.53 ± 1.17 in the patient group, −1.44 ± 1.1 in the control group; glenoid inclination was measured as 1.44 ± 3.93 patient group, 2.64 ± 3.81 in the control group; glenoid depth was measured as 1.69 ± 0.41 in the patient group, 2.12 ± 0.53 in the control group; humerus radius of curvature was measured as 29.70 ± 6.76 in the patient group, 24.98 ± 3.22 in the control group; glenoid axial radius of curvature was measured as 61.8 ± 13.52 in the patient group, 52.53 ± 15.69 in the control group; glenoid coronal radius of curvature was measured as 43.01 ± 7.47 in the patient group, 37.74 ± 6.89 in the control group; the bony shoulder stability ratio was measured as 0.35 ± 0.06 in the patient group and 0.44 ± 0.06 in the control group. In the statistical evaluation, the glenoid width (p &lt; 0.001), the glenoid height/width ratio (p &lt; 0.001), the glenoid version (p &lt; 0.001), the depth of the glenoid cavity (p &lt; 0.001), and the radius of curvature measurements of the humeral head (p &lt; 0.001) and the glenoid (axial, p &lt; 0.007; coronal, p &lt; 0.001) were found to be significantly different. Glenoid height and inclination were similar in both groups. Conclusions: The detection of bone morphological features that constitute risk factors for shoulder dislocations plays an important role in preventing shoulder dislocations. In this way, it provides essential data on personalized rehabilitation programs and treatment selection for recurrent dislocations. 

Effect of Glenohumeral Joint Bone Morphology on Anterior Shoulder Instability: A Case-Control Study

BACKGROUND
Glenoid concavity compression by rotator cuff muscle contraction is one of the key mechanisms in the stability of the glenohumeral joint.


PURPOSE/HYPOTHESIS
The purpose of this study was to evaluate the effects of glenoid concavity, as represented by the bony shoulder stability ratio (BSSR) and other factors, including glenoid bone defect size, on the surgical failure of arthroscopic stabilization procedures for recurrent anterior shoulder instability. The authors also aimed to determine the critical value of BSSR. It was hypothesized that both glenoid concavity and glenoid bone defect size would be correlated with surgical failure, with glenoid concavity having a stronger correlation.


STUDY DESIGN
Case-control study; Level of evidence, 3.


METHODS
A total of 120 patients who underwent arthroscopic stabilization procedures for recurrent anterior shoulder instability were included. Patients with bony Bankart lesions were excluded to eliminate the postoperative effects of bony fragment restoration on the glenoid concavity. For each patient, variable factors including BSSR, glenoid bone defect size, presence of off-track Hill-Sachs lesions, and age at first dislocation were recorded. Chi-square analysis and Student t test were performed to analyze the effect of each variable on surgical failure. Multivariate logistic regression analysis was used to determine the combined effect of >2 variables on surgical failure. The critical value of BSSR was analyzed using a receiver operating characteristic curve.


RESULTS
Nine patients (7.5%) had recurrent instability requiring revision surgery. BSSR (patients with recurrence, 18.6% ± 19.4%; patients without recurrence, 41.8% ± 10.5%; P = .01), glenoid bone defect size (17.5% ± 3.6% vs 11.7% ± 7.0%; P = .02), age at the time of first dislocation (18.8 ± 3.9 years vs 22.0 ± 6.5 years; P = .04), and number of suture anchors used (4.1 ± 0.3 vs 5.8 ± 1.6; P < .001) showed significant differences between patients with and without surgical failure. Multivariate logistic regression analysis revealed surgical failure to be correlated with BSSR (odds ratio, 0.849; P = .02) and the number of suture anchors used (odds ratio, 0.070; P = .03). The critical value of BSSR was 29.3% (area under the curve, 0.84; 95% CI, 0.67-1.00; P < .001; sensitivity, 78%; specificity, 93%).


CONCLUSION
Glenoid concavity is strongly correlated with surgical failure after arthroscopic stabilization procedures for anterior shoulder instability. The value of BSSR reflects shoulder instability caused by glenoid bone morphology more accurately than glenoid bone defect size.

Correlation of Glenoid Concavity With Surgical Failure After Arthroscopic Stabilization for Recurrent Anterior Shoulder Instability.

Objective To conduct a systematic review of modern literature data on the modern approaches in diagnosis and treatment of shoulder instability. Material and methods Searching for literature data was performed using the Pubmed and Google Scholar databases. Results The authors analyzed the results of conservative treatment of patients with shoulder instability and emphasized higher risk of instability recurrence, degeneration of anatomical structures and functional impairment in these patients. Surgery is advisable to restore shoulder stability and normalize its function. Several methods for stabilizing the shoulder have been proposed. The approaches to diagnosis and treatment of shoulder instability have been updated. Conclusion Successful treatment of shoulder instability is based on qualitative and complete assessment of soft tissues and bone structures. An individual approach considering bone tissue deficiency and individual needs of the patient is required.

[Shoulder instability: review of current concepts of diagnosis and treatment].

Current glenoid defect measurement techniques only quantify bone loss in terms of defect diameter or surface. However, the glenoid depth plays an important role in shoulder stabilization by means of concavity compression. We present a case of a professional wrestler who suffered from anterior shoulder instability after sustaining a bony Bankart lesion without loss of glenoid surface area but flattening of the concavity due to medialization of the fragment. The patient’s glenoid concavity was reconstructed arthroscopically by reduction and percutaneous screw fixation of the bony fragment along with a capsulo-ligamentous shift. Changes of the glenoid concavity with according alterations in the Bony Shoulder Stability Ratio (BSSR) were analyzed on pre-op, post-op, and follow-up CT scans. Postoperative CT scans revealed a deepened concavity (3.3 mm) and improved BSSR (46.1 %) compared to pre-op scans (0.7 mm; 11.3 %). Follow-up CT scans showed a slight remodeling of the glenoid concavity (3.2 mm) with steady BSSR (44.7 %). This case shows that the passive stabilizing effect of the glenoid can be compromised by loss of concavity despite the absence of loss of articular surface. Therefore, addressing the concavity loss and resulting reduction of the BSSR is recommended in these cases. Bony Bankart repair was successful in restoring the BSSR of the patients shoulder as determined by mathematical calculations based on CT scans.

/pdf/effect-of-glenoid-concavity-loss-on-shoulder-stability-a-2prqv98g65.pdf

Effect of glenoid concavity loss on shoulder stability- a case report in a professional wrestler

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Effect of glenoid concavity loss on shoulder stability- a case report in a professional wrestler