Glenoid shape in atraumatic posterior instability of the shoulder

A narrative review of little league shoulder: proximal humeral physis widening is only one piece of the puzzle, it is time to consider posterior glenoid dysplasia

Baseball athletes across all levels of play are at an increased risk for upper extremity injury due to the supraphysiologic demands on the shoulder and elbow during overhead throwing. Little league baseball players present with a unique subset of injuries that can affect the growth plate, commonly at the shoulder or the elbow. Ascertaining a diagnosis and plan of care for little league shoulder (LLS) historically focuses on the proximal humeral physis in skeletally immature throwing athletes presenting with shoulder pain. However, while not a current standard of care, posterior glenoid dysplasia is often present in youth baseball athletes presenting with LLS, warranting a shift in the way clinicians evaluate for and treat the youth baseball athlete's pathologic shoulder. Therefore, purpose of this narrative review is 2-fold: first, to describe the current standard of care as it relates to a diagnosis of LLS, and second, to critically describe a comprehensive evaluation process for youth throwing athletes with shoulder pain that includes screening for evidence of posterior glenoid dysplasia. This paper summarizes the current state of the available evidence for anatomic considerations of LLS in the baseball athletes throwing shoulder. Additionally, we provide a framework for clinical evaluation using a multidisciplinary approach to evaluate the entire kinetic chain of the youth baseball athlete presenting with LLS and posterior glenoid dysplasia. A case study is presented to describe common presentations, clinical and objective examinations, and a plan of care from time of evaluation to return to throwing.

Biomechanical study of 3D-printed titanium alloy pad for repairing glenoid bone defect

Background: The purpose of this study was to investigate the effect of 3D-printed technology to repair glenoid bone defect on shoulder joint stability. Methods: The shoulder joints of 25 male cadavers were tested. The 3D-printed glenoid pad was designed and fabricated. The specimens were divided into 5 groups. Group A: no bone defect and the structure of the glenoid labrum and joint capsule was intact; Group B: Anterior inferior bone defect of the shoulder glenoid; Group C: a pad with a width of 2 mm was installed; Group D: a pad with a width of 4 mm was installed; Group E: a pad with a width of 6 mm was installed. This study measured the distance the humeral head moved forward at the time of glenohumeral dislocation and the maximum load required to dislocate the shoulder. Results: The shoulder joint stability and humerus displacement was significantly lower in groups B and C compared with group A (p < .05). Compared with group A, the stability of the shoulder joint of group D was significantly improved (p < .05). However, there was no significant difference in humerus displacement between groups D and A (p > .05). In addition, compared with group A, shoulder joint stability was significantly increased and humerus displacement was significantly decreased in group E (p < .05). Conclusion: The 3D-printed technology can be used to make the shoulder glenoid pad to perfectly restore the geometric shape of the shoulder glenoid articular surface. Moreover, the 3D-printed pad is 2 mm larger than the normal glenoid width to restore the initial stability of the shoulder joint.

Reconstruction of recurrent shoulder dislocation with glenoid bone defect with 3D-printed titanium alloy pad: outcomes at 2-year minimum follow-up

BACKGROUND

To evaluate the outcome of shoulder arthroscopy-assisted implantation of three-dimensional (3D)-printed titanium pads for recurrent shoulder dislocation with glenoid bone defects.

METHODS

From June 2019 to May 2020, the clinical efficacy of 3D printed titanium pad implantation assisted by shoulder arthroscopy, for the treatment of recurrent shoulder dislocations with shoulder glenoid defects was retrospectively analyzed. The American Shoulder and Elbow Surgeons (ASES) shoulder, Rowe, and Constant scores were recorded before surgery and at 3 months, 6 months, 1 year, and 2 years after surgery. 3D computed tomography (CT) and magnetic resonance imaging were used to evaluate the location of the glenoid pad, bone ingrowth, joint degeneration, and osteochondral damage.

RESULTS

The mean age of the 12 patients was 21.4 (19-24) years and the mean follow-up time was 27.6 (24-35) months. The Visual Analog Scale score significantly improved from 5.67 ± 1.98 preoperatively to 0.83 ± 0.58 postoperatively (p = 0.012). The postoperative ASES score was significantly increased to 87.91 ± 3.47 compared with preoperative ASES score (46.79 ± 6.45) (p < 0.01). Rowe and Constant scores also improved from 22.5 ± 12.34 and 56.58 ± 7.59 preoperatively to 90.83 ± 4.69 and 90.17 ± 1.89 at 2 years postoperatively, respectively. CT performed 2 years after surgery showed that the pad perfectly replenished the bone-defective part of the shoulder glenoid and restored the articular surface curvature of the shoulder glenoid in the anterior-posterior direction, and the bone around the central riser of the pad was tightly united. Magnetic resonance imaging 2 years after surgery showed that the humeral head osteochondral bone was intact, and there was no obvious osteochondral damage.

CONCLUSIONS

3D printed titanium pads are a reliable, safe, and effective surgical procedure for treating recurrent shoulder dislocations with glenoid bone defects.

Occult, Incomplete, and Complete Posterior Labral Tears Without Glenohumeral Instability on Imaging Underestimate Labral Detachment

PURPOSE

To introduce a classification of posterior labral tear and describe clinical characteristics, magnetic resonance imaging (MRI)/magnetic resonance arthrography (MRA) findings, arthroscopic findings, and outcomes after arthroscopic repair for patients with posterior labral tears without glenohumeral instability.

METHODS

Sixty patients with posterior labral tear who underwent arthroscopic repair were analyzed retrospectively. Patients with shoulder instability were excluded. Tear patterns were classified into 3 types; occult (type 1), incomplete (type 2), and complete (type 3) based on MRI/MRA studies. A visual analog scale score for pain, American Shoulder and Elbow Surgeons score, Single Assessment Numeric Evaluation score for satisfaction, and return to sports were evaluated at a minimum follow-up of 2 years. Computed tomography arthrography was performed at a year follow-up for assess labral healing. The diagnosis was confirmed in arthroscopy, and arthroscopic labral repair without capsular plication was performed.

RESULTS

The mean patient age was 30.4 ± 6.9 years, and all patients were male. Forty-four patients (73.3%) were participating in sports. MRI/MRA studies identified 10 patients with type 1, 18 with type 2, and 32 with type 3 tears. Type 1 tear patients showed a significantly longer symptom duration than those with type 3 (32.5 ± 17.2 vs 18.2 ± 17.1 months; P = .015). In arthroscopic findings, 70% of type 1 tear was confirmed as incomplete or complete tears. The American Shoulder and Elbow Surgeons score improved from 79.6 ± 10.3 to 98.1 ± 3.7, and pain was relieved from 2.4 ± 0.7 to 0.2 ± 0.5 at the last follow-up visit with high labral healing rate (95%). Thirty-nine (88.6%) patients returned to sports at preinjury levels.

CONCLUSIONS

In active young men with shoulder pain during daily activities or sports despite programmed conservative treatment, posterior labral tears should be considered even when MRI/MRA findings are ambiguous. Arthroscopic posterior labral repair without capsular plication provided satisfactory clinical outcomes and a high labral healing rate.

LEVEL OF EVIDENCE

Level Ⅳ, case series.

Biomechanical Analysis of Posterior Open-Wedge Osteotomy and Glenoid Concavity Reconstruction Using an Implant-Free, J-Shaped Iliac Crest Bone Graft

BACKGROUND

Posterior open-wedge osteotomy and glenoid reconstruction using a J-shaped iliac crest bone graft showed promising clinical results for the treatment of posterior instability with excessive glenoid retroversion and posteroinferior glenoid deficiency.

PURPOSE

To evaluate the biomechanical performance of the posterior J-shaped graft to restore glenoid retroversion and posteroinferior deficiency in a cadaveric shoulder instability model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A posterior glenoid open-wedge osteotomy was performed in 6 fresh-frozen shoulders, allowing the glenoid retroversion to be set at 0°, 10°, and 20°. At each of these 3 preset angles of glenoid retroversion, the following conditions were simulated: (1) intact joint, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-shaped graft (at 0° of retroversion). With the humerus in the Jerk position (60° of glenohumeral anteflexion, 60° of internal rotation), stability was evaluated by measuring posterior humeral head (HH) translation (in mm) and peak translational force (in N) to translate the HH over 25% of the glenoid width. Glenohumeral contact patterns were measured using pressure-sensitive sensors. Fixation of the posterior J-graft was analyzed by recording graft micromovements during 3000 cycles of 5-mm anteroposterior HH translations.

RESULTS

Reconstructing the glenoid with a posterior J-graft to 0° of retroversion significantly increased stability compared with a posterior Bankart lesion and posteroinferior glenoid deficiency in all 3 preset degrees of retroversion (P < .05). There was no significant difference in joint stability comparing the posterior J-graft with an intact joint at 0° of retroversion. The posterior J-graft restored mean contact area and contact pressure comparable with that of the intact condition with 0° of retroversion (222 vs 223 mm², P = .980; and 0.450 vs 0.550 MPa, P = .203). The mean total graft displacement after 3000 cycles of loading was 43 ± 84 µm, and the mean maximal mediolateral graft bending was 508 ± 488 µm.

CONCLUSION

Biomechanical analysis of the posterior J-graft demonstrated reliable restoration of initial glenohumeral joint stability, normalization of contact patterns comparable with that of an intact shoulder joint with neutral retroversion, and secure initial graft fixation in the cadaveric model.

CLINICAL RELEVANCE

This study confirms that the posterior J-graft can restore stability and glenohumeral loading conditions comparable with those of an intact shoulder.

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.

The relationship of glenoid version and severity of glenoid bone loss in anterior shoulder instability patients: A retrospective cohort study

Background/objective

The effect of glenoid version on the severity of glenoid bone loss is not completely understood, although the variation of glenoid version angles is considered to reflect the degree of glenoid bone loss in anterior shoulder instability cases. The objective of this retrospective case-control study is to determine the relationship of the glenoid version and the severity of glenoid bone loss in a group of previously documented recurrent anterior shoulder dislocation patients.

Methods

We retrospectively collected magnetic resonance arthrogram (MRA) data from 72 patients with unidirectional recurrent anterior shoulder instability. The best-fit circle method was used to identify the percentage of glenoid bone loss. Measurements of glenoid labral, chondral, and bony versions were performed using the Friedman method.

Results

Using univariate regression analysis, it was found that a retroversion angle of more than 4 degrees was associated with an increased risk ratio for the occurrence of a critical glenoid defect by approximately 5 times.

Conclusions

24 Univariate logistic regression analysis, used to determine the presence of a critical glenoid bone defect, showed that both the bony version angle and the number of previous dislocations were significantly associated with the extent of glenoid bone loss. A retroversion angle of more than 4 degrees was associated with an approximately five-fold increase in the odds ratio for the presence of a critical glenoid defect. Surgeons may use the value of the measured glenoid version in prediction the required version of the reconstructive treatment.

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.

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

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.

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.

Arthroscopic Posterior Glenoid Reconstruction Using a Fresh Distal Tibia Allograft for Recurrent Posterior Instability

Posterior glenohumeral instability is a relatively uncommon cause of shoulder instability. Recurrent posterior instability with static posterior humeral head subluxation is often associated with critical glenoid bone loss. Unlike anterior instability, the amount of bone loss for posterior instability that requires surgical reconstruction remains a topic of debate. Several techniques have been described to treat critical bony defects in patients with recurrent posterior shoulder instability with the use of both autografts and allografts depending on the amount of bone loss present. Open posterior glenoid bone block procedure is associated with increased risk of complications and morbidity to the patient. As such, all-arthroscopic techniques have emerged with the advantage of allowing for the diagnosis and treatment of concomitant glenohumeral pathology and minimizing soft-tissue dissection through the posterior deltoid and rotator cuff muscles. Reported short-term outcomes of arthroscopic posterior bone block stabilization are promising; however, it remains a technically challenging procedure due to intra-articular graft insertion and subsequent fixation congruent to the posterior glenoid articular margin. We describe an all-arthroscopic technique using a fresh distal tibia allograft fixation using 2 partially threaded screws in conjunction with an arthroscopic Latarjet fixation set for a patient with recurrent posterior shoulder instability and associated glenoid bone loss.

Effect of Posterior Glenoid Bone Loss and Retroversion on Arthroscopic Posterior Glenohumeral Stabilization

BACKGROUND

Posterior glenohumeral instability is an increasingly recognized cause of shoulder instability, but little is known about the incidence or effect of posterior glenoid bone loss.

PURPOSE

To determine the incidence, characteristics, and failure rate of posterior glenoid deficiency in shoulders undergoing isolated arthroscopic posterior shoulder stabilization.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

All patients undergoing isolated posterior labral repair and glenoid-based capsulorrhaphy with suture anchors between 2008 and 2016 at a single institution were identified. Posterior bone deficiency was calculated per the best-fit circle method along the inferior two-thirds of the glenoid by 2 independent observers. Patients were divided into 2 groups: minimal (0%-13.5%) and moderate (>13.5%) posterior bone loss. The primary outcome was reoperation for any reason. The secondary outcomes were military separation and placement on permanent restricted duty attributed to the operative shoulder.

RESULTS

A total of 66 shoulders met the inclusion criteria, with 10 going on to reoperation after a median follow-up of 16 months (range, 14-144 months). Of the total shoulders, 86% (57/66) had ≤13.5% bone loss and 14% (9/66) had >13.5%. Patients with moderate posterior glenoid bone loss had significantly greater retroversion (-11.5° vs -4.3°; P = .01). Clinical failure requiring reoperation was seen in 10.5% of patients in the minimal bone deficiency group and 44.4% in the moderate group (P = .024). There was no difference between groups in rate of military separation or restricted duty. Patients with moderate posterior glenoid bone deficiency were more likely to be experiencing instability instead of pain on initial presentation (P < .001), were more likely to have a positive Jerk test result (P = .05), and had increased glenoid retroversion (P = .01).

CONCLUSION

In shoulders with moderate glenoid bone deficiency (>13.5%) and increased glenoid retroversion, posterior capsulolabral repair alone may result in higher reoperation rates than in shoulders without bone deficiency.

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

Biomechanics of posterior shoulder instability - current knowledge and literature review

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

The Influence of Bone Loss on Glenoid Version Measurement: A Computer-Modeled Cadaveric Analysis

PURPOSE

To characterize how increasing computed tomography (CT)-quantified glenoid bone loss influences measured version.

METHODS

Six embalmed cadaveric shoulders were used for this study. Glenoid bone defects were computer modeled in cadaveric shoulders; CT images were obtained and segmented using OsiriX software, creating 3-dimensional en face glenoids. Glenoid defects were made on CT images of intact glenoids superimposed with a glenoid clock face viewed en face to simulate anterior and posterior bone loss. Bony defects in various positions comprising 3%, 9.5%, and 19.5% were created posteriorly. Best-fit circles were superimposed to represent 10% and 25% defects anteriorly. Version was measured using the Friedman method.

RESULTS

The average glenoid version measured 4° of retroversion, 2° after 10% anterior bone loss, and neutral version in the 25% bone loss group. Version was significantly altered when we compared intact glenoids versus 10% and 25% anterior glenoid bone loss (P < .001). Increasing from 10% to 25% bone loss showed a significant difference in measured version (P = .025). Posterior defects from the 6:30 to 8:30 clock-face position averaged 4.6° of retroversion; from the 6:30 to 9:30 clock-face position, 6.2° of retroversion; and from the 6:30 to 10:30 clock-face position, 8.7° of retroversion. When comparing glenoid defects at the 6:30 to 8:30 clock-face position with those involving the 6:30 to 9:30 and 6:30 to 10:30 clock-face positions (P < .001), a 1° correction may be used for every 5% of bone loss to account for version changes seen with bone loss.

CONCLUSIONS

In this cadaveric analysis, glenoid version was altered in the setting of increasing posterior and anterior bone loss. A correction factor may be considered to account for this. When comparing glenoid defects at the 6:30 to 8:30 clock-face position with those involving the 6:30 to 9:30 and 6:30 to 10:30 clock-face positions (P < .001), a 1° correction may be used for every 5% of bone loss to account for version changes seen with bone loss.

CLINICAL RELEVANCE

This cadaveric study shows that glenoid bone loss alters glenoid version, as measured by CT, in a meaningful way. This information is important in managing anterior and posterior shoulder instability, and correction of measured version should be considered in this setting to provide an accurate and comprehensive evaluation.

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.

Posterior Glenohumeral Instability: Evidence-based Treatment

Posterior glenohumeral instability is an increasingly important clinical finding in athletic patients. Over the last decade, basic and clinical research has improved our understanding of the pathoanatomy and biomechanics of this challenging disorder, as well as our ability to diagnose and appropriately treat it. Although recurrent posterior shoulder instability is not as common as anterior instability, it is prevalent among specific populations, including football and rugby players, and may be overlooked by clinicians who are unaware of the typical physical examination and radiographic findings.

Outcomes Following Arthroscopic Repair of Posterior Labral Tears in Patients Older Than 35 Years

Although the results of arthroscopic management of posterior labral pathology in young athletes have been reported extensively in the literature, the clinical outcomes in older patients are unknown. This retrospective review included patients older than 35 years who underwent arthroscopic posterior labral repair. Functional outcome scores were collected, and subgroup analyses were performed to evaluate the impact of patient-specific factors. Forty-three patients met the inclusion criteria; average follow-up was 36.9 months (range, 24-54 months). Mean patient age at the time of surgery was 40.9 years (range, 35-57 years). Average outcome scores at final follow-up were Quick Disabilities of the Arm, Shoulder and Hand Scale (QuickDASH), 19±22; Simple Shoulder Test (SST), 9.9±3; Western Ontario Shoulder Instability Index (WOSI), 601±546; and Single Assessment Numeric Evaluation (SANE), 79.6%±23.4%. No significant differences in outcomes were observed in patients with preoperative symptomatic instability, active workers' compensation claims, or traumatic injury (P>.05). The presence of intraoperatively definable chondral damage (Outerbridge grade III or higher) was associated with significantly worse final functional outcomes (QuickDASH: 29 vs 11.9, P=.03; SST: 8.5 vs 10.9, P=.02; WOSI: 875 vs 407, P=.01; and SANE: 70.6% vs 86%, P=.05). One patient (2%) experienced a minor postoperative complication, and 3 patients (7%) required subsequent procedures: 2 total shoulder arthroplasties and 1 revision labral repair. The results of arthroscopic posterior labral repair in patients older than 35 years were variable and worse than those previously reported in younger patients. The presence of chondral damage at the time of the index procedure was a negative predictive factor. [Orthopedics. 2017; 40(2):e305-e311.].

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.

Anterior Shoulder Instability Is Associated With an Underlying Deficiency of the Bony Glenoid Concavity

PURPOSE

To determine whether anterior shoulder instability is associated with an inherent deficiency of the bony glenoid concavity, which results in a reduced bony shoulder stability ratio (BSSR).

METHODS

In this case-control study, we searched the institutional database for patients treated for unilateral recurrent anterior shoulder instability. We included 30 consecutive patients with atraumatic instability, 30 consecutive patients with traumatic instability, and 36 matched healthy controls, for a total of 96 shoulders. Computed tomography images of the unaffected shoulders of the instability patients were compared with images of the ipsilateral shoulders of age- and sex-matched healthy controls for differences in glenoid morphology. By use of a mathematical formula based on Pythagorean trigonometric identities, the mean BSSRs of the different groups were calculated and compared. Validation of the formula was accomplished by finite element analysis.

RESULTS

The mean BSSR of atraumatic instability patients was 17.9% ± 8.5% and therefore significantly lower than the mean BSSR of 31.1% ± 7.5% of the control group (13.2%; 95% confidence interval [CI], 9.1% to 17.4%; P < .001). The mean BSSR of the traumatic instability group was higher, at 23.9% ± 8.5% (P = .007), but still showed a deficit of 7.2% (95% CI, 2.8% to 11.7%; P = .002) compared with controls. The atraumatic instability group showed a mean reduction of 0.9 mm (95% CI, 0.6 to 1.1 mm; P < .001) in concavity depth and a decrease of 2.9° (95% CI, 0.4° to 5.3°; P = .021) in concavity retroversion, whereas the traumatic instability patients had a reduction of 0.4 mm (95% CI, 0.1 to 0.8 mm; P = .006) in concavity depth. Neither of the instability groups differed significantly from their respective controls in terms of glenoid concavity diameter, head radius, or glenoid vault morphology.

CONCLUSIONS

Anterior shoulder instability is associated with an inherent flattening of the bony glenoid concavity, which significantly decreases the BSSR. The deficiency appears to be more pronounced in patients with atraumatic instability than in patients with traumatic instability.

LEVEL OF EVIDENCE

Level III, case-control study.

Structure modeling of the glenoid: Relevance to shoulder arthroplasty

We applied shape modeling and principal component analysis (PCA) to discover glenoid bone structural relationships relevant to improving glenoid prosthesis features, fixation, and instrumentation. Knowledge of external bone morphology guides prosthesis shape and positioning, while internal bone morphology and bone density influence fixation. CT-based modeling defined nonarthritic glenoid subchondral bone surface and internal structure. First and second principal shape components were related to size and density. Reproducible structural parameters and glenoid feature relationships were discovered. Subchondral bone surface was approximated by a circle inferiorly and a triangle superiorly with the circle's center at a reproducible point along a superior-inferior line. Glenoid vault's maximum depth was at the circle's center, and the highest bone density was in posterior glenoid. Glenoid subchondral bone surface version varied from superior to inferior, but not by sex or side. Male subchondral bone surfaces were larger and more retroverted. Even if subchondral bone surfaces are deformed by arthritis, glenoid morphology can be identified by extra-articular landmarks, permitting location of the glenoid center and scapular orientation (glenoid version). Knowledge obtained from this study directs design of novel prosthesis features and instrumentation for use without pre-op CT or computer aided surgery.

Posterior chondrolabral cleft: clinical significance and associations with shoulder instability

BACKGROUND

A high signal intensity cleft between the labrum and articular cartilage of the posterior glenoid is commonly visible on MRI and has been suggested to be anatomic variation [3, 10, 23]. The association of a posterior cleft with variations in glenoid morphology or with shoulder instability is unknown.

QUESTIONS/PURPOSES

The purposes of this study were to determine if posterior chondrolabral clefts are associated with variations in glenoid morphology, and to determine if they are associated with shoulder instability.

PATIENTS AND METHODS

Shoulder MRI was performed in 1,264 shoulders, 1,135 male (89.8%), and 129 female (10.2%). A musculoskeletal radiologist blinded to history and outcomes evaluated the MR images for linear high signal intensity at the posterior chondrolabral junction and a rounded or truncated contour of the posterior glenoid. Glenoid version and depth were measured. Patients were followed prospectively for shoulder instability for 4 years. Univariate and multivariate statistical analysis were performed.

RESULTS

Posterior chondrolabral cleft was present in 114/1,264. Posterior chondrolabral cleft was associated with a rounded or truncated posterior glenoid. There were 9.5° retroversion in shoulders with a posterior cleft, and 7.7° retroversion in shoulders without a cleft. Shoulders with a posterior chondrolabral cleft were more likely to develop shoulder instability.

CONCLUSIONS

Posterior chondrolabral clefts are not uncommon on MRI. They are associated with a rounded or truncated posterior glenoid and a small but significant increase in glenoid retroversion. They are associated with shoulder instability.

Revision posterior shoulder stabilization

BACKGROUND

Revision arthroscopic posterior glenohumeral stabilization requires a thorough understanding of the static and dynamic stabilizers of the glenohumeral joint. The evaluation of these patients is complex but critical given the variety of possible underlying lesions.

METHOD

We reviewed the literature surrounding recurrent and revision posterior instability biomechanics, etiology, evaluation, treatment, and outcomes. We also reviewed our own database of posterior instability cases and isolated revision procedures to review our own outcomes and to highlight overall concepts.

DISCUSSION/CONCLUSION

Although other authors have argued that performing a revision procedure indicates for an open procedure and osseous augmentation, our experience has been that revision posterior stabilization arthroscopic soft-tissue repair alone may be indicated in selected patients. After identification of posterior glenoid bone loss/effective retroversion and mechanical failure of prior repairs, the majority of the patients with recurrence of posterior instability likely have either recurrent or persistent labral pathology or patulous capsules with occult multi-directional instability primarily manifesting in the posterior direction. These patients are best served with capsular shift, reefing, and plication, often requiring 180-270° repair and 4 or greater suture anchors. Because of significant heterogeneity in the clinical outcomes reported to date further research will be necessary to define the clinical outcomes in revision posterior stabilization.

Multidirectional instability of the shoulder: rotator interval dimension and capsular laxity evaluation using MR arthrography

OBJECTIVES

To compare the rotator interval and capsular dimension as measured on MR arthrography between patients with clinically diagnosed multidirectional instability (MDI) and control subjects with no instability.

MATERIALS AND METHODS

We retrospectively reviewed a consecutive series of 658 shoulders that had undergone MR arthrography between 2006 and 2010. Of these, 97 shoulders were included in the present study. These shoulders were divided into two groups according to the clinically established diagnoses. The MDI group comprised 47 shoulders with atraumatic multidirectional shoulder instability, and the control group comprised 50 shoulders with no instability. Two independent observers measured the width and depth of the rotator interval, and the capsular dimensions at the anterior, anteroinferior, inferior, posteroinferior, and posterior regions in the two groups using MR arthrography.

RESULTS

The rotator interval width and depth were significantly greater in the MDI group (width, observer 1, 17.7 mm, observer 2, 17.9 mm; depth, observer 1, 8.9 mm, observer 2, 8.8 mm) than in the control group (width, observer 1, 14.3 mm, observer 2, 14.5 mm; depth, observer 1, 5.9 mm, observer 2, 6.2 mm) (p < .001). The capsular dimensions at the inferior and posteroinferior regions were significantly larger in the MDI group (inferior, observer 1, 27.9 mm, observer 2, 27.8 mm; posteroinferior, observer 1, 27.0 mm, observer 2, 27.1 mm) than in the control group (inferior, observer 1, 25.7 mm, observer 2, 25.3 mm; posteroinferior, observer 1, 23.3 mm, observer 2, 23.6 mm) (p < .05). A width greater than 15.2 mm or a depth greater than 6.4 mm of the rotator interval, suggesting MDI, had sensitivities of 81 and 92 % for observer 1, and 79 and 94 % for observer 2, and specificities of 66 and 72 % for observer 1, and 62 and 66 % for observer 2, respectively.

CONCLUSIONS

Measurements of the rotator interval and the size of the distended inferior and posteroinferior joint capsule on MR arthrography are greater in shoulders with clinical MDI than in stable shoulders.

Posterior shoulder instability: current concepts review

PURPOSE

Posterior shoulder instability has been difficult to diagnose and even more challenging to manage. However, it is being diagnosed and treated more frequently, particularly after sports injuries. The purpose of this article is to review literature concerning the management of these pathologies.

METHODS

A literature review was carried out in the main medical databases to evaluate the several studies concerning the open and arthroscopic treatment of posterior shoulder instability.

RESULTS

Because of better awareness of the pathology, better technical investigations, and a better understanding of shoulder biomechanics, more and more mechanical factors that can cause posterior instability have been described. Structural abnormalities can be divided into bony abnormalities and soft-tissue abnormalities. Each group can also be divided into abnormalities caused by trauma (macro- or microtrauma) or congenital. These abnormalities can be treated with non-anatomic and anatomic stability procedures. During the last decades, the latter have been described more frequently, most of them arthroscopically.

CONCLUSION

For surgical treatment to be successful, the instability must be attributable to mechanical factors that can be modified by surgery. Because of better knowledge of the pathology, a more specific surgery can be performed. This lesion-specific surgery has improved clinical results compared to non-anatomic stability procedures, particularly when that surgery has been performed arthroscopically.

Posterior instability of the shoulder: diagnosis and management

Recurrent posterior instability of the shoulder can be difficult to diagnose and technically challenging to treat. Although not as common as anterior instability, recurrent posterior shoulder instability is prevalent among certain demographic and sporting groups, and may be overlooked if one is not aware of the typical examination and radiographic findings. The diagnosis itself can be difficult as patients typically present with vague or confusing symptoms, and treatment has evolved from open to arthroscopic surgical techniques. This article is intended to review the anatomy and biomechanics associated with posterior shoulder instability, to discuss the pathogenesis and presentation of posterior instability, and to describe the variety of treatment options and clinical results.

Simultaneous 3D assessment of glenohumeral shape, humeral head centering, and scapular positioning in atraumatic shoulder instability: a magnetic resonance-based in vivo analysis

BACKGROUND

Success rates in the treatment of atraumatic shoulder instability differ, and in vivo identification of the individual insufficient stabilizers is difficult.

HYPOTHESIS

Atraumatic shoulder instability is an inhomogeneous entity with varying alterations of the active and passive stabilizers. This might be a reason for inferior treatment results.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

Shoulders of 28 healthy volunteers and both shoulders of 14 patients with atraumatic instability and multidirectional laxity were examined in different arm positions using open magnetic resonance imaging. Three-dimensional postprocessing techniques were applied to determine 3D glenoid size and retroversion, radius of the humeral head, and curvature of the glenoid. The results of static stabilizers were compared with those of glenohumeral and scapular positioning in the same patients for identification of the individual insufficient stabilizers.

RESULTS

The atraumatic unstable shoulders showed an increased mean retroversion on both sides, the difference being significant on the affected side (9.4 degrees +/- 4.8 degrees vs healthy 3.9 degrees +/- 1.3 degrees ; P < .05) with a range of 2.6 degrees to 16.6 degrees . The curvature analysis demonstrated a pronounced flatness of the glenoid with a significantly increased mean radius (103.8 mm vs healthy 41.7 mm). The extent of these changes varied widely among patients. Comparison of the static stabilizers with glenohumeral and scapular positioning revealed that isolated changes of the active stabilizers exist in some patients, whereas no isolated changes of passive stabilizers were found.

CONCLUSION

All active and passive stabilizers need to be analyzed in patients with atraumatic instability because the magnitude of alteration varied widely among individuals. Different combinations of alterations of the stabilizers were found. The presented technique allows for in vivo identification of the specific alterations. This is necessary for a better understanding of individual pathomechanics and for initiating a specific causal treatment.

Morphology of the scapula relative to the reverse shoulder prosthesis

PURPOSE

To analyse the morphology of the scapula relative to the reverse shoulder prosthesis.

METHODS

Scapulas of 46 women and 27 men aged 16 to 84 (mean, 53) years with proximal humeral fractures (n=52) or recurrent antero-inferior instability (n=21) were assessed using 3-dimensional computed tomography (CT). For comparison, 108 cadaveric scapulas with unknown epidemiology were assessed using a goniometer and a caliper. The length of the glenoid neck, the angle between the glenoid surface and the upper posterior column of the scapula, and the angles between the major craneocaudal glenoid axis and (1) the base of the coracoid process and (2) the upper posterior column of the scapula were assessed.

RESULTS

The length of the glenoid neck was classified into short and long. In the respective CT and cadaveric groups, the anterior glenoid neck was short in 42% and 18% of scapulas and long in 58% and 82%, whereas the posterior glenoid neck was short in 34% and 60% of scapulas and long in 66% and 40%. The angle between the glenoid surface and the upper posterior column of the scapula was classified into types I (50-52 degrees) and II (62-64 degrees). In the respective CT and cadaveric groups, 61% and 71% of scapulas were type I and 39% and 29% were type II. All differences between groups were significant. The mean angles between the major craneocaudal glenoid axis and (1) the base of the coracoid process and (2) the upper posterior column of the scapula were 18 and 8 degrees, respectively.

CONCLUSION

Because of variations in scapular morphology, individualised adjustment is needed for reverse shoulder prostheses. Three-dimensional CT is valuable in preoperative planning.

Cadaveric and three-dimensional computed tomography study of the morphology of the scapula with reference to reversed shoulder prosthesis

Purpose

The purpose of this study is to analyze the morphology of the scapula with reference to the glenoid component implantation in reversed shoulder prosthesis, in order to improve primary fixation of the component.

Methods

Seventy-three 3-dimensional computed tomography of the scapula and 108 scapular dry specimens were analyzed to determine the anterior and posterior length of the glenoid neck, the angle between the glenoid surface and the upper posterior column of the scapula and the angle between the major craneo-caudal glenoid axis and the base of the coracoid process and the upper posterior column.

Results

The anterior and posterior length of glenoid neck was classified into two groups named "short-neck" and "long-neck" with significant differences between them. The angle between the glenoid surface and the upper posterior column of the scapula was also classified into two different types: type I (mean 50°–52°) and type II (mean 62,50°–64°), with significant differences between them (p < 0,001). The angle between the major craneo-caudal glenoid axis and the base of the coracoid process averaged 18,25° while the angle with the upper posterior column of the scapula averaged 8°.

Conclusion

Scapular morphological variability advices for individual adjustments of glenoid component implantation in reversed total shoulder prosthesis. Three-dimensional computed tomography of the scapula constitutes an important tool when planning reversed prostheses implantation.

Posterior-inferior glenoid rim shapes by MR imaging

Our purpose was to try to apply a CT classification of glenoid rim shapes to MR images and to determine the reliability of the subsequent MR classification by testing observer variability. Shoulder MR imaging exams of 54 consecutive patients were reviewed retrospectively by two musculoskeletal radiologists independently. Posterior-inferior glenoid rim shape was categorized, based on reported CT criteria, as triangle, "lazy-J" or "delta" using the most caudal MR section that unequivocally showed articular cartilage. The same studies were reviewed again one month later to test interobserver and intraobserver variability. Final determination of glenoid rim type was made by consensus. There were 31 males and 23 females with an average age of 42 years, range 14-75 years. Forty-one patients were referred for evaluation of nonspecific shoulder pain, 9 for suspected rotator cuff tear and 4 for instability. The most common shape was "lazy-J" with 32 patients (59%) having this type. The least common was delta shape, with 7 patients (13%) having this form. Fifteen patients (28%) had a normal triangle shape. There was significant interobserver variability in determining the shape of the glenoid rim with 17/54 (31%) discordant readings. For the "lazy-J" shape, the kappa value was .02, for the "delta" type, kappa value was .60 and for the triangle shape, kappa was .32. Intraobserver variability was 35% for radiologist A and 28% for radiologist B. Kappa values for intraobserver variability ranged from .53 to .85. Four patients had posterior instability, 3 were judged to have normal triangular inferior glenoid rims and 1 a "lazy J" type by Radiologist A. Radiologist B judged 2 of the instability patients as normal triangular and 2 as "lazy J". A CT classification of posterior-inferior glenoid rim shapes can be applied using MR imaging, however, there is significant observer variability that limits the applicability of this classification scheme with MR imaging.

Glenoid Dysplasia: Incidence and Association with Posterior Labral Tears as Evaluated on MRI

OBJECTIVE

Glenoid dysplasia is known to predispose affected patients to accelerated degenerative joint disease. We have observed that there is often an association between glenoid dysplasia and posterior labral tears. Our goal was to assess glenoid dysplasia as seen on MRI and to assess its association with posterior labral tears.

CONCLUSION

In our study population, we found that moderate to severe glenoid dysplasia is not a rare entity as seen on MRI, with an incidence of 14.3%. Furthermore, we found that there is a statistically significant increase in the incidence of posterior labral tears associated with shoulders with moderate or severe glenoid dysplasia compared with those shoulders with no dysplasia or mild dysplasia as evaluated on MRI. Even when the mild cases were included, the incidence of posterior labral tears was significantly increased versus healthy subjects, indicating that even mild cases of glenoid dysplasia may be clinically relevant.

Loss of chondrolabral containment of the glenohumeral joint in atraumatic posteroinferior multidirectional instability

BACKGROUND

Although the cause of posteroinferior instability of the shoulder has not been fully defined, glenoid version can be more completely measured when chondrolabral structures are included because conformity and containment of the glenohumeral joint are integral functions of both the articular cartilage and the labrum. The purpose of this study was to use magnetic resonance imaging-arthrography to evaluate the chondrolabral containment of the glenohumeral joint in patients with atraumatic posteroinferior multidirectional instability of the shoulder.

METHODS

We evaluated four measurements (osseous and chondrolabral glenoid version, labral height, and glenoid depth) on T2-weighted axial magnetic resonance-arthrography images of thirty-three shoulders with atraumatic posteroinferior multidirectional instability. Shoulders with a documented labral tear were excluded. The measurements were compared with those of thirty-three age-matched controls without glenohumeral pathology. The angles of version of the osseous and chondrolabral portions of the glenoid were measured in three consecutive planes (superior 25%, middle 50%, and inferior 75% in relation to the superior lip of the glenoid) perpendicular to the long axis of the glenoid.

RESULTS

The shoulders with posteroinferior instability had greater retroversion of both the osseous and the chondrolabral portion of the glenoid in the middle and inferior planes. The chondrolabral portion of the glenoid had more retroversion than the osseous portion in the inferior plane. The height of the posterior portion of the labrum was decreased in the inferior plane in the shoulders with instability. Glenoid depth in the middle and inferior planes was significantly shallower in the shoulders with instability.

CONCLUSIONS

Loss of containment in the chondrolabral portion of the glenoid in the middle and inferior planes is a consistent finding in shoulders with atraumatic posteroinferior multidirectional instability and is associated with loss of posterior labral height. It is unclear whether the retroversion of the posteroinferior aspect of the labrum is a cause or a consequence of atraumatic posteroinferior multidirectional instability, but this factor should be considered during surgical repair.