Posteroinferior glenoplasty can change glenoid shape and increase the mechanical stability of the shoulder

Posterior Shoulder Instability Part II - Glenoid Bone-Grafting, Glenoid Osteotomy, and Rehabilitation/Return to Play - An International Expert Delphi Consensus Statement

PURPOSE

The purpose of this study was to establish consensus statements on glenoid bone-grafting, glenoid osteotomy, rehabilitation, return to play, and follow-up for posterior shoulder instability.

METHODS

A consensus process on the treatment of posterior shoulder instability was conducted, with 71 shoulder/sports surgeons from 12 countries participating based on their level of expertise in the field. Experts were assigned to one of 6 working groups defined by specific subtopics within posterior shoulder instability. Consensus was defined as achieving 80-89% agreement, whereas strong consensus was defined as 90-99% agreement, and unanimous consensus was indicated by 100% agreement with a proposed statement.

RESULTS

All of the statements relating to rehabilitation, return to play, and follow-up achieved consensus. There was unanimous consensus that the following criteria should be considered: restoration of strength, range of motion, proprioception, and sport-specific skills, with a lack of symptoms. There is no minimum time point required to return to play. Collision athletes and military athletes may take longer to return because of their higher risk for recurrent instability, and more caution should be exercised in clearing them to return to play, with elite athletes potentially having different considerations in returning to play. The relative indications for revision surgery are symptomatic apprehension, multiple recurrent instability episodes, further intra-articular pathologies, hardware failure, and pain.

CONCLUSION

The study group achieved strong or unanimous consensus on 59% of statements. Unanimous consensus was reached regarding the criteria for return to play, collision/elite athletes having different considerations in return to play, indications for revision surgery, and imaging only required as routine for those with glenoid bone-grafting/osteotomies at subsequent follow-ups. There was no consensus on optimal fixation method for a glenoid bone-block, the relative indications for glenoid osteotomy, whether fluoroscopy is required or if the labrum should be concomitantly repaired.

LEVEL OF EVIDENCE

Level V Expert Opinion.

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.

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.

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

BACKGROUND

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE

IV; Systematic review.

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 shoulder instability managed by arthroscopic acromial pediculated bone-block. Technique

In posterior shoulder instability (recurrent dislocation, involuntary posterior subluxation or voluntary subluxation that has become involuntary), surgery may be considered in case of failure of functional treatment if there are no psychological contraindications. Acromial bone-block with pediculated deltoid flap, as described by Kouvalchouk, is an alternative to iliac bone-block, enabling triple shoulder locking by the blocking effect, the retention hammock provided by the deltoid flap and posterior capsule repair. Arthroscopy allows shoulder joint exploration and diagnosis of associated lesions, with opening and conservation of the posterior capsule; it greatly facilitates bone-block positioning and capsule reinsertion. The present report describes the procedure in detail.

LEVEL OF EVIDENCE

Technical note.

Comparison of Magnetic Resonance Imaging and Computed Tomography Scans of the Glenoid Version in Anterior Dislocation of the Shoulder

The glenoid version is an important factor in the etiology of anterior dislocation of the shoulder and the planning of shoulder surgery. Few reports compare the magnetic resonance imaging (MRI) measurements of the glenoid version with those of computed tomography (CT). This study aimed to show that it is possible to use MRI instead of CT, which is accepted as the gold standard today for the evaluation of the glenoid version. A total of 55 patients with a history of 1 nonsurgically treated unilateral anterior dislocation of the shoulder who had both MRI and CT records for the dislocated shoulders constituted the study group. The glenoid version was measured in the axial plane on MRI and CT. Mean glenoid version measured by the observers was -1.6°±4.7° (95% confidence interval, -2.3° to -0.8°) and -1.8°±4.3° (95% confidence interval, -2.5° to -1.2°) by CT and MRI, respectively (P=.126). The evaluation of the CT and MRI measurements made by the 3 observers (X, Y, and Z) revealed no significant difference, as the P values of X CT - X MRI, Y CT - Y MRI, and Z CT - Z MRI were .550, .406, and .238, respectively. Interclass correlation among the 3 observers for CT and MRI was 0.996 and 0.981, respectively. The imaging methods of MRI and CT can be interchangeably used in the evaluation of the glenoid version in cases of anterior dislocation of the shoulder. [Orthopedics. 2017; 40(4):e687-e692.].

Posterior open wedge osteotomy of the scapula neck for the treatment of advanced shoulder osteoarthritis with posterior head migration in young patients

BACKGROUND

Treatment of young, active patients with symptomatic glenohumeral osteoarthritis, excessive glenoid retroversion, and static posterior humeral subluxation is challenging. Correction of glenoid retroversion may lead to centric loading and perhaps recenter the humeral head. We describe the functional and radiologic outcomes after corrective osteotomy of the glenoid in this population of patients.

MATERIALS AND METHODS

In this retrospective study, we included 10 shoulders (8 patients) that were observed for a mean of 33.4 months (range, 24-52 months) after corrective osteotomy of the glenoid. The mean age at surgery was 41.5 years (range, 24-51 years). On standardized axial images, glenoid retroversion and posterior static humeral subluxation were measured preoperatively and postoperatively and at the final follow-up. At final follow-up, anterior and posterior axial radiographs were performed to determine humeral head position in different arm positions. Clinical follow-up included Constant-Murley score, subjective shoulder value, and patient satisfaction.

RESULTS

The mean Constant-Murley score improved significantly from 45.1 points (range, 24-71) to 64.1 points (range, 44-92; P < .001). The average degree of anterior flexion improved significantly from 117° (range, 50°-160°) to 143° (range, 110°-180°; P = .006). The mean glenoid retroversion changed from 16° (range, 11°-31°) preoperatively to 5° (range, 13° anteversion-16° retroversion; P = .003) at the final follow-up. The mean posterior static subluxation of the humeral head changed from 5 mm (range, 0-10 mm) preoperatively to 6 mm (range, 0-14 mm; P = .259) at the final follow-up.

CONCLUSIONS

This study shows that posterior open wedge osteotomy of the glenoid neck provides excellent correction of glenoid retroversion.

The importance of glenoid version in patients with anterior dislocation of the shoulder

BACKGROUND

Although increased retroversion of the glenoid has been shown to be an important factor in posterior instability of the shoulder, there are few studies reporting glenoid bone structure as a risk factor in anterior dislocation of the shoulder. This study aimed to compare glenoid version in patients with anterior dislocation of the shoulder and individuals in a control group with no shoulder problems before undergoing computed tomography and to assess a possible relationship between demographic characteristics and glenoid version angle.

METHODS

The study group comprised 63 patients (12 women and 51 men; mean age, 35.71 years) with 1 or multiple unilateral anterior dislocations of the shoulder (dislocated group), whereas 63 individuals (11 women and 52 men; mean age, 35.38 years) with no history of shoulder complaints and no signs of instability constituted the control group. The glenoid version angle was measured on an axial cut of the computed tomography scan.

RESULTS

The glenoid version angles on the dislocated side in the study group were significantly more anteverted than those of the dominant (P < .001) and nondominant (P = .023) shoulders of the control group. The version angles of dislocated shoulders significantly differed from those of nondislocated shoulders of both men (P = .041) and women (P = .049). There was no significant relationship between the glenoid version angle on the dislocated side and dislocation mechanism (P = .883), age group (P = .356), or number of dislocations (P = .971).

CONCLUSIONS

Glenoid version is an important factor for the development of anterior dislocation of the shoulder.

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.

The effect of defect orientation and size on glenohumeral instability: a biomechanical analysis

PURPOSE

The purpose of this study was to determine the relationship between bony stability and percentage of anterior glenoid bone loss and the effect of bone loss orientation.

METHODS

Twelve cadaveric shoulders were studied. Glenoid bone defects were simulated in two different osteotomy angles: 0° and 45° to the superoinferior (SI) axis of the glenoid. The force and displacement required for dislocation were measured under two compressive forces of 40 and 60N. Testing was performed for the intact glenoid and glenoid defects of 2, 4, 6, 8, and 10 mm from the anterior margin.

RESULTS

The maximum force for dislocation with the 2-mm glenoid defect was significantly decreased compared with intact glenoid (p = 0.01), and this force also significantly decreased with each increase in defect size (p < 0.05). The dislocation force for 45° osteotomy was significantly higher than that for 0° osteotomy for all defect widths up to 8 mm with 40N compression and 6 mm with 60N compression (p < 0.001). The displacement at dislocation did not significantly decrease until the 8-mm defect with the 45° osteotomy but significantly decreased with the 4-mm defect with the 0° osteotomy. The required force for dislocation with 60N compression was significantly higher than that with 40N compression for all osteotomy sizes and orientations.

CONCLUSIONS

The decrease in stability even with glenoid bone loss as small as 2 mm or 7.5 % of the glenoid width suggests that bony restoration is recommended whenever any bone loss exists. Bone defects parallel to SI axis may be more susceptible to recurrent instability, and shoulder muscle strengthening exercises may increase glenohumeral compressive force and thus improve glenohumeral stability. Bony restoration is recommended whenever bone loss exists even with small bone fragments particularly those in line with the superior-inferior axis of the glenoid.

Associations between in-vivo glenohumeral joint motion and morphology

Joint morphology has a significant influence on joint motion and may contribute to the development of rotator cuff pathology, but the relationships between glenohumeral joint (GHJ) morphology and in-vivo GHJ motion are not well understood. The objectives of this study were to assess measures of joint morphology and their relationship with in-vivo joint motion in two populations: shoulders with intact rotator cuffs (n=48) and shoulders with rotator cuff pathology (n=36, including 5 symptomatic tears, 9 asymptomatic tears and 22 repaired tears). GHJ morphology was measured from CT-based three-dimensional models of the humerus and scapula. In-vivo GHJ motion was measured during shoulder abduction using biplane x-ray imaging. Associations between GHJ morphology and motion were assessed with univariate and best subsets regression. The only morphological difference identified between the populations was the critical shoulder angle (intact: 34.5 ± 4.7°, pathologic: 36.9 ± 5.0°, p=0.03), which is consistent with previous research. In intact shoulders, the superior/inferior (S/I) position of the humerus on the glenoid during shoulder abduction was significantly associated with the glenoid's S/I radius of curvature (p<0.01), conformity index (p<0.01), and stability angle (p<0.01). Furthermore, the S/I position of the humerus on the glenoid was negatively associated with the critical shoulder angle (p=0.04), which contradicts previous research. No significant associations between GHJ morphology and GHJ motion were detected in shoulders with rotator cuff tears. It is unknown if rotator cuff pathology compromises the relationships between GHJ morphology and motion, or if the absence of this relationship is a pre-existing condition that increases the likelihood of pathology.

Differences in glenohumeral joint morphology between patients with anterior shoulder instability and healthy, uninjured volunteers

BACKGROUND

Traumatic glenohumeral joint (GHJ) dislocations are common, resulting in significant shoulder disability and pain. Previous research indicates that bony morphology is associated with an increased risk of injury in other joints (eg, the knee), but the extent to which bony morphology is associated with traumatic GHJ dislocation is unknown. This study assessed GHJ morphology in patients with anterior GHJ instability and in a control population of healthy volunteers.

METHODS

Bilateral computed tomography scans were used to measure GHJ morphology in both shoulders of 11 patients with instability and 11 control subjects. Specific outcome measures included the glenoid radius of curvature (ROC) in the anterior/posterior (A/P) and superior/inferior (S/I) directions, humeral head ROC, A/P and S/I conformity index, and A/P and S/I stability angle.

RESULTS

Compared with the control subjects, the glenoid of the instability the injured shoulder in patients with instability was flatter (ie, higher ROC) in the A/P (P = .001) and S/I (P = .01) directions and this finding was also true for uninjured, contralateral shoulder (A/P: P = .01, S/I: P = .03). No differences in GHJ morphology were detected between the instability patients' injured and contralateral shoulders (P > .07). Similarly, no differences in GHJ morphology were detected between the control subjects' dominant and nondominant shoulders (P > .51).

CONCLUSIONS

There are significant differences in GHJ morphology between healthy control subjects and both shoulders (injured and uninjured, contralateral) of patients diagnosed with anterior instability after GHJ dislocation. These findings are important clinically because they suggest that glenoid morphology may influence the risk of GHJ dislocation.

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.

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.

Stabilizing mechanism in bone-grafting of a large glenoid defect

BACKGROUND

Conventional wisdom suggests that the glenoid defect after a shoulder dislocation is anteroinferior. However, recent studies have found that the defect is located anteriorly. The purposes of this study were (1) to clarify the critical size of the anterior defect and (2) to demonstrate the stabilizing mechanism of bone-grafting.

METHODS

Thirteen cadaver shoulders were investigated. With use of a custom testing machine with a 50-N compression force, the peak translational force that was needed to move the humeral head and lateral humeral displacement were measured. The force was used to evaluate the joint stability. An osseous defect was created stepwise in 2-mm increments of the defect width. The bone graft was harvested from the coracoid process. The defect size was expressed as the estimated defect size divided by the measured glenoid length. Testing was performed with (1) the glenoid intact, (2) a simulated Bankart lesion, (3) the Bankart lesion repaired, (4) a 2-mm defect, (5) the Bankart lesion repaired, (6) the defect bone-grafted, (7) a 4-mm defect, (8) the Bankart lesion repaired, (9) the defect bone-grafted, (10) a 6-mm defect, (11) the Bankart lesion repaired, (12) the defect bone-grafted, (13) an 8-mm defect, (14) the Bankart lesion repaired, and (15) the defect bone-grafted.

RESULTS

Force and displacement decreased as the size of the osseous defect increased. The mean force after the formation of a defect of > or =6 mm (19% of the glenoid length) with the Bankart lesion repaired (22 +/- 7 N) was significantly decreased compared with the baseline force (52 +/- 11 N). Both the mean force (and standard deviation) and displacement returned to the levels of the intact condition (68 +/- 3 N and 2.6 +/- 0.4 mm, respectively) after bone-grafting (72 +/- 12 N and 2.7 +/- 0.3 mm, respectively).

CONCLUSIONS

An osseous defect with a width that is > or =19% of the glenoid length remains unstable even after Bankart lesion repair. The stabilizing mechanism of bone-grafting was the restoration of the glenoid concavity.

The effect of component positioning on intrinsic stability of the reverse shoulder arthroplasty

HYPOTHESIS

Anterior instability is one of the most common complications in reverse shoulder replacement. This study hypothesized that intrinsic stability of a reverse prosthesis varies with the degree of version of the humerus and glenoid components. This should provide guidelines on how to best position the implant components to decrease the rate of dislocation.

MATERIALS AND METHODS

Resistance to anterior dislocation of a reverse implant was measured in a mechanical testing machine by means of the stability ratio (ratio of peak dislocation/axial compressive forces). Versions of the humeral and glenoid components were modified in 10 degrees steps in the 90 degrees abducted and resting positions.

RESULTS

In both tested positions, the effect of humeral component version was highly significant. Only a glenoid component retroversion of 20 degrees led to a statistically significant drop in stability ratio for the 20 degrees abducted position. Intrinsic stability in the typical component positioning (neutral glenoid version and 20 degrees humeral retroversion) yielded comparably low intrinsic stability, which could only be improved by increasing anteversion of the humeral component.

DISCUSSION

Version of the humeral component is the critical factor for intrinsic stability. Version of the glenoid component is less important for intrinsic stability, but special care should be given to avoid retroversions of more than 10 degrees . Within this range, the surgeon can concentrate primarily on other parameters critical for long-term outcome (range of motion, secure fixation) when choosing the appropriate glenoid version.

CONCLUSION

Anterior stability can be improved by implanting the humeral component in neutral or with some anteversion.

Effect of an anterior glenoid defect on anterior shoulder stability: a cadaveric study

BACKGROUND

There have been few biomechanical studies to clarify which size of a glenoid defect is critical. However, those studies have assumed that the defect occurred anteroinferiorly. Recent studies have reported that the defect is located anteriorly rather than anteroinferiorly. Therefore, the effect of the anterior, not anteroinferior, glenoid defect on shoulder stability needs to be investigated.

HYPOTHESIS

The anterior glenoid defect would have a similar effect on anterior shoulder stability as that of the anteroinferior glenoid defect.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric shoulders were used (mean age, 74 years). The specimen was attached to a shoulder-testing device with the arm in abduction and external rotation. An osseous defect was created stepwise with a 2-mm increment of the defect width. The stability ratio was used to evaluate joint stability. With a 50-N axial force, the translational force applied to the humeral head was measured by a force transducer.

RESULTS

The stability ratio without a defect (32% +/- 6%) significantly decreased after creating a 6-mm defect (17% +/- 5%; P = .0001), which was equivalent to 20% of the glenoid length.

CONCLUSION

An osseous defect at 3 o'clock with a width that was equal to or greater than 20% of the glenoid length significantly decreased anterior stability.

CLINICAL RELEVANCE

The results suggest that reconstruction of the glenoid concavity might be necessary in shoulders with an anterior glenoid defect of at least 20% of the glenoid length.

Complex shoulder disorders: evaluation and treatment

Evaluation of patients with shoulder disorders often presents challenges. Among the most troublesome are revision surgery in patients with massive rotator cuff tear, atraumatic shoulder instability, revision arthroscopic stabilization surgery, adhesive capsulitis, and bicipital and subscapularis injuries. Determining functional status is critical before considering surgical options in the patient with massive rotator cuff tear. When nonsurgical treatment of atraumatic shoulder stability is not effective, inferior capsular shift is the treatment of choice. Arthroscopic revision of failed arthroscopic shoulder stabilization procedures may be undertaken when bone and tissue quality are good. Arthroscopic release is indicated when idiopathic adhesive capsulitis does not respond to nonsurgical treatment; however, results of both nonsurgical and surgical treatment of posttraumatic and postoperative adhesive capsulitis are often disappointing. Patients not motivated to perform the necessary postoperative therapy following subscapularis repair are best treated with arthroscopic débridement and biceps tenotomy.

Scapular inclination and glenohumeral joint stability: a cadaveric study

BACKGROUND

In shoulders with multidirectional instability, translation of the humeral head on the glenoid is increased in the midrange because of the following three reasons: the increased retroversion, a hypoplastic posteroinferior rim, and decreased scapular abduction during arm elevation. This study aimed to clarify the relationship between glenoid inclination and glenohumeral joint stability.

METHODS

Nine fresh-frozen cadaveric shoulders were tested. With a 50-N compressive load, the translation force was measured in the 3-o'clock, 6-o'clock, 9-o'clock, and 12-o'clock directions by using a tilt of 0 degrees , 5 degrees , 10 degrees , 15 degrees , and 20 degrees . When the glenoid was tilted in one direction, the translation force was measured in the direction of inclination and in the opposite direction. The stability ratio was then calculated.

RESULTS

The stability ratio in the 3-o'clock direction significantly decreased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 9-o'clock direction significantly decreased with a tilt of more than 15 degrees in the 9-o'clock direction and significantly increased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 6-o'clock direction significantly increased with a tilt of more than 10 degrees in the 6-o'clock direction.

CONCLUSIONS

The posterior and inferior stability increased with an anterior tilt of more than 5 degrees and with a superior tilt of 10 degrees , respectively. The anterior and posterior stability decreased with an anterior tilt of 5 degrees and with a posterior tilt of 15 degrees , respectively.

Direct injection of blood into the labrum enhances the stability provided by the glenoid labral socket

We tested the hypothesis that the stabilizing function of the labrum can be enhanced by inflating it with blood. In 6 fresh cadaveric glenoids, the anteroinferior stability provided by the glenoid was quantitated by measuring the maximal angle between the glenoid centerline and the direction of the force applied via a ball in the glenoid before the ball dislocated from the glenoid. This stability angle was measured for each of 4 different applied loads. These measurements were repeated after the anteroinferior labrum was augmented by the injection of fresh blood. Injection augmentation of the labrum significantly increased the measured stability angles in 5 of 6 specimens. The 1 outlier had a partial labral tear. The mean increase in stability for all 6 glenoids ranged from 19% to 30% for the different test loads. Labral injection with blood may be a useful adjunct in the surgical management of glenohumeral instability.

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.

Capsulolabral augmentation by blood injection increases the intrinsic stability provided by the glenoid

PURPOSE

To test the hypothesis that the intrinsic stability of the cadaveric glenoid can be augmented by the injection of blood into the labrum.

METHODS

The intrinsic stability of 10 fresh frozen cadaveric glenoids was assessed by measuring the balance stability angle. Pretreatment values of 8 directions in each glenoid were obtained. The labrum was then injected with blood freshly drawn from a volunteer. After the injected blood clotted, measurements of the balance stability angle of the 8 directions were again obtained.

RESULTS

The mean pre-injection balance stability angle for 7 of the 8 directions were significantly increased by the injection of blood: anterosuperior, from 25 to 35 degrees (p<0.005); anterior, from 27 to 34 degrees (p<0.01); anteroinferior, from 36 to 39 degrees (p<0.005); inferior, from 38 to 41 degrees (p<0.02); posteroinferior, from 35 to 42 degrees (p<0.01); posterior, from 27 to 35 degrees (p<0.0005); and posterosuperior, from 26 to 29 degrees (p<0.005). Cross-sections of injected labra demonstrated a firm clot within the labrum with substantial increases in thickness.

CONCLUSION

The intrinsic stability of cadaveric glenoids can be significantly augmented by the injection of blood into the labrum. It is possible that blood injection may be a useful primary or adjunct procedure in the open or arthroscopic management of glenohumeral instability.

Optimizing the glenoid contribution to the stability of a humeral hemiarthroplasty without a prosthetic glenoid

BACKGROUND

In a shoulder requiring arthroplasty, if the glenoid is flat or biconcave, the surgeon can restore the desired glenoid stability by using a glenoid prosthesis with a known surface geometry or by modifying the surface of the glenoid to a geometry that provides the desired glenoid stability. This study tested the hypotheses that (1) the stability provided by the glenoid is reduced by the removal of the articular cartilage; (2) the stability contributed by the glenoid is compromised by loss of its articular cartilage, and this lost stability can be restored by spherical reaming along the glenoid centerline; and (3) the stability of a reamed glenoid is comparable with that of a native glenoid and with that of a polyethylene glenoid with similar surface geometry; and (4) the glenoid stability can be predicted from the glenoid surface geometry.

METHODS

The stability provided by the glenoid in a given direction can be characterized by the maximal angle that the humeral joint reaction force can make with the glenoid centerline before the humeral head dislocates; this quantity is defined as the balance stability angle in the specified direction. The balance stability angles were both calculated and measured in eight different directions for an unused polyethylene glenoid component and eleven cadaveric glenoids in four different states: (1) native without the capsule or the rotator cuff, (2) denuded of cartilage and labrum, (3) after reaming the glenoid surface around the glenoid centerline with use of a spherical reamer with a radius of 25 mm, and (4) after reaming around the glenoid centerline with use of a spherical reamer with a radius of 22.5 mm.

RESULTS

The calculated and measured balance stability angles for each direction in each glenoid were strongly correlated. Denuding the glenoids of the articular cartilage reduced the glenoid contribution to stability, especially in the posterior direction. Reaming the glenoid restored the stability to values comparable with those of the normal glenoid. For example, the average calculated balance stability angle (and standard deviation) in the posterior direction for all eleven glenoids was 24 degrees for the native glenoids, 14 degrees for the denuded glenoids, 25 degrees for the glenoids reamed to a radius of 25 mm, and 33 degrees for the glenoids reamed to a radius of 22.5 mm. The values for the glenoids reamed to 25 mm (25 degrees ) were similar to those of a polyethylene glenoid of the same radius of curvature. For glenoids reamed to 22.5 mm, the average difference between the actual balance stability angle and that predicted from the glenoid geometry was 3.4 degrees +/- 2.4 degrees.

CONCLUSIONS

The glenoid contribution to shoulder stability was decreased by the removal of cartilage and labrum and was restored by spherical reaming to a level similar to resurfacing the glenoid with a polyethylene component.

Pathophysiology and treatment of atraumatic instability of the shoulder

The shoulder is stabilized mainly by negative intraarticular pressure when the arm is at the side of the body with all the muscles relaxed. During arm motion in the midrange of motion, the contraction force of the muscles provides dynamic stability. In shoulders with atraumatic instability, the joint capsule is thin and enlarged, making it more difficult to maintain the negative pressure. Decreased joint volume by capsular imbrication results in creating the negative intraarticular pressure. Imbalance of muscle forces may cause decreased abduction of the scapula during arm elevation or decreased concavity compression (or both), either of which may result in instability. Muscle exercises are effective in most cases of atraumatic instability. Congenital hypoplasia of the glenoid also contributes to decreased concavity compression. Glenoid osteotomy is the treatment of choice in such cases. One of these factors may play a role in the occurrence of atraumatic instability by itself or in combination. Better understanding of the pathophysiology of atraumatic shoulder instability is useful when selecting the best treatment option in each case.

Glenoid shape in atraumatic posterior instability of the shoulder

Glenoid shape is related closely to shoulder stability and its abnormality is thought to affect the humeral head position in shoulders with atraumatic instability. However, it is unclear how the glenoid shape in shoulders with atraumatic instability is different from the glenoid shape in normal shoulders. The current authors investigated glenoid shape of 45 healthy individuals (20 males and 25 females; average age, 22 years) and 20 patients with atraumatic posterior instability with multidirectional laxity (six males and 14 females; average age, 19 years) using three-dimensional magnetic resonance imaging. The tilting angles of the glenoid bone were measured in five consecutive planes perpendicular to the long axis of the glenoid and cross sections were divided into three types (concave, flat, convex). In healthy individuals, the average tilting angles from the bottom to the top of the glenoid bone were 3.0 degrees +/- 3.6 degrees, 1.0 degrees +/- 3.2 degrees, -1.0 degrees +/- 2.0 degrees, -2.3 degrees +/- 3.9 degrees, and -6.9 degrees +/- 3.7 degrees anteriorly, and tilting angles of patients were -6.1 degrees +/- 4.0 degrees, -4.0 degrees +/- 3.6 degrees, -4.8 degrees +/- 3.2 degrees, -5.5 degrees +/- 2.7 degrees, and -7.5 degrees +/- 3.1 degrees. The type of cross section also was different on the bottom plane where the concave shape accounted for 78% of healthy individuals whereas it accounted for 0% of patients. The loss of tilting angles and concavity of the inferior glenoid would correlate with the direction of the head translation in posterior instability.

Medially based anterior capsular shift of the glenohumeral joint. Passive range of motion and posterior capsular strain

The effect of a medially based anterior capsular shift on translational and rotational range of motion and posterior capsular strain was investigated in an in vitro model. Six cadaveric shoulders were tested in a robot-assisted shoulder simulator. Translational and rotational range of motion were reduced by the capsular shift, particularly with the shoulder at higher elevation angles. At 60 degrees of elevation, anterior translation was decreased 1.9 +/- 2.9 mm, and posterior translation was decreased 2.3 +/- 6.2 mm. External rotation was decreased 11.5 degrees +/- 10.2 degrees, and internal rotation was decreased 8.9 degrees + 5.7 degrees. Posterior capsular strain change was dependent on elevation angle. At 30 degrees of elevation, strain tended to increase 5.0% +/- 7.3% in the inferior aspect and 2.9% +/- 2.6% in the superior aspect, with no change detected in the medial aspect. At 60 degrees of elevation, strain increased 6.6% +/- 8.0%, 3.2% +/- 2.6%, and 4.4% +/- 3.5% in the inferior, middle, and superior aspects, respectively. Our results support the use of the medially based anterior shift for shoulders with anterior-inferior instability or multidirectional instability with posterior involvement.