Extensive skin laceration on the forearm due to closed reduction of a dislocated shoulder. A case report.

We report the case of an 80-year-old man who suffered an anteroinferior shoulder dislocation with rupture of the rotator cuff following a fall. An attempt at closed reduction under analgosedation resulted in extensive skin laceration on the elbow and forearm. The wound treatment was complex and resulted in numerous complications.

[Can a fall onto the shoulder (direct impact) cause a rotator cuff tear?] / Kann ein Sturz auf die Schulter (Direktanprall) einen Riss der Rotatorenmanschette verursachen?

The question of whether a fall directly onto the shoulder can cause a rotator cuff tear has occupied doctors (and courts) for many years. Experts who rely on the medical insurance literature usually reject the causality of the incident. There are no scientific studies on this. The report below describes a typical case in which a fall directly onto the shoulder caused a massive rotator cuff tear.

Devastating Pneumococcal Arthritis of the Shoulder After Two Corticosteroid Injections.

A 36-year-old man was treated with two intraarticular corticoid injections for intense pain and severely decreased range of motion of his left shoulder. After the second injection, he came back with fulminant arthritis. Microbiological examination revealed streptococcus pneumoniae. Open debridement, long-term antibiotics, and total shoulder replacement were necessary to restore acceptable shoulder function. The fulminant course with rapid destruction of the joint illustrates the risks of intraarticular corticoid injections. This case also shows that the diagnosis should be accurately made and risk factors excluded before considering injection as a treatment.

Can a simple fall cause a rotator cuff tear? Literature review and biomechanical considerations.

PURPOSE: A simple fall on the shoulder is often referred to as minor trauma that cannot cause a tendon tear but at best reveal a pre-existing rotator cuff pathology. We wanted to know whether this statement was true. The purpose of our study was therefore to summarize the causes of acute rotator cuff tears reported in the literature and provide a biomechanical explanation for tendon tears diagnosed after a fall. METHOD: We searched PubMed and included studies reporting rotator cuff tears occurring due to a trauma. The number of cases, the tendons involved, the age of the patients, and the nature of trauma were summarized. In addition, we noted any information provided by the authors on the pathogenesis of acute tendon ruptures. RESULTS: Sixty-seven articles with a total of 4061 traumatic rotator cuff tears met the inclusion criteria. A simple fall was the most common cause (725 cases) and the supraspinatus tendon was most frequently affected. The postulated pathomechanism is a sudden stretch of the tendon-muscle unit while contracting (eccentric loading). CONCLUSION: A simple fall can cause an acute rotator cuff tear and fall-related tears are not restricted to young individuals. They can affect patients of any age. The stresses occurring within the rotator cuff during an attempt to cushion a fall may locally exceed the tensile strength of the tendon fibers and cause a partial or full-thickness tear.

Causes of acromion and scapular spine fractures following reverse shoulder arthroplasty: a retrospective analysis and literature review.

PURPOSE: Fractures of the acromion and the scapular spine are serious complications after reverse total shoulder arthroplasty. They concern about 4 to 5% of the patients and always result in a significant deterioration of shoulder function. Different causes have been taken into consideration, particularly stress or fatigue fractures. The purpose of the present study was to analyse our own cases and to discuss the causes reported in the literature. METHODS: We reviewed our shoulder arthroplasty registry and the consultation reports of the last ten years. The charts and radiographs of all patients who had a post-operative fracture of the acromion or the scapular spine were carefully examined and the results were compared with those of an age- and gender-matched control group. RESULTS: Twelve patients with an average age of 79 years sustained a fracture of the acromion (n = 6) or the scapular spine (n = 6). The time interval between the operation and the fracture averaged 26 months and ranged from three weeks to 70 months. Eight patients (67%) had a trauma. Seven of them reported a fall on the corresponding shoulder and one a heavy blow on the acromion. The four non-traumatic fractures were attributed to poor bone quality. All 12 patients had immediate pain and difficulty to actively elevate the affected arm. The time interval between the fracture and its diagnosis averaged ten weeks (0 to 10 months). At final follow-up, all patients could reach their face and refused further surgery. Two patients rated their result as good, six as acceptable and four as poor. CONCLUSIONS: Our study cannot support the hypothesis that most acromion and scapular spine fractures after RSA are the result of increased tension in the deltoid or stress fractures. In our series, the majority of the fractures were related to a fall. Implantation of a reverse prosthesis exposes the acromion and makes it more vulnerable to direct trauma. Non-traumatic fractures were associated with poor bone quality.

Editorial Commentary: Does the Morphology of the Acromion Explain All Rotator Cuff Tears?

Given the high prevalence of rotator cuff tears and their socioeconomic impact, surgeons and researchers have tried to understand their etiology and pathomechanism for almost hundred years. Articles about tendon degeneration with increasing age dominate the literature, and numerous factors contributing to tendon degeneration have been identified. One of them, the lateral extension of the acromion, as quantitated using the acromion index or the critical shoulder angle, has become very popular in the last few years. Other big tendons in the human body, such as the distal biceps tendon, the Achilles tendon, or the patellar tendon, are also subject to degenerative changes, but they normally do not lose their continuity without a relevant trauma. This raises 2 questions: What makes the rotator cuff different from the other tendons, and why are there not more rotator cuff tears related to a trauma? What we do know is that risk factors for rotator cuff tear include trauma, dominant arm, and age, whereas the effect of a large acromion is more ambiguous.

Radiological and biomechanical assessment of displaced greater tuberosity fractures.

PURPOSE: Greater tuberosity fractures are challenging lesions concerning decision-making. In order to improve our treatment algorithm, we developed a new method, which allows predicting a possible subacromial conflict on standard anteroposterior radiographs, considering not only the displacement of the fragment but also the width of the subacromial space. METHODS: The measurement technique consisted of drawing three concentric circles on true anteroposterior radiographs. The inner circle (radius Rh) perfectly matched the humeral head surface. The medial circle (radius Rt) was tangent to the greater tuberosity, and the outer circle (radius Ra) touched the undersurface of the acromion. The ratio Rt/Rh, which describes how much the greater tuberosity projects above the articular surface, and the relationship (Rt-Rh)/(Ra-Rh), which quantifies the space occupied by the greater tuberosity under the acromion, were calculated and called Greater Tuberosity Index and Impingement Index, respectively. Five dry humeri were used to assess the influence of rotation and abduction on the Greater Tuberosity Index. The radiographs of 80 shoulders without any osseous pathology were analyzed to obtain reference values for both indices. Finally, greater tuberosity fractures with different displacements were created in five cadaver specimens, and subacromial impingement was correlated with these parameters. RESULTS: On anteroposterior radiographs, the greater tuberosity was most prominent in neutral rotation, regardless of abduction. In shoulders without osseous pathology, the Greater Tuberosity Index and the Impingement Index averaged 1.15 (range 1.06-1.28) and 0.46 (range 0.21-0.67). In the biomechanical experiments, the Impingement Index was a better discriminator for subacromial impingement than the Greater Tuberosity Index. A fracture with a displacement corresponding to an Impingement Index of 0.71 or greater was associated with subacromial impingement. CONCLUSIONS: Reduction of a displaced greater tuberosity fragment should be considered if the Impingement Index is 0.7 or greater. The measurement method is simple and reliable and has the potential to be used for the assessment of subacromial impingement in other conditions.

Acromion and glenoid shape: Why are they important predictive factors for the future of our shoulders?

The shape of the acromion differs between patients with degenerative rotator cuff tears and individuals without rotator cuff pathology.It can be assessed in the sagittal plane (acromion type, acromion slope) and in the coronal plane (lateral acromion angle, acromion index, critical shoulder angle).The inter-observer reliability is better for the measurements in the coronal plane.A large lateral extension (high acromion index or high critical shoulder angle) and a lateral down-sloping of the acromion (low lateral acromion angle) are associated with full-thickness supraspinatus tears.The significance of glenoid inclination for rotator cuff disease is less clear.The postulated patho-mechanism is the compression of the supraspinatus tendon between the humeral head and the acromion. Bursal side tears might be caused by friction and abrasion of the tendon. Articular side tears could be due to impairment of the gliding mechanism between tendon fibrils leading to local stress concentration. Further research is needed to understand the exact pathomechanism of tendon degeneration and tear. Cite this article: EFORT Open Rev 2017;2. DOI: 10.1302/2058-5241.2.160076. Originally published online at www.efortopenreviews.org.

Leukocyte- and platelet-rich fibrin (L-PRF) for long-term delivery of growth factor in rotator cuff repair: review, preliminary results and future directions.

Surgical repair of the rotator cuff repair is one of the most common procedures in orthopedic surgery. Despite it being the focus of much research, the physiological tendon-bone insertion is not recreated following repair and there is an anatomic non-healing rate of up to 94%. During the healing phase, several growth factors are upregulated that induce cellular proliferation and matrix deposition. Subsequently, this provisional matrix is replaced by the definitive matrix. Leukocyte- and platelet-rich fibrin (L-PRF) contain growth factors and has a stable dense fibrin matrix. Therefore, use of LPRF in rotator cuff repair is theoretically attractive. The aim of the present study was to determine 1) the optimal protocol to achieve the highest leukocyte content; 2) whether L-PRF releases growth factors in a sustained manner over 28 days; 3) whether standard/gelatinous or dry/compressed matrix preparation methods result in higher growth factor concentrations. 1) The standard L-PRF centrifugation protocol with 400 x g showed the highest concentration of platelets and leukocytes. 2) The L-PRF clots cultured in medium showed a continuous slow release with an increase in the absolute release of growth factors TGF-ß1, VEGF and MPO in the first 7 days, and for IGF1, PDGF-AB and platelet activity (PF4=CXCL4) in the first 8 hours, followed by a decrease to close to zero at 28 days. Significantly higher levels of growth factor were expressed relative to the control values of normal blood at each culture time point. 3) Except for MPO and the TGFß-1, there was always a tendency towards higher release of growth factors (i.e., CXCL4, IGF-1, PDGF-AB, and VEGF) in the standard/gelatinous- compared to the dry/compressed group. L-PRF in its optimal standard/gelatinous-type matrix can store and deliver locally specific healing growth factors for up to 28 days and may be a useful adjunct in rotator cuff repair.

Reverse total shoulder arthroplasty.

The radical changes in prosthetic design made in the mid 1980s transformed the historically poorly performing reverse ball-and-socket total shoulder prosthesis into a highly successful salvage implant for pseudoparalytic, severely rotator cuff-deficient shoulders. Moving the center of rotation more medial and distal as well as implanting a large glenoid hemisphere that articulates with a humeral cup in 155 degrees of valgus are the biomechanical keys to sometimes spectacular short- to mid-term results. Use of the reverse total shoulder arthroplasty device allows salvage of injuries that previously were beyond surgical treatment. However, this technique has a complication rate approximately three times that of conventional arthroplasty. Radiographic and clinical results appear to deteriorate over time. Proper patient selection and attention to technical details are needed to reduce the currently high complication rate.

Effects of glenoid component version on humeral head displacement and joint reaction forces: an experimental study.

The purpose of this study was to determine whether changes in glenoid version are associated with humeral head displacement and changes in the joint reaction forces, as these might contribute to instability or loosening in total shoulder replacement. A total shoulder prosthesis was implanted in neutral version in 6 cadaveric shoulders. Glenoid version was then changed in steps of 4 degrees toward more anteversion and retroversion. An increase in anteversion resulted in anterior translation of the humeral head and in eccentric loading of the anterior part of the glenoid. Retroversion was associated with posterior displacement and posterior loading of the glenoid. A change in rotation of the humeral component did not compensate for altered version of the glenoid component. These results suggest that both instability and glenoid component loosening may be related to the version of the glenoid component. Therefore, assessment of loosening and instability justifies precise assessment of glenoid component version.

Association of a large lateral extension of the acromion with rotator cuff tears.

BACKGROUND: Factors predisposing to tearing of the rotator cuff are poorly understood. We have observed that the acromion of patients with a rotator cuff tear very often appears large on anteroposterior radiographs or during surgery. The purpose of this study was to quantify the lateral extension of the acromion in patients with a full-thickness rotator cuff tear and in patients with an intact rotator cuff. METHODS: The lateral extension of the acromion was assessed on true anteroposterior radiographs made with the arm in neutral rotation. The distance from the glenoid plane to the lateral border of the acromion was divided by the distance from the glenoid plane to the lateral aspect of the humeral head to calculate the acromion index. This index was determined in a group of 102 patients (average age, 65.0 years) with a proven full-thickness rotator cuff tear, in an age and gender-matched group of forty-seven patients (average age, 63.7 years) with osteoarthritis of the shoulder and an intact rotator cuff, and in an age and gender-matched control group of seventy volunteers (average age, 64.4 years) with an intact rotator cuff as demonstrated by ultrasonography. RESULTS: The average acromion index (and standard deviation) was 0.73 +/- 0.06 in the shoulders with a full-thickness tear, 0.60 +/- 0.08 in those with osteoarthritis and an intact rotator cuff, and 0.64 +/- 0.06 in the asymptomatic, normal shoulders with an intact rotator cuff. The difference between the index in the shoulders with a full-thickness supraspinatus tear and the index in those with an intact rotator cuff was highly significant (p < 0.0001). CONCLUSIONS: A large lateral extension of the acromion appears to be associated with full-thickness tearing of the rotator cuff.

The effect of cementing technique on structural fixation of pegged glenoid components in total shoulder arthroplasty.

Although loosening of cemented glenoid components is one of the major complications of total shoulder arthroplasty, there is little information about factors affecting initial fixation of these components in the scapular neck. This study was performed to assess the characteristics of structural fixation of pegged glenoid components, if inserted with two different recommended cementing techniques. Six fresh-frozen shoulder specimens and two types of glenoid components were used. The glenoids were prepared according to the instructions and with the instrumentation of the manufacturer. In 3 specimens, the bone cement was inserted into the peg receiving holes (n = 12) and applied to the back surface of the glenoid component with a syringe. In the other 3 specimens, the cement was inserted into the holes (n = 15) by use of pure finger pressure: no cement was applied on the backside of the component. Micro-computed tomography scans with a resolution of 36 microm showed an intact cement mantle around all 12 pegs (100%) when a syringe was used. An incomplete cement plug was found in 7 of 15 pegs (47%) when the finger-pressure technique was used. Cement penetration into the cancellous bone was deeper in osteopenic bone. Application of bone cement on the backside of the glenoid prosthesis improved seating by filling out small spaces between bone and polyethylene resulting from irregularities after reaming or local cement extrusion from a drill hole. The fixation of a pegged glenoid component is better if the holes are filled with cement under pressure by use of a syringe and if cement is applied to the back of the glenoid component than if cement is inserted with pure finger pressure and no cement is applied to the back surface of the component.

Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis.

The presence of a notch at the inferior part of the scapular neck is a common radiographic finding in patients treated with a reverse Delta III shoulder prosthesis. It is thought that this notch is a result of mechanical contact between the polyethylene cup of the humeral implant and the inferior glenoid pole during adduction of the arm. This in vitro study assessed the effect of glenoid component positioning on glenohumeral range of motion in 8 shoulder specimens. Four different positions of the glenosphere were tested: glenosphere centered on the glenoid, leaving the inferior glenoid rim uncovered (configuration A); glenosphere flush with the inferior glenoid rim (configuration B); glenosphere extending beyond the inferior glenoid rim (configuration C); and glenosphere tilted downward 15 degrees (configuration D). The respective mean adduction and abduction angles in the scapular plane were -25 degrees and 67 degrees for configuration A, -14 degrees and 68 degrees for configuration B, -1 degrees and 81 degrees for configuration C, and -9 degrees and 75 degrees for configuration D. Placing the glenosphere distally (test configuration C) significantly improved adduction and abduction angles compared with all other test configurations (P < .001).

Radiographic and computed tomography analysis of cemented pegged polyethylene glenoid components in total shoulder replacement.

BACKGROUND: Glenoid loosening continues to be the primary reason for failure of total shoulder arthroplasty. The purpose of this study was to evaluate, with use of a sensitive and reproducible imaging method, the radiographic and clinical results of total shoulder replacement with a pegged, cemented polyethylene glenoid implant. METHODS: Forty-three patients (forty-seven shoulders) underwent a total shoulder replacement with a cemented polyethylene glenoid component with four threaded pegs. The patients were examined clinically, with fluoroscopically guided radiographs, and with computed tomography at an average of forty months. In addition to conventional scoring of radiographic lucency, an 18-point scoring system was used to quantify cement-peg lucencies in six zones of the back surface of the glenoid component as seen on computed tomography scans. RESULTS: On the average, the absolute Constant score improved from 39 points preoperatively to 70 points at the time of follow-up (p = 0.0001) and the pain score improved from 5 to 13 points (p = 0.001). The mean active anterior elevation improved by 34 degrees (p = 0.001) and the mean abduction, by 46 degrees (p = 0.006). Two patients had symptomatic glenoid loosening requiring revision. Twenty-one of the forty-seven shoulders had radiographic lucency around the glenoid pegs, and nine had progression of the lucency by at least two grades. Computed tomography detected lucencies, primarily at the bone-cement interface, in thirty-six shoulders. The scores for the lucencies seen on the computed tomography scans were associated with the radiographic lucency scores (p < 0.001), pain scores (p = 0.04), and abduction strength (p = 0.02). Computed tomography was more sensitive than radiography with regard to identifying the number of pegs associated with lucency and the size of the lucencies. The overall reproducibility of the scoring based on the computed tomography was higher than that of the radiographic scoring. CONCLUSIONS: Computed tomography provided a more sensitive and reproducible tool for the assessment of loosening of pegged glenoid components than did fluoroscopically guided conventional radiography. Further improvement in implant design and fixation technique appears to be necessary for long-term success of cemented glenoid components.

Influence of humeral prosthesis height on biomechanics of glenohumeral abduction. An in vitro study.

BACKGROUND: During shoulder replacement surgery, the normal height of the proximal part of the humerus relative to the tuberosities frequently is not restored because of differences in prosthetic geometry or problems with surgical technique. The purpose of the present study was to determine the effect of humeral prosthesis height on range of motion and on the moment arms of the rotator cuff muscles during glenohumeral abduction. METHODS: Tendon excursions and abduction angles were recorded simultaneously in six cadaveric specimens during passive glenohumeral abduction in the scapular plane. Moment arms were calculated for each muscle by computing the slope of the tendon excursion-versus-glenohumeral abduction angle relationship. The experiments were carried out with the intact joint and after replacement of the humeral head with a prosthesis that was inserted in an anatomically correct position as well as 5 and 10 mm too high. RESULTS: Insertion of the prosthesis in positions that were 5 and 10 mm too high resulted in significant and marked reductions of the maximum abduction angle of 10 degrees (range, 5 degrees to 18 degrees ) and 16 degrees (range, 12 degrees to 20 degrees ), respectively. In addition, the moment arms of the infraspinatus and subscapularis decreased by 4 to 10 mm. This corresponded to a 20% to 50% decrease of the abduction moment arms of the infraspinatus and an approximately 50% to 100% decrease of the abduction moment arms of the subscapularis, depending on the abduction angle and the part of the muscle being considered. CONCLUSIONS: If a humeral head prosthesis is placed too high relative to the tuberosities, shoulder function is impaired by two potential mechanisms: (1) the inferior capsule becomes tight at lower abduction angles and limits abduction, and (2) the center of rotation is displaced upward in relation to the line of action of the rotator cuff muscles, resulting in smaller moment arms and decreased abduction moments of the respective muscles. CLINICAL RELEVANCE: In patients managed with shoulder replacement surgery, limitation of range of motion, loss of abduction strength, and overload with long-term failure of the supraspinatus tendon are potential consequences of positioning the humeral head of the prosthesis proximal to the anatomic position.

The effect of capsular tightening on humeral head translations.

UNLABELLED: Idiopathic or surgical tightening of the glenohumeral joint capsule may cause displacement of the humeral head relative to the glenoid fossa and favor the development of instability and/or osteoarthritis. In the present investigation the relative position of the humerus to the glenoid fossa was determined at the end of the ranges of eight different passive movements before and after selective capsular plication in eight cadaveric shoulders to study the effects of selective capsular plications on the kinematics of the shoulder. While the capsule was in its unaltered state, translation of the humeral head was 3.8 mm superiorly in abduction, 7.3 mm antero-superiorly in flexion. In internal rotation in 0 degrees, 45 degrees and 90 degrees of abduction the head moved 6.1, 8.0 and 12.0 mm antero-inferiorly. In external rotation at 0 degrees of abduction the translation was 0.9 mm antero-inferiorly, at 45 degrees and 90 degrees of abduction it was 4.3 and 5.6 mm postero-inferiorly, respectively. Plications of the anterior part of the capsule reproducibly and significantly either increased or decreased translations during flexion (up to 5.9 mm anteriorly and up to 3.8 mm inferiorly), external rotation (up to 2.9 mm posteriorly and 1 mm inferiorly) and internal rotation (from 5.5 mm posteriorly to 2 mm anteriorly and up to 2.2 mm superiorly). Posterior plications had only little effect on translations (mainly a decrease of anterior translation during flexion of 2.8 mm). CLINICAL RELEVANCE: The 'obligate' glenohumeral translations which occur towards the end of passive shoulder movements are altered in a reproducible fashion by tightening specific parts of the glenohumeral joint capsule, as often carried out in treatment of shoulder instability. These alterations of the kinematics of the glenohumeral joint may be relevant for the development of static subluxation and osteoarthitis as seen after too tight plication in the treatment of instability [Int. Orthop. (SICOT) 67-B (1985) 709; J. Bone Joint Surg. Am. 72 (1990) 1193; J. Bone Joint Surg. Am. 66-A (1984) 169; J. Bone Joint Surg. Am. 65 (1983) 456].

Measurement of glenoid version: conventional radiographs versus computed tomography scans.

Glenoid version seems to play an important role in the stability and loading of the glenohumeral joint. The purpose of this study was to compare measurements of glenoid version on axillary views and computed tomography (CT) scans. Radiographs and CT scans of 25 patients evaluated predominantly for glenohumeral joint instability and 25 patients after implantation of a total shoulder prosthesis were analyzed by 3 independent observers. In all patients glenoid version was determined on an axillary view and on a CT scan at the mid-glenoid level. The mean glenoid version measured on CT scans was 3 degrees of retroversion in the instability group (range, 7 degrees of anteversion to 16 degrees of retroversion) and 2 degrees of anteversion in the total shoulder prosthesis group (range, 16 degrees of anteversion to 23 degrees of retroversion). Glenoid retroversion was overestimated on plain radiographs in 86%. The mean difference between measurements of glenoid version on axillary views and CT cuts was 6.5 degrees (range, 0 degrees -21 degrees ), and the coefficient of correlation between these measurements was 0.33 in the instability group and 0.67 in the prosthesis group. In conclusion, glenoid version cannot be determined accurately on standard axillary radiographs, either preoperatively or postoperatively. Studies that assess the role of glenoid component orientation should use a reproducible method of assessment such as CT.

Failure of suture material at suture anchor eyelets.

PURPOSE: In the repair of soft tissue to bone using suture anchors, failure of the suture material can occur at the anchor eyelet. This study examines the load strength at which suture material fails with different metallic suture anchor eyelets. TYPE OF STUDY: Biomechanical study. METHODS: Suture material (Ethibond No. 2, Ethicon, Norderstedt, Germany) was pulled out from 22 metallic suture anchor models at 60 mm/min, and tensile load at failure and failure mode were recorded. Tests were performed either by simultaneous pulling on 2 suture limbs in 3 different directions (straight, at 45 degrees, and at 45 degrees rotated by 90 degrees to the suture anchor axis) or by pulling on 1 suture limb while measuring the resulting force on the second limb. All tests were performed until suture failure. Pulling was performed in single tests on an Instron materials testing machine (High Wycombe, UK), with the anchors held by a vise. RESULTS: In all cases, the suture failed at the anchor eyelet. Failure load at straight loading ranged from 116 +/- 5 N to 226 +/- 5 N and from 69 +/- 5 N to 193 +/- 7 N when loaded at an angle of 45 degrees. The best results were found with the Statak 5.2-mm (Zimmer, Warsaw, IN): 177 N; Corkscrew 6.5-mm anchor (Arthrex, Naples, FL): 174 N; and PeBA 4.0-mm anchor (OBL Orthopaedic Biosystems, Scottsdale, AZ): 169 N. With each eyelet, sutures failed preferentially in 1 direction, depending on the presence of sharp edges. CONCLUSIONS: Suture material can be cut at suture anchor eyelets. Failure load depends on sharp edges on the eyelet and occurs at forces up to 73% below the breaking strength of the suture material on a smooth hook. Anchors with suture-protecting channels are particularly sensitive to the orientation in which the sutures are loaded.

Classification of glenohumeral joint instability.

Shoulder instabilities have been classified according to the etiology, the direction of instability, or on combinations thereof. The current authors describe a classification system, which distinguishes between static instabilities, dynamic instabilities, and voluntary dislocation. Static instabilities are defined by the absence of classic symptoms of instability and are associated with rotator cuff or degenerative joint disease. The diagnosis is radiologic, not clinical. Dynamic instabilities are initiated by a trauma and may be associated with capsulolabral lesions, defined glenoid rim lesions, or with hyperlaxity. They may be unidirectional or multidirectional. Voluntary dislocation is classified separately because dislocations do not occur inadvertently but under voluntary control of the patient.