Multidirectional instability of the shoulder: a systematic review with a novel classification

Abstract

Purpose

• A variety of instabilities are grouped under multidirectional instability (MDI) of the shoulder. This makes understanding its diagnostic process, presentation and treatment difficult due to lack of evidence-based consensus. This review aims to propose a novel classification for subtypes of MDI.

Methods

• A systematic search was performed on PubMed Medline and Embase. A combination of the following 'MeSH' and 'non-MesH' search terms were used: (1) Glenohumeral joint[tiab] OR Glenohumeral[tiab] OR Shoulder[tiab] OR Shoulder joint[tiab] OR Shoulder[MeSH] OR Shoulder joint[MeSH], (2) Multidirectional[tiab], (3) Instability[tiab] OR Joint instability[MeSH]. Sixty-eight publications which met our criteria were included.

Results

• There was a high degree of heterogeneity in the definition of MDI. Thirty-one studies (46%) included a trauma etiology in the definition, while 23 studies (34%) did not. Twenty-five studies (37%) excluded patients with labral or bony injuries. Only 15 (22%) studies defined MDI as a global instability (instability in all directions), while 28 (41%) studies considered MDI to be instability in two directions, of which one had to include the inferior direction. Six (9%) studies included the presence of global ligamentous laxity as part of the definition. To improve scientific accuracy, the authors propose a novel AB classification which considers traumatic etiology and the presence of hyperlaxity when subdividing MDI.

Conclusion

• MDI is defined as symptomatic instability of the shoulder joint in two or more directions. A comprehensive classification system that considers predisposing trauma and the presence of hyperlaxity can provide a more precise assessment of the various existing subtypes of MDI.

Level of Evidence

• III

Introduction

Multidirectional instability (MDI) of the shoulder is a complex and a rare condition. The incidence of MDI is thought to be low, although the exact incidence is difficult to establish due to the variations in diagnostic criteria of MDI over the years. Neer and Foster (1) published an early description of MDI in 1980, which served to highlight MDIs as a different entity from traumatic structural unidirectional instabilities. The key diagnostic characteristic of MDI was described as shoulder instability in two or more directions (1). Since then, however, there have been differences in the literature regarding the exact definition and classification of MDI. There are several reasons for the discrepancies in definition. MDI can present with a wide variety of symptoms, ranging from isolated shoulder pain on movement to frank multidirectional instability (2). In addition, some patients may be able to sublux or dislocate the glenohumeral joint voluntarily. These patients confound the clinical diagnosis as they are often asymptomatic and yet able to demonstrate significant subluxation or dislocation (3). The decision to include these patients within the MDI diagnosis is currently controversial as the literature has shown that voluntary dislocators may not respond as well to surgical intervention as non-voluntary ones.

It can also be challenging to determine a clear definition of MDI due to its intuitive overlap with generalized ligamentous laxity or hyperlaxity. While there can be an association between MDI and generalized ligamentous laxity (4), these terms should not be used interchangeably. Generalized ligamentous laxity can be physiological or associated with connective tissue disorders such as Marfan syndrome, Ehlers–Danlos syndrome, and benign joint hypermobility syndrome (5). These patients can be identified clinically utilizing Beighton’s criteria or if they exhibit external rotation ≥85° (6, 7). If these patients are asymptomatic, they should not be considered to have MDI, despite the apparent laxity of the joint in two or more directions. There is now an evolving distinction between asymptomatic generalized ligamentous laxity, unilateral instability on the background of generalized ligamentous laxity, and MDI (4).

Several classifications have been described for MDI, but no particular classification appears to be universally accepted. The instability classification by Rockwood (8) focused on the presence of a traumatic etiology and the volitional aspect of the dislocation. Rockwood grouped traumatic subluxations (without a frank dislocation) as type 1 and traumatic frank dislocations as type 2. MDI patients were grouped into type 3 – voluntary subluxation MDI with no trauma and type 4 – atraumatic involuntary subluxation. Thomas and Matsen (9) classically divided shoulder instability into one of two broad categories: traumatic, unilateral, Bankart, surgery (TUBS) and of atraumatic, multidirectional, bilateral, rehabilitation, inferior capsular shift (AMBRI). While AMBRI patients demonstrated many of the characteristics of an MDI patient, including some degree of laxity of the capsule, the exact definition of an MDI patient was not established. It is worthwhile noting that Thomas and Matsen’s description of the AMBRI group of patients was a conceptual one at the time and not based on published data (9). Gerber and Nyffeler (10) in 2002 were one of the first to include a multidirectional hyperlax subgroup in anterior instability explicitly. Thereafter, in 2010, Kuhn (11) published a new classification system for shoulder instability, termed as the FEDS (frequency, etiology, direction, and severity) classification and intentionally left out MDI in the classification. Kuhn described the concept of MDI as a flawed concept without consensus and opted to focus instead on the primary direction of instability. In addition, the FEDS classification did not include pain as a secondary sign of subtle instability. The variability of these existing classification systems makes it challenging to determine ideal treatment modalities and outcomes. Indeed, McFarland et al. (12) found that variations in criteria for diagnosis of MDI significantly affected the distribution of patients with the diagnosis and that the use of laxity testing resulted in an overestimation of patients with MDI. In addition, Warby et al. (13) performed a systematic review of conservative vs surgical treatment of MDI patients and found a high level of participant heterogeneity. There are thus high levels of heterogeneity currently surrounding the definition and classification of MDI.

This study aimed to conduct a systematic review to identify and highlight the variability of the definition of MDI in the existing literature and to propose a standardized classification to improve future clinical research.

Methods

This systematic review adhered to the principles outlined in the handbook of the Cochrane Collaboration (14) and the established guidelines from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The study protocol, including the search strategy, was registered on PROSPERO (registration number CRD42022293240).

Search strategy

A systematic search was performed on PubMed Medline and Embase from inception until 5 June 2022. A thorough combination of the following 'MeSH' and 'non-MesH' search terms and respective variations were used, with a manual search of the bibliography additionally performed: (i) Glenohumeral joint[tiab] OR Glenohumeral[tiab] OR Shoulder[tiab] OR Shoulder joint[tiab] OR Shoulder[MeSH] OR Shoulder joint[MeSH], (ii) Multidirectional[tiab], (iii) Instability[tiab] OR Joint instability[MeSH].

The following were considered for inclusion: (i) Studies involving human subjects with MDI; (ii) either diagnostic criteria for MDI stated in methodology or characteristics of MDI patients sufficiently described; (iii) at least three patients included in the study; (iv) level of evidence of study ranging 1 to 4. Studies were excluded if they fulfilled the following criteria: review articles, conference abstracts, commentaries, or letters to editors; cadaveric studies (without human subjects); less than three cases reported.

Study selection and data extraction

Two authors (PKAS and HSJ) independently screened and reviewed the studies for inclusion and exclusion in two stages: (i) title and abstract screen and (ii) full-text review of titles to determine study eligibility. Consensus or appeal to senior authors (AL and GN) were performed to resolve any discrepancies.

The primary data of interest were (i) the minimum number of directions to be classified MDI and dominant direction of instability; (ii) diagnostic criteria of MDI, exclusion criteria of the study, and, if separately described, definition of laxity; and (iii) pathological characteristics of MDI. Apart from the aforementioned outcomes, the following data were extracted in a standardized pro forma: study design and level of evidence, patient presentation, presence of pain or functional impairment, exclusion of voluntary dislocators or traumatic onset, and modality of assessment (clinic examination, examination under anesthesia, imaging, and arthroscopy).

Results

Study characteristics and quality assessment

The search strategy yielded 865 studies from two databases, with one additional study added through a manual search of the existing literature bibliography (Fig. 1). This comprised 528 unique studies after the removal of duplicates. Three hundred and eighty-five studies were excluded after title and abstract screening, with 143 studies remaining. We further excluded 75 studies following full-text review: 9 conference abstracts, 10 non-English studies, 3 studies with study types not fulfilling criteria, 15 studies with inaccessible full texts, and 38 studies without clear diagnostic criteria of MDI or clearly stated patient characteristics. A total of 68 studies were included in this systematic review after full-text review.

Figure 1.

PRISMA chart of the systematic literature review.

Definition of MDI

The definition of MDI is clinical and is derived from both patient history and physical examination. There are two important aspects of patients’ history: pain and symptomatic instability. The studies in this review were analyzed to determine the variability in the definition of a symptomatic MDI patient (Supplementary Table 1, see section on supplementary materials given at the end of this article).

When the history of presenting complaint was analyzed in this review, patients were deemed symptomatic when they presented with either pain, instability and/or subluxation, and/or dislocation in 45 studies (1, 13, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57).

Three studies defined a symptomatic patient as a patient with pain alone (58, 59, 60), while eight studies accepted instability and/or subluxation and/or dislocation alone (61, 62, 63, 64, 65, 66, 67, 68). Twelve studies did not explicitly state what patient history would constitute a symptomatic patient (69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80). Only one study included asymptomatic patients (75).

Twenty-four studies explicitly excluded voluntary dislocators (1, 19, 21, 22, 23, 28, 36, 37, 42, 43, 44, 45, 48, 50, 55, 59, 61, 62, 67, 68, 69, 70, 71, 73), while the rest of the studies did not.

In terms of etiology, 31 studies included both acute trauma and repetitive microtrauma (1, 13, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26, 28, 30, 35, 42, 43, 44, 49, 53, 56, 57, 58, 59, 62, 69, 70, 77, 78, 80). A single study included only repetitive microtrauma (32), while 33 studies excluded trauma as an etiology in the definition of MDI (19, 27, 29, 31, 33, 37, 41, 45, 47, 48, 50, 51, 52, 54, 55, 60, 63, 64, 65, 66, 67, 76, 79) Thirteen studies did not explicitly mention if trauma as an etiology was included or excluded (34, 36, 38, 39, 40, 46, 61, 68, 71, 72, 73, 74, 75).

Presence of labral or bony lesions

The presence of labral or bony lesions is closely associated with a traumatic etiology. Some of the published literature has chosen to exclude patients with labral or bony lesions. In this review, 25 studies excluded patients if bony lesions such as a SLAP tear, Bankart, or Hill–Sachs lesion was present (1, 26, 27, 31, 32, 33, 35, 36, 39, 40, 45, 54, 55, 58, 61, 63, 64, 65, 66, 67, 72, 73, 74, 76, 77).

Directions of instability

While it is traditionally accepted that MDI requires two or more directions of instability, the studies in this review had differing diagnostic criteria with regard to the number and type of direction of instability.

Fifteen studies (1, 25, 31, 33, 36, 38, 41, 43, 46, 50, 52, 55, 59, 66, 74) defined MDI based on global instability – that is to say, instability in all directions including anterior, posterior, and inferior direction. Twenty-eight studies (13, 16, 19, 21, 23, 24, 26, 27, 29, 30, 34, 35, 42, 44, 51, 53, 54, 56, 57, 62, 63, 65, 67, 69, 70, 75, 76, 80) defined MDI based on two or more directions, one of which had to include the inferior direction. Sixteen studies (17, 18, 20, 22, 28, 37, 45, 47, 48, 49, 60, 61, 71, 73, 77, 78) defined MDI based on two or more directions, where the inferior direction was not mandatory. Five studies (15, 39, 40, 58, 68) defined MDI as long as the inferior direction was present, and four studies (32, 64, 71, 79) were unclear with regard to direction of instability when defining MDI. When determining the presence of inferior instability on physical examination (Supplementary Table 2), all studies used the sulcus sign (Fig. 2), except for four which used inferior apprehension or subluxation (20, 32, 35, 50) and six studies where it was not explicitly mentioned (1, 18, 49, 77, 78, 79).

Figure 2.

Clinical photograph showing the presence of the sulcus sign of the left shoulder.

Presence of generalized laxity

Six studies included the presence of global ligamentous laxity as part of the definition of MDI (1, 32, 51, 58, 66, 80). Eight studies excluded patients with collagen-based disorders such as Ehlers–Danlos and Marfan syndrome from the MDI diagnosis (19, 30, 42, 44, 47, 54, 55, 71).

Discussion

This systematic review has highlighted that no consistent definition of MDI currently exists. MDI is defined as symptomatic instability in two or more directions. Establishing a standardized classification system is essential so that current assessments and treatment options can be more scientifically precise. In order to improve the accuracy of the classification, definitions of the symptomology commonly associated with MDI must also be established.

Symptomatic patient

In this review, it is apparent that the diagnosis of MDI should only be applied to symptomatic patients. Most studies (45/68, 66.2%) deemed symptomatic patients as those complaining of pain and/or pathological instability (apprehension, subluxation, and/or dislocation). Apprehension is defined as fear of imminent dislocation when placing the arm in abduction and external rotation and should be distinct from mere pain which can be related to inflammation, stiffness, and other shoulder pathologies (81, 82). The authors describe pathological instability as any instability that causes distress to the patient. It has also been previously described as instability that results in a loss of function and symptoms of pain, discomfort, paresthesia, apprehension, and/or fatigue (83, 84). It is important to recognize that pain alone can be a symptom of subtle instability (2). While pain alone as a symptom of instability was once deemed controversial, there is a growing body of evidence to suggest that pain can be the predominant symptom in micro-instability of the shoulder joint (85). During clinical examination, the direction of instability should also be determined with quantitative tests. Anterior and posterior instability can be assessed by utilizing a variety of clinical tests such as the apprehension and Jerk tests (3, 86, 87, 88). For inferior instability, the hyperabduction described by Gagey test can be utilized.⁹⁰ The authors recommend that the presence of pain and/or pathological instability as defined by apprehension, subluxation, and/or dislocation constitute a symptomatic patient.

Laxity and the unstable painful shoulder

Laxity is a normal, physiologic and asymptomatic finding that corresponds to translation of the humeral head in any direction to the glenoid (89). Laxity can be assessed with the sulcus sign (1), anterior–posterior drawer (87), hyperabduction tests (90), and external rotation of the elbow at the side (6, 89). The two former tests are only qualitative and should not routinely performed. It is thus poignant to note that while the presence of a sulcus sign only diagnoses laxity, it was used by the majority of the studies reviewed in the present article to determine inferior instability.

An unstable painful shoulder can also occur in patients with normal laxity after a traumatic event. However, these patients often present as pain only (as opposed to a sense of instability) during an apprehension maneuver in only one direction at clinical examination (2, 90). Careful pre-operative and/or arthroscopic examination often reveals evidence of subtle instability (i.e., labral tear, glenoid fracture, or Malgaigne (91) lesion) in majority of these patients (92). As subtle instability is only present in one direction and there is no associated hyperlaxity, the unstable painful shoulder should not be labeled as MDI or its variants.

Hyperlaxity

Hyperlaxity is constitutional, multidirectional, bilateral, and asymptomatic. It can result from systemic conditions or connective tissue disorders such as Marfan syndrome and Ehlers–Danlos syndrome (5). When generalized, hyperlaxity results in an increased range of motion of joints and distractibility (84) and is defined clinically with a Beighton score ≥4 (93). However, while the Beighton score can be easily performed, there is some concern that an elevated Beighton score does not translate to shoulder hyperlaxity, with published data showing poor correlation between the Beighton score and validated measures of shoulder laxity (5, 94). As such, with regard to the shoulder, hyperlaxity should be defined as increased mobility of the shoulder that is with an external rotation ≥85° with the elbow at the side (7, 95) (Fig. 3). Asymptomatic patients should again not be labeled as pathological laxity, regardless of the presence of generalized laxity or systemic collagen abnormalities. This non-pathological finding is a risk factor for instability but does not by itself demand treatment unless there is clear pathological laxity.

Figure 3.

(A) Clinical photograph of a patient in supine position demonstrating external rotation of the left shoulder of 90º. (B) Lateral view of the same patient clearly demonstrates left shoulder external rotation of 90º.

Pathological laxity, MDIs, and hypermobile painful shoulders

Pathological laxity of the inferior glenohumeral ligament is observed when passive abduction in neutral rotation in the glenohumeral joint is above 105°, if there is apprehension above 90° of abduction, or if a difference of more than 20° between the two shoulders is noted (96, 97).

MDIs represent a symptomatic instability of the glenohumeral joint as clearly shown by the present study. This was the most striking commonality among all the studies reviewed, with 67/68 (98.5%) in agreement. Another point of contention is the number of directions of instability (two vs three), and whether inferior instability is required to make a diagnosis of MDI. Neer and Foster’s original description stated that diagnosis of MDI requires instability in two or more planes of motion (1). In this review, 28/68 (41.2%) of the studies required two or more directions of instability, of which one had to be inferior, 16/68 (23.5%) of the studies followed the original description, simply requiring instability in two or more planes of motion, even in the absence of inferior instability, and 15/68 (22.1%) of the studies necessitate a global instability involving anterior, posterior, and inferior directions. As it stands, if the definition of MDI is made to mandatorily include inferior instability, almost one-quarter of the studies reviewed would be void. Certainly, while inferior instability is a sign of inferior capsular pathological laxity, the authors advocate that combined anterior and posterior instability should also be included within the MDI definition.

In addition, there appears to be no consensus in the articles within this systematic review regarding etiology. This may be heavily influenced by Matsen’s classic description of the AMBRI shoulder – that an atraumatic etiology is often the case in multidirectional instability. In addition, it is thought that the predominant pathophysiology of MDI is a redundant and capacious capsule (31, 76, 98). With such capsules, there is a large patulous inferior capsule and enlarged rotator interval. These abnormalities can result in an overall increased joint laxity due to the increase in the capsular volume. It is controversial whether or not overuse, repetitive microtrauma or overt major trauma significantly worsens the capsular integrity. Perhaps this thought process resulted in 36/68 (52.9%) of the studies excluding trauma as an etiology in the definition of MDI. While the authors agree that capsular hyperlaxity is likely pathophysiology for MDI, it is also important to consider traumatic MDI as a variant, as patients can often present in a similar fashion. This is the reason why any new classification should acknowledge the effect that trauma and its associated traumatic lesions can have on the definition and treatment of MDIs. The effect of a traumatic etiology can also differ between the hyperlax and normolax shoulder. Conceptually, the hyperlax shoulder may suffer less damage than a normolax shoulder for the same trauma, due to a lower inherent stability. Even though 25/68 (36.8%) of the reviewed studies excluded labral and bony injuries, the authors believe that the presence of such injuries should be accounted for within the classification as it can have a significant effect on treatment options and outcomes.

It thus appears that two multidirectional pathological hyperlaxity coexist: first, the classical MDI is a true subluxation or dislocation of the shoulder associated with structural lesions. It mostly occurs after trauma on young patients with hyperlaxity. Clinically, patients present an apprehension in more than one direction. Imaging reveals labral lesions and treatment is based on surgery associating repair of lesions and concomitant capsular shift. Secondly, the painful hypermobile shoulder occurs involuntarily in young hyperlax patients, often without any history of trauma. The complaint is mostly pain during mobilization, with or without subluxation, misdiagnosed as dislocation, and the treatment is conservative.

Voluntary dislocators

Voluntary dislocators can voluntarily reproduce subluxation or dislocation without distress. If these individuals were to be included within the definition of MDI, it would introduce significant heterogeneity as it is well accepted that these individuals do not require surgical treatment. A common demographic of these voluntary dislocators are children and pre-adolescents. The treatment of these patients would be for them to simply cease the habit (99). In the present review, 24/68 (35.3%) of the studies explicitly excluded voluntary dislocators. However, we included within the definition reproducible dislocators (that could have been previously voluntary dislocators); these individuals are able to reproduce a dislocation, even if this induces pain.

AB symptomatic multidirectional pathological laxity classification

Given the aforementioned controversies, it is timely for a new classification system to be established. Our proposed classification utilizes history taking and physical examination, which are both fundamental aspects of diagnosing MDI (Table 1). We excluded advanced imaging findings intentionally in an attempt to simplify the classification and improve its utility. In addition, this classification can also serve to differentiate pathological patients from physiological laxity who may not need advanced imaging in the first place.

Table 1.

Proposed classification of symptomatic multidirectional pathological laxity (AB symptomatic multidirectional pathological laxity classification).

	Normolax	Hyperlax
Atraumatic (A)	A1 Atraumatic MDI	A2 Hypermobile painful shoulder
Traumatic (B)	B1 Traumatic MDI	B2 Hyperlax MDI

The authors classify symptomatic multidirectional pathological laxity primarily as traumatic or atraumatic. The implications on treatment are that patients with a traumatic etiology may have concurrent labral or bony lesions in addition to a capacious capsule, which can be further refined through subsequent imaging workup. This can increase the technical difficulties in dealing with this subset of symptomatic multidirectional pathological laxity and requires more elements of surgical intervention. In addition, these ‘combination’ injuries cannot be compared to a pure MDI without bony lesions.

This classification divides patients with dynamic instability in two or more planes into two distinct groups, A and B, based on the presence of a traumatic etiology. This makes differentiating patients simple, as it can be performed based on clinical history alone. Within the groups, they are further differentiated based on the presence of hyperlaxity. This can be achieved by physical examination of the patients. As such, the AB classification can be easily utilized in the outpatient setting.

A1: Atraumatic MDI

Clinical presentation: Patients in this group present with symptomatic multidirectional instability without a traumatic etiology. It is important to differentiate this group from voluntary dislocators, who are asymptomatic.

Physical examination: There will be pathological instability in two or more directions of the shoulder joint. Patients are normolax and should not demonstrate ≥85° of external rotation of the shoulder joint.

Imaging: Standard radiographs of the shoulder joint may not demonstrate any abnormality, but MRI will reveal a capacious joint capsule and an absence of associated labral or bony lesions (Fig. 4).

Figure 4.

Axial T2-weighted MRI scan of the right shoulder revealing a capacious joint capsule with no associated labral or bony lesions.

Treatment: These patients will benefit from an initial course of physiotherapy. In the event of failure of non-surgical treatment, pancapsular plication (open or arthroscopic) can be considered. Surgical outcomes of group A patients are often less effective compared to group B patients due to the lack of discrete labral or osseous deficiencies (36, 100).

A2: Hypermobile painful shoulder

Clinical presentation: The hypermobile painful shoulder occurs in young patients without any history of trauma. The complaint is mostly pain during mobilization, with or without subluxation, and can be misdiagnosed as dislocation. These patients might have been previously voluntary dislocators that became reproducible ones.

Physical examination: There will be pathological instability in two or more directions of the shoulder joint. However, pain and/or subluxation is often the predominant sign, rather than overt dislocation. Patients will demonstrate hyperlaxity, as determined by ≥85° of external rotation of the shoulder joint.

Imaging: Standard radiographs of the shoulder joint may not demonstrate any abnormality but MRI will reveal a capacious joint capsule and an absence of associated labral or bony lesions.

Treatment: Non-surgical treatment is recommended in this subset of patients (101, 102).

Analgesics and physiotherapy with an emphasis on strengthening of the rotator cuff, deltoid, and peri-scapular stabilizers have yielded positive results (47).

B1: Traumatic MDI

Clinical presentation: Patients in this group present with symptomatic multidirectional instability after a traumatic etiology. Repetitive microtrauma is not deemed as a traumatic etiology.

Physical examination: There will be pathological instability in two or more directions of the shoulder joint. Patients are normolax and should not demonstrate ≥85° of external rotation of the shoulder joint.

Imaging: Standard radiographs of the shoulder joint should be carefully assessed for bony lesions of the glenoid and humeral head. Advanced imaging such as MRI is recommended to identify the presence of associated isolated or circumferential labral lesions, as well as bony lesions of the glenoid and humeral head (Fig. 5). There are often combination injuries resulting in the multidirectional nature of instability.

Figure 5.

(A) Anteroposterior plain radiograph showing Hill–Sachs and reverse Hill–Sachs lesions. (B) Axial CT arthrogram of the right shoulder showing the presence of a Hill–Sachs and reverse Hill–Sachs lesion.

Treatment: The ideal treatment is dependent on the symptomology, patient characteristics, and the extent of associated labral/osseous injuries. There should be a low threshold for surgical intervention in the event of persistent symptoms. Treatment consists of repair of the labral/osseous lesions and a concomitant capsular shift.

B2: Hyperlax MDI

Clinical presentation: Patients in this group present with symptomatic multidirectional instability after a traumatic etiology.

Physical examination: There will be pathological instability in two or more directions of the shoulder joint. Examination may reveal multidirectional subluxation and/or dislocation. Patients will demonstrate hyperlaxity, as determined by ≥85° of external rotation of the shoulder joint.

Imaging: Standard radiographs of the shoulder joint should be carefully assessed for bony lesions of the glenoid and humeral head. MRI will reveal a capacious joint capsule in addition to associated isolated or circumferential labral lesions, as well as bony lesions of the glenoid and humeral head (Fig. 6).

Figure 6.

Axial T2-weighted MRI scan of the right shoulder revealing a Hill–Sachs lesion (star), posterior labral lesion (arrow) with a capacious joint capsule.

Treatment: The ideal treatment is dependent on the symptomology, patient characteristics and the extent of associated labral/osseous injuries. There should be a low threshold for surgical intervention in the event of persistent symptoms.

It is the authors’ intention that, with this new classification system, the various subtypes of symptomatic multidirectional pathological laxity can be more accurately defined and compared. The strengths of this classification system are that it is easy to use and takes into consideration the classical controversies of symptomatic multidirectional pathological laxity, mainly: trauma as an etiology and the presence of pathological laxity. Doing so will allow for a more precise scientific analysis of symptomatic multidirectional pathological laxity and its treatment outcomes. This classification will also allow the inclusion of heterogenous studies that have previously been performed.

Conclusion

Multidirectional instability is defined as symptomatic instability of the shoulder joint in two or more directions. A comprehensive classification system that considers predisposing trauma and the presence of concomitant pathological laxity can provide a more precise assessment of the various existing subtypes of multidirectional instability.

ICMJE Conflict of Interest Statement

Alexandre Lädermann is a paid consultant for Stryker, Arthrex, and Medacta. He is the founder of FORE, BeeMed, and Med4Cast. He owns stock options of Medacta and Follow Health. The other authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the study reported.

Funding Statement

The study was funded by FORE (Foundation for Research and Teaching in Orthopedics, Sports Medicine, Trauma and Imaging in the Musculoskeletal System) (grant no. FORE 2022-38).

Patient consent

Written informed consent for publication of clinical details and/or clinical images was obtained from the patient/parent/guardian/relative of the patient.