Background
Traumatic instability of the shoulder joint is generally associated with a Bankart lesion, in which the anteroinferior glenoid labrum and inferior glenohumeral ligament (IGHL) detach from the glenoid. , Although open or arthroscopic surgery is the standard treatment approach for shoulder instability, there are several preoperative complications that directly influence patient outcome and surgical success. The most pertinent include the presence of glenoid bone loss, Hill–Sachs lesions (HSL), Bankart lesions, humeral avulsion of glenohumeral ligaments (HAGL), and anterior labroligamentous periosteal sleeve avulsion (ALPSA). As a result, surgeons must be able to properly identify these factors before surgical intervention and adjust treatment strategies accordingly. All of this is important to prevent complications such as recurrence after surgical intervention.
History and Physical Examination
A thorough history is a crucial first step in assessing a patient with suspected shoulder instability. Evaluation should begin with age, gender, antecedent function, hand dominance, degree of activity, and level of sports participation. Although these questions are seemingly standard, the answers may exclude the patient from surgery or provide evidence of preoperative complications. The history should also include specific information regarding age of first instability event, number of dislocations or subluxations, mechanism of injury, required manual reductions, positioning during injury, and prior intervention attempts. These details may provide insight into the risk of attritional bone loss and injury recurrence. For example, patients with glenoid bone loss typically describe a high-energy mechanism of injury and a prolonged history of instability symptoms. Furthermore, the age of first dislocation is an important prognostic indicator because approximately 90% of patients under the age of 20 years and 10% of patients over the age of 40 years can experience recurrence. Overall, the history provides critical information for determining the presence of preoperative complications before imaging and helps focus the physical exam.
The physical examination of a patient with shoulder instability is equally essential and includes direct comparison to the contralateral shoulder. General appearance can reveal muscular atrophy, surgical scars, and asymmetry. Palpation of the anterior and posterior glenohumeral, acromioclavicular, and sternoclavicular joints may identify point tenderness. However, location of pain is not a specific indicator of glenohumeral instability. Structure, function, neurovascular status, strength, and range of motion (ROM) should also be tested during the physical examination. Limited ROM may indicate additional pathology, diagnoses, or need for treatment. Specifically, significant stiffness must be addressed before surgical intervention to avoid progressive loss of motion. Shoulder stability must also be assessed to determine the presence of joint laxity, specifically within the various glenohumeral ligaments, because preexisting joint laxity has been associated with recurrence and postoperative failure rates. Elbow hyperextension, metacarpophalangeal hyperextension, and the thumb-to-forearm test should be particularly noted.
Additional evaluation of glenohumeral joint laxity may include the “sulcus sign” and “load and shift” tests. The sulcus sign test assesses the integrity of the rotator interval, which is comprised of the superior glenohumeral ligament (SGHL) and the coracohumeral ligament. The humerus is pulled inferiorly with the arm in 0 degrees of abduction and graded by the degree of subluxation. If the sulcus sign disappears when the test is repeated in external rotation, the rotator interval is considered competent. Laxity of the anterior and posterior capsule restraints can also be assessed by differing degrees of arm abduction during the anterior load and shift test. While the patient is supine, a small compressive load is applied to the humeral head for centralization within the glenoid fossa, and an anterior force is applied to translate the humeral head anteriorly. The arm is manipulated to neutral, 45 degrees, and 90 degrees of abduction to test the SGHL, middle glenohumeral ligament, and IGHL, respectively. Both maneuvers are useful in providing insight into the presence of instability and the possibility of a Bankart lesion. ,
The apprehension test is also useful in evaluating patients with anterior instability, aiding in diagnosis, and determining risk of recurrence. Progressive external rotation is applied to the shoulder with 90 degrees abduction and 90 degrees flexion of the elbow. Pain occurs in patients with either anterior instability or impingement and does not necessarily indicate a positive result. However, a sense of impending instability that is relieved by changing the direction of applied force from anterior to posterior is considered a positive relocation sign. The apprehension test has been heavily correlated with recurrent dislocation, with recurrence in 71.4% of patients with a positive sign and 36.8% of patients with a negative sign. Although not a perfect predictor of recurrence, the apprehension test is useful for categorizing patients as being at high or low risk of subsequent anterior shoulder dislocation. Furthermore, a positive apprehension test between 30 and 90 degrees of abduction strongly indicates bone loss and dictates preoperative imaging to further qualify the glenoid deficiency.
It is important to recognize factors that may predispose a patient to having a higher chance of recurrence after surgical intervention. All of these factors, either solo or in sum, are additive to the development of instability pathology. This includes: (1) increase in glenoid bone loss; (2) increase in humeral head Hill–Sachs size and/or orientation; (3) increase in size of the labrum tear; (4) turning an off-track lesion into an on-track lesion; (5) increase in frequency of ALPSA tears; 6) and additional cartilage injury. These patient factors based on history are presented in Box 24.1 .
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All of these may indicate a pathological finding as described and contribute to lesser success rates with certain types of surgical intervention. Besides patient history, there are also important examination factors that contribute to proper preoperative workup, counseling, and surgical procedure selection ( Box 24.2 ).
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Preoperative Diagnostic Imaging
In patients with glenohumeral instability, standard initial imaging includes plain radiographs with anteroposterior (AP) and axillary lateral views. Plain radiographs are an efficient, cost-effective, and low-radiation option for assessing bone abnormalities associated with instability. However, patient positioning can directly impact the diagnostic sensitivity, specificity, and accuracy in quantifying bone loss. , For example, the humeral head will overlap the glenoid and obscure the glenohumeral joint space in AP view. Because of these limitations, supplemental West Point, Didiee, and Bernageau views have been recommended to maximize sensitivity. Of these diagnostics, the Bernageau view is reported to be most accurate and reliable for assessing osseous lesions of the glenoid when directly compared with three-dimensional computed tomography (CT) imaging. In patients with anterior dislocations, AP radiographs in internal rotation and Stryker notch views may also be useful, as they allow for the visualization of a Hill–Sachs lesion ( Fig. 24.1 ). Hill–Sachs lesions occur when the posterolateral aspect of the humeral head impacts the glenoid rim and causes a compression fracture of the posterior aspect of the humeral head. The lesion is classified as either nonengaging or engaging if the bony concavity contacts the anterior glenoid with the arm in functional position, 90 degrees of abduction, and 0 to 130 degrees of external rotation. Treatment is dictated by engagement, significance of instability symptoms, and radiographic findings.
Because of the limitations of plain radiographs, magnetic resonance imaging (MRI) and CT scans of the shoulder with three-dimensional reconstruction with the humeral head digitally subtracted are useful modalities in quantifying preoperative complications ( Fig. 24.2 ). Although MRI is paramount in diagnosing shoulder instability, CT is the ultimate tool for depicting and quantifying skeletal changes. CT may demonstrate fractures, glenoid bone loss, glenoid version, and humeral head defects. Specifically, three-dimensional reconstruction with humeral head subtraction allows for en face analysis of the glenoid and allows the surgeon to quantify the attritional anterior–inferior bone loss. This measurement is critical because research has shown that patients with as little as 13.5% glenoid bone loss experience worse functional outcomes following primary surgical stabilization procedures. , Although MRI is the optimal method for evaluating soft tissue pathologies, CT arthrogram may also provide insight into the status of the labrum, rotator cuff, and ligamentous complex. Therefore a CT may provide a more complete view of the patient given the ability to assess both osseous and soft tissue defects.
Although MRI is the preferred method for analyzing soft tissues, it is inadequate for assessing associated bony injuries. , Therefore, this modality is most useful in determining the presence of a Bankart lesion, ALPSA, and HAGL. ALPSA is a type of Bankart lesion with disruption of the anteroinferior labrum resulting in medial displacement and inferior rotation of the torn fragment. Research has reported double the risk for instability recurrence after surgical repair in patients with an ALPSA lesion when compared with those without. In addition, these patients are more likely to experience significant erosion of the anterior glenoid rim and a higher incidence of a concurrent Hill–Sachs lesion. As such, the MRI is critical for differentiating between a simple Bankart or an ALPSA lesion and may drive treatment strategy.
Diagnostic MRI is also useful in identifying a HAGL lesion, which has been reported to present in approximately 9.3% of patients with anterior instability ( Fig. 24.3 ). Moreover, a recent systematic review by Bozzo et al. reported that younger male patients ( n = 118; mean age 22 years) were the most common demographic to present with HAGL lesions, and that 72% of all HAGL lesions resulted from sporting injuries. Magnetic resonance arthrogram imaging is useful in identifying the precise nature of the avulsion, and may be useful in diagnosing associated injuries. , In cases of multiple injuries, HAGL lesions may go unrecognized and be the source of recurrent anterior shoulder instability following operative management. Therefore, an undiagnosed or untreated HAGL may cause continued instability and even pain.
