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Shoulder Instability

  • Because of the shoulder’s extensive ROM, it is prone to instability.
  • The term encompasses a spectrum of disorders of varying degree, direction, and cause.
  • Instability should be distinguished from laxity.
    • Laxity is the symmetric translation of the humeral head over the surface of the glenoid without symptoms.
    • Instability occurs when the degree of translation becomes excessive and leads to symptoms.
  • Shoulder joint stability depends on various static and dynamic anatomic restraints.
    • Static restraints: Osseous anatomy (glenoid fossa and humeral head), joint capsule, glenohumeral ligaments (superior, middle, and inferior), and glenoid labrum
    • Dynamic restraints: The muscles and tendons of the rotator cuff, the scapular stabilizers
  • Shoulder instability is classified by:
    • Direction of dislocation: Anterior, posterior, or multidirectional
    • Degree: Dislocation, subluxation, microinstability
    • Force: Traumatic versus atraumatic
    • Patient contribution: Voluntary versus involuntary
Risk Factors
  • Anterior shoulder instability is common.
    • Risk of recurrence after a traumatic anterior shoulder dislocation varies with patient age:
      • 50-85% risk in those initially affected when <20 years old
      • 20% risk in those initially affected when >40 years old
  • Recurrent posterior shoulder instability most commonly presents with repeated episodes of subluxation with no history of shoulder injury.
    • Usually affects active males (<30 years old)
    • Many patients can demonstrate voluntary posterior shoulder instability.
  • MDI:
    • Usually atraumatic
    • Is poorly understood and typically results from a combination of excessive tissue laxity and muscular discoordination
    • Frequently, history of incidental or no trauma
  • Shoulder instability is associated with injury to the capsuloligamentous labral complex.
    • The Bankart lesion is a detachment of the anterior glenoid labrum and capsuloligamentous attachments.
    • Patients with recurrent anterior instability also often have anterior capsular redundancy.
  • Recurrent posterior instability may have a detached posteroinferior labrum (reverse Bankart lesion), a patulous posteroinferior capsule, and excessive glenoid retroversion.
  • Patients with MDI usually have a generalized increase in joint laxity and redundant capsule.
Mechanisms of shoulder dislocation are addressed elsewhere (see Shoulder Dislocation chapter).
Signs and Symptoms
Keys to accurate diagnosis of shoulder instability are a thorough history and physical examination.
  • Key information for the clinician to identify:
    • Initial episode of major, minor, or no trauma
    • Arm position at the time of the initial event (for determining direction of instability) but, more importantly, which arm positions reproduce symptoms
    • The necessity of a formal reduction maneuver for a dislocation and the presence of radiographs documenting a dislocation
    • Symptoms, pain location, exacerbating activities, and any voluntary component to the instability episodes
  • Patients with anterior instability typically:
    • Have a history of traumatic anterior shoulder dislocation (see Shoulder Dislocation chapter).
    • Report symptoms, such as pain or apprehension, during arm abduction, extension, and external rotation.
  • Patients with posterior instability:
    • Present with a sense of shoulder instability and looseness or episodes of recurrent subluxation, seldom dislocation
    • Experience symptoms with the arm flexed, adducted, and internally rotated (e.g., when pushing a heavy cart or during a seizure)
  • Patients with inferior instability may become symptomatic when carrying heavy objects, such as a suitcase, at the side.
  • Patients with MDI:
    • May have a family history of similar findings and personal history of other joint problems
    • Typically have history of minimal or no trauma
    • Commonly complain of pain, rather than episodes of subluxation or dislocation
    • Experience most symptoms in midrange rather than extreme shoulder motions
Physical Exam
  • Examine and compare both shoulders: Laxity, strength, and ROM.
  • Include inspection, palpation, ROM, and a thorough neurovascular examination.
    • Inspection may reveal atrophy or mild scapular dyskinesis.
    • Palpation may reveal focal tenderness.
  • Ask the patient to demonstrate the positions and actions that produce the symptoms.
    • Symptoms in extension, abduction, and external rotation suggest anterior instability
    • Symptoms in flexion, adduction, and internal rotation suggest posterior instability.
  • Patients with MDI often have generalized ligamentous laxity.
  • Evaluate shoulder laxity with the load-and-shift test (assesses amount of humeral head translation on the glenoid fossa in the anterior or posterior direction).
    • Patients with instability often have excessive translation and pain.
    • Patients with MDI may have excessive laxity bilaterally.
  • Assess inferior laxity with the sulcus test: Pull downward on the neutrally positioned arm, assess amount of inferior translation and presence of an anterior dimple (or sulcus) beneath the acromion.
    • Often increases translation or reproduces symptoms in patients with MDI
  • Reproduction of symptoms by provocative tests helps confirm the diagnosis of instability.
    • For anterior instability: Apprehension test:
      • Place the patient supine and abduct the shoulder 90°, flex the elbow 90°, and gradually externally rotate the arm until the patient reports pain or apprehension.
      • Relief of symptoms with the application of a posteriorly directed force on the anterior humeral head constitutes a positive relocation test, another sign of anterior instability.
    • For posterior instability:
      • Arm in 90° of elevation and internal rotation
      • Move the arm from the coronal to the sagittal plane and back while applying an axial load to the humerus.
      • Positive test: Humeral head subluxates over the glenoid rim, reproducing symptoms.
  • Radiographic evaluation should include AP and axillary views of the shoulder.
    • Plain radiographs frequently are negative, especially in subtle forms of instability.
    • Findings suggestive of anterior instability:
      • A posterolateral impression defect of the humeral head (Hill-Sachs lesion) suggests traumatic anterior dislocation.
      • An anterior-inferior glenoid rim fracture (a bony Bankart lesion)
    • Findings suggestive of posterior instability:
      • An anterior impression defect of the humeral head (reverse Hill-Sachs lesion)
      • Posterior lesions of the glenoid rim
  • CT scanning can help define humeral or glenoid abnormalities.
  • MRI is useful in identifying labral or capsuloligamentous pathology.
Diagnostic Procedures/Surgery
Examination under anesthesia and diagnostic arthroscopy are not routinely necessary, but they can be helpful in selected cases.
Differential Diagnosis
Conditions such as internal impingement syndrome or SLAP lesions may be confused with subtle forms of instability, especially in overhead athletes.
General Measures
  • Nonsurgical treatment is recommended for most 1st-time anterior dislocations (see Shoulder Dislocation chapter) and for posterior shoulder instability, MDI, and voluntary dislocators.
    • Modalities: Joint reduction (in the case of shoulder dislocation), followed by a period of activity restriction, immobilization, and rehabilitative exercises
    • The duration of immobilization is controversial.
  • Surgery may be recommended for recurrent traumatic anterior shoulder instability and for posterior instability or MDI after unsuccessful nonoperative treatment (6 months).
Special Therapy
Psychologic evaluation and treatment for patients with habitual voluntary shoulder instability
Physical Therapy
  • Rehabilitative programs emphasize strengthening of the shoulder’s dynamic stabilizers (particularly rotator cuff muscles and scapular stabilizers), regaining full ROM, restoring normal shoulder mechanics, improving proprioception, and avoiding provocative arm activities.
    • Progression of the rehabilitation protocol varies with the direction of instability, quality of the tissue, type of repair, and requirements of the patient.
    • In general, return to sports is restricted for 6-9 months after surgery for anterior instability and 9-12 months after surgery for posterior instability and MDI.
Patients with posterior instability from seizures should be treated with medication adjustment to reduce the seizure frequency.
  • The key concept in surgical treatment is the anatomic repair of the capsuloligamentous or labral abnormality rather than nonanatomic reconstructions.
  • Capsulorrhaphy (capsular tightening) enhances correction of instability by reducing capsular laxity and excessive joint volume.
  • Arthroscopic surgery:
    • For traumatic anterior instability:
      • Treatment of choice is Bankart repair (reattachment of capsulolabral structures to the glenoid rim) with suture anchors and supplemental anterior capsulorrhaphy.
      • Capsular tightening achieved with capsular plication or thermal shrinkage
    • For posterior shoulder instability: Arthroscopic capsulolabral repair and posterior capsulorrhaphy
    • For MDI: Arthroscopic plication or capsular shift procedures
  • Nonanatomic open reconstructive procedures:
    • Result in failure, loss of motion, and arthritis
    • Exception is the Bristow procedure (transfer of the coracoid process to the antero-inferior glenoid rim) for patients with large bony defects in the glenoid rim
  • Anatomic open reconstructive procedures:
    • For anterior shoulder instability, the classic is the open Bankart procedure.
      • Most commonly used surgical technique
      • Reattaches capsulolabral structures to the glenoid rim
      • Often combined with open capsulorrhaphy to reduce capsular redundancy
    • For symptomatic recurrent posterior instability:
      • Posterior capsulorrhaphy
      • Posterior bone block procedures (glenoid bone stock deficiency)
      • Rotational osteotomy of the proximal humerus (excessive retrotorsion of the proximal humerus)
      • Posterior glenoid osteotomy (abnormal glenoid retroversion)
    • For MDI:
      • Most common procedure is inferior capsular shift with associated closure of the rotator interval defect.
      • Postoperative immobilization with the arm in neutral rotation and 10-15° of abduction
  • Because of psychologic problems, surgery is contraindicated for patients with voluntary instability.
  • Prognosis is excellent after surgical treatment of recurrent anterior shoulder instability.
  • Posterior shoulder instability and MDI that fail to respond to nonoperative treatment have a good prognosis with surgical treatment.
  • The risk of recurrent instability after surgical treatment is ~3-10%.
  • The risk of recurrence is lower after open than after arthroscopic surgical procedures, particularly in contact athletes with recurrent instability.
  • Complications of open procedures include pain, decreased ROM, infection, neurovascular injury, late degenerative arthritis, subscapularis over tightening or rupture, and hardware-related problems (breakage, loosening, migration, and intra-articular penetration).
  • Complications of arthroscopic procedures include neurovascular injury, adhesive capsulitis, synovial fistula, and hardware-related problems.
  • 718.81 Shoulder instability
  • 831.1 Shoulder dislocation, anterior
  • 831.2 Shoulder dislocation, posterior
  • 831.3 Shoulder dislocation, inferior
Q: Should patients with voluntary instability undergo surgery?
A: Generally, no. Most patients with voluntary instability have underlying psychologic problems that the surgery cannot help and, thus, make poor surgical candidates.
Q: What are the indications for arthroscopic anterior shoulder stabilization?
A: Patients with acute traumatic anterior dislocation, without multiple dislocations, who have a Bankart lesion are the ideal candidates for arthroscopic stabilization. Assessing capsular laxity arthroscopically requires advanced surgical skills. Arthroscopic stabilization is preferred in overhead athletes (e.g., pitchers), but it has a higher failure rate than open repairs in contact athletes (e.g., football players).

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