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Posterior Shoulder Instability
Arthroscopic Repair
Posterior shoulder instability may present to the physician as an “isolated” condition in which the patient has sustained shoulder trauma and developed posterior shoulder instability with pain and apprehension especially with forward flexion and adduction of the shoulder. Typically the “jerk test” (Figs. 28–1A,B,C) will demonstrate the instability or elicit apprehension. This maneuver is also painful. A history of documented posterior dislocation is uncommon. X-rays, computed axial tomography scans, and magnetic resonance imaging (MRI) may show intraarticular changes compatible with recurrent posterior subluxations (Fig. 28–2).
Arthroscopic findings include a redundant posterior capsule, labral tearing, and osteochondral defects (i.e., reverse Hill-Sachs lesion and glenoid erosion) (Fig. 28–3). Rotator interval lesions and partial thickness cuff tears may also be present. Arthroscopic or open repairs and reconstructions of the posterior labrum and capsule are sufficient treatment (Fig. 28–4). A proper postoperative rehabilitation program is mandatory.
A second type of posterior instability pattern involves posterior instability as a component of multidirectional instability (MDI). With this patient, posterior instability signs are only one component of the clinical presentation and usually not the main complaint. Abnormal anterior and inferior laxity is present on physical exam. The patient often has a history of “micro” trauma with repetitive stress (such as swimming, throwing, etc.). The patient may have at one time sustained significant trauma to their shoulder with even an anterior discoloration, but now has a much more global instability problem. Testing (X-rays, MRIs, etc.) is variable and may show osteochondral lesions. Arthroscopy demonstrates global pathology to many structures (labral, capsule, cuff, and rotator interval). There may not be frank labral detachments, but the capsule will be attenuated. Arthroscopic repair needs to involve the anterior and posterior capsule as well as the rotator interval. Cuff repairs are occasionally needed.
Indications
Symptomatic, posterior instability.
Contraindications
1. Voluntary instability
2. Uncooperative patient
Mechanism of Injury
Often a fall to the outstretched arm or repetitive micro trauma with overhead activities.
Physical Examination
1. Positive apprehension sign (jerk test) with adduction, internal rotation, and forward flexion
2. Positive posterior drawer test
3. Inferior instability and positive Sulcus signs with MDI
Diagnostic Tests
1. Standard X-rays may demonstrate “reverse Hill-Sachs” lesions (unusual) and/or glenoid defects.
2. MRI may show osteochondral defect humeral heads and labral lesions.
3. Arthrogram shows a redundant capsule.
Special Considerations
May be associated with MDI. Beware of patients with voluntary dislocations/subluxations.
Preoperative Planning and Timing of Surgery
1. Extensive rehab program prior to surgery advised (especially strengthening external rotators).
2. Patient must cooperate with a rehabilitation program.
3. May need period of postop bracing.
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