Posterior shoulder instability is a spectrum of injury and pathology, ranging from mild subluxation (or recurrent posterior subluxation, RPS) to traumatic dislocation. Most patients who present with posterior instability report pain in the shoulder with provocative positions of the shoulder joint. Frank posterior instability is much less common than anterior instability, representing approximately 5-10% of all patients with pathologic shoulder instability.
Patients are candidates for surgical repair -- more specifically, arthroscopy -- when conservative measures such as physical therapy and activity modification have failed to alleviate symptoms. The patient history may include traumatic (or several traumatic) dislocations, electrocution with resultant posterior dislocation, or recurrent pain in the shoulder with posterior axial loading.
Physical examination may demonstrate abnormal load and shift testing, a positive jerk and Kim test, with or without findings of multi-directional instability (such as sulcus sign and joint hypermobility). Imaging findings may reveal osseous lesions on plain radiographs or capsulo-labral injury on MRI or MRI arthrography.
Arthroscopic reconstruction is indicated in the majority of surgical cases. Contraindications to arthroscopy may include osseous defects, a deficient capsule, and revision surgery (although these are not absolute contraindications to an arthroscopic approach).
Routine imaging includes AP, axillary, and outlet view radiographs. These images are inspected for excessive glenoid retroversion, osseous defects (reverse Bankart or Hill Sachs lesions), and loose bodies. Routine MRI or MRI arthrography is typically reviewed, which may demonstrate posterior labral pathology (Figure 1), inferior glenohumeral ligament injury, rotator cuff tears, SLAP lesions, or articular cartilage abnormalities.
Figure 1. Axial T2-weighted MRI arthrogram in a patient with recurrent posterior subluxation. The double asterisks indicate the presence of a posterior labral tear.
While the patient is under general anesthesia and interscalene block, load and shift testing may demonstrate excessive posterior translation of the humeral head relative to the glenoid fossa. A sulcus sign could also indicate multi-directional instability with incompetence of the rotator interval.
Patients are positioned in the operating room in the lateral decubitus position. A bean bag or sand bag is used to assist with positioning and avoid pressure injury. The affected extremity is typically placed in balanced arm traction at 45 degrees of abduction and slight (20 degrees) forward flexion using 10-15 pounds of traction (Figure 2). Alternatively, some authors have reported good outcomes using a beach chair approach.
Figure 2. Patient undergoing arthroscopic shoulder surgery in the lateral decubitus position
Approach and Technique
We typically use an all-arthroscopic technique for this procedure, with the main working portal being the posterior portal. The anterior portal is placed under direct visualization in the rotator interval and is used for viewing posteriorly. The posterior portal is placed slightly lateral to the traditional arthroscopic portal to assist with anchor placement. This allows the trajectory of the drill to be at a 45-degree angle to the glenoid face. Cannulas are placed in both portals to assist with suture management and for easy viewing both anteriorly and posteriorly.
With the scope in the posterior portal, a diagnostic arthroscopy is first performed to assess the spectrum of injury. The glenoid and humeral articular surfaces are inspected, as well as the tendons of the rotator cuff, the labrum, and the biceps tendon. The scope is then placed in the anterior portal and the working portal becomes the posterior portal.
Most patients will have an injury to the posterior labrum and capsule complex. A periosteal elevator is first used to elevate the damaged labrum and release scar tissue that may have formed between the labrum and glenoid interface (Figure 3). A motorized burr or shaver can then be used to abrade the glenoid rim. Anchors (ranging in size from 2 mm – 3 mm) are then sequentially placed along the posterior glenoid face in ascending order. Anchors are typically spaced 3-5 mm apart so that fragmentation of the posterior glenoid bone does not ocurr.
Figure 3. Arthroscopic view from the anterior portal. The posterior labrum and capsule is elevated off the glenoid margin with a periosteal elevator. The single asterisk indicates the capsule/labral complex.
The posterior suture limb of the anchor is shuttled using a suture hook and PDS suture (Ethicon, Somerville, NJ) around the labrum and capsule, and then tied to secure the labrum to the glenoid margin (Figure 4). Anchors are placed on the glenoid face at the articular margin to restore proper tension to the posterior band of the inferior glenohumeral ligament. Patients without frank instability but with posterior labral tears require a very minimal amount of capsular plication, whereas patients with frank instability require a larger volume of capsular reduction. This titration is achieved with the suture hook shuttling device, as more or less capsule can be grasped with each passage.
Figure 4. Arthroscopic view from the anterior portal. The suture hook is introduced inferior to the anchor and a PDS suture is relayed into the joint to shuttle the posterior suture from the anchor.
Once the labrum and capsule have been repaired to the posterior glenoid surface, the posterior portal is closed to complete the repair. The posterior cannula is withdrawn to a level just posterior to the capsule. A crescent suture hook loaded with PDS is used to penetrate on one side of the portal incision, and the suture is loaded into the shoulder joint. A penetrating suture grapser grabs the suture from the other side of the portal incision and the suture is tied just beyond the capsule. Varying the distance of the suture from the portal incision allows additional tension to be applied to the posterior capsule. The repair is completed when all sutures have been tied and the posterior portal is closed, preventing further posterior glenohumeral translation (Figures 5a-b).
Figures 5a-b. Arthroscopic view from the anterior portal. The capsule and labrum have been restored to the posterior glenoid margin (A, left). The posterior portal closure completes the repair in this patient with RPS (B, right).
Pearls and Pitfalls
- The lateral decubitus position with the arm in traction allows for easy access to the posterior capsule and may assist the novice arthroscopist.
- Placement of the posterior portal slightly lateral may allow for single posterior portal arthroscopic repair. Placement of the anterior portal high in the rotator interval allows for better visualization of the posterior capsule and labrum.
- Titrating the repair to the pathology is key to preventing excessive tightening or inadequate tension in patients with RPS or frank instability, respectively.
- Shuttling the posterior suture through the labrum may help to prevent suture entanglement. Alternatively, two working posterior portals can be established to assist with suture management.
- Placement of the anchors should occur perpendicular to the glenoid margin to prevent articular cartilage injury and to promote proper tension within the capsule and labrum.
The patient is placed in an abduction sling while under anesthesia. The patient is allowed to perform passive range of motion exercises at home immediately upon discharge. We allow 90 degrees of forward elevation and external rotation of 0 degrees by 4 weeks post surgery. After 6 weeks, the sling is discontinued and the patient begins active assisted range of motion exercises with slow progression to active range of motion without motion constraints.
After 4 months, the shoulder is often pain free, and near normal range of motion is achieved. Rotator cuff strengthening and conditioning is begun at this stage of the rehabilitation process. After 5 months, isokinetic and isotonic exercises are advanced. Beyond 6 months, patients are assessed for strength return and ability to begin sport specific activity. Patients who throw may begin a throwing program at this stage of the rehabilitation process. Competitive throwing is typically not attained until 12 months post surgery.
Arthroscopic posterior stabilization has achieved good outcomes with respect to recurrence and return to sports. Various studies have shown rates of recurrence ranging from 0-8%, with return to sport ranging from 89-100%.
Complications from surgery may include:
- Complex regional pain syndrome
- Persistent pain
- Recurrence of instability
- Nerve or vascular injury (rare with an all-arthroscopic approach)
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