CHAPTER 8 – Arthroscopic Repair of Posterior Shoulder Instability

Posterior instability is relatively uncommon compared with anterior instability of the shoulder. Most authors agree that posterior shoulder instability represents approximately 2% to 10% of shoulder instability cases. ^{[4] [8] [13]} Initial attempts to clarify the distinctions of posterior instability were made in 1962, when McLaughlin recognized that differences exist between “fixed and recurrent subluxations of the shoulder,” suggesting that the etiology and treatment of the two are distinctly different.^[15] More than 20 years later, in the early 1980s, Hawkins^[8] reviewed the difference between true dislocations and subluxations and noted that true recurrent posterior dislocations are rare compared with subluxation episodes. Since that time, additional knowledge has been gained in the differences between unidirectional and multidirectional, traumatic and atraumatic, acute and chronic, and voluntary and involuntary posterior instability. In many respects, each of these may represent a distinct form of posterior instability with its own underlying predispositions, anatomic abnormalities, and treatment algorithms. ^{[16] [18]} Our collective understanding of posterior shoulder instability continues to evolve.

Pathoanatomy

Recent advances in our understanding of the spectrum of posterior instability have been gained through the study of shoulder injuries in athletes, patients with generalized ligamentous laxity, and patients with posttraumatic injuries. Acute posterior dislocations typically result from a direct blow to the anterior shoulder or indirect forces that couple shoulder flexion, internal rotation, and adduction. ^{[4] [8]} The most common indirect causes are accidental electric shock and convulsive seizures. Because of incomplete radiographic studies and a failure to recognize the posterior shoulder prominence and mechanical block to external rotation, 60% to 80% of locked posterior dislocations are missed on initial presentation. Additional pathologic processes are frequently associated with posterior instability and include the reverse Hill-Sachs lesion, the reverse bony Bankart lesion, posterior capsular laxity, excessive humeral head retroversion or chondrolabral retroversion, and glenoid hypoplasia.

Preoperative Considerations

History

To diagnose posterior instability, the clinician must perform a thorough history and physical examination as well as maintain a high index of suspicion. A history of a posterior dislocation requiring formal reduction is more obvious; however, patients with recurrent posterior subluxation may present with more subtle findings. The majority of patients with recurrent posterior subluxation complain primarily of pain with specific activities, particularly in the provocative position (90-degree forward flexion, adduction, and internal rotation), ^{[4] [8]} more so than of instability.

Physical Examination

	•	Active and passive range of motion
	•	Palpation for tenderness
	•	Strength testing
	•	Evaluation for impingement
	•	Assessment for generalized ligamentous laxity

Stability Testing

	•	Load and shift test for anterior and posterior translation ( Fig. 8-1 )
	•	Sulcus sign (in both neutral and external rotation) for inferior translation
	•	Sulcus sign graded as 3+ that remains 2+ in external rotation is pathognomonic for multidirectional instability

Specific Tests

	•	Jerk test ( Fig. 8-2 )
	•	Kim test ( Fig. 8-3 )
	•	Circumduction test

Imaging

Plain Radiographs

	•	Including axillary view
	•	Evaluate for reverse Hill-Sachs lesions ( Fig. 8-4 ), glenoid pathologic changes (retroversion, fractures, and hypoplasia), bony humeral avulsion of the glenohumeral ligaments

Magnetic Resonance Arthrography

•

Evaluate labrum, capsule, biceps tendon, subscapularis integrity ( Fig. 8-5 )

Computed Tomography

•

Evaluate for glenoid version, locked dislocation ( Fig. 8-6 )

Indications and Contraindications

Many patients with recurrent posterior subluxation can be managed successfully without surgery. Numerous authors have proposed a period of no less than 6 months of physical therapy before surgical treatment is considered. Effect ive rehabilitation includes avoidance of aggravating activities, restoration of a full range of motion, and shoulder strengthening. Strengthening of the rotator cuff, posterior deltoid, and periscapular musculature is critical. The premise of such directed physical therapy is to enable the dynamic muscle stabilizers to offset the deficient static capsulolabral restraints. Nearly 70% of patients will improve after an appropriate rehabilitation protocol. The recurrent subluxation, however, is generally not eliminated, but the functional disability is diminished enough that it does not prevent activities. If the disability fails to improve with an extended 6-month period of directed rehabilitation, or in select cases of posterior instability resulting from a macrotraumatic event, surgical intervention should be considered.

Indications

	•	Patients with continued disabling, isolated, recurrent posterior subluxation after a rehabilitation program
	•	Recurrent posterior subluxation with a posterior labral tear
	•	Multidirectional instability with a primary posterior component
	•	Voluntary positional posterior instability

Relative indications include patients with an antecedent macrotraumatic injury.

Contraindications

	•	Patients not having completed a reasonable rehabilitation program
	•	A surgeon’s preference for traditional open techniques
	•	A large engaging reverse Hill-Sachs lesion requiring subscapularis transfer or an osteochondral allograft
	•	A large reverse bony Bankart lesion
	•	Patients with voluntary muscle instability
	•	Underlying psychogenic disorders, and patients unable or unwilling to comply with postoperative limitations

Relative contraindications may include chronic instability resulting in compromised capsulolabral tissue and patients who have undergone previous open surgery.

Because successful results have been achieved after arthroscopic treatment of posterior labral tears in contact athletes, arthroscopic reconstruction is not contraindicated in that population.

Surgical Technique

Anesthesia

The procedure can be performed under interscalene block or general endotracheal anesthesia with an interscalene block for postoperative pain control.

Examination Under Anesthesia

The examination under anesthesia is performed on a firm surface with the scapula relatively fixed and the humeral head free to rotate. A load-and-shift maneuver, as described by Murrell and Warren, is performed with the patient supine.^[12] The arm is held in 90 degrees of abduction and neutral rotation while a posterior force is applied in an attempt to translate the humeral head over the posterior glenoid. A sulcus sign test is performed with the arm adducted and in neutral rotation to assess whether the instability has an inferior component. A 3+ sulcus sign that remains 2+ or greater in external rotation is considered pathognomonic for multidirectional instability. Testing is completed on both the affected and unaffected shoulders, and differences between the two are documented.

Patient Positioning, Landmarks, and Portals

The patient is then placed in the lateral decubitus position with the affected shoulder positioned superior. An inflatable beanbag and kidney rests hold the patient in position. Foam cushions are placed to protect the peroneal nerve at the neck of the fibula on the down leg. An axillary roll is placed. The operating table is placed in a slight reverse-Trendelenburg position. The full upper extremity is prepared to the level of the sternum anteriorly and the medial border of the scapula posteriorly. The operative shoulder is placed in 10 pounds of traction and positioned in 45 degrees of abduction and 20 degrees of forward flexion. The bone landmarks, including the acromion, distal clavicle, and coracoid process, are demarcated with a marking pen.

After preparation and draping, the glenohumeral joint is injected with 50 mL of sterile saline through an 18-gauge spinal needle to inflate the joint. A posterior portal is established 1 cm distal and 1 cm lateral to the standard posterior portal to allow access to the rim of the glenoid for anchor placement (
Fig. 8-7

). An anterior portal is then established high in the rotator interval by an inside-to-outside technique with a switching stick. Alternatively, it can also be established by an outside-to-inside technique with the assistance of a spinal needle. Typically, only anterior and posterior portals are required to perform the procedure. An accessory 7-o’clock portal has been described but is not frequently used in our technique.

Diagnostic Arthroscopy

A diagnostic arthroscopy of the glenohumeral joint is then undertaken. The labrum, capsule, biceps tendon, subscapularis, rotator interval, rotator cuff, and articular surfaces are visualized in systematic fashion. This ensures that no associated lesions will be overlooked by poorly directed tunnel vision. Lesions typically seen in posterior instability include a patulous posterior capsule, posterior labral tear, labral fraying and splitting, widening of the rotator interval, and undersurface partial-thickness rotator cuff tears. After the glenohumeral joint is viewed from the posterior portal, the arthroscope is switched to the anterior portal to allow improved visualization of the posterior capsule and labrum. A switching stick can then be used in replacing the posterior cannula with an 8.25-mm distally threaded clear cannula (Arthrex, Inc., Naples, Fla), thus allowing passage of an arthroscopic probe and other instruments through the clear cannula to explore the posterior labrum for evidence of tears.

Specific Steps (
Box 8-1

)

1. Preparation for Repair

When the posterior labrum is detached, suture anchors are employed in performing the repair. The posterior labrum is visualized from both the posterior and anterior portals to appreciate the full extent of the tear (
Fig. 8-8

).

	•	The arthroscope then remains in the anterior portal, and the posterior portal serves as the working portal for the repair.
	•	An arthroscopic rasp or chisel is used to mobilize the torn labrum from the glenoid rim ( Fig. 8-9 ).
	•	A motorized synovial shaver or meniscal rasp is used to abrade the capsule adjacent to the labral tear and to débride and decorticate the glenoid rim to achieve a bleeding surface.

Box 8-1 

Surgical Steps

1.    Preparation for repair    2.    Placement of suture anchors    3.    Labral repair    4.    Posterior capsular shift    5.    Arthroscopic knot tying    6.    Completion of the repair    7.    Rotator interval closure

2. Placement of Suture Anchors

	•	Suture anchors are then placed at the articular margin of the glenoid rim, rather than down on the glenoid neck, to perform the labral repair ( Fig. 8-10 ).
	•	A posterior labral tear extending from 6-o’clock to 9-o’clock on a right shoulder is typically repaired with suture anchors at the 6:30, 7:30, and 8:30 positions.
	•	We prefer the 3.0-mm Bio-Suture Tak suture anchor with No. 2 FiberWire (Arthrex, Inc., Naples, Fla) because of the ease of placing the anchor on the glenoid surface, but a number of other commercially available anchors are also adequate.
	•	The suture anchor is placed with the sutures oriented perpendicular to the glenoid rim to facilitate passage of the most posterior suture through the torn labrum.
	•	Avoid inadvertent injury to the articular cartilage.

3. Labral Repair

	•	After placement of the suture anchors, a 45-degree Spectrum suture hook (Linvatec, Largo, Fla) is loaded with a No. 0 polydioxanone (PDS) suture (Ethicon, Inc., Somerville, NJ). The contralateral side hook is chosen (i.e., a left 45-degree hook for a right shoulder when it is introduced from the posterior portal). Alternatively, there are other commercially available suture passers and suture relays that will also suffice.
	•	The suture passer is delivered through the torn labrum and advanced superiorly, reentering the joint at the edge of the glenoid articular cartilage ( Fig. 8-11 ).
	•	Tension must be restored into the posterior band of the inferior glenohumeral ligament to re-establish posterior stability.
	•	Patients with acute injuries and less evidence of capsular stretching do not require the same degree of capsular advancement as do those with more chronic instability.
	•	In the setting of a labral tear with some capsular laxity, the suture passer is advanced through the posterior capsule approximately 1 cm lateral to the edge of the labral tear and then underneath the labral tear, to the edge of the articular cartilage, the so-called pleat stitch ( Fig. 8-12 ).
	•	Placement of as many pleat stitches as necessary in a patulous shoulder capsule can reduce capsular redundancy.
	•	The PDS suture is then fed into the glenohumeral joint, and the suture passer is withdrawn through the posterior clear cannula.
	•	An arthroscopic suture grasper is used to withdraw both the most posterior suture in the suture anchor and the end of the PDS suture that has been advanced through the torn labrum. This move detangles the sutures in the cannula.
	•	The PDS suture is then fashioned into a single loop and tightly tied over the end of the braided suture.
	•	The most lateral PDS suture, which has not been tied to the braided suture, is then pulled through the clear cannula ( Fig. 8-13 ).
	•	This advances the most posterior suture in the suture anchor behind the labral tear ( Fig. 8-14 ).
	•	A labral tear at the 7-o’clock position is advanced to the 7:30 suture anchor, and the 8-o’clock labral tear position is advanced to the 8:30 suture anchor. Additional sutures are then placed in similar fashion to complete the labral repair.
	•	If the capsule requires further tension, suture capsulorrhaphies can be performed in the intervals between the suture anchors directly to the newly secured labrum.
	•	Knots are tied after the passage of each suture, which allows continued assessment of the repair and the degree of the capsular shift achieved by each suture

4. Posterior Capsular Shift

	•	The majority of patients with unidirectional posterior instability and primary posterior multidirectional instability do not have a posterior labral tear and typically display significant capsular laxity at arthroscopy ( Fig. 8-15 ). An isolated posterior capsulorrhaphy is performed.
	•	Suture capsulorrhaphies are placed from inferior (6-o’clock) to superior (10-o’clock).
	•	The 6:30 capsular suture is typically advanced to the 7:30 position, and the reduction in capsular volume is assessed.
	•	Restoration of adequate tension in the posterior band of the inferior glenohumeral ligament is critical.
	•	Additional sutures are then placed at the 7:30, 8:30, and 9:30 positions on the capsule, advancing to the 8:30, 9:30, and 10:30 positions on the glenoid ( Fig. 8-16 ).
	•	Sutures are tied after each is passed. If the sutures are not tied until the end, one errant suture may necessitate removal of all other sutures to achieve correction.

5. Arthroscopic Knot Tying

	•	We prefer the sliding-locking Weston knot, but there are a number of arthroscopic knot-tying techniques that work well.
	•	What is most important is that the surgeon be familiar with the knot used and be skilled in its use.
	•	The posterior braided suture exiting through the capsule is threaded through a knot pusher, and the end is secured with a hemostat.
	•	This suture serves as the post, which in effect will advance the capsule and labrum to the glenoid rim when the knot is tightened.
	•	The knot should be secured posteriorly on the capsule and not on the rim of the glenoid to prevent humeral head abrasion from the knot.
	•	Each half-hitch must be completely seated before the next half-hitch is thrown.
	•	Placing tension on the non-post suture and advancing the knot pusher “past point” will lock the Weston knot.
	•	A total of three alternating half-hitches are placed to secure the Weston knot.

6. Completion of the Repair

	•	An arthroscopic awl is employed to penetrate the bare area of the humerus, under the infraspinatus tendon, in an effort to achieve some punctate bleeding to augment the healing response.
	•	The posterior capsular portal incision is then closed by passage of a PDS suture through the crescent Spectrum suture passer and retrieval of the suture with an arthroscopic penetrator.
	•	Varying the distance of the suture from the portal incision allows titration of the capsulorrhaphy.
	•	The PDS suture is then tied blindly in the cannula, closing the posterior capsular incision ( Fig. 8-17 )

7. Rotator Interval Closure

	•	In the setting of multidirectional instability with a primary posterior component, the rotator interval requires closure (defined by a 2+ or greater sulcus sign that does not improve in external rotation).
	•	The rotator interval is viewed with the arthroscope in the posterior portal.
	•	A crescent suture passer is advanced from the anterior portal through the anterior capsule just above the superior border of the subscapularis tendon 1 cm lateral to the glenoid.
	•	It is then passed through the middle glenohumeral ligament at the inferior border of the rotator interval. This makes up the inferior aspect of the rotator interval closure.
	•	A No. 0 PDS suture is then fed into the joint and retrieved with a penetrator through the superior glenohumeral ligament.
	•	The PDS suture is then withdrawn out the anterior cannula, and the knot is tied blindly in the cannula as the closure is visualized through the posterior portal.

Postoperative Considerations

Rehabilitation and Return to Play Recommendations

The rehabilitation program consists of a series of phases. Initially, the posterior capsule must be protected by avoiding extremes of internal rotation.

	•	Immobilization is maintained in an UltraSling (DonJoy, Carlsbad, Calif) for 6 weeks, abducting the shoulder approximately 30 degrees.
	•	Immobilization is removed for gentle passive pain-free range-of-motion exercises. We allow 90 degrees forward flexion and external rotation to 0 degrees by 4 weeks after surgery.
	•	The UltraSling is discontinued 6 weeks after surgery. Active-assisted range-of-motion exercises and gentle passive range-of-motion exercises are progressed, and pain-free gentle internal rotation is instituted.
	•	At 2 to 3 months after surgery, range of motion and mobilization are progressed to achieve full passive and active motion. Stretching exercises for the anterior and posterior capsule are instituted.
	•	By 4 months after surgery, the shoulder should be pain free. Concentration on eccentric rotator cuff strengthening is begun.
	•	At 5 months after surgery, isotonic and isokinetic exercises are advanced.
	•	At 6 months after surgery, throwing athletes undergo isokinetic testing. When patients are able to achieve at least 80% strength and endurance compared with the uninvolved side, an integrated throwing protocol is instituted.
	•	Throwers begin an easy-tossing program at a distance of 20 feet without a wind-up. Stretching and the application of heat to increase circulation before throwing sessions are critical.
	•	By 7 months, light throwing with an easy wind-up to 30 feet is allowed 2 or 3 days per week for 10 minutes per session.
	•	By 9 months after surgery, long, easy throws from the mid-outfield (150 to 200 feet) are allowed.
	•	By 10 months, stronger throws from the outfield are allowed, reaching home plate on only one or two bounces.
	•	At 11 months, pitchers are allowed to throw one-half to three-quarter speed from the mound with emphasis on technique and accuracy.
	•	By 12 months after surgery, throwers are allowed to throw from their position at three-quarter to full speed. When the throwing athlete is able to perform full-speed throwing for 2 consecutive weeks, return to full competition is permitted.
	•	Nonthrowing athletes and nonathletes are managed by criteria different from those for the throwing athletes. When patients are able to achieve at least 80% strength and endurance at the 6-month isokinetic testing compared with the uninvolved side, nonthrowing athletes begin a sport-specific program.
	•	In general, power athletes and contact athletes, such as weightlifters and football players, can return to full competition by 6 to 9 months after surgery. Noncontact athletes such as golfers, basketball players, swimmers, and cheerleaders can generally return to full competition by 6 to 8 months.

Complications

The complications include general risks of surgery, such as infection and hematoma formation, as well as risks particular to arthroscopic posterior shoulder stabilization, such as recurrent instability and stiffness.

PEARLS AND PITFALLS

•    There is open debate about whether the lateral decubitus or beach chair position better facilitates shoulder arthroscopy. We prefer the lateral position because we think it allows better access to both the anterior and posterior aspects of the shoulder. Placement of the shoulder in 10 pounds of traction in the position of 45 degrees of abduction and 20 degrees of forward flexion in effect displaces the humeral head anteriorly and inferiorly, bringing the posterior labrum into clear view. We have not been able to achieve such an unimpeded approach to the posteroinferior shoulder capsule in the beach chair position without imparting injury to the articular cartilage of the humeral head in the process.    •    We prefer to inject the glenohumeral joint with 40 to 50 mL of sterile saline before placement of the cannula into the glenohumeral joint. It inflates the joint to allow safer insertion of the cannula, limiting risk to the articular cartilage of the humeral head and glenoid.    •    After a determination of posterior labral disease or capsular laxity is made, a posterior working portal must be established. Placement of an 8.25-mm distally threaded clear cannula over a switching stick into the posterior portal will allow passage of both the crescent and 45-degree suture hooks. Smaller cannulas will not accommodate the 45-degree suture hook. We also recommend the use of suture anchors for capsulolabral reconstruction instead of suture capsulorrhaphy alone as it results in a more stable repair.    •    Difficulty in the placement of suture anchors can be encountered if the posterior portal is too far superior or medial in the posterior capsule. The conventional posterior portal is near 10-o’clock on the right glenoid, which makes approach to the posteroinferior glenoid difficult for the placement of suture anchors. We therefore place the posterior portal approximately 1 cm inferior and 1 cm lateral to the standard posterior portal in patients with demonstrable posterior instability on examination under anesthesia. When the posterior portal has been made too far superior, an auxiliary posterior portal can then be made inferior and lateral to the existing posterior portal. A spinal needle can be used in positioning the auxiliary portal at 7-o’clock on the glenoid and approximately 1 cm lateral to the glenoid rim on the posterior capsule for approach to the posteroinferior glenoid at a 30- to 45-degree angle in the sagittal plane. Cadaveric studies by Davidson and Rivenburgh[5] have shown the 7-o’clock portal to be a safe distance from the axillary nerve and posterior humeral circumflex artery (39 ± 4 mm) and the suprascapular nerve and artery (29 ± 3 mm). The use of blunt trocars in the placement of the portal further decreases the risk of neurovascular injury.    •    We do not routinely close the rotator interval in patients with unidirectional posterior instability. This practice is supported by several other studies in the literature.[13] Harryman et al[7] sectioned the rotator interval and found that in a position of 60 degrees flexion and 60 degrees abduction, a significant increase in posterior translation occurred. However, in posterior instability’s provocative position of 60 degrees flexion and 90 degrees internal rotation, no significant increase in posterior translation occurred after sectioning of the rotator interval. Furthermore, although imbrication of the rotator interval significantly decreased posterior translation at a position of 60 degrees flexion and 60 degrees abduction, it did not have a similar effect in the provocative position. A sectioned rotator interval did lead to a significant increase in inferior translation, which was corrected by imbrication of the rotator interval tissue. We do, however, perform rotator interval closure in patients with an inferior component to their instability, as defined by a 2+ or greater sulcus sign that does not improve in external rotation.

Results

Results of studies of arthroscopic repair of posterior shoulder instability are presented in
Table 8-1

.

Author	Followup	Outcome
Papendick and Savoie[13] (1995)	10 months	39 of 41 (95%) successful
McIntyre et al[11] (1997)	31 months	15 of 20 (75%) successful
Savoie and Field[15] (1997)	34 months	55 of 61 (90%) successful
Wolf and Eakin[18] (1998)	33 months	12 of 14 (86%) successful
Mair et al[10] (1998)	2-year minimum	9 of 9 (100%) successful
Antoniou et al[1] (2000)	28 months	35 of 41 (85%) successful
Williams et al[17] (2003)	5.1 years	24 of 26 (92%) successful
Kim et al[9] (2003)	39 months	26 of 27 (96%) successful
Fluhme et al[6] (2004)	34 months	15 of 18 (83%) successful
Bottoni et al[2] (2005)	40 months	16 of 18 (88%) successful
Provencher et al[14] (2005)	39 months	26 of 33 (79%) successful
Bradley et al[3] (2006)	27 months	91 of 100 (91%) successful