Fotios Paul Tjoumakaris, MD and James P. Bradley, MD
In recent years, posterior shoulder instability has become a recognized cause of shoulder pain and disability, particularly in overhead athletes. Although less common than anterior shoulder instability, posterior instability of the shoulder can be just as disabling and cause athletes to miss games or have reduced sports performance. Anterior instability typically presents to the clinician with a dislocation event, whereas posterior shoulder instability presenting complaints are often more vague (pain, loss of strength, etc). More commonly, patients presenting with symptoms likely suffer from recurrent posterior subluxation (RPS), and not necessarily frank glenohumeral instability. With a detailed history, physical examination, and appropriate imaging, the diagnosis is often easily made. With the emergence of advanced imaging techniques, such as magnetic resonance arthrogram (MRA), a clear picture of the pathology necessary to treat is evident. Management of associated pathology, such as capsular laxity, may often be necessary in many patients, making an accurate diagnosis and patient specific considerations important (sport of play, position, etc).
In years past, open shoulder stabilization of posterior shoulder instability was the gold standard; however, many patients treated under this paradigm continued to report symptoms. Higher-level athletes were often unable to return to their previous level of competition, necessitating a more effective treatment strategy. For this reason, arthroscopic techniques were developed and have continued to advance over the past 3 decades. An arthroscopic approach allows for a more detailed assessment of joint status, the ability to treat associated pathology, and an enhanced ability for both capsular and labrum repair. The results of arthroscopic treatment have outpaced those of open techniques and continue to evolve. The following chapter will outline and describe the arthroscopic management of posterior shoulder instability.
Whether a patient presents after an initial dislocation event, or with symptoms consistent with RPS, an initial trial of nonoperative management is typically attempted. Those patients who fail treatment with nonoperative management (activity modification, physical therapy, nonsteroidal anti-inflammatory medication, etc) and demonstrate imaging findings consistent with the diagnosis of posterior shoulder instability are surgical candidates. Additionally, those patients who qualify for surgery must also be cooperative and willing to engage in an extensive postoperative rehabilitation program. The majority of patients are candidates for arthroscopic repair; however, patients with capsular deficiency (from prior surgery) or who have significant bone abnormalities (glenoid retroversion, large reverse Hill-Sachs lesion) may be candidates for an open technique (allograft capsular reconstruction, glenoid wedge osteotomy, McLaughlin technique).
Patient History and Examination
The diagnosis of dislocation may have been missed after an initial evaluation. This often occurs after a fall on an outstretched hand in the position of adduction, slight forward flexion and internal rotation. Patients can often dislocate posterior after a seizure or an electrocution accident. Patients will report pain with any attempted range of motion and will often hold the arm at the side in a position of internal rotation. The majority of patients will often present with symptoms of RPS. This will often be the result of repetitive microtrauma to the posterior capsule and/or labrum. Athletes may report deep seated or posterior shoulder pain. They may report difficulty with overhead throwing or a loss of velocity. In some instances, patients may report clicking in the shoulder or a “clunk” when the arm is moved from adduction to an abducted position. Patients who present with a posterior glenohumeral dislocation will have a “locked” shoulder that is resting at the side in maximum internal rotation. The patient is often unable to have the arm externally rotated secondary to the entrapment of the lesser tuberosity on the posterior glenoid rim. Labrum provocative testing such as O’Brien’s test and the Mayo shear test may be positive. Specific posterior labrum tests such as the Kim test or “jerk” test may be present, and a posterior apprehension sign with load and shift testing may also help to rule in the diagnosis when positive. Pain or instability is classically elicited with the arm in the posterior apprehension position (flexion, adduction, and internal rotation).
Imaging (X-Rays and Magnetic Resonance Imaging/Computed Tomography)
Radiographs are often initially ordered and reviewed for glenohumeral dislocation. In rare instances, glenoid dysplasia or reverse Hill-Sachs lesions may be present on screening radiographs (Grashey AP, Y-view, axillary). Additional views (Stryker notch, West Point) can be obtained as well; however, these views are often better at evaluating posterior humeral head and anterior glenoid pathology that is often found in anterior glenohumeral instability. Computed tomography (CT) is often obtained when there has been a dislocation event or when significant osseous pathology is suspected. MRA of the shoulder is generally considered the gold standard and is helpful for detecting posterior labrum detachment as well as concealed labral tears (Kim lesion). A Kim lesion is an incomplete avulsion of the posterior-inferior labrum that is hidden by an intact superficial component. The MRA is also checked for posterior chondral erosion, paralabral cysts, and concomitant pathology of the superior and anterior labrum, biceps tendon, and the rotator cuff musculature (Figure 19-1).
The overall goal of posterior instability repair is to tailor the surgical technique to the individual needs and demands of the patient. Patients who present after a singular or multiple dislocation episodes (macroinstability) without bone defects will likely require posterior labrum repair in addition to capsular plication to prevent recurrence. Patients with microinstability (RPS) or those who are likely to return to overhead throwing are more likely to benefit from isolated posterior labrum repair without an extensive capsular plication to optimize their return to sport and specifically, throwing. Those patients who present with a multidirectional instability picture will likely require a combination of techniques around the shoulder to restore normal glenohumeral biomechanics.
Examination Under Anesthesia
Patients undergoing arthroscopic posterior labrum repair typically receive general anesthesia (for muscle relaxation) with or without interscalene nerve block for postoperative analgesia. While the patient is under anesthesia and in the supine position, range of motion is first checked for symmetry to the contralateral extremity. A load and shift test is then performed on the operative extremity and once again compared to the opposite shoulder. It is not uncommon for the humeral head to be displaced posteriorly over the glenoid rim rather easily; however, on release of posterior directed pressure, the humeral head should once again reduce into the glenoid socket. Any abnormal motion, clicking, grinding, or gross subluxation could indicate labrum pathology, or a glenoid or humeral head defect.
Our preferred patient positioning for arthroscopic posterior labrum repair is the lateral decubitus position. Although the beach chair position can be used, the lateral decubitus position lends itself naturally to excellent visualization of the posterior labrum, glenoid, and capsule. The arm is placed in an abducted position of 45 degrees with 20 degrees of forward flexion (this can be flexed more during placement of the most inferior anchor for better access and visualization). Ten to 15 pounds of longitudinal traction is usually applied for slight joint distraction and to maintain this abducted and forward-flexed posture of the shoulder. Additionally, the axilla should be kept free or padded to prevent neuropraxia on the down extremity. A peroneal pad is also placed on the lower extremity that the patient is resting on. The bed is typically angled 45 degrees away from anesthesia and the visualization tower is placed across the surgical field and at eye level to the surgeon for 360-degree viewing. A wide preparation is then performed to make sure that easy access to the shoulder both anteriorly and posteriorly can be achieved.
The acromion, coracoid process, and acromioclavicular joint are palpated and denoted prior to incision with a marking pen. The posterior portal to the shoulder is typically in line with the lateral edge of the acromion (slightly lateral to a traditional posterior portal). This portal is typically made 2 to 3 fingerbreadths below the acromion. This portal placement allows for tangential access to the posterior glenoid rim for future anchor placement if necessary (or if a single posterior portal technique is preferred). The joint is insufflated with 20 to 30 cc of normal saline from this portal prior to the stab incision. The anterior portal is placed next in an “inside-out” fashion in the rotator interval with a trajectory that is diagonal from the coracoid process to the anterolateral edge of the acromion. After portal placement, a 6- to 7-mm clear cannula can be placed anteriorly using a traditional dilation technique.
A 30-degree arthroscope is traditionally used and viewing is first undertaken from the posterior portal. Concomitant pathology such as superior labrum tears, anterior labrum tears, subscapularis tendon tears, undersurface rotator cuff tears (internal impingement), and chondral injury are evaluated. The biceps tendon is also critically evaluated by inspecting the biceps root, labrum just posterior to the biceps root, and the degree of pathology once the tendon is pulled into the joint from the anterior portal. Any synovitis or tendon damage should be assessed and the need for biceps tenodesis is critically evaluated. The posterior labrum is then evaluated in its entirety through the posterior portal from the inferior aspect by the axillary recess to just posterior to the biceps attachment. An arthroscopic probe from the anterior portal can be used to evaluate detachment of the labrum (Figure 19-2). Superficial debridement of the labrum is first undertaken with a 4.5-mm full radius shaver to remove free edge fraying to gain better visualization of the labrum.