32 Open Posterior Stabilization

10.1055/b-0039-167681

32 Open Posterior Stabilization

Joo Han Oh

Abstract

Posterior shoulder instability is mostly caused by acute traumatic events; it is rare and also challenging to treat. Patients with posterior instability have vague symptoms that make surgical decisions more difficult. Therefore, detailed history taking and thorough physical examination are crucial for proper patient selection and better outcomes. Despite rapid advances in arthroscopic treatment for posterior instability, there is still need for open surgery for challenging cases. If there is significant posterior capsular redundancy, open posterior capsulorrhaphy should be done. Since up to 40% of patients with posterior instability have concomitant posterior labral lesions, these can be repaired simultaneously with open posterior capsulorrhaphy. In the case of significant bone loss, dysplasia, or glenoid retroversion, bone graft on the posterior rim or wedged open osteotomy is required. With advances in surgical techniques and skills, numerous studies have reported good to excellent outcomes with open posterior capsulorrhaphy. However, most are level IV studies that are difficult to interpret. In terms of bony procedures, debate is ongoing regarding outcomes, since some studies reported complication rates as high as 36%. To ensure better outcomes, care must be taken to select the proper patients for surgery. As not every case can be treated by arthroscopic posterior stabilization, knowledge of open posterior stabilization would help the surgeon to plan and treat patients with challenging cases.

32.1 Introduction

Posterior shoulder instability, first described in 1838 in a patient who had an epileptic seizure, is rare but challenging to treat, and even difficult to diagnose due to vague symptoms. ¹ ^– ⁴ It is caused by an acute traumatic event, repetitive microtrauma, or atraumatic causes in only 2 to 5% of all cases. ⁵ ^– ⁸ Among individuals with posterior instability, up to 40% have concomitant posterior labral lesions. ⁹

With rapid advances in arthroscopy, many studies have reported high satisfaction rates and low recurrence rates. ¹⁰ ^– ¹² However, open surgery is still needed for revision, significant capsular insufficiency, poor-quality tissue, significant bone loss on glenoid, glenoid dysplasia, or retroverted glenoid. ⁹

32.2 Patient History and Physical Examination

As the symptoms are not always obvious, detailed history taking is important. Patients may have weakness or pain in their shoulder, and sometimes complain of difficulty performing pushups. The most important thing to ask is whether the patient’s main symptom is pain or instability. Patients who complain of pain usually describe it as a deep, posterior shoulder pain. ² ^, ¹³ The severity and frequency of the pain should also be determined. In addition, since most patients have had traumatic events, determining the details including the position of the arm at the time of injury is important. ¹⁴ ^, ¹⁵ Inquiring as to the number of prior dislocations or subluxations, the first and most recent episodes, and self-reduction or reduction by a medical professional may help the surgeon decide how to treat the patient. If the patient had prior surgeries, obtaining information about the procedures could aid in deciding the next step. In addition, chronicity, general laxity, family history of disease, and history of voluntarily reproduced instability should be determined, since those cases may have more difficulty achieving good outcomes. Finally, the surgeon should acquire the information about sports or work activity levels.

Range of motion (ROM) and pain location should be evaluated. Patients may have full ROM, but comparison with the contralateral shoulder should be assessed. Focal tenderness in the posterior glenohumeral joint area should be determined. Provocative tests, including the posterior stress test, jerk test, load and shift test, and Kim’s tests may help with diagnosing posterior instability. ⁷ ^, ¹⁶ In addition, a positive sulcus test in 30 degrees of external rotation while applying longitudinal traction suggests that the patient may have multidirectional instability and may need rotator interval closure. ¹⁷ Finally, it is crucial to determine whether the patient has general laxity. Patients with general laxity may have positive results in three of the following five tests: ability to perform thumb approximation to the volar surface of the forearm; ability to place the palm of the hand flat on the floor with the knees straight or show hyperextension of the second metacarpophalangeal joint greater than 90 degrees; ability to hyperextend the elbow over 10 degrees, or show genu recurvatum/hyperextension of the knee over 10 degrees. ¹⁸

32.3 Imaging Evaluation

32.3.1 Plain Radiographs

Standard X-rays including true anteroposterior (AP) view, “Y” view, and an axillary view provide critical information. Among the plain X-rays, the axillary view ( Fig. 32.1a) is the most informative for evaluating the relationship between the humeral head and glenoid. By evaluating X-rays, the surgeon can assess whether the patient has bony lesions such as a reverse Hill–Sachs lesion, reverse Bankart lesion, glenoid retroversion, or glenoid dysplasia.

**Fig. 32.1 (a)** The axillary view shows the relationship between the humeral head and the glenoid. **(b)** The percentage of glenoids remaining in patients with bone loss can be calculated by CT. **(c)** MR images facilitate evaluation of soft tissues of the shoulder including the labrum, capsule, rotator cuff muscles, and biceps.

32.3.2 Computed Tomography or CT Arthrography

CT with 3D images also help with planning by giving more detailed information of bone loss. The author calculates the percentage of glenoids remaining in patients with bone loss and glenoid version by use of CT ( Fig. 32.1b). Moreover, 3D images provide considerable information for planning if the patient needs a bone graft. CT arthrography is useful to evaluate any soft-tissue lesions as well as bone loss, such as a reverse Bankart lesion, capsular redundancy, or any concomitant anterior lesion of the glenoid.

32.3.3 Magnetic Resonance Imaging or MR Arthrography

MRI or MRA ( Fig. 32.1c) may help with evaluation of soft tissues of the shoulder including the labrum, capsule, rotator cuff muscles, and biceps. Furthermore, the existence of any bony edema, hematoma, or swelling may help distinguish between acute traumatic or chronic causes of posterior instability.

32.4 Operative Management: Overview

Numerous studies have reported various surgical techniques for posterior instability. ² ^, ⁶ ^, ⁹ ^, ¹⁵ ^, ¹⁹ ^– ²¹ However, possibly due to vague symptoms that cause difficulty in decision-making regarding the cause of shoulder pain, the outcomes have not been very satisfactory, compared to those in anterior instability. ²⁰ ^, ²²

One solution for posterior capsular redundancy, which is the most common reason for posterior instability, is capsular plication or shift. ⁹ This can be done by using arthroscopy only, but if significant capsular redundancy is found, treatment should be performed with open capsular shift. If the patient has a reverse Bankart lesion, it should be repaired. In addition, sometimes bone graft or posterior opening wedge osteotomy is needed to treat a large bone defect or excessive glenoid retroversion in an open posterior stabilization procedure. ²⁰ ^, ²³ ^– ²⁵ However, with open surgery, it is impossible to assess or treat other concomitant pathology such as a Bankart lesion, which requires arthroscopy before open surgery.

32.5 Operative Management: Technique

32.5.1 Patient Positioning

Under general anesthesia, the patient is positioned in a lateral decubitus position with a beanbag or anterior and posterior body support. Every protruding area of the patient that is in direct contact with the bed should be protected with padding. To prevent common peroneal nerve palsy, padding under the distal thigh is necessary. In addition, one pad should be placed below the axilla to prevent axillary nerve palsy. With slight flexion of the knee, stretching of the neurovascular system of the lower leg can be avoided. Draping should be done without causing any limitation of motion of the upper arm. Putting a pillow between the anterior chest and the arm with slight abduction can help stabilize the arm during surgery ( Fig. 32.2 ).

**Fig. 32.2** Abduction of the shoulder helps with superior retraction of the posterior deltoid. The arm is in the lateral decubitus position with 30 degrees of abduction.

Due to difficulty in observing the anterior glenoid in an open procedure, using a mechanical arm holder at the opposite side of the operating table is helpful for arthroscopic evaluation to explore any combined lesions and treat a Bankart lesion or perform rotator interval closure.

32.5.2 Surgical Approach

Among the various surgical approaches, the author prefers the vertical approach. It is the most cosmetic and has the advantage of exposing the glenohumeral joint without detaching the posterior deltoid. However, careful dissection should be done to avoid injury to the axillary nerve while splitting the distal area.

From the scapular spine at the same level of the acromioclavicular joint anteriorly, the incision should be made distally in the direction of the axillary fold. After dissecting subcutaneous tissues, the deltoid is exposed. By blunt longitudinal dissection through the posterior deltoid fibers above the posterior glenohumeral joint line, beginning from the scapular spine to approximately 4 to 5 cm distally, the infraspinatus and teres minor are exposed ( Fig. 32.3a). After identifying the interval between the infraspinatus and teres minor, continue dissection on the fat stripe over the raphe separating the two heads of the infraspinatus ( Fig. 32.3b). Usually, the raphe of the infraspinatus lies on the equator of the glenohumeral joint. Care should be taken to avoid confusing the raphe with the interval between the infraspinatus and teres minor, which lies below the equator of the glenohumeral joint. Splitting the infraspinatus has several advantages, such as obtaining good exposure to the posterior capsule, labrum, and glenoid, or preserving the insertion of the infraspinatus to the humerus. Careful separation of infraspinatus from the posterior capsule is needed due to the axillary nerve passing inferiorly and the suprascapular nerve passing around 15 mm medial to the line of the posterior glenoid rim ( Fig. 32.3c).

**Fig. 32.3 (a)** After longitudinal splitting of posterior deltoid fibers, the infraspinatus and teres minor are exposed. **(b)** The fat stripe over the raphe separating the two heads of the infraspinatus is shown and the axillary nerve is located below the teres minor. **(c)** The suprascapular nerve passes approximately 15 mm medial to the posterior glenoid rim and the axillary nerve passes inferior to the teres minor.

Careful dissection is needed while splitting the distal part of the deltoid to avoid axillary nerve injury.
If the surgeon does not want to dissect the deltoid, the infraspinatus and teres minor can be exposed by abducting the arm to 90 degrees and retracting the deltoid upward in the direction of the patient’s head. At this point, care should be taken at the inferior border of the teres minor to prevent injury to the axillary nerve or posterior humeral circumflex vessels ( Fig. 32.4 ).
When the interval between infraspinatus and teres minor is difficult to determine, try to dissect along a muscular section instead of at the humeral insertion site of two muscles.
Try to use a blunt elevator while dissecting infraspinatus from posterior capsule to avoid any damage to the suprascapular nerve medially.
By rotating the arm slightly externally, relaxation of the axillary nerve can be achieved to prevent any damage, while dissection and rotator interval dissection can also be facilitated if needed.