Shoulder Arthroscopy

The Lipscomb Clinic Sports Medicine Center

Shoulder Arthroscopy

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Introduction:

Arthroscopy of the shoulder has become a very common procedure. It was first described by Burman in the 1930’s, but has only become a useful tool in the past 10-15 years. In that time, innovations in camera designs and fiber optics, as well as the development of specialized tools have moved shoulder arthroscopy from a diagnostic procedure to a treatment modality. Despite the large number of arthroscopies performed each year, shoulder arthroscopy can represent a challenging case to an inexperienced surgeon.

Instruments:

The primary instrument for arthroscopic surgery is the fiber optic arthroscope (shown below). Arthroscopes come in a variety of diameters and lens angles, but the most common scope used in arthroscopy of the shoulder is the 4 mm, 30 degree scope. It consists of a lens encircled by fiber optic fibrils that provide light for visualization. The eyepiece at the other end has recently been replaced by a television camera that allows visualization on a television monitor so all members of the surgical team can view the procedure.

To maintain distention in the joint for visualization and hemostasis, fluid is pumped into the joint under pressure. This is usually accomplished by a computerized pump that precisely monitors the flow rate and intra-articular pressure.

Another essential instrument is the motorized shaver consisting of a rotating blade encased within a smooth sheath. The shaver is connected to suction which draws fluid and tissue into the rotating blade allowing tissue to be removed from the joint.

A variety of other instruments including tiny scissors, biting forceps, burrs for resecting bone and electrocautery for hemostasis are used for specific cases.

Patient Positioning:

There are two distinct ways to position the patient during arthroscopic surgery of the shoulder. The first is the lateral decubitus position in which the patient is lying on his or her side with the affected limb up. The position is held with an inflatable bean bag that wraps around the patient, stabilizing even an anesthetized patient. The arm is then connected to a traction apparatus that applies 10 to 15 pounds of traction to distract the joint. The torso is then rolled back 15-30 degrees to orient the glenoid surface parallel to the floor. The arm is then abducted 70 degrees and forward flexed 15 degrees to improve visualization.

The second option is the beach chair position. In this position, the patient is sitting upright with the back of the bed flexed 70-80 degrees. The arm is allowed to hand freely at the side. No traction apparatus is required. The patient is positioned so that the affected shoulder hangs off the side of the bed allowing full access to both the anterior and posterior aspects.

Each position has both advantages and disadvantages. The lateral decubitus position, due to the arm position and traction applied, offers better visualization of the sub-acromial space. Also, the arm is fixed in space, avoiding the need for an assistant to hold the arm. However, this position requires conversion to the beach chair position should the shoulder need to be opened. Also, complications can occur from the traction apparatus, although these cases are rare.

The beach chair position is more comfortable to the awake patient and allows full ROM of the arm in the OR (sometimes requiring an assistant). Also, it avoids the need to re-position the patient if the arthroscopic procedure is converted to an open procedure. With no traction applied, complications caused be excessive traction can be avoided, however, this is often at the expense of visualization.

Portal Placement:

Arthroscopic surgery is performed through small incisions known as portals. These incisions are usually one centimeter or less in length, so placement of the portal is critical. The anatomy of the shoulder should always be outlined at the beginning of the case, so later when the soft tissues are distended and distorted, the portals can be accurately placed.

The standard portals for shoulder arthroscopy are the posterior, anterior and lateral portals. The accessory portals include the accessory anterior and superior portals.

The posterior portal is the primary portal used for visualization. It is usually established first and allows visualization of most of the anterior, superior and inferior structures of the joint. It is placed 3 cm distal and 1 cm medial to the postero-lateral tip of the acromion. It is placed in the "soft-spot" of the shoulder formed by the interval between the infraspinatus muscle and the teres minor muscle. Therefore, this portal should traverse skin, subcutaneous tissue, posterior deltoid and joint capsule. Structures at risk with this portal include the posterior humeral circumflex artery, the axillary nerve and the scapular circumflex artery.

The anterior portal is the work-horse of the shoulder. Most of the instruments used within the gleno-humeral space are passed through this portal. It can be established with either and inside-out or outside-in technique. With the inside-out technique, the arthroscope in the posterior portal locates the precise position where the anterior portal should be and a rod is passed through the arthroscpopic cannula to exit the anterior shoulder.

A cannula is then passed retrograde over the rod, and the portal is established. The outside-in technique locates the precise placement be passing a needle through the anterior shoulder and visualizing where it enters the joint. When an acceptable position is found, an incision is made and the portal established. The portal should be placed lateral to the coracoid, roughly between the coracoid and the anterior acromion. The structure at risk with this portal is the musculocutaneous nerve.

The lateral portal is used in the sub-acromial space for decompression and visualization. It is located just lateral to the lateral edge of the acromion at its anterior aspect. The structure at risk is the axillary nerve.

The superior portal is seldom used but can prove invaluable is select cases. It is placed in the superior "soft-spot" bordered by the posterior edge of the clavicle, medial edge of the acromion and the anterior edge of the scapular spine. When used in the gleno-humeral joint, the portal passes through the supraspinatus muscle which prevents its routine use. The structures at risk are the suprascapular nerve and artery.

Arthroscopic Anatomy:

During arthroscopic surgery of the shoulder, two general areas of the shoulder are examined, the glenohumeral joint and the sub-acromial space above the rotator cuff. Within each general area, specific anatomic structures are visualized.

The first area examined is the glenohumeral joint. Within this space are several structures that must be viewed. These include the glenoid(G), humeral head(HH), biceps tendon(B), labrum, subscapularis tendon(SS), superior glenohumeral ligament(SGHL), middle glenohumeral ligament(MGHL), inferior glenohumeral ligament complex(IGHLC) and the undersurface of the rotator cuff.

Within the sub-acromial space, one should see the undersurface of the acromion, the distal end of the clavical, the undersurface of the acromiocalvicular joint, the sub-acromial bursa and the superior surface of the rotator cuff.

Specific Anatomic Structures:

The biceps tendon (B) attaches to the superior portion of the glenoid (G) and serves as one of two points of origin for the powerful biceps muscle. It is the primary structure used for orientation during arthroscopic surgery. It angles inferiorly 10-15 degrees from the horizontal to exit through the interval between the subscapularis (SS) and the supraspinatus, the rotator interval. The tendon is intimately associated with the superior labrum and should be smooth in appearance throughout its course.

The humeral head (HH) and glenoid (G) are the articulating surfaces of the shoulder joint and should be smooth throughout. Approximately 1/3 of the humeral head can be visualized at any given time through the arthroscope. The humeral head articulates with the glenoid which is pear-shaped and approximately Ľ the size of the humeral head. Thinning and fibrillation of the cartilage at the inferior portion is normal after the second decade of life.

Interspersed between these surfaces is a ring of tissue (glenoid labrum) that increases the stability of the joint by increasing the congruity between the surfaces. The labrum is 3-4 mm in thickness and is intimately associated with the inferior gleno-humeral ligament complex inferiorly and the superior gleno-humeral ligament and biceps tendon superiorly. The inferior portion should be firmly attached to the glenoid. It should be smooth throughout, although fraying is normal later in life.

The superior gleno-humeral ligament (SGHL) is the smallest of the three ligaments and runs from the base of the coracoid and superior labrum to the anatomic neck of the humerus. It prevents inferior instability with the arm in the adducted position. The ligament is often poorly visualized due to its location behind the biceps and its small size.

The middle gleno-humeral ligament (MGHL) runs from the superior and middle glenoid, scapular neck to the anterior neck of the humerus. It courses across the posterior surface of the subscapularis to which it is often adherent. This ligament functions to prevent anterior instability in the 45 degree abducted arm.

The inferior gleno-humeral ligament complex (IGHLC) is divided into anterior and posterior bands, with an axillary pouch between. This is the most important stabilizer of the shoulder functioning to prevent anterior instability in the 90 degree abducted arm.

The subscapularis (SS)tendon makes up the anterior portion of the rotator cuff muscles. This is a large tendon, only the most superior of which can be viewed from within the joint. It should be smooth throughout its course.

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The undersurface of the rotator cuff (RC) is a common site of partial rotator cuff tears. This confluence of tissue represents the insertion of the supraspinatus, infraspinatus and teres minor muscles which can be viewed at the insertion onto the humeral head.

Specific Clinical Problems:

Instability is often caused by detachment of the inferior gleno-humeral ligament complex from the inferior glenoid (Bankart lesion). This is often accompanied by stretching of the remaining fibers, leading to laxity in the shoulder. Although the detached ligament can be repaired arthroscopically, the deformation caused by the stretching is more difficult to address. Due to this, many surgeons prefer to treat this problem through an open procedure, especially in contact athletes.

Rotator cuff tears usually occur in the tendinous insertion on the lateral aspect of the humeral head. These can also be treated through the arthroscope. The torn tendon can be repaired to the bone using metal or plastic anchors. However, many surgeons feel that a more stable repair can be accomplished through a small, "mini-open" procedure.

Impingement syndrome results from bony encroachment on the rotator cuff, leading to inflammation and even rotator cuff tears.

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This often causes pain with elevation and internal rotation of the arm. Impingement is usually treated non-operatively, but resistant cases often require removal of the spur. This is ideally suited for arthroscopic surgery in which a small motorized burr is used to resect the bone. By performing the procedure through the arthroscope, less tissue is disrupted.

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