Shoulder Instability: Securing the Ball

Shoulder Instability: Securing the Ball

[Megan Moran, PA-C] A brief overview of our game plan today. We will review the anatomy and learn how shoulder instability might occur, what the evaluation of this pathology entails, and what techniques are available to help restore shoulder stability. Let us start off with anatomy and biomechanics.

When discussing shoulder instability, we are referring to the glenohumeral joint, the ball and socket joint within the shoulder. This is the most mobile joint in the body, but it is also very unstable. This is due to the round humeral head, also known as the ball, sitting on a relatively flat glenoid, also the socket. Since the bony structure does not impart much stability on its own, we rely on other structures such as muscles, tendons, and ligaments such as the glenohumeral ligaments here and the glenoid labrum to help surround the glenohumeral joint and secure the ball. However, excessive strain or force on these structures can lead to injury.

Shoulder instability occurs more frequently in young adult athletes, specifically in contact sports like hockey, rugby, or football, as seen here. The excessive strain or force to the glenohumeral ligaments and labrum can be a result of a traumatic injury, such as a football player falling to the ground or even repetitive microtrauma or overuse injuries, as we see here with these linemen pushing each other away, which can occur over time.

Instability can be further categorized by the direction in which the patient experiences their symptoms. In this animation, we are looking at a right shoulder from the side. Instability, or a complete dislocation event, can occur in a posterior or backward direction, inferior or below direction. Most commonly seen, is anterior or out towards the front of the body.

Let us go back to the football players. The mechanism of injury seen here, with the patient on the left falling to the ground on an outstretched arm, might result in anterior instability of the shoulder. However, with our players on the right, the act of pushing one another away results in the ball rubbing against the back of the shoulder socket and, over time, may result in posterior instability. Anterior dislocations seen here account for approximately 90% to 98% of all shoulder dislocations and will be the main focus for the rest of our discussion.

There are different mechanisms of injury that can lead to an anterior shoulder dislocation. Often, with contact athletes, this can occur by a direct blow to the shoulder in a position of compromise, like we see here, or what we refer to as the 90/90 position. A dislocation event can also occur by falling on an outstretched arm, as we saw earlier, or by a direct hit to the arm from behind.

After a dislocation event to the glenoid labrum, the O-shaped piece of cartilage that helps to stabilize the ball and socket joints can get torn or pulled away from the socket on the front of the shoulder. The resulting injury caused by this anterior and inferior injury to the glenoid labrum is called a Bankart tear. Sometimes, even a piece of bone fractures or breaks off with the glenoid labrum, which we refer to as a bony Bankart, which you see here in the CT scan.

Other sequelae can include a Hill-Sachs lesion, which can occur during an anterior dislocation where the back portion of the humeral head comes into direct contact with the front of the bony glenoid. The bony glenoid then compresses the bone of the humeral head and now creates a dent or a pothole similar to that on the road.

Now that we know a bit more about the glenohumeral joint, how dislocations happen, and the pathology that may result, what are the surgeon's next steps when a patient comes into their office. The clinician will perform a physical exam assessing for stability of the shoulder, using certain tests to assess for the different pathologies that may have occurred. X-rays are ordered to allow the medical team to ensure the shoulder is back in the socket or back in place, as well as to determine if there are any broken bones or fractures.

The orthopaedic surgeon may also order a CT scan or MRI to better evaluate the bone and soft tissue. An MRI seen here is best at evaluating the soft tissues such as the glenoid, labrum, and glenohumeral ligaments, to determine the amount they are stretched out or even torn. The orthopedic surgeon will also take into account several factors after a patient sustains a shoulder dislocation, including the patient's age, past medical history, activity level and type, and if the patient is in or out of their sports season.

Let us say the orthopedic surgeon has diagnosed the labral tear in a contact athlete. What is next? Although nonoperative management can be reasonable in certain patient populations when we are discussing treatment in a young athletic individual, studies show us that the risk of another dislocation is extremely high, and surgeons will carefully evaluate and consider early surgical intervention even just after one dislocation event.

For operative treatment of instability, we will be focusing on labral repairs so we can fix that Bankart lesion we previously discussed. Historically, this surgery was completed via a large open incision, but with technological advancements, this can now be performed using a minimally invasive approach via arthroscopy where we use a small camera through smaller incisions around the shoulder. Here, you see the common incision sites surgeons will use for this type of procedure.

To fix these labral tears, we are now using smaller soft-bodied knotless anchors where previously larger hard-bodied anchors were used that required knots to be tied. These smaller anchors allow for preservation of the native glenoid bone. To start a labral repair, an arthroscope, the camera, is placed in the back of the shoulder, while plastic cannulas are placed up front, which allows the surgeons to smoothly and safely use instruments required to complete the labral repair.

Here, a drill guide is introduced and placed at the rim of the glenoid. A pilot hole is then made and the soft anchor is introduced via the drill guide. After a series of steps, the blue and white repair suture is passed around the labral tissue and loaded into a shuttling suture that allows the surgeon to secure the labral tissue back to the glenoid bone. This process will then be repeated with multiple anchors dependent on how large the tear is until all the tissue is reapproximated back to bone.

In the case of an isolated labral tear, the recovery process can begin. As previously mentioned, a Bankart lesion is not the only type of pathology that can occur with shoulder instability. Labral tears can occur at the top or at the back of the labrum. Some patients may even have a Hill-Sachs lesion or impaction at the back of the humoral head. A procedure known as a remplissage, which is French for "to fill in," can help fill the defect.

If a patient has suffered from multiple anterior dislocations, they have likely lost native bone on the front of the glenoid, which then requires a bony procedure such as a Latarjet seen here to help restore shoulder stability. No matter what type of pathology, the goal of these procedures remains the same: to help our young patients and athletes get off the bench and back onto the field safely. Thank you for tuning in to OrthoPedia Patient.