How to Fix Shoulder Instability Due to Bone Loss

I have previously written about shoulder instability. At that time, I briefly mentioned that episodes of shoulder instability could cause injuries to the major bones of the shoulder. I want to delve into this topic a little deeper. More recent information shows us that these bone injuries have a critical role in the prognosis and treatment recommendations for those with shoulder instability.

As you may recall, instability of your shoulder is a term that describes when the two bones that form the primary shoulder joint, the Humerus (ball) and Glenoid (socket), become partially or completely separated.

There are many ways shoulder instability may develop. Although this can occur from having “loose” joints, this often results from trauma. Either way, bony injuries to either the ball or the socket can result when the ball moves out of the socket. If this happens, bone loss may occur either abruptly or slowly – a little bit with each instability episode over time.

What Causes Bone Loss in the Shoulder?

When trauma forces the ball out of the socket, an obvious fracture or possibly just slight wear of either joint bone may occur. Let’s look at when this happens with the most common type of shoulder instability, anterior instability. Anterior instability is when the ball comes out the front of the shoulder. The same phenomena can occur for posterior instability, as the Humerus is forced out the back of the shoulder. However, the bone injuries would appear on the opposite sides of the injured bones.

During anterior instability, the ball slips off the front edge of the Glenoid as it goes out the front of the shoulder joint. When this occurs, the back of the ball is likely to contact the front of the socket. If this happens significantly, the bone at the back of the Humerus or front of the Glenoid can fracture.

Why is instability more likely?

If we think of the Glenoid as a runway on an aircraft carrier and the Humerus as an airplane, we can better understand why narrower bones are problematic. Let’s also assume that the jet will fall off the carrier when its back tires cross the ship or runway’s edge. Therefore when the pilot initiates stopping and hits the brakes, the jet would be more likely to fall off the aircraft carrier if the carrier were shorter rather than longer. Similarly, if the airplane were shorter, the plane’s back tires would be more likely to cross the carrier’s edge sooner, and the plane would consequently be more likely to fall off the carrier, as well. Finally, if both the carrier and the aircraft were shorter, the likelihood of the jet falling off the aircraft carrier would be the greatest.

The bone defects on the Humerus and Glenoid similarly increase the risks of shoulder instability. Even small losses of bone on the Glenoid side, as little as 13% – only a few millimeters – can make a difference.

If a discrete fracture doesn’t occur, wear of the bones may occur, nonetheless. When a fracture occurs, displacement of the fracture fragments can result. Displacement means that the force from the injury moves the broken bone away from the joint surface, essentially lessening the available joint surface.

There are numerous potential treatments for shoulder instability based on the cause such as:

• Humeral Bone Loss

When indicated, we can perform an additional arthroscopic technique called a Remplissage procedure during the same surgery as your arthroscopic labral repair.

The Remplissage procedure involves attaching one of your rotator cuff tendons to the area of bone loss in the back of your shoulder (Hill Sachs Lesion). This attachment acts as a check-rein that restricts your Humerus from moving too far forward.

If we go back to the jet and aircraft analogy, the Remplissage functions much like the arresting cable that gets snagged by the jet’s tailhook at the back of the plane. These wires prevent the aircraft from traveling too far forward and thus help to prevent the airplane from falling off the carrier. The Remplissage works in the very same way for your Humerus and prevents it from falling off your Glenoid.

Alternatively and rarely, your surgeon can fill the bone defect in the back of your shoulder with a bone graft covered by cartilage and obtained from a cadaver. Depending on the size of the needed graft, this may be performed arthroscopically. However, usually, this procedure is completed through a larger open incision.

• Glenoid Bone Loss

When our Glenoid is short, or, as in our example, the aircraft carrier is short, our runway is short, and our Humerus, like a landing aircraft, is more likely to fall off the front. However, if we lengthen the runway, this becomes much more difficult. So when we have Glenoid bone loss, we aim to extend the Glenoid from front to back using a bone graft.

There are several ways to achieve this, all with some advantages and disadvantages. But overall, the success rates of these procedures are similar and overall very good. First, some techniques use your bone – autograft, and some use the bone of others who are deceased – allograft.

Autograft

Autograft options include using your coracoid (see picture above), a small bone in the front of your shoulder, along with its attached tendons – moving this from its native location and fixing it to the front of your shoulder. This procedure is called a Laterjet or Bristow procedure. Alternatively, bone from the crest of your pelvis can be harvested and fixed to the front of your Glenoid.

Allografts

The allograft options can also include bone from the pelvis crest, but a more enticing prospect is using a distal tibial allograft.

It turns out that the curve of all of our joint surfaces is the same, no matter the joint. As a result, using bone from the more readily available distal tibia (end of our leg bone at our ankle) is possible. This graft not only matches the natural curve of our Glenoid, but it allows for a larger, more dense graft coated on the joint surface by cartilage, just like our native Glenoid. These are benefits that other grafts, including the autograft options, cannot match.

It appears that the denser, more significant bone enables a better fit to the Glenoid with a graft that is less likely to absorb over time. Additionally, the more normal joint shape and cartilage covering the graft will hopefully result in lesser degrees of degenerative joint changes over time.

Most surgeons perform these procedures through an open incision. Some centers have shown promising early results when performing similar operations arthroscopically.

Take-Home Lessons

• Bone loss associated with instability can result from greater instability forces or numerous less violent instability episodes.

• This bone loss can occur on both the Humerus and Glenoid.

• Even lesser degrees of bone loss can lead to more frequent shoulder instability.

• Such bone deficiency can require more complicated surgical procedures to correct your instability.

• Often, these surgeries necessitate either a tendon transfer or an open bone graft.

To learn more about options for shoulder pain and instability, you can request an appointment or call us any time at (571) 250-5660 to speak with a Town Center Orthopaedics team member.