When someone breaks the arm bone (“humerus”), oftentimes the bone heals uneventfully without surgery. But things are different when the bone fracture happens to someone who already had a shoulder replaced: the presence of the replacement parts can compromise bone healing, and if surgery is needed, it can be quite difficult… That is one of the many reasons why it is so important to avoid accidents after shoulder replacement. Because these fractures involve a bone that already has a prosthetic implant inside, in Medicine these injuries are called “periprosthetic humeral fractures.” If a loved one has suffered a fracture of the humerus after replacement, our experience treating these injuries may help!
How Commonly Do These Injuries Happen?
Traditionally, the incidence of “periprosthetic humeral fractures” after shoulder replacement was quoted to be 1-2%. Since the number of shoulder replacements performed worldwide continues to rise, including older patients with balance issues and osteoporosis, we are witnessing a rise in the number of patients who suffer these injuries. One study estimated that there are approximately 750,000 people living with a shoulder replacement currently in the United States. With an estimated incidence of periprosthetic humeral fractures of at least 2%, every year 15,000 individuals or more could suffer one of these injuries!
What Has Changed Over Time…
In addition to the large number of individuals who live with a shoulder replacement, many of whom have osteoporosis and/or poor balance, the prosthesis that is implanted into the humerus at the time of shoulder replacement has been modified substantially over time. First, most replacements performed worldwide are reverse replacements. Second, cement fixation is less commonly used. Finally, the length of the humeral component has decreased over time, from long stems to short stems and stemless replacements.
New classifications are needed!
Older classifications of fractures of the humerus after shoulder replacement were developed before reverse was available, and when stems were for the most part long and often fixed with cement. The increasing use of reverse shoulder replacement and the growing implantation of shorter stems and stemless components has led surgeons to rethink how to classify these injuries. Consequently, we recently developed a classification system that considers reverse replacement, short stems and stemless prosthesis.
This classification is an adaptation to the shoulder of other classification systems used mostly for fractures after hip replacement. It describes the location of the fracture in reference to the humeral prosthesis, whether the humeral prothesis implanted has lost fixation, and the amount of bone stock remaining in the humerus. If you want to understand this classification better using medical literature, you can find additional information in the article below.
Our Current Thinking
Depending on the type of periprosthetic humeral fracture, treatment may vary widely. Fractures with minimal displacement in shoulders with well-functioning implants can oftentimes be managed successfully without surgery: the shoulder and arm are immobilized for a few weeks until the fracture heals on its own. On the contrary, badly displaced fractures and those complicating loose implants are better off with surgery. Our current thought process when surgery is needed is below.
If the humeral implant is well fixed but the fracture badly displaced or not showing signs of healing, internal fixation with plates and screws is typically best. However, this can be challenging: the humeral component is in the way of screws needed for fixation, and if the stem is very short (or after a stemless prosthesis) the bone on the upper end may not be much, and the surgeon must be ready to exchange the prosthesis if needed. A common strategy when internal fixation of periprosthetic humeral fractures is attempted is to augment metallic plate fixation with wires and/or bone graft in the form of a “bony plate” or “bone strut” from a donor.
If the humeral component must be changed, most surgeons will use stems that are longer than the component removed and still use plates and/or struts at the time of component exchange. In desperate situations where the remaining bone on the upper arm is really poor, surgery may entail use of a segment of graft from a donor with the prosthesis across the connection between graft and native bone (“allograft-prosthetic composite”) or replace the upper arm bone with a metallic prosthesis (in Medicine, these special prosthesis are called “modular metallic segmental replacements” or “tumor prosthesis”, since they are also commonly considered after removal of bone cancer).