It may come as a surprise to learn that some times the bones of the shoulder are shattered beyond repair. Fortunately, most shoulder fractures heal properly on their own. When surgery is required, surgeons can oftentimes put the broken pieces together with screws, plates, nails, sutures, or a combination (i.e., the fractured is fixed internally). But when there is a really bad fracture of the upper portion of the bone in the arm (fractures of the upper part of the humerus), shoulder replacement becomes the best solution.
Understanding some terms about shoulder fractures may be difficult!
The uppermost portion of the bone in the arm (humerus) and the socket (glenoid) of the shoulder blade form the shoulder joint. Fractures involving the upper humerus are called “proximal humerus fractures” (proximal meaning uppermost). The proximal humerus contains the humeral head and the tuberosities. The humeral head is the round portion covered by articular cartilage, a very special type of tissue that allows frictionless motion against the socket (also covered with articular cartilage). The tuberosities are prominent attachment sites for the tendons of the rotator cuff. There is a smaller tuberosity in the front (lesser tuberosity) for the attachment of the subscapularis, and a larger one on the side and back (greater tuberosity) for the attachment of the remaining rotator cuff tendons (supraspinatus, infraspinatus, and teres minor). The long head of the biceps lies in a groove separating the tuberosities. The remaining portion of the humerus is called the shaft.
Injuries can result in a fracture of the proximal humerus into one or more pieces. Shoulder surgeons refer to the pieces that are fractured and displaced as a “part”. For example, if the greater tuberosity is the only piece fractured and displaced, the surgeon will call the fracture a “two-part greater tuberosity fracture” (one part being the greater tuberosity, the other part is the rest of the bone). If the fracture separates all four pieces (each tuberosity, the head and the shaft), it is called a “four-part fracture”.
The humeral head is a particularly important “part”, since articular cartilage does not heal or regenerate. In addition, the humeral head depends on its connections with the tuberosities and the shaft for blood supply. If a fracture completely separates the head from all the other pieces, then the lack of blood supply halts healing and may result in death of the bone in the head (this complication of proximal humerus fractures is called “avascular necrosis” – which can also occur in other circumstances). Certain fractures will split the head in the middle (“head splitting fracture”), or sink a portion of the humeral head into itself, leaving an indentation, similar to a thumb pressing on a Ping-Pong ball (“head depression fracture”). Sometimes, not only is the humeral head separated from the rest of the pieces, but it is also dislocated out of the shoulder joint (“fracture-dislocation”).
How are these fractures assessed?
Simple fractures of the proximal humerus can be properly assessed using plain radiographs. However, complex fractures cannot be visualized well using x-rays alone. Computed tomography (CT scan) is extremely helpful. CT scans provide multiple two-dimensional radiographic views of bone sections. Digital data obtained from CTs can also be processed to render three-dimensional reconstructions, which can be rotated in space and allow surgeons to get a better understanding of the fracture pattern and displacement.
When is replacement considered?
Shoulder surgeons recommend shoulder replacement in the following circumstances: (1) severe damage to the humeral head articular cartilage, (2) loss of blood supply to the humeral head, or (3) when bone is too soft to be held with screws, plates or nails (bone softening is the result of osteoporosis and is more common in older individuals). In practical terms, this means that replacement will be considered for (a) three- and four-part fracture dislocations, (b) severe fractures that split or depress the humeral head, and (c) three- and four-part fractures in elderly patients with poor bone quality that would not allow reliable fixation.
How is replacement for a fracture done?
Surgeons use one of two types of shoulder replacements: an anatomic hemiarthroplasty (also known as “partial replacement” or “humeral head replacement”) or a reverse arthroplasty. In both styles of replacement, a metal stem is inserted into the canal of the humeral shaft. In a partial replacement, an artificial half-sphere is fixed on top of the stem to replace the humeral head and the fractured tuberosities are wrapped around the upper portion of the stem; the socket is not replaced. In a reverse replacement, an artificial half-sphere is fixed with screws to the socket and the artificial part is fixed on top of the stem has a concave plastic bearing; the fractured tuberosities are wrapped around the stem as well.
Which one is best, partial or reverse replacement? Why and when?
Now, that can be a complicated question! Partial replacement was the only option available until the early 2000’s. Studies have shown that when a partial replacement is done for fractures, the tuberosities do not always heal, and if they do not heal, they vanish over time. As a consequence, the rotator cuff will longer be attached, and function is really poor. The chance of healing is about 50/50: if the tuberosities heal, partial replacement typically provides a great outcome, but if not, patients can barely move their arm. Lack of tuberosity healing is statistically more common to happen in older patients and females, or when the tuberosities themselves are fractured in multiple pieces.
Reverse replacement was initially developed for patients with bad arthritis and a torn rotator cuff. It was only logical to try to use it for fractures as well, since the main problem with partial replacement is lack of cuff attachment when the tuberosities vanish (half of the time). Studies have shown that when a reverse prosthesis is used for fractures, tuberosity healing seems to occur more often. However, in some patients the tuberosities may still not heal; in the absence of greater tuberosity healing, a reverse prosthesis typically still allows individuals to raise the hand overhead, but moving the hand outwards (external rotation) is limited. Also, with a reverse prosthesis, even if the tuberosities heal, the mechanics of the prosthesis do not always allow patients to reach their hand behind their back. Finally, the artificial parts of a reverse prosthesis are more likely to fail mechanically compared to partial replacements.
Your shoulder surgeon will tell you which prosthesis is best for you. Partial replacement is typically selected for younger males with good bone quality, large tuberosity fragments, and the need for normal restoration of motion in all planes. Reverse replacement is more commonly recommended for elderly females with osteoporosis, especially if the tuberosities are badly fractured in multiple pieces. If the tuberosities heal, partial replacement provides better results, but half of the time the outcome will be poor because the tuberosities did not heal.
What is rehabilitation like after replacement for fracture?
Guess what the number one priority after either hemiarthroplasty or reverse procedure for a fracture is! You got it: healing of the tuberosities. That is why most shoulder surgeons recommend a 6-week period of immobilization. The tuberosities are wrapped around the prosthesis with sutures, and moving the shoulder right way may lead to the loss of tuberosity fixation. We believe it is best to place the arm slightly out in space (external rotation) by using an immobilizer with a small pillow. After the first six weeks, your surgeon will provide physical therapy instructions to regain motion, then strength. As with many other shoulder surgeries, shoulder replacement for a fracture may require one year or longer before a full recovery.