Joint replacements are very successful surgical procedures. Hip and knee replacements are most common, but shoulder replacements are common to! In a joint replacement, the damaged ends of the bones that form a joint are prepared to receive artificial parts that allow painless movement. Joint replacement is technically known as “arthroplasty” (from Greek “árthrosi” (άρθρωση) – joint; and “plastikí” (πλαστική) – to transform into something different). In the shoulder joint, artificial parts are inserted into the upper end of the arm bone (humerus) and the socket of the shoulder joint (the glenoid, part of the shoulder blade or scapula).
The shape of the shoulder joint bones is such that the top of the arm bone is spherical -the humeral head- whereas the glenoid socket has the shape of a small disk. Artificial parts designed for shoulder replacement may have these exact shapes: the part placed on the upper end of the humerus (humeral component) is spherical, and the part on the socket side is dish-shaped. Since these parts have the same shape as the human bones, they are called anatomic shoulder replacement. But there is another style of replacement with opposite shapes; a hemispherical component is inserted on the socket side, whereas the top of the humerus is replaced with a dish-shaped structure: the reverse shoulder arthroplasty. Now…, why would that be useful? And what do I need to know if I have been told I am a candidate for reverse joint replacement?
A little bit of history
The rotator cuff is a group of muscles and tendons extremely important for proper function of the shoulder joint (see our posts on rotator cuff repair: https://shoulderelbow.org/2016/11/28/rotator-cuff-tears/ and https://shoulderelbow.org/2016/12/12/arthroscopic-rotator-cuff-repair/). Many shoulders that need replacement have a well-preserved rotator cuff. However, if the rotator cuff is damaged, anatomic shoulder replacement does not function well. This has been known for decades, but a good solution did not exist until a French surgeon by the name of Paul Grammont developed reverse shoulder replacement. Reverse arthroplasty was specifically designed for damaged shoulder joints that needed replacement and also had a torn rotator cuff. The Food and Drug Administration approved implantation of reverse joint replacement in the United States in 2003, and the first reverse shoulder replacement at Mayo Clinic was performed in 2004. The benefits of reverse shoulder replacement were quickly noticed, and today, more than 15 years later, at least half -if not more- of the joint replacements I perform are reverse joint replacements.
How does it work, really?
Switching the geometry of the human shoulder from its native shape to a reverse configuration translates into two major changes: (1) the joint is more constrained and (2) the deltoid muscle gains more power to raise the arm.
In the native human shoulder -and after anatomic shoulder arthroplasty-, when we attempt to raise our arm, the humeral head tries to glide upwards on the surface of the socket; for good rotational movement, the rotator cuff keeps the humeral head centered on the socket. However, in the absence of a functional rotator cuff, oftentimes the arm cannot be raised until a reverse joint is implanted: now the socket is the moving part that glides, with more stability even in the absence of a rotator cuff. But also, implantation of a reverse replacement makes the joint longer. The resultant increased length of the deltoid – along with changes in its line of pull -, are theorized to result in a more efficient deltoid to raise the arm. That is why Professor Grammont named his prosthesis “Delta”, in reference to the deltoid muscle.
Any changes in 15 years of history?
As you can imagine, yes! The reverse prosthesis design released in 2003 in North America combined a relatively narrow sphere and a relatively long humeral implant fixed with cement. In addition, the humeral dish or bearing, made of plastic, was pretty flat in reference to the humerus bone. The combination of a narrow sphere and a flat plastic liner may translate into an excessively narrow and long shoulder joint; but more importantly, the plastic liner rubs abnormally with the shoulder blade, and both plastic and bone are eroded. Eventually, plastic and bone particles may inflame the joint and loosen the implants. This type of reverse design with such narrow sphere and a plastic bearing in line with the humerus shaft is called “medialized”, and the bone erosion that occurs over time is called “notching”.
Now look at a contemporary reverse prosthesis: a wider sphere and a steeper humeral bearing prevent notching, the humeral component length has been optimized to preserve bone, no cement is used, and the glenoid component has been optimized as well, with better fixation and use of less bone. We owe the idea of using a wider sphere to Dr. Mark Frankle and his glenoid “lateralized” design. Today, an active area of research involves understanding what is the ideal amount of lateralization of a reverse replacement, and whether it is best to lateralize on the glenoid side, the humeral side or both.
When is reverse replacement recommended?
Initially, reverse replacement was considered only for patients with a damaged shoulder joint combined with bad rotator cuff tearing, a condition called cuff tear arthropathy. Today, reverse arthroplasty is considered for many other conditions: very large rotator cuff tearsthat cannot be repaired (functionally irreparable cuff tears), fractures of the upper humerus (see our post on reverse for fracture at https://shoulderelbow.org/2016/10/24/bad-shoulder-fractures-and-shoulder-replacement/), and complications after fracture management, osteoarthritis with excessive bone loss on the socket or when the humeral head does not line up with the center of the socket, severe rheumatoid arthritis, reconstruction after surgery to remove a tumor, and others. In addition, reverse replacement is very commonly required when a previous replacement fails and needs to be redone.
What does the whole process involve?
Your shoulder specialist will determine if you are a candidate for reverse replacement based on your history, physical examination, and radiographs. Occasionally, magnetic resonance imaging is needed as well. If you decide to proceed with the recommendation of surgery, a computed tomography will be obtained prior to surgery in order to plan the procedure. We live in modern times, and believe it or not your computed tomography can be loaded into software that creates a virtual reconstruction of your shoulder, allows accurate planning, and even three-dimensional printing of your bones and guides if needed (more information of three-dimensional printing in orthopedic surgery can be found at https://shoulderelbow.org/2019/07/03/three-d-printing-orthopedic-surgery/).
You will walk into the hospital the day of surgery. Pain after shoulder surgery used to be feared by most, but times have changed! In my practice, a catheter is inserted close to the nerves that pick up the feeling from your shoulder (this procedure is called interscalene brachial plexus blockade). Local anesthetic injected through the catheter before surgery and for the first 24 hours after surgery allows a lighter anesthesia, and for many patients a pain-free experience. You can even take your catheter home! Surgery itself takes 1 to 2 hours, and most patients need to stay in the hospital at the most one night.
After surgery, your shoulder specialist will ask you to use a shoulder immobilizer for a few weeks, typically less than after anatomic shoulder replacement. You can, and should, move your hand, wrist and elbow almost immediately, and shoulder physical therapy typically takes three to four months to complete.
What are the downsides?
Most patients who recover well from a reverse replacement are delighted: no more pain, good motion of the shoulder, good strength… However, any surgical procedure carries the risk of complications. The complications I worry the most as a surgeon include infection [read more on infection after shoulder replacement at https://shoulderelbow.org/2019/01/03/shoulder-replacement-infection/], nerve injury, dislocation, and stress fracture. In addition, some individuals are never able to regain adequate internal rotation.
A good analogy to understand how stress fractures occur in the human skeleton relates to how an empty can of soda that is squeezed in the middle starts to break after twisting it in opposite directions for a while. After reverse replacement, something similar can happen. It is theorized that a tighter deltoid muscle after reverse increases the stress on the portion of the shoulder blade where the deltoid muscle takes off: the acromion or the spine of the scapula. As such, in a small number of patients, a few months into their recovery a spontaneous stress fracture occur, which leads to pain and loss of motion. Oftentimes, these fractures will heal by just resting the shoulder in an immobilizer for a few weeks. Rarely, surgery is required to fix the fracture.
In general, reverse shoulder arthroplasty reliably restores motion to raise the arm up in the air and to turn the arm out to the side (shoulder specialists call these motions “elevation” and “external rotation”, respectively). However, not every patient is able to reach behind his or her body after reverse replacement. Restoration of motion in this particular plane, called “internal rotation” is not always achieved. Some patients are able to, and some are not!
Luckily, with contemporary designs and better surgical techniques, bone loss leading to notching is uncommon and more and more patients are able to recover pretty good motion in all planes, including internal rotation.
Any restrictions? How long will it last?
Since reverse replacement involves implantation of artificial parts, the implants are subject to wear and tear with use. As such, your shoulder specialist may recommend avoiding certain activities, like lifting heavy weights overhead one handed, or pushing/pulling strongly. The plastic liner of the implant may wear out with overuse, and plastic particles shed into the joint may initiate inflammation, and create the environment for bone loss or implant loosening. With contemporary implants, 10 to 15 years of good use can be expected.
A few final thoughts..
The outcome of a surgical procedure depends to some extent on the experience of the surgeon, which relates to the number of replacements performed. Year after year, Mayo Clinic has continued to perform the largest number of shoulder replacements in the United States. By 2018, more than 10,000 primary and revision shoulder replacements had been performed in our Institution. We have developed a passion to perfect not only the operation but the whole patient experience, with emphasis in pain control, a faster recovery, and minimal restrictions. If you need us, here we are!