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Shoulder replacement is a surgical procedure in which all or part of the glenohumeral joint is replaced by a prosthetic implant. Such joint replacement surgery generally is conducted to relieve arthritis pain or fix severe physical joint damage.

Shoulder replacement surgery is an option for treatment of severe arthritis of the shoulder joint. Arthritis is a condition that affects the cartilage of the joints. As the cartilage lining wears away, the protective lining between the bones is lost. When this happens, painful bone-on-bone arthritis develops. Severe shoulder arthritis is quite painful, and can cause restriction of motion. While this may be tolerated with some medications and lifestyle adjustments, there may come a time when surgical treatment is necessary.

History
Shoulder replacement, also known as shoulder arthroplasty or glenohumeral arthroplasty, was pioneered by the French surgeon Jules Emile Péan in 1893. His procedure consisted of physically smoothing the shoulder joint and implanting platinum and rubber materials. The next notable case in the evolution of shoulder replacement procedures was in 1955 when Charles Neer conducted the first hemiarthroplasty, essentially replacing only the humeral head, leaving the natural shoulder socket, or glenoid, in tact. This procedure grew exponentially in popularity as time progressed; however, Neer noticed that his patients still suffered from deficits in strength despite resolving most of the pain. Eventually, Neer and other surgeons realized that this surgical approach caused migration of the prosthetic humeral head, which prompted the development of a procedure to replace not only the humeral component, but the glenoid component as well.

Throughout the development of the procedures, it became well accepted that the rotator cuff muscles were essential to produce the best outcomes in terms of strength, range of motion, and a decrease in pain. In addition to this finding, physical constraints of the normal ball-and-socket anatomy of the shoulder limited most developments in one way or another. For example, a heavily constrained system limited range of motion. and the inherent anatomy of the glenoid proved difficult to cement prosthetics and fixate components without fracturing it. These challenges and high rates of failure led to the development of the reverse total shoulder arthroplasty to overcome the limitations imposed by the natural shoulder anatomy.

The 1970s saw an exponential increase in surgical approaches using this methodology, and the number and variation of surgical techniques are many. However, in 1985 Paul Grammont emerged with a superior technique that is the basis for most reverse total shoulder arthroplasty procedures today. However, it is of note that the reverse total shoulder arthroplasty is primarily indicated in cases in which a patient has weak or torn rotator cuff muscles. In others, a conventional shoulder replacement may be indicated. Although Grammont continued to develop and refine his new technique too address minor complications that arose, it relied on 4 basic concepts that included the inherent stability and shape of the implant, as well as the placement of the implant relative to the natural glenohumeral joint.

Indications
The progression to shoulder replacement usually begins with the development of pain with movement of the shoulder and stiffness which will be conservatively managed with activity modification, physical therapy and non-steroidal anti-inflammatory (NSAID) drugs. Additionally, intra-articular corticosteroid injections (injection into the joint space) are another popular, conservative option. If all non-surgical, conservative treatment options fail and pain is affecting quality of life, then the shoulder replacement will likely be indicated. Various studies on shoulder replacements have confirmed this indication, noting specifically that severe glenohumeral arthritis as the cause.

Surgical Techniques
In traditional total shoulder arthroplasty the approach begins with separating the deltoid muscle from the pectoral muscles, facilitating access to the shoulder (glenohumeral) joint through a relatively nerve free passageway. The shoulder joint is initially covered by the rotator cuff muscles (subscapularis, supraspinatus, infraspinatus & teres minor) and the joint capsule (glenohumeral ligaments). Typically a single rotator cuff muscle is identified and cut to allow direct access to the shoulder joint. As this point, the surgeon can remove the arthritic portions of the joint and the secure the the ball and socket prostheses within the joint.

The development of safer, more effective techniques have led the to increased use of reverse total shoulder arthroplasty. Reverse total shoulder arthroplasties are typically indicated when the rotator cuff muscles are severely damaged. There are a few major approaches for reverse total shoulder arthrplasties. The first is the deltopectoral approach, which is the approach described above for the traditional total shoulder arthroplasty. This approach saves the deltoid, but requires the supraspinatus to be cut. The second is the transdeltoid approach, which provides a straight on approach at the glenoid. However, during this approach the deltoid is put at risk for potential damage. Both techniques are used, depending on the surgeon's preferences.

Implants
Various materials can be used to make prostheses, however the majority consist of a metal ball that rotates within a polyethylene (plastic) socket. The metal ball takes the place of the patient's humeral head and is anchored via a stem, which is inserted down the shaft of the humerus. The plastic socket is placed over the patient's glenoid and is typically secured to the surrounding bone via cement.

Recent advances in technology have led to the development of stemless as well as cementless replacements being used in the operating room. In addition, the increasing popularity of reverse total shoulder arthroplasty has led to availability of 29 new prostheses in 2016 alone.

Risks
Non surgery options are preferred treatment for a variety of reasons. Besides not wanting to risk the usual risks of surgery such as infection, shoulder replacement can lead to a variety of complications including rotator cuff tear and glenohumeral instability. However despite these risks, shoulder replacement shows promise with a low rate of complication which depending on the type of surgery is close to 5%.

Anesthesiological Considerations
Regional and general anesthesia are two methods that can be utilized when performing shoulder replacement. One example of a commonly used regional anesthetic is an interscalene brachial plexus block and it has been used in a number of shoulder procedures including instability repairs, proximal humeral prosthetic replacements, total shoulder arthroplasties, anterior acromioplasties, rotator cuff repairs, and operative treatment of humeral fractures. The benefits of utilizing regional anesthesia over general anesthesia include less intraoperative bleeding, more muscle relaxation, shorter recovery room and hospital stays, decreased use of opiods, and avoiding the side effects of general anesthesia. In addition, regional anesthesia may be more cost-effective because it reduces operating room turnover time and procedure time due to the patients waking up sooner after surgery.

The success rate of placing an interscalene brachial plexus block ranges from 84% to 98% according to some case studies. Major complications such as seizures, cardiac arrests, Horner's syndrome, hoarseness, and inadvertent spinal/epidural anesthesia could occur and therefore, patients should be carefully monitored during the insertion of the block until the end of the surgery. Currently, data on combined usage of general anesthesia and interscalene blocks are limited. Some indications for combined anesthesia include difficult airway management and longer surgical procedures.

A mixture of short and long-acting local anesthetics is used to prolong the duration as well as reduce the onset of the nerve block. Lidocaine is an appropriate short-acting local anesthetic and drugs such as levobupivacaine or ropivacaine are appropriate long-acting local anesthetics. The amount of drugs needed for a patient during shoulder replacement can range from 30 to 50 ml and is calculated based on the patient's characteristics as well as the specific anesthetic technique used.

Post-operative Analgesia
Shoulder replacement can cause severe to very severe pain especially during shoulder mobilization and therefore, postoperative pain management is extremely important for recovery. This is because joint tissues are well innervated from nociceptive input and therefore, a surgical procedure in the joint region would produce continuous deep somatic pain as well as muscle spasms.

The following anesthetics are methods commonly used to assist with post-operative shoulder replacement pain management:

Interscalenic Analgesia
Three types: Single shot interscalenic analgesia is preferably used during minor arthroscopic surgery because of its short duration but overall, it is still a useful alternative when continuous interscalenic analgesia cannot be performed. Interscalenic analgesia is most suited for the continuous infusion approach because shoulder replacement causes severe post-operative pain and the anatomic proximity of the interscalenic catheter to the shoulder joint provides quick relief. The interscalenic catheter can be used from three to five days depending on the type of surgery.
 * 1) Single shot
 * 2) Continuous infusion
 * 3) Patient controlled

Suprascapular with or without Axillary Nerve Blockade Combined with Local Anesthetic Wound Infiltration
Since the suprascapular nerve provides sensory information to 70% of the joint capsule, blocking this nerve can help with post-operative shoulder pain. A nerve stimulator, ultrasound device, or a needle insertion that is 1 cm above the midpoint of the scapular spine can quickly block the suprascapular nerve. Furthermore, blocking the axillary nerve together with the suprascapular nerve can further anesthetize the shoulder joint. The benefit of the suprascapular nerve block is that it avoids blocking motor function to parts of the upper limb innervated by the more inferior roots of the brachial plexus (C8-T1), which thus prevents the phrenic nerve from being blocked. Disadvantages to the suprascapular nerve block include using two separate needlings, blocking not all of nerves of the shoulder joint, and short duration of action. Some side effects for the procedure include pneumothorax, intravascular injection, and nerve damage. Although this technique provides more pain control compared to placebo, the technique is still inferior to the interscalene block.