The shoulder joint is formed where the humerus (the upper arm bone) meets the scapula (the shoulder blade).  The top of the humerus forms a ball known as the head of the humerus.  The scapula forms a shallow cup known as the glenoid.  This forms the shoulder socket.  The ball and socket joint of the shoulder is known as the glenohumeral joint. The surfaces of the humeral head and glenoid are capped with a layer of cartilage.  The cartilage that caps the ends of bones in joints is known as articular cartilage.  Articular cartilage is smooth and slippery.  This lowers friction in the joint and allows the bones to glide smoothly against one another as the shoulder moves.  Articular cartilage is slightly softer and more rubbery than bone.  A thick, viscous fluid known as synovial fluid (joint fluid) fills the joint.  Together, the articular cartilage and synovial fluid provide a cushion between the bones.  The joint is surrounded by a capsule known as the synovium which keeps the synovial fluid from leaking out. The shoulder joint is built to allow for a wide range-of-motion.  This allows the arm to reach high overhead, out to the side, behind the back, and out in front of the body.  However, because of its great mobility, the shoulder is one of the less stable joints in the body.  In other words, it dislocates more easily than other joints. A ring of fibrous cartilage surrounds the glenoid.  This is known as the labrum.  The labrum helps to fit the shallow glenoid to the round head of the humerus.  This deepens the socket and helps to make the shoulder more stable.  Ligaments (fibrous structures that hold one bone to another bone) and tendons (fibrous structures that hold muscles to bones) help to stabilize the shoulder as well by holding the humeral head in the socket.  Among these tendons is the rotator cuff.  The rotator cuff is a group of muscles that act to rotate and elevate the arm.  Their tendons surround and attach to the humeral head, forming a cuff.  Together, they pull the humeral head into the glenoid and help to keep it from dislocating. Degeneration of the Shoulder Joint The blood supply to articular cartilage is poor.  Without a healthy blood supply, nutrients are not readily available to the cartilage tissue.  When it is damaged, it does not heal as well as bone, skin, muscle, or other tissues. Years and decades of use can take their toll on the articular cartilage in any joint.  The shoulder is no exception.  As the glenoid and humeral head rub and strike against one another, the cartilage can begin to soften and crack.  Because cartilage does not heal as well as other tissue, the damage to the cartilage tends to worsen.  Over time cartilage can peel away, exposing bare bone.  As the smooth cushion between the humeral head and glenoid erodes, the bones begin to grind against one another.  This causes pain, grinding, and stiffness.  The condition has several names including degenerative joint disease, osteoarthritis, or simply arthritis. Everyone is subject to the wear and tear of arthritis.  In theory, everyone who lives long enough will end up with arthritis in the shoulders.  Why one person develops shoulder arthritis at a younger age than another person can be a difficult question to answer.  Factors include genetics, lifestyle, injuries, and other medical problems.  Arthritis that results from a specific injury or disease process is called secondary arthritis.  Arthritis with no readily identifiable cause is known as primary arthritis. A traumatic injury to the shoulder can instantly damage the articular cartilage and speed up the process of degeneration.  For example, a blow to the shoulder may fracture the glenoid and crack the articular cartilage.  Once the cartilage has cracked, it is easier for it to peel away.  Think about removing the shell from a hard-boiled egg.  It is impossible to simply peel off the shell.  But once the shell is cracked it is easy to remove the cracked pieces.  Arthritis that results from a traumatic injury is known as post-traumatic arthritis. Other medical problems such as gout, infection, and rheumatoid disease can be very hard on the joint and speed up the degenerative process. Many people who develop shoulder arthritis state that they have a parent, sibling, or grandparent who also suffered with arthritis.  "It runs in the family," they claim.  There is likely a genetic component that plays a role in the development of arthritis at a younger age.  Shoulder instability can also speed up the degenerative process.  If the humeral head does not sit securely in the glenoid, it changes the mechanics between the two bones.  This may place more pressure on one area of the humeral head or glenoid, causing the cartilage in that area to wear away more quickly.  Several structures are involved in shoulder stability including the labrum, rotator cuff, glenoid, joint capsule, shoulder ligaments, etc.  Dysfunction of any of these structures can affect the mechanics of the shoulder.  This dysfunction may be subtle and might not be identified. A lifestyle that involves heavy labor or repetitive shoulder activity can contribute as well.  If the wear and tear placed on the articular cartilage exceeds its ability to heal, the cartilage will begin to degenerate. Most people who develop osteoarthritis of the shoulder are unable to identify a clear cause. The severity of shoulder arthritis is often described using the term "chondromalacia."  Chondromalacia  means "softening of the cartilage."  Grade I chondromalacia is when the cartilage begins to soften.  Grade II chondromalacia is when the cartilage begins to crack and fissure.  The cartilage begins to look like crab meat at grade III.  Grade IV chondromalacia is when the cartilage has completely worn away, exposing bare bone.  The entire surface of the bone does not wear away at the same speed.  One area of the humeral head may have grade II chondromalacia while another area has grade IV chondromalacia. Diagnosing Shoulder Arthritis History People with osteoarthritis of the shoulder complain of pain within the shoulder joint.  They may complain of pain with attempting to use the arm, especially with overhead activity.  Often, they complain of a grinding or popping sensation within the shoulder joint as they move the arm.  This is known as crepitus.  The onset of pain is usually gradual, and pain worsens over a period of months to years.  Occasionally, arthritic pain begins after an injury.  A person may fall or otherwise injure the shoulder.  They seek medical treatment expecting to have a fracture, sprain, or other injury.  They are surprised to find out that they have arthritis (and that they had had arthritis since before the injury).  Some people function well and have minimal pain with shoulder arthritis.  An injury can aggravate the arthritic shoulder, resulting in a dramatic increase in shoulder pain. ྕ Pain with shoulder movement ྕ Gradual onset of worsening shoulder pain ྕ Grinding or popping Physical Exam A thorough physical examination seeks not only to find evidence of osteoarthritis, but also to rule out other causes of shoulder pain such as fractures, biceps tendinitis, rotator cuff tears, labral tears, nerve damage, etc.  The shoulder usually appears essentially normal.  The shoulder may be tender around the deltoid and glenohumeral joint.  There may be weakness and pain with attempts to raise or rotate the arm.  Popping and grinding can sometimes be felt or even heard with shoulder movement.  Just because the shoulder is arthritic does not mean that other problems are not present as well.  It is common to have both shoulder arthritis and a torn rotator cuff.  Passive range-of-motion (the person with shoulder pain relaxes while the examiner raises the arm for them) may be limited, depending on the severity of the degenerative changes.  Normal range-of-motion: o Forward flexion ≈ 180° o Abduction ≈ 180° o External rotation ≈ 100° o Internal rotation ≈ 90° Active range-of-motion (the person with shoulder pain attempts to raise and rotate their own arm) elicits pain if the rotator cuff is injured or damaged. Crepitus:  Popping and grinding can be felt by the examiner as the shoulder is manipulated. X-rays Depending on the severity of the degenerative changes, osteoarthritis can often be readily identified on x-rays.  X-rays will demonstrate narrowing of the joint space between the humeral head and glenoid.  They may also demonstrate osteophytes (bone spurs) and sclerotic bone (bone that appears more white on x-rays because it has hardened). If the humeral head appears to be sitting too high in relation to the glenoid, the rotator cuff is likely torn. X-rays are also helpful to rule out fractures, calcific tendinitis, acromioclavicular arthritis, tumors, and other problems. MRI (magnetic resonance imaging) X-rays are usually sufficient for diagnosing osteoarthritis of the shoulder, especially if the arthritis is moderate or severe.  However, MRIs can be helpful in identifying early arthritic changes that are not visible on x-rays.  An MRI may also be obtained if another cause of shoulder pain is suspected such as a rotator cuff tear.  Shoulder Arthroscopy Mild, early degenerative changes may not be visible on x-rays or even an MRI.  If no definitive cause of shoulder pain is identified and nonsurgical treatment is not effective, a diagnostic shoulder arthroscopy may be performed.  This involves introducing a slender camera called an arthroscope into the shoulder joint.  The inside of the shoulder joint can then be viewed on a monitor.  During the shoulder scope procedure, the articular cartilage is examined.  A small, metal probe can be used to examine the cartilage as well. Treating Shoulder Arthritis Initial treatment for osteoarthritis of the shoulder is usually non-operative.  Anti-inflammatory medications (NSAIDs) such as ibuprofen may help to reduce pain and inflammation.  A steroid (cortisone) injection into the glenohumeral joint may also be very helpful.  Physical therapy can help with stretching, range-of-motion exercises, strengthening, and scapular stabilization. NSAIDs Intra-articular (into the joint) steroid injection Rest (avoid strenuous, repetitive activity with the shoulder) Ice Physical therapy If symptoms do not improve with more conservative treatment, surgery may be recommended.  Surgical options for shoulder arthritis include: Arthroscopic debridement:  During a shoulder scope, the damaged cartilage may be smoothed and trimmed.  This may provide temporary relief from arthritic shoulder pain, but is not a definitive treatment.  This surgery may be considered if: o Arthritic changes are mild or o Shoulder arthroscopy is being considered to address other causes of shoulder pain in addition to the arthritis or o Shoulder replacement is not an option Resurfacing hemiarthroplasty:  The head of the humerus is partially removed and replaced with a metal implant.  If arthritic changes involve both the humeral head and glenoid, this is probably not a good option.  This surgery may be considered if: o Arthritic changes are present only on the humeral head and not the glenoid and o There is a desire not to remove too much bone Hemiarthroplasty:  The head of the humerus is removed and replaced with a metal prosthesis that has a stem that implants in the shaft of the humerus.  This is commonly used to treat fractures of the humeral head and neck.  If the glenoid is arthritic as well, this is probably not the best option.  This surgery may be considered if: o Arthritic changes are present only on the humeral head and not the glenoid or o The glenoid does not appear capable of holding a glenoid prosthesis Total shoulder arthroplasty:  The head of the humerus is removed and replaced with a metal prosthesis that has a stem that implants in the shaft of the humerus.  The glenoid is also replaced with a prosthesis.  This is a traditional shoulder replacement.  It provides great pain relief.  However, if there is a large rotator cuff tear it may not be the best option.  This surgery may be considered if: o Degenerative changes are severe and o The rotator cuff is intact Reverse total shoulder arthroplasty:  Reverse total shoulder replacement is similar to a traditional shoulder replacement.  However, the head of the humerus is replaced with a concave implant (cup) and the glenoid is replaced with a convex implant (ball).  In other words, the ball becomes the socket and the socket becomes the ball.  This changes the mechanics so that an intact rotator cuff is not necessary.  This surgery may be considered if: o Degenerative changes are severe and o There is a large rotator cuff tear or o A previous shoulder replacement was done and failed The traditional surgery for osteoarthritis of the shoulder is called total shoulder arthroplasty (shoulder replacement).  Shoulder replacement surgery is usually done under general anesthesia (completely asleep).  An injection may also be given by the anesthesiologist to numb the shoulder and arm.  An incision is made over the front of the shoulder.  Soft tissue is dissected out of the way and the shoulder joint is exposed.  The humeral head is dislocated and removed.  The glenoid is reamed and prepared to receive a prosthetic cup.  A prosthetic humeral head is then implanted into the shaft of the humerus.  The humerus, with its new humeral head, is pushed back into place in the shoulder socket.  The soft tissue around the joint is repaired and the skin is closed.  The incision is then dressed and the arm is placed into a sling. Not everyone with severe shoulder arthritis is a good candidate for surgery.  A shoulder replacement is an elective surgery and, while relatively safe, is not risk free.  The heart, kidneys, and other organs must be healthy enough for anesthesia.  People with infections such as tooth abscesses, urinary tract infections, and skin sores should not undergo shoulder surgery because of the risk that the infection may spread to the shoulder joint.  People with poorly controlled diabetes are poor surgical candidates because of the risk of infection and poor wound healing. If a rotator cuff tear is present, a traditional total shoulder replacement may not be a good option.  Shoulder pain may persist even after surgery because of the torn rotator cuff.  This also makes it difficult to raise the arm out to the side.  In a reverse total shoulder replacement the ball and socket are switched.  By switching the ball and socket, the mechanics of the shoulder are changed so that the deltoid muscle can take over for the rotator cuff in raising the arm to the side. Whether a traditional total shoulder replacement or a reverse total shoulder replacement is performed, a short hospital stay is usually advised.  Pain medication is made available and ice is applied to the shoulder.  Physical therapy begins the day after surgery.  Medication and other precautions are often recommended to lower the risk of developing a blood clot following surgery.  No active use of the arm or shoulder is permitted. Rehabilitation Following a Shoulder Replacement For the first four to six weeks, the goal is to allow the soft tissue to heal, protect the prosthesis, and restore some passive range-of-motion of the shoulder.  If there is too much activity following surgery, healing may be delayed and damage may be done to the prosthesis.  If there is not enough movement following surgery the shoulder may become stiff. Gentle passive range-of-motion exercises are begun.  In other words, the muscles of the shoulder should not be used to raise or rotate the arm, but the arm can be moved gently by a physical therapist.  The sling is worn for the first few weeks. After the first four to six weeks, more aggressive stretching can begin.  Assisted active range-of-motion may begin as well.  This means that the shoulder muscles can be used to begin raising the arm, but only with the assistance of a physical therapist, a well-instructed family member, or other trained person.  After several weeks, as the repair continues to heal, the surgeon and physical therapist will determine that it is time to begin active range-of-motion.  As passive and active range-of-motion improve, strengthening exercises may begin later on. Full recovery following a shoulder replacement takes about four to 6 months. Expectations Following a Shoulder Replacement Immediately following surgery, arthritic pain will be replaced with postoperative pain.  Pain will gradually improve.  Most people are very glad that they had the shoulder replaced after six to eight weeks. Shoulder replacement surgery is helpful in reducing pain and improving function.  However, range-of-motion will not return to the level it was before shoulder problems began.  Most surgeons recommend against strenuous activity such as heavy manual labor following a shoulder replacement. The implanted prosthesis does not last forever.  A total shoulder prosthesis is said to last about 15 years, but this varies greatly from person to person and is impossible to predict.