Shoulder Infection

Shoulder Infection

Normal Anatomy

The shoulder joint is the second largest and most mobile joint in the human body and can be easily understood if divided into three layers. The first layer is the deepest layer made up of the bones that form the foundation. There are three bones consisting of the arm bone (humerus), the shoulder blade (scapula), and the collar bone (clavicle). There is a rounded head on top of the arm bone called the humeral head and a saucer shaped surface of the shoulder blade called the glenoid which complements the humeral head and together they form the shoulder joint. A layer of cartilage (blue area) covers the articular surfaces of the humeral head and glenoid to provide a cushioned surface which allows for smooth pain free shoulder motion. These three bones unite to form three joints, which are held together by the second layer which keeps the bones from separating during shoulder movement, allowing the bones to function as a unit.



The second layer is comprised of collagen tissue fibers that attach to the bones on both sides of the joint and form the joint capsule. Within the joint capsule, are dense cordlike collagen bundles that unite to form ligaments that in strategic locations further enhance the stability of the jointby resisting the forces created when we perform our routine daily activities.




The rim of the glenoid is encircled by a rubbery fibro-cartilage tissue called the labrum. The labrum is an anchor point for the ligaments of the shoulder capsule and the long head of the biceps tendon which attach to it creating a suction seal mechanism when the humeral head is in contact with the glenoid. This sealing mechanism adds another joint stabilizing effect. The three shoulder bones form there joints called the Glenohumeral (GH) joint, Acromioclavicular (AC) joint, and the sternoclavicular (SC) joint.

The third layer in the shoulder is the muscle layer. Within the muscle layer, there are several potential spaces that carry the arteries which supply the bodies’ nutrition and nerves that deliver the commands sent by the brain and spinal cord for muscle movement. The most important muscle group in the shoulder is called the rotator cuff muscles. Theyare comprised of four muscles that begin (originate) in the shoulder blades’ flat surfaces and attach to the arm bone in an area called the greater tuberosity footprint as a common tendon unit. The four tendons formed by the four rotator cuff muscles interdigitate with one another forming a protective mechanism that prevents rotator cuff tendon tears from quickly spreading once they occur. The interdigitation also allows the four muscles to work together as a unit, carefully balancing the shoulder joint against the forces of the deltoid muscle to create precise shoulder movement. The deltoid muscle, biceps muscle and other muscles about the shoulder that balance the shoulder blade, called the scapular stabilizers complete the shoulder muscles that make up the third layer and together create a dynamic balanced force which allows for normal function. The major function of the rotator cuff muscles is to provide shoulder joint dynamic stability, shoulder joint motion and strength to the arm.

Pathology

The shoulder is one of the most well perfused areas of the human body and because of this ample blood supply to the shoulder which carries circulating white blood cells, offers excellent protection against infection, consequently makinga shoulder infection a rare occurence. In spite of this however, there are certain conditions that predispose individuals to having a shoulder infection:

1. A penetrating shoulder injury that is not cleaned and repaired properly or timely. This is why all penetrating injuries should seek medical advice for prophylactic antibiotics, a tetanus booster if one has not been received within a 10 year period for clean injuries and within a five year period for dirty wounds and also a cleaning (debridement) of the wound.
2. A Postoperative wound infection is another cause of a shoulder infection. During the post-operative period, the fresh wound is covered in sterile gauze until it seals which takes about seven days, so that organisms that are normal skin flora can invade the wound and cause an infection. This is why patients after surgery are advised to keep the dressing on and the wound dry for at least one week after surgery.
3. After a joint replacement (Arthroplasty) there is similar risk of infection if care is not provided to the post-operative wound. With a joint replacement, however, the risk for an infection is increased because the surgery required a large dissection increasing bleeding and tissue handling, the joint replacement (implant) is also a foreign object in the human body where micro-organisms can hide and avoid the antibiotics used during surgery for infection prevention. Individuals can also seed an implant in the body from infections occurring elsewhere in the body that travel though the bloodstream, like a tooth abscess, for example. This is why prophylactic antibiotics are recommended when visiting a dentist for a dental procedure.
4. A patient with a weak immune status. A weak immune status due to a chronic medical condition like diabetes or kidney failure, an inflammatory condition like rheumatoid arthritis, use of immunosuppressive medication or a patient with AIDS all suppresses the protective effects of the immune system and subsequentlyhave a significantincrease risk of infection.

Treatment

The treatment of a shoulder infection depends on several factors which include:

1. The initial cause of the infection
2. Whether the infection is superficial or deep and which tissues are involved
3. The length of time the infection has been present
4. The type of organism causing the infection
5. The general medical condition and nutrition of the patient
6. Whether an implant is present or another type of foreign body

When an infection is superficial, oral antibiotics, warm soaks and resting the extremity will often resolve the problem. If the infection has spread and lymph node involvement, fever, chills or other systemic causes accompany the infection, hospital admission for intravenous antibiotics, fluids and systemic support is preferred. If the infection is well loculated and fluctuant (soft) it is an abscess which is a surgical condition requiring incision and drainage. When a joint replacement has been done, it is prudent to admit the patient to the hospital for IV antibiotics in the first few days after surgery and have a low threshold for washing out the wound. If the infection of the joint replacement occurs weeks or months after the surgery, cultures are taken prior to giving antibiotics, the implant is usually removed and later reimplanted after the organism has been identified and IV antibiotics has been givenfor six weeks. If the patient with a joint replacement has poor health or a poor immune status, then leaving the joint without an implant may be the best option.