Shoulder Infections: Causes, Types, Symptoms, and Treatment

How do you get an infection in your shoulder?

An infection in the shoulder joint or surrounding tissues typically arises from the direct introduction of bacteria, fungi, or viruses during medical procedures or trauma, or less commonly, through the bloodstream from a distant infection site.

Understanding Shoulder Infections

The shoulder is a complex ball-and-socket joint, highly mobile and critical for upper limb function. While relatively uncommon, infections of the shoulder can be severe, leading to significant pain, loss of function, and, if untreated, irreversible joint damage or systemic illness. These infections can affect various structures, including the joint space itself (septic arthritis), the bone (osteomyelitis), or the surrounding soft tissues like bursae, tendons, and skin. Understanding the pathways through which pathogens can invade these areas is crucial for prevention and early intervention.

Common Pathways and Causes of Shoulder Infections

Infections in the shoulder generally occur through one of three primary mechanisms: direct inoculation, hematogenous spread, or contiguous spread.

• Direct Inoculation (Direct Introduction): This is the most common route for shoulder infections. It involves pathogens directly entering the joint or surrounding tissues from an external source.

  • Surgical Procedures: Any surgery involving the shoulder, such as arthroscopy, rotator cuff repair, labral repair, or shoulder replacement (arthroplasty), carries a risk of infection. Despite strict sterile techniques, bacteria can be introduced during the procedure. Periprosthetic joint infections (PJI) are a particularly challenging complication after shoulder replacement.
  • Injections: Injections into or around the shoulder joint, such as corticosteroid injections, hyaluronic acid injections, or platelet-rich plasma (PRP) injections, can introduce bacteria if proper aseptic technique is not meticulously followed.
  • Trauma: Puncture wounds, deep cuts, open fractures, or animal/human bites that penetrate the skin and reach the joint or bone can directly introduce pathogens.
  • Medical Procedures: Less common, but aspiration of joint fluid (arthrocentesis) or diagnostic biopsies can, in rare instances, lead to infection if sterility is compromised.

• Hematogenous Spread (Bloodstream Spread): In this pathway, bacteria or other pathogens from an infection elsewhere in the body travel through the bloodstream and settle in the shoulder.

  • Distant Infections: Sources can include skin infections (e.g., cellulitis, abscesses), urinary tract infections (UTIs), dental abscesses, pneumonia, or endocarditis (infection of heart valves).
  • Mechanism: The shoulder joint's synovial membrane, being highly vascular, can sometimes act as a filter, trapping bacteria circulating in the blood. This pathway is more common in children for osteomyelitis and in individuals with compromised immune systems or pre-existing joint damage.

• Contiguous Spread (Spread from Adjacent Tissue): This occurs when an infection from neighboring soft tissues or bone spreads into the shoulder joint or adjacent structures.

  • Local Soft Tissue Infections: An untreated skin infection (cellulitis) or an abscess near the shoulder can extend into the joint capsule, bursa, or bone.
  • Septic Bursitis: An infected bursa (e.g., subacromial bursa) can potentially spread to the joint if not contained.
  • Osteomyelitis: An infection originating in the humeral head or glenoid bone could potentially extend into the joint space.

Types of Shoulder Infections

The specific structure affected determines the type of infection:

• Septic Arthritis (Infectious Arthritis): This is an infection within the synovial fluid and lining of the shoulder joint. It is the most serious type of joint infection due to its potential for rapid cartilage destruction and permanent joint damage if not promptly treated.
• Osteomyelitis: An infection of the bone, most commonly affecting the humeral head or glenoid. It can be acute (sudden onset) or chronic (persisting for months or years).
• Soft Tissue Infections:
  • Cellulitis: A bacterial skin infection that can affect the skin and subcutaneous tissues around the shoulder. While not directly in the joint, severe cases can lead to contiguous spread.
  • Abscess: A localized collection of pus within the soft tissues or even within the joint itself.
  • Septic Bursitis: Infection of a bursa (fluid-filled sac) around the shoulder, such as the subacromial bursa.

Risk Factors for Shoulder Infections

Certain factors increase an individual's susceptibility to developing a shoulder infection:

• Compromised Immune System: Conditions that weaken the immune system, such as diabetes mellitus, HIV/AIDS, rheumatoid arthritis, cancer, chronic kidney disease, or long-term use of immunosuppressant medications (e.g., corticosteroids), make individuals more vulnerable.
• Pre-existing Joint Conditions: Joints affected by osteoarthritis, rheumatoid arthritis, or other inflammatory arthritides are more prone to infection.
• Recent Surgery or Injections: As discussed, any invasive procedure involving the shoulder increases risk.
• Prosthetic Joints: Individuals with artificial shoulder joints (total shoulder arthroplasty) are at a higher risk for periprosthetic joint infection, which can occur months or even years after surgery.
• Intravenous (IV) Drug Use: Sharing needles or using non-sterile injection practices significantly increases the risk of bloodstream infections that can seed joints.
• Skin Infections: Untreated skin infections or open wounds near the shoulder can serve as entry points for bacteria.
• Advanced Age: Older adults may have weakened immune systems and more co-morbidities, increasing their risk.

Recognizing the Signs and Symptoms

Recognizing the signs of a shoulder infection is crucial for timely treatment. Common symptoms include:

• Severe and Worsening Pain: Often sharp, throbbing, and persistent, worsening with movement.
• Swelling: Noticeable swelling around the shoulder joint.
• Redness and Warmth: The skin over the affected area may appear red and feel warm to the touch.
• Limited Range of Motion: Significant difficulty and pain when moving the shoulder, often leading to a complete inability to move it.
• Fever and Chills: Systemic signs of infection, indicating the body's response to the invading pathogens.
• General Malaise: Feeling unwell, fatigued, or weak.

Diagnosis and Treatment

If a shoulder infection is suspected, prompt medical evaluation is essential. Diagnosis typically involves:

• Physical Examination: Assessing pain, swelling, warmth, and range of motion.
• Blood Tests: Elevated white blood cell count (WBC) and inflammatory markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can indicate infection.
• Joint Aspiration (Arthrocentesis): A needle is used to withdraw fluid from the joint. This fluid is then analyzed for white blood cells, glucose levels, and sent for Gram stain and culture to identify the specific pathogen. This is the definitive diagnostic test for septic arthritis.
• Imaging Studies: X-rays may show joint space narrowing or bone erosion in later stages. MRI or CT scans can provide more detailed images of soft tissues, bone, and fluid collections.

Treatment usually involves a combination of:

• Antibiotics: Administered intravenously (IV) initially, then often switched to oral antibiotics once the infection is controlled and the specific pathogen is identified.
• Surgical Drainage and Debridement: For septic arthritis, surgical washout (arthroscopic or open) is often necessary to remove infected fluid, pus, and debris, and to prevent cartilage damage. For osteomyelitis, surgical debridement of infected bone may be required.

Prevention Strategies

While not all infections are preventable, several strategies can significantly reduce the risk:

• Aseptic Technique: Healthcare providers must adhere to strict sterile protocols during all injections, aspirations, and surgical procedures.
• Prompt Wound Care: Properly clean and dress any skin breaks or wounds near the shoulder.
• Manage Chronic Conditions: Individuals with diabetes or other immune-compromising conditions should diligently manage their health to strengthen their immune response.
• Treat Other Infections: Promptly seek medical attention for skin infections, UTIs, or other systemic infections to prevent hematogenous spread.
• Post-Surgical Care: Follow all post-operative instructions meticulously, including wound care and activity restrictions.

When to Seek Medical Attention

A shoulder infection is a medical emergency. If you experience sudden, severe shoulder pain accompanied by swelling, redness, warmth, fever, or an inability to move your shoulder, seek immediate medical attention. Delay in diagnosis and treatment can lead to irreversible joint damage, chronic pain, and potentially life-threatening systemic complications.

Conclusion

Shoulder infections, while less common than other orthopedic issues, represent a serious threat to joint health and overall well-being. They primarily result from direct pathogen introduction during medical procedures or trauma, or less frequently, from distant infections spreading through the bloodstream. Understanding these pathways, recognizing risk factors, and being vigilant for symptoms are critical steps for prompt diagnosis and effective treatment, ultimately safeguarding shoulder function and preventing long-term disability.