Antibiotic Spacer Shoulder: Understanding Its Role in Joint Infection Treatment

What is an Antibiotic Spacer Shoulder?

An antibiotic spacer shoulder is a temporary, implantable device used in orthopedic surgery, primarily to treat severe infections within the shoulder joint, especially following a shoulder replacement. It functions by delivering high concentrations of antibiotics directly to the infected area while simultaneously maintaining the joint's anatomical space and allowing for limited motion.

Understanding Shoulder Joint Infection

Infections of the shoulder joint, particularly periprosthetic joint infections (PJI) that occur after a total shoulder arthroplasty (shoulder replacement), are serious complications. These infections can lead to significant pain, loss of function, and potentially necessitate the removal of the implanted prosthesis. Treating such infections requires a comprehensive approach, often involving surgical intervention and prolonged antibiotic therapy. Traditional systemic (intravenous) antibiotics may struggle to penetrate the biofilm formed by bacteria on implant surfaces, making local delivery a highly effective strategy.

What is an Antibiotic Spacer?

An antibiotic spacer is a custom-made or pre-fabricated device designed to be temporarily implanted into the shoulder joint after the removal of an infected shoulder prosthesis or in cases of severe native joint infection. Its primary functions are twofold:

1. Local Antibiotic Delivery: It acts as a sustained-release drug delivery system, leaching high concentrations of antibiotics directly into the infected joint space.
2. Space Maintenance: It preserves the anatomical joint space and soft tissue tension, preventing contracture and facilitating a smoother, less complex second-stage surgery for definitive joint reconstruction.

Components and Design

Antibiotic spacers are typically constructed from polymethyl methacrylate (PMMA), also known as bone cement. This material is mixed with high-dose antibiotics during its preparation. Common antibiotics incorporated include vancomycin (effective against Gram-positive bacteria like Staphylococcus aureus) and tobramycin or gentamicin (effective against Gram-negative bacteria). The choice of antibiotics depends on the suspected or identified pathogens.

Spacers can be:

• Custom-molded: Shaped by the surgeon during the operation to mimic the resected humeral head and/or glenoid, fitting the patient's unique anatomy.
• Pre-formed: Manufactured in standard sizes and shapes, offering convenience and consistency.

The design often includes a central hole or canal to allow for the passage of bone and tissue, further promoting antibiotic diffusion and potentially allowing for drainage.

Purpose and Mechanism of Action

The antibiotic spacer serves several critical purposes in the management of shoulder joint infections:

• Targeted Antibiotic Delivery: By releasing antibiotics directly into the joint, the spacer achieves much higher local concentrations than systemic administration, which is crucial for eradicating resistant bacteria and penetrating biofilms. This also minimizes systemic side effects often associated with long-term high-dose intravenous antibiotics.
• Infection Control: The continuous release of antibiotics helps to suppress and eliminate the infection, preparing the joint for a subsequent definitive reconstruction.
• Joint Space Preservation: Maintaining the physical space between the humerus and glenoid prevents the surrounding soft tissues (capsule, ligaments, muscles) from scarring down and contracting. This is vital for preserving the range of motion and simplifying the second-stage surgery.
• Improved Patient Comfort and Mobility: While not designed for full weight-bearing, the spacer allows for some limited, pain-free movement, which can aid in early rehabilitation and improve the patient's quality of life during the interim period.

When is an Antibiotic Spacer Used?

The use of an antibiotic spacer is most commonly indicated in a two-stage revision arthroplasty for periprosthetic joint infection (PJI) of the shoulder. This procedure involves:

1. Stage One: Removal of the infected shoulder prosthesis, thorough debridement (cleaning) of the infected tissue, and insertion of the antibiotic spacer.
2. Stage Two: After the infection has been successfully eradicated (typically confirmed by blood tests and sometimes joint aspiration), the spacer is removed, and a new, sterile shoulder prosthesis is implanted.

Spacers may also be considered in other severe shoulder infections where temporary joint stabilization and local antibiotic delivery are beneficial.

The Surgical Procedure

The insertion of an antibiotic spacer occurs during the first stage of a two-stage revision surgery. The procedure typically involves:

• Incision: An incision is made over the shoulder joint.
• Prosthesis Removal: The infected components of the shoulder replacement (humeral head, glenoid component) are carefully removed.
• Debridement: All infected and necrotic (dead) tissue is meticulously removed from the joint capsule, surrounding muscles, and bone. This is a critical step for infection eradication.
• Spacer Insertion: The antibiotic-laden PMMA is then molded into the shape of the removed components and inserted into the joint, restoring anatomical alignment and maintaining space.
• Closure: The wound is closed, and often a drain is placed to remove excess fluid.

Post-Operative Care and Recovery

Following spacer insertion, patients typically receive a course of intravenous antibiotics for several weeks, followed by oral antibiotics. Physical therapy is initiated, focusing on gentle, passive, and active-assisted range of motion exercises to prevent stiffness and maintain mobility. Weight-bearing and strenuous activities are strictly limited to protect the temporary spacer. Regular blood tests (e.g., C-reactive protein, erythrocyte sedimentation rate) are performed to monitor for signs of persistent infection. The spacer usually remains in place for 6 to 12 weeks, or until the infection markers normalize.

Advantages of Using a Spacer

• High Local Antibiotic Concentration: Maximizes efficacy against infection while minimizing systemic side effects.
• Maintains Joint Space: Prevents soft tissue contracture, making the second-stage surgery technically easier and more successful.
• Allows for Limited Motion: Improves patient comfort and can aid in early rehabilitation.
• Improved Success Rates: Contributes to higher rates of infection eradication and successful definitive arthroplasty.
• Reduced Morbidity: Compared to a single-stage procedure in complex cases, the two-stage approach with a spacer often has better outcomes for infection control.

Potential Complications and Considerations

While beneficial, antibiotic spacers are not without potential complications:

• Spacer Dislocation or Fracture: Being a temporary device, it can dislocate or break, requiring further surgical intervention.
• Persistent Infection: Despite the spacer, the infection may not be fully eradicated, necessitating further treatment.
• Allergic Reaction: Rarely, patients can have an allergic reaction to the antibiotics or bone cement.
• Stiffness: While designed to prevent it, some degree of joint stiffness can still occur.
• Nerve or Vascular Injury: As with any surgery, there's a risk of damage to surrounding nerves or blood vessels.

Transition to Definitive Arthroplasty

Once the infection is confirmed to be clear, typically after several weeks to months, the patient is scheduled for the second stage of the revision surgery. During this procedure, the antibiotic spacer is removed, and a new, permanent shoulder prosthesis is implanted. This definitive arthroplasty aims to restore full joint function, reduce pain, and improve the patient's quality of life.

Conclusion

The antibiotic spacer shoulder is a cornerstone in the modern management of severe shoulder joint infections, particularly those involving prosthetic implants. By combining targeted local antibiotic delivery with mechanical space maintenance, it significantly improves the chances of infection eradication and facilitates successful, long-term joint reconstruction. Its use exemplifies a sophisticated, evidence-based approach to complex orthopedic challenges, prioritizing both infection control and the preservation of joint function for future definitive treatment.