Introduction to Orthopaedic Infections

Musculoskeletal infections—encompassing acute hematogenous osteomyelitis, septic arthritis, and periprosthetic joint infections (PJI)—represent some of the most challenging pathologies in orthopaedic surgery. Despite advancements in sterile technique, prophylactic antibiotics, and ultraclean operating environments, surgical site infections (SSIs) continue to cause significant morbidity, prolonged hospitalizations, and profound functional impairment.

This comprehensive masterclass synthesizes the foundational evidence regarding the etiology, prophylaxis, and diagnosis of orthopaedic infections. It provides practicing consultants, fellows, and residents with an evidence-based framework for mitigating infection risk, utilizing advanced diagnostic imaging, and executing precise surgical interventions.

Etiology and Host Factors

The pathogenesis of bone and joint infections is dictated by the complex interplay between microbial virulence factors (such as the staphylococcal glycocalyx and biofilm formation) and host immune defenses.

Immunocompromise and Systemic Risk Factors

Host defense abnormalities significantly predispose patients to musculoskeletal infections.
* Genetic Deficiencies: Conditions such as Leukocyte Adhesion Deficiency (an inherited defect in Mac-1, LFA-1, and p150,95 glycoproteins) severely impair neutrophil chemotaxis, leading to recurrent, life-threatening soft tissue and osseous infections.
* Hemoglobinopathies: Patients with sickle cell disease are uniquely susceptible to osteoarticular infections. Microvascular occlusion leads to bowel ischemia, allowing Salmonella species to translocate into the bloodstream and seed infarcted bone. However, Staphylococcus aureus remains a predominant pathogen even in this demographic.
* Intravenous Drug Use (IVDU): Injection drug users exhibit a high incidence of atypical bone and joint infections, frequently involving the axial skeleton (e.g., sternoclavicular joint, sacroiliac joint, and spine) with organisms such as Pseudomonas aeruginosa and MRSA.

Nutritional Assessment and Optimization

Malnutrition is a profound, often under-recognized risk factor for SSIs. Nutritional depletion impairs cell-mediated immunity, decreases phagocytic function, and delays wound healing.
* Biomarkers of Malnutrition: A total lymphocyte count of less than 1,500 cells/mm³ and a serum albumin level below 3.5 g/dL are highly predictive of postoperative infectious complications.
* Preoperative Optimization: Elective orthopaedic procedures, particularly total joint arthroplasty and complex spinal fusions, should be delayed in malnourished patients until nutritional parameters are optimized via enteral or parenteral support.

Clinical Pearl: Always assess the nutritional status of elderly patients presenting with hip fractures. Prospective assessments demonstrate a direct correlation between protein-calorie malnutrition and the incidence of postoperative wound sepsis in this vulnerable cohort.

Prophylaxis: Preoperative and Intraoperative Optimization

Preventing orthopaedic infections requires a multifaceted approach, targeting the operating room environment, surgical personnel, and the patient.

The Operating Room Environment

Airborne bacterial contamination, primarily consisting of skin squames shed by operating room personnel, is a major vector for deep sepsis in implant surgery.
* Ultraclean Air Systems: The landmark studies by Lidwell et al. demonstrated that ultraclean air systems (laminar flow) combined with body exhaust suits significantly reduce the incidence of deep joint sepsis following total hip and knee arthroplasty.
* Traffic Control: Minimizing operating room door openings and restricting personnel traffic are critical adjunctive measures to maintain positive pressure and laminar flow integrity.

Surgical Site Preparation and Hand Disinfection

• Hair Removal: Preoperative depilatory creams or clipping immediately prior to surgery are vastly superior to razor preparation. Razors create micro-abrasions that serve as nidi for bacterial colonization.
• Hand Scrubbing: Traditional 5-minute povidone-iodine or chlorhexidine scrubs have largely been replaced or supplemented by aqueous alcoholic hand-rubbing. Randomized equivalence studies demonstrate that 3-minute alcohol-based rubs are equally, if not more, efficacious in reducing bacterial colony-forming units (CFUs) while causing less dermal irritation.

Barrier Defenses

• Double Gloving: The routine use of double gloves reduces the risk of inner glove perforation and subsequent bloodborne operative infections.
• Advanced Liners: In high-risk trauma or procedures involving sharp osseous fragments, the use of polyester/stainless steel wire weave glove liners (gauntlets) provides an additional mechanical barrier against percutaneous injuries.

Systemic and Topical Antibiotic Prophylaxis

• Timing and Selection: Prophylactic intravenous antibiotics must be administered within 60 minutes prior to surgical incision to ensure peak tissue concentrations during the procedure. First-generation cephalosporins (e.g., Cefazolin) remain the gold standard for clean orthopaedic surgery.
• Open Fractures: The Gustilo-Anderson classification dictates prophylaxis. Grade I and II fractures require a first-generation cephalosporin. Grade III fractures necessitate the addition of an aminoglycoside (e.g., Gentamicin) for Gram-negative coverage, and high-dose Penicillin if clostridial infection (farm injuries) is suspected.
• Topical Antibiotics: The use of topical antibiotic irrigants (e.g., Bacitracin/Polymyxin) or antibiotic-loaded polymethylmethacrylate (ALBC) provides high local concentrations of bactericidal agents while minimizing systemic toxicity.

Surgical Warning: The use of electric cautery lowers the contamination threshold required to establish an infection. Judicious use of electrocautery, minimizing tissue charring and necrosis, is essential to preserve local host defenses.

Diagnostic Modalities in Orthopaedic Infections

The accurate diagnosis of acute osteomyelitis, septic arthritis, and PJI relies on a combination of serological markers, advanced imaging, and precise microbiological isolation.

Laboratory Biomarkers

• C-Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR): These acute-phase reactants are the first-line screening tools. CRP rises rapidly (within 6 hours) and peaks at 48 hours, making it an excellent marker for monitoring therapeutic response. ESR rises more slowly and may remain elevated for weeks.
• Synovial Fluid Analysis: In suspected septic arthritis, joint aspiration is mandatory prior to antibiotic administration. A synovial fluid white blood cell (WBC) count > 50,000 cells/mm³ with > 90% polymorphonuclear leukocytes (PMNs) is highly suggestive of infection. Counterimmunoelectrophoresis can rapidly detect microbial antigens in synovial fluid.

Advanced Imaging Techniques

• Magnetic Resonance Imaging (MRI): MRI is the gold standard for diagnosing acute musculoskeletal infections. It offers unparalleled soft-tissue contrast, identifying marrow edema, subperiosteal abscesses, and soft-tissue extension. T1-weighted images show confluent decreased signal in the marrow, while T2-weighted and STIR sequences demonstrate hyperintensity.
• Ultrasound: Highly sensitive for detecting joint effusions, particularly in the pediatric hip (transient synovitis vs. septic arthritis). It also allows for real-time, ultrasound-guided diagnostic aspiration.
• Computed Tomography (CT): CT is invaluable in chronic osteomyelitis for identifying osseous destruction, involucrum formation, and the presence of a sequestrum (necrotic bone fragment), which dictates the need for surgical debridement.

Radionuclide Scintigraphy

When MRI is contraindicated (e.g., retained hardware, pacemakers), nuclear medicine provides critical diagnostic data.
* Technetium-99m (Tc-99m) MDP Bone Scan: A three-phase bone scan is highly sensitive but lacks specificity. It demonstrates increased perfusion, blood pool, and delayed osseous uptake in osteomyelitis.
* Indium-111 Labeled Leukocyte Scan: Highly specific for acute infection. Autologous WBCs are labeled and reinjected, migrating to sites of active inflammation. It is particularly useful in differentiating infection from aseptic loosening in arthroplasty when combined with a Tc-99m sulfur colloid marrow scan.
* Gallium-67 Citrate: Binds to transferrin and lactoferrin at sites of infection. Often used in conjunction with Tc-99m to increase specificity.
* FDG-PET (Fluorine-18 Fluorodeoxyglucose): Positron emission tomography is emerging as a highly accurate modality for diagnosing chronic musculoskeletal infections, offering excellent spatial resolution and high sensitivity for metabolically active inflammatory cells.

Microbiological and Molecular Diagnostics

• Intraoperative Cultures: Obtaining multiple (minimum of 3 to 5) distinct tissue samples using separate instruments is the gold standard for diagnosing PJI and chronic osteomyelitis. Swabs of superficial wounds are notoriously inaccurate and should be avoided.
• Molecular Diagnostics: Polymerase Chain Reaction (PCR) techniques are revolutionizing the detection of fastidious or culture-negative organisms (e.g., Kingella kingae in pediatric populations).

Surgical Principles: Debridement of Acute Osteomyelitis and Septic Arthritis

While antibiotic therapy is the cornerstone of treatment, surgical intervention is mandated for abscess formation, joint space infections, or failure to respond to medical management.

Indications for Surgery

1. Aspiration-confirmed septic arthritis.
2. Subperiosteal or intraosseous abscess identified on MRI.
3. Chronic osteomyelitis with a radiographically confirmed sequestrum.
4. Clinical deterioration despite 48 hours of appropriate intravenous antibiotic therapy.

Patient Positioning and Anesthesia

• Anesthesia: General anesthesia with profound muscle relaxation is preferred to allow for thorough joint manipulation and debridement.
• Positioning: Depends on the affected joint. For a septic knee, the patient is placed supine with a sandbag under the ipsilateral heel to allow for full flexion and extension during irrigation. A well-padded tourniquet is applied but not inflated until after diagnostic fluid is aspirated, to avoid altering the synovial fluid characteristics.

Step-by-Step Surgical Approach: Septic Knee Arthrotomy

1. Incision: A standard medial parapatellar incision is utilized. The skin and subcutaneous tissues are incised sharply.
2. Arthrotomy: The joint capsule is incised. Purulent fluid is immediately evacuated and sent for aerobic, anaerobic, mycobacterial, and fungal cultures, as well as cell count and crystal analysis.
3. Debridement: A radical synovectomy is performed. All fibrinous exudate, necrotic synovium, and loculations are meticulously debrided using a combination of rongeurs and motorized shavers.
4. Irrigation: The joint is copiously irrigated with a minimum of 6 to 9 liters of sterile normal saline. Pulsatile lavage may be used, but care must be taken to avoid driving bacteria deeper into the soft tissues.
5. Closure: The joint capsule is closed loosely over a large-bore intra-articular drain (e.g., Hemovac) to prevent re-accumulation of purulence. The skin is closed with non-absorbable sutures or staples.

Pitfall: Failure to adequately debride the posterior compartments of the knee during an arthrotomy for septic arthritis is a common cause of persistent infection. Ensure thorough visualization and irrigation of the posteromedial and posterolateral gutters.

Postoperative Protocols and Rehabilitation

• Antibiotic Therapy: Intravenous antibiotics are continued postoperatively, tailored to the intraoperative culture sensitivities. The duration is typically 4 to 6 weeks, monitored by serial CRP and ESR levels.
• Drain Management: Drains are typically removed when output is less than 30 cc over a 24-hour period.
• Rehabilitation: Early passive range of motion (ROM) is instituted immediately postoperatively to prevent intra-articular adhesions and cartilage degradation. Continuous Passive Motion (CPM) machines are highly beneficial in the first 72 hours. Weight-bearing status is determined by the extent of osseous involvement and the stability of the joint.

Conclusion

The management of orthopaedic infections demands a rigorous, evidence-based approach. By optimizing host nutritional factors, strictly adhering to operating room environmental controls, and utilizing advanced diagnostic modalities such as MRI and Indium-111 scintigraphy, the orthopaedic surgeon can significantly reduce the incidence and morbidity of these devastating complications. When infection does occur, prompt recognition, targeted antimicrobial therapy, and aggressive, meticulous surgical debridement remain the unyielding pillars of successful eradication.

📚 Medical References

• Orthopaedic infections, Philadelphia, 1989, Saunders. Hitchcock TF, Amadio PC: Fungal infections, Hand Clin 5:599, 1989.
• Holms W, Ali MA: Acute osteomyelitis of