Hip Joint Infection

Epidemiology

The most common pathway for entry of infection into the nonreplaced adult hip joint is a hematogenous source. Bacteria from the urinary tract, lungs, skin, or other distant sites can enter the hip joint through inflamed or diseased synovial tissue. Although antegrade flow through the arterial system most likely contributes to most cases, the proximity of the hip to the Batson plexus provides the potential for retrograde venous introduction of bacteria from pelvic floor organs.

Direct introduction of bacteria into the hip joint can also occur through a variety of diagnostic and therapeutic procedures. Although direct joint inoculation historically has contributed to a small percentage of cases, increased use of arthrocentesis, arthroscopy, and open surgical approaches to treat nonarthritic and prearthritic hip conditions may increase hip joint infection rates. Repeated corticosteroid injections to treat hip osteoarthritis have been associated with an increased prosthetic joint infection risk following total hip arthroplasty.

Regional extension of infection from the lumbar spine, genitourinary structures, and lower gastrointestinal tract can also cause hip joint infection. This may occur by direct communication or by extension of infection along the iliopsoas tendon.

Risk Factors

Conditions that result in increased venous or arterial perfusion, capillary permeability, or synovial tissue inflammation elevate the potential for bacteria to enter into the hip ( Box 36.1 ). Impaired immune system surveillance—caused by host factors, disease, or pharmacologic immunosuppression—further contributes to an individual's susceptibility for joint sepsis ( Box 36.2 ).

Microbiology

The most common infecting organisms are similar to those encountered with other musculoskeletal infections. Staphylococcus aureus is the most frequently reported organism resulting in hip infection, accounting for between 30% and 60% of cases. Group A streptococcal bacteria are the second most commonly identified, and an increasing number of infections have been reported with a variety of gram-negative and anaerobic organisms ( Box 36.3 ). Recent trends indicate an increasing incidence of community-acquired methicillin-resistant strains of S. aureus (MRSA) in Western cultures. Among patients with osteonecrosis or sickle cell disease, salmonella has been reported as an organism with a predisposition for the hip at a higher incidence than nonsalmonella infection and may be associated with a chronic carrier state within the necrotic bone in susceptible individuals.