Bacteriology of callus of closed fractures of tibia and femur.

Background: More than 1% of closed fractures of lower limbs and 6% of orthopedic implants are complicated by inflammation caused by infection despite of all precautionary methods taken. The question arises whether this clinical complication is not caused by bacteria dwelling in limb tissues.

Methods: Skin, subcutaneous fat, muscle, and fracture gap callus were obtained from 71 adult patients operated on due to closed fractures of tibia or femur; 28 because of comminuted fractures and mal-alignment of bone axis with nonoperative means, and 43 due to delayed healing and unstable union.

Results: Aerobic bacteria were isolated from gap callus of 14% healing and 35% nonhealing fractures. No isolates were found in subcutis and only in 3% in muscles. No anaerobic bacteria were detected. Polymerase chain reaction amplifications of 16S rRNA were found positive in 42% of callus specimens proving presence of bacterial DNA even when no isolates were found. The 95% similarity of the genetic pattern of some strains from foot skin and callus, estimated with random amplification of polymorphic DNA technique, suggested their foot skin origin.

Conclusions: The colonizing bacterial cells and their DNA were detected in fracture callus but not in other deep tissues. Contamination was precluded by lack of isolates in disinfected cutis, subcutis, muscles, and materials used for sampling cultured after surgery. We suggest that certain strains of bacteria dwell in normal tissues of lower limbs and may cause inflammation upon stimulation by trauma. Their source may be tissue fluid, superficial and deep lymphatics, and lymph serving the physiologic transport to the regional lymph nodes of microorganisms penetrating foot skin during microinjuries.