Cigarette Smoke Exposure Impairs Fracture Healing in a Rat Model: Preferential Impairment of Endochondral over Membranous Healing.

Background: Cigarette smoking affects fracture repair, leading to delayed healing or nonunion.

Purpose: We sought to investigate if cigarette smoke differentially affects intramembranous and endochondral ossification in healing fractures, focusing on whether endochondral ossification is particularly impaired.

Methods: This study utilized a bilateral femur fracture model in Sprague Dawley rats to examine the impact of cigarette smoke exposure on healing of femur fractures, treated with either a custom-locked intramedullary nail or compression plating to induce endochondral and membranous ossification, respectively. Animals were exposed to tobacco smoke 30 days before and after surgery, with evaluations including radiographs, histomorphometry, and microCT at 10 days, 1, 3, and 6-months post-operation, and biomechanical testing at 3, 6 months.

Results: Sixty-eight animals were randomized to control or exposure groups (two died perioperatively), and 89% of the femora achieved union when harvested at 3 and 6 months. Smoke exposure delayed cartilaginous callus formation and bone maturation in nailed fractures compared to plated fractures and controls in same animals. Plated fractures in exposed animals exhibited little cartilage callus and healed like control animals. At 3 months, plated fractures were stiffer and stronger than nailed fractures in both groups, but these differences vanished by 6 months.

Conclusions: Plated fractures healed more rapidly and more completely than nailed fractures under both control and smoke-exposed conditions.

Clinical relevance: Using compression plating instead of IM nailing for closed long bone fractures may lead to better outcomes in patients who smoke compared to current results with nailing.