A study of distal tibial pilon fractures managed with external fixation followed by definitive fixation found no association between pin site overlap and the development of deep infection. The study, presented at the AAOS 2018 Annual Meeting by Jeffrey Potter, MD, FRCSC, also found no relationship between infection and the distance between proximal plate extent and pin site.

The investigators identified all pilon fractures treated at two Level 1 trauma centers over a period of 9 years (2005–2014) using CPT billing codes. They performed a retrospective review of patient records to identify demographic, injury, and treatment variables. Infection was defined as deep infection requiring one or more surgical débridement procedures. Review of digital imaging was carried out to classify the fracture pattern (AO/OTA classification), and to identify distance between the proximal extent of definitive fixation and external fixator pin sites.

The study group comprised 280 AO/OTA 43-b or 43-c type fractures in 277 patients (70 percent male, average age: 46 years) who underwent initial stabilization using spanning external fixation followed by definitive surgical intervention. Patients waited an average of 14 days (range: 7–20 days) between primary stabilization and definitive fixation. Twenty four percent developed deep infection requiring surgical intervention. No significant relationship could be identified with the association between pin site overlap and that of the development of deep infection and the relationship between infection and distance between proximal plate extent and pin site (P = 0.18 and P = 0.13, respectively).

Dr. Potter explained that treatment of fractures of the distal tibial plafond remains a surgical challenge, and management of these fractures has evolved over recent decades. Whereas early primary open reduction and internal fixation (ORIF) had once been the common practice, experience and research pointed to a decreased rate of soft-tissue complications with a two-staged protocol that consisted of initial fracture stabilization by spanning external fixation, followed by ORIF as soft tissues allow.

“A necessary complication of the two-staged protocol is the creation of pin tracts in the tibia shaft proximal to the zone of injury,” the study authors noted. “These pin tracts create a communication between deep tissues and the outside environment with resultant risk of a colonized deep wound within the surgical field.”

Colonized pin tracts are a recognized concern for deep infection in cases in which temporizing external fixation is being definitively replaced with intramedullary nailing, but the impact on plate osteosynthesis is not clear, Dr. Potter said. He noted that a recent study of a series of tibial plateau and pilon fractures indicated an increased infection risk occurring when definitive plate fixation overlapped with external fixator pin sites.

“In our opinion,” the study authors wrote, “understanding the relationship between pin site location and definitive plate fixation is important for two reasons. The first is that the stability of temporizing external fixation is affected by the distance of the tibial pin sites to the fracture; thus, attempts to keep pins well clear of planned definitive fixation may compromise stability. Second, avoidance of plate overlap with pin sites may lead surgeons to bias toward shorter constructs, possibly compromising definitive stability.”

The study sought to evaluate whether pin site overlap did indeed result in higher rates of infection, and if so, to determine whether there was length-dependent relationship between pin sites location and definitive fixation influencing the risk of infection.

Dr. Potter explained, “The use of temporizing external fixators in treatment of pilon fractures is quite common, both at our institution and as general practice. There was some debate among the staff at our institution, Massachusetts General Hospital and Brigham and Women’s Hospital (Harvard Combined Orthopaedic Trauma group), whether it was better to shorten the initial construct to provide better stability, or to lengthen the construct to keep pin sites as far away as possible from planned definitive fixation. Looking at the literature, there was some evidence to suggest that overlap of pin sites and definitive fixation increased the risk of infection. We wanted to first see if that was consistent with our group’s experience, and if so, to determine what a ‘safe’ distance was—that is, how far pin sites had to be from definitive fixation for there to be no significant increased risk of infection.”

Characterizing the study’s findings, he said, “First, and somewhat surprisingly, we could find no significant increased risk of deep infection in the presence of pin site overlap. From there, considering overlap did not increase deep infection risk, it perhaps wasn’t surprising that we could not find any increased risk of infection associated with proximity of definitive fixation to pin sites.”

As for the clinical takeaway, Dr. Potter said, “We would encourage surgeons to focus on creating the optimal construct when applying an external fixator to temporize pilon fractures, as dictated by the fracture pattern and soft-tissue injury. They should do this without sacrificing construct stability due to the possibility of pin sites overlapping with definitive fixation. Similarly, when applying definitive fixation, don’t sacrifice your definitive construct length in order to avoid overlapping pin sites” (Fig.1).

Limitations of the study include retrospective data collection and changing techniques over the duration of the study period.

In regard to future research, Dr. Potter said reaching a definitive answer to the questions surrounding the effect of pin site overlap is a worthwhile objective. “Although the topic doesn’t necessarily lend itself to a randomized trial, prospective data collection could provide a clearer answer,” he said.

He and his fellow authors concluded, “Information regarding pin site overlap is important, as it influences both initial and definitive constructs. Our results suggest that temporizing external fixation pins should be placed so as to obtain optimal stability of the construct with lesser emphasis on aiming to be absolutely outside the zone of future fixation.”

Dr. Potter’s coauthors of Scientific Paper 307, “Is the Proximity of External Fixator Pins to Eventual Definitive Fixation Implants Related to the Risk of Deep Infection in the Staged Management of Tibial Pilon Fractures?” are Quirine Van Der Vliet, MD, MSc; John Esposito, MD, MSc, FRCSC; Mitchel Harris, MD; Michael Weaver, MD; and Marilyn Heng, MD, MPH, FRCSC.

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org.