# Analysis of Microbiological Findings on the Surface of External Fixator Pins Comparing Steel Pins with Hydroxyapatite-Coated Pins

## TL;DR

This study compared steel and hydroxyapatite-coated pins in external fixators and found lower microbial growth on the coated pins, but no difference in infection rates.

## Contribution

The study provides new evidence on microbial retrieval rates between two pin types in external fixators.

## Key findings

- Hydroxyapatite-coated pins had significantly lower microbial retrieval rates than steel pins for best-looking pins.
- Staphylococcus aureus was the most common pathogen isolated from the pins.
- Clinical infection rates were similar between the two pin types despite differences in microbial retrieval.

## Abstract

To compare the microbial retrieval rates and the organism types on the surface of stainless-steel pins (SSPs) and hydroxyapatite-coated pins (HCPs) from external fixators (EFs).

The present prospective, non-randomized, multicenter, comparative interventional cohort study occurred from April 2018 to October 2021. The sample consisted of 44 patients with EFs, including 33 with SSPs and 11 with HCPs. We collected two pins from each patient, the one with the best and the one with the worst clinical appearance according to the Maz-Oxford-Nuffield (MON) classification, in an aseptic manner, and sent them for microbiological analysis.

The overall superficial infection (SI) rate was 52.3% (23 of 44 patients), affecting 45.5% (5 of 11) patients with HCPs and 54.5% (18 of 33) patients with SSPs (
p
 = 0.732). Of the 88 pins, 43.2% (38 of 88 pins) yielded microbial identification, with 42 pathogens isolated.
Staphylococcus aureus
was the most frequent organism, accounting for 59.5% (25 of 42 pathogens) of the positive samples. In the best-looking pins, the microbial retrieval rate was significantly lower in HCPs than SSPs, with 18.2% (2 pathogens in 11 pins) and 45.5% (15 pathogens in 33 pins), respectively (
p
 = 0.036). In the worst-looking pins, the microbial retrieval rate in HCPs and SSPs was 27.3% (3 pathogens in 11 pins) and 54.5% (18 pathogens in 33 pins), respectively (
p
 = 0.036).

Microbial retrieval rates were lower in HCPs than in SSPs. However, these differences did not impact clinical infection rates, which were similar in both groups.