In-vitro External Fixation Pin-Site Model Proof of Concept: A Novel Approach to Studying Wound healing in Transcutaneous Implants

Blake McCall*, Karan Rana, Kate Sugden, Sarah Junaid

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


External fixation is an essential surgical technique for treating trauma, limb lengthening and deformity correction, however infection is common, with infection rates ranging from 4.5 to 100% of cases. Throughout the literature researchers and clinicians have highlighted a relationship between excessive movement of the pin and skin and an increase in the patient’s risk of infection, however, currently no studies have addressed this role of pin-movement on pin-site wounds. This preliminary study describes a novel in vitro pin-site model, developed using a full-thickness human skin equivalent (HSE) model in conjunction with a bespoke mechanical system which simulates pin-movement. The effect of pin-movement on the wound healing response of the skin equivalents was assessed by measuring the expression of pro-inflammatory cytokines. Six human skin equivalent models were divided into three test groups: no pin as the control, static pin-site wound and dynamic pin-site wound (n = 3). On day 3 concentrations of IL-1α and IL-8 showed a significant increase compared to the control when a static fixation pin was implanted into the skin equivalent (p < 0.05) and (p < 0.005) respectively. Levels of IL-1α and IL-8 increased further in the dynamic sample compared to the static sample (p < 0.05) and (p < 0.0005). This study demonstrates for the first time the application of HSE model to study external-fixation pin-movement in vitro. The results of this study demonstrated pin-movement has a negative effect on soft-tissue wound-healing, supporting the anecdotal evidence reported in the literature, however further analysis of wound heading would be required to verify this hypothesis.
Original languageEnglish
Pages (from-to)403-411
Number of pages9
JournalProceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine
Issue number4
Early online date3 Mar 2024
Publication statusE-pub ahead of print - 3 Mar 2024

Bibliographical note

Copyright © IMechE 2024. This article is distributed under the terms of the Creative Commons Attribution 4.0 License ( which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (


  • External fracture fixation
  • human skin equivalent
  • pin-site infection
  • Surgical Wound Infection/therapy
  • Bone Nails
  • External Fixators
  • Humans
  • Wound Healing/physiology
  • Fracture Fixation/methods
  • Interleukin-8


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