Sub-cutaneous Surgical Implants for Percutaneous Pin Wound Healing

Employer: Shirley Ryan AbilityLab / RIC

Role: Research Engineer III

Tl;DR Direct skeletal attachment of prosthetic devices improves comfort by directly loading the skeleton vs. soft tissues. However, this requires a permanent hole in the skin barrier via a percutaneous rod which poses a large infection risk. Keeping the percutaneous site healed and clean is difficult b/c skin doesn't want to grow into the metal. These discs were designed to be placed subcutaneously, promote healing, vascularization, and tissue integration with the hardware.

Direct skeletal attachment of prosthetic device can reduce the break down of soft tissues and improve comfort by directly transfering loads to the skeleton vs through soft tissues. Traditional devices are donned and worn via a prosthetic socket, which is custom fabricated to each user and worn over the residual limb. With little to no ventilation, these sockets tend to be hot and sweaty which can lead to break down and irritation of the skin. Additionally, these sockets transfer the loads of the prosthesis to the user via the soft tissues interfacing the socket vs. the skeletal structure. This can lead to discomfort and worse, soft tissue damage, sores, and wounds.

Direct skeletal attachement deletes the traditional socket from the problem entirely by mounting the prosthesis directly to the skeleton of the user via a percutaneous intramedullary rod. Percutaneous pins and rods, and their associated complications, have been around for a long time. External fixation (ex fix) of compound or complex fractures is standard of care. However, there are two major differences with direct skeletal attachment, (1) where external fixation is usually temporary and typically takes places in high supervised, well resourced envionrments such as hospitals direct skeletal attachment is intended to be permanent and (2) ex fix pins do not typically go into the intramedullary canal of long bones where direct skeletal attachment needs the mechanical fixation and support of the long bone.

While direct skeletal attachment is a promising solution for better prostheses fit and force transfer, the permanent hole in the skin barrier requires innovation to avoid an open wound site, prevent infection, and promote healing. The surgical impants shown here were desinged to promote healing, tissue integration with the implant, and vascularization of the wound site to promote healing and improve immune response. You will notice microscopic topography on the implants as well as an array of holes. The size and shape of these features were specifically selected to allow for tissues to integrate into the implant, closing the wound site and adding a strain relief to surround tissues, as well as promote vascularization of the wound site to promote healing and aid in immune response.

A small trial was performed with these implants, but was set aside due to other priorities in the lab. Early results where promising with tissue integration on several of the implants.