Automated Device Developed for Limb Lengthening Adjustments

LinDi development team, from left: Stephanie Herkes with the device, Alvin Chou, Mario Gonzalez, Raquel Kahn, and Elaine Wong. (Jeff Fitlow/Rice University)

Student engineers at Rice University in Houston have developed a system that automatically adjusts distraction osteogenesis devices used to correct bone deformities that leave children with one limb shorter than the other. The LinDi — short for Linear Distractor — was designed in collaboration with Shriners Hospital for Children in Houston, as a senior-year undergraduate project.

Distraction osteogenesis is a rehabilitation technique that moves two segments of a bone slowly apart in such a way that new bone fills in the gap. To correct deformities due to trauma, infection, or congenital causes, surgeons break a bone and apply a distractor that stretches the bone as it heals and gently nudges the arm or leg to a more appropriate length.

The distractor uses long pins sunk right into the bone on either side of the surgical break. As the bone heals, but before it sets, the patient uses an Allen wrench to give the drive screw a quarter turn four times a day and push the pins further apart a tiny bit at a time. The current distraction osteogenesis process, however, requires making these manual adjustments faithfully and accurately, which can be difficult for children or even parents to fulfill.

Team members Raquel Kahn, Alvin Chou, Mario Gonzalez, Stephanie Herkes, and Elaine Wong took on the project at the urging of Gloria Gogola, an orthopedic surgeon at Shriners Hospital. “The process of limb lengthening — essentially creating a localized mini-growth spurt — works well for bones, says Gogola, “but is very hard on the soft tissues such as nerves and blood vessels.”

The engineers use a stepper motor to automate the distraction, and strain gauges to provide force feedback. A microcontroller interfaces the strain gauges with the stepper motor driver which drives the motor. The motorized, battery-operated LinDi adjusts the device almost 1,000 times every day, making the process more gradual and continuous, similar to actual bone growth. If the loads on the tissue are too high, the device shuts the motor off.

Current patients wear distractors for as long as it takes to complete the process, typically stretching a limb for two to four months. Each of the Rice students wore a standard distractor (minus the bone-drilling part) for 24 hours to get a feel for what patients endure.

LinDi is still a work in progress, with another group of Rice student engineers anticipated to continue development of the LinDi after the first team of students graduates. The original LinDi team conducted initial tests on animals in Shriner Hospital labs. The second student group is expected to continue the animal tests, as well as reduce the device’s size and weight to make it more comfortable for children.

In the following video, the Rice team tells more about and demonstrates the LinDi device.

Read more: Undergrad Engineers Design Improved Neck Stabilizer Brace

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