Machine Design

Leadscrew Assembly Redesign Makes Spine Implants Easier to Install

Haydon Kerk,


Engineers at Synthes, West Chester, Pa., developed a device they call the Synthes Quick Inserter-Distractor (Squid) that enables surgeons to widen the gap between a patient’s vertebrae for inserting a spacer without damaging bone or tissue. The hand-operated Squid for anterior approaches improves on older methods in which surgeons hammered spacers into place. Unfortunately, it could not be used in lateral approaches, a capability surgeons often need to avoid scar tissue. The company turned to Haydon Kerk, Waterbury, Conn., to help make the instrument more versatile.

Using the original Squid design as an initial “road map,” Synthes engineers redesigned the tool. “This is where Haydon Kerk’s flexible manufacturing methods really paid off,” says Pete Fatone, responsible engineer for the Squid. “For example, the method made it easy to change materials.”

Early on, Synthes tried to use steel nuts to ride on the Squid’s internal steel leadscrew because of the challenges associated with plastic and load-bearing stresses, says application engineer Tom Solon. “But steel-on-steel caused too much friction. Our rapid prototyping, along with Synthes testing, proved that our leadscrews’ smooth surfaces made classic polymer-based nuts practical.”

The original leadscrew assembly had two threaded nuts, says Solon. “But this made it almost impossible for both nuts to carry a load. We figured out how to use one nut and a bushing instead, which simplified the design, made the device easier to use, and cut manufacturing costs,” he says.

The finished Squid is significantly smaller and it weighs about half as much as the original instrument. What’s more, surgeons report that the Squid no longer requires as much force to use and it works well from lateral directions.

TAGS: Fasteners
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